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A synthetic, spectroscopic and magnetic susceptibility study of selected main group and transition metal… Cader, Mohamed Shah Roshan 1992

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A SYNTHETIC, SPECTROSCOPIC AND MAGNETIC SUSCEPTIBILITY STUDY OFSELECTED MAIN GROUP AND TRANSITION METAL FLUORO COMPOUNDSByM. SHAH ROSHAN CADERM.Sc., The University of British Columbia, 1986A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIES(Department of Chemistry)We accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAApril, 1992© M.S.R. CADER, 1992In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission._____________________Department of CItE WI/cThe University of British ColumbiaVancouver, CanadaDate ft TC)(36rQj , 1di9JDE-6 (2/88)ABSTRACTThis study was initiated in order to synthesize, and where appropriate, to investigate themagnetic properties of selected main group and transition metal cationic complexes, allstabilized by weakly basic fluoro anions derived either from the Brönsted superacids HSO3FandHSO3CF,or the Lewis acids SbF5 and AsF5.Of the preparative reactions, the solvolysis of metal(ll) fluorosulfates in excess SbF5according to:25-60°CM(SO3F)2 + 6SbF5 > M(SbF6)+ 2SbF9( O3)with M=Ni, Pd, Cu, Ag or Sn, is found to be a useful synthetic route to the correspondingdivalent hexafluoro antimonates. The products, as their precursors, are characterized as CdC12-type layered polymeric compounds. Relevant vibrational (Raman and IR), electronic and119Sn-Mössbauer spectra as well as magnetic susceptibility measurements and X-ray powderdata are reported. Several compounds prepared by this method display unusual features:Pd(SbF6)2is, like its fluorosulfate precursor, paramagnetic with the Pd2 ion in a 3A2g groundstate. Ag(SbF6)2,unlike its paramagnetic blue valence isomer, is diamagnetic and nearly whitein color, and is formulated as the mixed valency complex Ag(I)[Ag(III)(SbF64]. TheCu(SbF6)2compound also contains, in addition to Cu2 ions, small quantities of Cu(I) andCu(Ill) ions. Both Ni(SbF6)2 and Pd(SbF6)2exhibit temperature dependent low magneticmoments, indicative of antiferromagnetic exchange. Pd(SbF6)2also displays very weak ferromagnetism below —lOK.11The Sn(SbF6)2product from the above synthesis, and its precursor Sn(SO3F)2,react withexcess 1,3,5-trimethylbenzene(mesitylene or mes) to give the it-arene adducts Sn(SbF62mesand Sn(SOF)2mes in high yield. The adducts are characterized by elemental analysis andinfrared spectra. The adduct formation is followed by 119Sn Mössbauer spectroscopy. It isfound that only tin(ll) compounds with large, weakly nucleophilic anions are capable of formingmesitylene complexes, while SnC12,SnF2, and stannocene do not give any indication of adductformation under similar reaction conditions.The divalent fluorosulfates Ni(SO3F)2,Pd(SO3F)2and Ag(SO3F)2,precursors to theM(SbF6)2 compounds, and the mixed valency Pd(II)[Pd(IV)(SO6], as well as theircorresponding trifluoromethylsulfate derivatives Ni(SO3CF)2, Pd(SO3CF)2 andAg(SO3CF)2,investigated for their magnetic behavior by susceptibility studies down to -•4 K,show significant magnetic exchange, and except in Ag(SO3CF)2,the onset of magneticexchange becomes observable at low temperatures. The fluorosulfates are found to exhibitstrong ferromagnetism below —11 K, whereas the trifluoromethylsulfates behave as antiferromagnets with the spin interactions noted over a wider temperature range. The maximummagnetic susceptibilities of Ni(SO3F)2, Pd(SO3F)2 and Ag(SO3F)2 indicate saturationmagnetization, and hence for these compounds field dependent maximum magnetic momentsare obtained in the temperature range —5 to 10.5 K. Maxima in the susceptibility vs. temperature plots are noted for the antiferromagnets Pd(SO3CF)2and Ag(SO3CF)2at —4 and —13 Krespectively. Unlike in the corresponding divalent antiferromagnetic fluorides, no spin cantingis detected in the trifluoromethylsulfates at lower temperatures.Magnetic susceptibility measurements to —4 K are also carried out for the main groupmolecular cations withinO2[AsF6],Br2[Sb316] andI2[SbF1i]• The data are interpretedutilizing previous results from photoelectron spectroscopy, known crystal structures, magneticstudies on the superoxide ion and the ozonide ion, and in the case of Oj[AsF6],previous ESRstudies.111The magnetic properties of the three materials are quite different. Br2[Sb3F16]obeys Curie-Weiss law between 80 and 4 K. The magnetic moment decreases slightly from 2.04 B at roomtemperature to 1.93 B at 4 K. I2[SbF11] exhibits relatively strong antiferromagneticcoupling with a maximum in XM observed at -54 K. The magnetic moment (corrected for TIP)decreases from 1.92 B at 124 K to 0.41 B at 4 K. Experimental susceptibilities for thiscompound over the temperature range 300-4 K have been compared to values calculated usingthree different theoretical models for extended chains of antiferromagnetically coupledparamagnetic species. 02+[AsF6] exhibits Curie-Weiss behavior over the temperature range60-2 K. The magnetic moment, uncorrected for TIP, varies from 1.63 B at 80 K to 1.17 I.LB at 2K, and the presence of weak antiferromagnetic coupling in this material is suggested.ivTABLE OF CONTENTSPageABSTRACT iiLIST OF TABLES ixLIST OF FIGURES xiLIST OF SYMBOLS xiiiACKNOWLEDGEMENTS xivCHAPTER 1 INTRODUCTION 11.1 General Introduction 11.2 The Lewis Acid SbF5 31.2.1 Physical and Chemical Properties 31.2.2 Cationic Derivatives 41.3 The Transition Metal Fluorosulfates and Trifluoromethylsulfates 91.4 Post-Transition Metal Arene fl-Compounds 131.5 Magnetic Measurements 161.6 Objectives of this Study 20References 22CHAPTER 2 GENERAL EXPERIMENTAL 272.1 Introduction 272.2 Chemicals 272.2.1 Purification Methods 292.2.2 Synthetic Methods 29VPage2.3 Apparatus 312.3.1 Reaction Vessels 332.3.2. SbF5 Storage-bridge Vessel 332.3.3 S206F- Addition Trap 332.3.4 Pyrex Vacuum Line 372.3.5 Metal Vacuum Line 372.3.6 Dry Atmosphere Box 372.4 Instrumentation and Methods 382.4.1 Infrared Spectroscopy 382.4.2 Raman Spectroscopy 382.4.3 Nuclear Magnetic Resonance Spectroscopy 382.4.4 Electronic Spectroscopy 392.4.5 Mössbauer Spectroscopy 392.4.6 X-ray Photoelectron Spectroscopy 392.4.7 Magnetic Susceptibility Measurements 402.4.8 X-ray Powder Diffractometry 412.4.9 Differential Scanning Calorimetry (DSC) 412.4.10 Elemental Analyses 42References 42CHAPTER 3 METAL(II) HEXAFLUORO ANTIMONATES M(SbF6)2,M(ll) = Sn(II), Ni(II), Pd(ll), Cu(ll) AND Ag(ll) 433.1 Introduction 433.2 Experimental 463.2.1 General Synthetic Scheme to M(SbF6)2 463.2.2 Physical Properties and Analyses 473.2.2a Cu(SbF6)2 48viPage3.2.2b Pd(SbF6)2 483.2.2c f3-Ag(SbF6) 483.2.3 Alternate Synthetic Route to 3-Ag(SbF6)2 483.3 Results and Discussion 493.3.1 Synthesis 493.3.2 Vibrational Spectra 553.3.3 Electronic Spectra 623.3.4 Magnetic Susceptibility Measurements 663.3.5 X-ray Photoelectron Spectra 823.3.6 Attempted Synthesis of Au(SbF6)2 833.4 Conclusion 85References 87CHAPTER 4 MESITYLENE ADDUCTS OF TIN(II) FLUORO COMPOUNDS,Sn(SO3F)2C9H12and Sn(SbF6)2C9H12 904.1 Introduction 904.2 Experimental 934.2.1 Synthesis 934.2.1 a Synthesis of Sn(SO3F)21 ,3,5-(CH)C6H 934.2.1 b Synthesis of Sn(SbF6)2[1 ,3,5(CH] 944.3 Results and Discussion 954.3.1 Synthesis 954.3.2 119Sn Mössbauer Spectra 994.3.3 Infrared spectra 1014.4 Conclusion 108References 108viiPageCHAPTER 5 A LOW TEMPERATURE MAGNETIC STUDY OFTHE MOLECULAR CATIONS O2, Br2 AND I2 1115.1 Introduction 1115.2 Experimental 1125.3 Results and Discussion 1135.3.1 Synthesis 1145.3.2 Magnetic Measurements 1185.3.3 Br2[SbF16] 1185.3.4 O[AsF6] 1265•3•5 I2[SbF11f 1305.4 Conclusion 136References 137CHAPTER 6 MAGNETIC EXCHANGE IN M(II) SULFONATES,M(ll) = Ni(II), Pd(I1) AND Ag(II) 1416.1 Introduction 1416.2 Experimental 1446.3 Results and Discussion 1446.3.1 Ferromagnetism of M(II) fluorosulfates Ni(SO3F)2,Pd(SO3F)2,Pd(II)[Pd(IV)(SO3F6]and Ag(SOF) 1456.3.2 Antiferromagnetism of M(ll) thfluoromethylsulfatesNi(SO3CF),Pd(SO3CF)2and Ag(SO3CF)2 1636.4 Conclusion 176References 178CHAPTER 7 SUMMARY AND GENERAL CONCLUSIONS 181APPENDIX A 185APPENDIX B 194yinLIST OF TABLESTable 1.1:Table 1.2:Table 2.1:Table 3.1:Table 3.2:Table 3.3:Table 3.4:Table 3.5:Table 3.6:Table 3.7:Table 4.1:Table 4.2:Table 5.1:Table 5.2:Table 5.3:Table 6.1:Table 6.2:Table 6.3:Table 6.4:Table 6.5:Page562856576467686975100104106119120121146147148149150Solid Polyhalogen Cationic Derivatives of SbF5Solid Binary Transition Metal Derivatives of SbF5Chemicals Used Without PurificationVibrational Spectra of Ni(SbF6)2,Pd(SbF6)2and Cu(SbF6)2Vibrational Spectra of the Two Valence Isomers of Ag(SbF6)2Electronic Transitions and Ligand Field Parameters forNi(SbF6)2,Pd(SbF6)2and Related CompoundsLow Temperature Magnetic Data of Ni(SbF6)2Low Temperature Magnetic Data of Pd(SbF&2Low Temperature Magnetic Data of Cu(SbF6)2Magnetic Moment Data of Ni(SbF6)2for the Temperature Range—80 to 295 K119Sn Mössbauer Parameters of Relevant Tin(H) Compounds at 80 KInfrared Bands of Liquid Mesitylene and Bands Attributed toMesitylene in the Adducts Sn(SO3F)2mes and Sn(SbF6)2mesTable 4.3: Infrared Frequencies for Sn(SO3F)2and Sn(SnF6)2and BandsAttributed to the Anions in the Mesitylene Adducts Sn(SO3)2mesand Sn(SbF6)2mesMagnetic Data ofBr2[Sb3F16jMagnetic Data ofI2[SbF1j andO2[AsF6]Structural and Spectroscopic Information onO2[AsF6i,I2[SbF11],Br2[Sb3F16]and the corresponding Ions O2, Br2 and I2Low Temperature Magnetic Data of Ni(SO3F)2Low Temperature Magnetic Data of Pd(SO3F)2Low Temperature Magnetic Data of Pd(II)[Pd(IV)(SOF6]Low Temperature Magnetic Data of Ag(SO3F)2Magnetic Data of Ni(SO3F)2for the Temperature Range291 to 79KxPageTable 6.6: Magnetic Parameters of Ni(SO3F)2,Pd(SO3F)2,Pd(II)[Pd(IV)(SO3F]and Ag(SOF) 151Table 6.7: Experimental and Calculated Saturation Magnetic Susceptibilitiesof Ni(SO3F)2,Pd(SO3F)2,Pd(ll)[Pd(IV)(SO3F fJand Ag(SO3F)2 157Table 6.8: Magnetic Data of Ag(SO3CF)2for the Temperature Range 304 to 4 K 164Table 6.9: Low Temperature Magnetic Data of Pd(SO3CF)2 165Table 6.10: Low Temperature Magnetic Data of Ni(SO3CF)2 166Table 6.11: Magnetic Data of Ni(SO3CF)2for the Temperature Range 292 to 80 K 167xLIST OF FIGURESPageFigure 2.1: Apparatus for PreparingS206F 30Figure 2.2: Typical Pyrex Reaction Vessels 32Figure 2.3: Vacuum Filtration Apparatus 34Figure 2.4: Kel-F Tubular Reactor 35Figure 2.5: SbF5 Storage-bridge Vessel 36Figure 3.1: Raman Spectrum of -Ag(SbF6)2 58Figure 3.2: Crystal Structure of cz-Ag(SbF6)2 60Figure 3.3: Spin Allowed Electronic Transitions from 3A Ground Termfor Pd2 and Ni2 (d8) in Octahedral Ligand 1e1d 63Figure 3.4: Magnetic Moment vs. Temperature of M(SbF&2,M = Ni, Pd and Cu 70Figure 3.5: Magnetic Moment vs. Temperature of Ni(SbF6)2 74Figure 3.6: Magnetic Moment vs. Temperature of HF-Treated Cu(SbF6)2 80Figure 3.7: Magnetic Moment vs. Temperature of SbF5-Treated Cu(SbF6)2 81Figure 4.1: 119Sn Mössbauer Spectrum of Sn(SbF6)2mes at 77 K 102Figure 5.1: Magnetic Moment vs. Temperature ofBr2[Sb316],12[51J andO2[AsF6J 122Figure 5.2: Inverse Susceptibility vs. Temperature ofO2[AsF6j andBr2[SbF3F16J 123Figure 5.3: Crystal Structure of Br2[Sb3F16] 125Figure 5.4: Energy Level Diagram of the Dioxygenyl Ion with the a andit-Bonding 2p Orbitals 127Figure 5.5: Crystal Structure ofI2[SbF11J 131Figure 5.6: Magnetic Susceptibility vs. Temperature ofI2[SbF1] 132Figure 6.1: Proposed Structure of Pd(SO3F)2 143Figure 6.2: Inverse Susceptibility vs. Temperature of Ni(SO3F)2 152Figure 6.3: Inverse Susceptibility vs. Temperature of Pd(SO3F)2,Pd(II)[Pd(IV)(SOF6}and Ag(SO3F)2 154Figure 6.4: Magnetic Susceptibility vs. Temperature of Pd(SO3F)2at 7501 and 9625 G 155xiPageFigure 6.5: Magnetic Susceptibility vs. Temperature of Pd(H)[Pd(IV)(SO3F6]at750land9625G 156Figure 6.6: Magnetic Moment vs. Temperature of Pd(SO3F)2and Ag(SO3F)2 159Figure 6.7: Magnetic Moment vs. Temperature of Pd(SO3CF)2 170Figure 6.8: Magnetic Susceptibility vs. Temperature of Pd(SO3CF)2 171Figure 6.9: Magnetic Moment vs. Temperature of Ni(SO3CF)2and Ni(SO3F)2 173xiiLIST OF SYMBOLSN = AvogaLiro’s numberk = Boltzmann’s constantT = Absolute temperatureg = Lande splitting factor3 = Exchange coupling constantD = Zero-field splitting parameter= Spin-orbit coupling constantDq = Ligand field splitting parameterB = Racah parameter (interelectronic repulsion parameter)or Bohr magnetonSpin only magnetic momenteff = Effective magnetic momentXM = Molar magnetic susceptibilityXMCOff = Molar magnetic susceptibility corrected for diamagnetismCm = Curie constante = Weiss constantG = Magnetic field in Gauss= Quadrupole splitting= Isomer shiftxliiACKNOWLEDGEMENTSIt has been rewarding experience to work under the supervision of Professor F. Aubke.His guidance and encouragement were invaluable during the course of this work, and for this Iextend my sincere gratitude and thanks to him. I also wish to thank Professor R.C. Thompsonfor his constructive and valuable collaboration in this study over the past few years.Many thanks are also due to my co-workers Dingliang Zhang, Germaine Hwang, FredMistry and Walter Cicha for their pleasant friendship and enlightening discussions. Tom Otienoand Martin Ehiert are thanked for their kind assistance in obtaining the magnetic measurements.Thanks are also due to the members of the mechanical, glassblowing, and electronic shops fortheir technical expertise. I am also indebted to Mr. P. Borda for his microanalytical services.Special thanks are extended to Germaine Hwang for proof-reading this thesis and RaniTheeparajah for the excellent work done in typing the manuscript.Finally I would like to express my sincere thanks to my family for their kind understanding and words of encouragement throughout my years of graduate study.xivDEDICATEDTO MY MOTHERJ.BA. CADERxvCHAPTER 1INTRODUCTION1.1 GeneraJ IntroductionThe synthesis and physical study of solid compounds where unusual metal and nonmetal cations are stabilized by wealdy coordinating fluoro anions is an area of research whichhas grown steadily over the last two decades, and is the primary focus of this dissertation. Inrecent years, there has been an increasing interest shown both by chemists and physicists in thesynthetic and solid state properties of these rare cationic complexes, often obtainable only asderivatives of strong Brönsted (protonic) fluoroacids or Lewis acids (1, 2). The use of a widearray of physical methods including various magneto-chemical techniques to characterize thesecompounds has permitted structure-property relationships to be understood in detail and has alsoprovided rational approaches to the synthesis of new and unusual materials.The types of compounds which have been studied in this thesis are varied, and rangefrom main group non-metallic molecular cationic complexes to inorganic and organometalliccoordination polymers, where the organometallic polymers are t-arene adducts of the post-transitional metal Sn(ll) fluoro derivatives. The molecular cations and the transition metalcoordination polymers have been investigated for their magnetic properties to obtain information on the ground state electronic structure as well as to detect any magnetic exchange interactions between the paramagnetic centers (particularly at low temperature) in the respectivecompounds. Furthermore, spectroscopic and structural data (where available) have been utilizedin the interpretation of the magnetic behavior observed for the compounds.1The inorganic and organometallic polymers synthesized in this study containfluoroanions such as SbF6 and S03F, which are usually generated in superacidic media.Strong protonic fluoroacids and superacids have been used extensively as reaction media,solvents and synthetic reagents in both inorganic and organic syntheses (1). The role of theseacids and their anions in the synthesis and stabilization of unusual cations is of significance tothis work, since all the fluoro compounds studied here have anions which are derived fromeither the protonic fluoroacids HSO3Fand HSO3CF or the Lewis acids SbF5 and AsF5. Consequently, the corresponding anions of interest S03F, S03CF, SbF6,Sb2F11,Sb3F16 andAsF6 are all poorly coordinating, weakly nucleophilic anions, well capable of stabilizing avariety of electrophiic cationic centers either in solid compounds or in solutions.These fluoro anions are in general non-oxidizable and are reasonably resistant towardreduction and, when coordinating to transition metals, act as monodentate as well as bidentate ortridentate ligands, usually with bridging, rather than chelating configurations. The coordinatingability of the fluorosulfate SO3F, and the trifluoromethylsulfate SO3CF groups has beendiscussed relatively recently by Lawrence (3), and the generation and stabilization of varioushalogen and interhalogen cations in protonic fluoroacids and superacids has been reviewed inthe past by Gillespie and Morton (4), and many years later by Shamir (5).It is generally agreed that the anions mentioned above are all very weakly basic and havehigh group electronegativities. For a number of dimethyltin(IV) compounds of the type(CH3)2SnX (X = a fluoro or fluoroxy anion) with linear or near linear C-Sn-C groupings andbidentate bridging anions, the ‘19Sn Mössbauer parameters suggest the following order of anionbasicity: F- > S03CH > SOCF3 Z SOF > AsF6 > SbF Z Sb2F1f(6).These general concepts mentioned briefly above will now be discussed in some detail inthe following sections to provide the necessary background information for the extended study.21.2 The Lewis Acid SbF51.2.1 Physical and Chemical PropertiesAntimony(V) fluoride, SbF5 is generally regarded as the strongest molecular Lewis acid(7). It is a very viscous (460 cP at 20°C) (8), colorless liquid, with a specific gravity of 3.145g/cm3 at 15°C. It has a relatively high melting point (8.3°C) and a high boiling point (142°C)(la), compared to the Lewis acid AsF5 (mp = -80°C, bp = -53°C). This suggests a considerabledegree of association for the molecule, and vapor density measurements indicate aggregatescorresponding to (SbF5)3 at 150°C and (SbF5)2at 250°C (9). The polymeric structure of theliquid SbF5 has been established by 19F-NMR spectroscopy (10), and is found to have a cisfluorine bridged framework in which each antimony atom is surrounded by six fluorine atoms inan octahedral arrangement. In the solid state, SbF5 is tetrameric with octahedral coordinationachieved again by cis-bridging fluorine atoms (11).Antimony pentafluoride is a good oxidizing and a moderately strong fluorinating agent.As shown by conductomethc, cryoscopic, and related acidity measurements, it appears thatSbF5 is by far the strongest Lewis acid known, and hence is preferentially used in preparingstable metallic as well as non-metallic cationic derivatives. For the purpose of comparison, thefollowing order of acidity can be assigned for a series of Lewis acids (la): SbF5 > AsF5 > TaF5> BF3 > NbF5 > PF5. For their anions, the basicity is expected to increase in nearly the sameorder from SbF6 to PF6. Moreover, SbF5 also shows a remarkable ability to coordinate toprotonic fluoroacids such as HF, HSO3Fand HSO3CF,resulting in vastly enhanced acidity forthe conjugate superacid systems, where many types of unusual cations have been observed asstable species.31.2.2 Cationic DerivativesCation formation in SbF5 or in its conjugate superacid solutions is not resthcted tometallic species only, but occurs with equal frequency among non-metals such as halogen andpolyhalogen derivatives (4,5). In most instances SbF5 has proven to be an excellent fluoride-ionacceptor, and the hexafluoro anion SbF6 or polyanions of the type SbF6. (SbF5), n = 1 or 2,are readily formed. Some selected solid polyhalogen and binary transition metal cationicspecies stabilized by such anions are listed in Tables 1.1 and 1.2. Extensive research has beencarried out in our laboratory to study the possible extension of this fluoride-ion acceptor abilityof SbF5 to include a similar “fluorosulfate-ion transfer” via the solvolysis of fluorosulfatecompounds in SbF5 (12-15).The solvolysis process was initially used in our group to synthesize non-metallic cations(12,13,15), and later for the preparation of the dimethyltin(IV) cation (CH3)2Sn(16):C1O2S3F + 4SbF5 — C1O2[SbF1] + Sb2F9(SO3) [1.1]IX2SO3F + 4SbF5 — IX2[SbF11J + Sb2F9(SO3) [1.2](X = Cl or Br)Br(SO3F) + 7SbF5 — BrF2[Sb6] + 3Sb2F9( O) [1.3]2Br + 5206F + 1OSbF5 — 2Br[Sb3F16] + 2SbF9( O3) [1.4]212 + S206F + 8SbF5 .—> 2I[SbF11] + 2SbF9( O3) [1.5]CH3Sn(SOF)2+ 8SbF5 —> (CH3)2Sn[SbF11]+ 2SbF9( O3) [1.6]4Table 1.1: Solid Polyhalogen Cationic Derivatives of SbF5Compound Synthesis ReferenceC13[SbF6] Cl2 + CIF + SbF5 in HF 4Br2[Sb3F16J Br-t-B F5+Sb 17Br2 +S206F+ SbF5 1512[2111] + SbF5 in SO2 1812+S06FSbF 15C1F2[Sb6j CW3 + SbF5 19BrF2[Sb6] BrF3 + SbF5 20Br(SO3F)+ SbF5 15IF2[SbF6] IF3 + SbF5 21ICl2[SbF11] IC12SO3F+ SbF5 13IBrj[Sb2F11] IBr2SO3F+ SbF5 13ClF4[Sb6j C1F5 + SbF5 in HF 22BrF4[Sb2F1] BrF5 + SbF5 22IF4[SbF61 IF5 + SbF5 8BrF6[Sb2F1i] BrF5 + Kr2F3SbF6 23IF6[Sb2F11 IF+SbF5 245Table 1.2: Solid Binary Transition Metal Derivatives of SbF5Compound Synthesis ReferenceCr(SbF6)2 CrF2 + SbF5 in HF 25Mn(SbF6)2 Mn + SbF5 in SO2 26Fe(SbF6)2 FeF2+ SbF5 in HF 25Fe + SbF5 in SO2 26Co(SbF6)2 CoF2+ SbF5 in HF or SO2 25Co + SbF5 in SO2 26Ni(SbF6)2 NiF2 + SbF5 in HF 25Ni+SbF5inSO2 26Ni+SbF+F2 27Ag(SbF6)2 AgF2+ SbF5 in HF 25Zn(SbF6)2 ZnF2 + SbF5 in HF 25Cd(SbF6)2 ‘2 + SbF5 in HF 25Hg3(Sb2F11) Hg + SbF5 in SO2 286Two of the above halogen cations synthesized by the solvolysis route, i.e.Br2[Sb3Fi&andI2[SbF1J, are investigated in this work for their magnetic properties by low temperaturemagnetic susceptibility measurements. This improved preparative method (15) provides asimple and straightforward route to sufficiently large quantities of very pure paramagnetic Brjand 12+ compounds, and hence is of value in magnetic studies where highly pure materials aredesired. It is interesting to note that in Table 1.1, Br2[Sb3F16] andI2[SbF11} are the onlytwo solid polyhalogen cation derivatives that are paramagnetic.The volatile components formed in these solvolysis reactions (SbF4O3F) and morefrequently Sb2F9(SO3) where SbF5 is in an excess) can be removed easily in a dynamicvacuum (14), facilitating the isolation of pure solid products in very high yield. In this study,the solvolysis method is extended to divalent transition metal fluorosulfates as well.The polyhalogen derivatives of SbF5 listed in Table 1.1 are generally accepted to be ofionic structure, although there is evidence that in most of them some secondary cation-anioninteraction of various degrees does exist. Single crystal X-ray studies performed on twocompounds of interest to this study, i.e. Br2[Sb3F16] andI2[SbF1J, support an ionic formulation since the cation-anion contacts are rather long, although shorter than the sum of thevan der Waals radii, indicating a very small cation-anion interaction (17,18).Interestingly, the shortest FF contact distance inI2[SbF1i] is almost the largestcation-anion contact observed in a series of Sb2F1 derivatives with the following cations ofdecreasing contacts: SbCl4 > 12+ > XeF3 > Br2+ > BrF4. This decreasing distance indicatesan increase in the acidity for the cations (18). The Sb-F (terminal) distances in Br2[Sb3Fi&andI2[SbF11J (1.83 A and 1.85 A) are similar to those observed in SbF6 derivatives likeCW2[SbF6]and BrF2[Sb6j,namely 1.84 A and 1.835 A respectively (19,20).7The transition metal hexafluoroantimonates listed in Table 1.2 are, in most reportedinstances, formulated as metal difluoride adducts of the parent acid SbF5, and are of the type(25). This formulation is derived from a common synthetic route where the metaldifluoride is reacted with SbF5, usually in the presence of anhydrous l{F or SO2 to yield thedesired product. However, alternative structural forms like M(SbF6)2and MF(Sb211)are alsopossible for these products. When other preparative methods such as the oxidation of metals bySbF5 in SO2 (26) or metal fluorination with F2 in the presence of SbF5 (27) are used, the resulting products are conveniently formulated as M(SbF6):so2M + 4SbF5 > M(SbF6)2 + SbF35 [1.7]where M = Mn, Fe or Ni270°CNi + 2SbF5 + F2 > Ni(SbF [1.8]250 atmIn the case of cobalt, reaction [1.7] reportedly leads to the ternary CoF(SbF6)2(26), whereasmercury is converted toHg3(Sb2F11)(28).It is significant to note here that all the above routes to transition metal hexafluoroantimonates have various limitations and complications. Metal oxidation by F2 at elevatedtemperature may lead to higher oxidation state compounds, whereas oxidation by SbF5 may notbe a suitable method for metals with higher oxidation potentials than provided for by theSb(V)/Sb(llI) couple. In addition, the quantitative separation of the solid byproduct SbF35from the main product may prove to be the difficult (29), and consequently, impure materials areisolated as reaction products. Even the more versatile synthetic method of fluoride abstractionfrom MF2 by SbF5 (25) could lead to compounds of the type MF(Sb21 a structural isomer ofthe binary M(SbF6)2,due to an incomplete breakup of the MF2 lattice.8Some structural information on the transition metal derivatives of SbF5 (Table 1.2) hasbeen reported. For the Mn, Fe and Ni compounds obtained from SbF5 in SO2 (26), magneticmoment values at room temperature appear to indicate octahedral coordination for the metalcenters. Based on vibrational and X-ray powder data, Ni(SbF6)2which is synthesized from thehigh temperature fluorination of nickel in SbF5 (27), is shown to be related to the LiSbF6 structure by the occupation of only every second octahedral Li site with Ni2, leading to a layer typestructure. Furthermore, a crystal structure has been reported for the paramagnetic (vide infra)Ag(SbF6)2(25), where the Ag2 ion is located in a tetragonally elongated octahedral environment, which in turn implies a layer structure with iridentate bridging SbF6 moiety for thecompound. Except for the observed distortion due to the Jahn-Teller effect, the reportedstructure appears to be consistent with the proposed structure of the above mentioned Ni(SbF6)2compound (27).1.3 Transition Metal - Fluorosulfates and TrifluoromethylsulfatesThe transition metal sulfonates studied in this work can be considered as derivatives ofthe strong protonic fluoroacids fluorosulfuric acid (HSO3F) and trifluoromethylsulfuric acid(HSO3CF). The two acids rank among the strongest known protonic acids (1,3,7).Consequently, the corresponding anions S03F and SO3CF behave as weakly coordinatingligands, and are well suited to stabilize many unusual transition metal (as well as main group)cations. Compared to other poorly coordinating anions like perchiorate (C104j or tetrafluoroborate (BF4j, the SO3F and S03CF ions are arguably the most stable and non-oxidizingspecies available for synthetic purposes (3). Interestingly, almost all the transition metaltrifluoromethylsulfate compounds are made by the solvolysis of suitable metal salts in an excessof HSO3CF, and include many metal fluorosulfates as precursors (30,3 1). Therefore, it isappropriate to examine first the syntheses and properties of transition metal fluorosulfates(particularly the derivatives of electron rich metals) in some detail.9Fluorosulfate chemistry displays many parallels to halogen chemistry, and the fluorosulfate group may be viewed as a pseudohalide. Hence, the synthetic methods used in thepreparation of the flouorosulfates have striking parallels to those used in the synthesis of halides,with the necessary modifications.Two synthetic methods in general have been used to prepare a large number of transitionmetal fluorosulfate derivatives: (a) solvolysis of a corresponding metal salt such as MCi2,MSO4 or M(RCOO)2 in excess HSO3F, and (b) the oxidation of a metal with the stronglyoxidizing and fluorosulfonating reagent bis(fluorosulfuryl)peroxide, S206F (32,33) in thepresence or absence of HSO3F.Solvolysis is almost exclusively the route of choice for the synthesis of 3d-blockmetal(ll) fluorosulfates (34,35), whereas metal oxidation byS206Fyields a variety of electronrich 4d- and 5d-metal fluorosulfates, in particular Pd(U)[Pd(IV)(SO3F6](36), Ag(SO3F)2(37),Pt(SO3F)4(38) and Au(SO3F) (39) according to:HSO3FM + x12S06F > M(SOF), [1.9]where x 2, 3 or 4A major advantage to the use of theS2O6FJHSO3reagent combination in metal oxidation is that precursors, in the form of fine metal powders, are available in high purity for all thetransition metals, and consequently, very pure products can be isolated after the removal of theexcess reagents in a dynamic vacuum. Furthermore, some noble metal fluorosulfates such asPd(SO3F)2(36), Pt(SO3F)4(40) and Au(SO3F) (40) are also prepared by the oxidation of therespective metals by bromine monofluorosulfate, BrSO3F (41). However, the use of BrSO3F10instead ofS206F/HSO3in the synthesis of binary metal fluorosulfates offers no realadvantage, primarily asS206Fis initially required to synthesize BrSO3F.For these transition metal fluorosulfates, only a single molecular structure, that ofgold(llI) fluorosulfate, which was obtained by single crystal X-ray diffraction, has been reportedso far (42). The compound is a dimer and contains both monodentate and symmetricallybridging bidentate fluorosulfate groups. Unfortunately, the polymeric nature of most transitionmetal fluorosulfates and their resulting lack of volatility and solubility in HSO3F or othersuitable solvents have prevented the formation of single crystals, and hence structural evidencerests largely on vibrational spectra and magnetic properties.Fluorosulfates of the type M(SO3F)2appear to belong to a single structural type, derivedfrom the CdC12 layer structure, with one exception - the mixed valency Au(I)[Au(Ill)(SO3F4](43). The 0-tridentate bridging fluorosulfate group in M(SO3F)2results in M06-coordinationpolyhedra within the layer structure. Regular octahedra are found for M = Fe, Co, Ni, Pd, Zn,Cd and Hg (35,36,44), while the symmetry of the SO3F group appears to be reduced for M =Mn, Cu and Ag (35,37), with Jahn-Teller distortions expected for Cu2 and Ag2. This structuretype is also postulated for the divalent metal trifluoromethylsulfates Fe(SO3CF)2(45),Co(SO3F)2(46), Pd(SO3CF2(30) and Cu(SO3F)2(46), and also extends to divalentpre-transition and post-transition metal S03F, S03CF and SO3CH derivatives as well. Theonly two molecular structures reported so far for this type of compounds are that of Sn(SO3F)2(47a) and Ca(SO3H)2(47b). For the transition metal M(SO3R)2type compounds with R = F,CF3 or CH3, electronic spectra and magnetic data, where reported, confirm the structuralconclusions reached.A greater structural diversity is encountered for binary fluorosulfates of the generalcomposition M(SO3F). The dimeric structure of [Au(SO3F)]2(42) and the mixed-valency11Pd(II)[Pd(IV)(SO3F6](36) are clear exceptions. The mixed valency formulation follows theprecedent of PdF3 (48) and is supported by the magnetic behavior and the synthesis and structural characterization of bimetallic compounds of the types Pd(II)[M(IV)(SO3F6](M = Pt orSn) and Ba[Pd(IV)(SO3F6j(49). The fluorosulfate group appears to bond strongly to the M(IV)metal center and coordinates weakly to M(II), in an “anisobidentate” bonding mode. Therefore,it seems that where the SO3F (and the SO3CF or SO3CH)group functions as a polydentateligand, a bridging configuration is observed, resulting in stable solids, often viewed as coordination polymers. Moreover, the versatile coordinating ability of the fluorosulfate group, whichmay function as a mono-, hi-, or tn-dentate ligand leads to the stabilization of metal ions in high,intermediate, and low oxidation states.In contrast to the large number of binary transition metal fluorosulfate compoundsreported, only a small number of trifluoromethylsulfate derivatives are known. Almost all theM(SO3CF) species are made by the solvolysis of suitable metal salts in an excess ofHSO3CF. In the solvolysis of M(SO3F) in HSO3CF (30,31), the reaction initially proceedsaccording to:HSO3CFM(SO3F) + x HSO3CF > M(SO3CF)+ x HSO3F [1.10]where x = 2 or 3, M = Mn, Pd, Ag or AuHowever, the by-product HSO3F and the reactant HSO3CF undergo a degradationreaction and produce a series of products (50,51) which do not appear to interfere in theisolation of the trifluoromethylsulfates (30). As mentioned above, for the divalent iron, cobaltand copper derivatives a layered lattice structure involving hexacoordinated metal centers hasbeen suggested on the basis of vibrational and electronic spectra, as well as magnetic andMössbauer data (45,46). In a manner similar to the SO3F groups discussed previously, the12SO3CF groups act as bridging tridentate ligands in these compounds.Although the solvolysis of transition metal fluorosulfates in excess trifluoromethylsulfuric acid, which is a generally applicable method, should allow the synthesis of a comparatively large number of SO3CF compounds (30), only limited use has been made of thissynthetic possibility. The principal reasons for this are threefold: (a) As discussed in Section1.1, the SO3CF group has a basicity comparable to that of the SO3F group. An extendedsynthetic approach is not fruitful where compounds with similar properties and molecular structures result, as is often the case. (b) With vibrational spectroscopy used as a principal method ofstructural analysis, the coincidence of SO3 and CF3 stretching modes in S03CF causes agreater complexity, making vibrational assignments and structural conclusions frequentlyuncertain and ambiguous. (c) The S—C linkage in HSO3CF and its derivatives is sensitive tooxidative cleavage (30), and hence the acid’s use in the synthesis of high-valent metal derivatives with a good oxidizing potential, is not advisable. However, the S-C linkage, unlike the S-Fbond, is hydrolytically stable and hence chemistry in aqueous medium is possible withHSO3CF.There are nevertheless a number of interesting cases where metal trifluoromethylsulfatesdisplay fundamentally different magnetic properties from the coffesponding fluorosulfates, aswill be discussed in Chapter 6 of the text.1.4 Post-Transition Metai Arene it-CompoundsBoth main group and transition metal organometallic n-complexes have been studiedextensively, and a very large number of compounds have appeared in the chemical literature inthis field over the past few years alone. In this discussion, however, the emphasis is placed onthe relatively rare post-transition metal arene n-complexes. In terms of bonding, these13compounds differ significantly from most of the transition metal it-compounds for threeprincipal reasons (52):(a) Metals of the post-transition series contain no partially filled or empty valence dsubshells of comparable energy to those of the it orbitals of arene ligands. As a result,the it electron density of the ligand can be transferred only to a very small extent to the sor p type orbitals of the metal.(b) The filled d subshells of the metals are usually of much lower energy than the antibonding it’ orbitals of the arene ligand. Consequently, unlike the transition metal counterparts, back-donation from the d electrons to effect synergic bonding is not observed inpost transition it-complexes.(c) The effective atomic number rule, which is so useful in transition metal carbonyls andarene and Cp derivatives, is rendered ineffective and inapplicable in the case of posttransition metal derivatives.The consequence of factors (a) and (b) is a weak metal ligand interaction, leading tocompounds which are not as varied as the transition metal n-complexes. The study of neutralarene-metal complexes with the post transition metals in recent times has included the elementsGa, In, Tl, Sn, Pb, and Bi (53). However, these studies indicate that the it-interactions with theelements above the fourth period are very weak, resulting in reduced hapticity from a desired 6to i3 or 2 (53)Studies by Schmidbaur et al. (54) have concentrated on neutral arene complexes ofunivalent gallium, indium and thallium, which directly follow the d block elements. Both monoand bis(arene) complexes have been synthesized and characterized, and among these is the14mixed mono and bis(arene) thallium complex, [(Mes)6T14][GaBr whose crystal structure wasalso solved. This complex is actually a skeletal framework of tetrameric T14(GaBr),with oneor two mesitylene molecules alternately coordinated to the Tl+ cations. In the MesTl+ unit, theTl is located directly above the face of the ring, implying 6 coordination. A similar structurewas also found for the gallium analogue (55) [Mes)4Ga]GaC1]indicating that, althoughweak, it-interactions do exist with univalent Group 13 metals.It is significant to note that in the above studies it was found that the complex saltsT1A1C14,TIA1Br4 and T1GaC14all dissolved in hot benzene to give colorless crystals upon cooling. However, when dried under a stream of dry N2, the benzene content of the crystals steadilydecreased, implying very weak it coordination of the benzene ligand to the Ti center.Apparently, only the mesitylene ligand afforded a dry, isolable product. Strauss et al. (56) havealso synthesized TI-Mes complexes such as [Tl(OTeF5)(Mes)2},but found that this compoundalso loses all traces of the weakly bound arene ligands under N2 atmosphere or in vacuo. Therefore, it appears that the high lability of these arene ligands makes synthesis and purification avery delicate task, even though the synthesis itself is relatively simple (i.e., arene addition to asuitable substrate).It is apparent from the above studies that the electronic configurationnd10(n+1)s2plays aparticularly important role in the metal’s affinity for arene ligands. In view of this, the nextlogical step is to explore the divalent Group 14 elements (which have the same electronicconfiguration) to investigate their affinities for arene ligands. In fact, the synthesis and structureof the arene M(II) complexes(C6H)M(AlCl42(C6H),M=Pb(1I) or Sn(II), have been reportedby Amma and co-workers (57,58). The X-ray crystallographic study of the compounds reveals apolymeric chain structure, with a benzene ring wealdy bound in a manner to the M(II) center.In this thesis, the synthesis and characterization of arene adducts of divalent tin fluoro derivatives which contain the weakly coordinating SbF6 and SO3F ligands will be considered.151.5 Magnetic MeasurementsMagnetic susceptibility measurements, when recorded as a function of temperature,provide primarily information regarding the nature of the ground state of the paramagnetic ions.The extent of the information that can be obtained is related to the accuracy of the measurements, the range of temperature over which the measurements are carried out, as well as to thepurity of the samples used. The magnitude and temperature dependence of the magneticmoment data of magnetically dilute systems are determined by several factors such as groundstate occupancy and degeneracy, crystal field symmetry, spin-orbit coupling and electrondelocalization effects. The theory of magnetic susceptibilities of paramagnetic molecularspecies and transition metal complexes is well covered in several texts (59). In magneticallyconcentrated systems, the factors mentioned above are also present, and any magnetic interaction is superimposed upon these single-ion phenomena. Furthermore, it is now recognizedthat magnetic exchange interactions are not at all uncommon in inorganic compounds, evenwhere magnetic dilution (usually at room temperature) appears at first sight to be dominant. It isfor this reason that magnetic susceptibility measurements should be performed, where possible,over as wide a temperature range as possible.Qualitatively, magnetic exchange interactions may be thought of as arising fromunpaired spin densities on neighbouring paramagnetic centers, being aligned either parallel oranti-parallel to each other, resulting in ferromagnetism or antiferromagnetism respectively.Magneto-structural relationships emphasize the importance of such factors as thestereochemistry around the paramagnetic center, the efficiency of orbital overlap which may bedirect or via a superexchange pathway, the geometry of the bridging anions, the types ofsubstituents on the bridging group and the nature of any nonbridging groups. The theoreticalaspects of magnetic exchange phenomena and the models used to interpret the empirical datahave been the subject of extensive investigations (60).16The main group molecular complexes and several of the transition metal derivativesstudied in this work for their magnetic properties contain unusual paramagnetic cations in thesolid state, which are stabilized by weakly basic fluoroanions. Nearly all the previous magneticmeasurements on the molecular cations and the divalent sulfonates have been carried out athigher temperatures only, where in most instances, magnetic exchange interactions are notdetected.The halogen cations I2 and Br2 are shown to have 2H3g ground states with the firstexcited states21I2g at approximately 5100 and 2800 cmt above the ground state, respectively,both in the gas phase (61) and in solution (15). The magnetic moment in both cases is expectedto be independent of temperature due to the absence of thermally accessible excited states, andpredicted to have a value of 2.0 B at higher temperatures, in analogy to the 1’eff of the NOmolecule, discussed by van Vieck several years ago (62):Peff = 2[(1 — e + xe”)/(x + xe)]1/2 [1.11]where x = VkT.= Spin-orbit coupling constantk = Boltzmann’s constantT = Absolute temperatureIn an earlier report, Gillespie and Mime (63) showed the magnetic moment of in asolution of HSO3F to be 2.0 ± 0.1 Kemmitt et al. (64) reported a magnetic susceptibilitystudy on (SbF5)21, a material thought to contain the ‘2 cation, and found magnetic momentsthat ranged from 2.25 B at room temperature to 2.05 B at 100 K. Considering the uncertaintyin the chemical composition of the material, not much significance could be attached to thesevalues. A later work from our group, where theI2[SbF1i] and [Br2][Sb3F16Jcompounds17were synthesized by an improved method (15), indicated the possible existence of antiferromagnetic interaction between the‘2 cations, with jj values of 2.15 and 1.68 B at 295 and81 K respectively. Furthermore, the Br2 species was found to be magnetically dilute in thetemperature range 297 to 80 K, and a magnetic moment close to 2.0 B was obtained for thecompound (15). This is in contrast to a previous study, where a room tempreature value of1.6 11B had been reported for the Br2 derivative (17).In contrast to the and Br2 cations, the dioxygenyl cation 02 (with ground state21f2g and first excited state2113ag at —1480 cmt above ground state) investigated in this workhas been the subject of several previous magnetic studies (65-68). The 02+ cation can beprepared by a variety of methods, and is stabilized in the solid state by various fluoroanions,leading to complexes like02[PtF6] (69), O2[BF4] (70), O2[AsF6] (71), and O2[SbF6](71). The magnetic behavior ofO2[PtF6} over the temperature range 77-298 K has been postulated to be similar to that of NO, and the magnetic moment was reported as 1.57 1.LB at roomtemperature (65). A magnetic moment of 1.66 B has been found for theO2[SbF6]-compound(68b), and a value of 1.70 B forO2[BF4J (68a). Two previous studies onO2[AsF6] down to4 K give contradictory results. The study by Grill et al. (67) indicates no magnetic ordering ofthe 02+ cations down to 4 K, whereas weak O2O2+ interaction is suggested in the work ofDiSalvo et al. (66).Even though in all the above studies the eff values reported for the O2 salts fall wellbelow the spin only value of 1.73 B’ no satisfactory reason has been given so far to explain thiscurious phenomenon. It appears, however, that sample purity and identity play an importantrole in the interpretation of magnetic data of the O2 salts.Several transition metal sulfonate derivatives studied here for their magnetic propertiescontain paramagnetic cations in unusual coordination environments. As in PdF2 (48), in18Pd(SO3F)2(36) and Pd(SO3CF)2(30) compounds, the Pd(ll) ions (d8) with 3A2g ground statesare located in octahedral environments, a situation found only in some of their cationic andanionic derivatives. Similarly, the two silver derivatives Ag(SO3F)2(37) and Ag(SO3CF)2(31) investigated in this work have remained, in addition to the AgF2 compound (72), the onlysimple binary compounds of Ag(I1) with a d9 configuration.Previous magnetic susceptibility measurements down to —80 K on Pd(SO3F)2,“Pd(SO3F)” and Ag(SO3F)2 indicated that these fluorosulfate derivatives were relativelymagnetically unconcentrated in that temperature range with Peff values of 3.34, 3.45 and 1.92 Brespectively (36,37). Furthermore, their susceptibilities followed the Curie-Weiss law withpositive Weiss constants. The trifluoromethylsulfate derivative Ag(SO3CF)2was found to bean antiferromagnetic compound, with Xmax at —138 K (31).Only two other binary fluorosulfate and trifluoromethylsulfate derivatives, Ir(SO3F)4(73) and Fe(SO3CF)(45), are known up to now to be magnetically concentrated. However,unlike in Ag(SO3CF)2,the magnetic moments obtained for Ir(SO3F)4are only slightly belowthe calculated values, suggesting weak antiferromagnetic coupling down to —80 K (73). TheFe(SO3CF)compound is magnetically more concentrated than the iridium species, exhibitingmagnetic moments which are significantly less than the expected values, and which alsodecrease with decreasing temperature, although no maximum is detected in the susceptibilitycurve down to —80 K (45). As in the cases of palladium and silver derivatives mentioned above,no low temperature magnetic data are available for these complexes.The antiferromagnetic coupling observed in all the above mentioned sulfonates is notunusual for magnetically concentrated transition metal fluoro compounds, since antiferromagnetism, rather than ferromagnetism, appears to be the more common type of magnetic exchange interactjon among the majority of these compounds (59). Moreover, in most instances19these antiferromagnetic transition metal fluoro derivatives contain small monoatomic ligands(59b,c), whereas the sulfonate coordination polymers studied in this work are composed of themuch larger polyatomic S03F and SO3CFç ligands.1.6 Objectives of this StudyThe research work presented in this thesis can be categorized into two general, but interrelated sections: (A) Synthesis and characterization of divalent metal coordination polymers,and (B) Magnetic susceptibility studies on unusual main group and transition metal cations. Thespecific types of research relevant to these two sections are summarized below.(A) Synthesis and Characterization(i) The solvolysis of main group fluorosulfate derivatives in the Lewis acid SbF5 wasextended in the present study to include the transition metal fluorosulfates according to:25-60°CM(SO3F)2 + 6SbF5 > M(SbF + 2SbF9( O3) [1.12]SbF5Where M = Ni, Pd, Cu, Ag or (Sn)The ready availability of the M(SO3F)2precursors, the low oxidation potential of SbF5,and the easy removal of the volatile byproduct Sb2F9(SO3), as well as mild reactionconditions and the possibility of using glass vessels as reactors were all positive factorsin choosing the above solvolysis preparation. The divalent metal hexauluoro anlimonatesobtained were characterized, where appropriate, by elemental analysis, vibrational,electronic and 119Sn Mössbauer spectra, and magnetic susceptibility measurements.20(ii) The favorable properties of 1 ,3,5-trimethylbenzene (mesitylene) as a ii-adduct ligand andthe possible participation of the lone pair electrons of the Mössbauer nuclide Sn in the +2state in bonding by being donated to the antibonding it’ ligand orbitals are contributingfactors in the syntheses of the post-transition metal Sn(ll) arene adducts according to:25°CSn(SO3F)2+ mes > Sn(SO3F)2mes [1.131mesitylene25°CSn(SbF6)2+ 2 mes > Sn(SbF6)2mes [1.14]mesitylene(mes = mesitylene)The adducts isolated were characterized by elemental analysis, infrared and tt9Sn-Mössbauer spectra.(B) Magnetic Susceptibility Studies(i) Low temperature magnetic susceptibility measurements down to —4 K were performedon02[AsF6j,Br2[SbFi& andI2[SbF1i]’ in order to compare the magneticbehavior of the three cations. These paramagnetic homonuclear derivatives seem to bethe only three stable and isolable cations formed by non-metals that are suitable for solidstate magnetic studies. The two dihalogen cations 12+ and Br2+ were investigated forpossible exchange interactions, and the dioxygenyl cation 02+ was studied here toexplain its observed low magnetic moment values. Furthermore, the application of vanVleck’s theory of molecular paramagnetism to solid state cations was also examined.(ii) Several Group 10 and Group 11 divalent transition metal sulfonate compounds wereconsidered in this study as likely materials to exhibit magnetic exchange interations.21The metal fluorosulfates Pd(SO3F)2,“Pd(SO3F)”and Ag(SO3F)2,previously describedas relatively magnetically dilute down to —80 K, were re-investigated down to —4 K fortheir low temperature magnetic properties. The nickel(ll) fluorosulfate, Ni(SO3F)2was,however, measured in the temperature range —291 to 2 K. 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Chem., 11, 2260 (1972).41. F. Aubke and R.J. Gillespie, Inorg., Chem., 7, 599 (1968).42. H. Wiliner, S.J. Rettig, J. Trotter, and F. Aubke, Can. J. Chem., 69, 391 (1991).43. H. Wiliner, F. Mistry, 0. Hwang, F.G. Herring, M.S.R. Cader, and F. Aubke, 3. FluorineChem., 5, 13 (1991).44. S.P. Mallela and F. Aubke, Can. J. Chem., , 382 (1984).45. J.S. Haynes, J.R. Sams, and R.C. Thompson, Can. J. Chem., 59, 669 (1981).46. A.L. Arduini, M. Garnett, R.C. Thompson, and T.C.T. Wong, Can. J. Chem., 53, 3812(1975).47.a) D.C. Adams, T. Birchall, R. Faggiani, R.J. Gillespie, and J.E. Vekris, Can. J. Chem., ,2122 (1991).24b) F. Charbonnier, R. Faure, and H. Loiseleur, Acta Crvst, 1478 (1977).48. N. Bartlett and P.R. Rao, Proc. Chem. Soc., 393 (1964).49. K.C. Lee and F. Aubke, Can. J. Chem., , 2058 (1979).50. G.A. Olah and T. Ohyama, Synthesis, 5, 319 (1976).51. R.E. Noftie, Inorg. Nuci. Chem. Lett., j, 195 (1980).52. H. Schmidbaur, Angew. Chem. mt. Ed. Engi., 24, 893 (1985).53. H. Schmidbaur, W. Bublak, B. Huber, and G. Muller, Angew. Chem. mt. Ed. Engi., .,26 (1987).54. H. Schmidbaur, W. Bublak, I. Riede, and G. Muller, Angew. Chem. mt. Ed. Engi., 5,24, (1985).55. H. Schmidbaur, U. Thewalt, and T. Zafiropoulos, Z. Naturforsch, 1642 (1984).56. S.H. Strauss, M.D. Nairot, and O.P. Andersen, Inorg. Chem., 25, 3850 (1986).57. E.L. Amma, P.F. Rodesiler, and M.S. Weininger, Inorg. Chem., jj, 751 (1979).58. P.F. Rodesiler, Th. Auel, and E.L. Amma, J. Am. Chem. Soc., 97,7405 (1975).59.a) R.J. Myers, “Molecular Magnetism and Magnetic Resonance Spectroscopy”, PrenticeHall Inc., Englewood Cliffs, New Jersey, 1973.b) E.A. Boudreaux and L.N. Mulay (Ed.), “Theory and Applications of MolecularParamagnetism”, John Wiley and Sons, New York, 1976.c) R.L. Carlin, “Magnetochemistry”, Springer-Verlag, Berlin, 1986.60.a) W.E. Hatfield, W.E. Estes, W.E. Marsh, M.W. Pickens, L.W. ter Haar, and R.R. Wellerin “Extended Linear Chain Compounds”, Ed. J.S. Miller, Vol. 3, Plenum Press, NewYork, pp. 43-50, 1983.b) A.P. Ginsberg, Inorg. Chim. Acta. Rev., 5, 45 (1971).c) C.J. O’Connor, Prog. Inorg. Chem., 22. 203 (1982).61. A.B. Cornford, D.C. Frost, C.A. McDowell, J.L. Ragle, and l.A. Stenhouse, J. Chem.Phys., M 2651 (1971).2562. J.H. van Vieck, “Electric and Magnetic Susceptibilities”, Oxford University Press,London, 1932.63. R.J. Gillespie and J.B. Mime, Inorg. Chem., , 1577 (1966).64. R.D.W. Kemmitt M. Murray, V.M. McRae, R.D. Peacock, M.C.R. Symons, and T.A.O’Donnell, I. Chem. Soc., A862 (1968).65. N. Bartlett and S.P. Beaton, Chem. Comm., 167 (1966).66. F.J. DiSalvo, W.E. Falconer, R.S. Hutton, A. Rodriguez, and J.V. Waszczack, J. CheniPhys., 2575 (1975).67. A. Grill, M. Schieber, and 3. Shamir, Phys. Rev. Lett., 747 (1970).68.a) V.1. Belova, V. Ya. K. Syrkin, D.V. Bantov, and V.F. Sukhoverkhov, Russ. J. Inorg.Chem., (Engi. Trans.), j.., 772 (1971).b) V.1. Belova, V. Ya. Rosolovskii, and E.K. Nikitina, Russ. 3. Inorg. Chem., (Engi.Trans.), .j, 772 (1971).69. N. Bartlett and D.H. Lohmann, J. Chem. Soc., 5253 (1962).70. J.N. Keith, 1.3. Solomon, I. Sheft, and H.H. Hyman, Inorg. Chem., 7, 230 (1968).71. D.E. McKee and N. Bartlett, Inorg. Chem., U 2738 (1973).72. P. Fischer, G. Roult, and D. Schwarzenbach, 3. Phys. Chem. solids, 32, 1641 (1971).73. K.C. Lee and F. Aubke, J. Fluorine Chem., i, 501 (1982).26CHAPTER 2GENERAL EXPERIMENTAL2.1 IntroductionThis chapter will deal with general experimental techniques, chemical sources, purification procedures and the syntheses of starting materials used in this study. Specific syntheticprocedures will be described in the appropriate chapters.Since most of the compounds involved in this work are extremely hygroscopic, they hadto be handled in an environment free of moisture. Hence, standard vacuum line techniques wereemployed for the transfer of volatile liquids, and less volatile liquids and solids weremanipulated inside an inert atmosphere dry box. All reactions were performed inside wellventilated fumehoods.Reactions were monitored by weight where possible, and the removal of volatilematerials in vacuo was usually done at room temperature. However, where liquids with lowvapor pressures like SbF5 or HSO3Fwere involved, elevated temperatures had to be used evenunder vacuum conditions.Fluorolube grease type 25-1OM (Halocarbon Corporation) was used to lubricate groundglass connections to maintain vacuum tight conditions.2.2 ChemicalsSome chemicals were used without purification as received, and these are listed in Table272.1, along with their sources and purities. The other chemicals used were purified orsynthesized according to the methods described below.Table 2.1: Chemicals Used Without PurificationChemical Source Purity (%)Ag, -100 mesh Alfa 99.95Au, -20 mesh Alfa 99.99Pd, -60 mesh Alfa 99.95Pt, -60 mesh Alfa 99.90Sn, -100 mesh Alfa 99.99‘2 Fisher 99.9CuF2 Alfa 99.5AgF2 Aldrich 98.0SnF2 Matheson 98.0AgSbF6 Aldrich 98.0AsF5 Ozark Mahoning reagent gradeHF Matheson reagent gradeSnC12 BDH reagent gradeKJ Fisher 99.95CaH2 BDH reagent gradeNaC5H Aldrich 2.0 M solution in THF282.2.1 Purification Methods(a) SbF5, obtained from Ozark Mahoning, was purified (1) first by purging the crude liquidof most HF by bubbling dry N2 through in a 500 mL two-necked Pyrex flask fitted with agas inlet tube and Drierite guard tube. Subsequent purification was done by repeateddistillation, first at atmospheric pressure in a stream of dry N2 and later in vacuo.(b) HSO3F, from Orange County Chemicals, was purified by double distillation in a Pyrexapparatus under a counter flow of dry N2 at atmospheric pressure (2). The constantboiling fraction at 162-163°C was collected into Pyrex storage vessels.(c) HSO3CF, from Aldrich, was purified by repeated vacuum distillation and stored inPyrex vessels for synthetic use.(d) Br2, from Aldrich, was stored in a Pyrex vessel containing P205 to exclude moisture andKBr to remove Cl2.(e) Mesitylene (1 ,3,5-Trimethylbenzene), obtained from Aldrich, was dried over CaH2 forone week and distilled in vacuo prior to use.2.2.2 Synthetic Methods(a) Bis(fluorosulfuryl) peroxide,S206Fwas prepared in one to two kilogram quantities bythe reaction of SO3 and F2, using AgF2 as catalyst and N2 as carrier gas (3). Thesynthesis was carried out at —180°C in a flow reactor made of Monel metal (Figure 2.1).The crude liquid product was condensed into Pyrex vessels, cooled to -78°C withdry ice.29CToF2cylinderCrosbyPressureGuogeF2OutletToFlowm.t.rCopper6Whlt.y-f3-Hok.413Volv.Autoclav.Engln..rlngValv.sReactorTrapOilTubeAB25C—7C—7WCCOLLECTIONVESSELSFigure2.1:ApparatusforPreparingS206FMost of the potentially explosive byproduct FSO3 was removed by intemittentlywarming the product to room temperature and cooling down to -78°C. Further purification was achieved by pumping on the product overnight at -7 8°C to remove any residualFSO3. Unreacted SO3 was removed by extracting the crudeS206Fwith concentratedH2S04 in a separatory funnel. A product obtained by this route may contain a smallamount of disulfuryl difluoride,S205Fwhich has no effect on the synthetic reactions,except where a stoichiometric amount of S206F is required. The purified colorlessliquid was vacuum distilled into large (500-1000 mL) one-part Pyrex storage vesselsequipped with Kontes Teflon stem stopcocks. The purity of the reagent was checked byboth JR and 19F-NMR spectroscopy.(b) BrSO3F was synthesized by reacting Br2 with a slight excess ofS206F (4) in a longstem one-part Pyrex reactor. The excess S206Fwas required to remove any unreactedBr2 from the liquid product. The BrSO3F obtained by this method can be vacuumdistilled directly from the Pyrex vessel when required.2.3 Apparatus2.3.1 Reaction VesselsOne part glass Pyrex reactors of 25-100 mL capacity were used when solid productscould be isolated by removing the volatiles in vacuo. These round bottom reactors were fittedwith Kontes Teflon stem stopcocks and had side arms extending to B 10 ground glass cones(Figure 2.2(a)). If high pressures were anticipated during reactions, 3 mm thick-wall rather than2 mm normal wall vessels were employed.To facilitate the isolation of products by filtration, two-part reactors made from 50-10031KONTESTEFLONSTEMtJ(b)Figure2.2:TypicalPyrexReactionVessels(a)OnePartReactor(b)TwoPartReactorB—1OGROUNDGLASSCONEB—19GROUNDGLASSJOINTB—1OGROUNDGLASSCONE50—lOOmLBO1IOM(a)FLASKSmL round bottom flasks were utilized (Figure 2.2(b)). A typical reactor consisted of a roundbottom flask with a B 19 ground glass cone fitted with a “drip lip” to trap possible grease-contaminated liquids. The corresponding adaptor top had a Kontes Teflon stem stopcockbetween the B 19 socket and a B 10 cone. During reaction work-up, the adaptor could besubstituted by an appropriate equipment - such as a vacuum filtration apparatus, seen in Figure2.3. The design of the filter was adopted from the one described by Shriver (5).A Kel-F tubular reactor (Figure 2.4) was employed for syntheses involving liquid HF.The Kel-F tube (2 cm o.d. and 1.2 cm i.d.; obtained from Argonne National Laboratory, USA)was held by a Monel top adaptor equipped with a Whitey valve (type 1KS4-316) which could befitted to a metal vacuum line.2.3.2. SbF5 - Storage-bridge VesselThe purified liquid SbF5 was stored in a dual purpose one-part Pyrex container as shownin Figure 2.5. The two Kontes Teflon stem stopcocks and BlO ground glass joints made itfeasible for the vessel to be attached to a glass vacuum line and a Pyrex reactor simultaneously.SbF5 could then be distilled directly from the storage vessel into the reactor via the side armextension.2.3.3 S206F- Addition TrapWhere exact amounts of S206F had to be used, a 1.00 or 4.00 mL graduated pipetequipped with an overflow bulb and fitted on top with a Kontes Teflon stem stopcock wasemployed. The side arm of the trap ended in a BlO ground glass cone, which could beconnected to a Pyrex T-shaped bridge for the transfer ofS206F. Determination of the preciseamount ofS206Fused was obtained by weight difference.33Figure 2.3: Vacuum Filtration ApparatusB—1O GROUNDGLASS CONE50—lOOmIROUND BOflOMF1.ASKKONTES TEFLONSTEM STOPCOCKGLASS FRIT(MEDIUM POROSITY)B—19 GROUNDGLASS JOiNT34C’2SC.)ScpFigure 2.4: Kel-F Tubular ReactorWhitey ValveMonel Alloy TopKel—F TubeCopper FerruleBrass Nutm2cm35Figure 2.5: SbF-Storage-bridge VesselB—iC GROUNDGLASS CONEKONTES TEFLON STEMSTOPCOCK8cmE1)LflB—iC GROUND GLASSSOCKET362.3.4 Pyrex Vacuum LineA general purpose glass vacuum line, consisting of five Kontes Teflon stem stopcockswith B 10 ground glass sockets, was used. The manifold was approximately 60 cm long, and adetachable safety trap, cooled with liquid N2, was placed between the manifold and the vacuumpump to protect the pump from volatile corrosive materials. Typical vacuum generated on thisline was about 10.2 torr.2.3.5 Metal Vacuum LineFor the reactions involving liquid HF, a metal vacuum line was used. It was operated ina manner similar to that of the Pyrex line. The metal manifold was constructed using 6 cm o.d.Monel tubing equipped with Whitey valves (type 1KS4-316), and connected to a liquid N2cooled safety trap via a Teflon adaptor.2.3.6 Dry Atmosphere BoxHygroscopic solids and low volatility liquids were manipulated inside a Vacuum Atmosphere Corporation ?DriLabH Model DL-001 SG dry box, filled with K-grade N2 gas. Theremoval of moisture inside the dry box was accomplished by circulating the nitrogen overmolecular sieves located in the “Dri-Train” Model HE-493. The molecular sieves were periodically regenerated by heating in a stream of 10% H2 mixed with N2. Fresh P205 was also keptinside the dry box to exclude any residual moisture.372.4 Instrumentation and Methods2.4.1 Infrared SpectroscopyRoom temperature IR spectra were recorded using three types of spectrometers: (a)Nicolet 5DX Fr-IR, (b) Perkin Elmer 1710 FT-IR, and (c) Perkin Elmer 598.Samples were run on thin solid films pressed between AgCl or AgBr windows, withtransmission ranges down to —400 and —250 cmt respectively. The high reactivity of thecompounds studied precluded the use of mulling agents or other window materials. Sampleswere prepared inside the dry box and the spectra were recorded immediately after removing thesamples from the box. Spectra of gaseous samples were recorded using a glass cell of 10 cmpath length, fitted with AgBr windows and a Kontes Teflon stem stopcock. All spectra werecalibrated with a polystyrene reference.2.4.2 Raman SpectroscopyRaman spectra were obtained with a Spex Ramalog 5 Spectrophotometer equipped witha Spectra Physics 164 argon ion laser, using the 514.4 nm green line as the excitationwavelength. Solid samples were packed in the dry box into melting point capillaries,temporarily sealed with Fluorolube grease and then immediately flame-sealed.2.4.3 Nuclear Magnetic Resonance SpectroscopyThe FT-NMR spectra were obtained on a Varian XL-300 multinuclear spectrometer,with the following operating frequencies and external references: (a) 1H = 300 MHz, TMS; (b)= 282.23 1 MHz, CFC13. The solutions were either loaded into 5 mm NMR tubes inside the38dry box or, in the case of volatile liquids, transferred via a static vacuum into NMR tubes fittedwith B 10 ground glass cones and then flame sealed. Low temperature spectra were recorded bycooling the probe with liquid N2 and controlling the temperature with a high precision thermocouple.2.4.4 Electronic SpectroscopySolid state electronic spectra in the near infrared and visible regions (4,000 to 30,000cm-1) were recorded on a Cary 14 spectrophotometer. Samples were prepared in the dry box,and run as mulls in either SbF5 or Fluorolube oil as mulling agent in a Teflon cell fitted withquartz windows of 2.5 cm diameter. The absorbance level was adjusted with neutral densityfilters. Nujol mull spectra in the UV-visible range (12,000 to 50,000 cm4) were run on aHewlett Packard 8452-A diode array spectrophotometer using the same Teflon Cell describedabove.2.4.5 Mössbauer SpectroscopyThe 1195n Mössbauer spectra were recorded on a constant acceleration spectrometer (6).Data counts were accumulated on a Tracer-Northern TN-1706 multichannel analyzer, linked tothe mainframe computer via an IBM-PC. The y-ray source used was Ba9SnO3,and theDoppler Velocity Scale was calibrated with an iron foil absorber and a 57Co source. The chemical shifts were measured relative to Sn02.2.4.6 X-ray Photoelectron SpectroscopyX-ray photoelectron spectra were recorded with a Varian IEE-15 spectrometer using AlKa X-rays of 1486.6 eV energy. The detachable XPS sample probe was taken inside the dry39box where powdered samples were thinly dusted onto 2 cm length 3M Scotch tapes, which werewrapped around the sample slugs. The carbon 1S binding energy peak at 284.0 eV was usedas a calibrant in all the measurements. The chemical shift is taken as the difference between themeasured binding energy of a peak and that of the chosen standard atomic peak for a givenenergy level. The accuracy of the measurements is estimated to be ±0.1 eV.2.4.7 Magnetic Susceptibility MeasurementsVariable temperature magnetic susceptibility measurements from —2.0-124 K were madeusing a Princeton Applied Research Model 155 Vibrating Sample Magnetometer, internallycalibrated with ultrapure nickel (7). Temperature equilibration was obtained using a JanisResearch Company Model 153 Cryostat and a Princeton Applied Research Model 152Cryogenic temperature controller. Accurately weighed samples of --200-300 mg were loadedinto Kel-F capsules inside the dry box and sealed with epoxy resin.Temperature measurements were taken with a chromel vs. Au-0.02% Fe thermocouple,located in the sample holder immediately above the sample. The thermocouple was calibratedusing the known susceptibility vs. temperature behavior of tetramethylethylenecliammoniumtetrachiorocuprate (II) and checked with mercury tetrathiocyanatocobaltate (II). From thescatter in data points of four different calibrations, the temperatures are estimated to be accurateto ±1% over the range studied. Thermocouple potentials were measured using a Fluke 8200Adigital voltmeter. Magnetic fields of 7501, 9225, and 9625 G were employed, and set to anaccuracy of 0.5%, and measured with a F.W. Bell Inc. Model 620 Gaussmeter. The accuracy ofthe susceptibility values is estimated to be ±1%.A Gouy balance, equipped with a Mettler AE 163 balance was used in the temperaturerange —80-300 K to measure the susceptibility of some compounds. Samples were packed in a40Pyrex tube containing an air-tight Teflon cap. Measurements were made in a nitrogenatmosphere at a field strength of 8000G and HgCo (NCS)4 was again used as a calibrant. Theaccuracy of the susceptibility values obtained by this method is estimated as ±5%. Correctionswere made for the diamagnetic contribution of the holders and the molar susceptibilities werecorrected for diamagnetism using the following values (8) (units of 10-6 cm3 mol-1): SO3F 40;S03CF 46; SbF6 80; Sb3F16-218; Sb2F11 149; AsF6 72; O2 7; Br2 61; 89; Ni2 11;Pd2 25; Pd4 18; Cu2 11; Ag2 24.2.4.8 X-ray Powder DiffractometryX-ray powder diffraction patterns were obtained using a RU 200B series RigakuRotating Anode Diffractometer operating at 12 KW maximum power output. The Diffractometer detected Cu Ka target radiation through a 200 urn nickel filter with a horizontal-type NalScintillator probe. A horizontal goniometer was used for the rotating anode. The diffractometerwas interfaced with a DMaxIB computer system driven by an IBM PS/2. The peak-findingprogram was provided by Rigaku.Finely powdered samples were put on two sided 3M Scotch tapes attached to glass slidesand protected from moisture by sealing the samples with plastic film. All preparations werecarried out inside the dry box and samples were analyzed as soon as they were removed fromthe dry box.2.4.9 Differential Scanning Calorimetry (DSC)DSC studies were performed using a Mettler DSC-20 cell interfaced with a MettlerTC1O TA processor and a Swiss Matrix printer. Finely powdered samples of approximately2-4 g were sealed into aluminum pans and mounted on the measuring cell, under a dry N2 flow41rate of 50 mI/mm. The samples were scanned through a temperature range of 35 to 450°C with4°C per minute increments.2.4.10 Elemental knalysesCarbon, hydrogen and some of the sulfur analyses were performed by Mr. Peter Borda ofthis Department. All other elemental analyses were carried out by the Analytische Laboratorien,Gummersbach, Germany.References1.a) W.W. Wilson and F. Aubke, J. Fluorine Chem., 13, 431 (1979).b) W.W. Wilson, R.C. Thompson, and F. Aubke, Inorg. Chem., j, 1489 (1980).2. J. Barr, R.J. Gillespie, and R.C. Thompson, Inor. Chem., , 1149 (1964).3.a) J.M. Shreeve and G.H. Cady, Inorg. Synth., 2, 124 (1963).b) G.H. Cady, Inorg. Synth., 11, 155 (1967).4. F. Aubke and R.J. Gillespie, Inorg. Chem., 2, 599 (1968).5. D.F. Shriver, “The Manipulation of Air Sensitive Compounds”, McGraw Hill Book Co.,New York, 1969.6. J.R. Sams and T.B. Tsin, Inorg. Chem., .14, 1573 (1975).7. J.S. Haynes, K.W. Oliver, S.J. Rettig, R.C. Thompson, and J. Trotter, Can. J. Chem., 62,891 (1984).8. Landolt-Börnstein, Numerical data and functional relations in Science and Technology,Vol. 2, Magnetic properties of coordination and organometallic compounds, Springer-Verlag, Berlin, 1966.42CHAPTER 3METAL(1I) HEXAFLUORO ANTIMONATES M(SbF6)2,M(ll) = Sn(J1), Ni(I1), Pd(II), Cu(ll) AND Ag(H)3.1 IntroductionAntimony(V) fluoride, SbF5, is commonly regarded as the strongest molecular Lewisacid (1). Conversely the anions SbF6 and the related Sb2F11-are extremely weak nucleophiles(2), capable of stabilizing a wide range of electrophilic cations, both in solid compounds and inHF-SbF5superacid solution (3).The objective of this study was the synthesis and characterization of SbF6 salts formedby divalent metal cations. The synthetic route chosen was the solvolysis of metal fluorosulfatesin liquid SbF5 according to the general route:25-60°CM(SO3F)2 + 6SbF5 > M(SbF + 2SbF9( O3) [3.1]with M = Sn, Ni, Pd, Cu, or Ag.Early work by Gillespie and Rothenbury (4), and a subsequent investigation by our group(5) into the antimony-fluoride-fluorosulfate system, form the basis for this synthetic reaction.The byproduct Sb2F9O3which is the most volatile component in this system, facilitates theready removal of the SO3F- group from the reaction mixture.As mentioned previously in Chapter 1, initial uses of the solvolysis reaction in SbF5 haveinvolved the stabilization of non-metallic cations, such as C102+ (6), a series of triatomic inter-43halogen cations (7), or the dihalogen cations Br2 and I2 (8) (see Chapter 4) in solidcompounds. Use of this method in the synthesis of the first stage graphite salt C8SbF6 (9) andstabilization of the dimethykin(IV) cation as (CH3)2Sn(SbF11)2 (10) illustrate its versatility.There has been a variety of alternative methods used for the synthesis of hexafluoroantimonates of divalent metals, and two of the compounds discussed here (Ni(SbF6)2(11,12)and Sn(SbF6)2(13)) had been prepared when this study was started. All methods have the useof SbF5 in common, even though the routes vary. Metal oxidation either by elemental fluorineor by SbF5 in SO2 solution has allowed the synthesis of Ni(SbF&2(11,12) as well as Fe(SbF6)2and Mn(SbF6)2(12). However, there are obvious limitations to this approach. Where higheroxidation states are accessible, direct fluorination may result in oxidation beyond the +2 state,unless the reaction conditions are well understood and carefully controlled. Oxidation by SbF5fails for metal with higher oxidation potentials than provided for by the Sb(V)/Sb(III) couple(Appendix A-i). Quantitative separation of the reduced product, solid SbF35,may prove tobe difficult, and mixed fluoride-hexafluoroantimonates like CoF(SbF6)(12) may form instead.Fluoride abstraction from MF2 by SbF5 in SO2 or anhydrous HF may be a more versatilesynthetic method (13,14), but here another problem surfaces: the MF2 lattice could beincompletely broken up under the reaction conditions. This can lead to the formation ofMF(Sb21i)’ a structural isomer of M(SbF6)2,and consequently chemical analysis becomesinconclusive. When moving from ionic SbF6 to coordinated SbF6 in these compounds, vibrational spectra become more complex and are less readily interpreted. As a consequence,formulation as MF2SbF5 is employed in a recent publication for materials obtained in thismanner (14).There is a fair amount of evidence for the existence of cations of the type [MFI+,[M2F3j, and [MF1 when AsF6 is used as a counter anion (15,16), and a crystal structure44obtained on AgF2s5(17) shows a chain-type cation [AgF] with AsF6 as counter anion. InAgF2Sb5however, a true Ag2 appears to be present and the crystal structure supports itsformulation as Ag(SbF6)2(14).The advantages of using the M(SO3F)2-excess SbF5 solvolysis method as a viablesynthetic route to metal(II) hexafluoro antimonates are summarized below:(i) M(SO3F)2precursors are readily available either from the solvolysis of SnC12 or NiC12,or the corresponding Ni(ll) or Cu(II) benzoates or other carboxylates in HSO3F(18), orby the use ofS206Fin the case of Pd(SO3F)2(19) and Ag(SO3F)2(20).(ii) In all instances further oxidation by SbF5 appears unlikely, since higher oxidation statesfor the metals cannot be achieved with the potential provided for only by theSb(V)/Sb(ffl) couple.(iii) Vibrational spectra allow monitoring of the reaction by probing the absence of SO3F-vibrations. All the vibrational bands due to SbF6 appear below —750 cm1, whereasSO3Fstretching vibrations are present well above this value (see Appendix A-2).(iv) Reactions can be carried out under mild conditions in glass vessels and followed byweight. This also facilitates detection of any color changes that may occur during thereaction process.The reasons for the preparation and selection of these five M(SbF6)2compounds for thisstudy, with M = Sn, Ni, Pd, Cu, or Ag are two-fold:(i) To avoid structural ambiguities of the type observed above, it became necessary to45obtain a 119Sn Mössbauer spectrum on a sample of Sn(SbF6)2prepared by a differentroute and to compare it to the spectrum reported previously (13). Furthermore, it wasfound previously that the SbF6 and Sb2F11 anions allow a close approach to the true(CH3)2Sn cation (10) on account of their low nucleophilicity. The same anions, it isfelt, also permit the closest approach to a true Sn2 cation. In both instances, 119Sn-Mdssbauer spectroscopy can be effectively employed.(ii) Significant ferromagnetism was observed at low temperature in the fluorosulfates ofPd2 and Ag2 (Chapter 6, also ref. 21) with a weaker manifestation of this interestingcoupling phenomenon seen also in the analogous Ni(SO3F)2 compound. However,surprisingly the Cu(SO3F)2compound is magnetically dilute to low temperatures (seeChapter 6). Therefore it is of interest to study the magnetic properties of the four corresponding transition-metal SbF6 derivatives at temperatures below 80 K.Since Ni(SbF6)2had been obtained previously by all three methods (11,12,14) discussedabove, its formation by solvolysis in liquid SbF5 is viewed as a test case. A final point of interest concerns the nickel(II) and palladium(ll) compounds. The Pd2 and Ni2 ions in thefluorosulfate are located in an octahedral coordination environment which is unusual for Pd2+,and as a result paramagnetic Pd(ll) and Ni(11) with 3A2g ground state is found in both Ni(SO3F)2and Pd(SO3F)2. It is expected that similar paramagnetic ions are present in the correspondingNi(SbF6)2and Pd(SbF6)2compounds as well.3.2 Experimental3.2.1 General Synthetic Scheme to M(SbF6)2The fluorosulfates Ni(503F)2(18), Cu(SO3F)2(18), Sn(SO3F)2(18), Pd(SO3F)2(19),46and Ag(SO3F)2(20) were all synthesized according to published methods.A general synthetic method was applied to the solvolysis reactions in liquid SbF5.Approximately 500 mg of the M(SO3F)2compound was transferred inside the inert-atmospherebox into a preweighed reaction vessel, and -P10 mL of freshly purified SbF5 was addedsubsequently by vacuum distillation. The reaction vessel was warmed up, initially to roomtemperature, and subsequently to 50-60°C in an oil bath. Detailed temperatures and reactiontimes are given below.Only the reactions of Pd(SO3F)2 (purple —> light-grey) and Ag(SO3F)2(black-brown— yellow-green —> off-white) involved perceptible color changes of the solid reactant and themixture remained heterogeneous throughout. The initially very viscous antimony(V) fluoridebecame less viscous after about 24 h and the mixture could be stirred effectively with amagnetic stirrer. Volatiles were removed in a dynamic vacuum. A sample of Ni(SbF6)2,madefrom Ni and SbF5 by fluorinating with F2 (11), was obtained from Dr. Karl 0. Christe ofRocketdyne, U.S.A.3.2.2 Physical Properties and AnalysesBoth Ni(SbF6)2(11,12,14) and Sn(SbF6)2(13) are known compounds. Their identitieswere ascertained by weight and by infrared spectroscopy. Formation of both Ni(SbF6)2andSn(SbF6)2required reaction times of 14 and 2 days at 60 and 50°C, respectively. The JRfrequencies observed for Ni(SbF6)2are listed in Table 3.1. For Sn(SbF6)2the following JRbands were found (estimated intensities are in parentheses): 700 (s, sh), 678 (s), 648 (s), 620(m), 595 (ms), 571 (ms), 520 (m, sh), 477 (m), 432 (w).473.2.2a Cu(SbF6)2Reaction time 10 days, reaction temperature 50°C, white hygroscopic solid that isthermally stable up to 210°C.Anal. Calcd. for CuSb2F12: Cu, 11.88; Sb, 45.51; F, 42.61%.Found: Cu, 11.65; Sb, 45.75; F, 42.47. Total: 99.87%.3.2.2b Pd(SbF6)2Reaction time 14 days, reaction temperature 50°C, light-grey solid, very hygroscopic andthermally stable up to 250°C.Anal. Calcd. for PdSb2F12:Pd, 18.62; Sb, 42.14; F, 39.45%.Found: Pd, 18.35; Sb, 41.90; F, 39.18. Total: 99.43%.3.2.2c f-Ag(SbF6)Reaction time 10 days, reaction temperature 25°C, creamy white, hygroscopic solid,melts at 180-182°C to clear liquid.Anal. Calcd. for AgSb2F11:Ag, 19.25; Sb, 43.45; F, 37.25%.Calcd. for AgSb2F12:Ag, 18.62; Sb, 42.03; F, 39.35%.Found: Ag, 18.65; Sb, 42.30; F, 39.06. Total: 100.01%.3.2.3 Alternate Synthetic Route to 3-Ag(SbF6)2Two other preparative methods for 3-Ag(SbF6)2using the silver compounds AgSbF6andAgF2 as precursors are shown below:48a) 0.323 g of AgSbF6was allowed to react with an excess ofS206Fat room temperature.The color of AgSbF6 changed immediately from white to black-brown. The excessS206F was removed in vacuo and subsequently replaced by an excess of SbF5. Themixture was kept at room temperature for 2 days, then heated at 60°C for 2 h. A whitesolid of the composition Ag(SbF6)2was isolated by removing the excess SbF5 in vacuoand identified by its JR spectrum.b) 0.436 g (2.99 mmol) of AgF2 was loaded inside the dry box into a Kel-F reactor togetherwith 4.50 g (20.8 mmol) of SbF5. About 6.5 mL anhydrous HF was distilled into thismixture in vacuo. After warming to room temperature under magnetic stirring, a light-yellow solid formed immediately. The solution’s initial color was light blue, whichfaded quickly. Removal of all volatiles yielded again a compound corresponding to thecomposition Ag(SbF6)2as a cream-colored solid.3.3 Results and Discussion3.3.1 SynthesisAs noted previously (6-10), solvolysis reactions of fluorosulfates in a large excess ofSbF5 proceed smoothly and frequently without any color change of the solid reactant. Hence,rather long reaction times are chosen to ensure complete conversion. Two indications that areaction takes place are a noticeable decrease in the viscosity of SbF5 after about one day, and aslight increase in the vapor pressure above the reaction mixture. Both observations may beattributed to the formation ofSb2F9(SO3)(7).To reduce the viscosity even further in order to stir the heterogeneous mixture moreeffectively, slightly elevated reaction temperatures are chosen. Removal of all volatiles49proceeds easily in a dynamic vacuum, with the reaction flask at room temperature.It is noteworthy that after pumping overnight, the correct weight for M(SbF6)2 isobtained. Previous use of this synthetic method (6-8,10) had in all instances led to productswhere molecular cations are stabilized by Sb2F1f,and in one case (8) even by Sb3F16. For thespherical, less electrophilic M2+ cations, SbF6 appears to be the more suitable counter anionallowing formation of layered materials, as discussed below. In any event, neither productweights on isolation, nor chemical analyses, nor vibrational spectra give any indication ofSb2F1 containing intermediates or by-products.Of the resulting compounds, Ni(SbF6)2(11) and Sn(SbF6)2(13) are identified by theirweights and their previously reported IR spectra. The 119Sn Mössbauer spectrum of Sn(SbF6)2shows a single broad line (r’ = 1.35 mm s1) caused by unresolved quadrupole splitting. Theisomer shift is found at 4.39 mm s1 relative to Sn02, in excellent agreement with the previouslyreported value (13).The solvolysis of Ag(SO3F)2is expected to lead to the recently reported blue form ofAg(SbF6)2since solutions of Ag2 in HF are deep blue in color. The X-ray diffraction studyhad revealed a true Ag2 ion in a distorted octahedral environment (14). However, in this studythe course of the solvolysis and the final product obtained are unanticipated. The initial blackbrown color of Ag(SO3F)2quickly disappears and a greenish-blue solid slowly changes to yellow in color. Ultimately a cream-colored, diamagnetic solid is isolated, which melts at -480°Cwithout decomposition to a clear, colorless liquid.The magnetic behavior, the color, and the observed lack of solubility in anhydrous HF(22) suggest the possible presence of univalent silver in the resulting yellow compound. Analternative formulation of the reaction product as AgSb2F11 is, however, not supported by the50weight change during reaction, a complete chemical analysis (see experimental section), thevibrational spectrum, or the chemical behavior of the material. Furthermore, with paramagneticdivalent silver well established in Ag(SO3F)2(20), the other reactant, the Lewis acid SbF5, canhardly be regarded as a reducing agent. A possible reductive decomposition of the reactionproduct appears unlikely, since besides excess SbF5,Sb29(SO3F)is the only volatile productformed during the reaction process.The chemical behavior of the white Ag(SbF6)2is not consistent with the presence of Agin the reaction product. Unlike other silver(I) salts, the material will not undergo furtheroxidation by S206F in the presence or the absence of HSO3F. In contrast, AgSbF6 isimmediately oxidized by S206Falone, to give a black-brown solid, with an increase in weightconsistent with the composition Ag(SbF6)(SO3F). Subsequent solvolysis of this material inSbF5 proceeds in an identical manner to the solvolysis of Ag(SO3F)2,suggesting a viable alternative synthetic route to the white diamagnetic Ag(SbF6)2.Strong evidence for the presence of silver in an oxidation state higher than +1 comesfrom the hydrolysis of Ag(SbF6)2 in aqueous KI solution. The reaction proceeds veryvigorously and‘2 and 02 (where the latter evolves with rapid bubbling) are produced. Formation of 2 may in part be due to oxidation by Sb(V) in an acidic environment (23), but evolutionof 02 can only be caused by Ag(II) or Ag(llI) ((24), also Appendix A-i):2Ag + H20 —÷ 2Ag + 2W + 1/202 [3.2]andAg2 + 2K1 — AgI + 1/212 + 2K [3.3]In summary, all evidence suggests that the material obtained in the solvolysis of51Ag(SO3F)2in SbF5 is J3-Ag(SbF6)2,a valence isomer of the previously reported a-Ag(SbF6)2(14).Attempts were made to synthesize the a-form using the published method (14), whereAgF2was reacted with SbF5 in anhydrous HF according to:HFAgF2 + 2SbF5 > Ag(SbF [3.41These syntheses are only partialiy successful if a slight excess of SbF5 (ratio SbF5:Ag2= 2.32)over the stoichiometric amount is used. Even here a fair amount of solid -Ag(SbF6)2forms inaddition to a blue solution, from which crystalline a-Ag(SbF6)2is obtained by slow evaporationof the volatiles. When a larger excess of SbF5 is used (SbF5:Ag2= 6.01), -Ag(SbF62is theonly product. The blue color of the HF solution quickly fades within an hour. Removal of theHF and the excess SbF5 yields pure 3-Ag(SbF6)2.It seems that formation of a-Ag(SbF6)2in HF represents an acid-base titration with boththe cation Ag2(50l)and the final product a-Ag(SbF2stable in, and isolable from, anhydrousHF. Similar behavior is reported for all other transition-metal hexafluoro antimonates of theM(SbF6)2or MF2SbF5type (14). On the other hand, p-Ag(SbF6)2is insoluble in anhydrousHF, suggesting structural differences.The observed diamagnetism of the compound is best explained by assuming a mixed-oxidation-state compound of the composition Ag(I)Ag(Ill)(SbF64.To account for the diamagnetism, Ag3 should be in a square planar, or at least in a tetragonally elongated, octahedralenvironment while Ag+ would be located in a tetragonally compressed, nearly linear coordination environment. Argentic oxide, AgO, represents a precedent, according to neutron diffractionstudies on this compound (25). The black-brown color, also found for the recently reported52oxides Ag203 (26) and Ag304 (24), is seemingly common to binary oxides and oxysalts of di-or trivalent silver, e.g. the sulfonates Ag(SO3F)2(20) or Ag(SO3CF)2(27), and may possiblybe due to a charge transfer transition (28). In contrast, alkali metal salts containing the [AgF4]ion are reported to be yellow (25,29), while AgF2 and many Ag(ffl) fluoro derivatives are blue(30), just like a-Ag(SbF6)2(14).It appears, then, that all the observations mentioned above support formulation of the[3-form as Ag(I)Ag(Ill)(SbF64;however, the inability to oxidize Ag further withS206Fis notconsistent with an ionic formulation as silver(I) tetrakis(hexafluoroantimonato)argentate(Ill),Ag[Ag(SbF6)4].No report has been published so far of any other valence isomeric pair of the Ag(II) vs.Ag(I)Ag(ITI) type. The above mentioned AgO is reported to be Ag(I)Ag(llI)02(25), but a trueAg(ll)O appears to be still missing. However, the crystal structure of Ag304 (24) shows bothAg(ll) and Ag(III) in square planar coordination sites, and mixed oxidation-state compounds ofthe type Pd(II)Pd(IV)X6,with X F (31) or SO3F (19), are known for palladium, the neighboring element in the 4d series, with Pd(llI)X3so far unknown. Little is known, at least with regardto structure, about the paramagnetic red-brown compound AgF3 (32). The mixed valency formula Ag(II)Ag(IV)F6has been proposed but the product may still contain some impurities (33).Observations made during the course of this study suggest that a-Ag(SbF6)2may beirreversibly converted to the [3-valence isomer. This conversion occurs at room temperature, ifSbF5 is present in an excess, either in the presence or absence of HF. It is therefore not surprising that all the attempts made to synthesize pure a-Ag(SbF6)2from AgF2 and SbF5 in anhydrousHF (14) produce [3-Ag(SbF6)2as well, as an insoluble precipitate in addition to the blue solution.Removal of the solvent at -7 8°C in a dynamic vacuum affords a mixture of the two valenceisomers.53Heating the isomeric mixture allows transformation to the pure [3-form. Following thisconversion by differential scanning calorimetry indicates two endothermic events, a sharp peakat 100°C, and a broad peak at 139-140°C. The latter peak coincides with the melting point,where a colorless liquid forms. The [3-form melts at —180°C, consistent with differential scanning calorimetry. Absence of the peak at 100°C suggests interpretation of this thermal event asa phase transition from a-Ag(SbF6)2to [3-Ag(SbF6)2.It seems likely that electron transfer between two Ag2 ions to give Ag and Ag3 ismediated by an antimony(V) fluoro species (SbF5 or SbF6). Considering the observations maderegarding the relative stability of the two valence isomers, it is surprising that [3-Ag(SbF6)2hasnot been reported while the a-form has.The solvolysis of Pd(SO3F)2in SbF5, on the other hand, does not appear to change theelectronic structure of the Pd2 ion (31,34). The electronic spectra and magnetic susceptibilitydata clearly show that in Pd(SbF6)2,the palladium ion, like in its parent compound, remains as aparamagnetic Pd2 species. However, in Cu(SbF6)2,the solvolysis product of Cu(SO3F)2,identification of all the copper ions as purely divalent may not be possible. Magnetic measurements taken on Cu(SbF6)2also indicate, as in the case of [3-Ag(SbF6)2,mixed valency althoughto a more limited extent. This is discussed in more detail in Section 3.3.4, which deals withmagnetic studies.It is of interest to note here that this solvolysis behavior leading to unexpected mixedvalent products is exhibited by the two transition metal precursor compounds Cu(SO3F)2andAg(SO3F)2with HJahnTeller ions”, i.e. Cu2 and Ag2 (d9).543.3.2 Vibrational SpectraThe infrared spectra obtained for Ni(SbF6)2,Pd(SbF6)2,Cu(SbF6)2,and -Ag(SbF6)2,together with the Raman spectra for the last two compounds, are summarized in Tables 3.1 and3.2. Also included are the previously reported Raman spectra for Ni(SbF6)2 (11) anda-Ag(SbF6)2(14) as well as an approximate band description, also proposed previously (11).However, this description pertains only to the Ni2,Pd2, and Cu2 compounds in Table 3.1.The Raman spectrum of [3-Ag(SbF6)2is illustrated in Figure 3.1. Attempts to obtain a Ramanspectrum of Pd(SbF6)2result in partial sample decomposition. Apparently the excitation line ofthe Ar laser falls within ii2 of the electronic spectrum of Pd(SbF6)2.Agreement with the JR and Raman spectra previously reported for Ni(SbF6)2(11) is verygood with only a minor exception: an JR band at 585 cm1 attributed to out of phase forbridging SbF3 group is not observed in this study. This band does not have a counterpart in theRaman spectrum, and may be spurious. The band description in Table 3.1 has been amendedslightly. There is only a partial comparison possible with the vibrational spectra reported forNiF2SbF5(14). The limited number of bands listed, six Raman and four JR bandswith five non-coincidences, suggests an incomplete listing. Nevertheless, the Raman bandsreported for NiF2•2SbF5 (14) are all observed with similar relative intensities in the Ramanspectrum of Ni(SbF6)2(11). Since the reported X-ray powder data have the principle lines incommon (11,14; see also Appendix A-3), it is reasonable to conclude that the two compoundsare identical.This is possibly not the case for Cu(SbF6)2reported here, and CuF2Sb5(14). Veryintense Raman and IR bands at 725 cm1 (see Table 3.1) are apparently not observed forCuF2Sb5 (14). However, the case for polymorphism as evidenced by magnetic measurements (see Section 3.3.4) is by no means as strong as in the case of the two forms of Ag(SbF6)2.55Table3.1:Vibrational SpectraofNi(SbF6)2,Pd(SbF6)2,andCu(SbF6)2Ni(SbF6)2a)Ra.b)Ni(SbF6)2IRPd(SbF6)2IRCu(SbF6)2IRCu(SbF6)2RaApproximateBandDescriptionAl.)[cm1]Tnt.1)[cm1]mt.1)[cm1Tnt.1)[cm-1]Tnt.Al)[cm-1]mt.for M(SbF6)2;M=Ni,PdorCu742(1)738vs730s,sh729s725(65)l)asSb13’outofphase717(12)721s,sh716vs707vs,b721(70)lJasSbF3tinphase710(44)710vs698s672s709(18)lJSbF3toutofphase674(100)672m667ms665m671(100)1SbF3tinphase657(22)631m630m633masSt3boutofphase618(5)621m,sh615ms617m620(4)l)SbF3’outofphase568(2)573s570m556ms592(8)l.)3SSbFbinphase560w,sh550w,sh511(2)521mw522ms496ml)SbF31’inphase465m450(8)348(0+)350w,sh345m395(7)M”F-Sbstretching322(5)330w335m,sh335(11)308(24)310w—300w305(19)299(25)295w285w295(26)Sb-Fdeformationmodes272(3)270(29)Abbreviations:s=strong,m=medium,w=weak,v=very,sh,=shoulder,b=broad,as=asymmethc,sym=symmetric,t=terminal,b=bridginga)Additionalbands at246, 220and198cm1andshoulders at172,146,and130cmb)Ref.14Table3.2:VibrationalSpectraoftheTwoValenceIsomersofAg(SbF6)2-Ag(SbF6)2Ra-Ag(SbF6)2JR(X-Ag(SbF6)2Raa)C-Ag(SbF6)2IRa)ApproximateBandDescriptiont\D[cm1]mt.)[cm1]mt.M)[cm1jmt.1)[cmmt.720sh(12)719s,sh700sh(33)692vs692vs682(100)673sSbF’stretching659(93)654s668(100)668ms651sh(30)658(75)640m600(16)602m600(37)1580(31)f583wSbFbstretching526(4)515vw552(20)554w490ms496w365(1)368mwMFSbstretching357w,sh312sh(13)303(32)301shSbFdeformation290•(18)283s290(37)278sa)Ref.14.Figure 3.1: Raman Spectrum of -Ag(SbF6)2750682700 650 600 550 500 450 400 350 300 250v, cm165970065!600303312 29058The available structural information on M(SbF6)2compounds facilitates a discussion ofthe vibrational data shown in Table 3.1. A common CdC12-type layer structure is proposed forNi(SbF6)2,based on X-ray powder diffraction data (11), and evident for a-Ag(SbF6)2from theX-ray single crystal diffraction study (14) (Figure 3.2). The structure for Ni(SbF6)2is deduced,starting from the well known LiSbF6 structure (35) by placing Ni2 into every second, nearlyoctahedral Li site (11). In a-Ag(SbF6)2,Ag2 is situated in a tetragonally elongated octahedralsite (Figure 3.2(c)), resulting in almost square planar coordination, similar to the coordination inAgF2 (36). SbF6 acts as a thdentate bridging group (Figure 3.2(b)), with the bridging fluorines,Fb, and the terminal fluorines, Ft, in fac-octahedral positions. Unlike the SbF31’ unit, thecorresponding SbF3t trigonal pyramid is remarkably regular with two dsb..Ft --1.836 A and oneslightly longer at 1.846 A.The vibrational assignment for Ni(SbF6)2by Christe et al. (11), adopted here in thisstudy, suggests a useful subdivision into SbF3tstretching modes found above —660 cm1 andSbF3t) below —635 cm1. Each set is further divided into symmethc and asymmetric in-phaseand out-of-phase modes. The basic difference between both sets, SbF3b and SbF3t, is that theformer belong to a filled, and the latter to an unoccupied octahedral hole in the M(SbF6)2-layerstructure.The data summarized in Table 3.1 for M(SbF6)2with M = Ni, Pd, and Cu, show indeed acommon group of four strong vibrations, some small band splittings for Cu(SbF6)2 notwithstanding, which are assigned as SbFt vibrations. Most prominent among them is a Ramanband at —670 cm1, which is clearly the strongest band in the respective spectra. Interestingly,this band is found as well for a number of additional M(SbF6)2compounds with M = Mg, Zn,Fe, Co, and Cu (14), in the same position, and always of the highest intensity. This is notunexpected, since the reported X-ray powder diffraction data had indicated the existence of twostructurally related triads, consisting of the hexafluoro antimonates of Mg, Zn, and Ni, and those59Figure 3.2: Crystal Structure of cz-Ag(SbF6)2(Ref. 14)(a) The Unit Cell (b) ORTEP view of [SbF6] anion(c) ORTEP view of Ag2 environmentF(3)60of Fe, Co, and Cu (14). However, the structural differences between the two triads appear to beso small that they do not seriously affect the positions of the USbF3tbands. In the Raman data,the 670 cm1 band is attributed to a symmetric in-phase SbF3tstretching mode, which suggestsa common SbF3L grouping in both triads as well as in Cu(SbF6)2reported in this work. Acorresponding IR band of medium intensity is observed in all instances as well. This band isfound for Pd(SbF6)2 at 667 cm1. In addition, there is a close correspondence betweenNi(SbF6)2and Pd(SbF6)2in both JR band positions and intensities to suggest isostructuralcompounds.The remaining M(SbF6)2compounds reported by Gantar et al. (14) with M = Cr, Pb, andCd, differ slightly in both vibrational spectra and X-ray powder diffraction data. The highestintensity Raman band is now found at about 650 cm1. Even for these compounds, as for all theothers (14), formulation as M(SbF6)2is suggested. None of the vibrational data reported here orpublished previously (11,14) suggest the presence of the anion Sb2F11, by comparison topublished precedents (13,37,38).The vibrational data for both forms of Ag(SbF6)2 in Table 3.2 show interestingdifferences. Both have two very intense Raman bands, rather than one, in the uSbF3tregion, at668 and 658 cm’ for a-Ag(SbF6)2and at 682 and 659 cm1 for the f3 form (see Figure 3.1). Ineach case the band with the largest Raman shift also has the highest intensity, and yet in spite ofthe incomplete band listing for a-Ag(SbF6)2,there appears to be some structural similaritybetween the two forms. Only a rather general band description is suggested, because there maybe some band overlap for 3-Ag(SbF6)2,while the listing for the a-form appears, as stated above,to be incomplete.The distorted layer structure formed for a-Ag(SbF6)2with all tetragonally elongatedoctahedral holes occupied by Ag2, and concommitant tetragonally compressed, vacant sites61(14) provide a suitable model for the valence isomer as well. Regular occupation of half of thecompressed holes by Ag and half of the elongated holes by Ag3 would allow retention of thelayer structure, where Ag achieves linear and Ag3+ square planar coordination. Conversely,two types of vacant sites are formed with two sets of SbFt vibrations and different bandpositions for the SbFb stretching modes as well, consistent with observations.3.3.3 Electronic SpectraElectronic mull spectra were recorded for the nickel and palladium hexafluoroantimonates, and it appears based on these spectra that the solvolysis of Ni(SO3F)2 andPd(SO3F)2in SbF5 does not lead to a change in the electronic structures of Ni2 and Pd2 ions.The resulting compounds Ni(SbF6)2and Pd(SbF6)2,like their precursors, are paramagnetic(Section 3.3.4). It is therefore not surprising that the magnetic results and the vibrational spectrapoint to octahedrally coordinated Ni(ll) and Pd(II) in Ni(SbF6)2and Pd(SbF6)2.These two compounds show similar three-band electronic spectra, which can beattributed to d-d transitions. Although no extinction coefficients were obtained to support theassignment due to the insolubility of the compounds in a suitable solvent, it seems that theligand field parameters Dq and B derived from such an assignment are very reasonable,particularly in comparison to the reported Dq and B values of the two parent compoundsNi(SO3F)2(39) and Pd(SO3F)2(19).The electronic ground term for a d8 ion in an octahedral ligand field is 3A2g and threespin allowed d-d transitions to the excited triplet-terms are expected. The energy level diagramfor a d8 ion in an octahedral field is given in Fig. 3.3. The band positions of the observedelectronic spectra and the calculated ligand field parameters of Ni(SbF6)2, Pd(SbF6)2,Ni(SO3F)2(39) and Pd(SO3F)2(19) are listed in Table 3.3. It seems that the agreement in band62Figure 3.3: Spin Allowed Electronic Transitions from 3A25 Ground Term for Pd2 andNi2 (d8) in Octahedral Ligand Field\\\_________________________________\3P/////////V;3 V2 11\\\igig2g2g\\\\free—ion\‘terms weak flgand field terms63Table 3.3: Electronic Transitions and Ligand Field Parameters for Ni(SbF6)2,Pd(SbF6)2and Related CompoundsCompound Electronic Transition Energy lODq B B/B° d Reference(cm-1) (cm-’)1a 3cNi(SbF6)2 6740 11300 22400 6740 899 0.832 This workNi(SO3F)2 - 12400 23300 7340 912 0.844 39Pd(SbF6)2 11900 18200 26700 11900 613 0.739 This workPd(SO3F)2 11800 17400 27000 11800 606 0.730 19a i: 3A2g __> 3T2gb 2: 3A2g 3Tig (F)C 1)3: 3A2g 3Tig(P)d B/B° = f3, where B° is the free ion value obtained from Ref. 34(a).64positions for Ni(SO3F)2/Ni bF6)and Pd(SO3F)2IPd bF6)pairs suggests similar coordination environments for the Ni2+ and Pd2+ in the fluorosuifate and hexafluoroantimonatederivatives.In addition, the Dq and B values reported here also point to a close structural similaritybetween the two types of compounds. For Pd(SO3F)2(19), like for most fluorosulfates ofdivalent metals (18), a layer structure based on the CdC12 prototype is postulated. As discussedin Section 3.2, the same structural type is reported for a-Ag(SbF6)2(14) and implicitly also forNi(SbF6)2(1 1).Paramagnetic Pd2+ complexes with fluorometallate anions have precedents. Complexesof the general type Pd[MF6], with M = Pd, Pt, Ge, or Sn, have been known for over 25 yearsnow (31), and their magnetic susceptibility measurements have been reported down to 80 K.The presence of MF62 anion would suggest a different structural type, but the coordinationenvironment of Pd2 should again be octahedral.The ligand field parameters, the octahedral splitting Dq and the interelectronic repulsionterm B are obtained by using the appropriate equations (see Appendix A-4) as suggested byLever (34(b)). The increase in Dq and the decrease in j (defined as B/B°, where B° is the freeion value) when moving from Ni(ll), (3d8) to Pd(II), (4d8) are not unexpected in view of thehigher nuclear charge and more spacially diffuse 4d orbitals for palladium (40).Although no splitting of any of the bands is observable, the broad nature of the bandsmakes it difficult to confinn or deny the possible existence of distortion in the octahedralcoordination sphere of the respective metal centers.653.3.4 Magnetic Susceptibility MeasurementsMagnetic susceptibilities over the temperature range of —2 to 80 K are recorded forNi(SbF6)2,Pd(Sb13)2,and Cu(SbF&2on a P.A.R. vibrating sample magnetometer. Relevantdata are summarized in Tables 3.4, 3.5 and 3.6 respectively, and the plot of the magneticmoments vs. temperature for all three compounds is given in Figure 3.4.As discussed in the experimental section, attempts to obtain pure a-Ag(SbF6)2inquantities large enough for a bulk magnetic measurement were not successful. The results ofmeasurements made, on what is obviously a mixture of the two valence isomeric forms, allowonly limited conclusions, since the small amount of paramagnetic material in the sample did notpermit the extension of the measurements to temperature higher than 65 K. Generally, forparamagnetic materials with one or two unpaired electrons, the vibrating sample magnetometerused in this work is useful to —90 K. In the temperature range of 65-3 K the magnetic momentcalculated for cx-Ag(SbF6)2appears to be independent of temperature with a shallow maximumat --6 K before falling off. It is unclear whether the observed dilute magnetic behavior is due toa-Ag(SbF6)2,or caused by 3-Ag(SbF6)2acting as a diluent.The diamagnetism of -Ag(SbF6)2 is confirmed by measurements made at roomtemperature, using the Gouy technique. The measured susceptibility of -68 x 10 cm3 mo11 isless than the sum of Pascal constants of -128 x 10-6 cm3 mol1;however, the Gouy balance usedis insufficiently sensitive for a more accurate determination of diamagnetic susceptibilities. Inaddition, trace amounts of a-Ag(SbF6)2could be responsible for the slight discrepancy, as wellas temperature independent paramagnetism (TIP).As seen in Figure 3.4, the magnetic moment decreases gradually with decreasingtemperature for Ni(SbF6)2and Pd(SbF6)2,before a steep decline becomes apparent at —10 K,66Table 3.4: Low Temperature Magnetic Data of Ni(SbF6)2Temperature [K] XMCOff x i05 [cm3mol1] Peff B181.67 750 2.2177.78 780 2.2074.08 820 2.2069.72 870 2.2065.31 920 2.1960.15 1000 2.1954.20 1100 2.1847.60 1240 2.1740.05 1450 2.1530.80 1850 2.1426.28 2150 2.1321.17 2610 2.1016.20 3280 2.0611.00 4560 2.007.72 6060 1.935.34 8020 1.854.78 8660 1.824.32 8990 1.763.70 9770 1.702.99 10340 1.572.50 10730 1.472.00 11160 1.3467Table 3.5: Low Temperature Magnetic Data of Pd(SbF6)2Temperature [KJ XMCOIT x105 [cm3moP1] J4ff [PB]81.50 1460 3.0977.55 1530 3.0873.91 1600 3.0769.77 1680 3.0665.19 1770 3.0460.03 1900 3.0254.00 2060 2.9947.15 2300 2.9539.80 2630 2,8931.10 3210 2.8330.45 3260 2.8226.55 3620 2.7721.60 4200 2.6920.80 4310 2.6816.50 5220 2.6210.80 8410 2.709.94 9170 2.707.12 11270 2.535.84 11720 2.345.26 11830 2.234.76 11910 2.134.36 11910 2.044.00 11950 1.963.64 11950 1.873.37 11990 1.802.99 11990 1.692.29 11990 1.452.10 12020 1.4268Table 3.6: Low Temperature Magnetic Data of Cu(SbF6)2Temperature [K] XMCOff x [cm3mol1] eff [ILBI81.83 370 1.5678.06 390 1.5674.24 410 1.5770.11 440 1.5765.65 470 1.5760.44 510 1.5754.45 560 1.5651.40 590 1.5647.95 640 1.5640.55 750 1.5630.70 980 1.5526.00 1150 1.5521.22 1410 1.5516.25 1820 1.5411.00 2690 1.547.46 3970 1.545.56 5420 1.554.24 7290 1.574.04 7250 1.493.02 8890 1.472.40 10750 1.441.97 12480 1.401.86 13230 1.4069Figure 3.4: Magnetic Moment vs. Temperature of M(SbF6)2,M=Ni, Pd and Cuf2K<T<82K12.:•‘ Pd(SbF6)22-.. .-o-.-o.-.o.-.o 0 Ni(SbF6)21.5—i4 •...+....•.--4...•..•-.•..• • Cu(SbF6)21-0 20 40 60 80 100TEMPERATURE,K70indicative of possible antiferromagnetic ordering. An additional contributing factor to the sharpdrop in the magnetic moment values at very low temperatures could come from zero-fieldsplitting of the triplet spin states in the nickel and palladium compounds. It was shown inSection 3.3.3 wher’ the electronic spectra of both Ni(SbF6)2and Pd(SbF6)2were discussed thatthe ground term of Ni2 and Pd2 ions in these two compounds is3A2g.For ad8-ion in an octahedral ligand field with 3A2g ground term, the magnetic momentcan be expressed as follows (41):4?. 4ji = (8)112 (1— ) = (1— ) [35]e lODq S.O. lODqwhere ? = spin-orbit coupling constant = J2 for d8.lODq = ligand field splitting parameter= spin-only magnetic moment = [4S(S+l)]112Since the ground term discussed here is 3A2g a first-order orbital contribution to the magneticmoment is not expected. However, through spin-orbit coupling, which is expected to be quitelarge for second and third row transition metals, the observed magnetic moment is enhancedbeyond the spin-only value. In the absence of any magnetic exchange between the paramagneticcenters, the moment calculated is independent of temperature and should depend only on . andlODq. The sign of is negative for transition metals where the d-shell is more than half full,and therefore according to equation [3.5], for Ni2 and Pd2 ions Peff greater than isexpected.For Pd(SbF6)2,using equation [3.5] with lODq = 11,900 cm (Table 3.3) and theestimated value of ?. for Pd2 = 1600/2 cm4 (42), a temperature independent-moment of 3.59 Bis obtained. The observed magnetic moment of 3.09 B at —82 K is reasonable when compared71to the predicted value, since the magnetic moment in Pd(SbF6)2has been lowered by anti-ferromagnetic exchange, as evident from the plot in Figure 3.4.A slight increase in the magnetic moment is observed in the Pd(SbF6)2plot (also to avery small extent in Cu(SbF6)2,just before dropping off at very low temperatures. Theobserved weak effect is reproducible and two possible interpretations are suggested: (a) a phasetransition occurs at --10 K and (b) very weak ferromagnetism is responsible for the small effect.The latter explanation is favored here because there are a number of precedents forsimultaneous ferromagnetic and antiferromagnetic ordering in fluoro derivatives ofpalladium(ll). Very weak ferromagnetism is observed in PdF2 (43), which has a rutile structure(44), and in the ternary fluorides Pd(ll)Pd(IV)F6and Pd(U)Pt(IV)F6(45). According to a recentcrystal structure reported for the latter compound (46), there may even be a close structuralrelationship: Pd(ll)Pt(IV)F6has a LiSbF6 structure. For Pd(ll)(SbF6)2a layer structure issuggested, which, as discussed above, is also derived from the LiSbF6prototype, with half of theoctahedral holes occupied by Pd2 compared to all holes filled for Pd(ll)Pt(IV)F (46).Some similarity in magnetic behavior is also evident from the I’80eff values, which arefor the ternary palladium(ll) fluorides in the range of 2.7 to —3.0 B for the seriesPd(II)M(IV)F6,with M = Pd, Pt, Ge or Sn (31a), while for Pd(SbF6)2,where Pd2 is slightlymore dilute, a value of 3.09 B is found.Substantially higher magnetic moments (3.30-3.60 B) are found for the correspondingfluorosulfato complexes of palladium(II) (19b), where the bulkier fluorosulfate groups appear toprevent antiferromagnetic exchange. It is interesting to note that at low temperatures (—20 K)significant ferromagnetism has been observed for two members of this group Pd(SO3F)2andPd(ll)Pd(IV)(SO3F6(see Chapter 6). The former, like Pd(SbF6)2,has a layer structure, derived72from the CdC12 type, and both appear to have the Pd2 ion in very similar electronic environments at room temperature, as reflected in their respective electronic mull spectra (Table 3.3)discussed in Section 3.3.3.The magnetic moments observed for Ni(SbF6)2are rather low (g = 2.21 B at —82 K),even though the moments are reduced by possible antiferromagnetic exchange (see Figure 3.4and Table 3.7). If there is no magnetic exchange between the paramagnetic Ni2+ centers,equation 3.5 can again be utilized to calculate the temperature independent moment. The lODqvalue of the compound is 6740 cm1 (Table 3.3), and the estimated value of . for Ni2 is 644/2cm1 (42) which when substituted in equation 3.5 yields al1eff value of 3.37 B•In order to understand the unusual magnetic results of Ni(SbF6)2,two other Ni(SbF6)2samples, made by different methods were also investigated for their magnetic properties. Asample was obtained for this study from Dr. Karl 0. Christe of Rocketdyne, U.S.A., which wasprepared from Ni, SbF5 and F2 under high temperature and pressure (11). The second samplewas synthesized for this study from NiF2 and SbF5 in anhydrous HF according to the publishedmethod (14). The low temperature magnetic moment vs. temperature plot of these two samplesis given in Figure 3.5 (see Appendices A-5 and A-6 for data).In addition, magnetic measurements were also taken using a Gouy balance on thesolvolysis sample as well as on the above mentioned high temperature fluorination product (11).Results of this high temperature study are given in Table 3.7.Although all the three samples of Ni(SbF6)2display the common behavior of temperature dependent low magnetic moments, it is rather puzzling to note that their moments differ sosubstantially. The plots of ieff vs. T display very similar slopes which suggests the possiblepresence of a common magnetic substance at different concentrations in these samples. The73Figure 3.5: Magnetic Moment vs. Temperature of Ni(SbF6)23.4 -,o o [A]0 °0000000- C’.•. . . . . [B]C••2.6- g •..2.4- o..CCL.L I0 20 40 60 80 100TEMPERATURE,K[A] Gift sample, from Ni + F2 + SbF5, Ref. 11[B] Sample from NiF2 + SbF5 in HF, Ref. 1474Table 3.7: Magnetic Moment Data of Ni(SbF6)2for the Temperature Range 8O to 295 KNi(SbF6)2a Ni(SbF6)2b[Ni(SO3F)2+ SbF5] [Ni + F2 + SbF5JTemperature (K) ILeff (PB)C Temperature (K) p. (JtB)’290.5 2.64 293.5 4.25268.5 2.61 268.8 4.16251.0 2.61 251.0 4.11234.5 2.61 234.5 4.07218.0 2.60 218.0 4.02200.3 2.58 201.0 3.97176.0 2.58 177.0 3.90151.0 2.56 151.5 3.81126.3 2.45 127.5 3.73101.8 2.42 103.0 3.6186.5 2.31 86.5 3.5378.0 2.26 78.0 3.46a This workb Gift sample, made according to Ref. 11Ceff = 2.828 [(Xmoi - TIP)T]1/2;= 2320 x 10-6 cm3 mo1175solvolysis product from this study appears to have the lowest magnetic moments, whereas thegift fluorination sample exhibits moments which are unexpectedly high for an octahedrallycoordinated Ni(I1) species (Table 3.7). The sample made using HF as solvent medium hasmoments (measured up to —80 K only, Figure 3.5) which fall between the above two sets ofvalues. Furthermore, a Ni(SbF6)2sample made from the oxidation of Ni by SbF5 in SO2solution is reported as having a magnetic moment of 3.16 1B at 294 K (12).It is also important to note here that if the symmeuy of the ligand field acting on a d8 ionlike Ni(II) is allowed to be lower than cubic and this low symmetty component is large enough,then a spin free-spin paired (triplet-singlet) equilibria may occur in the paramagnetic ions of thecompound (47,48). This could reduce the magnetic susceptibility of the system, yieldingmagnetic moments lower than expected. Although this situation is observed mostly in Ni(II)complexes, it is reported to occur almost exclusively in solutions and is dependent on thesolvent, concentration and temperature (47). Therefore, this unusual behavior may not be asignificant factor in this solid state magnetic study of Ni(SbF6)2. However, the existence ofsuch systems in the solid state cannot be ruled out completely.The temperature dependent low moments obtained for the solvolysis sample may be dueprimarily to the following factors: (a) possible antiferromagnetic interaction between the Ni(II)centers, which will lead to lower than expected moments; (b) small amounts of nickel ions inoxidation states other than +2 acting as cliluents to predominantly octahedral Ni(ll) ions in thelattice; and (c) a combination of factors (a) and (b) which will result in lower magneticmoments for the compound.The contribution of antiferromagnetism toward lower moments can be seen clearly inboth Figure 3.5 and Table 3.7, where in the latter tabulation the small contribution (320 x 10-6cm3 mo11) from the temperature independent paramagnetism (TIP) to the susceptibility has76been removed, since this contribution is relatively significant at higher temperatures.However, as no Xmax is observed in the susceptibility data, antiferromagnetism alonecannot account for such low moments in the solvolysis product. Therefore, the existence ofsmall quantities of other nickel ion species than octahedral Ni(II) in the lattice may have to beconsidered as a possibility.Interestingly, two octahedrally coordinated spin paired Ni(ffl) fluoro compounds,K3NiF6 and Na3iF6 have been reported in the literature (49), where the elongation of the[NiF6]3 octahedron is ascribed to the Jahn-Teller effect to be expected for the t2g6eg’configuration. The magnetic moment ofK3NiF6is given as 2.51 and 2.12 B at 295 and 90 Krespectively (50), although the large temperature dependence of the moments is surprising for an2Eg ground term, unless thermal equilibrium between low and high spin configurations (49)and/or antiferromagnetism is taken into consideration. It is however still rather difficult torationalize the generation and hence the presence in the solvolysis product of nickel ions inoxidation states other than +2, since the parent compound Ni(SO3F)2is well characterized as aNi(ll) octahedral complex, both by electronic spectra (39) and magnetic studies (Chapter 6).The magnetic moments calculated at higher temperature for the fluorination product(Table 3.7) in contrast, are significantly above the values expected for a d8 Ni(II) complex. Itwas shown earlier that equation [3.5] predicts a temperature independent moment of 3.39 1B’whereas the moment obtained at room temperature of this compound exceeds this value bynearly one Bohr magneton. As discussed in Section 3.1, the obvious limitation in the hightemperature synthesis of Ni(SbF6)2is that direct fluorination may lead to oxidation of the metalbeyond the +2 state. This is possible in nickel where higher oxidation states are accessible andthe metal can be oxidized under severe conditions up to the +4 state (40). However, as pointedout above, the known octahedral Ni(ffl) fluoro compounds are of the spin-paired type (49) and77Ni(IV) derivatives like (CIF2O)Ni6and K2NiF6 (5 1,40) are diamagnetic with the low-spint2g6 configuration. Therefore, the origin of the high magnetic moments calculated for thiscompound is not clear, especially as the compound has been sufficiently characterized usingmicroanalysis, vibrational spectroscopy and X-ray powder diffraction (11). However, a verylikely cause of the high magnetic moments for this sample can be Ni metal impurities. Since Nimetal is ferromagnetic, trace amounts of it would cause significantly larger ).teff values for thesample. Furthermore, the metal saturates at relatively low magnetic fields, and as ‘eff is proportional to (XMT)”2,this will result in decreasing moments with decreasing temperatures for thecompound. Field dependent magnetic susceptibility studies are required to verify this possibleferromagnetic contamination of the samples.The magnetic moments obtained for Cu(SbF6)2are given in Table 3.6, and appear to beindependent of temperature down to —4 K. It is also of interest to note here that of the fourtransition metal fluorosulfate precursors used for this study, only Cu(SO3F)2is magneticallydilute to low temperatures (Chapter 6). The moments of Cu(SbF6)2are lower than expected fora Cu(II) (d9) ion in an octahedral ligand field (52). Since the ground term 2Eg has no orbitalangular momentum associated with it the moments should be close to the spin only value of 1.73B in the first approximation. However, spin-orbit coupling can occur between the 2E groundterm and the higher lying 2T2g term, leading to slightly higher moments predicted by the following expression (41):2?. 2APeff (3) ( 1 lODq = (1 lODq [3.6]where the terms used are as in equation [3.5].It was noted earlier in Section 3.3.2 that the vibrational spectrum of Cu(SbF6)2made viathe solvolysis method is slightly different when compared to that of CuF2Sb5(14). This was78taken as a clue to the possible existence of polymorphism in the two forms of Cu(SbF6)2,although to a very limited extent than in the case of Ag(SbF6)2.Magnetic measurements obtained on several samples of Cu(SbF6)2also indicate thispossibility (Figures 3.6 and 3.7), with Cu(I), Cu(II), and Cu(III) present in an equilibrium of thetype:k12 Cu(II) Cu(I) Cu(Ill), k2 >> k1 [3.7]k2with the ratio k2/k1 differing very slightly relative to the experimental conditions of theformation reaction and the subsequent treatment of the reaction product. Solvolysis ofCu(SO3F)2in SbF5 appears to generate small quantities of Cu(I) and Cu(III) ions, in addition tothe relatively larger number of Cu(ll) ions (k2 >> k1). The diamagnetic Cu(I) and Cu(llI) ionsseem to act as diluents to the paramagnetic Cu(ll) centers, thereby lowering the observedmagnetic moments of the compound below the expected values. This could also account for thetemperature independent magnetic moment behavior of the compound, where the Cu(II) centersare now more dilute than in the corresponding Pd(II) or Ni(ll) derivatives.When the product is treated with anhydrous HF for 3 days, equilibrium [3.7] is shiftedfurther to the left (k2 >>> k1), resulting in an increase in the Cu(II) ions present in thecompound. Consequently, the magnetic susceptibility of the sample is enhanced to a small butsignificant extent leading to correspondingly higher magnetic moments (Figure 3.6). Theopposite effect is found when Cu(SbF6)2is re-reacted with an excess of SbF5 for a prolongedperiod of time, —6 to 8 weeks (Figure 3.7). In all instances, no weight changes were observed inthe vacuum dried products.79Figure 3.6 Magnetic Moment vs. Temperature of HF Treated Cu(SbF6)21.8-aD— Cu(sbF6)21.6- 0 + excess HF0Z I I— Cu(SbF6)201.4-C-)LIzo 1.2-1—0.8-0 20 40 60 80 100TEMPERATURE,K80Figure 3.7: Magnetic Moment vs. Temperature of SbF5 Treated Cu(SbF6)21.8-1.6- ‘ • • . . . • • .— Cu(SbF6)2zI I° o o o o o ° ° °— Cu(SbF6)20 I 0 0 0 0+ excess SbF5C-)LJzç 1.2-1—0.8- I I0 20 40 60 80 100TEMPERATURE,K81The presence of Cu(I) and Cu(IH) ions, in addition to Cu(H) in Cu(SbF6)2is not totallyunexpected, since both Ag(II)(SO3F2and Cu(H)(SO3F2which contain “Jahn-Teller ions” (d9),could behave in a similar manner toward SbF5, generating Ag(I), Ag(llI) and to a lesser degreeCu(I), Cu(llI) ions in their respective reaction products. As in the case of 3-Ag(SbF6)2,theCu(I) and Cu(llI) centers could be accommodated in the layer structure of Cu(SbF6)2,withCu(I) in a linear and Cu(ffl) in a square planar environment respectively.3.3.5 X-ray Photoelectron SpectraAttempts were made to characterize the f3-Ag(SbF6)2and Cu(SbF6)2compounds usingX-ray photoelectron measurements. It was hoped that the difference in Binding Energy (BE)between the cations in oxidation states +1, +2, and ÷3 could be utilized to identify these ionspresent in the silver compound as Ag(I), Ag(III) and in the copper compound as Cu(I), Cu(II),and Cu(Ill) respectively. The reported BE values corresponding to these oxidation states (for agiven energy level) were reconfirmed by a series of measurements carried out with relevantsilver and copper fluoro complexes.For the XPS study of -Ag(SbF6)2compound, the 3d512 energy level is chosen, which isfound at BE = 366.8 eV in Ag(0). The Ag(I) and Ag(llI) BE peaks for the same energy level areexpected at —367.7 and —371.0 eV respectively (53,54). The sample was scanned in the BErange of 357 to 377 eV. Unfortunately, for the 3d52 level, only a broad band spanning a BErange of —367.5 to 370 eV is obtainable, with no resolution of the relevant peaks expected forthe Ag(I) and Ag(Ifl) species. It is however possible that the two peaks corresponding to thetwo silver ions are hidden under the broad band centered at —369 eV. A similar situation isobserved when the alternate energy level 3d2 is chosen for the measurements.82The XPS spectra obtained for Cu(SbF6)2show a more complicated spectral pattern. Theenergy level 2P3 located at BE = 932.2 eV for Cu(O) is chosen, and BE peaks of Cu(I), Cu(II)and Cu(Ill) corresponding to this energy level are expected at 932.6, 936.1 and 938.0 eVrespectively (53,54,55). However, in this compound, only small amounts of Cu(I) and Cu(ffl)ions are expected to be present (see Section 3.3.4), in contrast to the silver compound, whereAg(1) and Ag(ffl) ions are present in equimolar quantities.The BE range scanned for Cu(SbF6)2is from 921 to 941 eV, and as in the silvercompound, no distinct peaks corresponding to the three oxidation states are observed. Thebroad band obtained covers an energy range of —932.5 to 938 eV, and is split by several intensesatellite lines. This phenomenon is commonly seen in the XPS spectra of cupric compounds,and the number and the splitting of the peaks are found to be sensitive to the chemical environment of the ions (55). This situation is further complicated by the reduction of Cu(ll) ions whensubjected to X-rays, and consequently, additional satellite peaks may appear in the spectra (55).Although no individual peaks at energy level 2P312 are seen in the spectra, it is againpossible to have the less intense Cu(I) and Cu(ffl) peaks hidden under the broad band, since theenergy range of the band covers the three BE values of the copper ions Cu(I), Cu(II), and Cu(III)expected in Cu(SbF6)2.3.3.6 Attempted Synthesis of Au(SbF&2Gold(lI) fluorosulfate, which was synthesized recently in our group by the reduction ofAu(SO3F) with either gold powder or CO (56), was selected as the precursor to react withexcess SbF5 in the attempted preparation of the corresponding gold(ll) hexafluoro antimonate,Au(SbF6)2. The gold compound has been formulated as a mixed valency, diamagneticAu(I)[Au(III)(SO3F41complex, based on magnetic measurements and vibrational spectra (56).83Therefore, it was expected that the resulting binary compound may also have the compositionAu(I) [Au(III)(SbF64],analogous to the diamagnetic -Ag(SbF6)2compound.However, in contrast to the other four transition metal fluorosulfate precursors, thereaction of Au(SO3F)2with excess SbF5, carried out in a manner similar to the other preparations discussed in this chapter (equation 3.1), does not yield the anticipated binary productAu(SbF6)2. InsteaLt, the synthesis follows the reaction scheme shown below, yielding a ternarycompound:60°CAu(SO3F)2+ excess SbF5 > Au(SO3F)(SbF6 [3.8121 daysThe values of x and y (typically x = 1 to 1.5, and y = 2-x), calculated from microanalytical data,seem to vary slightly and appear to depend on the reaction conditions. The bright yellowAu(SO3F)2gradually turns color to give a dark brown-green powder. When the reaction isperformed at elevated temperatures, a dark brown, very viscous liquid which may form due tothe melting or decomposition of the lower temperature product, is isolated. Infrared spectra runon several samples clearly show the presence of both SO3F and SbF6 groups, and magneticmeasurements indicate a diamagnetic compound, as anticipated.Interestingly, when diamagnetic gold(III) fluorosulfate Au(SO3F),which is synthesizedby the oxidation of gold powder withS206Fin HSO3F(57), is reacted with excess SbF5 underthe same experimental conditions (equation [3.8]), a dark blue-green powder is isolated, againwith composition Au(SO3F)(SbF6where the values of x and y (typically x =2 to 2.3 andy =3-x), are dependent on the reaction conditions. However, this ternary compound, in contrast,is weakly paramagnetic. The low temperature magnetic data, tabulated in Appendix A-7, yieldmoments that range from 0.52 to 0.72 B at 82 and 2.7 K respectively. These values are84tentative, since the composition of the compound (and hence the molar mass) cannot be determined accurately. It is important to note here that like in the fluorides, where both AuF andAuF2 are unknown (33), examples for lower valent fluoro derivatives of gold are so far lacking.It is conceivable that Au(SO3F),which is dimeric in the solid state (58) when reactedwith SbF5, may undergo a reduction process to a veiy slight extent. This reduction of the goldcompound may be due to the inability of substituent SbF6 anions to suitably stabilize the higheroxidation state and hence strongly oxidizing Au(Ill) species, and consequently, may lead to theformation of small quantities of paramagnetic Au(II) ions in the solid lattice. This observationappears to be valid also for the solvolysis reaction of Sn(IV)(SO3F4in SbF5. When about0.679 g of Sn(SO3F)4,made according to a published method (59) is reacted with an excess ofSbF5 for two weeks at 60°C, a white solid that corresponds to the composition Sn(SbF6)2isisolated. The reduction of the Sn(IV) species to Sn(II) could occur according to:60°CSn(SO3F)4+ 6SbF5 > Sn(SbF + 2SbF9( O3) + S206F [3.91and2S06F + SbF5 —* 2S0F + 2S03 + 02 [3.10]The decomposition of S206F in the presence of SbF5 (5) leads to byproducts which are allremovable in a dynamic vacuum and consequently solid Sn(SbF6)2is obtained in high yield.3.4 ConclusionSolvolysis of M(ll) fluorosulfates with M = Sn, Ni, Pd, Cu or Ag, in antimony(V)fluoride is found to be a useful synthetic route to the corresponding metal(ll) hexafluoro85antimonate compounds. Even though alternate synthetic routes to compounds of the typeM(SbF6)2are known, only the solvolysis method leads to the Pd(SbF6)2and the f3-Ag(SbF6)2compounds. The latter complex, unlike a recently reported paramagnetic, blue valence isomer isdiamagnetic and based on its chemical and magnetic behavior, formulated as a mixed valencyAg(I)[Ag(III)(SbF64]species. Additionally, the copper compound synthesized by this routealso appears to be unique, with Cu(ll) and, to a lesser extent Cu(I) and Cu(llI) ions, all presentsimultaneously in the lattice of Cu(SbF6)2, as confirmed by low temperature magneticsusceptibility measurements.The Ni(SbF6)2compound prepared via solvolysis appears to be structurally similar to thecompound obtained by the high temperature fluorination method. However, in the solvolysissample the nickel centers are predominantly found as Ni(II) ions, whereas in the fluorinationproduct trace Ni metal impurities seem to be present, which is evident from their respectivemagnetic studies.Ligand field analyses of the electronic spectra of Ni(SbF6)2and Pd(SbF6)2indicate that,like in their fluorosulfate precursors, the Ni(ll) and Pd(ll) ions are located in approximateoctahedral ligand fields with 3A2g ground terms. Both compounds exhibit temperaturedependent low magnetic moments, most likely due to antiferromagnetic exchange. Additionally, Pd(SbF6)2shows very weak ferromagnetism below -40 K.It appears, based on X-ray powder data and vibrational spectra that a common CdC12-type layer structure is present in all the M(SbF6)2compounds synthesized in this study, althoughultimate structural proof will have to come from single crystal X-ray diffraction studies. Thelack of solubiity of the compounds in suitable solvents like anhydrous HF and their highreactivity toward many of the organic solvents present substantial obstacles to the crystal growthprocess.86References1. P.L. Fabre, J. Devynck, and B. Tremillon, Chem. Rev., , 591 (1982), and referencestherein.2. S.P. Mallela, S. Yap, J.R. Sams, and F. Aubke, Inor. Chem., , 4327 (1986).3. G.A. Olah, G.K.S. Prakash, and J. Sommer, “Superacids”, John Wiley and Sons, NewYork, 1985, and references therein.4. R.J. Gillespie and R.A. Rothenbury, Can. J. Chem., 42,416 (1964).5. W.W. Wilson and F. Aubke, J. Fluorine Chem., j.j 431 (1979).6. P.A. Yeats and F. Aubke, J. Fluorine Chem., 4, 243 (1974).7. W.W. Wilson, J.R. Dalziel, and F. Aubke, J. Inor. Nuci. Chem., 37, 665 (1975).8. W.W. Wilson, R.C. Thompson, and F. Aubke, Inorg. Chem., i, 1489 (1980).9. S. Karunanithy and F. Aubke, J. Fluorine Chem., fl 541 (1983).10. S.P. Mallela, S. Yap, J.R. Sams, and F. Aubke, Rev. Chim. Minerale, j 572 (1986).11. 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Vogel, “Quantitative Inorganic Analysis”, 3rd Edition, John Wiley and Sons, NewYork, 1961.24. B. Standke and M. Jansen, Angew. Chem. mt. Ed., , 77 (1986).25. J.A. McMillan, Chem. Rev., 2. 65 (1962) and references therein.26. B. Standke and M. Jansen, Angew. Chem. mt. Ed., 24, 118 (1985).27. P.C. Leung, K.C. Lee, and F. Aubke, Can. J. Chem., 7, 326 (1979).28. L. Helmholtz and R. Levine, J. Am. Chem. Soc., 4, 354 (1942).29. W. Klemm, Angew. Chem., , 468 (1954).30. B.G. Muller, Z. Anorg. Aug. Chem., 3, 196 (1987) and references therein.31.a) N. Bartlett and R.P. Rao, Proc. Chem. Soc., 393 (1964).b) R.P. Rao, Ph.D. Thesis, University of British Columbia, 1965.32. R. Bougon, T.B. Huy, M. Lance, and H. Abazli, Inorg. Chem., 23, 3667 (1984).33. B.G. Muller, Angew. Chem. Tnt. Ed. Engi., , 1081 (1987).34.a) B.N. Figgis, “Introduction to Ligand Fields”, John Wiley and Sons, New York, 1966.b) A.B.P. Lever, I. Chem Educ., 4, 711 (1968).35. J.H. Burns, Acta Crvst., .15, 1098 (1962).36. P. 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Inorg. Chem., , 37 (1964).48. G. Maid, I. Chem. Phys., 2. 651 (1958).49. G.C. Allen and K.D. Warren, Inorg. Chem., 8, 1895 (1969).50. W. Klemm, W. Brandt, and R. Hoppe, Z. Anorg. Aug. Chem., 3, 179 (1961).51.a) W.W. Wilson and K.O. Christe, Inorg. Chem., , 3261 (1984).b) R. Hoppe in “Inorganic Solid Fluorides”, Ed. P. Hagenmuller, Academic Press, NewYork, 1985.52. Landolt-Börnstein, Numerical Data and Functional Relationships in Science andTechnology, Vol. 2, Magnetic Properties of Coordination and Organometallic TransitionMetal Compounds, Springer-Verlag, Berlin, 1966.53. T.A. Carlson, “Photoelectron and Auger Spectroscopy”, Plenum Press, New York, 1975.54. C.D. Wagner in “Practical Surface Analysis by Auger and X-ray PhotoelectronSpectroscopy”, Ed. D. Briggs and M.P. Seth, John Wiley and Sons, Newe York, 1983.55. D.C. Frost, A. Ishitani, and C.A. McDowell, Mol. Phys., 24, 861 (1972).56. H. Willner, F. Mistry, G. Hwang, F.G. Herring, M.S.R. Cader, and F. Aubke, J. FluorineChem., , 13 (1991).57. K.C. Lee and F. Aubke, Inorg. Chem., ., 389 (1979).58. H. Wiliner, S.J. Rettig, J. Trotter, and F. Aubke, Can. J. Chem., 69, 391 (1991).59. S.P. Mallela, K.C. Lee, and F. Aubke, Inorg. Chem., 2, 653 (1984).89CHAFFER 4MESITYLENE ADDUCTS OF TIN(II) FLUORO COMPOUNDS,Sn(SO3F)2C9H12and Sn(SbF62C9H124.1 IntroductionArene ic-complexes, where low valent post-transition metal centers act as acceptors, andbenzene or various alkyl benzenes, function as ic-donors, form a small but interesting group ofweakly bound complexes. Structural and bonding aspects of these compounds have becomemore widely known through the work of Amma et al. (1), and Schmidbaur et al. (2). A reviewon the more general topic of ic-complexes of main group elements has also appeared recently(3).Arene complexes of the post-transition metals are best regarded as donor-acceptoradducts, with the arene ic-system being the donor component. For Group 13 metal derivatives,an increased arene donor strength through electron releasing substituents leads to enhancedstability of the complexes. However, as observed in X-ray crystal structure studies, the metalligand interactions are not strong enough in these complexes to induce significant distortions ofthe arene rings (2). Consequently, complexes with low thermal stability are usually isolated(1,2).Within this group of it-complexes, interest has focussed mainly on arene complexes withunivalent metal centers such as Ag(I), Cu(I), Hg(I), Ga(I), In(I) and Tl(I) and comparativelylittle is known about similar compounds with the Group 14 centers like Sn(II) (4-7) and Pb(II)(1,8). There are commonly two reasons given for the paucity of arene H-complexes in group 14:90a) as exemplified by the structural chemistry of divalent tin (9), the 52 pair is stereochemicallyfar more active than in compounds of isoelectronic In(I) and consequently the Sn(II) derivativesare apparently less inclined to form it-complexes with arenes (2); b) lattice energies for Sn(II)and Pb(II)-salts tend to be considerably higher than those of Ga(I), In(I), or Tl(I) salts. Thenon-polar, it-donating arenes are normally incapable of breaking up such lattices effectively. Toreduce the lattice energy and to facilitate complex formation, salts with large, univalent anionsare chosen and the majority of arene it-complexes reported so far feature tetrahalometallate (III)anions of the type MX4 with M=B, Al, Ga, In or Ti, and X=Cl or Br (1-8) as counter anions;however weakly basic anions like OTeF5 appear to be suitable as well (10).The tin(II)-ic-arene complexes reported so far are limited largely to mono-arenecomplexes with either Sn2 (4) or the chloride bridged moieties such as (Sn2C1) (5) or(Sn4Ci)(7) as acceptors, but recently the first bis(arene) complex has been reported as well,[(‘6-CH2SnC1(AlC1)J(6). Benzene functions primarily as donor, bonded to tin in the rj6-mode, and A1C14 is the counter anion, with Cl atoms bridging to tin. Frequently, however,arenes are also found in the lattice, without being coordinated to tin (4,6,7). Detailed crystalstructures (see Appendix A-8) are reported for all compounds (4-7) and have been used in thedevelopment of bonding concepts based on the Molecular Orbital theory ((1, 4, 5), AppendixA-9).The interest in the chemistry of tin for this work stems from the following two specificrelated objectives: a) the use of 119Sn Mössbauer spectroscopy as a structural tool (this spectroscopic technique has not been applied so far to this small group of tin complexes) and, b) thestabilization of “bare”, non - or very weakly coordinated cations like Sn2 (11) orR2Sn (12).As discussed in Chapter 3, two compounds of interest, tin(II)bis(fluorosulfate), Sn(SO3F)2andtin(II)bis(hexafluoroantimonate), Sn(SbF62 (13), both originally reported by Gillespie andcoworkers (14), appear to be capable of functioning as potential acceptors in arene it-complexes.91Both compounds give rise to broad single line 119Sn Mössbauer spectra with largepositive isomer shifts relative to Sn02, and, in the case of Sn(SO3F)2,a small resolvablequadrupole splitting (11, 14) suggests non-directional, nearly spherical distribution of the 5s2electron pair. In addition, it had been shown previously, based on 119Sn Mössbauer parameters,that the anions SbF6- and Sb2F1fare extremely wealdy basic and the least nucleophilic anionswhen stabilizing the cation (CH3)2Sn with a linear C-Sn-C group (12). Therefore, it wasexpected the SbF6 anion to be ideally suited to stabilize the “bare” Sn2 ion equally well. Thesingle line 119Sn Mössbauer spectrum with an isomer shift of 4.39 mm s1 relative to Sn02obtained for Sn(SbF6)2(see Chapter 3), which is a shift of about 0.45 mm s’ lower thansuggested by calculations for Sn2 (15), indicate that steric factors rather than lownucleophilicity of the counter anion may be important. The list of stannous compounds withsingle-line 119Sn Mössbauer spectra and isomer shifts higher than the ones observed forSn(SbF6)2provides a clue. Sn[Sn(SO3F)6],4.48 (11); Sn(ClO42(15-crown5),4.53 (16);Sn(SbF2As3,4.66 (17); and Sn[Sn(SOCF14.69 mm s1 relative to Sn02 (18) allapproach a true Sn2 more closely than Sn(SbF6)2and all involve sterically more hinderedligands than SbF6. A crystal structure for Sn(SbF2As3(17), where the Lewis base AsF3 iscoordinated to tin as well, indicates 9-coordinate tin. The use of crown ether ligands (16) alsosupports the view that steric factors play an important role in stabilizing the “bare” Sn2 ion.Furthermore, the two anions of the compounds, SO3F and SbF6, as seen earlier inChapter 3, function frequently as weakly coordinating, tridentate ligands towards divalent metalions giving rise to layer structures, based on the CdCl2-prototype. This structural type iscommonly found for most sulfonates of divalent metals, and the recently reported structure ofSn(SO3F)2confirms this structural type, where a three-dimensional framework of SO3F groupslinked by O-Sn-O bridges with the two crystallographically independent fluorosulfates acting astridentate bridging ligands between the tin atoms is indicated (19). The structure of Ag(SbF6)2(20) (Chapter 3, Figure 3.2) may serve as an example for the layer structure formed by92M(SbF6)2. Both SO3F and SbF6 are very weakly basic, and covalent contributions to thelattice energies of their tin(J1) salts should be small. Alternatively, both anions may stabilizearene complexes of tin with the help of oxygen or fluorine bridges. As donor, 1,3,5-trimethylbenzene (mesitylene) is chosen, because it is expected and found (2) to be a betterdonor than benzene. 119Sn Mössbauer spectroscopy is proven to be a useful technique for thisinvestigation. Its application to the study of tin(II) compounds has been reviewed previously(21).4.2 Experimental4.2.1 SynthesisSn(SO3F)2was obtained from SnCI2 and HSO3F(22) as described (23), and Sn(SbF6)2was prepared from the solvolysis of Sn(SO3F)2in an excess of SbF5 as pointed out in Chapter 3,Section 3.2. Stannocene,(5-CH)2Sn, was synthesized from SnCI2 and NaC5H. The crudeproduct was purified by sublimation and its purity checked by microanalysis.4.2.la Synthesis ofSn(SO3F)21,3,5-(CH)C6HTo a one part reactor a sample of Sn(SO3F)2(1.06 g, 3.35 mmol) was added, and afterevacuation of the reactor, dry mesitylene (—7 mL, —50 mmol) was transferred into the reactionvessel via a distillation bridge. The white suspension was stirred in vacuo at room temperaturefor three days. Excess mesitylene was removed in vacuo at -20 to -15°C (ice/NaCl bath) over aperiod of three days yielding 1.39 g of a white powder, of the composition Sn(SO3F)2mes, witha decomposition point of 97.2-98°C.93Anal calcd. forC9H12F2O6Sn: C, 24.74; H, 2.77; F, 8.70; S, 14.67; and Sn, 27.16%.Found: C, 25.77; H, 2.87; F, 8.53; S, 14.84; and Sn, 27.10%.An alternate preparation with mesitylene removed in vacuo at 50C gave the followinganalysis:Anal. calcd.: C, 24.74; H, 2.77; and S, 14.67%.Found: C, 24.97; H, 2.80; and S, 14.55%.JR bands and estimated intensities [cm1]: 2910w,b, 2860vw, 1760vw, 1604m,1575w,sh, 1446w, 1337w, ll9lvs, 1127w,sh, 1054vs, 888s, 786w, 667w, 589ms, 544m, 507vw,and 405m.4.2.lb Synthesis ofSn(SbF6)2[1,3,5(CH3CH]To the bottom portion of a two part reactor, freshly prepared Sn(SbF6)2(3.11 g, 5.27mmol) was added. The flask was then fitted to the lower end of a filtration apparatus (24). Onthe top end of the filtration apparatus a seond 100 mL flask was fitted and the entire apparatuswas then evacuated. Through a Teflon valve in the bottom chamber of the apparatus mesitylene(15 mL, 108 mmol) was transferred via a distillation bridge. Upon exposure to the mesitylenevapor, the white powder immediately turned yellow and then during the filtration, pale, offwhite. When the mesitylene distillation was complete, the suspension was stirred in vacuo for1.5 hours. The apparatus was inverted, and the mixture filtered. The filtrate flask was cooled to-10°C (ice/NaC1 bath) and the mixture was left to filter for 17 hours.When gravity filtration was complete, the filtrate chamber of the apparatus wasevacuated to further dry the solid. The apparatus was refilled with dry nitrogen inside the drybox, and the filtrate chamber was evacuated again. At the end of this drying procedure, a pale,94off-white solid (4.18 g, 5.04 mmol, 95.5% yield) was obtained together with a yellow-greenfiltrate, which was discarded. The product was transferred to a two part reactor and was furtherdried in vacuo for 24 hours at room temperature. No further weight change was observed. Thesolid decomposed at 69.5-71.5°C to a greenish yellow liquid.Anal. calcd. forC18HF2Sb2n: C, 26.03; H, 2.91; F, 27.45; Sb, 29.32; Sn, 14.29%.Found: C, 26.87; H, 3.00; F, 27.31; Sb, 29.05; Sn, 14.20; Total 100.43%.JR bands and estimated intensities [cm-1]: 2920mw, 2860w, 1601m, 1580m, 469w,1384m, 1168vw, lO8Ovw, lO4Ovw, 1007w, 960vw,b, 860w, 687s, 671vs, 635s, sh, 580m,b,544m, 5 12w, 440w, and 395w.4.3 Results and Discussion4.3.1 SynthesisThe previously reported synthesis of Sn(II) containing benzene it-complexes (4-7)involves either the reaction of SnC12 and A1C13 at different mole ratios and temperatures (4,5),or of molten Sn(A1C14)2(6, 7) with the arene to give either Sn2, (Sn2Cl)or (Sn4Cl)’containing complexes as colorless crystals. Crystalline material suitable for single crystal X-raydiffraction studies are obtained (4-7) in all instances. The course of the reaction appears to beinfluenced in part by the mole ratios of the reactants used and in part by the reaction temperature. The different products obtained, with Sn2 or (SnCl)’, n = 2 or 4, are not totallysurprising since in the binary system SnC12-A1C3,phase studies (9) have revealed the existenceof two distinct phases: SnC12A13 and SnC12AlCl3. It appears that the same two phasescrystallize now in the form of ,t-arene complexes with A1C14 as a coordinated counter ion and inseveral instances with the lattice arene present (4, 6, 7).95The synthetic reactions reported here differ in a number of ways. Binary rather thantertiary reaction mixtures are used, the reaction temperature is room temperature and the tin(U)substrates are synthesized and characterized prior to their reaction with mesitylene.Addition of mesitylene occurs smoothly according to:250CSn(SO3F)2+ mes > Sn(SO3F)2mes [4.1]mesityleneor25°CSn(SbF6)2+ 2 mes > Sn(SbF6)2mes [4.2]mesitylenemes = l,3,5-trimethylbenzene (mesitylene), and the two complexes are formed in nearlyquantitative yield. Solid material remains throughout the reaction and in case of Sn(SO3F)2asacceptor, there is no visible sign of a reaction, except for an increase in the bulk of the solidresidue. Complete removal of excess mesitylene in vacuo is difficult to judge and the conditionsquoted in the experimental section were arrived at by trial and error. It does appear that samplessubmitted for microanalysis (C, H, and S content) immediately after isolation had small amountsof residual mesitylene trapped while samples sent to Germany for further analysis (S, Sn, Sb,and F content) seemed to have lost the excess reactant.The reaction of mesitylene with Sn(SbF6)2differs even further. A 2:1 complex formsand a color change to bright yellow is noted as soon as the tin salt is exposed to mesitylenevapor. However the color of the solid quickly fades during product isolation and an off-whitesolid is obtained in very high yield together with a yellow-green filtrate. The origin of theinitially observed color is unclear. A UV-visible spectrum taken as Nujol mull on a solidsample at this stage shows an intense UV-absorption at —240 nm tailing off in the visible region96with weak shoulders at 486, 580 and 656 nm respectively.Observations made during product isolation suggested that the intense color seen wasdue to a by-produc., which was soluble in excess mesitylene. A complex formed by mesityleneand small, residual amounts of SbF5 becomes a distinct possibility. Furthermore, the addition ofmesitylene to pure SbF5 resulted in an intensely colored dark brown solid, which was notinvestigated further. There is little doubt that the final product, like other arene complexes ofGroup 13 and 14 metals (1-8), is a white solid.The use of gravity filtration as a means of product isolation is important in the case ofthe Sn(SbF6)2mes synthesis. Attempts to isolate this compound by slow, careful removal ofexcess mesitylene in vacuo or in a stream of dry N2 at room temperature and at -5°C lead topartial decomposition and materials that analyze as Sn(SbF6)21 .5mes. In addition, the producthas a slight yellow tint.The thermal stability of both mesitylene complexes described here is limited.Sn(SO3F)2mes melts with decomposition at 97-98°C while Sn(SbF6)2mes has a decomposition range of 69.5-71.5°C, where a greenish yellow liquid forms.Attempts to extend the mesitylene addition reaction to three other tin(ll) compoundswere unsuccessful. Both SnC12 and SnF2 were recovered unchanged. Both salts have Sn2+ indistorted octahedral environments (7) and the structures of SnC12 (25) and orthorhombic SnF2(14,26), one of the two polymorphic forms, may be regarded as layer structures. It can beconcluded that the lattice energies of both compounds are too high and adduct formation doesnot occur in these two compounds.97Stannocene,(5-CH)2Sn, has a molecular structure with a tilted arrangement of theC5H-rings (27) and presumably a stereochemically active electron pair. Its 119Sn Mössbauerspectrum shows a quadrupole splitting of 0.86 mms (28). The compound dissolves inmesitylene, but stnocene is again recovered unchanged after removal of the arene in vacuo.The 1H NMR spectrum of stannocene in mesitylene is studied down to -40°C, but only rathersubtle changes are noted. The principle resonance due to stannocene (29) shifts from 5.96 ppmin CDC13 to 5.91 ppm relative to TMS in the presence of mesitylene while J1H - 119/7Snchanges from 15.76 Hz to 15.16 Hz. Beginning at -20°C and becoming more pronounced at-40°C, a second, smaller and rather broad resonance at 5.88 ppm emerges with a similar separation of the satellite peaks. Mesitylene resonances appear almost in the same position as in puremesitylene as single lines at 2.28 (CH3) and 6.78 (C-H) ppm and do not shift with decreasingtemperature. While there may be a weak interaction between stannocene and mesitylene atreduced temperature, all attempts to isolate a reaction product by low temperature filtration havefailed.Therefore, it appears that tin(ll) is sufficiently acidic only when bulky and very weaklynucleophilic anions like A1C14, S03F and SbF6 are present, and when lattice energies arereduced in the resulting layer structures. From a correlation of 119Sn Mössbauer data ofdimethyltin(IV) salts (12) it seems that SbF6 is the weaker nucleophile of the two fluoroanions,and formation of a 2:1 complex with mesitylene is not unexpected, while Sn(SO3F)2forms a 1:1complex only. Complex formation by addition of mesitylene to a solid tin(ll) salt as describedhere does not lead to the formation of single crystals suitable for structural studies. Henceevidence for the presence of n-arene complexes has to come from two other sources, i.e. 119SnMdssbauer and vibrational spectra, to be discussed subsequently.984.3.2 119Sn Mössbauer SpectraIsomer shifts, relative to Sn02 for tin(1I) compounds, fall within the range of —2.1mm s1, viewed as the borderline between Sn(II) and Sn(IV), and values of about 5.1-7.7 mm s1for a “bare’t Sn2 have been calculated where a spherically distributed 5S2 electron pair (9,15) isconsidered. Experimental values obtained have not reached the ionic limit. The highest valuesreported so far are 4.69 mm s1 for the tin(II) moiety in Sn(II)[Sn(IV)(SO3CF)&(18) and 4.66mm s1 for Sn(SbF6)2As3(17), where an X-ray diffraction study reveals a distorted nine-coordinated environment for Sn2+.In these close approaches to a Sn2+ ion no quadrupole splitting is observed(17,18); however,with decreasing isomer shift, first line broadening already evident for Sn(SbF6)2,is noted andeventually small but well resolved quadrupole splittings are found (30). Hence 119SnMössbauer spectroscopy provides two criteria which determine the ionic character of Sn(II)compounds: (a) the isomer shift which should be high, close to or in excess of 4.69 mm s’relative to Sn02,and (b) the quadrupole splitting which should be zero.Some 119Sn Mössbauer data of Sn(II) compounds which are of interest to this study arelisted in Table 4.1. Of the five tin(II) compounds studied here Sn(SO3F)2(4.18 mm s1) andSn(SbF6)2(4.44 mm c1) have the highest isomer shifts of those listed and only the former has asmall, resolvable quadrupole splitting. Not unexpectedly, the more acidic Sn(SbF6)2is thebetter acceptor, seemingly capable of coordinating two mesitylene donors, while Sn(SO3F)2forms a 1:1 complex only.Upon arene uptake the isomer shift is reduced by 0.17 mm s1 for Sn(SO3F)2and by 0.40mm s for Sn(SbF6)2. This reduction suggests that mesitylene is interacting with Sn(ll) and,judging by the magnitude of the shift, that in the case of Sn(SbF6)2mes both mesitylene99Table 4.1: 119Sn Mössbauer Parameters of Relevant Tin(I1) Compounds at 80KIsomer Shift Quadrupole SplittingCompound 8 [mm s1] rel. to Sn02 LLEQ [mm s1] ReferenceSnF2 (orthorhombic) 3.30 2.15 14SnF2 (tnonoclinic) 3.49 1.61 14(r5-CH)2Sn 3.74 0.86 28a(n-C6)S (A1C14 3.93 0 4cSnC12 4.08 0.66 15cSn(SO3F)2 4.18 0.68 14Sn(SOF)mes 4.01 1.04 This workSn(SbF6)2 4.44 0 14Sn(SbF2mes 4.04 1.13 This workAccuracy limits for 6 and AEQ are ± 0.03 mm 54100molecules are probably coordinated to tin. A similar isomer shift of 3.93 mm s1 is reported for(-CH)Sn(AlCl4)26(4c) but no Mössbauer data appear to have been reported for the twoSnC12-A1C3phases (9), which would allow an estimation of the decrease in the isomer shiftupon arene addition. The reduction in the isomer shift upon binding to mesitylene isaccompanied by an increase in quadrupole splitting to 1.04 mmst for Sn(SO3F)2mes whereasfor Sn(SbF6)2mes a slightly asymmetrical doublet (see Figure 4.1) with a £S.EQ value of 1.13mm s1 is obtained. These findings are consistent with trends on 6 and summarized above.The occurrence of quadrupole splitting suggests an increase in asymmetry in thecoordination environment of tin(1I) when coordination to only oxygen or fluorine changes toinclude coordination to the arene as well. For both mesitylene adducts the 1195n Mössbauerparameters obtained remain well within the range reported for typical tin(II) compounds (21).The addition of mesitylene to Sn2, as suggested by the 119Sn Mössbauer data, is expected tocause a change in the manner in which the anions SO3F and SbF6 coordinate to tin. Thischange in anion denticity is probed by infrared spectroscopy and discussed in the subsequentsection.4.3.3 Infrared SpectraAttempts to obtain Raman spectra of both mesitylene adducts are unsuccessful and quickdarkening of areas exposed to laser light indicates thermal degradation is occurring even at verylow laser power. Hence evidence rests on infrared spectra obtained on solid films betweensilver halide windows.Both infrared and Raman spectra for Sn(SO3F)2(14, 23) and Sn(SbF6)2(14) have beenreported previously, and for tridentate SbF6-groups present in M(SbF6)2compounds a usefulvibrational assignment has been presented (13, 31). As discussed previously in Chapter 3,101Figure 4.1:c0Cl)Cl)E(I)C0H119Sn Mössbauer Spectrum of Sn(SbF)2mes at 77K0 1.5 3.0 4.50I0&9896C0-75 -6.0 -4.5 -3.0 -1.5Velocity (mms1)102Section 3.3.2, to account for the observed spectral complexity in the SbF-stretching region, asubdivision into metal coordinated, through fluorine bridges SbFb, and non-coordinated orterminal SbFt stretches is suggested with the former usually between 550 and 650 cm1 and thelatter above 650 cm1 (31). Vibrational bands reported for Sn(SbF6)2(14) allow such a divisionas well, even though a distorted environment around tin introduces additional complexity.Assignments for Sn(SO3F)2have suggested the presence of ionic SO3F with the symmetry ofthe anion reduced from C3,, for the free ion to Cs due to coordination to tin (14, 23), but thereare still unresolved problems, best reflected in the occurrence of two equally intense bands at--770 and 830 cm1 possibly due to iSF(A1)and a splitting found for 3S0(A1). It seems moreappropriate here to view the spectrum as being due to two non-equivalent SO3F-groups withapproximately C3,, symmetry with some band overlap in the areas of deformation modes. Thisimplies either ionic groups or more likely 0-tridentate groups. As mentioned previously, theseconclusions are further confirmed by the recently published crystal structure study of Sn(SO3F)2by Adams et al. (19).Addition of mesitylene to both Sn(II) compounds has two general effects: a) the infraredspectrum is dominated in both instances by bands due to the SO3F and SbF6 groups, respectively, with all mesitylene bands of very low intensity, and b) the vibrational spectra of theanions appear to change, and at least the SbF6 bands reflect a change in anion coordination.Low intensity of vibrational bands due to organic groups is commonly found for organotin(IV)salts (32), and this feature appears to extend to the mesitylene adducts of tin(U) salts as well.The observed infrared frequencies for the two mesitylene adducts are listed in theexperimental section together with estimated relative intensities. The discussion in this sectionwill center around two aspects, (a) the mesitylene bands in neat mesitylene and in thecomplexes, and (b) the “anion” bands before and after mesitylene addition to Sn(SO3F)2andSn(SbF6)2,respectively. Vibrational bands attributed to mesitylene are listed in Table 4.2 for103Table 4.2: Infrared Bands of Liquid Mesitylene and Bands Attributed to Mesitylene inthe Adducts Sn(SO3F)2mesand Sn(SbF6)2mesMesitylene Sn(SO3F)2mes Sn(SbF6)2mes[cm1]Tnt. [cm1]Tnt. [cm-1]mt.3018 s2921 vs 2910w,b 2920mw2860 s 2860 vw 2860 vw2730m1760 m-w 1760 vw1715 m-w1608vs 1604m,1575w,sh 1601m,1580m1512w1473s 1446w 1469w1442 m, sh1375m-s 1384mll7Ovw 1168vw1037 s 1080 vw, 1040 vw, 1007 w932vw 960vw,b882vw 860w835 vs 786w687 vs 667 w 687 ms561w,b 544m515w 507vw 512w443m 440w421 m411m 395wSee Table 4.3 for abbreviations104both adducts and compared to bands observed for liquid mesitylene. The listing of bands for theadducts is incomplete because of the very low intensity mentioned above which causes mediumand weak bands to be unobservable and in case of Sn(SO3F)2mes, partial overlap of mesitylenebands with more intense anion bands, in particular in the region of 800-1300 cm’.In regions where no anion bands are expected, small band shifts are observed, mostly tolower frequencies. The aromatic C=C stretch at 1608 cm1 in free mesitylene is a goodexample. This peak is shifted to 1604 and 1601 cm1 for Sn(SO3F)2mes and Sn(SbF6)2mesrespectively. The lower frequency indicates a very slight withdrawal of it electron density of thearomatic ring towards tin.Interestingly, some bands assigned to bonded mesitylene appear to be split compared tothose of free mesitylene. This is noticeable in the 1570-1610 cm1 region of both spectra, andespecially in the 1000-1200 cm’ region for Sn(SbF6)2mes. The splitting can be attributed to areduction in symmetry of the bonded mesitylene, and/or the presence of two non-equivalentmesitylenes, in particular in Sn(SO3F)2mes. However some solid state splitting is possible aswell.All features affecting bands due to mesitylene are subtle, and the observed features are ingeneral consistent with a very weak interaction between the arene and the two Sn(11) salts.The infrared bands attributed to the anion are summarized in Table 4.3 and are comparedto the reported values for the parent compounds Sn(SO3F)2(14, 23) and Sn(SbF6)2(14). ForSn(SO3F)2mes the JR spectrum is dominated by an intense broad band centered at 1054 cm1and two bands at 1191 and 1127 cm1. These are assigned collectively as SO3 stretching modes,probably masking some of the less intense motions of the mesitylene component in the adduct.105Table4.3:InfraredFrequenciesforSn(SO3F)2andSn(SbF6)2andBandsAttributedtotheAnionsintheMesityleneAdductsSn(SO3F)2mesandSn(SbF6)2mesSn(SO3F)2aSn(SO3F)2mesApproximateSn(SbF6)2bSn(SbF6)2mes[cm]mt.[cm1hit.BandDescription[cm]Tnt.[cm]mt.for C3,,AssignmentCAssignmentC1290s,sh1337wuSO3(E)741m, sh1240vsll9lvs713sSbFt671vsuSbF61180s,sh1127w,sh676msinandout635s,shas.(Ei)650sofphase1062s1054vsuSO3(A1)629sSb.Fb-.613shinandout833s888soSF(A1)—575shofphase580m, bUSbF6(E2g)772s786w606mSO3(E)477wSbF6-592m589ms313shdeformations292m573s544möSO3(A1)271m554s403m405möSO3F(E)395shaRef.23bRef.14CRefs.13and31Abbreviations:s=strong,v=very,as=asymmetric,m=medium,shshoulder,t=terminal,w=weakb=broadb=bridgingCThe most noticeable change appears to have occurred in the S-F stretching region. Thetwo intense bands at 772 cm1 and 833 cm1 in Sn(SO3F)2 (Table 4.3) are now replaced by asingle strong band at 888 cm1,with a weak band at 786 cm1 (possibly due to mesitylene).From this overall band distribution and the increased wave number of the US-F band, itappears that a change in denticity of the anion has taken place due to mesitylene adductformation. The findings are consistent with a bidentate, possibly bridging configurationtentatively formulated as [(ri6-mes)Sn(SO3F)2]rather than an ionic (perturbed) or tridentategrouping (33).Compared to the rather complicated pattern observed for Sn(SbF6)2in the region of520-750 cm1 (Table 4.3), the band pattern displayed by the anion in the adduct Sn(SbF6)2mesis very simple: a very strong band at 671 cm1, a sharp, medium band at 635 cm1, and a weakband at 580 cm1 are found. For a free SbF6 anion, a peak at —660 cm’ is attributed to theasymmetric stretch with Raman active bands observed at —660 again and at 575 cm1. Thepattern observed for Sn(SbF6)2mes suggests the presence of a wealdy coordinated SbF6anion. Peak splitting in the SbF6 stretching region produces bands at 671 and 635 crn1, withthe loss of a symmetry center allowing detection of a Raman active fundamental at 580 cm1(34).It appears then that addition of mesitylene has a different effect on the anion bands inSn(SO3F)2mes and Sn(SbF6)2mes, respectively. In the former adduct the SO3F group seemsto be still coordinated to tin, but more likely in a bidentate, possibly bridging manner. InSn(SbF6)2mes only weak coordination of the SbF6 group is evident and any departure from anionic SbF6 with°h symmetry is rather slight. It is unfortunate that in particular for thiscompound support from Raman spectroscopy is lacking due to sample decomposition in thelaser light, as mentioned earlier.107The findings for Sn(SbF6)2mes are consistent with the view that both mesitylenegroups are coordinated to tin, which in turn is supported also by the 119Sn M6ssbauer spectra.4.4 ConclusionDirect addition of an arene, in this case mesitylene, to suitable Sn(II) salts likeSn(SO3F)2 and Sn(SbF&2 at room temperature, and product isolation well below roomtemperature, allow the high yield synthesis of veiy wealdy bound mesitylene complexes.However, only microcrystalline materials result which precludes structural studies by singlecrystal X-ray diffraction. The adducts are characterized by chemical analysis and infraredspectra and their formation is followed by 119Sn Mössbauer spectroscopy. This spectroscopicmethod allows not only product characterization, but also, using the isomer shift and the absenceof quadrupole splitting as criteria, the identification of other suitable substrates for complex formation. It is observed that only tin(II) compounds with large, weakly nucleophilic anions arecapable of forming mesitylene adducts, while SnC12, SnF2 and stannocene do not give anyindication of adduct formation under similar conditions.References1. A.G. Gash, P.F. Rodsiler, and E.L. Amma, Inorg. Chem., j., 2429 (1974).2.a) H. Schmidbaur, Angew. Chem. mt. Ed. (English), 4, 893 (1985).b) H. Schmidbaur, W. Bublak, B. Haber, and G. Muller, Angew. Chem. mt. Ed. (English),, 234 (1987).3. P. Jutzi, Adv. Organomet. Chem. , 217 (1986).4.a) Th. Auel and E.L. Amma, J. Am. Chem. Soc., 90, 5941 (1968).b) H. Luth and E.L. Amma, J. Am. Chem. Soc., 91,7515 (1969).108c) P.F. Rodsiler, Th. Auel, and E.L. Amma, J. Am. Chem. Soc., 97, 7405 (1975).5.a) M.S. Weininger, P.F. Rodsiler, A.G. Gash, and E.L. Amma, J. Am. Chem. Soc., 4,2135 (1972).b) M.S. Weininger, P.F. Rodsiler, and E.L. Amma, Inorg. Chem., Ia. 751 (1979).6. H. Schmidbaur, T. Probst, B. Huber, 0. Steigelmann, and G. Muller, Organomet. ,1567 (1989).7. H. Schmidbaur, T. Probst, B. Huber, G. Muller, and C. Kruger, 3. Organomet. Chem.,, 53 (1989).8. Th. Auel and E.L. Amma, 3. Am. Chem. Soc., 9Q, 5941 (1968).9. J.D. Donaldson, Prog. Inorg. Chem., , 287 (1967) and references herein.10. S.H. Strauss, M.D. Noirot, and 0.P. Anderson, Inorg. Chem., 2, 3851 (1986).11. S.P. Mallela, S.T. Tomic, K. Lee, J.R. Sams, and F. Aubke, Inorg. Chem., , 2939(1986).12. S.P. Mallela, S. Yap, J.R. Sams, and F. Aubke, Inorg. Chem., 5, 4327 (1986).13. M.S.R. Cader and F. Aubke, Can. J. Chem., 2, 1700 (1989).14. T. Birchall, P.A.W. Dean, and R. 3. Gillespie, J. Chem. Soc. A, 1777 (1971).15.a) J.K. Lees and P.A. Flinn, Phys. Lett., j, 186 (1965); and J. Chem. Phys., 4, 882(1968).b) P.A. Flinn, G.K. Shennoy, F.E. Wagner, Eds., HMössbauer Isomer Shifts”, North-Holland Publishing Co., Amsterdam, 1978, p. 593 ff.c) J.D. Donaldson and B.J. Senior, 3. Chem. Soc. (M, 1821 (1967).16. R.H. Herber and G. Carrasquilo, Inorg. Chem., , 3693 (1981).17. A.J. Edwards and K.I. Khallow, Chem. Comm., 50 (1984).18. R.J. Batchelor, J.N.R. Ruddick, J.R. Sams, and F. Aubke, Inorg. Chem., .j, 1414(1977).19. D.C. Adams, T. Birchall, R. Faggiani, R.J. Gillespie, and J.E. Vekris, Can. J. Chem., 9,2122 (1991).10920. D. Gantar, I. Leban, B. Friec, and J.H. Holloway, 3. Chem. Soc. Dalton Trans., 2379(1987).21. R.V. Parish in “Mössbauer Spectroscopy Applied to Inorganic Chemistry”, Vol. I, Ed.G.J. Long. Dienum Press, New York, 1984.22. J. Barr, R.J. Gillespie, and R.C. Thompson, Inorg. Chem., a, 1149 (1964).23. C.S. Alleyne, K. O’Sullivan Mailer, and R.C. Thompson, Can. 3. Chem., , 336 (1974).24. D.F. Shriver, “The Manipulation of Air-Sensitive Compounds”, McGraw-Hill, NewYork, 1969.25. R.E. Rundle and D.H. Olson, Inorg. Chem., 3, 596 (1964).26. J.D. Donaldson, R. Oteng, and B.J. Senior, Chem. Comm., 618 (1965).27. A. Almenningen, A. Haaland, and T. Motzfeld, 3. Organomet. Chem., 7., 97 (1967).28.a) P.G. Harrison and J.J. Zuckerman, 3. Am. Chem. Soc., 9, 2577 (1970).b) T.S. Dory and J.J. Zuckerman, J. Organomet. Chem., 264, 295 (1984).29. L.D. Dave, D.F. Evans, and G. Wilkinson, 3. Chem. Soc., 3684 (1959).30.a) J.G. Stevens and V.E. Stevens in “Mössbauer Effect Data Index”, Plenum Press, NewYork, 1958.b) J.J. Zuckerman in “Chemical Mössbauer Spectroscopy”, Ed. R.H. Herber, Plenum Press,New York, 1984.31. K.O. Christe, W.W. Wilson, R. Bougon, and P. Charpin, J. Fluorine Chem., , 385(1982).32. P.A. Yeats, J.R. Sams, and F. Aubke, Inorg. Chem., ii, 2634 (1972).33. W.W. Wilson and F. Aubke, Inorg. Chem., fl, 326 (1974).34. A.M. Qureshi, A.H. Hardin, and F. Aubke, Can. 3. Chem., 4, 816 (1971).110CHAPTER 5A LOW TEMPERATURE MAGNETIC STUDY OFTHE MOLECULAR CATIONS O2, Br2 AND I25.1 IntroductionOnly a limited number of compounds with paramagnetic homonuclear ions of nonmetallic main group elements are known. Of these, compounds with diatomic cations stabilizedby very weakly basic fluoroanions are the subject of this study. The cations in this group consistof the dioxygenyl cation Oj’, first discovered in O2[PtF6] by Bartlett and Lohmann (1), andthe two dihalogen cations I2 and Br2, first identified in solutions of strong acids and super-acids by Gillespie et al. (2,3).Single crystal X-ray diffraction studies were subsequently reported forBr2[Sb3F16] (4)andI2[SbF1J (5), while powder diffraction studies have afforded a more limited structuralinsight into a number of dioxygenyl salts (6). For the dihalogen cations, electronic spectra of thesolvated species (2,3), resonance Raman spectra (7), and magnetic measurements at roomtemperature (2,4(a)) have allowed some information on the electronic structure, suggesting a2fl3jg ground state (10). In addition, the study by Herring and McLean (8) has pointed out theclose similarity between the solvated cations I2+(1v) and Br2(SOlV) and their gaseous counterparts as studied by photoelectron spectroscopy (9) or molecular spectroscopy (10). This strongresemblance should permit at least an approximation of the energy separation to the nearestexcited states, not only for the dihalogen cations, but also for 02+, where a21,’2g ground state isindicated (10).111The objectives of the present study which involves low-temperature magnetic susceptibility measurements on suitable compounds containing the three homonuclear diatomic cationscan be summarized as follows:(i) To investigate the magnetic behavior of what appear to be the only three suitableparamagnetic molecular cations formed by non-metals. Structural and spectroscopicinformation mentioned previously should help in the interpretation.(ii) To explore whether, and to what extent, van Vleck’s theory of molecular paramagnetism(11), developed 60 years ago, can be applied to solid-state cations. So far, nitric oxide,NO, has served as the best example; however, useful experimental data for this moleculedo not extend into the condensed phase due to intermolecular association.(iii) To examine the reasons why the magnetic moments reported so far for O2 salts fall wellbelow the spin-only value of 1.73 B• Measurements down to very low temperaturesshould allow the detection of magnetic behavior consistent with antiferromagneticexchange, which is a possible cause for reduced magnetic susceptibilities.(iv) To compare the magnetic susceptibilities ofI2[SbF11J and Br2[Sb3F16J below—80K, since earlier measurements above that temperature (12) had suggested anti-ferromagnetic coupling forI2[SbF11],but not forBr2[Sb3F16j.5.2 ExperimentalBothBr2[Sb3Fi& andI2[SbF1i] were synthesized according to the method reportedby Wilson et al. (12). This method involved the oxidation of previously purified Br2 andresublimed 12 by bis(fluorosulfuryl) peroxide, S206F at a precise 2:1 mole ratio, and the112subsequent solvolysis of the product mixture in an excess of freshly distilled antimony(V)fluoride. The reactions were followed by weight and the purity checked by melting points.Br2[Sb3F16] (4.777 g, 5.762 mmol) was obtained from 0.924 g (5.782 mmol) of Br2and 0.5724 g (2.89 1 mmol) ofS206Fafter solvolysis in —10 g of SbF5 at room temperature andremoval of all volatiles in vacuo. The bright red solid melted at 84 ± 1°C (lit. 85.5°C) (12).I2[SbF1J- (2.775 g or 3.928 mmol) was synthesized from 0.9986 g (3.934 mmol) ‘2 and0.3895 g (1.967 mmol) ofS206F and subsequent solvolysis in —12 g of SbF5 at 50°C. Theblack-blue solid isolated after the removal of all volatiles melted at 129 ± 1°C (lit. mp. 127°C)(12).A sample of02[AsF6j was obtained from Dr. Karl 0. Christe of Rocketdyne. Thecompound was synthesized by UV photolysis of 02, F2, and AsF5 in quartz. Magnetic fieldstrengths of 7501, 9225, and 9625 G and a temperature range of —2-124K were used in thisstudy. Molar magnetic susceptibilities, XM, were corrected for diamagnetism and forBr2[Sb3F16]-andI2[SbF1], slightly larger X values were used than reported previously(12). The magnetic moments of the Br2 and compounds were corrected for temperature-independent paramagnetism (TIP = 120 and 68 x 10 cm3 mol1 respectively, calculated asdescribed in the text). The Curie-Weiss law in the form XM = CmITO is used throughout.5.3 Results and DiscussionThe discussion of the magnetic behavior of the three cationic species will center aroundthree aspects:(i) The selection of suitable compounds for this study in the light of previous magneticsusceptibility studies.113(ii) The magnetic measurements onO2[AsF6],I2[SbF1], andBr2[Sb3F16J.(iii) An attempted interpretation of these results.5.3.1 SynthesisMagnetic measurements on a single compound in the current study require —300-500 mgof high-purity sample for duplicate measurements when the vibrating sample magnetometer isused, while the Gouy measurements require between 1 and 2 g. All cations are extremelyreactive and only‘2 is sufficiently stable in HSO3F- bF5 solution (2,12), not undergoingdisproportionation or further oxidation. This rules out purification by recrystallization as ageneral procedure for all the three salts. The limited thermal stability reported for all materialshas so far precluded purification by sublimation. Hence, synthesis on the desired scale frompure starting materials, with little or no chance for side-reactions and facile product isolation,becomes the only route to the compounds of this study.There appears to be no real choice among the Br2 containing compounds, sincestructural and spectroscopic details on Br2[AsF6] (14), the only other Br2 salt, are not readilyavailable. The original synthesis ofBr2[Sb3F16} (4), from BrF5,Br2, and SbF5, did produce asample suitable for a single-crystal X-ray diffraction study, but judging by the reported physicaldata, in particular the melting point and a magnetic moment of Peff — 1.6 B’ the productobtained from this method appears to be unsuited for this study.A similar problem arises in the case of the‘2 species as well. The method used for thepreparation of single crystals ofI2[SbF11] (5), the oxidation of 12 by SbF5 in SO2, is notsuited for the preparation on a larger scale, as is evident from the reported analytical data (5).The problem appears to be the quantitative separation of the by-products SbF3 or SbF35.114Formation of anions of the type Sb3F14 becomes a possibility and, in addition, a diamagneticcompound of the compositionI2[(SbF6) b14] has recently been obtained by thissynthetic route (15) with reaction conditions only slightly different.Substitution of SO2 by AsF3 as solvent appears to lead toI2[SbF1] of a higher purity,butI2[Sb3F16] may form as a by-product as well (16). Any uncertainty in the molar mass ofthe product will limit the usefulness of a magnetic study. Other materials considered unsuitablefor this study, as mentioned in Chapter 1, include the substances formulated as (SbF5)21(17) andthe insufficiently characterized12[’aF6J (17).An alternate synthetic route to bothI2[SbF1i] andBr2[Sb3F16],the oxidation of 12or Br2 by stoichiometric amounts of bis(fluorosulfuryl) peroxide and subsequent solvolysis in anexcess of SbF5 according to:50°C212 + S206F + 8SbF5 > 2I[SbF11] + 2SbF9SO3, [5.1]25°C2Br + S206F + 1OSbF5 > 2Br1Sb3F6] + 2SbF9SO3, [5.2]has produced sufficiently large quantities of both compounds for a magnetic study between 298and 80 K using the Gouy technique (12). With all starting materials readily purified and thevolatile byproduct Sb2F9O3(18) easily separated from the product, this method, employed inthe present study, was chosen as the most appropriate route to the synthesis of bothI2[SbF1i]andBr2[Sb3F16].With well over a dozen different O2 salts reported so far, this group of compoundsappears to offer a wider choice, but here additional problems surface, which seem to haveadversely affected earlier magnetic studies. Some of the reported compounds, O2[PtF6] (1),115O2[PdF& (19),02[RuF6j (20), orO2[RhF6] (20) have two different paramagnetic centersin the same molecular unit. The initial approach by Bartlett and Beaton (21) involving thesubtraction of the molar susceptibilities of N0[PtF&- from those obtained for02[PtF6] hasclearly allowed th identification of 02+ as a paramagnetic ion; however, magnetic exchangebetween 02 and Pt(V) (d5) is a plausible contributing factor for the observed decreasing trendof the magnetic moments attributed to 02+ with decreasing temperature. Magnetic ordering dueto 02 Pt(V) exchange has subsequently been reported for this compound (23).In addition, the high-pressure synthesis of dioxygenyl salts from 02/F mixtures andeither metal fluorides or the metal itself (20,22,24) in metallic reactors has often resulted inmaterials with ferromagnetic contaminants (19,23). Although monel impurities can be recognized by the characteristic Curie temperature of 335 K and corrections have been attempted(23), such materials remain suspect in magnetic susceptibility studies. This is due to thepossible existence of weak antiferromagnetic ordering in such materials contaminated withmonel.UV photolysis in quartz vessels (25) represents a more suitable synthetic method, but anumber of 02 salts such as02[BF4] (26) and02[GeF5] (27) prepared in this manner showrather limited thermal stability. Nevertheless, a magnetic study of02[BF4J between 293 and85 K has been reported (28a), but only limited conclusions were reached.For the products obtained from the reaction of 02 and F2 with SbF5 by either UVphotolysis or high-pressure synthesis, some structural ambiguity has been noticed. This problemarises since in these reactions, a variety of [SbF5+iJ type anions may be formed to stabilizethe 02 species. Both 02[SbF6j and 02[SbF1i1 are well characterized (6,24), andO2[Sb3F16] has been postulated as well (29). The problems caused by this structural116ambiguity are apparent from magnetic susceptibility studies on “O2[SbF6j”reported in theSoviet literature (28).To avoid similar problemsO2[AsF6] obtained by UV photolysis (25) was chosen forthis study. An additional reason for this choice is the availability of structural information onthis compound. A phase transition at 255 ± 3 K (30) results in a rhombohedral distortion of thecubic structure found at room temperature (6) This distortion is also evident from ESR studiesdown to 4 K (23,3 1). Conclusions reached regarding the ground state of 02 in these ESRstudies are useful in the interpretation of our low temperature susceptibility results.There have been two previous magnetic susceptibility studies of02[AsF6] down to4 K, with rather contradictory results. In a study by Grill et al. (32), no magnetic ordering of the02+ cations is observed down to 4 K, while weak 0202+ exchange is suggested in anotherstudy (23) based on the small Weiss constant obtained. However, these conclusions arerendered somewhat tenuous because of ferromagnetic monel impurities in the sample, requiringcorrection of the susceptibility data (23).In all previous magnetic susceptibility studies of 02k, the magnetic moments obtainedover the whole temperature range are well below the spin-only value of 1.73 B’ and explanations have varied from suggesting “van-Vleck behavior” (22) in analogy to the behavior of NO(11), to invoking the presence of 17% of an unidentified, magnetically inert impurity in02[AsF6] (32). Likewise in some studies down to 80 K (28), values for O2[SbF&appear to decrease with decreasing temperature, while for the structurally related02’IAsF6],I1eff is said to be invariant with temperature to 4 K (32). It is unclear why there are so manydiscrepancies and contradictions in previous studies. It is felt, however, that sample identity andpurity play a major role here.1175.3.2 Magnetic MeasurementsThe results of our magnetic susceptibility studies onBr2[Sb3Fid below 80 K, togetherwith results obtained in an earlier study (12) at higher temperatures, are summarized in Table5.1. Both sets of XM and eff data have been calculated using the same diamagnetic correctionand TIP values (279 and 120 x 10-6 cm3 mo11,respectively). The agreement between the datasets in the overlap region is excellent for this compound.The data obtained here forI2[SbF11] andO2[AsF6} are given in Table 5.2. Becauseof poor agreement in the 100 K region with the earlier Gouy data (12), the current study wasextended with the vibrating sample magnetometer up to 124 K for the I2 compound. Additionally, the measurements for the 02+ compound was also extended down to 2 K in the hope (notrealized, unfortunately) of observing a maximum in the susceptibility data of this compound atvery low temperatures. Pertinent structural and spectroscopic features of the three compoundsstudied and of the three cations, 02+, Br2+, and 12+, either as solvated or gaseous species, aresummarized in Table 5.3.The contrast in the magnetic properties of the three paramagnetic cationic speciesstudied in this work is clearly evident from the plots of magnetic moment versus temperatureshown in Figure 5.1. Two of the compounds,02[AsF6] and Br2[Sb3F16],exhibit CurieWeiss behavior over a wide temperature range, as is seen by the plots of 1/XM vs. T given inFigure 5.2.5.3.3 Br2[SbF16]The magnetic behavior ofBr2[Sb3F16}appears to be rather straightforward and will bediscussed in detail first. The 1/XM versus T plot of this compound indicates Curie-Weiss118Table 5.1: Magnetic Data ofBr2[Sb3F16]Temperaturea XM X 106 L’eff (JIB)b(K) (cm3mol1)297 1870 2.04275 2010 2.04255 2160 2.04235 2330 2.03213 2530 2.03193 2780 2.03172 3070 2.02151 3430 2.00131 3900 1.99116 4500 2.02104 4910 2.0080.0 6130 1.9681.1 6070 1.9673.5 6720 1.9765.7 7440 1.9655.0 8870 1.9643.7 10900 1.9431.4 15000 1.9321.4 21900 1.9310.2 45700 1.939.88 45900 1.904.20 111300 1.93a First twelve data points from Ref. 12.b Corrected for TIP using 11eff = 2.828 ((XM - TIP)T)1t with TIP = 120 x 10-6 cm3 mo11.119Table 5.2: Magnetic Data ofI2[SbF1] and O2[AsF6iI2[SbF1J- O2[AsF6]Temperature XM X 106 ffa (RB) Temperature XM x 106 ffb (iB)(K) (cm3mo11) (K) (cm3mo11)124.1 3770 1.92 80.1 4170 1.63117.5 3860 1.89 76.3 4410 1.64106.5 4290 1.90 72.7 4650 1.6498.6 4510 1.87 68.5 4950 1.6590.9 4730 1.84 64.3 5480 1.6584.3 4900 1.81 59.2 5600 1.6381.2 5030 1.80 53.2 6170 1.6276.8 5120 1.76 46.5 6990 1.6171.8 5300 1.73 42.9 7520 1.6166.6 5380 1.68 39.1 8200 1.6063.5 5470 1.66 30.3 10530 1.6058.4 5560 1.60 25.3 12430 1.5951.9 5560 1.51 20.5 15100 1.5744.9 5090 1.34 15.3 19700 1.5536.9 4910 1.20 10.1 28800 1.5231.6 4700 1.08 7.12 37500 1.4627.4 4490 0.98 5.92 44500 1.4527.1 4520 0.98 5.28 48300 1.4321.8 4300 0.86 4.78 52200 1.4111.6 4270 0.62 4.62 52700 1.408.64 4290 0.54 4.40 54800 1.396.30 4490 0.47 4.04 59400 1.394.54 4790 0.41 2.70 70400 1.232.40 75500 1.202.10 81300 1.17a Corrected as in Table 3.1 with TIP = 68 x 106 cm3 mo11b Not corrected for TIP120Table 5.3: Structural and Spectroscopic Information on O2IAsF6],I2[SbF1i]’Brj’1Sb3F16] ,and the Corresponding Ions O2, Br2and I2Data, X Denotes 0, Br, or I O2[AsF6J Br2[Sb3F16J I2[SbF11]or°2g) or Br2+(g) or12g)Shortest XX non-bonding 4 to4•05a 6.445 4.29interaction [A] (ref. 28b,30) (ref. 12, 4b) (ref. 12, 6)van der Waals Radii 1.52 1.85 1.98for X [A] (ref. 34)Ground state of X2(g) 2hhl/2g 23f2g 23/2gSpin orbit coupling 185 (ref. 52) 2820 ± 40 5125 ± 40(ref. 53) (ref. 53)const. [cm1]for X2(g) 195 (ref. 10) 3141 ± 160 5081 ± 60(ref. 55) (ref. 55)tS.E(2fl1/2g2h13/2 )As above forX2(l) [cm1] --- 2890 (ref. 12) 5190 (ref. 2)Diamagnetic Correction (ref. 56) 79 279 238[10-6 cm3 mo11]a Estimated from powder diffraction data121Figure 5.1: Magnetic Moment vs. Temperature of Br2[Sb3F16],I21SbF1], andO[AsF6]2-__--- 0— - --CD0- 8 - —.-.—_...._..-—.—1.5- F, //zLii 1 //04/1 4Z / ° Br2[Sb3F16jo // .I[sb11]—• O2[AsF60.5- w/0-0 20 40 60 80 100 120 140TEMPERATURE,K122-J0()-J0w0U)DU)C-)zC,0TEMPERATURE,K100Figure 5.2: Inverse Susceptibility vs. Temperature of O2[AsFj andBr2[Sb3F16]0025020015010050000,0‘Pt/A’0’/0’/0’///////0’/.—.-.0 O2[AsF6J. Br[Sb3F160 20 40 60 80123behavior over the temperature range from 80-4 K (Cm = 0.49 ± 0.01 cm3 mo11 K, 9 = -0.74 ±0.01 K). The magnetic moments (even when corrected for TIP) decrease slightly withtemperature. A TIP correction had been arbitrarily assigned in the earlier work (12) in order tobring the magnetic moments in the high-temperature region into agreement with the value of2.0 B predicted by theory (11) for a species with a2H3g ground state and no thermally accessible excited state (see Table 5.3).The correction for TiP in the present study was taken as 4N32/3zE (33), where sE is theenergy separation between the ground 2fl3g and the next excited state with which it ismixing. The AE value for Br2 is the spin-orbit coupling constant, , and for this species,estimated at 2890 cm1 for the solvated ion (Table 5.3), and using this value a TIP of 120 x 10-6cm3 mo11 is calculated. Magnetic moments calculated using this TIP correction are within ±2%of the theoretical value of 2.0 B over the wide temperature range of 297-55 K (Table 5.1).The cause of the very small drop in the moment, particularly at very low temperatures(corresponding to the effect of a Curie-Weiss rather than Curie law behavior) is not certain.Although the shortest non-bonding BrBr contact at 6.445 A (4b) is too long to invokesignificant direct magnetic interaction (Figure 5.3), F”Br contacts ranging from 2.86-3.34 A,comparable to or shorter than the sum of the van der Waals radii of 3.32 A (34), suggest thepossibility of very weak exchange via bridging anions. However, the effect is very minor and itis reasonable to conclude that inBr2[Sb3F16] the Br2 cation is in a thermally isolatedground state and there is no conclusive evidence for any magnetic exchange between paramagnetic centers down to 4.2 K. In this regardBr2[Sb3F16] is somewhat unique, since for allother paramagnetic main group species, including 02 (35), the recently studied ozonides, K03Rb03,and Cs03 (36), and solid 02 (37), as well as ‘2 and O2 (discussed below), at least weakantiferromagnetic coupling has been suggested.124Figure 5.3:[Br][Br]Crystal Structure of Br2ISb3F16] (redrawn using data from ref. 4b)abCVzX—X, bond lengthX ... F, closest contacttSb..F (terminal)Sb...F(btidIng)R tbrid,IrterB4Sb3F1IMenoclinic13.58 i 0.02 A7.71 * 0.01 A14.33 ±0.02 A93.7 a 0.21497 A33.68 g cm342.15 A2.86 A1.83 A2.10; 1.97 A1,110r Br—Br2 = 6.445A1255.3.4 O[MF(]The magnetic properties of02[AsF6] are similar to those of the Br2 compound in thatCurie-Weiss behavior is followed (Figure 5.2), although over a more limited temperature rangeof 60-2 K. Here the Curie constant Cm, is significantly smaller and the absolute value of theWeiss constant, 101, greater (C = 0.34 ± 0.01 cm3 moi1 K, 0 = -1.90 ± 0.01 K). Consequently,the effective magnetic moments are significantly smaller for02+[A5F6J and show a strongertemperature dependence, particularly in the low temperature region (Figure 5.1). A slightdeparture from linear behavior in the Curie-Weiss plot is noted (Figure 5.2) above 60 K. Thismay be significant, as it coincides with the observed broadening of the ESR line (23), possiblycaused by tumbling motions of 02 in the crystal lattice.These findings are at variance with a previous report by Grill et al. (32), who observedCurie-Weiss behavior for 02+ with a positive 0 value (according to our formulation of the law)of 0.7 K. The results of our study are in reasonable agreement with those of DiSalvo et al. (23),who obtained Cm = 0.309 cm3 mol-1 K and 9 = -0.8 K (sign changed from (23) to conform toour formulation of the law), although it must be taken into consideration that a temperature-independent paramagnetism contribution as well as corrections for ferromagnetic impuritieswere made in the earlier work.In this work the susceptibilities of 02 were not corrected for TIP. A crystal-fieldanalysis of ESR data for02[AsF6]- suggests the separation between the ground and firstelectronic excited state to be 1480 cm1 (Figure 5.4), caused by both spin-orbit coupling andcrystal-field splitting due to 02 being in a site of orthorhombic or lower symmetry (31). In thiscase one is clearly not dealing with pure21i2g and 2113flg states and it is not clear what the TIPcorrection should be. In any event, the large separation between the states means such a correction will be small, and hence ignoring it should not significantly affect the conclusions.126Figure 5.4: Energy Level Diagram of the Dioxygenyl Ion with the a and it-Bonding 2pOrbitals (Ref. 31)2pJ*_ __T2pit (2÷2)j-2p ii2p H(a) (b) (c)free ion spin—orbit spin—orbitcoupling. ? coupling+ orthorhombicfield,127When considering the magnitude of the magnetic moment, it is observed thatforO2[AsFj the measured magnetic moments in the range of 1.6 B at the higher temperatureregion agree well with values predicted using the average g values, gay of 1.89 (23) and 1.905(31) obtained by ESR. Using the equation for the magnetic moment of a single electron B =g[S(S+1)11/2,values of 1.64 and 1.65 B are obtained respectively for the above two gay data.As described by Goldberg et al. (31), both crystal-field splitting and spin-orbit couplingcontribute to the ground state inO2[AsF6]-. In a pure2fllag ground state the spin and orbitalcontributions cancel, and there is no first-order paramagnetism associated with this state (33).If this were the case for O2 with negligible thermal popuation of excited states, onlytemperature-independent paramagnetism would be present. This is clearly not the case here.The crystal-field interactions have the effect of quenching the orbital contribution, although notcompletely, resulting in a ieff value slightly below the spin-only value. Quite the opposite effectis observed for the alkali metal superoxides, MO2 with M = Na, K, Rb, Cs (35). Here theground state is and in all instances the .teff values are well above the spin-only value of1.73 B’ as was found forI2[SbF11] andBr2[Sb3F16Y(12).The decrease in neff values with decreasing temperature forO2[AsF6], particularlysignificant below —20 K, requires further consideration. With a splitting of 1480 cm1 separating the ground state from the nearest excited state, the variation in the effective magneticmoment with temperature observed here cannot be accounted for by the sort of van Vieckbehavior observed for gaseous NO (33). The existence of antifeffomagnetic exchange betweenparamagnetic centers must be considered as a possibility.The limited structural information available on O2[AsF6} (25,31,38) derived frompowder diffraction data does not permit an accurate determination of the shortest OO nonbonding contact distance. Estimates of 4.00 (30b) and 4.05 A (32) respectively, which were128used to argue against 0”{) interaction, are simply half the unit cell length ad2 for the room-temperature phase (25,31,38). The distance ad2 describes the separation between the masscenters of the 02+ cations, which are assumed to be in the most probable sites. The low-temperature phase, which is directly relevant to this study, has a powder diffraction pattern thathas not been successfully indexed (30); hence the conclusion (32) that there can be no antiferromagnetic exchange in02[AsF61-because the 02 ions are too far apart is most likely invalid.For02[MnF9],where a single crystal X-ray diffraction study at room temperature andat -150°C is reported (39), non-bonding 00 contacts of 3.86 A are detected at -150°C withvalues of 3.98 A observed at room temperature. However, the anion is described as a doublechain of cis-bridged MnF6 octahedra with 02 cations between the anion layers, and theresulting structure is not comparable with that of02[AsF6]. Moreover, susceptibility studieson this material would not be suitable for the purposes of this work as the magnetism would becomplicated by the presence of Mn4+, a second paramagnetic center.With the sum of the van der Waals radius 3.02 A for two oxygen atoms, one wouldreasonably expect distances of 3.2-3.3 A as the limit for significant direct antiferromagneticexchange. This estimation is corroborated by recent reports on the structures of the alkali metalozonides K03 (40,41,42), Rb03 (40,4 1) and Cs03 (43), all of which exhibit significant antiferromagnetism (34) than02[AsF6], and where 00 non-bonding contacts range between3.01-3.15 A for K03 and 3.01-3.30 A for Rb03, respectively. For Cs03, where antiferromagnetic exchange is rather weak (36), only powder data are reported (43) and indexed, suggesting Cs03 to be iso-structural with Rb03. The unit-cell dimensions indicate slightly longer 00contacts for this compound (42). Contact distances of the order of those observed in theozonides could be present in02[AsF61 and this could account for its observed magneticproperties.1295.3.5 I[SbF11]In a previous report from our group on12+[SbF1] it was shown that a TIP correction inexcess of that assumed for the Br2+ compound was required to bring the experimental room-temperature moment into agreement with the value of 2.0 B predicted by theory (12). Inaddition, it was suggested in the earlier work that the observed decrease in the magnetic momenton decreasing the temperature to 80 K may arise from antiferromagnetic exchange betweencontiguous cations in the crystal lattice, where the shortest Fl non-bonding contact distance(5) is found to be 4.29 A (Figure 5.5). Magnetic measurements onI2[SbF1] down to 4.2 Kreported here confirm the presence of antiferromagnetic coupling. The susceptibility rises to amaximum at —54 K, then decreases on further cooling (Figure 5.6). The rise again in susceptibility on cooling below l0 K is probably due to trace amounts of paramagnetic structuralimpurity, as is often observed in antiferromagnetically coupled systems (13).In view of the clear evidence that this system is exchange-coupled, there is no justification for arbitrarily reducing the room-temperature moment to 2.00 B with an appropriate TIPcorrection, as was done previously (12). Indeed, in view of the fact that the 23/2j 21t2gseparation is significantly greater in the compound compared to Br2 (see Table 5.3), anyTIP would be expected to be smaller in the former. TIP for (calculated as described abovefor Br2j is 68 x 10.6 cm3 mo11 and magnetic moments calculated employing this value aregiven in Table 5.2. The decrease in with decreasing temperature is consistent with antiferromagnetic coupling; interestingly though, the absolute values in the high-temperature regionare in excess of the theoretically predicted value of 2.0 B (11).An attempt is made here to analyze the magnetic susceptibility data of I2 (including thedata from 295-130 K from ref. (12)) according to three theoretical models for antiferromagneticexchange in one-dimensional systems. For a magnetically concentrated system with spins Si130Figure 5.5: Crystal Structure of Ij[Sb2F11] (redrawn using data from ref. 5)2]r1+ T+4.29A£2 2ISb2FjMonoclinicI 13.283(5)Ab L314(3)AC 5.57J(2)AP 103.75(2)V 597.5 A3Dcsi 3.92gcm2 2X—X, bond enth 2.557(4) AX ... F, closest contact 2.89 ArSbF(termin.I) 1.85 AtSb_E(brIdgng) 2.00 AR brd./’ter 1.08131>-F—-jF—U-LUCU)DU)C-)F—LUzFigure 5.6: Magnetic Susceptibility vs. Temperature ofI2[SbF11].(Circles are experimental data; Solid line is the best fit to the IsingS’ = 112 model)0rOC-)r05o0c1000 100 200 300TEMPERATURE (K)132and S, the nearest neighbor exchange coupling is given by the Hamiltonian Hex ()NH = -23 Z aSjzSz + I3S1SJX + ySYSY [5.3]where S1Y and S1z are the components of the spin vector S1 of the ith atom, N the number ofmagnetic atoms and 3, the exchange coupling constant, which can either have a positive ornegative value, i.e. ferromagnetic or antiferromagnetic interaction. The values of a, f3 nd y inequation (4.3) define the nature of the exchange coupling. When a = = = 1, the isotropicHeisenberg exchange Hamiltonian results. In the extreme situation where a = 1 and f = y = 0,the Ising model is described (anisotropic coupling).The isotropic Heisenberg Hamiltonian has been extensively examined but no exactsolutions are presently known. However, results of many approximate methods exist (45). Forthe Ising model Hamiltonian, closed-form solutions are available for both the parallel andperpendicular magnetic susceptibilities of the S = 1/2 system (46).Considering the2113/2g ground state of I2 as having an effective spin S’ = 3/2 (47), ourdata were fitted to an isotropic Heisenberg model developed by Weng (48), employing thefollowing polynomial expression and appropriate coefficients given by Hiller et al. (49) for themolar susceptibility:Ng23XM= kT[A + Bx2][1 + Cx + Dx31’ [5.4]where x = kT/IJI.133In the above equation (and equations [5.6] and [5.7], see below) g is the Lande splittingfactor, the Bohr Magneton, N the number of spins in the lattice, k Boltzmann constant, T thetemperature and 3 the exchange coupling constant. The values of the coefficients for S=1/2 andS=3/2 are as follov s:S A B C D1/2 0.2500 0.18297 1.5467 3.44433/2 1.2500 17.041 6.7360 238.47Allowance was made for paramagnetic impurity by modelling it as a Curie paramagnet with a gvalue equal to that of the bulk sample, i.e. =Ng2f3S(S+1)/3kT. Expressing XM from equation [5.4] as hain’ the susceptibility expression including paramagnetic impurity isX [lP1x.jn +1Xpara The experimental data were fitted to this expression using g, J, and P asfitting parameters. The best fit was considered to be that set of fitting parameters which gavethe minimum value of the function F (50):nF = [‘/ E (X1calcd - X’obs / X’b)2]1” [5.5]where n is the number of data points, and X’cacd and X’0b5 are the calculated and observedsusceptibilities, respectively. For S’ = 3/2, the best fit of the data for I2 was with 3 = -7.2 cm1,the effective g = 1.23, P = 0.0035, and F = 0.0560. In view of the molecular anisotropy of themagnetic species, the anisotropic Ising model should be examined as well. Unfortunately, whilean exact solution exists for the parallel susceptibility of the Ising S = 3/2 case (51), there is nosolution for the perpendicular case and hence one cannot analyze the powder data according to134this model.An alternative approach to the data analysis is to consider the possibility that the fourfold degeneracy of the ground 2fl3flg state has been lifted by second- or higher-orderinteractions with excited states, leaving a thermally isolated Kramer’s doublet as the onlysignificantly thermally populated ground level. In this case one needs to consider an effectivespin, S’ = 1/2, and here both Heisenberg and Ising models are available. Employing again theWeng model and equation [5.4], a best fit between theory and experiment was obtained with 3 =-28 cm1,effective g = 2.72, P = 0.0061, and F = 0.0487.As mentioned earlier, exact solutions for both the parallel and perpendicular susceptibilities for the anisotropic Ising S’ = 1/2 case are available, and the data were analyzed usingthe equations of Fisher (46):(Ng22 \ /2IJ1 ‘\Xii I lexp.i J [5.6]\ 4kT/ \kT// Ng232\ / IJI 131 / (IJI)= I 1[tanh j — J + Sech2 j JI [5.7]\81J1 / \kT/ kT \kT /Assuming Xwder = 1/3XII + 2/3, the best fit was generated with 3 = -38 cm1, effective g =2.61, P = 0.0054, and F = 0.0368. The agreement between experiment and theory for this IsihgS’ = 1/2 case is illustrated in Figure 5.6 where the solid line is calculated from theory. Theagreement between experiment and theory for the other two models is visually very similar tothat shown in Figure 5.6, although in both cases the agreement is slightly poorer, as is indicatedby the higher F values. In all three cases, as the temperature is lowered the experimentalsusceptibilities rise more steeply to a higher maximum value and then decrease more steeply135when compared to the calculated susceptibilities.The analysis of the magnetic susceptibility data clearly indicates that in the lattice of12[SbF1] contiguous ions are relatively strongly antiferromagnetically coupled, althoughit does not provide a clear answer to the question of whether or not the thermally occupiedground state at low temperatures is a pure 23Rg state. Measurements of magnetic susceptibilities at low temperatures on suitably oriented single crystals to obtain values (47) wouldbe informative, but would require the synthesis of relatively large crystals of the material.It is important to note that the antiferromagnetic coupling observed here forI2[SbF11Jis distinctly different from the dimerization process suggested for‘2(1v) in HSO3F(2), just asthe solid-state structure ofI2[SbF11] differs from the structures ofI42[AsF6] andI42[(SbF6) b3F14J(15) where square planar, diamagnetic 142+ cations are found.5.4 ConclusionMagnetic susceptibility measurements to 4.2 K are reported for O2[AsF6j,Br2[Sb3F16], andI2[SbF11j. The data are interpreted utilizing previous results fromphotoelectron spectroscopy of the gaseous cations, known crystal structures, magnetic studies onthe superoxide ion and the ozonide ion, and in the case of02+[AsF6],previous ESR studies.The magnetic properties of the three materials are quite different. Br2[Sb3F16]obeysCurie-Weiss law between 80 and 4 K: Cm = 0.49 ± 0.01 cm3 mo11 K and e = -0.74 ± 0.01 K(with TIP = 120 x 10-6 cm3 mol1). The magnetic moment decreases slightly from 2.04 B atroom temperature to 1.93 B at 4 K. I2[SbF11] exhibits relatively strong antiferromagneticcoupling with a maximum in X observed at 54 K. the magnetic moment (corrected for a TIPcontribution of 68 x 10 cm3 mo11) decreases from 1.92 B at 124 K to 0.41 B at 4 K.136Experimental susceptibilities for this compound over the range 300-4 K have been compared tovalues calculated using three different theoretical models for extended chains of antiferromagnetically coupled paramagnetic compounds.The major difference in magnetic behavior between Br2+ and 12+ is due to structuraldifference betweenBr2[Sb3F16]andI2[SbF1J. Magnetic exchange through contiguous ‘2ions is suggested by the crystal structure ofI2[SbF11J. The shortest FI non-bonding contactis 4.29 A, comparable to the sum of the van der Waals radii of 3.96 A. In Br2[Sb3F16] theshortest Br”Br contact is 6.445 A, about 2.8 A longer than the van der Waals distance, anddirect magnetic exchange becomes improbable as discussed above.O2[AsF6] exhibits Curie-Weiss behavior over the range 60-2 K (Cm = 0.34 ± 0.01 cm3mo11 K, 8 = -1.90 ± 0.01 K). The magnetic moment, uncorrected for TIP, varies from 1.63 Bat80Kto1•7B at2K.Finally, in theO2[AsF6],there appears to be weak antiferromagnetic coupling that mayinvolve either super-exchange through intervening AsF6 anions (the smallest anion of the threeencountered in this study) or even direct weak O0 interaction.References1.a) N. Bartlett and D.H. Lohmann, Proc. Chem. Soc., 115 (1962).b) N. Bartlett and D.H. Lohmann, 3. Chem. Soc., 5253 (1962).2. R.J. Gillespie and J.B. Milne, Inorg. Chem., , 1577 (1966).3.a) R.J. Gillespie and M.J. Morton, Chem. Comm., 1565 (1968).b) R.J. Gillespie and M.J. 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Landolt-Börnstein, Numerical data and functional relations in science and technology,Vol. 2, Magnetic properties of coordination and organometaflic transition metal compounds, Springer-Verlag, Berlin, 1966.140CHAPTER 6MAGNETIC EXCHANGE IN M(II) SULFONATES,M(ll) = Ni(I1), Pd(ll) AND Ag(ll)6.1 IntroductionThe sulfonates described in this Chapter include the metal(II) fluorosulfates Ni(SO3F)2,Pd(SO3F)2,Ag(SO3F)2and “Pd(SO3F)”,more appropriately formulated as the mixed valencycompound Pd(II)[Pd(IV)(SOF6],and the metal(ll) thfluoromethylsulfates Ni(SO3CF)2,Pd(SO3CF)2,and Ag(SO3CF)2.These compounds can also be considered as transition metalderivatives of the strong sulfonic acids I-{SO3Fand HSO3CF respectively. The anions SO3Fand S03CF have the potential to coordinate to the metal ions as bidentate or tridentatebridging ligands (1-5), and consequently polymeric, layered materials with paramagnetic metalcenters are formed. As pointed out in Chapter 3, only a limited number of paramagnetic binaryfluoro compounds of divalent nickel, palladium and silver has been synthesized so far, andtherefore it is of interest to study the magnetic properties of the above sulfonates which are rarebinary fluoro derivatives of the respective divalent metals.Several transition metal fluorosulfate and trifluoromethylsulfate compounds have beenstudied previously for their magnetic properties in the higher temperature range, usually down to—80 K only (1-4,6-15). Interestingly, it appears that among the fluorosulfates, only Jr(SO3F)4and its derivativeCs2[Ir(SO3F)](11) are magnetically concentrated, and in the trifluoromethylsulfates magnetic exchange is detected only in Fe(SO3CF)(14) and Ag(SO3CF)2(4). Theexchange coupling observed in all four of these derivatives is reported as antiferromagnetic.This is significant and not totally unexpected, since the majority of the magneticallyconcentrated transition metal fluoro compounds exhibit antiferromagnetism rather than ferro- or141ferrimagnetism (16).Ferromagnetic ordering is hence a rare phenomenon in ionic solids, and is largelyconfined to small groups of transition (d-block) and lanthanide metal -oxides, -chalcogenidesand -halides with distinct structural features that permit one, two or three dimensional exchangevia monoatomic anions (17, 18). However, in contrast the four metal(II) fluorosulfatecompounds studied here contain the polyatomic SO3F anion and show significant ferromagneticexchange at low temperatures. Previous magnetic measurements down to —80 K on the binaryfluorosulfates Pd(SO3F)2(2), Ag(SO3F)(3) and “Pd(SO3F)”(2), showed that the compoundswere relatively magnetically unconcentrated in that temperature range, and their susceptibilitiesfollowed the Curie-Weiss law closely with small positive Weiss constants.The three metal(lI) trifluoromethylsulfate compounds Ni(SO3CF)2,Pd(SO3CF)2andAg(SO3CF)2investigated here for their magnetic behavior have all been synthesizedpreviously (4, 5, 19) although no variable temperature susceptibility studies have been reportedfor the Ni(SO3CF)2and Pd(S03CF)2compounds until now. A previous high temperaturestudy on the Ag(SO3CF)2compound indicated that the Ag(ll) ions in the sample were coupledantiferromagnetically (4). Therefore, the two analogous nickel and palladium derivatives wereinvestigated in this work to determine whether these compounds are also magneticallyconcentrated with antiparallel spins. In addition, magnetic measurements were run on theAg(SO3CF)2compound at lower temperatures to verify the previously reported higher temperature susceptibility data.It is significant to note here that the metal(ll) fluorosulfates and the irifluoromethylsulfate analogs described in this Chapter are assumed to have the common CdC12-type structure,which is also seen in the metal(II) hexafluoroantimonates discussed in Chapter 3. Layered structures of the type seen in Sn(SO3F)2 (20a) and Ca(SO3H)2(20b) have been previously142proposed for a number of divalent metal sulfonates (6, 10, 13, 15), on the basis of magneticproperties and vibrational spectra. It was proposed that these compounds adopt a polymerictwo-dimensional structure, where each metal site is surrounded by an octahedral arrangement(tetragonally distorted in the silver derivatives) of oxygen ligands, as illustrated for Pd(SO3F)2in Figure 6.1.Figure 6.1: Proposed Structure of Pd(SO3F)20 0Metal S 0 F1436.2 ExperimentalThe synthetic procedures for the preparation of metal(ll) fluorosulfates Ni(SO3F)2(13),Pd(SO3F) (2), Ag(SO3F)2 (3), “Pd(SO3F)t’(2), and the metal(ll) trifluoromethylsulfatesNi(SO3CF)2(19), Pd(SO3CF2(5) and Ag(SO3CF)2(4) have been described in detail previously. These methods were followed in the present study as well. Attempts were made tosynthesize “Pd(SO3CF)”,the corresponding trifluoromethylsulfate derivative of “Pd(SO3F)t’,but in all instances the solvolysis of “Pd(SO3F)”in excess HSO3CF (5) led to the binaryPd(SO3CF)2compound only.All the reactions were monitored by weight, and the purity of the products wasdetermined by elemental analysis and IR spectroscopy. Magnetic data were corrected forTemperature Independent Paramagnetism (TIP) using the following reported lODq values[cm1]: Ni(SO3F)2,7340 (1); Pd(SO3F)2 11770 (1); Ag(SO3F)216600 (3) and Ni(SO3CF)27350 (19).6.3 Results and DiscussionThe magnetic data obtained on the M(II) sulfonates with M=Ni, Pd and Ag, clearlyindicate two distinct types of magnetic exchange present in the two groups of compounds. Allthe M(II) fluorosulfates studied here exhibit strong ferromagnetic exchange at lower temperatures, whereas the M(II) trifluoromethylsulfates show antiferromagnetism with varying degreesof magnetic concentration over a wider temperature range. Therefore, the discussion of themagnetic results can be conveniently divided into two parts, ferromagnetism and antiferromagnetism of the respective sulfonate derivatives. Ferromagnetism will be discussed first and ingreater detail, since this phenomenon is rare and unusual in transition metal fluoro compounds.1446.3.1 Ferromagnetism of M(ll) fluorosulfates Ni(SO3F)2, Pd(SO3F)2,Pd(II)[Pd(IV)(SOF]and Ag(SO3F)2Previous magnetic susceptibility measurements on the three palladium and silverfluorosulfates investigated here indicate that the compounds are relatively magnetically dilutedown to —80 K (2,3). No detailed magnetic study exists in the case of Ni(SO3F)2. Therefore,measurements on Pd(SO3F)2,Ag(SO3F)2and “Pd(SO3F)”are extended down to —4 K (—2 Kfor Pd(SO3F)2)and Ni(SO3F)2is studied in the temperature range of —291 to 2 K. The pertinentmagnetic data obtained with the vibrating sample magnetometer in the lower temperature rangeare presented in Tables 6.1, 6.2, 6.3 6.4, and the Gouy measurements of Ni(SO3F)2from —291 to79 K are given in Table 6.5. A summary of the relevant magnetic parameters on all four fluorosulfates is listed in Table 6.6 (see Appendices B-i to B-3 for additional magnetic data).For Pd(SO3F)2,“Pd(SO3F)”and Ag(SO3F)2,previous higher temperature measurements were presented as plots of 1/XM vs. T, which were linear, and had positive Weissconstants (Table 6.6), indicative of Curie-Weiss behavior. The magnetic moments calculatedfor the three compounds (1-3) were in good agreement with expected values for approximatelyoctahedrally coordinated Pd(II)(d8)and Ag(II)(d9)species. A similar situation is observed inthe case of Ni(SO3F)2,where the inverse susceptibility vs. temperature graph in the highertemperature region also gives a straight line plot (Figure 6.2). However, the Weiss constantobtained here 0.41 K is relatively small and hence Ni(SO3F)2appears to be magnetically dilutedown to —80 K. The 1eff value of about 3.27 B (Table 6.5) in this temperature range is notunexpected for Ni(SO3F)2,with the Ni(II) ions located in octahedral ligand sites (13,21; see alsoChapter 3).145Table 6.1: Low Temperature Magnetic Data of Ni(SO3F)2Temperature (K) XMCOff x 106 Peff (P.B)a(cm3mol1)81.72 15520 3.1677.72 16370 3.1674.02 17250 3.1769.72 18370 3.1865.19 19740 3.1859.86 21590 3.1954.40 23880 3.2047.60 27390 3.2140.40 32800 3.2431.25 43800 3.3026.23 54310 3.3720.65 71640 3.4315.98 100200 3.5711.17 170500 3.907.60 329600 4.476.30 502700 5.035.08 670900 5.224.24 766000 5.104.12 775700 5.053.37 839100 4.752.60 880500 4.282.30 900000 4.07a= 2.828 [(xMcoff - TIP)T]112; TIP = 8N2/10Dq = 285 x 10 cm3 mo11Magnetic field = 9225 G.146Table 6.2: Low Temperature Magnetic Data of Pd(SO3F)2., COlT X 106 Peff (IB)aTemperature (K)(cm3mol1)82.06 19010 3.5279.89 19560 3.5278.33 20060 3.5376.60 20610 3.5474.47 21250 3.5472.55 21950 3.5570.28 22640 3.5567.95 23520 3.5665.77 24640 3.5963.40 25740 3.6060.73 27060 3.6158.00 28620 3.6355.00 30600 3.6651.40 33020 3.6747.90 36130 3.7144.50 39870 3.7640.60 45170 3.8231.23 66750 4.0821.35 127300 4.6616.50 211800 5.2911.25 574900 7.198.11 1015000 8.115.99 1162000 7.464.32 1215000 6.483.88 1236000 6.193.30 1248000 5.742.70 1258000 5.211.74 1271000 4.20a= 2.828 .[(xMCOIT - TIP)T11/2;TIP = 8Nj32/lODq = 177 x 10 cm3 mo11Magnetic field = 7501 G.147Table 6.3: Low Temperature Magnetic Data of Pd(H)[Pd(W)(SO3F6]Temperature (K) XMCO X 106 eff (IIB)a(cm3moP1)82.28 21220 3.7478.73 22130 3.7374.64 23460 3.7470.34 24860 3.7465.88 26750 3.7560.60 29130 3.7655.00 32420 3.7848.00 37180 3.7844.20 40610 3.7940.60 44880 3.8231.65 60000 3.9027.23 73720 4.0121.75 98300 4.1416.34 155000 4.5011.17 355300 5.637.94 581500 6.085.98 663400 5.635.08 681600 5.26a Peff = 2.828 [XMCOIT X TI1/2Magnetic field = 7501 G.148Table 6.4: Low Temperature Magnetic Data of Ag(SO3F)2Temperature (K) XM X 106 eff (JB)a(cm3mol1)82.06 7950 2.2778.28 8450 2.2974.53 9070 2.3270.34 9840 2.3565.82 10840 2.3860.50 12300 2.4355.00 14270 2.5047.95 17560 2.5944.35 20080 2.6640.55 23560 2.7630.85 40400 3.1526.58 58350 3.5221.23 110400 4.3316.34 277000 6.0210.53 605800 7.147.40 688000 6.385.08 730300 5.454.54 735300 5.17a Peff = 2.828 [(XMCOnI. - TIP)T1112; TIP = 4N132/lODq =63 x 10 cm3 mo11Magnetic field = 7501 G.149Table 6.5: Magnetic Data of Ni(SO3F)2for the Temperature Range 291 to 79 KTemperature (K) XMCOff X 106 eff (B)a(cm3mo11)291.3 4840 3.26271.0 5240 3.28253.1 5580 3.27235.7 5970 3.27219.0 6420 3.28201.7 6940 3.28177.6 7860 3.28152.0 9120 3.28127.5 10920 3.29103.0 13250 3.2787.0 15690 3.2779.0 17100 3.26a 1’eff = 2.828 [(XM’°’ - TIP)T]112; TIP = 8Nj32/lODq = 285 x 10 cm3 mo11Magnetic field = 8000 G.150Table 6.6: Magnetic Parameters of Ni(SO3F)2,Pd(SO3F)2,Pd(ll)[Pd(IV)(SO3F6]and Ag(SO3F)2Compound Temperature Weiss Const. ie j.Lff (max)b Tm (ff max)1’ ReferenceRange (K) 0 (K) (B) (RB) (K)Ni(SO3F)2 291—79 0.41±2 3.27 This work81.7—2.3 5.27 4.78Pd(SO3F)2 299—103 13±4 3.34 (1)82.1—1.7 8.11 8.11 This work“Pd(SO3F)” 334—107 10±2 3.45 (1)82.3—5.1 6.08 7.94 This workAg(SO3F)2 301—80 20±2 1.92 (3)82.1—4.5 7.14 10.53 This worka Values for 290 K.b Values for magnetic field = 7501 G.151Figure 6.2:-J0>-F—-JFaLU(-)U)(1)(-)FLUz0Inverse Susceptibility vs. Temperature of Ni(SO3F)2r€) 250-()from Curie—Weiss Low (29V79K)K“ 200-150-100-50-0Cm = 1 .34 cm3 moEt Ke =0.41.0 50I I100 150 200 250 300TEMPERATURE,K152The low temperature plots of 1/XM vs. T for Pd(SO3F)2,“Pd(SO3F)1’and Ag(SO3F)2areshown in Figure 6.3. Extrapolation of the higher temperature linear portion ((Pd(SO3F)2and“Pd(SO3F)”> 11 K, Ag(SO3F)2>14 K) of these plots produces intercepts on the temperatureaxis in excellent agreement with the values reported earlier (Table 6.6). In the lowertemperature region all four compounds show a temperature independent 1/XM (and therefore XM)behavior as the temperature is lowered. This change in the temperature dependence of themagnetic susceptibility at low temperature is illustrated for Pd(SO3F)2and ‘Pd(SO3F)1’inFigures 6.4 and 6.5, where the field dependence of the susceptibility in this region is also shownfor the two compounds.The approximate maximum susceptibilities expected for these compounds can becalculated with the following (spin only) expression given by Carlin (22):Msat = NgpS [6.1]where Msat = saturation magnetic moment (M/H = Xt)N = Avogadro’s numberg Lande splitting factor= Bohr magnetonS = Spin system, S=1 (Pd(II)) and S=1/2 (Ag(II))The maximum or saturation magnetization situation corresponds to the alignment of allthe magnetic spins parallel to the external field (H), where the magnetization becomes independent of field and temperature. The saturation susceptibility values calculated using equation [6.11are compared with the observed maximum susceptibilities for Ni(SO3F)2, Pd(SO3F)2,“Pd(SO3F)”and Ag(SO3F)2in Table 6.7.153Figure 6.3: Inverse Susceptibility vs. Temperature of Pd(SO3F)2,Pd(ll)[Pd(IV)(SOF]and Ag(SO3F)2140-I120-o Pd(SO3F)20,• Pd(II)[Pd(V)(SO6]100-— . Ag(SO3F)2>-80-60- I(/) ID •LI) c .(_) 40-•0LJz .2O-t0—0 20 40 60 80 100TEMPERATURE,K154Figure 6.4:140-Magnetic Susceptibility vs. Temperature for Pd(SO3F)2at 7501 and 9625 G120- SS1008060c%J0x0C-)>--JcLC.)DLI)C-)zC)0 AT 7501G• AT 9625G40-2000•_0 oc• ooo20 40 60 80 100I I I ITEMPERATURE,K155C><00>-I--JcLi-JC)V.)V.)0ILJzC,Figure 6.5: Magnetic Susceptibility vs. Temperature for Pd(II)[Pd(IV)(SO3F6]at7501 and %25 G799998-399999-200000-0o AT 7501G• AT 9625G0I I I20 40 60•TEMPERATURE,K80 100156Table 6.7: Experimental and Calculated Saturation Magnetic Susceptibilities ofNi(SO3F)2,Pd(SO3F)2,Pd(II)[Pd(W)(SO3F6]and Ag(SO3F)2% saturation =Compound XM sat. calculateda XM’ max. observeda Temp. (XM’ max) XM max. x 100(cm3mo!4) (cm3 mo!) (K) XM sat.Ni(SO3F)2 1.488 1.041 2.69 70Pd(SO3F)2 1.488 1.271 1.74 85“Pd(SO3F)” 1.488 0.682 5.08 46Ag(SO3F)2 0.744 0.735 4.54 99a Susceptibility data for magnetic field = 7501 0.157It appears from the data in Table 6.7 that the magnetic behavior observed at lowertemperature in Ni(SO3F)2,Pd(SO3F)2and Ag(SO3F)2may be largely a result of saturationmagnetization. As a consequence, the magnetic moments of these compounds are temperaturedependent and pacs through maxima at -5, —8, and —10.5 K respectively (Table 6.6). This isillustrated in the magnetic moment vs. temperature plot for Pd(SO3F)2and Ag(SO3F)2in Figure6.6. Spin saturation in the mixed valent “Pd(SO3F)’ may be achieved at higher magneticfields, since closer approach to saturation magnetization would be expected at stronger appliedfields. Even at a field of 7501 G, the magnetic moments of this compound shows temperaturedependent behavior and has a maximum at —8 K.In the Ni(SO3F)2,Pd(SO3F)2and “Pd(SO3F)”compounds, the paramagnetic Ni(ll) andPd(II) ions have been shown to be in octahedral environments with 3A2g ground states (1,2,21).Although there is no orbital contribution to the susceptibility associated with this state, to firstorder, zero-field splitting via second order spin orbit coupling could lift the triplet spindegeneracy which can significantly affect the magnetic properties of such systems, particularlyat low temperatures.The average susceptibility <X> of powder samples (X>=(X11+2X±)/3) in the presence ofzero-field splitting for S=1 spin systems is obtained from the expression (22):= 2Ngt (2/x —2 exp(-x))/(x + exp(-x)) [6.2]3kT 1 + 2 exp(-x)where x = DIkT, D = zero-field splitting parameter, k = Boltzmann’s constant, and N, g and Bas defined for equation [6.1].158Figure 6.6: Magnetic Moment vs. Temperature of Pd(SO3F)2and Ag(SO3F)2I.zUaC)UzI I40 60TEMPERATURE,Ko Pd(SO3F)2• Ag(S03F)29-8-7-6-5-4.2C0 20180 100159In general, the value of D is only a few wavenumbers, and with kT —205 cm1 at roomtemperature, D/kT <c 1. However, at lower temperatures D/kT becomes significant, therebyaffecting the measured susceptibilities of these samples. The sign of D could be either positiveor negative, and in the case of nickel, both signs have been observed (22).Attempts were made to fit the magnetic susceptibility data to equation [6.2]. However,only very poor fits were obtained, which indicates clearly that this effect cannot explain themagnetic behavior exhibited by the nickel and palladium complexes. Moreover, the magneticbehavior of Ag(SO3F)2cannot be rationalized by this effect, since in Ag(II) ions with 2Bigground states, the possibility of zero-field splitting does not exist.The magnetic properties observed in these four fluorosulfate compounds bear a strongresemblance to those reported for the binary chlorides FeCI2, CoCl2 and NiC12 by Starr et al.(23). Neutron-diffraction studies on the iron and cobalt compounds have revealed ferromagneticcoupling between the metal centers within each layer (intralayer exchange), and weak antiferromagnetic coupling between layers (interlayer exchange) (24). This magnetic behavior, termedmetamagnetism, has been extensively reviewed for other compounds as well (25). Interestingly,the binary chlorides mentioned above have the typical CdCl2-type structure, with each layer ofthe metal atoms separated by two layers of chlorine atoms from the next metal atom layer. Eachmetal atom layer forms a two-dimensional hexagonal network in which every metal atom hassix near neighbours (26).Furthermore, in a number of layer type fluorides containing Jahn-Teller ions, theintralayer ferromagnetic couplings are found to be much stronger than the interlayer antiferromagnetic couplings, and as a result ferromagnetism is observed in these compounds (17).Similar interactions may be present in “the Jahn-Teller compound” Ag(SO3F)2studied in thiswork as well.160Similar crystal and magnetic structures are possible for the M(II) fluorosulfatesexamined in this work. Indeed, layer structures based on the CdC12 prototype have also beenproposed for the compounds discussed here, as mentioned in the introductory section of thischapter (see also Figure 6.1). The apparent lack of solubility of these metal fluorosulfates in asuitable solvent such as fluorosulfuric acid, HSO3F, has so far precluded single crystal X-raydiffraction studies as well as magnetic measurements on oriented crystals leading to studies onparamagnetic anisotropy.It is significant to note that octahedral Pd(II) ions with a 3A2g ground state is found onlyin Pd(SbF6)2(Chapter 3), PdF2 (27), Pd(503F)2Pd(SO3CF)2,and in some of their cationicand anionic derivatives, just as AgF2 (28), Ag(SO3F)2and Ag(503CF)2have remained theonly simple binary compounds of Ag(II) with a d9 configuration. However, the fluorides AgF2(28), PdF2 (27), and NiF2 (30) are essentially antiferromagnetic compounds, and compare moreappropriately with the trifluoromethylsulfate derivatives discussed in the next section. In PdF2,NiF2,and AgF2,weak ferromagnetism is observed due to a canting of the spins (27,28,30).The ternary Pd(II)[Pd(IV)F61is reported to have a significant ferromagnetic componentat low temperatures, although the complex is weakly ferromagnetic over a wide temperaturerange (17, 18, 29). In contrast, the structurally similar Pd(II)[Pd(IV)(SO3F6]is found here as astrongly ferromagnetically coupled compound. The fluorosulfate ligand seems to bond stronglyto the Pd(IV) center and weakly to Pd(ll), in an “anisobidentate” bonding mode (1,2). A largenumber of M(II) M’(IV)F6 type fluorides with both M and M’ transition metals such as Pd, Ptand Ni, have been studied for their ferromagnetic contribution (17,18) as already noted above inthe case of the Pd2F6compound. Ferromagnetism in these compounds may be associated withcationic ordering, which is observed in Pd2F6 from neutron diffraction measurements (29).Magnetic ordering at low temperatures is explained in these ternary species by a mechanismwhere the spins of the eg2 electrons of the divalent metals (t2g6eg2) are ferromagnetically161coupled via a superexchange interaction involving the 2p fluorine orbitals and the empty egorbitals of the tetravalent cations (17,18).Therefore, it has been shown that when cationic ordering in M(II) and empty eg orbitalson the transition metal M([V) are present, ferromagnetism can occur in these bimetalliccompounds. This may be applicable to the Pd(II)[Pd(IV)(SO3F6]complex as well, although themuch larger SO3F- anion may significantly affect the extent of ferromagnetic interaction.Interestingly, when the tetravalent cation is replaced by a non-transition metal ion such asSn(IV) or Ge(IV), magnetic ordering is not observed even at 4.2 K (17). This observationappears to be valid for the ternary bimetallic fluorosulfates as well. A number of previouslysynthesized fluorosulfate derivatives with three different divalent metals where the tetravalentcation is Sn(IV) were studied for their low temperature magnetic properties in this work.The compounds chosen were Ni(ll)[Sn(IV)(SO3F6](31), Cu(II)[Sn(IV)(SOF6](31) andAg(lJ)[Sn(IV)(SO3F61(3). The magnetic measurements obtained for these three samples aregiven in Appendices B-4, B-5, and B-6. It is clear from these data that the compounds are relatively magnetically dilute to ‘—4 K.Furthermore, previous high temperature magnetic measurements onPd(II)[Sn(IV)(SO3F6J(2) and Ag(II)[Sn(IV)(SO3F6j(3) indicated Curie-Weiss behavior forthe compounds down to liquid nitrogen temperature. However, stronger magnetic exchange interactions may be present at lower temperatures in Ag(II)[Pt(1V)(SO3F6j(3) andPd(II)[Pt(IV)(SO3F & (2), where the tetravalent cation is a transition metal ion, i.e. Pt(IV), although no magnetic exchange is observed in the two samples down to —80 K (3,2).Even though the above described superexchange mechanism may be valid for thePd(II)[Pd(IV)(SO3F6]complex, for the binary Ni(SO3F)2,Pd(SO3F)2,and Ag(SO3F)2compounds detailed magneto-structural relationships cannot be made, especially in the absence of162structural evidence from single crystal X-ray studies. This is also true in the case of thecorresponding thfluoromethylsulfate derivatives discussed below.Crystal growth was, however, attempted for Pd(SO3F)2,“Pd(SO3F)’and Ag(SO3F)2,utilizing the method employed to obtain single crystals of Au(SO3F),the structure of whichwas reported recently by our group (32). Unfortunately, the highly polymeric compoundsformed only microcrystalline materials, unsuitable species for single crystal measurements.In the following section, antiferromagnetic behavior in the divalent nickel, palladium andsilver thfluoromethylsulfates will be discussed in some detail.6.3.2 Antiferromagnetism of M(II) trifluoromethylsulfates Ni(SO3CF)2,Pd(SO3CF)2and Ag(SO3CF)2It was mentioned in the introduction that in previous magnetic susceptibility studies to—80 K, the only four sulfonates which had detectable magnetic exchange all showed antiferromagnetism, which is observed more frequently than ferromagnetism in magneticallyconcentrated transition metal compounds (16,33).In this study, the magnetic measurements on Ag(SO3CF)2were extended down to —4 Kto complete the earlier Gouy work, and also to detect unusual magnetic properties, if any, atlower temperatures. The results of the low temperature study are given in Table 6.8, togetherwith the previous Gouy data obtained for the compound. Similarly, the Pd(SO3CF)2andNi(SO3CF)2complexes are investigated here for their possible antiferromagnetic behavior, andpertinent low temperature data for the two compounds are shown in Tables 6.9 and 6.10 respectively. The nickel compound is also measured in the higher temperature range of —292 to 80 Kby the Gouy method, and the results of this work are presented in Table 6.11.163Table 6.8: Magnetic Data of Ag(SO3CF)2for the Temperature Range 304 to 4 K‘Temperature (K) XMCOff x 106 (ii(cm3mo11)304 1100 1.64278 1150 1.60254 1200 1.56226 1270 1.52204 1320 1.47179 1380 1.41154 1420 1.32128 1430 1.21108 1390 1.1082.06 650 0.6678.28 630 0.6370.34 620 0.5965.82 610 0.5760.38 570 0.5347.80 550 0.4640.40 540 0.4231.85 540 0.3726.35 520 0.3321.40 520 0.3016.55 510 0.2611.20 510 0.218.04 510 0.185.34 510 0.154.39 510 0.13a First nine data points from Ref. 4.b Not corrected for TIP; I1eff 2.828 [xMCOt X 11h12164Table 6.9: Low Temperature Magnetic Data of Pd(SO3CF)2COlT x 106 eff (B)aTemperature (K)(cm3mo[1)123.2 6950 2.62118.0 7220 2.61112.8 7460 2.59108.2 7730 2.59103.0 8030 2.5797.97 8330 2.5593.46 8690 2.5588.31 9020 2.5284.81 9350 2.5281.95 9670 2.5278.33 9970 2.5074.47 10180 2.4670.23 10540 2.4368.46 10630 2.4165.59 10990 2.4060.40 11530 2.3654.45 12190 2.3051.40 12550 2.2747.92 13030 2.2444.20 13510 V 2.1940.32 14140 2.1431.60 15700 1.9920.88 17970 1.7316.00 19020 1.5610.75 20220 1.327.52 21060 1.135.78 21330 0.995.62 21630 0.994.32 21720 0.873.70 21330 0.792.99 21270 0.712.40 21270 0.642.10 21240 0.60a Not corrected for TIP; 11eff 2.828 [(XMCOff X T]1”2165Table 6.10: Low Temperature Magnetic Data of Ni(SO3CF)2Temperature (K) XMCOff x 106 Ieff (B)a(cm3mol1)81.78 16620 3.2777.72 17360 3.2674.19 18200 3.2669.72 19240 3.2565.19 20570 3.2560.15 22160 3.2454.00 24290 3.2247.60 27270 3.2140.10 31970 3.1930.80 41390 3.1825.93 48220 3.1520.70 58650 3.1115.90 74230 3.0710.42 105700 2.967.16 140000 2.835.92 159800 2.754.85 181500 2.654.78 182100 2.643.96 200300 2.523.29 213900 2.373.11 220000 2.342.79 230400 2.272.60 234600 2.212.50 236200 2.17aeff = 2.828 [(xMcoff - TIP)T11/2;TIP = 8N32/10Dq = 284 x 10 cm3 mo11166Table 6.11: Magnetic Data of Ni(SO3CF)2for the Temperature Range 292 to 80 KTemperature (K) XMCOff x 106 neff (B)a(cm3mo11)291.8 5270 3.41286.2 5390 3.42269.3 5700 3.42251.7 6050 3.41234.5 6450 3.40218.0 6890 3.39200.3 7380 3.37175.7 8310 3.36150.0 9540 3.33125.5 11320 3.33103.0 13510 3.3086.5 15740 3.2779.6 16890 3.25a 1eff = 2.828 [(xMcoff - TIP)T]112; TIP = 8N32/10Dq = 284 x 10 cm3 mo11167The previous magnetic report on Ag(SO3CF)2where antiferromagnetic behavior wasseen with Xm at —138 K (4) is further confirmed by the present low temperature study. Themagnetic moments decrease continuously with decreasing temperature, and the susceptibility also folio ‘s a similar trend, falling rapidly in value below the Nel temperature (Table6.8). The very small magnetic moments observed down to —4 K indicate that the compound hasno ferromagnetic component present in the low temperature region. This behavior ofAg(SO3CF)2is in contrast to the magnetic behavior of AgF2, in which ferromagnetism isdetected below 163 K (28).Therefore, it seems that structural differences in AgF2 and Ag(SO3CF)2play significantroles in determining the extent of antiferromagnetic coupling, although the exact exchangemechanism remains still unclear in the Ag(SO3CF)2compound. It has been shown that inoctahedrally coordinated transition metal d9 fluorides, the Jahn-Teller effect leads to twocrystallographic distortions, termed ferro and antiferrodistortive ordering, with the former favoring antiferromagnetism and the latter ferromagnetism (34). In AgF2, the ferromagnetic units arecoupled antiparallel, which give a bulk 3D antiferromagnetism to the compound, although spincanting produces a small ferromagnetic component below 163K (28). However, in layer typefluoride structures with Jahn-Teller ions, the intralayer ferromagnetic couplings are muchstronger than the interlayer antiferromagnetic couplings, as postulated in the case of Ag(SO3F)2discussed earlier, leading to ferromagnetism (17). But in contrast, the magnetic behaviorobserved in Ag(SO3CF)2may arise from strong interlayer antiparallel coupling of the spinswith weak intralayer exchange, resulting in a bulk 3D antiferromagnetism for the compound.The magnetic data obtained for Pd(SO3CF)2also clearly indicate antiferromagneticbehavior, where the magnetic moments calculated in the temperature range —123 to 2K showtypical temperature dependent low values (Table 6.9). The moments decrease with decreasingtemperature, and a sharp decline becomes apparent below —40K, as seen in the magnetic168moment vs. temperature plot for the compound illustrated in Figure 6.7. From a previouslyunpublished study in our group, the room temperature magnetic moment for Pd(SO3CF)2wasfound as 2.90 B (35). This value seems to be reasonable when compared with the l.Leff of 2.62B obtained at 123 K in this study (Table 6.9), and it also confirms the continuous decreasingtrend of the magnetic moments with decreasing temperatures. The higher temperature eff valueis not unexpected for an octahedrally coordinated Pd(II), where the moments are lowered byantiferromagnetic exchange.The magnetic susceptibility vs. temperature plot of Pd(SO3CF)2,shown in Figure 6.8,has a Xm at approximately 4K. This is conclusive evidence, as in Ag(SO3CF)2,that the spinsin the palladium compound are coupled antiferromagnetically. The appearance of Xm at a verylow temperature, in contrast to the Xm observed at 138 K in Ag(SO3CF)2(4), indicates that inthe palladium compound the antiferromagnetic interaction is much weaker than in thecorresponding silver species. It is not uncommon however, to observe stronger spin couplingsin ad9-Jahn-Teller system than in ad8-octahedral system.Significant differences are also noted between the magnetic behavior of Pd(SO3CF)2and its fluoride derivative PdF2. The difluoride, although antiferromagnetic with a Neltemperature of --217K, shows a ferromagnetic magnetization component (“weak ferromagnetism”) below this temperature (27). Consequently, the magnetic moment of 1.84 Bfound at room temperature has a much larger value at lower temperatures. This magneticbehavior of PdF2, as in the case of AgF2 (28), is accounted for by Moriya’s theory of single-ionmagnetocrystalline anisotropy (30), where the preferred direction of magnetization is differentfor the nonequivalent magnetic ions, leading to a canting of the spins.This is in contrast to the magnetic properties of Pd(SO3CF)2,in which a continuousdecreasing trend of the magnetic moments with decreasing temperatures is observed (Figure169I—z0Qwz0Figure 6.7: Magnetic Moment vs. Temperature of Pd(SO3CF)232.521.50.50 20 40 60TEMPERATURE,K80 120 140170(0x0:2N,2()I--Ja:iI—01JC)(nC)I—UzC):2TEMPERATURE,KFigure 6.8: Magnetic Susceptibility vs. Temperature of Pd(SO3CF)22500020000150001000050000 20 40 60 80 100 120 1401716.7), with the susceptibility also falling off below the Nel temperature of —4 K (Figure 6.8). Itappears from these observations that in Pd(SO3CF)2the dominant magnetic interaction isantiferromagnetic and unlike PdF2, weak ferromagnetism is not seen at lower temperatures inthe thfluoromethylsulfate compound.The magnetic results of Ni(SO3CF)2,illustrated in Tables 6.10 and 6.11, show temperature dependent magnetic moments that decrease with the gradual lowering of the temperature,indicative of antiferromagnetic interaction among the Ni(ll) centers. Excellent agreement isnoted between the Gouy and the vibrating sample magnetometer data for the overlap region.The Gouy data (Table 6.11) in the temperature range 292 to 80 K are plotted as vs. T, andthe following Weiss and Curie constants are obtained respectively: 8 = -12.56 K and Cm = 1.52cm3 mo11 K. The negative Weiss constant is characteristic of antiferromagnetism, and thisbehavior in Ni(SO3CF)2is further confirmed by the low temperature magnetic data given inTable 6.10.The of 3.41 B calculated at room temperature falls within the expected range for anoctahedrally coordinated Ni(II) species. However, curiously this value is slightly larger than themoment of 3.26 B found at the same temperature for the corresponding Ni(SO3F)2(Table 6.5),although both compounds appear to have similar electronic environments for the respectiveNi(fl) ions with near identical lODq values (1,21,19). Furthermore, the antiferromagneticNi(SO3CF)2is expected to have a lower moment at room temperature than its ferromagneticfluorosulfate derivative, analogous to the palladium and silver derivatives discussed previously.Interestingly, when the low temperature magnetic moments are plotted against temperature, the effects of magnetic coupling interactions for Ni(SO3CF)2and Ni(SO3F)2becomeobservable nearly at the same temperature, but are of opposite nature, as illustrated in Figure6.9.172Figure 6.9:Iz0()bJzMagnetic Moment vs. Temperature of Ni(SO3CF)2and Ni(SO3F)26-5-4-• Ni(SO3F)2o Ni(SO3CF3)23-220 40 60TEMPERATURE,K80 100173In contrast to Pd(SO3CF)2and Ag(SO3CF)2,the nickel derivative does not have aXmax in its susceptibility data. Therefore, the decrease of the moment values with decreasingtemperature is less pronounced in the case of Ni(SO3CF)2(Table 6.10).These observations indicate that the antiferromagnetic interaction in the nickel species isrelatively weak in comparison to that in the palladium and silver derivatives. The magneticbehavior observed in Ni(SO3CF)2differs also from the reported antiferromagnetism of thecorresponding binary fluoride NiF2, where a weak ferromagnetic moment is detected below theNe1 temperature of 73.2 K, which is attributed, as in AgF2 and PdF2 discussed previously, tospin canting (30). The theoretical basis of this phenomenon has been developed extensively byMoriya in his study of the magnetic behavior of NiF2 (30).In concluding this discussion on the magnetic exchange interactions of the M(II)sulfonates, a few comments will be made here regarding the magnetic behavior of thecorresponding copper derivatives. A previous magnetic study of Cu(SO3F)2and Cu(SO3F)2(down to 100 and 127 K respectively) indicated that the salts are essentially magnetically dilutewith moments normally observed for hexacoordinated copper(II) (15). For this work, themagnetic measurements on the Cu(SO3F)2is extended down to —4 K, and a summary of the datais given in Appendix B-7. The compound was synthesized according to the method describedby Alleyne et al. (13). The magnetic moments calculated are independent of temperature andremain close to the expected value of —2.0 B down to —4 K. Good agreement is also noted inthe overlap region between the previous high temperature neff values and the low temperaturemoments of this study. The reason for this magnetically dilute behavior of Cu(SO3F)2is notclear, and it is rather surprising to note that while Ag(SO3F)2shows strong magnetic exchangebelow —10 K, the corresponding Group 11 copper derivative is magnetically dilute down tovery low temperatures. Interestingly, the copper(II) difluoride is antiferromagnetic with a Neltemperature of 69 K, and as seen previously in AgF2,PdF2 and NiP2, spin canting produces a174weak ferromagnetic moment below the Nel temperature in CuF2 as well (37).In summary, it may be envisioned that in the layer type metal(ll) sulfonates discussed inthis Chapter, magnetic exchange may occur preferentially via one of two possible spin interactions: ferromagnetism in the fluorosulfate compounds could arise from strong intralayerparallel spin coupling, while in the corresponding trifluoromethylsulfate derivativespredominant interlayer spin coupling could lead to an antiparallel arrangement of the spins inthe lattice. Alternatively, the O-S-O bridging angle in the two types of sulfonates may favorferromagnetism and antiferromagnetism for the fluorosulfates and trifluoromethylsulfatesrespectively. Although the exchange pathway cannot be stated clearly in these compounds dueto a lack of X-ray crystal data, it is interesting to note that in the divalent sulfates FeSO4,NiSO4and CuSO4 which also have oxygen bridging extended 3D lattice structures, antiferromagneticordering is postulated to occur through the O-S-O bridges (38,39). Furthermore, neutron diffraction data obtained on FeSO4 and NiSO4 indicate magnetically ordered sheet-type structures, andthe structurally similar CrVSO4 appears to have ferromagnetically ordered sheets which stackantiferromagnetically (38). In other examples involving sulfate derivatives, the compounds arefound as linear chains, and their magnetic properties have been analyzed utilizing either theIsing or Heisenberg exchange coupling models (40).In the case of the sulfonates discussed here, however, analyzing the magnetic data ismade difficult by several factors. The choice of either the Ising or Heisenberg 2-D model isusually not appropriate for the metal(II) sulfonates. These models do not apply to a systemwhere three-dimensional interactions are also present in the lattice structure. The onedimensional models of the type used in Chapter 5 cannot be utilized for the sulfonates for thesame reason. The available 2-D Heisenberg model is not applicable in this instance, as thismodel only takes into account interactions between one paramagnetic center and only the four(but not six) nearest neighbors in a square array. In contrast, for the metal(II) sulfonates, the175proposed structure consists of each metal center being surrounded by six nearest neighbours (seeFigure 6.1). It appears that the degree and sign of magnetic exchange in these compounds is afunction of the O-S-O bridging angle, the M-O and S-O bond distances and the steric andelectronic properties of the CF3 and F groups. Unfortunately, in the absence of any X-ray singlecrystal data it is rather difficult to make detailed magneto-structural correlations for these sulfonates in order to explain the observed magnetic interactions.6.4 ConclusionThe paramagnetic divalent fluorosulfates Ni(SO3F)2,Pd(SO3F)2,Pd(ll)[Pd(IV)(SO3F6],and Ag(SO3F)2 and their corresponding trifluoromethylsulfate derivatives Ni(SO3CF)2,Pd(SO3CF)2and Ag(SO3CF)2investigated for their magnetic properties show significantmagnetic exchange, and except in Ag(SO3CF)2,the effects of magnetic exchange becomeobservable at low temperatures. Two types of magnetic interactions are seen in the respectivegroups of compounds. The fluorosulfates exhibit ferromagnetism at all temperatures, whereasthe trifluoromethylsulfates couple antiferromagnetically with the spin interactions noted over awider temperature range.The fluorosulfates Pd(SO3F)2,“Pd(SO3F)”and Ag(SO3F)2were initially described asrelatively magnetically dilute down to —80 K, and similarly, the Ni(SO3F)2compound studiedhere in the temperature range —291 to 2 K also follows the Curie-Weiss law between —291 and79 K with Cm 1.34 ± 0.01 cm3 mo[1 K and 8 = 0.41 ± 2 K. For the ferromagnetic M(II)fluorosulfates, the following field dependent maximum magnetic moments are obtained in thetemperature range —5 to 10.5 K: Ni(SO3F)2 5.22 B (5 K), PdSO3F)2 8.11 (8 K),“Pd(SO3F)”6.08 PB (8 K), and Ag(SO3F)27.14 B (10.5 K). Furthermore, the maximummagnetic susceptibility values of Ni(SO3F)2,Pd(SO3F)2and Ag(SO3F)2appear to indicate, forthe magnetic fields used, saturation magnetization where all the magnetic spins align parallel to176the external magnetic field. Although the mixed valency fluorosulfate “Pd(SO3F)”showssignificant ferromagnetism at low temperatures, the structurally similar bimetallic fluorosulfatesNi(ll)[Sn(IV)(SO3F6j,Cu(H)[Sn(IV)(SO3F6]and Ag(II)[Sn(IV)(SO3F6]are found to bemagnetically dilute down to —4 K with calculated temperature independent magnetic momentsof —3.3, —2.0, and —1.8 B respectively.In contrast to the fluorosulfates, the divalent trifluoromethylsulfate derivatives coupleantiferromagnetically, and maxima in the susceptibility vs. temperature plots are noted forPd(SO3CF)2and Ag(SO3CF)2at —4 and —138 K respectively. However, Ni(SO3CF)2doesnot show a Xm in its susceptibility plot, indicative of a weaker magnetic concentration in thecompound. The magnetic moments of the three compounds decrease continuously with decreasing temperatures, and hence no ferromagnetic contribution to the magnetic moments is detectedat lower temperatures. Therefore, the antiferromagnetic behavior observed in Ni(SO3CF)2,Pd(SO3CF)2,and Ag(SO3CF)2seems to differ from that seen in the corresponding antiferromagnetic fluorides NiF2,PdF2, and AgF2,where a ferromagnetic magnetization component dueto spin canting is detected at lower temperatures.Although the exchange pathways of the divalent sulfonates cannot be explainedadequately due to a lack of X-ray single crystal data, the common layer type structure appears toindicate a possible intralayer vs. interlayer spin interaction, leading to predominantly paralleland antiparallel spin arrangements in the respective fluorosulfate and trifluoromethylsulfatelattices. However, the magnetic behavior observed in these sulfonates may be dependent on theO-S-O bridge angle, which may result in ferro- or antiferromagnetism for the respective groupsof compounds investigated in this study.177References1. K.C. Lee and F. Aubke, Can. J. Chem., 5, 2473 (1977).2. K.C. Lee and F. Aubke, Can. J. 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The solvolysis product show temperature dependent low values, whereas thefluorination sample has unexpectedly high magnetic moments, which also decrease withdecreasing temperature.As a preparative method, there appears to be a wide synthetic potential for this solvolysisroute to the corresponding metal hexafluoro antimonates, since a large number of well characterized transition metal fluorosulfates are available as precursors.The transition metal precursors of the hexafluoro antimonates, the divalent fluorosulfatesNi(SO3F)2,Pd(SO3F)2,Ag(SO3F)2,and the ternary “Pd(SO3F)1’all exhibit ferromagneticexchange at lower temperatures. Additionally, the three binary fluorosulfate compoundsindicate saturation magnetization at very low temperatures. In contrast, the correspondingtrifluoromethylsulfates Ni(SO3CF)2,Pd(SO3CF)2 and Ag(SO3CF)2 couple antiferromagnetically, and for the last two compounds Xm are also found in their susceptibility vs. temperature plots. The antiferromagnetism observed in these compounds differ from that seen inthe corresponding binary fluorides, in that no ferromagnetic magnetization component due tospin canting is detected even at very low temperatures. Interestingly, both the divalenthexafluoro antimonates and the sulfonates studied in this work have a common layered structurewhich is based on the CdCl2prototype.Furthermore, the two post-transition metal layered compounds Sn(SO3F)2 andSn(SbF6)2,which are structurally similar to their transition metal derivatives mentioned above,form it-arene adducts with mesitylene(mes) to give the weakly bound complexes Sn(SO3F)2mesand Sn(SbF6)2mes in high yield. The reduction of the lattice energies in the layer structures ofthe parent tin compounds by the wealdy nucleophilic anions SbF6 and SO3F appear tofacilitate adduct formation, with the weaker nucleophile SbF6 been the more effective of thetwo ions, leading to the 2:1 complex with the arene. Mössbauer data of the adducts indicate182partial back-donation of the 5s electrons of tin to the antibonding it’’ orbitals of mesitylene tofurther stabilize the tin-arene bond, giving rise to synergic bond characteristics.The remaining group of non-transition metal fluoro complexes, the molecular speciesO2[AsF6],Br2[Sb316] andI2[SbF1i]’ which were investigated for their low temperaturemagnetic behavior, exhibit magnetic properties that are quite different for the three derivatives.This is reflected in the magnetic data of the respective complexes, measured down to -4K. Ofthe halogen compounds, Br2[Sb3F16J is magnetically dilute to low temperatures, whereasI2[SbF1] show relatively strong antiferromagnetic coupling with a Xm at 54K. As inBr2[Sb3F16J, the O2[AsF6] compound also exhibits Curie-Weiss behavior down to lowtemperatures, but weak antiferromagnetic exchange seems to be present in the very low end ofthe temperature region. InBr2[Sb3F16],the shortest non-bonding Br”Br distance is too largeto invoke direct orbital overlap, but in12+[SbF1]magnetic exchange can occur via contiguous12+ ions, where the non-bonding II distance is comparable to the sum of the van der Waalsradii. The low values observed forO2[AsF6],which are below the spin only magneticmoment value, result from crystal field interactions in the solid lattice that partially quench theorbital contribution to the magnetic susceptibility.183APPENDICES184APPENDIX AA-i: Standard Reduction Potentials of Selected (M/M9 Couples*Electrode Potential (V)Ni2 + 2e —> Ni -0.250Pd2 + 2e —> Pd +0.987Cu + e — Cu +0.521Cu2 + 2e — Cu +0.337Cu2 + e — Cu -i-0.153Ag + e — Ag +0.7991Ag2 + e — Ag +1.980Au + e —> Au +1.691Au3 + 3e —> Au +1.498Sn2 + 2e — Sn -0.136Sn + 2e — Sn2 +0.15Sb205+ 6H + 4e —> 2SbO + 3H20 +0.58 1Sb205+ 2W + 2e —> 2SbO4+ H20 +0.479+ 4e — 2H0(1) +1.22902 + 4W + 4e — 2H0(g) +1.185* From J.E. Huheey, “Inorganic Chemistry”, 2nd Ed., Harper and Row, New York, 1978.185A-2:FrequencyRangeofVibrationalFundamentalsforFluorosulfateGroup00-BondingFrequencyRange(cm-1)orECoordination—________ModeStretchingBandDeformationBondCOVALENTi’(S—O)v,,,.(S—O)v(S—F)IFiTRIDENTATE>.(so3)-P(-)PURELYv.,.,,(S—O)i.(S—F)61_,.,,(S03)6(SO3)Uciw’zzicriciIONIC=is(S—O)v(S—F)7,,i.(SOF)IONICV/ZZZJv,,,,(SO2)Li9fi7(5.J)DOPERTURBEDrzz’r(502F)(SOi).(s—a)-.‘COVALENTp0i,,,(SO)(SO7)Q(50)(SO2F)0I-‘CE]ODDMONODENTATE8.(SOi)?.,(s-F)Civ(S—F)7(SO2F)v..ym(S02)COVALENTw(S—O)is(S—F)6(S07)i,(S-F)r(SO2F)BIDENTATE[f//AciiirjD0,,,,(SO2)(SO2)7(so2F)14001000800II1200600400A-3: X-ray Powder Data for Ni(SbF6)2[Ni(SO3F)2+ SbF5la [Ni + F2 + SbF5] [NiF2 + SbF5]Cd-space (A), Intensity d-space (A), Intensity d-space (A), Intensity4.60 rn-s 4.61 rn-s 4.56 rn4.17 s 4.24 s 4.26 m4.03 w 4.17 rn3.71 s 3.75 s 3.68 s2.702 rn 2.744 rn-s 3.58 rn2.534 m-w 2.576 m-w 2.70 rn2.344 m-w 2.363 m 2.51 w2.273 rn-s 2.252 s 2.33 w2.224 rn 2.207 rn-w 2.22 m2.167 rn 2.125 rn-w 2.10 w1.859 rn 1.881 rn 1.86 rn1.841 m 1.819 rn1.768 w 1.746 w1.714 rn-s 1.728 s1.704 rn 1.681 m 1.70 m1.648 rn 1.646 m1.625 w 1.61 m1.553 vw 1.550 vw1.534 rn-w 1.521 rn 1.50 w1.493 m 1.491 m 1.47 w1.465 rn 1.447 m-w 1.44 w1.426 w 1.420 rn-w1.398 w 1.377 w1.352 w 1.332 ma This workb Christe et at, J. Fluorine Chem., 4, 287 (1987)C Gantar et at, 3. Chem. Soc. Dalton Trans., 2379 (1987)187A-4: The Assignments and Energies of Octahedral Ni(IT) and Pd(II) (d8) Ligand FieldSpectra, According to Lever,* are as Follows:3A2g _> 3T2g 1)1 = lODq3A2g _* 3Tig(F) = 7.5B + l5Dq - 1/2(225B + lOODq2 - 18ODqB)’a3A2g 3Tig(P) = 7.5B + l5Dq + 1/2(225B + lOODq2- 18ODqB)12and,3+u2-3i1=15B* A.B.P. Lever, J. Chem. Educ., 45,711(1968).[see also: Yu-Sheng Dou, J. Chem. Educ., 67, 134 (1990)].188A-5: Low Temperature Magnetic Data of Ni(SbF6)2Made from Ni, F2 and SbF5Temperature [K] x 106 [cm3mol1] Peff B1a81.83 17140 3.3578.06 17930 3.3574.19 18740 3.3369.72 19830 3.3365.19 21030 3.3160.15 22660 3.3055.00 24620 3.2947.90 27610 3.2540.60 32010 3.2230.80 41040 3.1826.00 47840 3.1521.00 57360 3.1015.90 73240 3.0510.30 105600 2.957.16 140500 2.846.30 153800 2.785.18 174200 2.694.40 191900 2.603.96 201700 2.533.46 207900 2.403.11 215800 2.322.89 219900 2.252.79 221800 2.22a Uncorrected for TIP189A-6: Low Temperature Magnetic Data of Ni(SbF6)2Made from NiF2 and SbF5 in HFTemperature [K] XMCOff x 106 [cm3mol4] Peff B1a81.83 12000 2.8078.06 12490 2.7974.19 13170 2.7969.72 14000 2.7965.19 14900 2.7960.15 16130 2.7955.00 17750 2.7947.90 20070 2.7740.60 23450 2.7631.23 30160 2.7426.40 35040 2.7221.00 43070 2.6915.90 55980 2.6710.75 78900 2.607.16 114600 2.566.15 132600 2.555.16 151700 2.504.40 173500 2.474.04 190700 2.483.70 199400 2.433.29 211000 2.363.11 218100 2.332.89 225600 2.28a Uncorrected for TIP190A-7: Low Temperature Magnetic Data of Au(SO3F)(SbF6Temperature [K] XMCOff x 106 [cm3mol4]a ff [j.t]81.78 410 0.5274.24 460 0.5269.72 560 0.5665.25 630 0.5860.21 690 0.5854.20 820 0.6047.40 980 0.6140.00 1250 0.6330.85 1820 0.6725.60 2340 0.6920.60 3070 0.7115.85 4240 0.7310.30 7010 0.766.84 11500 0.796.30 14800 0.864.32 20570 0.844.20 21090 0.843.37 22170 0.772.69 24300 0.72a Experimental MW of compound = 734.88 g mol1191A-8: Crystal Structures of Some Arene-Sn(U) Complexes(a) C6HSnC1 (Aid4) (b) p-(CH3)2C64SnCJ (AICJ4)Cr3)CI(3(c) [(C6H2SnCI (AICI4)12 (d) C6HSn(AICI4)2C6HC(2) (1)192A-9: Qualitative MO Diagram of [(arene)Ga] Complex (C6 Symmetry)Ea Gac6vHOMOeaLUMOa193APPENDIX BB-i: Low Temperature Magnetic Data of Ni(SO3F)2at Magnetic Field = 7501 GTemperature [K] XMCOff x 106 [cm3mol1] eff [IB]a81.61 15470 3.1877.72 16310 3.1874.19 17180 3.1969.49 18380 3.2065.19 19700 3.2159.86 21590 3.2254.00 23950 3.2247.60 27460 3.2340.02 33160 3.2630.35 45210 3.3125.75 55730 3.3920.48 73180 3.4615.75 104700 3.6310.42 200000 4.087.04 417400 4.856.30 534400 5.195.18 726200 5.494.78 813200 5.584.40 873100 5.544.32 879100 5.513.37 963100 5.102.89 1017000 4.852.69 1041000 4.73a Uncoffected for TIP194B-2: Low Temperature Magnetic Data of Pd(SO3F)2at Magnetic Field = 9625 GTemperature [K] XMCOff x 106 [cm3mol1J 14ff 1JLB]a81.50 18900 3.5177.89 19840 3.5270.17 22590 3.5660.50 27090 3.6254.40 30610 3.6547.90 36090 3.7240.30 45460 3.8331.50 64760 4.047.42 875200 7.215.64 955100 6.564.32 984400 5.833.54 998000 5.322.60 1006000 4.572.20 1010000 4.221.84 1013000 3.86a Uncorrected for TIP195B-3: Low Temperature Magnetic Data of Pd(JJ)[Pd(IV)(SO3F6]atMagnetic Field = %25 GTemperature [KJ ZMCOff x 106 [cm3moP1] eff B]a82.33 21070 3.7374.98 23360 3.7461.00 30070 3.8348.60 38330 3.8632.10 59150 3.9022.30 96310 4.1412.15 285700 5.276.84 537300 5.425.08 604400 4.96a Uncorrected for TIP196B-4: Low Temperature Magnetic Data of Ni(II)[Sn(IV)(SO3F6]Temperature [KJ XMCOff x 106 [cm3mol1] I.Lff [1.LBIa81.56 16610 3.2977.83 17460 3.3073.91 18470 3.3069.49 19560 3.3065.02 20830 3.2959.98 22600 3.2953.85 24950 3.2847.45 28330 3.2840.30 33300 3.2830.70 43750 3.2825.85 51580 3.2721.05 63720 3.2815.50 85710 3.2610.06 134900 3.306.44 223400 3.394.46 321200 3.394.24 340600 3.40a Uncorrected for TIPMagnetic field = 7501 G197B-5: Low Temperature Magnetic Data of Cu(II)[Sn(IV)(SO3F6]Temperature [K] XMCOff x 106 [cm3mol1] ff []a81.50 6540 2.0677.83 6830 2.0674.08 7100 2.0569.83 7550 2.0565.31 8010 2.0560.09 8600 2.0354.10 9520 2.0347.55 10700 2.0240.00 12730 2.0230.80 16280 2.0026.10 19360 2.0121.35 23630 2.0116.15 30650 1.9910.48 46260 1.977.19 66730 1.965.84 82150 1.965.00 95270 1.954.78 98560 1.944.32 109700 1.953.02 140500 1.842.40 168800 1.80a Uncorrected for TIPMagnetic field = 9225 G198B-6: Low Temperature Magnetic Data of Ag(II)[Sn(W)(SO3F6]Temperature [K] x 106 [cm3mol1] ff [&81.61 5010 1.8177.55 5230 1.8073.68 5490 1.8069.26 5970 1.8264.90 6330 1.8159.68 6890 1.8153.12 7710 1.8146.94 8730 1.8140.20 10300 1.8230.36 13640 1.8225.30 16640 1.8320.18 20070 1.8015.05 26320 1.789.76 39680 1.766.44 57840 1.736.15 61370 1.745.34 68870 1.724.62 77760 1.703.96 91000 1.703.37 103600 1.672.69 112400 1.562.50 116200 1.52a Uncorrected for TIPMagnetic field = 9225 G199B-7: Magnetic Data of Cu(SO3F)2for the Temperature Range 312 to 4 KTemperature [K] XMCOff x 106 [cm3mol1] Peff312 1830 2.08300 1900 2.08287 1970 2.07272 2090 2.08240 2350 2.08211 2660 2.08181 3060 2.07152 3620 2.07123 4460 2.07100 5460 2.0781.78 6500 2.0578.06 6850 2.0574.36 7290 2.0769.94 7780 2.0765.77 8320 2.0859.98 8950 2.0655.00 9880 2.0748.10 11180 2.0641.60 13100 2.0831.80 17280 2.0926.65 20600 2.0921.83 25170 2.0916.90 33010 2.1111.13 52110 2.158.70 71180 2.225.91 77690 1.914.20 85130 1.69a First ten data points from Ref. 15, Chapter 6.b Corrected for TIP (TIP = 100 x 10*6 cm3 mo11,Ref 15, Chapter 6)Magnetic Field = 9225 G200

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