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Coordination chemistry of lanthanides with multidentate ligands Yang, Li Wei 1995

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COORDINATION CHEMISTRY OF LANTHANIDES WITH MULTIDENTATELIGANDSbyLI WEI YANGM.Sc., Fudan University, Shanghai, China, 1988B.Sc., Fudan University, Shanghai, China, 1985A 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 standardki.......THE UNIVERSiTY OF BRITISH COLUMBIAOctober 1995© Li Wei Yang, 1995In 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.The University of British ColumbiaVancouver, Canada/ 9rDepartment of (H & M / Sliz yDateDE-6 (2/88)ABSTRACTA number of potentially heptadentate N403 and nonadentate/dinucleating N603ligands are reported: tris(((2-hydroxy-3-methoxybenzyl)amino)ethyl)amine (H33-MeOaea)), 2-(2’ -hydroxyphenyl)- 1 ,3-di[3’ -aza-4’ -(2”-hydroxy-5 “-halophenyl)-prop-4’ -en-1’-yl]-1,3-imidazolidine (H3Xapi, X = H, Cl, Br), N, N’, N”’-tris(2-hydroxybenzyl)triethylenetetraamine (H3(1,2 ,4-btt)), and its acetone adduct 1 -(2’-hydroxybenzyl)-2,2-dimethyl-3-[3’ ,6’ -diaza-3 -(2”-hydroxybenzyl)-7’ -(2”-hydroxyphenyl)-heptyl]- 1 ,3-imidazolidine (H31 ,2,4-ahi)), H3dha3tren, and I ,4,7-tris(((2-hydroxy-5-bromobenzyl)amino)propyl)- I ,4,7-triazacyclononane (H3Brapt). The Schiffbase ligands H3Xapi (X = H, Cl, Br) are the products of the condensation reaction oftriethylenetetraamine (trien) with 3 equiv of unsubstituted or substituted salicylaldehyde.The Schiff base H3(dhatren) is prepared by the reaction of the tripodal tris(2-aminoethyl)amine (tren) and dehydroacetic acid. All the amine phenol ligands H3(3-MeOaea), I-Iq(1,2,4-btt) andH3(1,2,4-ahi), andH3Brapt are the KBH4 reduction productsof the Schiff bases derived from the reactions of tren with 3 equiv of o-vanillin, trien with3 equiv of salicylaldehyde, and 1,4,7-tris(3-aminopropyl)-1,4,7-triazacyclononane(taptacn) with 3 equiv of 5-bromosalicylaldehyde, respectively.A series of mononuclear, homodinuclear, and heterodinuclear (with copper)lanthanide complexes with the aforementioned ligands were synthesized. The reactionsof lanthanide nitrates with one equiv of N403 ligands produce mononuclear nine-coordinated complexes, [Ln(H3L)(N0j(H3L = N403 ligands). wherein the ligandadopts a tridentate capping coordination mode. The N603 ligand H3Brapt reacts withlanthanide triflates to give 1:1 complexes. In the presence of a base (sometimes in theabsence of a base), other different coordination geometries are formed (depending on theligand framework, rigidity, cavity size, and donor atom number): the six-coordinatebis(Iigand) bicapped complexes [Ln(H3(3-MeOaea))2](N0);the mononuclear seven“coordinate encapsulated complexes Ln( 1 ,2,4-btt) (obtained from the reactions oflanthanide salts withH3(l,2,4-ahiD; the homodinuclear sandwich complexes [Ln(Xapi)]2;an Nd-H3dhatrenpolymer; and a heterodinuclear complex LaCu(Brapt)(N03)2.The ligands and the metal complexes were fully characterized by a variety oftechniques: elemental analysis, UV/vis, IR and NMR spectroscopy, and massspectrometry; the structures of several ligands and metal complexes were determined bysingle crystal X-ray diffraction. Crystals of[Ln(H3(3-MeOaea))2](N0)•xHO•yMeOH(En = Pr, x = 5.56, y = 0.44; and Ln = Gd, x = 5.96, y = 0.66) are isomorphous. In bothcomplexes, the three phenolate 0 atoms of each of the two tridentate amine phenolligands coordinate to the metal ions in a slightly distorted octahedral geometry, while thesecondary amine N atoms are protonated and uncoordinated. In the ligand H3apistructure, strong intramolecular hydrogen bonding occurs between the hydroxy hydrogenatoms and the azomethine (or secondary) nitrogen atoms. The structure of Yb(1,2,4-btt)has a distorted pentagonal bipyramidal coordination geometry around the Yb3 ion,which is coordinated by an N403 donor set. In the structure of [La(Brapi)]2,the rigidbackbones of both ligands force the chelating arms to spread wide to bridge the two metalions, which gives a new eight-coordinated sandwich dimeric structure. Spontaneousconversion of the capped species to this new sandwich dimer, together with the evidenceof variable-temperature 1H NMR of [La(Clapi)] in DMSO-d6,indicates that these newsandwich complexes are very stable (at least kinetically) and extremely rigid. The X-raystructure of the polymer [Nd(N03)(Hdhatren)] reveals that two neodymium atomsform a dinuclear center through four bridging nitrate groups, and the ligand serves to linkthese neighbouring dinuclear centers to form a polymer in a three dimensional array.Each neodymium atom is coordinated by nine oxygen atoms, one from each of twoseparateH3(dhatren) ligands, and the remaining seven from five nitrate groups whichutilize three different coordination modes. The geometry around each of the metal ions isInbest viewed as a monocapped square antiprism. The crystal structure of the hydrolyzedH3dhatren is also reported, indicating that the ligand has a keto-enamine form.lvTABLE OF CONTENTSAbstract iiTable of Contents VList of Tables XList of Figures xiiiList of Abbreviations, Symbols, Acronyms xvAcknowledgements xixDedication xxChapter I General Introduction 1References 12Chapter II Synthesis and Characterization of Tris(((2-hydroxy-3-methoxy-benzyl)amino)ethyl)amine and its Complexes 152.1. Introduction 152.2 Experimental Section 17Synthesis of Ligands 182.2.1 H3vantren 182.2.2 3(3-MeOaea) 18Synthesis of Metal Complexes 192.2.3 [Pr(H(3-MeOaea))(N03)3] 192.2.4 [Nd(H(3-MeOaea))(N0)] 192.2.5 [Pr(H(3-MeOaea))2](N03)3 202.2.6 [Nd(H(3-MeOaea))1(N0) 202.2.7 [Gd(H(3-MeOaea))21(N03)3 202.2.8 [Yb(H(3-MeOaea))2](N0)3 21VConversion of Capped to Bicapped Species 21Attempted Conversion of Bicapped toEncapsulated Species 222.3 Results and Discussion 222.3.1 Synthesis and Characterization of Ligands 222.3.2 Synthesis and Characterization of MetalComplexes 232.3.3 Crystal Structures of [Pr(H3(3-MeOaeaD2](NO3)and [Gd(H(3-MeOaea))](N0)262.3.4 Possible Conversion between DifferentConformational Species 28References 31Chapter ifi Potentially Heptadentate Imidazolidine-containing N403 SchiffBases and N403Amine Phenols: Influence of Backbone Rigidityon Compound Structure 333.1. Introduction 333.2 Experimental Section 35Synthesis of Ligands 363.2.1 H3api 363.2.2 H3Clapi 373.2.3 H3Brapi 373.2.4 H3(1,2,4-btt) andH3(l,2,4-ahi) 38Synthesis of Lanthanide Complexes 393.2.5 [Ln(Xapi)] 393.2.6 [La(H3Xapi) N0)] 403.2.7 [Ln(HXapi) NO (Ln = Gd, Yb) 403.2.8 [Ln(l,2,4-btt)] 41vi3.2.9 [Ln(H(1,2,4-btt))(N0)].41Spontaneous Conversion of Capped toSandwich Species 423.3 Results and Discussion 423.3.1 Synthesis and Characterization of Ligands.. 423.3.2 Synthesis and Characterization of MetalComplexes 493.3.3 Spontaneous Conversion of Capped toSandwich Species 613.3.4 Crystal Structure ofH3api 633.3.5 Crystal Structure of Yb(l,2,4-btt) 663.3.6 Crystal Structure of [La(Brapi)]2 703.3.7 Concluding Remarks 75References 76Chapter IV Complexation of the Potentially Heptadentate LigandH3dhatrenwith Lanthanides: Architecture of a [Nd(N03)3(H3dha3tren)]nPolymer with Profuse Modes of Nitrate Coordination 794.1. Introduction 794.2 Experimental Section 81Synthesis of Ligand and Metal Complexes 814.2.1 H3dhatren 814.2.2 Nd(dhatren)0.5NaNO 1 .5H20 824.2.3 Pr(dhatren).0.5NaNO.1 H 834.2.4 Ln(Hdhatre )(N0)(Ln = La, Pr, Nd,Gd, Yb) 834.3 Results and Discussion 834.3.1 Synthesis and Properties ofH3dhatren 83VII4.3.2 Metal ComplexesLn(H3dhatre )(N0)(Ln = La, Pr, Nd, Gd, Yb) 854.3.3 Crystal Structure of(H3dha2tren)N0 884.3.4 Metal Complexes Ln(dhatre )0.5NaNO1.5H20(Ln = Pr, Nd) 904.3.5 Crystal Structure of[Nd(Hdhatren)(NO)] 94References 101Chapter V Lanthanide(III) and Copper(ll) Complexes of 1,4,7-Tris(((2-hydroxy-5-bromobenzyl)amino)propyl)- 1 ,4,7-triazacyclononane... 1035.1. Introduction 1035.2 Experimental Section 109Synthesis of Ligands 1105.2.1 Diethylene-1,4,7-triamine Tritosylate 1105.2.2 Ethyleneglycol Ditosylate 1105.2.3 1 ,4,7-Triazacyclononane Tritosylate 1115.2.4 1 ,4,7-Triazacyclononane.3HC1 1125.2.5 1 ,4,7-Triazacyclononane 1125.2.6 1,4,7-Tris(2-cyanoethyl)-1 ,4,7-triaza-cyclononane 1135.2.7 1 ,4,7-Tris(3-aminopropyl)- 1 ,4,7-triaza-cyclononane 1135.2.8 H3Brapt 114Synthesis of Metal Complexes 1155.2.9 Ln(Tf)3 (Ln = La, Nd, Gd, Y, Yb) 1155.2.10 Ln(HBrapt)(Tf)(L =La, Y, Yb) 1155.2.11 Cu2(HBrapt)(N03) 116Viii5.2.12 Cu(Brapt)(NO3) . 1165.2.13 LaCu(Brapt)(N0) 1175.3 Results and Discussion 1185.3.1 Synthesis and Characterization of Ligands.. 1185.3.2 Synthesis and Characterization ofLanthanide Complexes 1205.3.3 Synthesis and Characterization of Copper(ll)and La-Cu Complexes 127References 131Chapter VI Conclusions and Suggestions for Future Work 134References 137Appendices 138I)’LIST OF TABLESPageTable 1.1. Ionic Radii (Ln3)for Common Coordination Numbers ofLanthanides 3Table 2.1. Selected Bond Lengths (A) for [Pr(H3(3-MeOaeaD2](N05.56H200.44CH3Hand [Gd(H(3-MeOaea))21(N0•5.96H00.66CH 28Table 2.2. Selected Bond Angles (°) for [Pr(H3(3-MeOaea))2](N05.56H200.44CH3Hand [Gd(H(3-MeOaeaD2](N0•5.96H00.66CH 29Table 3.1. 1H NMR Data for the Various Schiff BasesH3Xapi (in CDC13).... 44Table 3.2. 13C NMR Data for the Various Schiff BasesH3Xapi (in CDC13)... 46Table 3.3. Analytical Data for the Lanthanide Complexes of the VariousSchiff Base and Amine Phenol Ligands 50Table 3.4. Infrared Spectral Data (cnr1,KBr disk) for the LanthanideComplexes of the Various Schiff Base and Amine PhenolLigands 52Table 3.5. Mass Spectral Data for the Lanthanide Complexes of theVarious Schiff Base and Amine Phenol Ligands 60Table 3.6. ‘H NMR Data for the Dinuclear Lanthanum Complexesof the Various Schiff Bases (in CDC13) 55Table 3.7. Bond Lengths (A) and Angles (deg) in H3api with EstimatedStandard Deviations 65Table 3.8. Bond Lengths (A) and Angles (deg) in One of the TwoIndependent Molecules of Yb( I ,2,4-btt) with EstimatedStandard Deviations 68xTable 3.9. Bond Lengths (A) and Angles (deg) in [La(Brapi)]2 withEstimated Standard Deviations 73Table 4.1 Analytical Data for the Lanthanide Complexes ofH3dhatren 87Table 4.2 Infrared Spectral Data (cm-1,KBr disk) for the LanthanideComplexes ofH3dhatren 88Table 4.3 Mass Spectral Data for the Lanthanide Complexes of H3dha3tren.. 89Table 4.4. Bond Lengths (A) and Angles (deg) in(H3dha2tren)(N0).0with Estimated Standard Deviations 92Table 4.5. Bond Lengths (A) and Angles (deg) in [NdiNO3)3(H3dha3tren)]nwith Estimated Standard Deviations 98Table 5.1 1H and 13C NMR Data forH3Brapt in CDC13 121Table 5.2 Analytical Data for Larithanide Triflates 122Table 5.3 Analytical Data for the Lanthanide ComplexesLn(HBrapt)(CFSO3)3 122Table 5.4 Mass Spectral Data for the Lanthanide ComplexesLn(H3Brapt)(CFSO) 123Table 5.5 Infrared Spectral Data (cm-1,KBr disk) for the LanthanideComplexes Ln(H3BrapQ(CFSO) 123Table A. 1. Selected Crystallographic Data for [Pr(Hi(3-MeOaeaD2] N03)•5.56H20•O.44CH3H 139Table A.2. Selected Crystallographic Data for [Gd(H(3-MeOaea))](N05.96HO0.6 CH3H 140Table A.3. Selected Crystallographic Data for H3api 141Table A.4. Final Atomic Coordinates (Fractional) and B (A2) forH3api 142Table A.5. Selected Crystallographic Data for Yb(l,2,4-btt)0.5MeOH 144Table A.6. Final Atomic Coordinates (Fractional) and Beq (A2) forYb(l,2,4-btt)•0.5MeOH 145XITable A.7. Selected Crystallographic Data for [La(Brapi)]2•2CHCI3 148Table A.8. Final Atomic Coordinates (Fractional) and Beq (A2) for[La(Brapi)]2CHCl3 149Table A.9. Selected Crystallographic Data for(H3dha2tren)(N0)•0 151Table A.1O. Final Atomic Coordinates (Fractional) and Beq (A2) for(H3dha2tren)(N0). 2 152Table A.l 1. Selected Crystallographic Data for [Nd(NO3)(Hdhatren)] 154Table A.12. Final Atomic Coordinates (Fractional) and Beq (A2) for[Nd(H3dha3tren)(NO3)3] 155XliLIST OF FIGURESPageFigure 1.1. Influence of paramagnetic ions on proton relaxation time 2Figure 1.2. The lowest strain energy geometry for the six- and five-memberedchelate rings (calculated using molecular mechanics) 8Figure 2.1. ORTEP view of the [Gd(H3(3-MeOaeaD2] cation([Pr(H3(3-MeOaeaD2] is isostructural) 27Figure 3.1. 1H NMR spectra (400 MHz) ofH3Clapi (top) and [La(Clapi)]2(bottom) in CDCI3 at room temperature 57Figure 3.2. UV/VIS spectra of H3api, Gd(Hapi)(N0)and [Gd(api)]2inDMSO at room temperature. Gd(H3api)(N0 slowlydecomposes in DMSO, while [Gd(api)]2is stable 58Figure 3.3. UVIVIS spectra of the spontaneous conversion of 0.3 mMGd(H3api)(N0)to [Gd(api)]2at room temperature in methanol.. 62Figure 3.4. ORTEP drawing (top) and stereo packing diagram for unit cell(bottom) of H3api with numbering schemes 64Figure 3.5. ORTEP drawing of one of the two independent Yb(1,2,4-btt)molecules in Yb( 1 ,2,4-btt).0.5MeOH 67Figure 3.6. ORTEP drawing of [La(Brapi)]2 in [La(Brapi)].2CHC13 71Figure 4.1 Portion of ‘H NMR spectra (400 MHz) of H3dha3tren in CDC13(top) and CDC13-20(bottom) at room temperature 86Figure 4.2. ORTEP thawing of(H3dha2tren)(N0)0with numberingschemes 91Figure 4.3. ORTEP drawings of the coordination environment of Ndin [Nd(N03)3(Hdhatren)]n (left) and of one [Nd(N03)(H3dhatren)] unit, both with numbering schemes 95Figure 4.4. ORTEP stereoview of polymer [Nd(N03)(Hdhatren)]n 96XIIIFigure 5.1 Variable temperature 1H NMR spectra of La(H3Brapt)(Tf)3in CD3N 124Figure 5.2 Enthalpy and entropy for isomerization of La(H3Brapt)(Tf)3in CD3N 125Figure 5.3 UV/vis spectra (300-800 nm) ofCu2(HBrapt)(N03)2,Cu2(Brapt)(N03), and LaCu(Brapt)(N0)2in methanol atroom temperature 128Figure 5.4 UV spectra (200-350 nm) ofH3Brapt, Brapt3La(H3Brapt)(Tf,Cu2(Brapt)(N03),and LaCu(Brapt)(N03)2 in methanol at roomtemperature 130xivLIST OF ABBREVIATIONS, SYMBOLS, ACRONYMSAbbreviation MeaningA Angstrom(s); equivalent to 1 x 10-10 meterAPT attached proton testdegree CelsiusCalcd calculatedCN coordination numbercone. concentratedcyclam 1,4,8,11 -tetraazacyclotetradecanechemical shift in parts per million (ppm) (NMR) orvibrational bending mode (IR)DCI desorption chemical ionization (in mass spectrometry)dec. decompositiondha dehydroacetic acid or dha chelating armDMF N, N-dimethyl formamideDMSO dimethyl sulfoxideDO3A 1,4,7, 10-tetraazacyclododecane-N, N’, N”-triacetic acidDOTA 1,4,7, 10-tetraazacyclododecane-N, N’, N”, N”-tetraaceticacidDotarem Gd(Ifl) complex of DOTADTPA diethylenetriamine-N, N, N’, N”, N”-pentaacetic acidEDTA ethylenediaminetetraacetic acidequiv equivalentEl electron impact (in mass spectrometry)FAB fast-atom-bombardment (in mass spectrometry)g gram(s)xvH3(aea) tris(((2-hydroxybenzyl)amino)ethyl)amineH3(1 ,2,4-ahi) 1 -(2’ -hydroxybenzyl)-2,2-dimethyl-3-[3 ‘ ,6’-diaza-3 ‘-(2”-hydroxybenzyl)-7’-(2”-hydroxyphenyl)-heptyll- 1,3-imidazolidineH3api 2-(2’ -hydroxyphenyl)- I ,3-di[3 ‘-aza-4’ -(2”-hydroxyphenyl)-prop-4’ -en-I’ -yl]-l ,3-imidazolidineH-bond hydrogen bondH3(5-Braea) tris(((2-hydroxy-5-bromobenzyl)amino)ethyl)amineH3Brapi 2-(2’-hydroxy-5 ‘ -bromophenyl)- 1 ,3-di[3’ -aza-4’-(2”-hydroxy-5”-bromophenyi)-prop-4’ -en-i’ -yl]- 1,3-imidazolidineH3Brapt 1 ,4,7-tris(((2-hydroxy-5-bromobenzyl)amino)propyi)-1,4,7-triazacyclononaneH3(1,1 ,4-btt) N, N, N” ‘-tris(2-hydroxybenzyl)triethylenetetraamineH3(1 ,2,4-btt) N, N’, N” ‘-tris(2-hydroxybenzyl)triethylenetetraanineH3(5-Claea) tris(((2-hydroxy-5-chlorobenzyl)aniino)ethyl)amineH3Clapi 2-(2’ -hydroxy-5’ -chiorophenyl)- 1 ,3-di[3 ‘-aza-4’ -(2”-hydroxy-5”-chlorophenyi)-prop-4’ -en-i’ -yl]- 1,3-imidazolidineH3datren tris2’-hydroxy-4’,5’-dimethylacetophenone-2-imino)ethyl)amineH3hatren tris((2-hydroxyacetophenone-2-imino)ethyl)amine(3-MeOaea) tris(((2-hydroxy-3-methoxybenzyl)aniino)ethyl)amineH3saltren tris((salicylideneimino)ethyl)aniineH3trac tris((acetylacetone-2-imino)ethyl)amine or tris(3-aza-4-methylhept-4-ene-6-on- 1-yl)amineH3vantren tris((3-methoxysalicylideneimino)ethyl)aminexviIR infraredLSIMS liquid secondary ion mass spectrometryMagnevist Gd(llI) complex of DTPAmp melting pointMRI magnetic resonance imagingmlz mass-to-charge ratio (in mass spectrometry)NMR nuclear magnetic resonanceOnmiscanTt1 Gd(ffl) complex of bis(methyl)-DTPAORTEP Oak Ridge Thermal Ellipsoid Programppm parts per millionProhance 1O-(2-hydroxypropyl)-l ,4,7,lO-tetraazacyclododecane-1 ,4,7-triacetate gadolinium(llI)rel. relativesen 1,1, 1-tris(4-amino-2-azabutyl)ethanestn 1,1,1 -tris(5-amino-2-azapentyl)ethanetacn 1 .4,7-triazacyclononanetaetacn 1 ,4,7-Iris(2-aminoethyl)- 1 ,4,7-triazacyclononanetame 1,1,1 -tris(aminomethyl)ethanetap 1 ,2,3-triaminopropanetaptacn 1 ,4,7-tris(3-aminopropyl)- 1 ,4,7-triazacyclononaneTc the transition temperature at which superconductingproperties appear or disappeartcetacn 1 ,4,7-tris(2-cyanoethyl)- 1 ,4,7-triazacyclononane2,3,2-tet N, N-bis(2-aminoethyl)- 1 ,3-propanediamineTf trifluromethanesulfonate; CF3S0 triflateTHF tetrahydrofurantren tris(2-aniinoethyl)aminexviitrien triethylenetetraamineTs p-toluenesulfonylUV ultravioletvis visibleVT variable temperatureYb( 1 ,2,4-btt) { N, N’, N” -tris(2-oxobenzyl)triethylenetetraamineytterbiumxvii’ACKNOWLEDGEMENTSFirst, I would like to thank Dr. Chris Orvig for his guidance, understanding andspecial support for a mom student throughout the course of these studies. The help givenby support staff, in particular Mrs. Marietta Austria, Mrs. Liane Darge, Mr. Peter Borda,and technical staff at the mass spectrometry laboratory, is greatly appreciated.My special thanks go to Dr. Alex McAuley, Dr. Mary Rodopoulos, and MartinMa for their help in the organic syntheses; to Dr. Richard Pincock and Tilly Schreindersfor their understanding and support above and beyond the call of duty during my difficulttime. I also owe a great debt to Dr. Steve Rettig for his invaluable help in thedetermination of all crystal structures.This would not be complete without acknowledging the support andencouragement of all members of the ‘Equipe Orvig Team’ past and present, especiallyPete Caravan, Shuang Liu, Mark Lowe, Roger Luo, Marco Meichior, and Ika Setyawati.I would also like to express my appreciation for support and love from the otherside of the ocean: my parents and my mother-in-law for encouraging me to study abroad,and for taking good care of my daughter. I certainly cannot wait to let my lovely littlegirl Pondie know that mom has finally finished her studies. (Insofar as she can remember,mom is always studying.)Finally my deepest gratitude is extended to my husband Ming for hiswholehearted support, love and understanding. Without him this accomplishment wouldnot have been possible.In addition, financial support from U.B.C. in the form of a teaching assistantshipis gratefully acknowledged.xixTo my husband Ming, and my daughter Pondie, with much love.xxChapter! IntroductionChapter I General IntroductionLanthanides have a historical name of “rare earths”. They are not rare, however,but are widely dispersed in many areas around the world. For a long time, they wererelegated to the bottom of the periodic table as an appendix. This inattention has had asharp reversal recently with the application of rare earths as NMR shift reagents1 inorganic chemistry, and as a replacement for Ca2+ in biological systems.2 Since then, theuse of the lanthanides NMR and spectroscopic properties has created a burgeoninginterest in the physics and chemistry of these elements. Their applications toluminescence,3 superconductors,4 catalysis,5’6 NMR imaging,3 andradiopharmaceuticals have brought them to a prominent place in modem science.Our initial interest in lanthanides was due to their utilization as contrast agents fornuclear magnetic resonance imaging (MRI). MRI is now an important tool for theclinical diagnosis and evaluation of a variety of diseases]’8 The image intensity in NMRimaging, largely composed of the paramagnetically shifted NMR signal of water protons,is dependent on nuclear relaxation time. Paramagnetic metal ions can decrease therelaxation time of nearby nuclei, thus enhancing the image contrast between normal anddiseased tissues.9”° Among paramagnetic metal ions, Gd(llI) draws the widest attentiondue to its high number of unpaired electrons and short proton relaxation time (Figure1.1).Even though the magnetic properties of Gd(III) appear to be ideal for use as acontrast agent, free Gd(III) is toxic. It will interact with amino acids, protein, tissues, andcells,2 and it can also be stored for relatively long periods of time in the liver and spleen,with slow excretion.11 The metal ion must be administered in some less-toxic form, i.e.as a complex.1Chapter 1 Introductionrel. effect10 -9-8-7-6 -543‘1nPflnnnrrfl flflPnCr3 Fe3 Co2 Cu2 Pr3 Sm3 Bu2 Th3 Br3Mn2 Fe2 Ni2 Ce3 Nd3 Eu3 Gd3 Dy3 Yb3Figure 1.1. Influence of paramagnetic ions on proton relaxation time. 12General requirements for such a complex are high stability, kinetic inertness, andhigh relaxivity (the relaxivity is the efficiency with which the complex enhances theproton relaxation rates of water; it is proportional to the number of water moleculescoordinated to the metal ion8). Also, the structure of the complex determines itsbiodistribution and thus its excretion pathway. Most commonly, complexes which arehydrophobic are taken up by the liver and undergo hepatobiliary excretion, whereascomplexes which have low molecular weights and are hydrophilic are filtered out througha renal pathway.8To design a specific chelating ligand for lanthanides, it is necessary to understandthe nature of lanthanide (III) ions. Lanthanides have large ionic radii, which fall in therange 0.86 -1.03 A13 (coordination number CN = 6), with lanthanum (III) being the2Chapter 1 Introductionlargest and lutetium (III) being the smallest. The progressive decline in an ionic radius(Table 1.1) is commonly termed as the “lanthanide contraction”. This occurs because,although each increase in nuclear charge is balanced by a simultaneous increase inelectronic charge, the directional characteristics of the 4f orbitals cause the 4? electronsto shield themselves and other electrons from the nuclear charge only imperfectly. Thus,each unit increase in nuclear charge produces a net increase in attraction for the wholeextranuclear electron charge cloud and each ion shrinks slightly in comparison with itspredecessor. As a result of this contraction, the charge density of these cations increasesTable 1.1. Ionic Radii (Ln3)for Common Coordination Numbers of Lanthanides.2Ionic Radii (A)Element CN6 CN7 CN8 CN9La 1.03 1.10 1.16 1.22Ce 1.01 1.07 1.14 1.20Pr 0.99 - 1.13 1.18Nd 0.98 - 1.11 1.16Sm 0.96 1.02 1.08 1.13Eu 0.95 1.01 1.07 1.12Gd 0.94 1.00 1.05 1.11Tb 0.92 0.98 1.04 1.10Dy 0.91 0.97 1.03 1.08Ho 0.90 - 1.02 1.07Er 0.89 0.95 1.00 1.06Th 0.88 - 0.99 1.05Yb 0.87 0.93 0.99 1.04Lu 0.86- 0.98 1.03Ca 1.00 1.06 1.12 1.18Y 0.90 0.96 1.02 1.083Chapter! Introductionwhen the series is traversed. Thus some ligands will preferentially bind to the lighterlanthanides (La-Eu) because of the need for a large ionic radius for unstrained binding ofthe ligand, whereas other ligand systems will prefer the heavier lanthanides (Gd-Lu) dueto their higher charge densities and smaller ionic radii. Generally, the coordinationnumber of lanthanide complexes exceeds six.’4 Indeed, very few six coordinate speciesare known. For biological molecules, their coordination numbers are often 8 or 9.Lanthanide ions display the typical characteristics of hard acids, and have a great affinityfor hard bases such as oxygen (hard and soft acid and base (HSAB) principle’5. Thebinding between the ion and the ligand is predominantly ionic. This means that there islittle stereochemical preference within the first coordination sphere. Thus thecoordination numbers and geometries are primarily determined by ligand characteristicssuch as conformation, donor atoms, sizes, number and solvation effects. Lanthanidecomplexes can therefore have a variety of geometries.A number of acyclic chelating ligands, mostly polyamine-based polycarboxylicacids (i.e. ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaaceticacid (DTPA)), have been studied over the years.16 Gd(DTPA)(H20) (MagnevistTM)was the first imaging agent used in humans,17 due to its high stability constant (log K =22.5 18) and one coordinated water molecule;19 however, this complex has severaldrawbacks: it has a negative charge which results in a relatively high osmolality underphysiological conditions and consequently undesired side effects such as dehydration,blood pressure changes, coma, etc..20 The complex does not cross membranes whichmakes the imaging of heart and brain impossible; it possesses low kinetic stability, andlow proton relaxivity. In order to develop better contrast agents, various changes havebeen made to the backbones, as well as to chelating pendant groups. Most attention hasbeen paid to the macrocyclic polyaza-based polycarboxylate ionic complexes8’2023 (i.e.4Chapter 1 Introduction1,4,7,1 O-tetraazacyclododecane-N, N’, N’, N”-tetraacetic acid (DOTA)), acyclic (i.e.bis(amide)-DTPA) and cyclic (i.e. 10-substituted 1,4,7.10-tetraarzacyclododecane-N, N’,N”-triacetic acid (DO3A)) polyaza-based polycarboxylate neutral complexes.20’429/__\ —COOHN N N“—COOHCOOHDTPA bis(amide)-DTPA(R = Me, M3 = Gd3: OmniscanTM)DOTA substituted DO3A(M3 = Gd3:Dotarem)HAM(R =CH2H(Me)OH, M3 = Gd3:Prohance)Chart 1.1HOOC—\HOOC—’RHNOC—\ /__\N NHOOC—” KCO2H/—CONHRN(M3= Gd3:Magnevisttmt)HOOC—\-—\,-—COOH“—‘ ‘—COOHHOOCmN—COOH)HOOC—’ “—“ ROHPtexaphyrinOH5Chapter! Introduction(Chart 1.1) Macrocyclic complexes are in general more thermodynamically stable andkinetically inert than acyclic analogues which have same donor arrangements, whileneutral complexes can cross membranes. Currently, ProhanceTM, OmniscanTM, andDotarem (Chart 1.1) are used in certain clinical situations for enhanced tumordetection.3°Together with Magnevist’1’4,these are the only four chelates used clinically;all of them are based on polyamine polycarboxylic acids. Other ligands such as HAM31and texaphyrin32 were reported to have 3 to 5 water coordination sites in metalcomplexes which resulted in high relaxivity. They are generally thought to be promisingnext-generation MM agents.With only a few commonly used contrast agents, there is clearly a need to developother kinds of stable complexes for clinical use. Of particularly interest are potentiallyheptadentate (and higher), tribasic ligands derived from the Schiff base condensation ofpolyamines with hydroxyacetophenones, or salicylaldehydes, and from the reduction ofthese Schiff bases to their corresponding amine phenols (polyaminopolyphenolateligands). Polyamines as backbones have received a greal deal of attention from syntheticorganic chemists because of their presence in a number of siderophores,33’4and becauseof their potential in cancer chemotherapy.35 Lanthanides prefer donor atoms in the orderO >> N >> S. Amines alone are not good donors for lanthanides; however, whenincorporated with oxygen-containing binding groups such as carboxylates, they werefound to form quite stable complexes with nitrogen atoms coordinated to Ln.36 Like thepolyaminopolycarboxylates, it is possible in the polyaminopolyphenolates that thecoordination of oxygen donors serves to anchor the ligand while the amine moietycoordinates secondarily. Over the years, the work done on Ln-polyaniinopolycarboxylatecomplexes for MRI has greatly helped the understanding of the coordination properties ofpolyaminopolycarboxylates; however, the knowledge about Ln-polyaminopolyphenolate6Chapter 1 Introductioncomplexes is very limited. In fact, there has been little attention paid to the phenolategroup as an anionic oxygen donor for lanthanides due to the weak acidity of the hydroxylgroup (pKa of phenol - 10). Bearing the criteria of MRI agents in mind, our group hastried to explore and to enrich the coordination chemistry of this type of ligand with thelanthanides. Our interest stems from: a) their ease of preparation and their versatility asligands which can be easily tailored to fit a number of binding requirements, and to affordneutral complexes with lanthanides; b) the potential for variation on the ligand backbone.(Much precedent for backbone variation is found, for example, in the extensive literatureof EDTA and DTPA derivatives synthesized as bifunctional chelating ligands to linkmetalloradionuclides such as 90Y to monoclonal antibodies37);c) the substituents on thearomatic benzene rings incorporated into the Schiff base ligands could be varied in orderto modify the lipophilicity of a metal complex whilst retaining the same coordinationenvironment (this feature was incorporated to allow a maximum of possible biologicalchanges within a minimum of chemical changes); d) the deprotonated phenolate group asa pendant is negatively charged and basic, and so prefers the acidic lanthanide ion muchmore than neutral oxygen donors do; e) reduction of imine CH=N linkages may giveamine CH-NH functionalities stable with respect to hydrolysis. It was hoped that thehigh denticity of these ligands would be a major driving force for the formation of stablecomplexes, and that the complexes would exhibit possible water coordination sitesopposite the bridging tertiary nitrogen, thus allowing inner-sphere interactions of themetal ion with water molecules.It is worth mentioning that polyamines with two carbon atoms between twoadjacent nitrogen atoms will be our main focus, as they will form 5-membered chelaterings if the metal ion is incorporated. Usually, an n-dentate ligand yields a more stablemetal complex than n unidentate ligands of similar type (the chelate effect.38) The* DiamagneticY(III) has similar properties to Ln(llJ), and has an ionic radius close to that of Ho(III) (Table1.1).7Chapter 1 Introductiongreater stability of complexes with 5- or 6-membered chelate rings is a general empiricalfinding. For larger metal ions, complexes of chelating ligands that form 5-memberedchelate rings tend to be of higher stability than of those that form 6-membered chelaterings.36 In the most stable conformations of 5- and 6-membered chelate rings (Figure1.2), the ‘bite-size” of the 5-membered ring (2.83 A) is greater than that of the 6-membered ring (2.51 A), and the angle of the metal ion which is subtended in the 5-membered ring is smaller with a greater metal donor distance. Any ring that can comeclose to either of two arrangements will thus be of low strain energy. Lanthanide ionshave large ionic radii which give long M-N bond distances, and have high coordinationnumbers which result in small N-M-N bond angles. Overall, the formation of 5-membered chelate rings is expected to give the complex an additional stability.69°A2.50 AFigure 1.2. The lowest strain energy geometry for the six- and five-membered chelaterings (calculated using molecular mechanics).36Over a period of several years, our group has designed and synthesized severalpotentially heptadentate N4O3 ligands based on the Schiff base condensation of acyclicamines with f3-diketones, or 13-hydroxyketones, and later with a variety ofsalicylaldehydes; the reduction products of the latter are amine phenols. Several novelstructures with these ligands have been found (Chart l.2).3941 A Schiff base can beforced to form an encapsulated structure, although the resulting complex undergoesSChapter! Introductionreaction chemistry which clearly shows that this structure is not favored; an amine phenolcan form very stable, insoluble encapsulated dimer./NLn NO\0encapsulatedN-H H—N I±NLL’0—N0_Ln N00-00\ /N0Chart 1.2cappedAs a continuing project, a series of NO3 (n = 4, 6) ligands were designed andsynthesized in this work. The effects on coordination to metal ions, caused by variationsof the substituted groups on phenyl rings, ligand framework, as well as the donor groups,were explored. Metal complexes of these ligands were synthesized and fullycharacterized by elemental analysis, IR, UV/vis and NMR spectroscopy, massspectrometry, and in the case of several metal complexes, X-ray crystallography. It wasdiscovered that it is possible to generate a myriad of coordination geometries for theselanthanides, and to understand further their coordinating behavior.Another aspect of the research is concerned with the ‘architecture of the ligand’,meaning that rigidity is incorporated into the backbone of the flexible multidentateligand; by stiffening the ligand skeleton, the coordinating groups can be preoriented forcoordination to the metal ion, so as to decrease the unfavorable entropy contributions.36encapsulated dimer9Chapter 1 IntroductionThis consideration would seem to be particularly important in the design of ligandscontaining high donor atom numbers, where large numbers of presumably repellingoxygen and nitrogen donor atoms are present, and energies required to assume the correctconformation for complex formation could be large. Stability would be improved if theligand has a conformation more close to that of the metal complex. In Chapters 3 and 5,the rigid imidazolidine ring and 1,4,7-triazacyclononane macrocyclic ring wereintroduced into the ligand backbone. The resulting ligands form quite stable complexes.It is noteworthy that we are not only interested in small-size macrocycles as atemplate for holding the pendant groups in the appropriate conformation for binding, butwe are also interested in the binding of the macrocycles themselves. There has long beenrecognition that the stability constants for macrocyclic complexes were much higher thanthe open-chain complexes having the same donor arrangements; the additional stability istermed as the ‘macrocyclic effect,42 which is largely due to the higher degree ofpreorganization of the macrocycle (i.e. cyclam vs 2,3,2-tet). In the open-chain amine,NH NH NH NHCxL_ NH’ NH2,3,2-tet cyclamrepulsive forces must be overcome because the nitrogen donor groups are far apart in thefree ligand and must be forced closer together to form the complex, while in the* preorganization, suggested by D. J. Cram,43 refers to the degree to which the conformation of the ligandbound to metal ion compares with that in the absence of metal ion (free ligand).10Chapter 1 Introductionmacrocyclic analog, the repulsion between the donor atoms has already been overcomeby the preorganization. The incorporation of metal ions into the cavity could immobilize,or reduce significantly, the lability such that demetallation may be impeded.Apart from the examination of the coordination chemistry of lanthanide complexesas potential MRI agents, this research project has another goal, to explore the potential ofthe polydentate NnOm ligand as a dinucleating ligand --- a term used to describe apolydentate ligand capable of simultaneously binding two metal ions in close proximity.The study of metal-metal (both d-d and f-d) interactions has been an important area ofresearch for chemists and physicists due to their potential impact on catalysis (i.e.activation of small molecules such as CO, C02 NO, O2), bioinorganic chemistry (i.e.modelling of some metalloenzymes45), and material science (i.e. molecularmaterials,46’7 superconductors4). The magnetic and spectroscopic properties14 oflanthanides have made them good candidates as relaxation agents48 for metalloproteins inorder to obtain structural information, and as one of the components in magnets orsuperconductors.49 In terms of a ligand suitable for including both lanthanide andtransition metal ions, the polydentate NnOm ligands are of particular interest because oftheir high denticity and different affinities of oxygen and nitrogen donors towardsdifferent hard/soft metal ions.50 In both previous 41 and present studies ofN4O3 ligands,it was discovered that it is quite easy to have oxygen donors coordinate to lanthanide ionswhile all the nitrogen donors are uncoordinated (capped species in Chart 1.2) leavingthem for the coordination of softer transition metal ions such as Cu(II). In Chapter 5, apreliminary study on a dinuclear La-Cu system is conducted, and some results are brieflydiscussed.11Chapter 1 IntroductionReferences(1) Hinckley, C. C. J. Am. Chem. Soc. 1969, 9], 5160.(2) Evans, C. H. Biochemistry of the Lanthanides; Plenum Press: New York, 1990.(3) Lanthanide Probes in Life, Chemical and Earth Sciences; Bunzli, 1.-C. G.;Choppin, G. R., Eds.; Elsevier Science Publisher, B. V.: New York, 1989.(4) Sleight, A. W. Acc. Chem. Res. 1995, 28, 103.(5) Huskens, J.; Kennedy, A. D.; van Bekkum, H.; Peters, J. A. J. Am. Chem. Soc.1995, ]17, 375.(6) Magda, D.; Miller, R. A.; Sessler, 1. L.; Iverson, B. L. J. Am. Chem. Soc. 1994, 1]6,7439.(7) Runge, V. M. Enhanced Magnetic Resonance Imaging; C.V. Mosby Company: St.Louis, Missouri, 1989.(8) Lauffer, R. B. Chem. Rev. 1987, 87, 901.(9) Brasch, R. C. Radiology 1983, ]47, 781.(10) Pykett, I. L. Sd. Am. 1982, 246, 78.(11) Wedeking, P.; Tweedle, M. F. NucI. Med. Biol. 1993, 20, 679.(12) Weinmann, H.-J.; Brasch, R. C.; Press, W. R.; Wesbey, G. E. Am. J. RadioL 1984,]42, 619.(13) Shannon, R. D. Acta Cryst. 1976, A32, 751.(14) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon Press:Oxford, England, 1984.(15) Pearson, R. G. J. Ant. Chem. Soc. 1963, 85, 3533.(16) Sessler, I.E.; Mody, T. D.; Hemmi, G. W.; Lynch, V. Inorg. Chem. 1993,32, 3175and references therein.(17) Laniado, M.; Weinmann, H. J.; Schorner, R. F.; Speck, U. Physiol. Chem. Phys.Med. NMR 1984, 16, 157.12Chapter 1 Introduction(18) Martell, A. E.; Smith, R. M. Critical Stability Constant; Plenum Press: New York,1974; Vol. 1, p 282.(19) Gries, H.; Miklautz, H. Physiol. Chem. Phy. Med. NMR 1984, 16, 105.(20) Chang, C. A. Invest. Radiol. 1993,28, 821.(21) Delgado, R.; Sun, Y.; Motekaitis, R. J.; Martell, A. E. Inorg. Chem. 1993, 32, 3320.(22) Kodama, M.; Koike, T.; Mahatma, A. B.; Kimura, E. Inorg. Chem. 1991, 30, 1270.(23) Loncin, M. F.; Desreux, J. F.; Merciny, E. Inorg. Chem. 1986, 25, 2646 andreferences therein.(24) Kumar, K.; Chang, C. A.; Francesconi, L. C.; Dischino, D. D.; Malley, M. F.;Gougoutas, J. Z.; Tweedle, M. F. Inorg. Chem. 1994, 33, 3567.(25) Kumar, K.; un, T.; Wang, X.; Desreux, J. F.; Tweedle, M. F. Inorg. Chem. 1994,33, 3823 and references therein.(26) Geraldes, C. F. G.; Urbano, A. M.; Hoefnagel, M. A.; Peters, J. A. Inorg. Chem.1993, 32, 2426.(27) Aime, S.; Botta, M.; Dastrá, W.; Fasano, M.; Panero, M. Inorg. Chem. 1993, 32,2068.(28) Aime, S.; Anelli, P. L.; Botta, M.; Fedeli, F.; Grandi, M.; Paoli, P.; Uggeri, F.Inorg. Chem. 1992, 31, 2422.(29) Carvaiho, J. F.; Kim, 8.-H.; Chang, C. A. Inorg. Chem. 1992, 31, 4065.(30) Parker, D. Chem. Brit. 1994, October, 818.(31) Smith, P., H.; Brainard, 3. R.; Morris, D. E.; Jarvinen, G. D.; Ryan, R. R. I Am.Chem. Soc. 1989, 111, 7437.(32) Sessler, 3. L.; Hemnii, G.; Mody, T. D.; Murai, T.; Burrell, A.; Young, S. W. Acc.Chem. Res. 1994, 27, 43.(33) Eng-Wilmot, D. L.; van der Helm, D. I Am. Chem. Soc. 1980, 102, 7719.(34) Peterson, T.; Falk, K.-E.; Leung, S. A.; Klein, M. P.; Neilands, J. B. J. Am. Chem.Soc. 1980, 102, 7715.13Chapter 1 Introduction(35) Bergeron, R. J.; Garlich, J. R. Synthesis 1984, 782 and references therein.(36) Hancock, R. D.; Martell, A. E. Chem. Rev. 1989, 89, 1875.(37) Hider, R. C.; Hall, A. D. In Frog. Med. Chem.; Ellis, G. P. and West, G. B., Eds.;Elsevier Science Publishers: B. V., 1991; Vol. 28; p 41.(38) Schwarzenbach, G. Helv. Chim. Acta 1952, 35, 2344.(39) Liu, S.; Gelmini, L.; Rettig, S. J.; Thompson, R. C.; Orvig, C. J. Am. Chem. Soc.1992, 114, 6081.(40) Berg, D. J.; Rettig, S. J.; Orvig, C. J. Am. Chem. Soc. 1991, 113, 2528.(41) Smith, A.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1988, 27, 3929.(42) Martell, A. E.; Hancock, R. D.; Motekaitis, R. J. Coord. Chem. Rev. 1994, 133, 39and references therein.(43) Cram, D. J.; Kaneda, T.; Helgeson, R. C.; Brown, S. B.; Knobler, C. B.; Maverick,E.; Trueblood, K. N. J. Am. Chem. Soc. 1985, 107, 3645.(44) Fraser, C.; Ostrander, R.; Rheingold, A. L.; White, C.; Bosnich, B. Inorg. Chem.1994, 33, 324 and references therein.(45) Hathaway, B. J. In Comprehensive Coordination Chemistry; Wilkinson, G., Gillard,R. D. and McCleverty, J. A., Eds.; Pergamon: Oxford, England, 1987; Vol. 5; p533.(46) Kollmar, C.; Kahn, 0. Acc. Chem. Res. 1993, 26, 259.(47) Andruh, M.; Ramade, I.; Codjovi, E.; Guillou, 0.; Kahn, 0.; Trombe, J. C. J. Am.Chem. Soc. 1993, 115, 1822.(48) Bertini, I.; Luchinat, C. NMR ofFaramagnetic Molecules in Biological Systems;The Benjamin/Cummings Publishing Company, Inc.: Menlo Park, California, 1986,p273.(49) Benelli, C.; Caneschi, A.; Gatteschi, D.; Guillou, 0.; Pardi, L. Inorg. Chem. 1990,29, 1750 and references therein.(50) Alexander, V. Chem. Rev. 1995, 95, 273.14Chapter II H3(3-MeOaea) Ligand SystemChapter II. Synthesis and Characterization of Tris(((2-hydroxy-3’methoxybenzyl)amino)ethyl)amine and its Complexes2.1 IntroductionStudies of metal complexes involving ligands having seven donor atoms arerelatively rare. Of those ligands studied, most were based on the Schiff basecondensation of tris(2-aminoethyl)amine (tren) with various ketones and aldehydes due totheir ease of synthesis. For the first row transition metal complexes of the tren basedSchiff bases trenpy,1’2H3saltren,35 and trenpyrol6 (Chart 2.1), the bond between themetal ion and the apical tertiary nitrogen atom was weak to non-existent. Studies oflanthanides with the tren-based Schiff bases H3saltren, H3trac, H3hatren and H3datrenhave also been reported.79 It was noted previously8that when all seven donor atoms ofa tripodal Schiff base coordinated to a lanthanide (Yb3), the resulting complex washighly unstable and very sensitive to moisture and strong a-donor solvents such asDMSO and pyridine. The instability of these complexes likely results from the metal-enhanced hydrolysis of the ligand in water, or from solvent competition. To obviate thisproblem, we have recently reported10the three potentially heptadentate (N403)aminephenol ligands H3aea, H3(5-Claea) and H3(5-Braea) (Chart 2.1), which were prepared bythe reduction of the corresponding Schiff bases. These ligands form cappedmononuclear, [Ln(H3(5-Xaea))(NO)],and encapsulated homodinuclear, [Ln(5-Xaea)]2lanthanide complexes (see Chart 1.2) depending on the conditions of preparation. Astructural study revealed the first example, [Gd(aea)]2CHCl3of a homodinuclearbinary lanthanide complex [Ln(5-Xaea)]2with heptadentate ligands)0 The formation ofthe dinuclear structure was probably caused by the high coordination requirements oflanthanide ions.15Chapter 11 113(3-MeOaea) Ligand SystemIn order to study the effect of substituents at the ortho- (or 3-) position of thearomatic rings on the coordination properties of the N403 amine phenol ligands towardslanthanide metal ions, and to force the two halves of the [Ln(5-Xaea)]2dimers apart, anew amine phenol ligand, tris(ft2-hydroxy-3-methoxybenzyflamino)ethyl)amine (H33-MeOaea)) has been prepared, where the 3-substituents of the phenyl rings are methoxygroups. In this chapter, the synthesis, structures, and characterization of H3(3-MeOaea)NHçoP3— NtrenpyR1trenpyrol H3tracR2N3c1g R1R,H3aea: R1=R2HH3saltren: R1 = R2 H (5-Claea): R1= H R2= ClH3hatren: R1CH3R2H H3(5-Braea): R1=H R2=BrH3datren: R1 = CH3 R2= CH3 (3-MeOaea): R1 = OMe R2= HChart 2.116Chapter II H3(3-MeOaea) Ligand Systemand its capped, [Ln(H3(3-MeOaea))(N03)3] (Ln = Pr, Nd), and bicapped, [Ln(H3(3-MeOaea))2](N03)3 (En = Pr, Nd, Gd, Yb) complexes, will be described.2.2 Experimental SectionMaterials. Hydrated lanthanide salts, tris(2-aminoethyl)amine (tren), potassiumborohydride, and o-vanillin were obtained from Aldrich or Alfa and were used withoutfurther purification.Instrumentation. NMR spectra (200 Mz and 500 Mz) were recorded on BrukerAC-200E(1H- COSY and APT 13C NMR) and Varian XE 500 (H, 13C, 1H-3Cheteronuclear correlation) spectrometers, respectively. Chemical shifts in ppm arereported as 6 downfield from TMS; assignments were based on ‘H - 1H COSY and 1H -‘3C heterocorrelation spectra with the attached proton test (APT). Mass spectra wereobtained with either a Kratos MS 50 (electron-impact ionization, El) or an AEI MS-9(fast-atom-bombardment ionization, FAB) instrument. Only the most intense peaks in anisotopic envelope are listed; appropriate isotopic ratios were seen where multiple isotopeswere present. Infrared spectra were recorded as KBr disks in the range 4000-400 cm1 ona Perkin-Elmer PE 783 spectrometer and were referenced to polystyrene. Melting pointswere measured on a Mel-Temp apparatus and are uncorrected. Analyses for C, H, N wereperformed by Mr. Peter Borda in this department.X-ray Crystallography. All of the crystal structures reported in this thesis weredetermined by Dr. Steven J. Rettig of the UBC structural chemistry laboratories. For thetables of selected crystallographic data of [Pr(H3(3-MeOaea))2](N0)and [Gd(H3(3-MeOaea))2](N03),please refer to Tables A.l and A.2 in appendices.17Chapter II H3(3-MeOaea) Ligand SystemSynthesis of Ligands2.2.1 Tris((3-methoxysalicylideneimino)ethyl)amine (H3vantren).To a solution of o-vanillin (9.12 g, 60 mmol) in methanol (20 mL) was added tren(2.92 g, 20 mmol) in the same solvent (10 mL). The resulting orange solution was stirredfor 10 minutes while an orange yellow precipitate formed in an exothermic reaction.After the mixture cooled, the precipitate was filtered off, washed with diethyl ether, anddried in air. The yield was 9.85 g (93%), mp 133-134 OC (lit11 119-120 °C). Anal. calcd(found) forC30H6N406.5CHOH: C, 64.88 (65.12); H, 6.78 (6.79); N, 9.92 (9.81).Mass spectrum (El): m/z = 548 (Mt [C30H6NO]). JR (cm1,KBr disk): 3600-2200(br, VOH), 3000-2800 (w or m, VCH), 1635, 1480 (vs br, VCN and VCC). 1H NMR(CDC13,the atom labelling is the same as that of the amine phenols in Chart 2.1): 2.78 (t,6H, Ha); 3.46 (t, 6H, Hb); 3.80 (s, 9H, OCH3); 5.80 (d, 3H, Hg, 3JHH = 6.8 Hz); 6.48 (t,3H, Hh, 3JHH = 6.8 Hz); 6.80 (d, 3H, H1,3HH = 6.8 Hz); 7.75 (s, 3H, He); and 14.20 (brs, 3H, OH). 13C NMR (CDC13): 55.8 (Cb); 56.0 (OCH3); 57.1 (Ca); 113.6 (C1); 117.3(Ch); 118.1(Cd); 123.4 (Cg); 148.4 (C; 152.6 (Ce); 166.2 (Cc).2.2.2 Tris(((2-hydroxy-3-methoxybenzyl)amino)ethyl)amine(H33-MeOaea))To a solution of H3vantren (5.48 g, 10 mmol) in methanol (100 mL) was addedKBH4 (2.12 g, 40.0 mmol) in small portions over 30 mm. After the addition wascomplete (the orange color disappeared and the solution was colorless or pale yellow), thereaction mixture was stirred for an additional hour. The solvent was removed underreduced pressure and the residue was taken up with chloroform (250 mL), washed with10% NH4OAc solution (100 mL) and water. The organic fraction was separated anddried over anhydrous MgSO4. The solution was filtered and chloroform was removed ona rotary evaporator to give a pale yellow solid. The solid was dried overnight undervacuum. The yield was 4.35 g (85%) mp 42-45 oC. Anal. Calcd (found) for18Chapter II H3(3-MeOaea) Ligand SystemC30H42N06O.5CHC1:C, 59.63 (59.84); H, 6.97 (6.97); N, 9.12 (9.14). Mass spectrum(FAB): m/z = 555 ([M+1],[C30H43NO]). IR (cm1,KBr disk): 3600-2200 (br, VO..Hand vN4i), 3000-2800 (w or m, vc,H), 1590 (s, ÔNH); 1490-1420 (vs, VCC). ‘H NMR(CDC13): 2.50 (m, 6H, Ha); 2.64 (m, 6H, Hb); 3.80 (s, 9H, OCH3); 3.92 (s, 6H, He); 6.25(br s, 3H, OH/NH); 6.54 (d, 3H, H1,3HH = 6.8 Hz); 6.68 (t, 3H, Hh, 3JHH = 6.8 Hz), 6.75(d, 3H, Hg, 3J1IH = 6.8 Hz). 3C NMR (CDC13): 46.0 (Cb); 52.1 (Ce); 54.2 (Ca); 55.9(OCH3); 110.8 (Ca; 118.6 (CiJ; 120.7 (Cg); 123.1 (Cd); 147.2 (; 147.9 (Ce).Synthesis of Metal Complexes2.2.3 [Pr(H(3-MeOaea))(NO)J4O.To a solution of Pr(N03)5H20(417 mg, 1.0 mmol) in methanol (30 mL) wasadded H3(3-MeOaea) (556 mg, 1.0 mmol) in chloroform (10 mL); a precipitate formedimmediately. The reaction mixture was stirred for 2 hours. The precipitate was filteredoff, washed with ethanol and diethyl ether, and dried in air. The yield was 530 mg(56%). Anal. Calcd. (found) forC30H5N7O19Pr: C, 37.78 (37.59); H, 5.28 (4.97); N,10.28 (10.03). Mass spectrum (FAB): m/z = 819 (Pr(H3(3-MeOaeaD(NO3)2]), 693([Pr(H(3-MeOaea))]). JR (cnr1, KBr disk): 3700-2500 (br, vo,H); 1595 and 1570 (w,oN-H); 1380, 1280 (s, VN.O).2.2.4 {Nd(H(3-MeOaea))(NO]3HO’2C .A procedure similar to that for [Pr(H3(3-MeOaea))(N0]40was employedusing Nd(NO3)5H20(420 mg, 1.0 mmol) and H3(3-MeOaea) (556 mg, 1.0 mmol). Theyield was 730mg (73%). Anal. calcd. (found) forC3256N7dO20:C, 38.32 (38.12); H,5.63(5.30); N, 9.77 (9.53). Mass spectrum (FAB): mJz = 694 ([Nd(H(3-MeOaea))]j. JR(cm1,KBr disk): 3700-2500 (br, v.jj); 1595, 1570 (w, ON.H) 1380, 1280 (s, VN,O).19Chapter II H3(3-MeOaea) Ligand System2.2.5 [Pr(H3(3-MeOaea))](N0)’H0’5CO .To a solution of Pr(N03)5H20(210 mg, 0.50 mmol) in methanol (30 mL) wasadded H3(3-MeOaea) (556 mg, 1.0 mmol) in chloroform (10 mL); a precipitate formedimmediately. Upon addition of 2N NaOH (2.0 mL) dropwise, the precipitate redissolvedto give a clear solution. The solution was filtered immediately and the filtrate was leftstanding at room temperature; slow evaporation yielded microcrystals. These werecollected by filtration, washed with ethanol and diethyl ether, and dried in air. The yieldwas 435 mg (54%). Suitable crystals were selected for X-ray diffraction study. Anal.Calcd. (found) forC65H106N1O27Pr: C, 48.36 (48.37); H, 6.62 (6,51); N, 9.54 (9.17).Mass spectrum (FAB): rn/z = 1247 ([Pr(H2(3-MeOaea))2]), 693 ([Pr(H(3-MeOaea]).JR (cm1,KBr disk): 3700-2500 (br, voH); 1600, 1575 (w, SNH); 1385, 1285 (s, vNo).2.2.6 [Nd(H(3-MeOaea))1(N0)yO’6C0H.The complex preparation was similar to that for [Pr(H3 ( 3-MeOaea))2](N03)’H05CHOHusing Nd(N03)5H20(210 mg, 0.50 mmol) andH3(3-MeOaea) (556 mg, 1.0 mmol). The yield was 410mg (50%). Anal. Calcd. (found)forC66110N1dO28:C, 48.05 (48.23); H, 6.72 (6.66); N, 9.34 (9.08). Mass spectrum(FAB): m/z = 1249 ([Nd(H2(3-MeOaea))21) and 694 ([Nd(H(3-MeOaea))j). JR (cm-1,KBr disk): 3700-2500 (br, voH); 1600, 1575 (w, SN-u); 1380, 1285 (s, vNo).2.2.7 [Gd(H(3-MeOaea))](NO)y5O2CH.Method 1. A procedure similar to that for [Pr(H3(3-MeOaea))2](NO3)HO’5CHHwas employed using Gd(N03)6H20(225 mg, 0.50 mmol)and (3-MeOaea) (556 mg, 1.0 mmol). The yield was 470 mg (59%). Suitable crystalswere selected for X-ray diffraction study. Anal. Calcd. (found) forC62H102GdN 1028:C, 46.35 (46.33); H, 6.40 (6.24); N, 9.59 (9.26). Mass spectrum (FAB): m/z = 126220Chapter Ii H3(3-MeOaea) Ligand System([Gd(H23-MeOaea2]) and 710 ([Gd(H(3-MeOaeaD]j. JR (cm-1, KBr disk): 3700-2500 (br m, voH); 1600, 1575 (w, oN-H); 1388, 1288 (s, VNO).Method 2. Solutions of Gd(NO3)6H2O(225 mg, 1.0 mmol) in methanol (30mL) and of H3(3-MeOaea) (556 mg, 1.0 mmol) in chloroform (10 mL) were mixed and aprecipitate formed immediately. After stirring for 2 hours, the precipitate was filtered off,washed with ethanol and diethyl ether, and dried in air. The yield was 700 mg (60%).The product was shown by JR, PAB-MS and elemental analysis to be identical (withvarying solvation) to that obtained by method 1.2.2.8 [Yb(H3(3-MeOaea))](N0H04C .The complex was prepared similarly to [Gd(H3(3-MeOaeaD2](N03)5H20•2CHO using Yb(N03)5H20(225 mg, 0.50 mmol) and H3(3-MeOaea)(556 mg, 1.0 mmol). The yield was 500 mg (50%). Anal. Calcd. (found) forC64H106N1O28Yb: C, 46.57 (46.68); H, 6.47 (6.32); N, 9.33 (9.04). Mass spectrum(FAB): m/z = 1280 ([Yb(H3-MeOaea2]) and 726 ([Yb(H(3-MeOaea))]). JR (cm-1,KBr disk): 3700-2500 (br m, voH); 1600, 1576 (w, SNH); 1390, 1285 (s, vNo).Conversion of Capped to Bicapped SpeciesTo a suspension of [Ln(H3(3-MeOaeaD(N03)3] (Ln = Pr or Nd) in a mixture ofmethanol (30 mL) and chloroform (10 mL) was added 2N NaOH (2.0 mL) dropwise; thesuspension became clear and then cloudy. After stirring for 10 minutes, the mixture wasfiltered (the solid was shown by JR to be lanthanide hydroxide). The filtrate was leftstanding at room temperature; slow evaporation of solvents afforded a microcrystallineproduct. This product was collected by filtration, washed with ethanol and diethyl ether,and dried in air; it was shown by JR and elemental analysis to be identical (with varying21Chapter II H3(3-MeOaea) Ligand Systemsolvation) to that obtained from the reaction of the appropriate lanthanide nitrate withH3(3-MeOaea) in the presence of sodium hydroxide.Attempted Conversion of Bicapped to Encapsulated Species.Solutions of Gd(N03)5H20(225 mg, 0.50 mmol) in methanol (30 mL) and ofH3(3-MeOaea) in chloroform (10 mL) were mixed. Upon addition of 2N NaOH (3.0 mL)dropwise, the cloudy solution went clear. The solution was filtered and the filtrate wasleft standing at room temperature. After 3-4 hours a small amount of microcrystallinesolid formed. The solid was separated by filtration, washed with methanol and dried inair. The product was shown by JR. FABMS and elemental analysis to be theencapsulated complex, [Gd(3-MeOaea)]4H20. Anal. Calcd. (found) forC30H47GdNO1:C, 46.14 (46.22); H, 6.07 (5.63); N, 7.17 (6.93). Mass spectrum(FAB): m/z = 732 ([NaGd(3-MeOaea)]j. JR (cm1,KBr disk): 3700-2500 (br m, vo.jj);3240 (m, vNH); 1595, 1570 (w,8N-H). The filtrate and washings above were combined;further evaporation afforded microcrystals, which were shown by elemental analysis to bea mixture of encapsulated and bicapped complexes.2.3 Results and Discussion2.3.1 Synthesis and Characterization of LigandsThe Schiff base H3vantren was prepared from the reaction of tren with 3 equiv ofo-vanillin (Scheme 2.1) and was readily characterized. The IR spectrum contained astrong band at 1630 cm1, characteristic of imine C=N bonds of Schiff bases. Althoughthe preparation of this compound has been reported,11 there were some discrepanciesbetween the properties of that substance and the material described herein.22Chapter II H3(3-MeOaea) Ligand SystemNH2MeOH KBH4 M4OH OH MeOH OHOCH3 OCH3 OCH3Scheme 2.1.The KBH4 reduction of the Schiff base produced the amine phenol (H33-MeOaea)). The new compound was soluble in polar solvents such as chloroform andmethanol, and was hydrolytically stable under both basic and acidic conditions. Theanalytical and spectral data were completely consistent with the proposed formulation.The JR spectrum of H3(3-MeOaea) showed the disappearance of the characteristic imineC=N band at 1630 and the appearance of a new band at 1590 from N-Hbending vibrations. The ‘H NMR spectrum (in CDC13)showed the presence of benzylichydrogen signals at —4 ppm instead of the imine CH=N hydrogen signals at -8 ppm.These observations confirmed that the C=N bonds were reduced to CH2-N aminelinkages.2.3.2 Synthesis and Characterization of Metal ComplexesUnlike the reactions ofN403 Schiff bases (H3trac, H3hatren and H3datren)7’8andthree other N403 amine phenols (H3aea, H3(5-Claea), H3(5-Braea)),’0reactions ofH3(3-MeOaea) with Ln3 in the presence of 3-4 equiv of sodium hydroxide or acetateproduced a new type of six-coordinate bis-ligand lanthanide complex (bicapped in Chart23Chapter II H3(3-MeOaea) Ligand System2.2) with a formulation of [Ln(H3(3-MeOaeaD2] N0)(En = Pr, Nd, Gd, Yb). In thepresence of 6-8 equiv of sodium hydroxide, the reaction of H3(3-MeOaea) withGd(N03)6H20produced a small amount of encapsulated complex [Gd(3-MeOaea)Jfirst, and then a mixture of both encapsulated and bicapped complexes. No analyticallypure encapsulated complexes, [Ln(3-MeOaea)j, were isolated from the similar reactionsfor Pr, Nd or Yb. When more sodium hydroxide (>10 equiv) was employed, lanthanidehydroxide precipitated. All bicapped complexes were characterized by elementalanalysis, IR, FABMS and, for [Pr(H3(3-MeOaea)’)2]and [Gd(H3(3-MeOaea))2],byX-ray crystallography.bicappedChart 2.2As was found with some Schiff bases7’8 and the other three amine phenols(H3aea,H3(5-Claea),H3(5-Braea)),1°reactions of H3(3-MeOaea) with 1 equiv of alanthanide nitrate salt in the absence of base produced capped complexes with aformulation [En(H3(3-MeOaea))(N0)](En = Pr, Nd). Bicapped complexes, [Ln(H3(3-MeOaea2](NO3)3 for En = Gd and Yb, were isolated under similar conditions. Thiswas probably caused by the smaller sizes of Gd3+ and Yb3+. The capped complexes are24Chapter II F13(3-MeOaea) Ligand Systemquite air-stable and were easily converted to bicapped complexes by reaction with 3-4equiv of sodium hydroxide. The capped complexes most likely have a nine-coordinatestructure very similar to that which was found and structurally characterized in[Yb(H3trac)(N0)].8The spectral (JR and FAB) and analytical data were completelyconsistent with the indicated formulations.The encapsulated complex [Gd(3-MeOaea)] showed JR bands at 3240 cm-’ and1595 cm-’ from N-H stretching and bending vibrations, respectively, of the coordinatedsecondary amine groups. Bicapped complexes showed N-H stretches, which arecharacteristic of the hydrogen bonded N-H---O portions of the ligand, and JR bands at1380 and 1280 cm-’ from nitrate anions (vN,o). These were absent in the encapsulatedmononuclear and dinuclear complexes. New bands appeared below 600 cm-1 in thespectrum of each coordinated ligand and are difficult to assign because of the lowenergies associated with these vibrations.The FAB mass spectra of encapsulated, capped, and bicapped complexes wereobtained in a 3-nitrobenzyl alcohol matrix in the positive detection mode. The FABspectrum of [Gd(3-MeOaea)] showed a molecular ion peak at m/z = 710 from [Gd(H(3-MeOaea))] without trace of a dimer peak from [Gd(3-MeOaea)]2. This clearlyestablished the monoligand nature of this complex. Jn the FAR spectra of two cappedcomplexes, peaks from [Ln(H(3-MeOaea))] and [Ln(H(3-MeOaea))(NO weredetected. The FAB spectra of the bicapped complexes showed peaks from monoligandand bis(ligand) cations with no [Ln(H3(3-MeOaea))(NO)2]peaks as were seen in thespectra of the capped complexes. These observations suggest that the nitrate anions inthe bicapped complexes are uncoordinated and are consistent with the structural findingsfor [Ln(H3(3-MeOaea))2] (Ln = Pr and Gd).25Chapter II Hg(3-MeOaea) Ligand System2.3.3 Crystal Structures of[Pr(H3(3-MeOaea))21(N03)3 and[Gd(H(3-MeOaea))z](N03)3[Pr(H3(3-Me0aea))2] and [Gd(H3(3 -MeOaea) )2] are isomorphous andisostructural. The ORTEP drawing of [Gd(H3(3-MeOaeaD2] is illustrated in Figure2.1. It shows the numbering scheme followed in both structures. Selected bond lengthsand bond angles in [Ln(H3(3-Me0aeaD2] (Ln = Pr, Gd) are listed in Tables 2.1 and 2.2,respectively. In the unit cell there are four [Ln(H3(3-Me0aea))2](N0)moieties andmany partially occupied waters or methanols of solvation. The water and methanolsolvate molecules (5.56 and 0.44 for the Pr, 5.96 and 0.66 for the Gd derivative) aredisordered over nine different sites (only one of which - 0(12) - is fully occupied). Thecomplex cation [Ln(H3(3-Me0aeaD2] is centrosymmetric with the two amine phenolligands facially binding to the metal center in a slightly distorted octahedral coordinationgeometry. The coordinated amine phenol ligands are tridentate with three deprotonatedphenolate 0 atoms coordinating to the metal center and the three secondary amine Natoms protonated. The capping tertiary nitrogen NO) atom is ‘tucked in” with its lonepair of electrons pointed at the Ln atom. The three arms of one amine phenol ligand forma left-handed screw down the tertiary N-Ln axis while the three arms of the other aminephenol ligand form a right-handed screw. Both intra-arm (average H---0 = 2.29 A for Prand 2.30 A for Gd) and inter-arm (average H---0 = 2.13 A for Pr and 2.12 A for Gd)hydrogen bonds are observed in each coordinated amine phenol ligand, in which three Hatoms (HO), H(3) and H(5)) are oriented endo while the other three hydrogen atoms(H(2), H(4) and H(6)) are oriented exo. Each of the three endo oriented H atoms formboth intra-arm and inter-arm hydrogen bonds with two nearest phenolate 0 atoms whilethree exo oriented H atoms form intermolecular hydrogen bonds with the uncoordinatednitrate anions. Within each structure, the Ln-0 bonds are indistinguishable at the 3aconfidence level (average Ln-0 = 2.341 (4) A for Pr and 2.283 (5) A for Gd). Three trans26Chapter II 113 (3-MeOaea) Ligand SystemFigure 2.1. ORTEP view of the [Gd(H3(3-MeOaea))2] cation([Pr(H3(3-MeOaea))2] IS isostructural).C301.C27C28C291-14C 12CliClHZCaC34CsCs27Chapter II H3(3-MeOaea) Ligand SystemTable 2.1. Selected Bond Lengths (A) with Standard Deviations for[Pr(H3(3-MeOaeaD](N0)5.5600.44CH30H and[Gd(H(3-Meoaea))21(N05.96H20 0.66CH3H.[Pr(H3(3-Me0aea))2](N03)3 [Gd(H3(3-Meoaea))2](N0)5.56H20O.44CH30H •5.96H0•0.6 CHHPrO) - 0(1) 2.337 (2) Gd(l) - 0(1) 2.278 (2)PrO) - 0(3) 2.342 (4) Gd(1) - 0(3) 2.288 (3)PrO) - 0(5) 2.345 (2) Gd(1) - 0(5) 2.284 (2)0-Ln-O angles are crystallographically dictated to be 1800 in each complex cation. Theintra-ligand 0-Ln-0 angles average 83.3 (1.4)° for Pr and 84.4 (l.O)° for Gd while theinter-ligand 0-Ln-0 angles average 96.7 (1 .4)° for Pr and 95.6 (1 .0)° for Gd. Theshrinking of the intra-ligand 0-Ln-0 angles is probably caused by inter-arm hydrogenbonding and the expansion of the inter-ligand O-Ln-0 angles by the crowding betweenthe two coordinated amine phenol ligands. The chemical compositions of the twocomplexes that are derived from the X-ray analyses are in very good agreement withmicroanalytical data for the batches of crystals employed in the structure determinations.2.3.4 Possible Conversion between Different Conformational Species.We recently reported several potentially heptadentate Schiff base ligands (H3trac,H3hatren and H3datren) and their lanthanide complexes.7’8 These ligands were eithertridentate in capped complexes, [Ln(H3L)(N0](H3L = H3trac, H3hatren andH3datren), or heptadentate in encapsulated complexes, [Ln(L)J (L = trac3, hatren3 and28Chapter ii H3(3-MeOaea) Ligand SystemTable 2.2. Selected Bond Angles (°) with Standard Deviations for[Pr(H3(3-MeOaeaD](N0)5.5600.44CH30H and[Gd(H(3-MeOaeaD]( 05.9600.66CH3 Hf1[Pr(H3(3-MeOaeaD2](N03)3 [Gd(H(3-Me0aea] NO3)y5.56H200.44CHH 5.96H200.6 CHH00) - PrO) 00)’ 180.0 00) - Gd(1) 0(1)’ 180.000(1)-Pr(1)0(3) 82.4(1) 0(1)-Gd(1)0(3) 83.90)00)— PrO) 0(3)’ 97.6(1) 00)— Gd(1) 0(3)’ 96.1 (1)00) - PrO) 0(5) 84.9(1) 00) - Gd(1) 0(5) 85.63 (8)00) - PrO) 0(5)’ 95.1 (1) 00) - Gd(1) 0(5)’ 94.37 (8)0(3) - Pr(1) 0(3)’ 180.0 0(3)-Gd(1) 0(3)’ 180.000(3)- PrO) 0(5) 82.7 (1) 0(3) - Gd(1) 0(5) 83.80 (9)0(3)- PrO) 0(5)’ 97.30) 0(3) - Gd(1) 0(5)’ 96.209)0(5)- PrO) 0(3)’ 180.00 0(5) - Gd(1) 0(3)’ 180.00a Primes refer to symmetry operation (1/2 - x, 1/2-y, 1- z).datren3-), depending on the conditions of preparation. The N403amine phenols (H3aea,H3(5-Claea), H3(5-Braea)) also form two kinds10 of lanthanide complexes: capped (in theabsence of a base) and encapsulated dimer [Ln(L)]2 (L = aea3, 5-Claea 3, 5-Braea)(inpresence of sodium hydroxide). The amine phenol ligand (H3(3-Me0aea)) reported inthis study forms capped complexes, [Ln(H3(3-Meoaea))(N0](Ln = Pr, Nd), and six-coordinated bis(ligand) bicapped complexes, [Ln(H3(3-Me0aea))2] N)(Ln = Pr, Nd,Gd, Yb) depending on the conditions of preparation. These results clearly show that the29Chapter II H3(3-MeOaea) Ligand System3-methoxy groups of the phenyl rings have a profound influence on the coordinationbehavior of the N403 amine phenol ligands towards lanthanide metal ions.Because of the large size of the Ln3 ions, the binding between lanthanide metalsand donor atoms is predominantly ionic in character, and the cations display a strongpreference for negatively charged 0 donor ligands.12 Therefore it is not unexpected thatthe two amine phenol ligands in [Ln(H3(3-MeOaeaD2](N0)coordinate to the metal ionwith only phenolate 0 donors. Furthermore, coordination numbers of lanthanidecomplexes are generally high and stereochemistries are largely determined by the stericrequirements of the coordinated ligands.’2 In these bicapped complexes [Ln(H3(3-MeOaeaD2](N03),the coordination geometry around the metal center is a trigonallydistorted octahedron. The steric hindrance from the 3-methoxy groups of the twocoordinated amine phenol ligands prevents the approach of other 0 donor ligands such asH20 and thus six-coordinated bis-ligand bicapped complexes, [Ln(H3(3-MeOaeaD2](N03)3, were enforced. Furthermore, the interstrand H-bonds highly stabilizebicapped complexes, which makes conversion from bicapped to either encapsulated orencapsulated dimeric complexes very difficult.In H3aea,H3(5-Claea), and H3(5-Braea), the 3-substituents of the phenyl rings arehydrogens. The capped complexes [Ln(HL)(N0](H3L = H3aea, H3(5-Claea), H3(5-Braea)) can be easily converted to encapsulated dimeric complexes [Ln(L)]2by adding3-4 equiv of a base (acetate or hydroxide). The formation of dinuclear complexes doesnot cause significant crowding between the two coordinated amine phenol ligands. InH3(3-Meoaea), the hydrogen atoms at 3-positions of the phenyl rings are replaced bythree bulky methoxy groups. If (3-Me0aea) were to coordinate to the metal atom as aheptadentate ligand like trac3 in [Yb(trac)]7 or (aea)3 in [Gd(aea)]2,’° the sterichindrance between the methoxy groups in the same ligand in [Ln(3-Meoaea)j wouldweaken the bonding between phenolate 0 atoms and the metal center while the crowding30Chapter II H3(3-MeOaea) Ligand Systembetween the methoxy groups in two amine phenol ligands in [Ln(3-MeOaea)]2preventsformation of a dinuclear structure. Therefore, the capped complexes [Ln(H3(3-MeOaeaD2](N03)3 cannot be easily converted to either encapsulated [Ln(3-MeOaea)j orencapsulated dimeric complexes [Ln(3-MeOaea)]2under similar conditions.The steric effects of three methoxy groups are also seen in the reaction of alanthanide nitrate with 1 equiv ofH3(3-MeOaea). For large metal ions such as Pr3(ionic radii13: 0.99 A and 1.13 A for 6 and 8 coordination, respectively) and Nd3 (ionicradii13: 0.98 A and 1.11 A for 6 and 8 coordination, respectively), the coordination of atridentateH3(3-MeOaea) to the metal center does not cause significant crowding betweenthe three 3-methoxy groups and the three bidentate nitrate anions; capped complexes[Ln(H3(3-MeOaeaD(N0)3](Ln = Pr and Nd) are formed. For Gd3 (ionic radii13: 0.94A and 1.05 A for 6 and 8 coordination, respectively) and Yb (ionic radii: 0.87 A and0.985 A for 6 and 8 coordination, respectively), the steric hindrance from 3-methoxygroups prevents the approach of all three bidentate nitrate anions. Therefore, thecoordination of the second tridentate H3(3-MeOaea) becomes favorable and six-coordinated bis-ligand complexes [Ln(H(3-MeOaea))2](N0)(Ln = Gd, Yb) areformed.References.(1) Kirchner, R. M.; Mealli, C.; Bailey, M.; Howe, N.; Tone, L. P.; Wilson, L. J.;Andrews, L. C.; Rose, N. J.; Lingafelter, E. C. Coord. Chem. Rev. 1987, 77, 89.(2) Wilson, L. J.; Rose, N. J. J. Am. Chern. Soc. 1968, 90, 6041.(3) Alcock. N. W.; Cook, D. F.; McKenzie, E. D.; Worthington, J. M. Inorg. Chim.Acta. 1980, 38, 107.31Chapter II H3(3-MeOaea) Ligand System(4) Malek, A.; Dey, G. C.; Nasreen, A.; Chowdhury, T. A.; Alyea, E. C. Synth. React.Inorg. Met. -Org. Chem. 1979, 9, 145.(5) Cook, D. F.; Cummins, D.; McKenzie, E. D. J. Chem. Soc. Dalton. 1976, 1369.(6) Sim, P. G.; Sinn, E. lnorg. Diem. 1978, 17, 1288.(7) Berg, D. J.; Rettig, S. J.; Orvig, C. J. Am. Chem. Soc. 1991, 113, 2528.(8) Smith, A.; Rettig, S. J.; Orvig, C. Jnorg. Chem. 1988, 27, 3929.(9) Alyea, E. C.; Malek, A.; Vougioukas, A. E. Can. J. Chem. 1982, 60, 667.(10) Liu, S.; Gelmini, L.; Rettig, S. J.; Thompson, R. C.; Orvig, C. I Am. Chem. Soc.1992, 114, 6081.(11) Rothin, A. S.; Banbery, H. J.; Berry, F. J.; Hamor, T. A.; Jones, C. J.; MeCleverty,3. A. Polyhedron 1989, 8,491.(12) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon Press:Oxford, England, 1984.(13) Shannon, R. D. Acta Crvst. 1976, A32, 751.32Chapter III ll3XapL/H(1,2,4-ahi) Ligand SystemChapter III Potentially Heptadentate N403 Imidazolidine-containingSchiff Bases and N403 Amine Phenols: Influence of Backbone Rigidityon Compound Structure3.1 IntroductionHigh stability is an important prerequisite for potential MM contrast agents in orderto resist acid or cation mediated decomplexation. Tris(2-aminoethyl)amine is a tripodalspacer; when it reacts with chelating pendants to form N403 Schiff bases, the three armsare bridged by a nitrogen atom which can undergo an “umbrella” type inversion.1 Thismay be the main cause of the low stabilities of lanthanide-Schiff base complexes. Inorder to explore potential lanthanide complex stability as a function of rigidity in theligand and to enforce a specific spatial arrangement of donor atoms in the uncomplexedstate, we have taken advantage of the known27 imidazolidine ring formation reaction(shown in Scheme 3.1 on page 43) to prepare the N403 Schiff bases based on the H3Xapiframework (H3api,H3Clapi, H3Brapi - see list of abbreviations and Chart 3.1). Theseligands are potentially heptadentate but should have their chelating arms spread wide toallow for bridging of two metal ions. H3api has been reported previously,47ironically asa nuisance by-product of a side-reaction in Schiff base formation with multidentateamines. When H3api coordinated to metal ions such as Co(ffl), Fe(llI), Mn(llI), Ga(llI),Al(III), Co(II), Ni(II), Cu(II) in a 1:1 ratio,6’7 it was found that one molecule ofsalicylaldehyde split off to decrease the steric constraints of the ligand around the metalion and an N402 chelate formed. It was also reported that no arm was lost if a 2:1 ratiowas employed for Fe(III).4 Studies on its sulfonated analog3 and evaluation of itsmethoxy-substituted analog as a potential 68Ga radiopharmaceutical for myocardialimaging2 have also been performed. In order to have a better understanding of the33Chapter III H3XapIJH(1,2,4-ahi) Ligand Systemcoordination chemistry and the steric effects of this ligand, a series of the lanthanidecomplexes of this Schiff base and its isomeric amine phenol reduction products havebeen characterized. The complexes of chloride- and bromide-substituted Schiff baseswere also examined in order to facilitate crystallization and handling.(L:M)I\N ‘ -Nt“O-nç -—‘b9M = transition metal ionsIn this chapter, the first structurally characterized homodinuclear complex[La(Brapi)]2in which two identical ligands together form two compartments to give asandwich LM2 structure is presented, as well as the novel conversion of a complex inwhich a tridentate capped ligand spontaneously incorporates two lanthanide ions into the2:2 Ln:L sandwich species, a conversion which shows that these sandwich Schiff basecomplexes are very stable (at least kinetically). Schiff base complexes have been studiedextensively since it is recognized that many complexes of this type with NO donor setsmay serve as models for biologically important metal-containing species;8 however, instudies of dinuclear complexes, the emphasis has been mainly on macrocyclic ligands,macrocycles with one open side (one-side-off or end-off compartmental ligands), or/\N34Chapter III H3Xapi/H3(1, 2,4-ahi) Ligand Systempolypodal ligands.8 Although several crystal structures of homodinuclear lanthanidecomplexes have been reported,915 none of them has the sandwich structure.X=H H3apiH3Xapi X = Cl H3ClapiX = Br H3BrapiH3(1 ,2,4-ahi)3.2 Experimental SectionI’NH HNNH NHOOH /\Materials and Methods. Hydrated lanthanide salts, thethylenetetramine hydrate(trien), potassium borohydride, salicylaldehyde, 5-chlorosalicylaldehyde, and 5-bromosalicylaldehyde were purchased from Aldrich or Alfa and were used withoutfurther purification.I’r N’ThHNHO-7H3(1 ,2,4-btt)OH\/Chart 3.1H3(l,1,4—btt)35Chapter 1ff H3Xapi/H3(L2,4-ahi) Ligand SystemNMR spectra (200, 400, and 500 MHz) were recorded on Bruker AC-200E(1H-COSY and APT 13C), Bruker WH-400(1H- COSY), and Varian XL 500 (1H, 13C, and‘H-’3C heteronuclear correlation) spectrometers, respectively. NMR data were reportedas 6 (ppm) downfield from external TMS or internal solvent. Mass spectra were obtainedwith a Kratos MS 50 (electron-impact ionization, El), a Kratos Concept II H32Q (Cstliquid secondary ion mass spectrometry, LSIMS), or an AEI MS-9 (fast atombombardment, FAB) instrument. UV/VJS spectra were recorded on a Shimadzu UV2100 spectrometer.X-ray Crystallography. For the tables of selected crystallographic data, andfractional coordinates ofH3api, [La(Brapi)]2and Yb(l,2,4-btt), please refer to Tables A.3- A.8 in appendices.Syntheses of Ligands.3.2.1 2-(2’-Hydroxyphenyl)-1,3-di[3’-aza-4’-(2”-hydroxyphenyl)-prop-4’-en-1’-yl]-1,3-imidazolidine (H3api).This was synthesized by a literature preparation5with some modification. Asolution of 2.92 g (20 mmol) trien in 20 mL ethanol was added to a solution of 7.32 g (60mmol) salicylaldehyde in 10 mL ethanol. A bright yellow precipitate formedimmediately. The product was isolated by filtration, washed with diethyl ether and driedat room temperature for a yield of 6.8 g (75%), mp 101-103 OC. Anal. calcd (found) forC27H30N40:C, 70.72 (70.40); H, 6.59 (6.49); N, 12.22 (12.02). Mass spectrum (El):36Chapter III H3Xapi/H(1,2,4-ahi) Ligand Systemm/z 458 (M = H3apft). Infrared spectrum (cm-1, KBr disk): 1637 (vs, tCN), 1613,1585, 1500, 1485, 1465, 1420 (vs or s, vc=c). 1H and 13C NMR data are listed in Tables3.1 and 3.2, respectively. Recrystallization from methanol afforded X-ray qualitycrystals.3.2.2 2-(2’-Hydroxy-5’-chlorophenyl)-1,3-di[3’-aza-4’-(2”-hydroxy-5”-chlorophenyl)-prop-4’-en-i’-yI]-i,3-imidazolidine(H3CIapi).A solution of 2.92 g (20 mmol) trien in 20 mL ethanol was added to a hot solutionof 9.36 g (60 mmol) 5-chiorosalicylaldehyde in 100 mL ethanol. A yellow precipitatedeposited at once. The suspension was cooled in an ice bath. The product was filteredout, washed with diethyl ether and dried at room temperature yielding 8.8 g (79%), mp150-152.5°C. Anal. calcd (found) forC27H13N40:C, 57.71 (57.40); H, 4.84 (4.88);N, 9.97 (9.73). Mass spectrum (EU: ,n/z 561 (M =H3C1api). Infrared spectrum (cm-1,KBr disk): 1647 (s, UCN), 1585, 1486, 1455 (m or s, uc=c,). ‘H and ‘3C NMR data arelisted in Tables 3.1 and 3.2, respectively.3.2.3 2-(2’-Hydroxy-5’-bromophenyl)-i,3-di[3’-aza-4’-(2”-hydroxy-5”-bromophenyl)-prop-4’ -en-i’ -yI]-i,3-imidazolidine (H3Brapi).This was synthesized by the procedure outlined above forH3(Clapi) using trien(2.92 g, 20 mmol) and 5-bromosalicylaldehyde (12.12 g, 60 mmol). The yield was 10.7 g(77%), mp 149-152°C. Anal. calcd. (found) forC27HBr3N4O:C, 46.64 (46.58); H,3.91 (3.96); N, 8.06 (8.11). Mass spectrum (ED: tn/z 696 (M = H3Brapij. Infraredspectrum (cm1,KBr disk): 1635 (s, vCN), 1575, 1480, 1443 (all m or s, tcc). 1H and13C NMR data are listed in Tables 3.1 and 3.2, respectively.37Chapter III H3Xapi/H(1,2,4-ahi) Ligand System3.2.4 1-(2’-Hydroxybenzy))-2,2-dimethyl-3-[3’,6’-diaza-3’-(2”-hydroxybenzyl)-7’-(2”-hydroxyphenyl)-heptyl]-1,3-imidazolldine(H1,2,4-ahi)).To a suspension of 6.8 g (15 mmol) H3api in 20 mL methanol was added 2.7 g (50nimol) potassium borohydride in small portions over 30 minutes. The Schiff basedissolved gradually. Continued stirring for another 30 minutes ensured that the yellowcolor disappeared completely. The solution was rotary-evaporated to near dryness; to theresidue was added a solution of 5.2 g ammonium acetate in 50 mE water. The mixturewas extracted with chloroform (2 X 200 mL). The organic fractions were combined,washed with water (2 X 100 mE), dried over 16 g anhydrous magnesium sulfate for 30minutes, and clarified by filtration. Rotary-evaporation of the solvents resulted in oilyproducts, which were converted into a pale yellow solid by trituration with acetone. Theyield was 1.5 g (20 %), mp 86-88.5 oC. Anal. calcd. (found) forC30H4NOy1/2H20: C70.15 (70.26), H 8.04 (7.93), N 10.91 (10.93). Infrared spectrum (cm-1,KBr disk): 3700-2100 (br 5, VNH, o-H) 1615(m), 1595(s) (SN-H); 1490(vs), 1460(s) (tc=c). 1H NMR(CDC13): 7.24-6.65 (m, phenyl, 1211); 3.82 (s, benzyl H, 2H); 3.72 (s, benzyl H, 2H);3.70 (s, benzyl H, 2H); 2.81(s) and 2.68(d) (NCH2CH, 12H); 1.18 (s, CH3 6H). Thesimplified resonances for the backbone hydrogens and benzylic hydrogens suggested thatthe compound was a mixture of acetone adducts ofH3(1,2,4-btt) (which was proven byX-ray structures, vide infra) and by-productH3(1,1,4-btt).’6 Mass spectrum (FAB): rn/z506 (M = mixture of [H4(1,2,4-ahi)] and [H41,1,4-ahi)1), 465 (M = mixture of[114(1 ,2,4-btt)] and [114(1,1 ,4—btt)]).In order to obtain an NMR spectrum of the purified ligand H3(1,2,4-btt),decomposition of the complex Yb(1,2,4-btt) was employed. Yb(1,2,4-btt) 0.0308 g wasdissolved in 9 mL 11Cl (0.1 M) and trisodium phosphate (0.145 g) in a small amount ofwater was added; a white precipitate formed immediately. This solid was removed by38Chapter III H3Xapi/H3(1,2,4-ahi) Ligand Systemfiltration and washed with chloroform. The aqueous solution was extracted withchloroform (3 X 15 mL), and the organic fractions were combined and dried overanhydrous magnesium sulphate for 15 minutes. Rotary-evaporation of the solvent gave ayellow oil of pure H3(1 ,2,4-btt). 1H NMR (CDC13): 7.34-6.71 (m, phenyl, 12H); 5.42 (brs, OH, 3H); 3.96 (s, benzyl H, 2H); 3.77 (s, benzyl H, 2H); 3.68 (s, benzyl H, 2H); 2.72-2.60 (m, NCH2CH, 12H). Reaction of acetone with the pureH3(l,2,4-btt) gave thepureH3(1,2,4-ahi). 1H NMR (CDC13): 7.2-6.6 (m, phenyl, 12H); 4.00-3.54 (m, benzylH, 6H); 2.92-2.42 (m, NCFT2CH, 12H); 1.22 (s, CH3 3H); 1.12 (s, CH3 3H).Syntheses of Lanthanide Complexes.Since many of the syntheses were similar, detailed procedures are given only forrepresentative examples. All lanthanide complexes and their analytical data are listed inTable 3.3. JR spectral and mass (FAB or LSIMS) spectral data are reported in Tables 3.4and 3.5, respectively. 1H NMR data for [La(Xapi)]2 are reported in Table 3.6.3.2.5 [Ln(Xapi)]. mH2O.Method 1. A solution of H3Xapi (0.5 mmol) in 20 mL chloroform was added to asolution of Ln(N03)ynH2O(0.5 mmol) in 100 mL methanol. The mixture wasneutralized with 0.35 g sodium acetate (excess). The solution was kept at roomtemperature for several days while tiny crystals formed; the solvent was then decanted.The product was rinsed with water, ethanol and diethyl ether, and dried at roomtemperature, mp > 200 OC dec. Only the lanthanum complexes were soluble inchloroform. The mass spectra of the other [Ln(Xapi)]2mH2Ocomplexes could not beobtained because of their low solubilities in common solvents or matrices. The infraredspectra of the [Ln(Xapi)]2mHOcomplexes were almost superimposable in the 1400-1700 cm1 region with that of [La(Xapi)]2. Crystals of [La(Brapi)12suitable for X-ray39Chapter III H3Xapi/H3(L2,4-ahi) Ligand Systemdiffraction were obtained by dissolving the pure complex in chloroform and inducingcrystallization by the diffusion of methanol.Method 2. A solution of H3Xapi (0.5 mmol) in 20 mL chloroform was added to asolution of Ln(N03)nHO(0.5 mmol) in 100 mL methanol. The solution was kept atroom temperature for about one week and the solvent was then decanted. The solidproduct formed was rinsed with water, ethanol and diethyl ether, and dried at roomtemperature. Characterization showed these products to be identical to those obtained bymethod 1.3.2.6 [La(HXapi) N0)].To a solution of the respective ligandH3Xapi (0.5 mmol) in 10 mL chloroform wasadded dropwise a solution of La(N03)6H20(0.5 mmol) in 10 mL methanol. Themixture was poured into 100 mL diethyl ether and the yellow solid precipitatedimmediately. The product was washed with chloroform, and diethyl ether, and dried onvacuum line at 60 OC for one week, mp > 200 OC dec.3.2.7 [Ln(H3Xapi)(NO3)3].mHO (En = Gd, Yb).To a solution of Ln(N03)mH2O(0.5 mmol) in 10 nt methanol was added asolution ofH3Xapi (0.5 mmol) in 10 mL chloroform and a yellow powder precipitated atonce. The product was isolated by filtration, washed with chloroform and diethyl ether,and dried at room temperature, mp > 200 OC dec. The infrared spectra of theLn(H3Xapi)(N03)3 complexes were almost superimposable in the 1400-1700 cm’ regionwith that of La(HXapi)(N0. The complexes were insoluble in chloroform, andslightly soluble in methanol and ethanol; they demetallated in DMSO.40Chapter III H3XapiIH(1,2,4-ahi) Ligand System3.2.8 {N, N’, N” ‘-Tris(2-oxobenzyl)triethylenetetraamine}ytterbium(III)Yb(1,2,4-btt).A solution of 0.25 g (0.5 mmol) of the product of the KBH4 reduction of H3api (amixture ofH3(l,1,4-ahi) andH3(l,2,4-ahi)) in 20 mL chloroform was mixed with asolution of 0.22 g (0.5 mmol) Yb(N0-5H0in 25 mL methanol. The solution becamecloudy on the addition of a solution of 0.06 g NaOH, and was filtered immediately.Keeping the solution at room temperature for several days yielded colorless, plate-likecrystals suitable for X-ray diffraction. The solvent was decanted, and the product wasdried with diethyl ether, mp > 200 OC dec. The infrared spectra of the Ln(l,2,4-btt)complexes were almost superimposable in the 1400-1700 cm-’ region with that ofYb(1,2,4-btt). The solubilities of the complexes in common organic solvents were so low(jiM) as to be observed only by UV/VIS.3.2.9 [Ln(H(1,2,4-btt))(N0.To a solution of Ln(N03)nH2O(0.5 mmol) in 10 mL methanol was added asolution ofH3(1,2,4-ahi) (0.5 mmol) in 10 mL methylene chloride. Upon adding diethylether, a white powder precipitated at once. This product was isolated by filtration,washed with methylene chloride and diethyl ether, and dried in vacuo at 60 OC for oneweek, mp > 200 OC dec. The infrared spectra of theLn(H3(1,2,4-btt))(N0)complexeswere almost superimposable with that ofLa(H3(1,2,4-btt))(N0)in the 1400-1700 cm1region. The complexes were insoluble in chloroform, methylene chloride, and somewhatsoluble in methanol.41Chapter III H3Xapi/11(1,2,4-ahi) Ligand SystemSpontaneous Conversion of Capped, Mononuclear Schiff Base Complexes toSandwich, Dinuclear Schiff Base Complexes.All the sandwich complexes can be obtained through the spontaneous conversion ofcapped species to sandwich dimer, only representative spectra are given in Figures 3.2and 3.3. Gd(Hapi)(N0)was dissolved in methanol (0.3 mM) and the solution wasmonitored over seven days at room temperature in the range 240-600 nm.3.3 Results and Discussion3.3.1 Synthesis and Characterization of Ligands.Three potentially heptadentate Schiff bases were prepared by the condensation oftrien with 3 equiv of salicylaldehyde or 5-substituted salicylaldehyde (Scheme 3.1). Amixture of the isomeric amine phenolsH3(1,2,4-btt) andH3(1,1,4-btt) was obtained bythe KBH4 reduction of H3api. PureH3(1,2,4-btt) was obtained by the decompositon ofits Yb complex.The 1H and 13C NMR data for the three Schiff bases are given in Tables 3.1 and 3.2and the 1H NMR spectrum ofH3Clapi is shown in Figure 3.1. 1H and 13C NMR spectralassignments for the Schiff bases were based on 1H- COSY and1H-3C heteronuclearcorrelation with the attached proton test (APT). Analytical data were consistent with theproposed formulations. Infrared spectra of the Schiff bases showed peaks around 1640cm1, characteristic of imine C=N bonds. It is noted that in these Schiff bases, fivemembered imidazolidine rings were formed at the backbone after the condensation andthat the middle arm was therefore unique from the other two arms (clearly shown in the42Chapter III H3XapifH3(L2,4-ahi) Ligand SystemH 0OH+3xa) KBH4b) NH4OAcX= H, CL BrNHI\rN HN\HOOH HOH3(1,2,4—btt)Me2COH3(1 ,2,4-ahi)HOScheme 3.1OH\/H2N NH NH 2EtOHH3XapixH3apiI’H3(1,1,4—btt)(by-product)43Chapter III H3Xapi/H3(J,2,4-ahi) Ligand SystemTable 3.1. 1H NMR Dataa for the Various Schiff Bases (in CDC13)x1X= H, Cl, BrSH3api H3Clapi H3Brapi assignt3.41(m, 2H) 3.40(m, 2H) 3.39(m, 2H) 1eq b2.65(m, 2H) 2.66(m, 2H) 2.65(m, 2H) H1 b2.95(m, 2H) 2.93(m, 2H) 2.93(m, 2H) 2eq b2.62(m, 2H) 2.64(m, 2H) 2.64(m, 2H) H2’ b3.570, 4H)3.82(s, H)8.23(s, H)3.570, 4H)3.77(s, H)8.15(s, H)3.560, 4H)3.76(s, H)8.14(s, H)H3H4H57.19(d, 2H) 7.16(s, 2H) 7.29(s, 2H) H76.84(t, 2H) H87.27(1, 2H) 7.22(d, 2H) 7.34(d, 2H) H96.92(d, 2H)6.98(d, H)6.85(d, 2H)6.94(s, H)6.81(d, 2H)7.07(s, H)H10H136.79(m, H)7.220, H) 7.14(d, H) 7.27(d, H)H14H153567158944Chapter III H3XapLIH(1,2,4-ahi) Ligand System6.79(m, H) 6.66(d, H) 6.61(d, H) H1610.65(br s, H) 10.42(br s, H) 10.42(br s, H) OH1913.20(br s, 2H) 13.06(br s, 2H) 13.09(br s, 2H) OH18a Recorded at 500 MHz. b Assignments of axiaL/equatorial hydrogens are tentative.1H NMR spectra). Two phenolic OH resonances were observed at about 10 and 13 ppmin a 1:2 ratio. These two downfield signals can be explained by the intramolecularhydrogen bonding of the phenolic OH with an unsaturated azomethine nitrogen or tertiarynitrogen which causes a decrease in the shielding at the hydroxy hydrogen. However theOH resonances on the terminal arms are further downfield than that of the middle arm.The explanation is that, for the terminal arm, the O-H---N group lies coplanar with thearomatic ring (proven in the X-ray structure of H3api, vide infra), hence the proton isfurther deshielded by the induced aromatic ring current, as has been seen before in relatedstudies. 17Borohydride reduction of the unsubstituted Schiff base H3api suggested that thefinal pureH3(l,2,4-ahi) was the acetone adduct ofH3(l,2,4-btt) (the oily product, provenby ‘H NMR). This suggestion was supported by the FAB mass spectrum which showedtwo peaks, at in/z 506 (for [H4(l,2,4-ahi)]) and m/z 465 (for [H4(l,2,4-btt)J+). Theinfrared spectra showed the disappearance of the C=N band at 1637 cm-’ and theappearance of two new bands at 1595 and 1615 cm-’, due to N-H bending vibrations. The1H NMR data indicated the absence of CH=N hydrogen resonances at about 8 ppm andthe presence of new benzylic CH2 resonances at about 4 ppm, confirming the reduction ofthe unsubstituted Schiff bases.45Chapter Iii H3Xapi/Hç’1,2,4-ahi) Ligand SystemTable 3.2. 13C NMR Data” for the Various Schiff Bases (in CDC13) (the atomicnumbering is the same as that in Table 3.1)H3api H3Clapi H3Brapi assgnt51.1 51.0 51.0 C152.7 52.6 52.6 C258.4 58.2 58.1 C389.5 88.9 88.8 C4166.0 165.0 164.9 C5120.8 122.4 122.9 C6131.3 130.5 133.5 C7118.5 123.1 109.9 C8132.2 132.1 134.9 C9116.9 118.5 119.0 C10161.0 159.6 160.1 C11118.6 119.4 120.0 C12130.8 130.2 133.0 C13118.6 123.3 110.3 C14130.2 130.1 133.0 C15116.9 118.4 118.9 C16158.2 156.7 157.2 C17“Recorded at 125 MHz in CDCI3.Comparison of the 1H NMR data betweenH3(1,2,4-btt) and its acetone adductH3 (1 ,2,4-ahi) showed a large difference for the benzylic hydrogen resonances. In46Chapter III H3Xapi/H3(1,2,4-ahi) Ligand SystemH3(l,2,4-btt), three identical peaks for the benzylic hydrogens appeared because of theasymmetric nature of the molecule. After the formation of the adduct, the three peaksbecame a complex series of multiplets engendered by the rigidity of the 5-memberedimidazolidine ring preventing the free rotation of the benzylic carbon of one end anddifferentiating the two hydrogens on that carbon. This rigidity also resulted in theinequivalency of the two methyl groups (originating from acetone), which gave twosinglets in the 1H NMR spectrum. Reduction of the two 5-substituted (Cl, Br) Schiffbases to make H3Xahi analogs showed that the microanalyses* were consistent with thereduced formulations, but the complex 1H NMR spectra suggested that these productswere mixtures of isomers; efforts to purify these compounds were unsuccessful.It is interesting to note here that the five-membered imidazolidine ring formed inthe Schiff base condensation was opened during the reduction, which likely resulted inthe middle arm migration (Scheme 3.2). The by-product was the ligandH3(jl,1,4-btt)which was identified in the X-ray structure of the In( 1,1 ,4-btt) complex.16 This probablycan be explained by the formation of stabilized iminium ions present in protic solvents,18as shown in Scheme 3.2. The C=N linkages on the terminal arms are reduced first, thenthe lone pairs on the secondary nitrogens begin to attack the carbon to form intermediate(b). The intermediate (b) can either give the productH3(l,2,4-btt) through reduction, orform another intermediate (c), which leads to the minor by-productH3(l,l,4-btt). Afteracetone addition, another five-membered imidazolidine ring was formed at the backbone.As will be discussed later, the five-membered ring formed in the reduction will reopenandH3(l,2,4-ahi) will appear as (1,2,4-btt)3 after complexing.* Calcd (found) forC27H331N40.H(H3Clahi): C 55.34 (55.47); H 6.02 (5.72); N 9.56 (9.30);calcd (found) forBrO.0.5H(HBrahi): C 51.58 (51.44); H 6.16 (5.83); N 9.25 (8.98).47Chapter III H3Xapi/H3(J, 2,4-ahi) Ligand SystemNHOH+ROH +R0I’HNThH +OH(d)1 [H]I-13(1,1,4-btt)1KBH4OH+ROH4÷ROHII÷R0[H]N”ThINHOH3(1,2,4—btt)acetoneH3(1 ,2,4-ahi)(by-product)Scheme 3.2. Proposed Mechanism for the Reduction of the Schiff Base H3api.H3api (a)I’NTh(c) (b)‘ICCNHNHCN N\NH48Chapter III H3Xapi/H(1,2,4-ahi) Ligand System3.3.2 Synthesis and Characterization of Metal Complexes.Study of reactions of lanthanides with potentially heptadentate N403 ligands hasrevealed four coordination types: encapsulated,’9capped,20 encapsulated dimer,9 andbicapped21 as shown in Charts 1.2 and 2.2. Here again the first two structures, as well asa new sandwich-like structure, were found.F—ç NN /).-O /Ln Ln/—o-\/\:sandwich dimerChart 3.2Homodinuclear lanthanide complexes (sandwich structure) with the formulation[Ln(Xapi)]2 were prepared from reactions of Ln3 with these potentially heptadentateSchiff bases in the presence of excess weak base (acetate). These sandwich complexescould also be prepared from the reaction of a lanthanide nitrate salt with 1 equiv of theSchiff base because of the instability of these capped Schiff base complexes and theirspontaneous conversion to sandwich dimeric complexes. The new sandwich dimericcomplexes have been characterized by JR spectroscopy and elemental analysis (1H NMR,mass spectrometry and UV/VIS spectroscopy are only available for the lanthanum49Chapter III H3Xapi/H3(J,2,4-ahi) Ligand SystemTable 3.3. Analytical Data for the Lanthanide Complexes of the Various Schiff Baseand Amine Phenol Ligands.calcd. (found), %compound C H N[La(api)]2 54.55 (54.48) 4.58 (4.52) 9.43 (9.25)[Pr(api)]2 54.37 (54.35) 4.56 (4.53) 9.39 (9.21)[Nd(api)]2.2H0 52.49 (52.25) 4.73 (4.43) 9.07 (9.13)[Gd(api)].H 52.16 (52.43) 4.54 (4.47) 9.01 (8.97)[Yb(api)]2.2H0 50.15 (50.00) 4.52 (4.41) 8.66 (8.78)La(H3api) N0).0.5EtO 42.45 (42.30) 4.30 (4.30) 11.95 (12.07)Gd(Hapi)(N0.0.52 40.00(39.90) 3.85 (3.80) 12.09 (12.11)Yb(H3api)(N0) 39.66 (39.46) 3.70 (3.77) 11.99 (12.06)[La(Clapi)12 46.48 (46.78) 3.47 (3.48) 8.03 (7.92)[Pr(Clapi)]2 46.34 (46.07) 3.46 (3.44) 8.01 (7.95)[Nd(Clapi)12 46.12 (45.89) 3.44 (3.49) 7.97 (7.87)[Gd(Clapi)].CHC13 42.58 (42.98) 3.18 (3.29) 7.22 (7.26)[Yb(Clapi)]2.2H0 43.24 (43.24) 3.49 (3.45) 7.47 (7.53)La(H3Clapi)(N0).0.5EtO 37.70 (37.47) 3.49 (3.50) 10.61(10.64)Gd(HClapi)(N0.H2 35.13 (34.85) 3.17 (3.01) 10.62 (10.39)Yb(H3Clapi)(N0).0 34.54 (34.24) 3.11 (3.11) 10.44 (10.22)[La(Brapi)]2 39.02 (38.80) 2.91 (3.04) 6.74 (6.60)[PrQBrapi)12 38.93 (38.65) 2.90 (2.97) 6.72 (6.64)[Nd(Brapi)]2 38.36 (38.30) 2.98 (2.89) 6.63 (6.51)[Gd(Brapi)]2.3H20 37.00 (36.96) 3.10 (2.85) 6.39 (6.18)50Chapterlil H3Xapi/H3(1,2,4-ahi) Ligand System[Yb(Brapi)]2.2H20 36.72 (36.60) 2.97 (2.70) 6.34 (6.22)La(H3Brapi)(N0).2.5MeOH 32.20 (32.56) 3.39 (3.07) 8.91 (8.89)Gd(HBrapi)(N0 31.23 (31.09) 2.62 (2.65) 9.44 (9.05)Yb(H3Brapi)(N0) 30.76 (30.89) 2.58 (2.70) 9.30 (9.26)La(H(1,2,4-btt))(N0.MeOH 40.93 (40.81) 4.91 (4.94) 11.93 (11.86)Gd(H3(l,2,4-btt))(N0).0.5EtO 41.22 (41.42) 4.89 (4.71) 11.60 (11.66)Yb(H(1,2,4-btt))(N0.0.5Et 40.47 (40.93) 4.80 (4.76) 11.39 (11.78)La(1,2,4-btt).CHC13. H 44.49 (44.39) 5.07 (4.76) 7.41 (7.47)Gd(1,2,4-btt).0.5H0 51.65 (51.41) 5.46 (5.46) 8.92 (8.85)Yb(l,2,4-btt) 51.10 (50.95) 5.24 (5.39) 8.83 (8.67)complexes), and, for [La(Brapi)]2.2CHC13by X-ray crystallography. Thesehomodinuclear complexes contain two lanthanide ions. Instead of forcing N403 donoratoms from one ligand onto one metal ion as reported for the encapsulated dimer,9 eachof the metal ions in the sandwich structure is coordinated by two N20 donor sets, onefrom one ligand, one from another. Two phenolate 0 atoms, from the middle ann of eachligand, act as bridges between the two metal centers and complete the coordinationsphere. Compared to the infrared spectra of capped complexes, the 0-H and N03 bandsdisappeared in the sandwich complexes, and the C=N frequencies underwentbathochromic shifts upon coordination to the metal ions. 1H NMR data of [La(Xapi)]2are listed in Table 3.6, and the comparison of the 1H NMR spectra between the ligandH3Clapi and its complex [La(Clapi)]2 in CDC13 is shown in Figure 3.1. In H3Clapi, the5-membered ring enforces considerable rigidity, which results in two different hydrogenresonances for both H1’s and H2’s; the terminal arm can freely rotate, and only one peak5’Chapter III H3XapL/H3(I,2,4-ahi) Ligand SystemTable 3.4. Infrared Spectral Data (cm-1,KBr disk) for the Lanthanide Complexes of theVarious Schiff Base and Amine Phenol Ligandscomplex IR bands[La(api)]2 1622vs(vc=N); 1 600s, 1 540s, 1480vs, i47Ovs,1450s(°cc)[Pr(api)]2 l63Ovs(0cN); 1600s, 1540s, l478vs, 1470vs,i45Svs(uc=c)[Nd(api)]2.2H20 l63Ovs(Uc=N); 1 600vs, 1 540s, 1478vs, 1470vs,[Gd(api)]2.H20 1 635vs(uci); 1 600s, 1 542m, 148 is, l474vs,[Yb(api)12.2H20 1 63OvsQoc=N); 1 605vs, 1540s, 1474vs,l455vs(vc=c)La(H3api)(N03)3.0.5Et2O 1648v5(tc=N); 1607s, 1536s, 1496- 1438br s(tcó;l29Ovs(vN03-)Gd(H3api)(N0).0.52 l652vs(tcN); 1610s, 1540s, 1485vs(vcc); 1390vs,129OV5QoNO3-)Yb(H3api)(N0) l6S2s(tcN); 1610m, 1540m,l487s(tcc); 1388s,1 3O0m(uo-)[La(Clapi)]2 i63Ovs(vcN); 1598w, i532s, 1471vs,l425w(vcc)[Pr(Clapi)]2 1 630vs(o.j); 1598w, i530s, 1470vs, l422w(tcc)[Nd(Clapi)]2 I 630vs(v&sj); 1600w, i532s, i474vs,l422w(vcc)[Gd(Clapi)]2.CHC13 163Ovs(ojç); 1598w, 1530s, 1470vs, l422w(vcc)[Yb(Clapi)].2H0 163Ovs(ucN); 1600w, 1 532s, 1474vs, l422w(tcc)52Chapter III H3Xapi/H3(J, 2,4-ahi) Ligand SystemLa(H3Clapi)(N03).O.5Et2O 1648vs(t&N); 1606w, 1521 s, 1484vs(tcc);l286s(uNo3-)Gd(H3C1api)(NOH2O l6S2vsCUc=N); 1615w, 1528s, 1507-1450brvsCucc); 1388s, l300br s(tNo3-)Yb(H3Clapi)(N0)H20 l6S4vsCuc=N); 1613w, 1 529s, l49Ovs(tcc);1390vs, l300br s(vNo-)[La(Brapi)] l63Ovs(tcN); 1589s, 1528s, 1480vs, 1470vs,[Pr(Brapi)]2 l62Svs(tc=N); 1589m, 1530m, 1 470vs,l48w(tcc)[Nd(Brapi)]2 l62Svs(ucN); 1590m, 1530m, 1470vs,l420w(tc=c)[Gd(Brapi)]2.3H0 1627vs(tcN); 1 590m, 1 530s, 1470vs,l420w(vcc)[Yb(Brapi)]2.2H20 163Ovs(tcN); I 590m, 1 530m, 1470vs,1 420w(tc)La(H3Brapi)(N03).2.5MeOH l648vs(t&N); 1605w, 1518s, l476vsQucc); 1286brvs(tNo3-)Gd(H3Brapi)(N0) l6SOvs(tcN); 1608m, 1521 s, 1480br vs(vc=ó;1390m, l300br vs(uN03-)Yb(H3Brapi)(N0) l6SOvs(tcN); 1610w, 1520s,l48Ovs(tcc);1 388vs, 129OS(tNoç)La(H3(1 ,2,4-btt))(N03).MeOH I 59Om(3çj); 1473vs, l45Ovs(uccj; 1 380vs,l300br s(tNO3-)Gd(H3(1 ,2,4-btt))(N03).0.5EtO 1 593s(SNH); 1480vs. 1450vs (tc,c); 1300-1 260br53Chapter III H3Xapi/H(1,2,4-ahi) Ligand SystemYb(H3(1 ,2,4-btt’))(N03).O.5Et 1595s(ÔN.H); 1480vs, l45OvsQuc=ó; 1380m,l300vs(tNo-)La( 1 ,2,4-btt).CHC13.2H0 1 595s, 1563m(6N11); 1482vs, 145 lvs(tc=c)Gd(l,2,4-btt).O.5H 1595s, 1562w(SN..H); 1480vs,l4SOs(vc=c)Yb( 1 ,2,4-btt) 1 598vs,1565m(6NH); 1488vs,1455vs(tcc)is observed for the two H3’s. After coordinating to the metal ion, both the backbone andthe arms are more rigid, the singlet of the two H3 hydrogens is split into two multipletsassigned to H3eq and H3ax, and the peak for H5 of CH=N moves upfield while the peaksfor Hieq and H2eq move downfield as far as 4.9 and 3.68 ppm, from 3.40 and 2.93 ppm inthe ligand, respectively. (Assignments of Hax and Heq are tentative and are distinguishedby the fact that the hydrogens in pseudoaxial environments are usually more shieldedthan those in pseudoequatorial environments.22)Unlike those for other unstable Schiffbase lanthanide complexes, the UVIVIS spectra of the sandwich lanthanide complexes inDMSO showed that the complexes are quite hydrolytically stable in this stronglycoordinating solvent (Figure 3.2). This unusual property can be explained by therestricted rotation of the ligands and their certain degree of preorganization. Martell andHancock23 have noted that addition of C-methyl groups to the ethylene bridge of EDTAdecreases the rotation of the ligand and gives complexes of uniformly higher complexstability. We expect that these sandwich complexes have high thermodynamic stabilities,also.There are three geometries available to most eight-coordinated metal ions: cube,square antiprism, and dodecahedron. These forms are energetically very similar and thecube can be easily distorted to an antiprism or dodecahedron by inter-ligand repulsions;2454Chapter III H3XapiJH3(1,2,4-ahi) Ligand SystemTable 3.6. 1 NMR Data’ for the Dinuclear Lanthanum Complexes of the VariousSchiff Bases (in CDC13)X= H, CL Br6[La(api)]2 [La(Clapi)]2 [La(Brapi)]2 assignt4.97(q, 2H)2.90(q, 2H)3.16(m, 2H)2.80(m, 2H)4.90(q, 2H)2.91(q, 2H)3.68(m, 2H)2.77(m, 2H)4.90(m, 2H)2.91(m, 2H)3.63(m, 2H)2.76(m, 2H)1eq bHlb2eq bH2b3.87(m, 4H)3.82(s, H)7.39(s, H)3.92(m, 2H)3.12(m, 2H)3.72(s, H)7.41(s, H)3.94(m, 211)3.130, 2H)3.71(s, H)7.41(s, H)H3bH41156.74(d, 2H)’ 6.77(d, 2H) 6.92(s, 2H) 1176.340, 2H)b 1187.120, 2H)b 7.05(q, 2H) 7.16(d, 2H) H96.50(d, 211)b 6.42(d, 211) 6.37(d, 2H)C239)15 x 126.91(d, H)b6.440, HP6.91(d, H) 7.04(s, H) 1113111455Chapter III H3Xapi/H3(1, 2,4-ahi) Ligand System6.64(t, H)b 6.68(q, H) 6.82(d, H) Hl56.25(d, fl)b 6.24(d, H) 6.19(d, H) Hl6a Recorded at 400 MHz. b Assignments of hydrogen pairs 7/10, 8/9, 13/16, 14/15 in[La(api)]2 complex and axiaL/equatorial hydrogens are tentative.generally steric nonrigidity is observed. In order to examine the fluxionalities of thesandwich dimeric complexes, variable temperature 1H NMR spectra of [La(Clapi)]2 inDMSO-d6were obtained between 20 OC and 100 OC. There were no significant changesin the spectral parameters except for some very minor shifts in the signals; these shifts areprobably caused by thermal vibrations of the coordinated ligand framework. Thisobservation showed that the structure remained the same, undergoing no fluxionalprocesses and confirming its extreme rigidity, greater than that of the LnDOTAcomplex.25Reaction of a Schiff base with I equiv of a lanthanide salt in a small volume ofsolvent in the absence of a weak base produces mononuclear complexes (capped) withthe formulation [Ln(H3Xapi) N0)]. The sequence of the addition of the startingmaterials is very important for the lanthanum complexes. When a solution of ligand wasadded to a solution of the lanthanum ion, the elemental analyses always showed higherhydrogen and carbon percentages, despite the fact that the products were washed withchloroform to remove possible impurities- the ligand and the sandwich complex. Whenthe sequence was reversed, the analyses of the La complexes fit the formulation. UV/VISspectra of these complexes in methanol were different from those of ligands, suggestingthe coordination of the ligands to the metal ions. In DM50 the UV/VIS spectra showed56Chapter III HjXapifH3(I .2,4-ahi) Ligand SystemFigure 3.1. ‘H NMR spectra (400 MHz) of H3CIapi (top) and [La(Clapi)]2(bottom) inI I I I8.5 8.0 7.5 7,0 6.51 H4N19N,5H10 H<Lr015 CI9 CII I6.0 5.5PPMI I I I I I5.0 4.5 4.0 3.5 3.0 2.5 2.0I I I I8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0PPMCDC13 at room temperature.H3H,H5H9H,5NUH15H3ClapiH loxH2KHi.qI-13I CI‘hI’H10H.H15H loxH20x57Chapter III H3Xapi/H3 (1 2,4-ahi) Ligand SystemFigure 3.2. UV/VIS spectra of H3api, Gd(Hapi)(N0)and [Gd(api)]2 in DMSO at.02.0‘.5hO0.50.0room temperature. Gd(Hapi)(N0)slowly decomposes in DMSO, while[Gd(api)J2is stable.A (nm)500240 300 360 42058Chapter III H3Xapi/H(J,2,4-ahi) Ligand Systemthe spectrum of the free ligand. In this strong a-donor solvent, the complexes seem todecompose to form the solvated Ln3+ species. The infrared spectra of these complexesshowed two bands around 1390 and 1300 cm-’, which can be assigned to the bidentatenitrates. Broad bands at 3700-2200 cm-’ belong to 0-H stretching vibrations in theprotonated ligands. C=N groups were not coordinated and their JR bands moved upfieldcompared to those in the ligands (because of delocalization, coordination of phenoloxygen resulted in a stronger azomethine bond). New bands below 600 cm-’ were likelyto be tLn..O or tLnN however, assignments of these bands are very difficult in thisregion because of the low energies associated with these vibrations.26 Theseobservations are similar to those of the previously reported nine coordinate cappedcomplexes.2°The mass spectra of both the sandwich lanthanum complexes and all the cappedcomplexes were obtained in a 3-nitrobenzyl alcohol matrix in the positive-ion detectionmode (Table 3.5). In the spectra of the most capped complexes, base peakscorresponding to the [NLnLI+ were detected and there were no molecular ion peaks. Forthe sandwich lanthanum complexes, both monomeric ([HLaXapff’j and dimeric([H(LaXapi)2J) molecular ion peaks were detected with the intensity of the latter beingsimilar to that of the former. This is consistent with the structural finding for[LaBrapi]22CHC13. In the spectra of all three sandwich lanthanum complexes, therewere also fragmentation patterns indicative of the respective ligand.Reactions of an amine phenol with 1 equiv of a lanthanide nitrate in the presence ofdiethyl ether produced the mononuclear capped complexes with the formulation[Ln(H3(l,2,4-btt))(N0)]or, in the presence of excess strong base (hydroxide),59Chapter III H3Xapi/H3(1,2,4-ahi) Ligand SystemTable 3.5. Mass Spectral Data for the Lanthanide Complexes of the Various Schiff Baseand Amine Phenol Ligandscomplex[La(api)]2 1 189([H(ML)2]);595([HMLj)La(H3api) N0.0.5EtO 1 189([H(tvEL)jj;721([M(H3L) N0]j;595([HML])Gd(H3api)(N0).0.52 6l4([HML])Yb(Hapi)(N0 756([M(H3L) N02]j;630( [HiML])[La(Clapi)12 1 395([H(ML)2]j;697([HML]jLa(H3Clapi)(N0).O.5Et 1 395([H(ML)]j;823([M(HL) N0]j;697([L])Gd(H3Clapi)(N0).H20 7 18([HML]jYb(HClapi)(N0. 734([HML])[La(Brapi)]2 1663([H(ML)2]+); 831([HML])La(H3Brapi)(N0).2.5MeOH 831 ([HMLJ)Gd(FlBrapi)(N0 850([HML])Yb(H3Brapi)(N&) 992([M(H3L) NO1);866([HML]jLa(H3(1 ,2,4-btt))(N03).MeOH 1201 ([H(ML)]);863([M2L(NO]);601([HML]+)Gd(H3(1 ,2,4-btt))(N03).O.5Et 1 238([H(ML)]j; 61 8([HML])Yb(H(l,2,4-btt))(N0.0.5EtO931([ML(NO)]);636([HML]jLa( I ,2,4-btt).CHCI3.2H 601 ([HML])Gd(1,2,4-btt).O.5H0 618([HMLj)60Chapter III H3Xapi/H(1,2,4.ahi) Ligand SystemYb( 1 ,2,4-btt) 635([HMLj)encapsulated [Ln(1,2,4-btt)]. Mass spectral and infrared data were consistent with theappropriate formulations. Both encapsulated and capped complexes showed JR bands at1598-1560 cm-1 arising from N-H bending vibrations and molecular ions [HLn(1,2,4-btt)]+ were found in the mass spectra, confirming their thermal robustness. There werealso fragmentation patterns indicative of the respective ligand.3.3.3 Spontaneous Conversion of Capped to Sandwich Species.Unlike other stable capped complexes, the Ln(H3Xapi)(N0)capped complexesare air-stable but very unstable in solution and spontaneously convert to sandwich dimers.The discovery of the novel spontaneous conversion of a capped ligand species to asandwich ligand species in methanol was fortuitous. After mixing the lanthanide saltsand the ligands in a 1:1 ratio in a large volume of methanol, the expected precipitation ofthe capped complexes led unexpectedly to the recovery of the sandwich complexes. Thisbehavior was common across the lanthanide series, and the spontaneous conversionspectra were only recorded in detail for the Gd-H3api system (0.3 mM) as shown inFigure 3.3. The first spectrum was recorded immediately after dissolving the cappedcomplex Gd(Hapi)(N0)in methanol, and the subsequent spectra were recorded overseven days. The peak at 319 nm disappeared gradually and a new peak around 360 nmappeared as a precipitate of [Gd(api)]2 formed. Insolubility of the product preventedfurther study but both the spectra in solution and the characterization of the solid productproved the spontaneous conversion.61Chapter III Hy,Xapi/H3 (12 4-a/il) Ligand SystemFigure 3.3. UV/VIS spectra of the spontaneous conversion of 0.3 mM Gd(H3api)(N0)to.02.01.51.00.50.0to [Gd(api)]2 at room temperature in methanol.A (nm)250 300 40062Chapter III H3XapUH(I,2,4-ahi) Ligand System3.3.4 Crystal Structure ofH3api.Selected bond lengths and bond angles for H3api are listed in Table 3.7 while theORTEP drawing and the packing pattern are illustrated in Figure 3.4. The molecule isrendered quite rigid by the formation of a five-membered imidazolidine ring and by thepresence of three strong intramolecular hydrogen bonds (O(1)-H(l’)---N(2) = O(2)-H(2)---N(3) = O(3)-H(3)---N(4) = 1.64 A) and a very weak intermolecular hydrogen bondinginteraction ( C(6)-H(13)---O(3) = 2.51 A, angle C(6)-H(13)-O(3) = 137°). The fivemembered imidazolidine ring adopts an envelope conformation with C(2) lying out of theplane defined by N(1), N(2), CU), and C(3). Both N(2)-C(6)-C(7)-N(4) and N(1)-C(4)-C(5)-N(3) adopt gauche conformations (torsion angles: N(1)-C(4)-C(5)-N(3) =-176.6(2)°; N(2)-C(6)-C(7)-N(4) = -178.O(2)°). The whole ligand structure resembles abigT.The intermolecular hydrogen bond distance between ethylene hydrogen (H(13)) onone molecule and oxygen (0(3)) on the terminal arm of another molecule is 2.51 A,suggesting a C-H---0 intermolecular hydrogen bonding interaction, which results in ahighly ordered packing pattern (Figure 3.4). The ability of carbon atoms to act as protondonors in hydrogen bonds has been the subject of controversy for many years; however, alandmark study by Taylor and Kennard27 in 1982 provided conclusive evidence of theexistence of C-H---Y hydrogen bonds in crystals. These authors showed that C-H---Ycontacts are electrostatic, and that the distance between the hydrogen and the acceptoratom is shorter than the sum of their van der Waals radii, and C-H---Y angle is in therange of 90°-l80°. These C-H---Y bonds are mainly found in amino acids andnucleosides.28 The more acidic the hydrogen on the carbon atom, the more easily the CH---Y bond can form. The H and 0 van der Waals radii are 1.2 A and 1.5 A,respectively. Since the H---0 distance in the structure of H3api is 2.51 A, shorter than63Chapter III ll3Xapi/113 (12 4-ahi) Ligand SystemFigure 3.4. ORTEP drawing (top) and stereo packing diagram for unit cell (bottom)of H3api with numbering schemes.03C24C25C19C20C18C17021-12C12HiSciido C901C2664Chapter III H3Xapi/H3(1, 2,4-ahi) Ligand SystemTable 3.7. Selected Bond Lengths (A) and Angles (deg) in H3api with EstimatedStandard Deviations.Bond Lengths00) - C(9) 1.364(3) N(4) - CC) 1.457(3)0(2) - C(16) 1.358(3) N(4) - C(21) 1.277(2)0(3) - C(23) 1.359(3) CU) - C(8) 1.507(3)NW-CU) 1.471(2) C(2)-C(3) 1.496(3)NO) - C(2) 1.457(3) C(4) - C(5) 1.5 17(3)NO) - C(4) 1.459(3) C(6) - C) 1.507(3)N(2)- CU) 1.489(2) C(8) - C(9) 1.393(3)N(2) - C(3) 1.480(3) C(14)-C(15) 1.448(3)N(2) - C(6) 1.461(3) C(15)-C(16) 1.392(3)N(3) - C(S) 1.464(3) C(21) - C(22) 1.455(3)N(3)-C(14) 1.271(3) C(22) - C(23) 1.390(3)Bond AnglesC(1)- NO) - C(2) 104.4(2) CU) - C(8) - C(13) 119.8(2)C(1)- NO) - C(4) 112.3(2) C(9) - C(8) - C(13) 118.2(2)C(2)-N(1)-C(4) 113.1(2) 0(1)-C(9)-C(8) 121.3(2)C(1) - N(2) - C(3) 106.8(2) 0(1) - C(9) - COO) 118.4(2)C(1) - N(2) - C(6) 113.3(2) C(8) - C(9) - COO) 120.2(2)C(3) - N(2) - C(6) 112.7(2) N(3) - C(14) - C(15) 122.2(2)C(S) - N(3) - CO4) 118.3(2) C(14) - C(15) - CO6) 121.6(2)CC) - N(4) - C(21) 119.2(2) C(14) - C(15) - C(20) 120.0(2)NO) - CU) - N(2) 103.4(2) C(16) - C05) - C(20) 118.3(2)65Chapter III H3Xapi/H(1,2,4-ahi) Ligand SystemN(1)- CU) - C(8) 111.2(2) 0(2) - CU6) - C(15) 121.3(2)N(2)- CU) - C(8) 113.9(2) 0(2) - CU6) - C(17) 118.8(3)N(I) - C(2) - C(3) 102.7(2) C(15) - C(16) - C(17) 119.9(2)N(2) - C(3) - C(2) 105.5(2) N(4) - C(21) - C(22) 121.4(2)NU) - C(4) - C(5) 110.7(2) C(21) - C(22) - C(23) 121.1(2)N(3) - C(5) - C(4) 109.8(2) C(21) - C(22) - C(27) 120.3(3)N(2) - C(6) - C) 112.7(2) C(23) - C(22) - C(27) 118.7(2)N(4)- CC) - C(6) 108.1(2) 0(3) - C(23) - C(22) 121.5(2)CU) - C(8) - C(9) 121.9(2) 0(3) - C(23) - C(24) 118.1(3)C(22) - C(23) - C(24) 120.4(2)2.7 A, an intermolecular C-H---0 hydrogen bonding interaction is indicated. Althoughthere are reports on the hydrogen bonding between aromatic It hydrogen andelectronegative atoms,29 in this molecule, the intermolecular distance between 0(3) andH(18) is 2.89 A, too long to be considered a H-bond interaction. The C-H---0 hydrogenbonding interaction is the main determinant in the ordered packing arrangement of thissmall molecule, and prevents the disorder seen in the H3Clapi structure’6by enforcingthe jig-saw fit of the molecules in the unit cell.3.3.5 Crystal Structure of Yb(1,2,4-btt).A single crystal structure determination of Yb(1,2,4-btt) showed this to be aencapsulated complex with pentagonal bipyramidal coordination. The bond lengths andbond angles are listed in Table 3.8 and the ORTEP drawing is illustrated in Figure 3.5.The asymmetric unit of the Yb complex contains two independent Yb(l,2,4-btt)molecules (with very slight differences in bond lengths and angles) and a methanol66Chapter 111 H3Xapi/H3 (12 .4-ahi) Ligand SystemFigure 3.5. ORTEP drawing of one of the two independent Yb(1,2,4-btt) molecules inYb( 1 ,2,4-btt).O.5MeOH.C13t1Z czsC17ClitieCZ6CZ4COClCZlC14CO£5N3HZ£20tie67Chapter III H3Xapi/H3(1,2,4-ahi) Ligand SystemTable 3.8. Selected Bond Lengths (A) and Angles (deg) in One of the Two IndependentMolecules of Yb(1,2,4-btt) with Estimated Standard Deviations.1.5 11(5)Bond LengthsYb(1)-0(1) 2.160(3) N(3)-C(4) 1.481(6)Yb(1) - 0(2) 2.145(3) N(3) - C(5) 1.477(6)Yb(1) - 0(3) 2.170(3) N(4) - C(6) 1.474(6)Yb(1)- NO) 2.485(4) N(4) - C(21) 1.482(7)Yb(1) - N(2) 2.551(4) CU) - C(2) 1.524(7)Yb(1) - N(3) 2.470(4) C(3) - C(4) 1.506(6)Yb(1) - N(4) 2.483(4) C(S) - C(6) 1.497(8)00) - C(9) 1.322(5) C(7) - C(8) 1.507(7)0(2)-C(16) 1.339(6) C(8) - C(9) 1.409(6)0(3) - C(23) 1.338(6) C(14)-C(15) 1.510(7)NO) - CU) 1.474(6) C(15) - C(16) 1.397(7)NO) - C(7) 1.502(6) C(21) - C(22) 1.508(7)N(2) - C(2) 1.485(6) C(22) - C(23) 1.399(7)N(2) - C(3) 1.495(6) 0(4) - C(28) 1.360)N(2)-C(14)Bond Angles00) - Yb(1) - 0(2) 169.40) Yb(1) - N(3) - C(4) 108.0(3)00)-Yb(1) - 0(3) 98.70) Yb(1) - N(3) - C(S) 110.9(3)00)— Yb(1) — NO) 80.40) Yb(1) — N(4) — C(6) 112.1(3)0(1)-Yb(1)-N(2) 98.90) Yb(1)-N(4)-C(21) 113.6(3)00)-Yb(1) - N(3) 82.70) C(4) - N(3) - C(S) 113.7(4)00)- Yb(1) - N(4) 77.70) C(6) - N(4) - C(21) 113.6(4)0(2)—Yb(1) — 0(3) 88.10) N(1) — CU) — C(2) 111.1(4)68Chapter III H3XapiIH(1,2,4-ahi) Ligand System0(2) — Yb(1)— NO) 108.8(1) N(2) — C(2) — CU) 112.4(4)0(2)-Yb(1) - N(2) 80.00) N(2) - C(3) - C(4) 111.8(4)0(2) - Yb(1) - N(3) 87.20) N(3) - C(4) - C(3) 107.3(4)0(2) - Yb(1) - N(4) 96.000 N(3) - C(5) - C(6) 107.9(5)0(3)-Yb(1)- NO) 81.2(1) N(4) - C(6) - C(5) 108.9(4)0(3) — Yb(1) — N(2) 143.10) NO) — C) — C(8) 113.4(4)0(3)-Yb(1) - N(3) 146.30) C(7) - C(8) - C(9) 120.0(5)0(3)-Yb(1) - N(4) 77.80) C(7) - C(8) - C(13) 120.6(5)NO) -Yb(1) - N(2) 70.20) C(9) - C(8) - C(13) 119.4(5)NO) —Yb(1) — N(3) 131.70) 00) — C(9) — C(8) 120.4(5)NO) -Yb(1) - N(4) 146.70) 00) - C(9) - COO) 121.5(5)N(2) -Yb(1) - N(3) 68.20) N(2) - C(14) - C(15) 114.8(4)N(2) -Yb(1) - N(4) 137.80) N(4) - C(21) - C(22) 110.7(4)N(3) -Yb(1)- NO) 69.60) C(14) - C(15) - C(16) 120.6(5)Yb(1)-0(1) - C(9) 134.0(3) CO4) - C(15) - C(20) 120.4(5)Yb(1) - 0(2)-C(16) 134.4(3) C(16)-C(15) - C(20) 118.8(5)Yb(1) - 0(3) - C(23) 132.5(3) C(15)-C(16)-C(17) 119.4(5)Yb(1)- NO) - CU) 115.6(3) C(21) - C(22) - C(23) 120.1(5)Yb(1)- NO) - C(7) 109.5(3) C(21) - C(22) - C(27) 120.6(6)Yb(1) - N(2) - C(2) 106.4(3) C(23) - C(22) - C(27) 119.2(6)Yb(1) - N(2) - C(3) 112.6(3) C(22) - C(23) - C(24) 118.2(5)Yb(1) - N(2) - C(14) 109.3(3) C(8) - C(9) - COO) 118.1(5)CU) - NO) - C(7) 112.9(4) 0(2) - C(16) - CO5) 120.6(5)C(2) - N(2) - C(3) 108.8(4) 0(2) - C(16) - C(17) 120.0(5)C(2) - N(2) - C(14) 109.50) 0(3) - C(23) - C(22) 121.3(5)C(3) - N(2) - C(14) 110.1(4) 0(3) - C(23) - C(24) 120.6(5)69Chapter III H3Xapi/H(1,2,4-ahi) Ligand Systemmolecule. The oxygen atom of the methanol solvate is (74:26) twofold disordered. Theligand is triply deprotonated, and all seven donor atoms (N403)are coordinated to themetal ion. However, unlike the In(l,1,4-btt) complex,16 N(1), N(2), N(3), N(4), 0(3) ofpentagon and Yb are not all in the same plane; atoms N(3) and N(4) are above the plane,while N(2) and 0(3) are below the plane. The Yb-0 distances average to 2.158 A,similar to that of the Yb(trac) complex.19 The Yb-N distances average 2.497 A. Thebond angle between 0(l)-Yb-0(2) is 169.4(l)°, consistent with these two oxygens inaxial positions. It is not surprising that this complex has distorted pentagonal bipyramidalgeometry. After complexation, the imidazolidine ring in the ligand opened, which madethe backbone and the three arms more flexible. Pour nitrogens and one oxygen of aterminal arm easily wrapped around the metal ion, while the remaining two armsstretched out to occupy the axial positions. There appear to be no undue constraints onthe framework. There are only a few examples30’1 of lanthanide complexes withpentagonal bipyramidal arrangments, none of them (until now) being binary complexeswith one heptadentate ligand coordinating one metal ion.3.3.6 Crystal Structure of [La(Brapi)]2.The ORTEP drawing of [La(Brapi)]2is illustrated in Figure 3.6. The bond lengthsand bond angles are listed in Table 3.9. The unit cell contains dinuclear [La(Brapi)]units with two CHC13 molecules in the crystal lattice for each dimer. The complex hastwo identical eight-coordinated lanthanum atoms, each of which is surrounded by anN40 donor set. The two lanthanum centers are bridged by two phenolate oxygen atoms(one from each of the two middle arms of the two heptadentate ligands). The twolanthanum and two bridging oxygen atoms form a planar four-membered ring with a70Chapter III H3Xapi/H3 (12,4-aid) Ligand SystemFigure 3.6. ORThP drawing of {La(Brapi)]2 in [La(Brapi)]2.2CHC13.C4C2271Chapter III H3Xapi/H(J,2,4-aht) Ligand Systemmetal-metal separation of 4.023(1) A and angles at the oxygen bridgehead of 109.8 (2)°.The molecule is centrosymmetric. The geometry around each lanthanum atom can beviewed as a square antiprism, in which one square is composed of donor atoms 00),0(2), NO), N(3), and the other of 0(1), Q(3)* N(2)*, N(4)*. The La-N bond lengths are2.879(8) A, 2.902(7) A, 2.617(8) A, 2.607(9) A for La(1)-N(1), La(1)N(2)*, La(1)-N(3),La(1)_N(4)*, respectively, with an average of 2.75 1 A. These are consistent with thosefound in the eight coordinated La(III) complexes of N-(2-dimethylaminoethyl)salicylideneimine11and 1,4,7,10-tetrakis(2-carbamoylethyl)-1,4,7,10-tetraazacyclododecane.32The La-0 bond lengths fall into two categories. Thebridging La(1)0(1)* and La(1)-0(1) distances in the four membered ring are 2.466(5) Aand 2.451(6) A, respectively, while the terminal La-O bond lengths are 2.342(7) A(La(1)-0(2)) and 2.324(7) A (La(1)0(3)*), shorter than those of Eu-0 bond distances inthe crystal structure of Na(EuDOTA.H0).4H33after correction for the ionic radiusdifferences of the two metal ions. Since the bridging oxygen atoms 00) and 0(1) formtwo strong La-0 bonds, their basicity should be lowered relative to that of the singlebonded 0 atoms; the average bridging La-0 distances (2.459 A) are 0.126 A longer thanthose of terminal La-0 bonds (2.333 A).Although the formation of a dinuclear structure is not a surprise, this new opensandwich-like structure is unexpected. This no doubt arises from the rigid fivemembered imidazolidine ring in the ligand backbone; this forces the ligand into a moreopen configuration rendering impossible the coordination of all the donor atoms of oneligand to one metal ion. Instead, these two ligands cooperate with each other to form twocompartments which accommodate one metal ion each.72Chapter III H3Xapi/H(1,2,4-ahi) Ligand SystemTable 3.9. Selected Bond Lengths (A) and Angles (deg) in [La(Brapi)]2with EstimatedStandard Deviations.Bond Lengthsatom atom distance atom atom distanceLaO) La(1)a 4.023(1) La(l) 0(1) 2.451(6)LaO) 0(1)’ 2.466(5) La(l) 0(2) 2.342(7)LaØ) 0(3) 2.3240) La(l) N(l) 2.879(8)LaO) N(2) 2.9020) La(1) N(3) 2.617(8)LaO) N(4) 2.607(9) 0(1) C(9) 1.334(10)0(2) C(16) 1.30(1) 0(3) C(23) 1.30(1)NO) CU) 1.490) NO) C(3) 1.47(1)NO) C(4) 1.480) N(2) CØ) 1.480)N(2) C(2) 1.490) N(2) C(6) 1.480)N(3) C(S) 1.450) N(3) C(14) 1-280)N(4) CC) 1.470) N(4) C(21) 1.290)CU) C(8) 1.500) C(2) C(3) 1.530)C(4) C(S) 1.500) C(6) CC) 1.52(1)C(8) C(9) 1.380) C(21) C(22) 1.460)C(14) C(15) 1.450) C(15) C(16) 1.400)C(22) C(23) 1.420)Bond Anglesatom atom atom angle atom atom atom angle00) LaO) 0(3) 144.8(2) 00) LaO) N(2)° 82.9(2)00) LaO) N(4) 142.6(3) (1) LaO) Q(3) 84.8(2)73Chapter III H3XapL/H(1,2,4-ahi) Ligand System0(1y La(1) N(2) 68.7(2) 0(1) LaO) N(4)a 110.6(2)0(2) La(1) NO) 111.3(2) 0(2) La(I) N(3) 69.2(2)0(3)’ LaO) NQ) 84.5(2) Q(3) LaO) N(3) 76.4(3)NQ) LaO) N(2) 146.2(2) NO) LaO) N(4) 147.6(3)N(2) LaO) N(4)a 64.4(3) LaØ) 00) La(1)a 109.8(2)La(1’)a 00) C(9) 118.9(5) La(1)a 0(3) C(23) 137.3(7)LaO) NO) C(3) 105.7(6) C(1) NO) C(3) 105.0(8)C(3) NO) C(4) 111.2(8) La(1)a N(2) C(2) 105.9(6)C(1) N(2) C(2) 104.8(8) C(2) N(2) C(6) 112.9(8)LaO) N(3) C(14) 128.7(8) 00) LaO) O(1) 70.2(2)00) La(1) 0(2) 83.7(2) 00) LaO) NO) 69.0(2)00) La(1) N(3) 109.7(2) 0(1) LaO) 0(2) 143.0(2)0(1 La(1) NO) 83.9(2) 0(1) LaO) N(3) 143.8(3)0(2) LaO) 0(3)l 128.8(2) 0(2) La(1) N(2) 82.8(2)0(2) LaO) N(4)a 75.0(3) 0(3) LaO) N(2) 111.2(2)0(3)a LaO) N(4)a 68.9(3) NO) LaO) N(3) 64.0(3)N(2y’ La(1) N(3) 147.1(2) N(3) LaO) N(4) 91.2(3)LaO) 0(1) C(9) 122.8(6) LaO) 0(2) C(16) 135.1(8)LaØ) NO) CO) 118.5(5) LaO) NO) C(4) 108.6(6)CU) NO) C(4) 107.7(8) La(1)a N(2) C(1) 118.3(5)La(1)a N(2) C(6) 107.1(6) CU) N(2) C(6) 108.0(7)LaO) N(3) C(5) 113.0(6) C(S) N(3) C(14) 118.3(10)LaO)a N(4) C(7) 111.8(8) C(7) N(4) C(21) 118(1)NO) CO) C(8) 113.7(8) N(2) C(2) C(3) 106.4(8)NO) C(4) C(S) 113.4(9) N(2) C(6) C(7) 113.2(9)C(1) C(8) C(9) 122.3(8) C(9) C(8) C(13) 1200)0(1) C(9) C(10) 1200) N(3) C(14) C(15) 126.9(10)74Chapter III H3Xapi/H3(1,2,4-ahi) Ligand SystemC(14) C(15) C(20) 1150) 0(2) C(16) C(15) 124(1)C(15) C(16) C07) 116.9(9) C(21) C(22) C(23) 1220)C(23) C(22) C(27) 1210) 0(3) C(23) C(24) 1210)La(1)a N(4) C(21) 129.6(8) N(1) CU) N(2) 103.9(7)N(2) CU) C(8) 114.2(8) N(l) C(3) C(2) 105.6(8)N(3) C(5) C(4) 108.5(9) N(4) C(7) C(6) 1070)C(1) C(8) C(13) 1170) 00) C(9) C(8) 121.400)C(8) C(9) COO) 118.3(9) C(14) C(15) C(16) 122.600)C(16) C05) C(20) 1210) 0(2) C(16) C07) 118(1)N(4) C(21) C(22) 124(1) C(21) C(22) C(27) 1150)0(3) C(23) C(22) 1230) C(22) C(23) C(24) 1140)a Symmetry operation: 1/2-x, l/2-y, -z.3.3.7. Concluding RemarksA series of Schiff bases has been prepared from the condensation reactions ofvarious salicylaldehydes with trien, however the reduction gives different productsbecause of the migration of hydroxybenzyl arm. Purification of the amine phenol can beachieved by the decomposition of the resultant complex. Characterization of the Schiffbase H3api shows it to be nicely preorganized due to the rigid five-memberedimidazolidine ring and inter-, intra-molecular hydrogen bonding, especially the C-H---Ointermolecular hydrogen bonding interactions result in the ordered packing pattern.Unlike other Schiff base complexes, reactions of lanthanides with these preorganizedligands yield new sandwich dimeric complexes which are very rigid and quite stable, asevinced by the novel spontaneous conversion of a capped ligand complex to a sandwichdimeric complex, and by the variable temperature 1H NMR of [La(Clapi)]2 in DMSO-d675Chapter III H3XapUH3(1,2,4-ahi) Ligand Systemsolution. Although no water is bonded to the metal ion in the sandwich dimericcomplexes, it offers the possibility for the design of new ligands to allow water exchange,an important factor for MRI agents.Despite the different position of the middle arm, X-ray structures show that theN40 cavity of amine phenol ligand fits th very well16 and that the cavity is slightly toosmall for Ln3 ions. Generally the better fit between the metal ion and the cavity, themore stable is the resulting complex. The enlargement of the cavity can be achieved bychanging the number of the donor atoms and carbons at the backbone, as will bediscussed in Chapters 5 and 6.References(I) Rauk, A.; Allen, L. C.; Milson, K. Angew. Chem. mt. Ed. Engl. 1970, 9,400.(2) Tsang, B. W.; Mathias, C. J.; Green, M. A. I NucI. Med. 1993, 34, 1127.(3) Evans, D. F.; Jakubovic, D. A. I Chem. Soc. Dalton Trans. 1988, 2927.(4) Bailey, N. A.; McKenzie, E. D.; Worthington, J. M.; McPartlin, M.; Tasker, P. A.Inorg. Chim. Acta. 1977, 25, L137.(5) Isobe, T.; Kida, S.; Misumi, S. BulL Chem. Soc. Japan. 1967,40, 1862.(6) Sarma, B. D.; Ray, K. R.; Sievers, R. E.; Bailar, J. C., Jr. I Am. Chem. Soc. 1964,86, 14.(7) Sarma, B. D.; Bailar, I. C., Jr. J. Am. Chem. Soc. 1955, 77, 5476.(8) Guerriero, P.; Vigato, P. A.; Fenton, D. E.; Hellier, P. C. Acta Chem. Scand. 1992,46, 1025.(9) Liu, S.; Gehtini, L.; Rettig, S. J.; Thompson, R. C.; Orvig, C. I Am. Chem. Soc.1992, 114, 6081.(10) Ribot, F.; Toledano, P.; Sanchez, C. Inorg. Chim. Acta. 1991, 185, 239.76Chapter III H3XapIJH(1,2,4-ahi) Ligand System(11) Blech, P.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. J. Chem. Soc. Dalton Trans.1990, 3557.(12) Kahwa, I. A.; Folkes, S.; Williams, D. J.; Ley, S. V.; O’Mahoney, C. A.;McPherson, G. L. J. Chem. Soc., Chem. Commun. 1989, 1531.(13) Rebizant, J.; Spinet, M. R.; Barthelemy, P. P.; Desreux, J. F. J. Inclusion Phenom.1987, 5, 505.(14) Harrison, D.; Giorgetti, A.; Bunzli, J.-C. G. J. Chem. Soc., Dalton Trans. 1985,885.(15) Baraniak, E.; Bruce, R. S. L.; Freeman, H. C.; Hair, N. J.; James, J. Inorg. Chem.1976, 15, 2226.(16) Yang, L.-W.; Liu, S.; Wong, E.; Rettig, S. 3.; Orvig, C. Inorg. Chem. 1995, 34,2164.(17) Gunduz, N.; Gunduz, T.; Hursthouse, M. B.; Parkes, H. G.; Shaw, L. S.; Shaw, R.A.; TUzun, M. J. Chem. Soc. Perkin Trans. H. 1985, 899.(18) Salerno, A.; Ceriani, V.; Perillo, I. A. J. Heterocyclic Chem. 1992, 29, 1725.(19) Berg, D. J.; Rettig, S. J.; Orvig, C. J. Am. Chem. Soc. 1991, 113, 2528.(20) Smith, A.; Rettig, S. 3.; Unrig, C. Inorg. Chem. 1988, 27, 3929.(21) Liu, S.; Yang, L.-W.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1993, 32, 2773.(22) Silverstein, R. M.; Bassler, 0. C.; Morrill, T. C. Spectrometric Identification ofOrganic Compounds; 4th ed.; John Wiley & Sons: 1981.(23) Hancock, R. D.; Martell, A. E. Chem. Rev. 1989, 89, 1875.(24) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements; Pergamon Press:Uxford, England, 1984.(25) Desreux, J. F. Inorg. Chem. 1980, 19, 1319.(26) Alyea, B. C.; Malek, A.; Vougioukas, A. E. Can. J. Chem. 1982, 60, 667.(27) Taylor, R.; Kennard, U. J. Am. Chem. Soc. 1982, 104, 5063.77Chapter III H3Xapi/H3(1,2,4-ahi) Ligand System(28) Jeffrey, G. A.; Saenger, W. Hydrogen Bonding in Biological Structures; Springer-Verlag: Berlin, Germany, 1991.(29) Atwood, J. A.; Hamada, F.; Robinson, K. D.; On, G. W.; Vincent, R. L. Nature.1991, 349, 683.(30) Rogers, R. D.; Voss, B. J.; Etzenhouser, R. D. Inorg. Chem. 1988, 27, 533.(31) Atwood, D. A.; Bott, S. G.; Atwood, J. L. J. Coord. Chem. 1987, 17,93.(32) Morrow, J. A.; Amin, S.; Lake, C. H.; Churchill, M. R. Inorg. Chem. 1993, 32,4566.(33) Spirlet, M.-R.; Rebizant, J.; Desreux, J. F.; Loncin, M.-F. Inorg. Chem. 1984, 23,359.78Chapter IV H3dha3tren Ligand SystemChapter IV Complexation of the Potentially Heptadentate LigandH3dha3tren with Lanthanides: Architecture of a[Nd(N03)3(H3dha3tren)]fl Polymer with Profuse Modes of NitrateCoordination4.1 IntroductionStabilities of lanthanide-Schiff base complexes have been found improvedremarkably by varying the ligand characteristics such as reducing the imine C=N bondsto stable amine -RCH-NH- linkages,1’2and changing the tripodal tren backbone to alinear trien backbone.3 The facility with which one can vary the preorganization, cavitysize, coordination geometry, and rigidity of the ligand makes possible the synthesis of aseries of lanthanide complexes with different geometries, a series in which fivecoordination modes have thus far been found (Chart 4.1 1-5) The goal of this work is tounderstand further the influence of various chelating pendants of the ligand on thecoordination chemistry of lanthanide complexes by replacing the phenolate groups inH3saltren (see Chart 2.1) with the dha chelating groups to formH3dhatren (Scheme4.1). Dehydroacetic acid (dha) is a weak acid with pKa 5.26,6 stronger, however, thanphenol (pKa 10). The ring oxygen of dha should have a higher affinity for lanthanideions than that of the phenolate group. It has been reported that lanthanide ions form quitestable complexes with dha (i.e. log La@ha)3 = 10.35; log 3Er(dha)3 = 12.036). Atechnetium complex of a H3dha3tren analog has a rigid structure and undergoes noconformational change at temperatures up to 50 OC.7 H3dhatren can be readilysynthesized from the condensation reaction of tris(2-aminoethyl)amine (tren) withdehydroacetic acid (dha).8 It is tribasic in order to conserve an overall neutral complexcharge, and it contains both lipophilic hydrocarbon chains and polar carbonyl groups79Chapter IV H3dhatren Ligand Systemwhich might increase the water solubility and lipophilicity of its complexes;* theconjugated ring preserves some aromaticity. The oxygen-rich nature of the arms canpotentially induce electronic changes and alter the metal-binding properties of thenitrogen and the exocyclic oxygen atoms. In this chapter, some unusual properties of itslanthanide complexes, which might be helpful in preparing multinuclear, and possiblypolymeric, arrays of rare earth ions, are reported.(encapsulatedencapsulated dimerbicappedChart 4.1N-H H—N H-NI I )\%- I I I0 0 0-’I40—N_Ln N—O3+00\/N0cappedsandwich dimer*neutral charge, water solubility and lipophilicity are important factors for in viva mobility ofmetal complex imagthg agents.HN / NH(Ln ) F— —,N N N N280Chapter IV H3dharren Ligand System4.2 Experimental SectionMaterials Hydrated lanthanide salts, tris(2-aminoethyflamine (tren), anddehydroacetic acid were purchased from Aldrich or Alfa and used without furtherpurification. Ethanol was dried over 4A molecular sieves.Instrumentation. NMR spectra (200 and 400 MHz) were recorded on Bruker AC200E and WH-400 spectrometers, respectively. NMR data were reported as 8 (ppm)downfield of external TMS. Mass spectra were obtained with either a Delsi NermagRb-bC (desorption chemical ionization, DCI), a Kratos MS 50 (electron-impactionization, El), an AU MS-9 (fast atom bombardment, FAB), or a Kratos Concept II HQ(Cs liquid secondary ion mass spectrometry, LSIMS) instrument. UVJVIS spectra wererecorded on a Shimadzu UV-2 100 spectrometer.X-ray Crystallography. For the tables of selected crystallographic data and finalatomic coordinates of(H3dha2tren)N0 and [Nd(H3hatren)(NO)],please refer toTables A.9 - A. 12 in appendices.Preparations of the Ligand and its Complexes4.2.1 H3dhatren.This synthesis is simpler than the reported preparation.8 To a suspension of 10 g(60 mmol) of dehydroacetic acid in 100 mL anhydrous ethanol was added a solution of2.92 g (20 mmol) of tren in 10 mL ethanol. The mixture was heated at 60 OC for 20minutes, and then poured into 500 mL diethyl ether. A yellow powder formedimmediately. The suspension was kept in an ice-bath for approximately one hour, and81Chapter IV H3dha3tren Ligand Systemthe solid was then filtered out, washed with diethyl ether, and dried in air. The yield was12.0 g (86 %). Anal calcd (found) forC30H6N409.5H2:C 59.50 (59.64), H 6.16(6.08), N 9.25 (9.19). Mass spectrum (DCI): m/z = 597 (M =H4dha3trenj. JR (cm-1,KBr disk): 1700, 1662, 1640-1560, 1478 (all vs or s, tc=o). 1H NMR (200 MHz,CDC13): 6 2.0 (s, 9H, CH3), 2.5 (s, 9H, CH3), 2.9 (t, 6H, NCH2CH), 3.6 (q, 6H,NCH2CH), 5.5 (s, 3H), 13.9 (hr s, 3H, NH).The ligand H3dhatren can be hydrolyzed, losing one arm, to form(H3dha2tren)N0 in a wet methanol solution of Yb(N03). Anal calcd (found) forC2231N5OgH:C, 50.09 (50.29); H, 6.26 (6.23); N, 13.28 (13.11). Mass spectrum(LSJMS): ni/z = 447 (M =H3dha2trenj. JR (cm1,KBr disk): 1710, 1660, 1630-1575(all vs or s, Vc=o, tc=c). 1H NMR (400 MHz, D20): 6 1.9 (s, 6H, CH3), 2.3 (s, 6H,CH3), 2.65 (t, 4H, NCH2CH), 2.75 (t, 2H, NCHCH3), 3.0 (t, 2H,NCH2CH),3.4 (t, 4H, NCH2CH), 5.4 (s, 2H).4.2.2 Nd(dhatren)O.5NaNO 1.5H20.A solution ofH3dhatren (0.35 g 0.5 mmol) in 5 mL chloroform was added to asolution of Nd(N03).5H20(0.22 g 0.5 mmol) in 20 mL anhydrous ethanol and a whiteprecipitate formed immediately. Upon gradual addition of sodium acetate (0.12 g, 1.5mmol) in 10 mL methanol, the precipitate dissolved to give a pink solution from whichpink crystals formed slowly. The yield was 0.21 g (48 %). Most of the crystals crackedafter a few days. A crystal suitable for the X-ray diffraction was mounted in its motherliquor (however, the elemental formula of the X-ray structure sample picked from thesame bulk product was not the same as that of the bulk product, vide infra). Analytical,infrared spectral and mass (LSJMS) data are listed in Tables 4.1, 4.2 and 4.3,respectively. UV/vis spectra in MeOH, CHC13 and DMSO, as well as the 1H NMR82Chapter IV H3dhatren Ligand Systemspectrum in methanol, were similar to those of the ligand. A sodium flame test waspositive.4.2.3 Pr(dhatren).O.5NaNO3.1.5H20.The green crystals were synthesized by the same procedure as for the Nd analog.The yield was 0.23 g (55 %). Analytical, infrared spectral and mass (LSIMS) data arelisted in Tables 4.1,4.2 and 4.3, respectively.4.2.4 Ln(H3dhatren)(N03h (Ln = La, Pr, Nd, Gd, Yb)To a solution ofH3dhatren (0.5 nimol) in 10 mL chloroform was added dropwisea solution of Ln(N03)nH2O (0.5 mmol) in 10 mL methanol. Diethyl ether was vapourdiffused into the mixture and the solid precipitated gradually. The product was washedwith diethyl ether, and dried in vacuo at 60 OC overnight, all mp > 200 OC dec.Analytical, infrared spectral and mass (El or FAB) data are listed in Tables 4.1, 4.2 and4.3, respectively. The complexes dissolve in methanol, and are insoluble in chloroform.4.3 Results and Discussion4.3.1 Synthesis and Properties of H3dha3tren.Because of the resonance forms available to dehydroacetic acid (dha), reaction oftren with dha raises two questions. Which is the condensation site: the carbonyl of thering (to give la/lb in Scheme 4.1) or the carbonyl of an acetyl group at the side-chain (togive 2a/2b)? What is the conformation of the Schiff base ligand: the enol-imine (lb/2b)or keto-enamine (la/2a) form?83Chapter IV H3dha3tren Ligand SystemH3dhatrenScheme 4.1It has recently been shown, on the basis of an X-ray structure and NMR spectra,9that in 2-acetylcyclohexanone (where both a ring carbonyl and an acetyl group arepresent) ethylenediamine reacts preferentially with the carbonyl of the ring, rather thanwith the acetyl group, as had been originally proposed.’° In the reaction of tren withdha, we found, however, that the carbonyl of the acetyl group at the side chain was thepreferred reaction site. Crystal structures of both (H3dha2tren)N0,and the ligandH3dha3tren in the Nd complex, proved conclusively that the condensation reaction didoccur at the acetyl side chain, excluding the possible existence of ring carbonylderivatives (Ia) and (ib) in Scheme 4.1. The X-ray structures showed conclusively thatthe arms were in the tautomeric keto-enamine form (2a), as are most Schiff bases whichNH 0113dharing carbonylacetyl carbonylNH2trenor(la)or(ib)0 0(2a)OH(2b)84Chapter IV H3dha3 tren Ligand Systemare derived from f3-diketones and aliphatic amines.11’2 The preference of the Schiffbase for the keto-enamine over the enol-imine structure was confirmed in solution(CDC13)by the 1H NMR CH2-N coupling which showed a multiplet at 3.6 ppm for thea-hydrogen atoms of the secondary amine fragment coupled with hydrogen atoms onboth the adjacent methylene carbon and the neighboring nitrogen atoms. On treatmentwith D20, this signal simplified to a triplet (Figure 4.1) as a result of NH2 <--> ND2exchange. The crystal structure, as well as the 1H NMR spectrum in CDC13,confirmedthat H3dha3tren has the same keto-enamine conformation in the solid state as in thesolution, even though this conformation may have slightly less resonance stablization.13This is, however, favored by N-H---O hydrogen bonding which is generally stronger thanN---H-O hydrogen bonding.12 In this compound, the 1H NMR spectrum in CDC13showed a broad peak at 13.9 ppm, indicative of strong intramolecular hydrogen bonding.4.3.2 Metal ComplexesLn(Hdhatre )(N0)(Ln = La, Nd, Pr, Gd, Yb)Reactions of a lanthanide salt with one equiv ofH3dhatren in a mixture ofmethanol and chloroform, diffused with ether vapour, produce powders with theformulation Ln(H3dhatren)(N03)3. Mass spectral and infrared data were consistentwith the indicated formulation. In the mass spectra, Ln(H3dha3tren)(NO3)2 peaks wereobserved, indicative of the coordination of nitrate oxygens to the metal ions. Thecoordination of nitrate groups were also confirmed in the infrared spectra, which showedtwo peaks around 1380 and 1280 cm-1. These complexes most likely have a cappedstructure (Chart 4.1) very similar to that which was found and structurally characterizedin Yb(H3trac) N0).4In the infrared spectra, ligand bands in the complexes weresuperimposable on those of the free ligand. There is no absorption between 1660-1620cm1, excluding the C=N bond linkage of ligand in the complexes. The ‘H NMR data85Chapter IV H3dha3tren Ligand SystemFigure 4.1. Portion of 1ii NMR spectra (400 MHz) ofH3dhatren inCDC13 (top) and CDCI3-20(bottom) at room temperature.ppmL3.5 3.086Chapter IV H3dha3tren Ligand SystemTable 4.1 Analytical Data of the Lanthanide Complexes ofH3dhatren.calcd.(found), %C H NNd(dha3tren)0.5NaNOyl.5H2 44.63 (44.67) 4.49 (4.73) 7.81 (7.56)Pr(dhatren)0.5NaNO31.5H2O 44.81 (45.00) 4.51 (4.64) 7.84 (7.73)La(H3dhatren)(N0.3H2 36.93 (36.85) 4.34(4.10) 10.05 (9.80)Pr(Ildhatren)(N0)3.2.5H2 37.20 (37.38) 4.27 (4.24) 10.12 (9.82)Nd(Hdhatren) N0.3.50 36.40 (36.20) 4.38 (4.21) 9.90 (9.69)Gd(Hdhatren) N0.0.5EtOH.2H 37.27 (37.26) 4.34 (4.02) 9.81 (9.57)Yb(Hdhatren) N0).0.5EtO .H237.36 (37.55) 4.15 (4.40) 9.84 (9.47)showed that the ligand was not bound to the metal ion in methanol because theparamagnetic shifts were very small (<0.5 ppm) in the Nd, Pr, Gd, Yb complexes. Thechemical shifts for the diamagnetic lanthanum complex and the uncomplexed ligandwere essentially identical with, and were quite close to, those of the paramagneticlanthanide complexes. If the ligand were tightly bound in these complexes, theparamagnetic shifts should be much greater and the spectra should be broadened.4UV/vis spectra corroborated that the ligand was off in methanol solution, and washydrolyzed consequently, which was proven by the crystal structure of (H3dha2tren)N0(vide infra).87Chapter IV H3dhatren Ligand SystemTable 4.2. Infrared Spectral Data (cm-1,KBr disk) for the Lanthanide Complexes ofH3dhatren.complex IR bandsNd(dha3tren)0.5NaNO31.5H20 1712s, 1690s, 1662m, 1640-1530br s, 1478s(c=o, DCC), 1387 (VNO)Pr(dhatren)0.5NaNO’1.5H20 1702, 1692, 1660, 1640-1540, 1475 (s, co,cc), 1390 (tNo)La(H3dhatren)(N0.320 3700-2800 (m, tOH, N-H), 1678, 1608, 1480(s, vcc vc=o), 1390, 1310 (s, vNo)Pr(Hdhatren)(N0).2.5H2 3700-2700 (m,t0H, N-H) 1675, 1600, 1480(s, c=c, co), 1390, 1300 (s, No)Nd(H3dhatren) N0.3.50 3700-2700 (m, o$1, N-H) 1680, 1600, 1480(s, c=c, c=o), 1385, 1300 (s, tNC)Gd(Hdhatren) N0).0.5EtOH.2H23700-2700 (m, VQ41, N-H) 1672, 1600, 1475(s, c=c, co), 1385, 1300 (s, VN-O)Yb(H3dhatren) N0.0.5EtO .H 3700-2600 (m, 1)0H, N-H) 1680, 1605, 1478(s, vco), 1388, 1310 (s, No)4.3.3 Crystal Structure of(H3dha2tren)N0.In our first attempts to investigate the coordination properties of the tripodal ligandH3dha3tren with various metal ions, it was discovered that in wet methanol it ishydrolyzed to form(H3dha2tren). The further hydrolysis of the two remaining arms is88Chapter IV H3dhatren Ligand SystemTable 4.3. Mass Spectral Data (El, FAB, or LSIMS) for the Lanthanide Complexes ofH3dhatren.complex ,n/zLn(H3)(NO2 HLnL H4LNd(dha3tren)O.5NaNO3 1.5H20 597Pr(dhatren)0.5NaNO 1 .5H20 735 597La(H3dhatren)(N0.32 859 733 597Pr(Hdhatren)(N0.2.5 861 735 597Nd(Hdhatren) N0).3.50 738 597Gd(Hdhatren) N0.O.5EtOH.2H 878 752 597Yb(Hdhatren) N0.O.5EtO .H2 894 768 597prevented by the formation of the insoluble nitrate salt(H3dha2tren)N0. In order toH3dhatren (H3dha2tren) NO3examine bond parameters in the uncomplexed ligand, the nitrate salt (H3dha2tren)N0V3SNH0N03--- H?NLn(N03)0NMeOH89Chapter IV H3dha3tren Ligand Systemwas crystallized, and its crystal structure was determined. Bond lengths and bond anglesfor(H3dha2tren)N0 are listed in Table 4.4 while an ORTEP diagram is illustrated inFigure 4.2. The two arms were found in the tautomeric keto-enamine form with thehydrogen located on the nitrogen atom. The two arms are parallel (dihedral angle within6°) with the methyl groups on the exocyclic double bonds (C(4) and C(14)) oriented inopposite directions. The hydrogen atoms of the C(20) methyl group of(H3dha2tren)(N0)• 2 were (1:1) disordered with respect to a rotation about the C(17)-C(20) bond. Since the exocyclic keto-oxygen has greater electron density than theexocyclic ester-oxygen, it is not unexpected that all three intramolecular hydrogen bondsform between the exocyclic keto-oxygen and hydrogen atoms on the primary orsecondary amines. The H-bond length of H(2)---0(6) is 1.76 A, longer than that of H( 1)---0(3) (1.71 A). This is because 0(6) forms a second weaker H-bond with a primaryamine hydrogen (H(4)---0(6) = 1.93 A, N(4)-H(4)---0(6) = 159°). The nitrate grouphydrogen bonds to the ligand through one of the primary amine hydrogens (H(3)---0(9)= 1.90 A, 0(9)---H(3)-N(4) = 162°). The bond lengths (Table 4.4) show that the twoSchiff base arms of the ligand are quite delocalized. The C-0 lengths (average 1.26 A)are much closer to that of a C=0 double bond (1.24 A) than a C-0 single bond (1.33 A);the C-N bond lengths are the same as those found in another averaged structure (1.31A).54.3.4 Metal ComplexesLn(dha3tren)O.5NaNO1.5H2(La = Pr, Nd).Synthesis of these complexes was finally achieved with great difficulty. Thedryness of the solvents, as well as the selection of the metal ion was found to be crucialto the preparation. Only the Pr3 and Nd3 complexes could be prepared from thereaction of Ln(N03)nH2OwithH3dhatren and 3 equiv of anhydrous sodium acetate ina mixture of absolute ethanol, chloroform and methanol. (Reaction of La(NO3),90Chapter IV H3dha3 tren Ligand SystemFigure 4.2. ORTEP drawing of(H3dha2tren)(N03).H20 with numberingscheme.03H3H4H406C’sCiaCi?HZHiCS05Cs04 OiCzo91Chapter IV H3dhatren Ligand SystemTable 4.4. Bond Lengths (A) and Angles (deg) in(H3dha2tren)(N0). 2 withEstimated Standard Deviations.Bond Lengths (A)0(1) — C(6) 1.411(6) 0(1)—C) 1.363(6)0(2) - C(6) 1.196(6) 0(3) - C(9) 1.257(5)0(4) - C(16) 1.405(5) 0(4) - C(17) 1.362(5)0(5) - C(16) 1.208(5) 0(6) - C(19) 1.256(4)NO) - C( 1) 1.471 (5) NO) - C(11) 1.476 (5)NO) - C(21) 1.469 (5) N(2) - C(2) 1.465 (5)N(2)- C( 3) 1.309 (5) N(3)- CO ) 1.468(5)N(3) - C(13) 1.306(5) N(4) - C(22) 1.471 (5)CU) - C(2) 1.504(6) C(3) -. C(4) 1.498(6)C(3) - C(5) 1.425(6) C(S) - C(6) 1.434(6)C(S) - C(9) 1.440(6) CC) - C(8) 1.3 14(7)CC) - COO) 1.487(7) C(8) - C(9) 1.419(6)C(11)-C(12) 1.517(6) C(13)-C(j14) 1.496(6)C(13)-C(15) 1.433(6) C(15)- C(16) 1.431(6)C05) - C(19) 1.428(6) C(17)-C(18) 1.317(6)C(17) - C(20) 1.500(7) C(18) - C(19) 1.435(6)C(21) - C(22) 1.505(6) 0(7) - N(S) 1.184(5)0(8) - N(S) 1.176(6) 0(9) - N(S) 1.226(5)Bond AnglesC(6) - 00) - CC) 122.7(4) C(16) - 0(4) - C(17) 122.2(4)CU) — NO) — C(11) 111.7(4) CU) — NO) — C(21) 109.6(3)CU 1)— N(1) — C(21) 111.0(3) C(2) — N(2) — C(3) 130.4(4)92Chapter IV H3dhatren Ligand SystemGd(N03),Yb(N03)with H3dha3tren ligand gave the final product containing no ligandvisible in infrared spectra) Elemental analyses suggested the formulationLn(dhatren)-O.5NaN0y1.5H0, while infrared spectra showed strong nitrate peaksC(12) - N(3)-C(13) 127.4(4) NO) - CU) - C(2) 111.8(4)N(2) - C(2)- CU) 109.6(4) N(2) - C(3) - C(4) 118.8(5)N(2) - C(3) - C(5) 118.3(4) C(4) - C(3) - C(5) 122.8(5)C(3) - C(S) - C(6) 119.3(5) C(3) - C(5) - C(9) 120.6(5)C(6) - C(S) - C(9) 120.1(5) 0(1) - C(6) - 0(2) 114.3(5)00) - C(6) - C(5) 116.4(5) 0(2)-. C(6) - C(S) 129.4(6)00) - C(7) - C(8) 121.0(5) 0(1) - CC) - COO) 112.5(5)C(8) - CC) - COO) 126.5(6) CC) - C(8) - C(9) 122.7(5)0(3) - C(9) - C(S) 123.8(5) 0(3) - C(9) - C(8) 119.2(5)C(S) — C(9) — C(8) 117.0(5) NO) — CO 1) — C( 12) 111.9(4)N(3)—C(12)—C(11) 109.1(4) N(3)—C(13)—C(14) 118.3(4)N(3)-C(13)-C(15) 118.0(4) C(14)-C(13)-C(1S) 123.7(4)C(13)- CUS) - C(16) 118.7(4) C(13) - CUS) - C(19) 121.4(4)C(16) - C(1S)- C09) 119.9(5) 0(4) - C(16) - 0(5) 112.4(4)0(4)-C(16)- CUS) 117.3(4) 0(5) - C(16) - C(15) 130.3(5)0(4)-C(17) - C(18) 120.8(5) 0(4)-C(17) - C(20) 111.2(5)C(18)-C(17) - C(20) 128.0(5) C(17)-C(18) - C(19) 122.7(5)0(6) - C(19)- CUS) 124.2(4) 0(6) - C(19) - C(18) 119.2(4)CUS) - C(19) - C(18) 116.6(4) NO) - C(21) - C(22) 113.9(4)N(4) - C(22) - C(21) 112.6(4) 0(7) - N(S) - 0(8) 116.2(6)OC) - N(S) - 0(9) 124.2(6) 0(8) - N(S) - 0(9) 119.5(6)93Chapter IV H3dhcitren Ligand Systemaround 1380 cm-1, and both complexes gave positive sodium flame tests. The complexesdemetallated in methanol and DMSO, as evinced in the UV/vis and ‘H NMR spectra,demonstrating the instability of these complexes over periods of time in donor solvents.Our inability to prepare other lanthanide complexes, and the instability of the Pr and Ndcomplexes are consistent with a lack of flexibility in the chelating pendants due to theexocyclic ring double bond, and the weaker basicity of the exocyclic keto-oxygen on theconjugate chelate ring as compared with a phenolate oxygen, for example.134.3.5 Crystal Structure of[Nd(U3dhatren)(NOhj.Although characterization of the bulk samples of the lanthanide complexes gavethe formulation Ln(dha3tren)0.5NaNOyl.5HO, the single crystals picked from thesame batch* gave the polymeric structure with the empirical formulationNd(H3dhatren)(NO3).Bond lengths and bond angles of the coordination sphere in[Nd(H3dha3tren)(NO3)3] are listed in Table 4.5 while the ORTEP diagrams of thecoordination environment around the metal ion and the three dimensional polymer (instereo) are illustrated in Figures 4.3 and 4.4, respectively. The two neodymium atomsform a dinuclear center through four bridging nitrate groups, and neighbouring dinuclearcenters are linked together by the ligands to build a polymer in a three dimensional array.Each neodymium atom is coordinated by nine oxygens, and the geometry around each ofthe metal ions is a monocapped square antiprism and the Nd-Nd distance is 4.06 A.As is shown in Figure 4.3, among the nine oxygen atoms coordinated to theneodymium atom, two exocyclic keto-oxygen atoms are from two separate ligands with* There are three different shapes of crystals: cube, parallelepiped and trigonal prism. They allshare the same unit cell.94Chapter IV H3dhatren Ligand SystemFigure 4.3. ORTEP drawings of the coordination environment of Nd in[Nd(N03)3(Hdha3tren)]n (left) and of one [Nd(N03)(Hdhatren)]unit, both with the numbering scheme.03 018C2408018012do011NdI*01 01502C2 1C1401803C22N4C23Ndl*CI SC19C2007C3095Chapter IV H3dha3 weiz Ligand SystemFigure 4.4. ORTEP stereoview of polymer [Nd(N03)(Hdhatren)ln.96Chapter IV H3dha3tren Ligand Systeman average Nd-a distance of 2.49 A, similar to that found in an eight-coordinateneodymium acetylacetonate complex14 and a nine-coordinate neodymium oxalatecomplex.15 The other seven oxygen atoms are from three kinds of nitrate ligands,classified in terms of their coordination modes to each of (Nd(1), Nd(1)*). One is thebridging (unidentate, unidentate) mode -- the N(5) nitrate spans two Nd atoms throughthe two oxygen atoms 0(10) and 0(11). The Nd-O distances are Nd(1)-O(1O) = 2.36(1)and Nd(1)O(11’)* = 2.418(9) A, and the corresponding N-O distances are 1.23(1) A and1.30(1) A, respectively, with the enlarged O-N-O angle of 130(1)°. A second mode isthe simple bidentate nitrate (N(7)) -- the nitrate group forms a four-membered chelatering incorporating one neodymium atom with Nd(1)-0(17) = 2.545(8) A and Nd(1)-0(16) = 2.603(8) A, consistent with those found in the ten-coordinatedaquonitratoneodymium complex16 and eleven-coordinated bipyridylnitratoneodymiumcomplex.17 The corresponding N-O distances are 1.23(1) A and 1.29(1) A, respectively,and the O-N-O angle is 117W°. (The atoms of the four-membered ring Nd(1), Nd(1)*,0(13), 0(13)* are all in the same plane, which is almost perfectly perpendicular to theeight-membered ring composed of Nd(1), 000), 0(11), N(5), Nd(1)*, 0(10)*, 00 1)*N(5)*.) The third mode is the bridging (bidentate, unidentate) nitrate (N(6)) -- the nitrateligand bridges the two Nd atoms with one oxygen atom (0(13)), while the other oxygenatom (004)) is only coordinated to one Nd. Generally, when bridging oxygen atomsform two strong M-O bonds, their basicity should be lowered from that of a singlybonded oxygen atom and their bond lengths are accordingly longer. However, the Nd-Odistances (Nd(l’)-0(14) = 2.541(7) A and Nd(1)-O(13) = 2.594(7) A) coordinated to oneNd atom, are much longer than that to another Nd atom (Nd(1)O(13)* = 2.418(7) A).The N-0 distances in this unusual nitrate are as to be expected; the N-O related to theunbridging oxygen (N(6)-O(l4)) is 1.240) A, much shorter than N(6)-O(13) of related tothe bridging oxygen (1.340) A).97Chapter IV H3dhatren Ligand SystemTable 4.5. Bond Lengths (A) and Angles (deg) in [Nd(N03(H3dha3tren)]n withEstimated Standard Deviations.Bond Lengthsatom atom distance atom atom distanceNd(1) 0(3) 2.481(8) 003) N(6) 1.340)Nd(1) 0(6)* 2.486(7) 0(14) N(6) 1.24(1)Nd(1) 0(10) 2.360) 005) N(6) 1.560)Nd(1) 001)* 2.418(9) 0(16) NC) 1.29(1)Nd(1) 003) 2.594 (7) 007) NC) 1.23(1)Nd(1) 003)* 2.419(7) 008) NC) 1.200)Nd0) 004) 2.541(7) N(2) C(3) 1.270)Nd0) 006) 2.603(8) N(3) C(13) 1.30(1)Nd(1) 007) 2.545(8) N(4) C(23) 1.31(1)0(1) C(S) 1.400) C(3) C(6) 1.45(2)0(1) C(9) 1.360) C(S) C(6) 1.450)0(2) C(S) 1.190) C(6) CC) 1.420)0(3) CC) 1.270) CC) C(8) 1.430)0(4) C(1S) 1.420) C(8) C(9) 1.30(2)0(4) C09) 1.370) C(13) C(16) 1.430)0(5) C(1S) 1.230) C(1S) C(16) 1.42(2)0(6) C(17) 1.240) C(23) C(26) 1.420)OC) C(25) 1.370) C(25) C(26) 1.46(2)OC) C(29) 1.38(2) C06) C07) 1.45(1)0(8) C(25) 1.210) C(17) C(18) 1.400)0(9) C(27) 1.220) C(18) C(19) 1.320)000) N(S) 1.230) C(26) C(27) 1.440)98Chapter IV I-I3dhatren Ligand System0(11) N(5) 1.30(1) C(27) C(28) 1.44(2)002) N(5) 1.62(2) C(28) C(29) 1.31(2)Bond Anglesatom atom atom angle atom atom atom angle0(3) Nd(1) 0(6)* 70.5(3) 0(13) Nd(1) 004) 52.0(2)0(3) Nd(1) 0(10) 142.3(3) 0(13) Nd(1) 006) 135.7(3)0(3) Nd(1) 0(10* 78.9(2) 003) Nd(1) 007) 147.6(3)0(3) Nd(1) 003) 121.1(2) 0(13)* Nd(1) 004) 121.7(2)0(3) Nd(1) 0(13)* 143.7(2) 0(13)* Nd(1) 006) 73.5(3)0(3) Nd(1) 0(14) 71.9(2) 0(13)* Nd(1) 007) 83.5(2)0(3) Nd(1) 006) 75.9(3) 0(14) Nd(1) 006) 1380(3)0(3) Nd(1) 0(17) 91.2(3) 0(14) Nd(1) 0(17) 154.2(3)0(6)’ Nd(1) 0(10) 71.8(3) 0(16) Nd(1) 0(17) 49.2(3)0(6)’ Nd(1) 0(10* 145.3(3) Nd(l) 0(3) C(7) 134.9(8)0(6)’ Nd(1) 0(13) 111.7(2) Nd(1)” 0(6) C(17) 147.4(8)0(6)’ Nd(1) 0(13)* 140.4(3) Nd(1) 0(10) N(S) 138(1)0(6)’ Nd(1) 0(14) 81.1(2) Nd(1)* 0(11) N(S) 133.8(9)0(6)’ Nd(1) 006) 112.6(3) Nd(1) 003) Nd(1)* 108.2(2)0(6)’ Nd(1) 0(17) 74.8(2) Nd(l) 003) N(6) 89.4(6)000) Nd(1) 0(10* 136.3(3) Nd(1)* 003) N(6) 150.3(7)0(10) Nd(1) 003) 72.9(3) Nd(1) 004) N(6) 94.2(7)000) Nd(1) 0(13)* 72.0(3) Nd(1) 006) NC) 94.9(7)000) Nd(1) 004) 101.5(3) Nd(1) 007) NC) 99.4(8)000) Nd(1) 006) 120.4(3) 0(10) N(S) 001) 130(1)000) Nd(1) 0(17) 79.8(3) 0(10) N(5) 002) 1190)000* Nd(1) 003) 70.7(2) 001) N(S) 002) 112(1)99Chapter IV ll3dhatren Ligand System0(l1)* Nd(1) 0(l3)* 74.2(3) 0(13) ?(6) 0(14) 122(1)0(11)* Nd(1) 0(14) 73.9(3) 0(13) N(6) 0(15) 1160)0(11)* Nd(1) 006) 74.0(3) 004) N(6) 005) 121(1)0(11)* Nd(1) 007) 122.9(3) 006) N(7) 0(17) 1170)0(13) Nd(1) 0(13)* 71.8(2) 0(16) N(7) 0(18) 119(1)0(17) N) 008) 1240)Symmetry operations: (*) 2-x, l-y, 1-z; (‘) l12+x, l/2-y, -1/2+z; (“) -112+x,l/2-y, 12+zThe nitrate group can coordinate to a metal ion in many ways. The commoncoordination modes are shown in Scheme 4.2. Most nitrate complexes contain only oneor two coordination modes; it is very rare to have many nitrate modes within onecompound. To our knowledge, only one complex, [{Ph2Te(N03)}01-Ph7Te(N03)(OH),’8has more than two modes. The [tSd(H3dhatren)(N0)1structureis the first lanthanide compound that contains so many nitrate modes in one threedimensional polymeric molecule.Coordination of the ligand to the metal ion results in three distinct hydrogen bonds.In one arm, the hydrogen HO) on the secondary amine N(2) intramolecularly hydrogenbonds with the coordinated exocyclic keto-oxygen 0(3), and with the nearby coordinatedoxygen of the nitrate group. The H( 1 )---0(3) and H( 1 )---0( 14) distances are 1.84 A and2.28 A respectively, and the corresponding N-H---0 angles are 136° and 131°. The H-bond also causes lengthening of the corresponding C-0 bond (C(7)-0(3) = 1.270) A)compared to the non-H-bonded C-0 length (C(17)-0(6) = 1.24(1) A). In the second ann,after coordination of the exocyclic keto-oxygen 0(6) to the Nd atom, an intramolecularH-bond forms between the exocyclic ester-oxygen 0(5) and the hydrogen H(2) on the100Chapter IV H3dha3tren Ligand Systemsecondary amine (H(2)---O(5) = 1.79 A, N(3)-H(2)---O(5) = 134°). The H-bond of H--0 (ester) is a bit weaker than that of H---0 (keto). In the third free arm, the hydrogenbonding is unchanged from that in the free ligand.0N M’ “N—C,o,“0M0,0\0 ° ° M N—C/ K’M N—C—M MM CM M “C’MM C4 C’C 4IN\ /‘M’ “MMjMM’M MScheme 4.2 Common Nitrate Coordination ModesReferences(1) Liu, S.; Yang, L.-W.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1993, 32, 2773.(2) Liu, S.; Gelmini, L.; Rettig, S. J.; Thompson, R. C.; Orvig, C. J. Am. Chem. Soc.1992, 114, 6081.(3) Yang, L.-W.; Liu, S.; Wong, E.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1995, 34,2164.(4) Berg, D. J.; Rettig, S. J.; Orvig, C. J. Am. Chem. Soc. 1991, 113, 2528.(5) Smith, A.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1988, 27, 3929.101Chapter IV H3dha3tren Ligand System(6) Sitran, S.; Fregona, D. J. Coord. Chem. 1990, 22, 229.(7) Liu, S.; Rettig, S. 1.; Orvig, C. Inorg. Chem. 1991, 30, 4915.(8) Carugo, 0.; Castellani, C. B. Polyhedron 1992, 11, 21.(9) Fernandez-G., J. N.; EnrIquez, R. G.; TobOn-Cervantes, A.; Bernal-Uruchurtu, M.I.; Villena-I., R.; Reynolds, W. F.; Yang, 1.-P. Can. J. Chem. 1993, 71, 358.(10) Moss, K. C.; Robinson, F. P. Can. J. Chem. 1973, 51, 505.(11) Tan, S.-F.; Ang, K.-P.; Jayachandran, H. L.; Jones, A. J.; Begg, W. R. J. Chem.Soc. Perkin 111982,513.(12) Brown, N. M. D.; Nonhebel, D. C. Tetrahedron 1968, 24, 5655.(13) Silverstein, R. M.; Bassler, G. C.; Morrill, T. C. Spectrometric Identification ofOrganic Compounds; 4th ed.; John Wiley & Sons: 1981.(14) Aslanov, L. A.; Porai-Koshits, M. A.; Dekaprilevich, M. 0. J. Struct. Chem. (Eng.TransL) 1971, 12,431.(15) Kahwa, I. A.; Fronczek, F. R.; Selbin, 1. Inorg. Chim. Acta 1984,82, 161.(16) Rogers, D. J.; Taylor, N. 1.; Toogood, G. E. Acta Cryst. 1983, C39, 939.(17) Al-Rasoul, K.; Weakley, T. J. R. Inorg. Chim. Acta 1982, 60, 191.(18) Alcock, N. W.; Harrison, W. D. J. Chem. Soc. Dalton Trans. 1982, 1421.102Chapter V H3Brapt Ligand SystemChapter V Lanthanide(III) and Copper(II) Complexes of1,4,7-Tris(((2-hydroxy-5-bromobenzyl)amino)propyl)-1,4,7-triazacyclononane5.1 IntroductionTripodal polydentate amine phenol ligands are of particular interest to us because ofthe high affinity of concomitant phenolate oxygen and amine nitrogen donors for trivalentmetal ions, and because of the intrinsically three-dimensional cavities imposed by thepreorganized ligand framework.1 In previous work,16 our group has reported fourtripodal amine phenol ligand systems (Chart 5.1): (i) a tren-based (tren = tris(2-aminoethyflamine) symmetric N403 amine phenol, in which three chelating arms arebridged by a tertiary nitrogen atom; (ii) a trien-based (trien = triethylenetetraamine)asymmetric N403 amine phenol; and (iii) and (iv) tame- and tap-based (tame = 1,1,1-tris(aminomethyl)ethane; tap = 1,2,3-triaminopropane) N30 amine phenols, in whichthree chelating arms are bridged by a tertiary carbon atom. In the tren- or trien-basedN403amine phenols, the coordination modalities are largely dependent on the size and donoratom selectivity of the metal ions. For the large lanthanide ions, the cavity of the N403amine phenol ligands is slightly too small to completely enclose the metal ion, andformation of dinuclear,4bicapped complexes,3and distortion of coordination geometry2has been reported. For the small group 13 metal ions Al3 and Ga3, the cavity is toolarge for all seven donors to coordinate to the metal ion; therefore, six-coordinate cationiccomplexes of tren-based ligands were isolated;6 the cavity seems to match the largerindium(Ill) the best.2’6(all seven donor atoms coordinated In(ffl) without any strain on theligand framework.) In the tame- and tap-based N30 amine phenol ligands,1’5the C-bridged framework can be considered more preorganized than the N-bridged one since it103Chapter V 113Brapt Ligand Systemcan not undergo an umbrella type inversion as the tertiary nitrogen does.7 On the otherhand this rigid framework is quite flexible through the three chelating arms; angles A, B,and C (Chart 5.1) can be compressed or expanded within a small range to accommodatetap-based (R = H, Cl, Br) N30Fltame-based (R = H, Cl, Br) N3ORtren-based (R = H, Cl, Br) N4O3HOHtrien-based N4O3Chart 5.1A AR R RI’CN HN”ThI’rNH HNThNHOH\/104Chapter V H3Brapt Ligand Systemmetal ions of different sizes. All six-coordinate complexes of the group 13 metalsaluminum, gallium and indium were formed without significant strain on the coordinatedligand framework.5 In order to delineate the influence of changes in the ligand frameworkon the fit between the cavity size of an amine phenol ligand and the size of a coordinatedlanthanide ion, and to take advantage of the non-inverting C-bridged framework,hexaamine 1,1, 1-tris(4-amino-2-azabutyl)ethane (sen8) and 1,1, 1-tris(5-amino-2-azapentyl)ethane (stn) (Chart 5.2) were chosen as backbones for the syntheses of the N603N H2sen taetacn taptacnstnChart 5.2ligands H3sal3sen and H3sal3stn, respectively, and their corresponding amine phenols(Scheme 5.1). The increase of the cavity size from the tame-based N30amine phenol tothe sen- or stn-based N603amine phenol should have a closer fit for the large lanthanideions. Unfortunately, the reaction of sen with 3 equiv salicylaldehyde did not afford thepure Schiff base H3sal3sen; instead, both the primary and secondary amines react withsalicylaldehyde to give a mixture of ligands containing three and four phenols (Scheme5.1). There is an equilibrium between these two Schiff bases since H3sal3sen is stericallyfavored while reactivity of both primary and secondary amines allows the formation of105Chapter V H3Brapt Ligand SystemHN+HOH4sal4sen which is sterically unfavored. (At this stage, all the attempts to purify Schiffbase H3sal3sen have been unsuccessful.*)+ H o21:3 ratioor1:4 ratioH3salen H4salenScheme 5.1To solve this problem, analogous three-dimensional hexaamines 1,4,7-tris(3-aminopropyl)- 1 ,4,7-triazacyclononane (taptacn) and 1 ,4,7-tris(2-aminoethyl)- 1,4,7-triazacyclononane (taetacn) (Chart 5.2) were considered. Most importantly, the 9-* Several methods were tried: a) TLC (no suitable solvent or solvent pair was found for the separation); b)formation of a 1:1 lanthanide complex did not cause an isolable precipitate to form; c) reaction ofCo(sen)C13with salicylaldehyde did not occur (Co3 was used as a template, however, both the primaryand secondary amines were inactive after coordination to the metal ion).106Chapter V H3Brapt Ligand Systemmembered ring is quite rigid, and should impose rigidity on the ligand framework in amanner similar to the tertiary carbon of sen or sth. Although there have been reports on thecomplexes of taptacn with transition metal ions,9 no studies have been reported on thefunctionalization of taptacn. In this chapter, the synthesis and characterization of the firsttaptacn-based amine phenol ligand 1 ,4,7-tris(((2-hydroxy-5-bromobenzyl)amino)propyl)-l,4,7-triazacyclononane (H3Brapt) is reported, as well as its lanthanide complexes.Variable temperature 1H NMR of Ln(H3Brapt)(Tf) in CD3N suggests that thecoordination mode of the ligand changes across the lanthanide series.NNBr6BrH3BraptThe synthesis of a dinuclear La-Cu complex with this ligand is also explored.Exchange interactions involving transition and rare earth metal ions are relevant to manydifferent scientific fields.10 In solid-state physics, rare earth ions have been used tomodulate the properties of magnets.’012 In biological studies, lanthanide ions have beenused as relaxation agents for metalloproteins in order to obtain structural information insolution.13 Recently much attention has been paid to the new superconductors of* The transition temperature at which superconducting properties appear or disappear.107Chapter V H3Brapt Ligand Systemthe YnBamCuxOy type, where the substitution of Y with lanthanides does not vary thesuperconductive properties of materials.14’5 Some coordination compounds have alreadybeen considered as useful precursors in the preparation of mixed oxides.1618 All thesestudies demand that the nature of the interaction of the lanthanide ions with the transitionmetal ions should be better understood, especially in order to establish useful structural-magnetic relations.Polydentate ligands can readily act as polynucleating ligands. In the case ofdinucleating ligands, several types have been synthesized (Chart 5•319), mostly by metaltemplating Schiff base condensation; however, only limited numbers of asymmetric4-- N’’O’’N_-NN 0 NN0NRN 0macrocycles side-off acyclic ligands end-off acyclic ligandsNONpolypodal ligands constrained remote chambersChart 5.3dinucleating ligands, which are suitable for the formation of Ln-transition metal dinuclearcomplexes, have been synthesized.17’8 H3Brapt is a potential asymmetric dinucleatingligand; it has two potential inequivalent compartments. The lower compartment hasoxygen donors which should bind preferentially to metal ions capable of very ionic108Chapter V H3Brapt Ligand Systembinding, such as lanthanide ions, while the upper compartment contains nitrogen donorswhich can be incorporated into more covalent binding, such as with transition metal ions.Since we were interested in understanding the coordinating behavior of H3Brapt as adinucleating ligand, the synthesis and characterization of a La-Cu complex is presented inthis chapter.5.2 Experimental SectionMaterials. Hydrated lanthanide salts, lanthanide oxides,trifluromethanesulfonic acid, ethylene glycol, diethylenetriamine, triethylamine, ptoluenesulfonyl chloride, sodium hydride, sodium, acrylonitrile, potassium borohydride,and 5-bromosalicylaldehyde were purchased from Fisher, Aldrich or Alfa and were usedwithout further purification. DMF was dried over CaO overnight and then distilled fromCaO at reduced pressure. 60 % NaH was rinsed with petroleum ether before use (caution!NaH is explosive when it contacts with water). Water was deionized (BarnsteadD8902 and D8904 cartridges) and distilled (Corning MP-1 Megapure still). Ethanol wasdistilled from magnesium under Ar immediately prior to use. Methylene chloride wasdried over 3 A molecular sieves. Manipulations of moisture sensitive compounds wereaccomplished with Schlenk line and syringe techniques and the use of an N2-filledglovebox, as specified in the experimental procedures below. Lanthanide triflates20’1 andhexaamine taptacn22 were synthesized using modified literature methods.Instrumentation. NMR spectra (200, 300, and 400 MHz) were recorded onBruker AC-200E, Varian XL 300 or Bruker WH-400 spectrometers, respectively. NMRdata were reported as S (ppm) downfield from external TMS or internal solvent. Mass109Chapter V H3Brapt Ligand Systemspectra were obtained with a Kratos MS 50 (chemical ionization, CI), or a Kratos ConceptII H32Q (Cs liquid secondary ion mass spectrometry, LSIMS) instrument. UV/visspectra were recorded on either a Shimadzu UV-2 100 (range: 200-800 nm) or a Cary 5UV-VIS-NIR (range: 200-3000 nm) spectrometer.Syntheses of Ligands5.2.1. Diethylene-1,4,7-triamine-tritosylate2Diethylenetriamine 8.26 g (0.08 mol) and NaOH 9.6 g/\ /j\ (0.24 mol) were dissolved in 80 mL water. This solutionHN N NHo2s o2s so2 was added dropwise to p-toluenesulfonyl chloride (TsC1): : i 45.6 g(0.24 mol) in 240 mL diethyl ether. The mixture11 6 was stirred for 2 hours at room temperature. The product12CH3 7CH3 CH3was filtered off and washed with water, then diethyl ether.Recrystallization from MeOH yielded a white solid. Theyield was 30 g (70 %), mp 157-159 oC. 1H NMR (200 MHz, acetone-d6): 7.7 (d,phenyl, 4H9); 7.58 (d, phenyl, 2H4); 7.37 (d, phenyl, 4H10); 7.33 (d, phenyl, 2H5); 6.5(t, NH, 21-1); 3.06 (m, CH28ff); 2.2 (s, CH3 9H). 13C NMR (50 MHz, CDC13):130.0 (C9); 129.8 (C4), 127.3 (C10), 127.2 (C5), 50.6 (C2), 42.6 (C1), 21.5 (C7 andC12). Mass spectrum (CI, NH3 gas): m/z 583 (M + NH4j; 567 (M + 1).5.2.2 Ethyleneglycol ditosylate23Ethylene glycol 18.6 g (0.3 mol) in pyridine (1000 mL) was cooled toO OC underN2. TsC1 114 g (0.6 mol) was added in small portions. The solution was stirred at 0 OC110Chapter V H3Brapt Ligand Systemfor 5 hours and then poured onto crushed ice (1000 mL). This wasacidified with concentrated HCI until pH = 1 (about 1000 rnL HC1).02S SO2 The resulting white precipitate was filtered out, washed with cold3 Zwater, recrystallized from hot methanol, and dried in vacuo at 60 OC4’%.5 overnight prior to use. The yield was 50 g (50 %), mp 120-122 OC.6CH3 CH31H NMR (200 MHz, CDC13): 7.7 (d, phenyl, 4H3); 7.2 (d, phenyl,4H); 4.1 (s, CH24W; 2.4 (s, CH3 6H). 13C NMR (50 MHz, CDC13): 145.0(C2), 132.1 (C5), 129.7 (C3), 127.7 (C4), 66.5 (CH2C),21.4 (CH3). Mass spectrum(CI, NH3 gas): m/z 388 (M + NH4j.5.2.3. 1,4,7-Triazacyclononane tritosylate22Diethylene- 1 ,4,7-triaminetritosylate (24.1 g,SO2 0.0427 mol, dried in vacuo at 60 OC overnight)(TS Ts = was dissolved in dry DMF (500 ) to wifich wasNTs Ts’i added 60 % NaH 4 g’ (0.17 mol). The solution6CH3was heated to 70 OC and stirred under N2 for 30minutes. A solution of ethyleneglycol ditosylate 15.8 g (0.0427 mol) in dry DMF (200rnL) was then added dropwise over a 4.5-hour period. The solution was maintained at 70OC under N2 for a further 23 hours. The volume was reduced to about 120 mL (bydistillation), and the solution was added slowly, with stirring, to 1200 mL ice and water.The product was stored in the refrigerator overnight, filtered, washed with water, EtOH,and ether, and dried in air for 2 days, then in vacuo at 60 OC overnight. The yield was 23g (90 %). 1H NMR (200 MHz, CDC13): 7.6 (d, phenyl, 6H), 7.2 (d, phenyl, 6H), 3.3(s, CH2 12H), 2.4 (s, CH3 12H). ‘3C NMR (50 MHz, CDC13): 143.9 (C2), 134.6(C5), 129.9 (C3), 127.5 (C4), 51.9 (CH2C),21.6 ( CH3). Mass spectrum (LSIMS):m/z 592 (M + 1). TLC (eluent: CH1:MeOH = 99:1) showed one spot in the final* NaH is in slight excess because there is a loss when it is rinsed with diethyl ether.111Chapter V H3Brapt Ligand Systemproduct with Rf = 0.37 (compared to 0.63 and 0.19 for the starting materialsethyleneglycol ditosylate and diethylene- 1 ,4,7-triaminetritosylate, respectively). All thecharacterization indicated that this product was pure and was used in the next step withoutfurther purification.5.2.4. 1,4,7-Triazacyclononane trihydrogenchioride (tacn•3HC1)221 ,4,7-triazacyclononane tritosylate (23 g) was added to4H2”\ concentratedH2S04(35 mL); the brown mixture was heated atH2N H2N” Cl3 160 OC for 30 minutes under N2. The solution was then cooled\ / to room temperature before being added dropwise to coldethanol (184 mL). Diethyl ether (322 mL) was also addedduring the addition. After being stored overnight in the refrigerator, the brown precipitatewas filtered, dissolved in water, and Norit was added. The solution was boiled for 15minutes, filtered, and the solvent removed on the rotovap. Concentrated HC1 (23 mL) wasadded, followed by ethanol (138 mL). The white solid was filtered, washed with ethanol,diethyl ether, and recrystallized from aH2OIEtOH (40 mL/240 mL) mixture. The yieldwas 8.2 g (90 %). 1H NMR (200 MHz, D20): 3.5 (s, NHCHCH). 13C NMR (50MHz, D20): 45.1.5.2.5. 1,4,7-Triazacyclononane (tacn)22Method 1. Tacn3HC1 (8.1 g) was dissolved in deionized water (18f mL) and the pH was brought to 13 by the addition of NaOH pelletsN\H__H1 (4.24 g, 2.8 equiv). The desired product was extracted into chloroformby a continuous extraction for 48 hours. The layers were separated, andthe aqueous layer was extracted with chloroform (2 X 20 mL). The combined chloroformlayers were dried over sodium sulphate, and subsequently filtered. The solvent wasremoved to yield a pale yellow oil containing some colorless crystals; this was stored in the112Chapter V H3Brapt Ligand Systemfreezer. The yield was 2.8 g (64 %). 1H NMR (200 MHz, CDC13): 2.7 (s,NHCH2CH). 13C NMR (50 MHz, CDC13): 47.1. Mass spectrum (LSJMS): m/z 130(M + 1). The product was pure and no recrystallization was needed.Method 2. In 5.2.4, after decolorization, NaOH was added to the aqueoussolution to adjust pH to 13. The resulting precipitate was filtered out, and the viscoussolution was CHC13-extracted continuously for 2 days, followed by the same workup as inMethod 1. The yield was 4.5 g (90 %).5.2.6. 1,4,7-Tris(2-cyanoethyl)-1,4,7-triazacyclononane(tcetacn)92.0 g 1,4,7-triazacyclononane was refluxed inCNacrylonitrile (30 mL, 10-fold excess) for 2 hours underf_N m an atmosphere of N2. The excess solvent was removedNC______ CN by rotary evaporation, leaving a yellow oil. Theproduct was dried at 60 OC in vacuo overnight. Theyield was 3.8 g (85 %). H NMR (200 MHz,CD3N): 2.8 (t, NCH2CHN), 2.7 (s, NCH2CH), 2.5 (t, CH2N). 13C NMR (50MHz, CD3N): 120.8 (CN), 55.9 (NCHCHN), 54.4 (NCH2CH), 17.3 (CH2CN).Mass spectrum (LSIMS): m/z 289 (M + 1), 248 (M - CH2N).5.2.7. 1,4,7-Tris(3-aminopropyl)-1,4,7-triazacyclononane(taptacn)9Na metal (3 g) was suspended in refluxing toluene (100N mL). To this mixture was added dropwise a solution ofNit ( H2N tcetacn (2.0 g) in absolute ethanol (20 mL) over a 1 hourperiod. The mixture was further refluxed for 2.5 hours at113Chapter V H3Brapt Ligand Systemwhich point all the Na had dissolved. After cooling, the precipitate was removed byfiltration and rinsed with toluene four times. The solvent was removed by rotaryevaporation and the residue was subsequently extracted with hot petroleum ether (10 x 25mL). The combined fractions were filtered, and on removal of solvent, a pale yellow oilremained. The yield was 1.44 g (69 %). 1H NMR (200 MHz, CD3N): 2.7 (s,NCH2CH), 2.65 (t, NCH2CH),2.5 (t, CH2N), 1.5 (q,CH2N)5.2.8. 1,4,7-Tris(((2-hydroxy-5-bromobenzyl)amino)propyl)-1,4,7-triazacyclononane (H3Brapt)A solution of 5-bromosalicylaldehyde (3.18 g, 3.3 equiv) in 30 mL anhydrousethanol was added dropwise to a hot solution of taptacn (1.44 g) in 10 mL anhydrousethanol under N2. The red mixture was refluxed for 20 minutes, and then cooled; an oilyproduct had formed at the bottom of the flask. The volume of the mixture was thenreduced to about 10 mL by bubbling N2 through the solution. After storage in therefrigerator overnight, the supernatant was decanted, and the red oil was dried in vacuaovernight. The 1H NMR in CDC13 showed a singlet at 8.2 ppm, indicative of the Schiffbase, which was used without further purification in the reduction step below.To a suspension of the above red oil in 20 mL hot methanol was added 0.9 gpotassium borohydride solid in small portions over 30 minutes. The Schiff base dissolvedgradually to give an orange solution. After treatment with Norit, the orange solution wasevaporated to near dryness, and a solution of 1.6 g ammonium acetate in 20 mL water wasadded to the residue. The mixture was extracted with chloroform (2 X 80 mL). Theorganic fractions were combined, washed with water (2 X 50 mL), dried over anhydrousmagnesium sulfate for 15 minutes, and clarified by filtration. Rotary evaporation of thesolvent resulted in an oily product, which was converted into a pale orange solid in vacua.The yield was 2.07 g (50 %), mp 46-48 °C. The compound is soluble in chloroform,methanol, and acetone. Anal. calcd. (found) for36H51BrNO2H0.5CHCl:C114Chapter V H3Brapt Ligand System48.10 (48.47), H 6.03 (5.76), N 8.74 (8.55). Infrared spectrum (cm1,KBr disk): 3600-3200 (br w, NH, o-H) 2913, 2804 (m, vcH), 1570 (w, 6N-H), 1470 (s, vcc), 1260 (s,vco). Mass spectrum (LSIMS): m/z 857 (M + 1), 671 (M -CH2(OH)PhBr), 485 (M -2{CH(OH)PhBr}). 1H and 13C NMR data are listed in Table 5.1.Synthesis of Metal Complexes5.2.9 Preparation of Starting Materials Ln(Tf)3 (Ln = La,21 Nd,Gd, Y, Yb20)Ln203 + 6 CF3SOH---->2 Ln(CF3SO)+ 3 H20Trifluromethanesulfonic acid was added to a suspension of a lanthanide oxide inwater, and excess oxide was added to bring the pH to 4-7. The undissolved oxide wasthen removed by filtration, and the water was evaporated on a rotary evaporator. Theresulting solid was dried at 160-200 OC for 1 day in vacuo and was used without furtherpurification. The Gd, Y and Yb salts were prepared similarily except that the reactionmixture was refluxed for one hour before filtration. Elemental analyses are shown in Table5.2.5.2.10. Ln(H3Brapt)(Tf)A solution of lanthanide triflate (0.06 mmol) (weighed quickly as a solid in the air,then transferred to a Schienk line) in 15 mL dry ethanol was added to a hot solution ofH3Brapt (0.06 mmol) in 15 mL dry ethanol by cannula under N2. The color of theresulting pale yellow solution turned to golden yellow after refluxing for another 45minutes. The solution was rotary evaporated to near dryness; to the residue was added 10mL anhydrous methylene chloride, and a pale orange solid formed immediately. The solidwas filtered out quickly in the air, washed with anhydrous methylene chloride, and dried115Chapter V H3Brapt Ligand Systemin vacuo at 65 OC overnight. The yield was between 70 % - 80 %. These compounds arevery soluble in methanol, acetonitrile and THF, and are stable in air. 1H NMR spectra forLn(H3Brapt)(CF3SO3)3 were recorded between - 40 and 70 OC, and forLa(HBrapt)(CFSO3)3, the spectra are shown in Figure 5.1. UV/vis spectrum is shownin Figure 5.4.5.2.11 Cu(HBrapt)(N03)A solution of 7 mg (0.03 mmol) cupric nitrate in 5 mL acetonitrile was added to asolution of 25 mg (0.03 mmol) H3Brapt in a 20 mL 1:1 mixture of methanol andchloroform. The deep green solution was heated for 30 minutes, and was then keptstirring at room temperature for another 4 hours. The solution was reduced to 10 mL anddiethyl ether was vapour diffused in to give a green solid. The final product was washedwith diethyl ether, and dried at 60 OC in vacuo overnight. The yield was 0.012 g (74 %).The compound is soluble in methanol, acetonitrile and insoluble in chloroform. Anal.Calcd. (found) forC36H49Bru2N8O9: C, 39.14 (39.04); H, 4.47 (4.71); N, 10.14(9.96). Mass spectrum (LSIMS): m/Z 1041 (Cu2(HBrapt)(NO orH2Cu(HBrapt)(NO3)2); 916 (Cu(H2Brapt)j; 855 (H4Braptj. Infrared spectrum (cm-1,KBr disk): 3700-2500 (br m, UN..H 0-H); 1610, 1580 (s, ÔNH); 1467 (s, vcd; 1380,1300 (s, vNo). The 1H NMR spectrum gave sharp peaks within the range of 0 to 8 ppm,suggesting that the two copper(ll) ions are coupled and that the compound is diamagnetic.UV/vis spectrum is shown in Figure 5.3.5.2.12 Cu(Brapt)(N03)A solution of 0.014 g (0.06 mmol) cupric nitrate in 10 niL acetonitrile was added toa solution of 0.025 g (0.03 mmol) H3Brapt in a 10 mL 1:1 mixture of methanol andchloroform. After addition of 0.006 g (0.1 nimol) triethylamine in 5 mL methanol, thesolution was heated for 30 minutes, then stirred for another 4 hours. Diffusion of ether116Chapter V H3Brapt Ligand Systemvapour into the green solution gave a green solid, which was filtered out, and dried at 60OC in vacua overnight. The yield was 0.022 g (73 %). The compound was partiallysoluble in acetonitrile, and dissolved very slowly in methanol. Anal. Calcd. (found) for36H48BrCu2N760.5CHC1:C, 39.81 (39.40); H, 4.44 (4.50); N, 8.90 (9.22). Massspectrum (LSIMS): m/Z 1041 (HCu2Brapt)(NO)or3Cu(Brapt)(NO2);916(Cu(H2Brapt)j; 855 (H4Braptj. Infrared spectrum (cm-1,KBr disk): 3700-2500 (br w,tN.H, 0-H); 1610, 1580 (w, 3N.H); 1467 (s, ‘c=c); 1300 (s, tNo). UV/vis spectra areshown in Figures 5.3 and 5.4.5.2.13. LaCu(Brapt)(N03)z.A solution of 0.025 g (0.06 mmol) La(N03in 10 mL methanol was added to asolution of 0.05 g (0.06 mmol) H3Brapt in 5 mL chloroform, with a yellow precipitatebeing formed immediately. Upon the addition (with stifling) of a solution of 0.014 g(0.06 mmol) Cu(N032in 10 mL methanol, the precipitate disappeared to give a deepgreen solution. To the mixture, a solution of 0.018 g (0.3 mmol) triethylamine in 10 mLmethanol was added dropwise, and a green solid formed gradually. The cloudy solutionwas kept at reflux for 2 days, and the resulting green solids were filtered out, washed withmethanol followed by diethyl ether, and dried in vacua at 60 °C overnight. The yield was0.028 g (41 %). Anal. Calcd. (found) forC3H48BruLaN8O925H0.5CHCl:C,35.99 (35.89); H, 4.28 (4.13); N, 8.72 (8.36). Mass spectrum (LSIMS): m/z 1041(HCu(Brapt)(NO3)2); 916 (Cu(H2Brapt)j; 855 (H4Braptj. Infrared spectrum (cm1,KBr disk): 3700-2700 (br m, tN-H, 0-H); 1580 (w, SN-H); 1467 (vs, tcc); 1300 (s,tNo). UV/vis spectra are shown in Figures 5.3 and 5.4.117Chapter V H3Brapt Ligand System5.3 Results and Discussion.5.3.1 Synthesis of Ligands.The starting macrocycle tacn and hexaamine taptacn were prepared by amodification of the McAuley22synthesis. The reactions outlined in Scheme 5.2 led to theformation of pure tacn, which was stored in the freezer. The synthetic method was furtherimproved by avoiding the HC1 salt (method 2); this increased the yield dramatically. Thehexaamine taptacn was obtained by the reaction of tacn with acrylonitrile in a Michaeladdition, followed by the reduction of the cyano groups to primary amines (Scheme 5.3).Excess acrylonitrile was employed to prevent incomplete functionalization (i.e. productswith only one or two pendant arms24). Taptacn must be used immediately in the next step,otherwise it is slowly oxidized.9 The potentially nonadentate/dinucleating N603 aminephenol H3Brapt was prepared by the KBH4 reduction of the Schiff base derived from thereaction of taptacn with 3 equiv 5-bromosalicylaldehyde (Scheme 5.3). The analytical andspectral data were completely consistent with the proposed formulation. The 1H NMRspectrum in CDC13 showed the presence of a benzylic hydrogen signal at — 4 ppm insteadof an imine CH=N hydrogen signal at 8 ppm, confirming the reduction of C=N bonds toCH2-N amine linkages. Liquid secondary ion mass spectrometry (LSIMS) resulted inmolecular ions of H4Brapt+ at m/z 857, and the consecutive loss of another two pendantarms on fragmentation.5.3.2 Synthesis and Characterization of Lanthanide Complexes.Reaction of the free ligand with 1 equiv of a lanthanide triflate under anhydrousconditions produces mononuclear complexes with the formulationLn(H3Brapt)(Tf) (Ln =La, Y, Yb). Analytical, mass spectral and infrared data were consistent with the indicatedformulation. The LSIMS mass spectra were obtained in a thioglycerol matrix in the118Chapter V H3Brapt Ligand Systempositive detection mode. Peaks corresponding to Ln(H3Brapt)(Tf)3, HLn(Brapt), andH4Brapt were detected, a mass pattern very similar to that for the N403capped species,25/-\NaTsN N NTsNa + TsO OTsTs4DMFNTs TsN\ Iconc. H2S04160°Cmethod 1 conc.— (pH — 13) method 2C1H2N H2N NH HNtacnNaOHpH-- 13NH HN\ /tacnScheme 5.2119Chapter V HBrapt Ligand Systemalthough the N403 ligand has the tripodal tertiary nitrogen as a spacer while the N603ligand has a triazamacrocycle as a spacer. No dimeric species were seen in the spectra.tacnNH2 ( H,NtaptacntcetacnNalethanolptolueneBrH3BraptCHOb) KBH4Scheme 5.3CH,=CHCNHN NHKCN(NNC N N CNrefluxnBr120Chapter V 1138rapt Ligand SystemTable 5.1 1H and 13C NMR Dataa forH3Brapt (CDC13).4HNNH HN5HOlOH \()HOBr10BrBH3Brapt‘H assgnt 6 ‘3C assgnt 6Hj 2.58 (s, 12H) Ci 56.6H2 2.65 (t, 6H) C2 57.8H3 1.59 (m, 6H) C3 27.6H4 2.43 (t, 6H) C4 47.8H5 3.90 (s, 6H) C5 52.2C6 124.8H7 7.07 (s, 3H) C7 131.2C8 110.6H9 7.21 (d, 3H) C9 131.0H10 6.65 (d, 3H) C,0 118.4C,, 157.8a Recorded at 200 MHz (1H NMR) or 75 MHz(13C NMR) in CDC13.121Chapter V H3Brapt Ligand SystemTable 5.2 Analytical Data for Lanthanide Triflatescalcd. (found) %compound C HY(CF3SO) 6.72 (6.71) 0.00 (0.00)La(CF3SO) 6.15 (6.16) 0.00 (0.00)Nd(CF3SO) 6.09 (6.21) 0.00 (0.00)Gd(CF3SO) 5.96 (6.09) 0.00 (0.00)Yb(CF3SO) 5.81 (5.75) 0.00 (0.1)Table 5.3 Analytical Data forLn(H3Brapt)(CFSO).calcd. (found) %compound C H NLa(H3Brapt)(CFSO)Et 33.10 (33.17) 3.86 (3.58) 5.65 (5.55)Y(Brapt)(CFEtOH2.5 H2C1 31.66 (31.66) 3.79 (3.71) 5.09 (4.77)Yb(HBrapt)(CFSOEt 32.36 (32.21) 3.78 (3.50) 5.52 (5.12)Variable temperature ‘H NMR spectra of La(H3Brapt)(Tf) in acetonitrile-d3suggest the existence of two isomers as shown in Figure 5.1. At room temperature, thereare two singlets around 4 ppm for the benzylic hydrogens, indicative of two species; therest of the peaks are broadened and cannot be interpreted due to overlap. Cooling the122Chapter V H3Brapt Ligand SystemTable 5.4 Mass Spectral Data (LSIMS) forLn(H3Brapt)(CFSO.complex mhzLa(H3Brapt)(CF3SO3)3 1442 (La(H3Brapt)(CFSO3)3)), 993 (HLaBrapt’),857 (H4BraptjY(H3Brapt)(CFSO) 942 (HYBrapti, 857 (H4BraptjYb(HBrapt)(CFSO 1026 (FlYbBraptj, 857 (H4Brapt)Table 5.5 Infrared Spectral Data (cm-1,KBr disk) forLn(H3Brapt)(CFSO.complex JR bandsLa(H3Brapt)(CFS0) 3700-2700 (m, DNH, o-H) 1468 (s, tCC), 1270 (s, tco)1230, 1220, 1020, 636 (s, sQ or c-p)Y(H3Brapt)(CFSO) 3700-2700 (m, VNH, o-H) 1468 (s, tCC), 1270 (s, ‘co)1230, 1220, 1024, 636 (s, tjj or c-F)Yb(H3Brapt)(CFSO) 3700-2700 (m, VNH, 0-H), 1470 (s, VCC), 1280 (s, vc..o)1230, 1220, 1022, 640 (s, l)J or c-s)NMR sample yields a large number of poorly resolved peaks. Only the singlets for thebenzylic hydrogens suggest that the molecule is symmetric and not rigid, otherwise an AB123Chapter V II3Brapt Ligand SystemFigure 5.1 Variable temperature 1H NMR spectra of La(HBrapt)(Tf)3in CD3N. (*:isomer I; 4*: isomer m4*** *70 OC65°CI55°C45 O35 OC6.07.0 5.0 4.0 3.0ppm1242.0Chapter V H3Brapt Ligand Systemquartet should be seen.’ As the temperature is raised, the peaks are gradually sharpened.Three low intensity resonances of the minor isomer can be clearly detected in the 1H NMR;all of them are phenyl and benzylic hydrogens. The observable chemical shift differencebetween the benzylic and phenyl hydrogens and the coincidence of the ethylenic hydrogensof the two isomers, taken together, suggest that the main difference between two isomersis probably in the pendant coordinating behavior of the secondary nitrogens and thephenolate oxygens, not in the backbone. Also, as the temperature changes, one dynamicprocess, conversion of one isomer to another isomer, was observed due to the relativepopulation change of two isomers.I I I I2.90 2.95 3.00 3.05lIT (x 1O3,K1)In order to obtain the enthalpy (AFT) and entropy (AS) for the conversion, ln K vslIT is plotted as shown in Figure 5.2. The equilibrium constant K, at each temperature,for the conversion between the two isomers can be calculated from the relative areas of two1.2—1.0-C0.80.6—ln K = -2.24 x io (l/T) ÷ 7.90= -0.997I I3.10 3.15 3.20S3.25Figure 5.2 Enthalpy and entropy for isomerization ofLa(H3Brapt)(Tf) in CD3N.125Chapter V H3Brapt Ligand Systembenzylic signals. Because the two benzylic peaks overlap in each case, K was estimatedeither by integration of signals (assuming the singlet is symmetric) or from the ratio of twopeak heights (assuming the line widths are the same for two peaks). The error between thetwo methods is estimated to be within 5 %. Based on eq (1) rearranged to eq (2), theintercept (ASOIR) and the slope (- AH0IR), the calculated enthalpy and entropy for theconversion are 18.6 ± 0.9 kJ moE1 and 66 ± 2.71 moE1K-1, respectively.AG0=RTlnK=zXHOTASO eq(l)ln K = - AH0/R (1ff) + AS0/R Slope = - AHO/R; Intercept = AS0/R eq (2)Although it is common to have isomers in complexes containing macrocycles,26’7the entropy difference is usually small or close to zero from simple unimolecular processessuch as conformational interconversion or internal rotation.28 The positive entropy for thisisomeric interchange suggests that the isomerization is not associated with the backbonemacrocycle, an observation consistent with the variable temperature 1H NMR. It ispossible that one isomer is a capped species in which the ligand is a tridentate 03 ligand,and the other isomer is an encapsulated species in which the ligand acts as an N30ligand(Scheme 5.4); conversion of the capped species to the encapsulated species results in therelease of several bound solvent molecules to give a positive entropy change. Attempts togrow crystals to elucidate even one of the structures of these two proposed species are stillunderway. In the ytterbium complex, the paramagnetic ion causes a magnetic field-induced line broadening, which makes the dynamic analysis difficult; however, theincrease of peak broadening with the increase of temperature suggests that there are twoisomers in slow exchange, otherwise the peaks would be sharpened due to a paramagnetictemperature effect.29 Isomers were also observed in the yttrium complex; however, poor126Chapter V H3Brapt Ligand Systemresolution obviated the discovery of an apparent trend for the change of the relativeabundance of the two isomers across the lanthanide series.A0 0m bound solvent molecules÷ (n-m) solvent molecules(n> m)Scheme 5.4. Proposed Isomerization ofLa(H3Brapt)(Tf) in CD3N.5.3.3 Synthesis and Characterization of Copper(II) and La-CuComplexes.Reactions of cupric nitrate with H3Brapt resulted in the formation of dinuclearcomplexes in the presence or absence of a weak base. In the absence of a base, mixingequimolar quantities of ligand and metal gave a 1:2 complex, instead of the expected 1:1complex. The ligand was doubly deprotonated because the excess ligand can itself act as aweak base. The elemental analysis and spectral data are consistent with the formulationCu2(HBraptXNO3)2. In the mass spectrum, peak 1041 can be either Cu2(HBrapt)(NO3)or Cu(HBrapt)(NO3)+because these two species have the same mass and similarisotope patterns. 1H NMR showed sharp peaks between 0 and 8 ppm, indicating theexistence of two coupled Cu(ll) ions, otherwise a strong paramagnetic shift should ben bound solvent molecules127Chapter V H3Brapt Ligand Systemobserved. The UV/vis spectra (300-800 nm) ofCu2(HBrapt)(N03,Cu2(Brapt)(N03),and LaCu(Brapt)(N03)2in methanol at room temperature are shown in Figure 5.3.£442 = 1286 M-1 cm-’. Since the free ligand does not absorb in this region, the band atFigure 5.3 UV/vis spectra (300-800 nm) ofCu2(HBrapt)(N03,Cu2(Brapt)(N03),and LaCu(Brapt)(N03)2in methanol at room temperature.0.80.6-0.44II •:ç— Cu2(Brapt)(N03)0.2Cu2(HBrapt)(N03)2’600 7000.0 I I I300 400 500 800Wavelength (nm)Cu2(HBrapt)(N03)has one peak at 442 nm with an extinction absorption coefficient of128Chapter V H3llrapt Ligand System442 nm is assigned to ligand to copper charge transfer.30 There is no d-d transition bandbelow 1000 nm, suggesting that the two copper(II) ions have four-coordinategeometries.31 In the presence of excess Et3N, mixing 2:1 metal:ligand gave the complexCu2(Brapt)(N03) in good yield. This complex has the mass pattern similar to that ofCu(HBrapt)(N03).Cu2(Brapt)(N03) can also be obtained by adding a weak base todeprotonate Cu2(HBrapt)(N03;however, addition of HNO3 to a solution ofCu2(Brapt)(N03)in methanol gave an UV/vis spectrum which is different from that ofCu(HBrapt)(N0,suggesting the reaction is irreversible. The UV/vis spectrum ofcomplexCu2(Brapt)(N03has one intense peak at 388 nm (E388 = 3041 M-1 cm-1)with ashoulder around 426 nm (s426 = 2690 M1 cm-1). One weak, broad absorption band atabout 610 nm is attributed to the d-d transition. These features clearly indicate structuraldifferences between the two complexes. It is possible that at least one of the twocopper(II) ions inCu2(Brapt)(N03)is five-coordinate.31’2Because copper always gives 1:2 complexes whether the starting ligand to metalratio is 1:1 or 1:2, to prepare the dinuclear La-Cu complex 1 equiv of lanthanum ion wasadded first to a solution of the ligand, followed by 1 equiv of Cu(II). The final elementalanalysis and spectral data suggested the formulation LaCu(Brapt)(N03)2.The formationof this heterodinuclear complex was also confirmed by comparing the UV spectra of thelanthanum complex, the copper complex, and the La-Cu complex in the range 200-350 nm(Figure 5.4). La(H3Brapt)(Tf’) has peaks at 256 nm and 294 nm, while thehomodinuclear copper complexCu2(Brapt)(N03has peaks at 210 nm and 290 nm. TheLa-Cu complex gives three intense peaks at 210 nm, 246 nm and 296 nm, correspondingto an addition of the lanthanum and copper complexes. Because lanthanide ions readilyform capped 03 bound species with tripodal amine phenol ligands,24’5 and becauseCu(ll) forms stable complexes with tacn or tacn-based amines,24’323it is likely that theinitial reaction of H3Brapt with the harder lanthanum ion has the harder oxygen donors 03coordinated, and the softer nitrogen donors coordinate to the softer copper ion. The129Chapter V H3Brapt Ligand Systemdifferences in the coordination sites facilitate the formation of this pure heterodinuclearcompound, which represents a starting point for the further study of f-d interactions.UV spectra (200-350 nm) of H3Brapt, Brapt3-,La(H3Brapt)(TflCu2(Brapt)(N03),and LaCu(Brapt)(N02in methanol at roomtemperature.2.5 - H3BraptFigure 5.4C,;IVI’I.//‘AI UI4!—La(H3Brapt)(Tf)/\LaCu(Brapt)(N03)2Brapt -2.0 -1.5 -1.0 -0.5 -0.0 -200I-—--—240I I I I280 320Wavelength (nm)130Chapter V H3Brapt Ligand SystemReferences(1) Liu, S.; Wong, E.; Rettig, S. 3.; Orvig, C. Inorg. Chem. 1993, 32, 4268.(2) Yang, L.-W.; Liu, S.; Wong, a; Rettig, S. 3.; Orvig, C. Inorg. Chem. 1995, 34,2164.(3) Liu, S.; Yang, L.-W.; Rettig, S. 3.; Orvig, C. Inorg. Chem. 1993, 32, 2773.(4) Liu, S.; Gelmini, L.; Rettig, S. J.; Thompson, R. C.; Orvig, C. J. Am. Chem.Soc. 1992, 114, 6081.(5) Liu, S.; Wong, E.; Karunaratne, V.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1992,32, 1756.(6) Liu, S.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1992, 31, 5400.(7) Rauk, A.; Allen, L. C.; Milson, K. Angew. Chem. mt. Ed. Engl. 1970, 9, 400.(8) Geue, R. J.; Searle, G. H. Aust. J. Chem. 1983, 36, 927.(9) Bushnell, G. W.; Fortier, D. G.; McAuley, A. Inorg. Chem. 1988, 27, 2626.(10) Benelli, C.; Caneschi, A.; Gatteschi, D.; Guillou, 0.; Pardi, L. Inorg. Chem.1990, 29, 1750 and references therein.(11) Andruh, M.; Ramade, I.; Codjovi, E.; Guillou, 0.; Kahn, 0.; Trombe, 3. C. J.Am. Chem. Soc. 1993, 115, 1822 and references therein.(12) Sagawa, M.; Fujimura, S.; Togawa, N.; Yamamoto, H.; Matsuura, Y. J. AppI.Phys. 1984, 55, 2083.(13) Bertini, I.; Luchinat, C. NMR of Paramagnetic Molecules in BiologicalSystems; The Benjamin!Cunimings Publishing Company, Inc.: Menlo Park,California, 1986, p 273.(14) Tarascon, 3. M.; Mckinnon, W. R.; Greene, L. H.; Hull, G. W.; Vogel, B. M.Phys. Rev. B 1987, 36, 226.(15) Murphy, D. W.; Sunshine, S.; van Dover, R. B.; Cava, R. J.; Batlogg, B.;Zahurak, S. M.; Schneemeyer, L. F. Phys. Rev. Lett. 1987, 58, 1888.131Chapter V ll3Brapt Ligand System(16) Chen, L.; Breeze, S. R.; Rousseau, R. J.; Wang, S.; Thompson, L. K. Inorg.Chem. 1995, 34, 454 and references therein.(17) Aguiari, A.; Bullita, E.; Casellato, U.; Guerriero, P.; Tamburini, S.; Vigato, P. A.Inorg. Chim. Acta 1994, 219, 135.(18) Casellato, U.; Guerriero, P.; Tamburini, S.; Sitran, S.; Vigato, P. A. I Chem.Soc. Dalton Trans. 1991, 2145.(19) Guerriero, P.; Vigato, P. A.; Fenton, D. E.; Hellier, P. C. Acta Chem. Scand.1992, 46, 1025.(20) Smith, P. H.; Reyes, Z. E.; Lee, C.-W.; Raymond, K. N. Inorg. Chem. 1988,27, 4154.(21) Smith, P. H.; Raymond, K. N. Inorg. Chem. 1985, 24, 3469.(22) McAuley, A.; Rodopoulos, M., Private communication.(23) Kristiansen, P. 0.; Dale, 3. J. Chem. Soc. Chem. Commun. 1971, 670.(24) Fortier, D. G.; McAuley, A. J. Chem. Soc. Dalton Trans. 1991, 101.(25) Smith, A.; Rettig, S. I.; Orvig, C. Inorg. Chem. 1988, 27, 3929.(26) Aime, S.; Botta, M.; Ermondi, G. Inorg. Chem. 1992, 31, 4291.(27) Geraldes, C. F. G. C.; Alpoim, M. C.; Marques, M. P. M.; Sherry, A. D.; Singh,M. Inorg. Chem. 1985, 24, 3876.(28) Desreux, J. F. Inorg. Chem. 1980, 19, 1319.(29) Swift, T. J. In NMR of Paramagnetic Molecules - Principles and Applications;La Mar, G. N., Horrocks, W. D., Jr. and Hoim, R. H., Eds.; Academic Press:New York, 1973; p 67.(30) Hathaway, B. J. In Comprehensive Coordination Chemistry; Wilkinson, 0.,Gillard, R. D. and McCleverty, J. A., Eds.; Pergamon: Oxford, England, 1987;Vol. 5; p 533.(31) Lever, A. B. P. Inorganic Electronic Spectroscopy; Elsevier: 1984, p 554.132Chapter V H3Brapt Ligand System(32) MeLachian, 0. A.; Fallon, 0. D.; Martin, R. L.; Spiccia, L. Inorg. Chem. 1995,34, 254.(33) Chaudhuri, P.; Wieghardt, K. Prog. Inorg. Chem. 1987, 35, 329.133Chapter VI Conclusions and Suggestions for Future WorkChapter VI Conclusions and Suggestions for Future WorkThe primary objective of this research was to investigate the coordinationchemistry of lanthanides with multidentate ligands, with the eventual long-term aim ofdeveloping chemistry which might be applied to the development of new MRI contrastagents. The interaction of lanthanide ions with transition metal ions in close proximity isalso a focus, because of its potential applications in various fields such as materialscience. The preceding chapters described the synthesis and characterization of a widevariety of lanthanide complexes of differing coordination geometries, the understandingof which can serve as an indicator for future work.A series of NO3 (n = 4, 6) ligands were synthesized and their reactions withlanthanide(III) ions and copper(ll) ion were carried out under different conditions. In theabsence of a base, rapid reactions of N403ligands with one equiv of lanthanide nitratesgenerally produce the previously known capped, mononuclear complexes in which theligand coordinates in an 03 tridentate fashion. In the presence (sometimes absence) of abase, different coordination geometries were obtained, depending on such ligandcharacteristics as conformation, substituents, flexibility, cavity size, and donor atomnumbers, as summarized below.Reactions of H3(3-Me0aea) with lanthanide nitrate produce unusual new bicappedsix-coordinate (roughly octahedral) lanthanide complexes. The bulky 3- or orthosubstituents of the phenyl rings have a profound influence on the coordination of theN403 amine phenol ligand to lanthanide ions. The steric hindrance from the bulky 3-methoxy group of the phenyl ring makes the formation of either monomeric encapsulated134Chapter VI Conclusions and Suggestions for Future Workor dimeric encapsulated complexestvery difficult. When phenolate groups are replacedby dha chelating arms, the resulting Schiff baseH3dhatren is found to be a relativelyweakly chelating ligand, but in conjunction with nitrate it is capable of building polymericarrays of lanthanide ions. The structure of [Nd(H3dhatren)(N03)3]n, which containsthree distinct nitrate coordination modes in one three dimentional polymer, has beensolved.Unlike many hydrolytically unstable Schiff base complexes, reactions oflanthanides with rigid Schiff bases H3Xapi (X = H, Cl, Br) yield new sandwich dimericcomplexes, which are very rigid and very stable (at least kinetically), as evinced by thenovel spontaneous conversion of a capped ligand complex to a sandwich dimericcomplex, and by the variable temperature ‘H NMR of [La(Clapi)]2 in DMSO-d6solution.This unusual stability is probably due to the preorganization of the ligand aided by therigid five-membered imidazolidine ring and inter-, intra-molecular hydrogen bonding asshown in the crystal structure of H3api.The reduction of the Schiff base H3api gives two different products (H31,2,4-btt)andH3(1,l,4-btt)), because of the migration of a hydroxybenzyl arm. Purification of theamine phenol H3(l,2,4-btt) can be achieved by the decomposition of the resultantcomplex. Despite the different position of the middle arm in these two ligands, X-raystructures show that the N403 cavity of amine phenol ligand fits In3 very well1 and thatthe cavity is slightly too small for Ln3 ions. Generally, the better the fit between themetal ion and the cavity, the more stable is the resulting complex. This could be achievedby employing the polyazamacrocycles as backbones, because they tend to form morethermodynamically stable and kinetically inert metal complexes than open chainanalogues having the same donor arrangments (the macrocycle effect); the nitrogen donor* . . .These two geometries can be easily obtained when only the 5- or para-substituents are present.135Chapter VI Conclusions and Suggestions for Future Workatom numbers and ring size can be successively altered to satisfy different sizes of metalions.In very recent work not described in this thesis, preparation of tn-, tetra-, andpenta-azabased macrocycles via either the Richman-Atkins method2 ((ct,coditosylamino)amine + di(methane- or p-toluene-)sulfonate esters) or via the Tabushimethod3 (mono- or di-ester + linear polyamine) has been undertaken. With the Tabushimethod (Scheme 6.1), the structure carries the functionalities of both macrocyclicpolyamines and oligopeptides. The substituted group can also be incorporated into theside chain to give bifunctional ligands.CH2= :co2Mexo XOJHN NH________Oo+ CH2O+&(X=H2,O)Scheme 6.1So far, four amide-containing macrocyclic oxo polyamines have been synthesizedand identified by TLC,4 NMR spectroscopy and mass spectrometry (Chart 6.1). Thepurification of these ligands, and the attachment of pendant chelates to the macrocyclering are underway, and will be the subject of future work.Reactions of the N603 ligand H3Brapt with lanthanide triflates produce 1:1complexes which likely have the capped geometry in which the ligand acts as an 03ligand, and/or the encapsulated geometry in which the ligand acts as an N30ligand.136Chapter VI Conclusions and Suggestions for Future WorkAttempts to obtain crystals to elucidate the structures are still underway. Thesecomplexes are quite stable in both solid and solution states. H3Brapt can also act as adinucleating ligand. A heterodinuclear complex LaCu(Brapt)(N03)2 is obtained whichrepresents a starting point for the further study of mixed metal complexes and theirmagnetic properties. Magnetic moment measurements with temperature, and thedetermination of structures remain to be carried out.0I I NFl FIN NH HN(2 NH FIN FIN NH HN Nildioxo[15]aneN4 oxo[15]aneN45 dioxo[16]aneN56 oxo[16]aneN57Chart 6.1References.(1) Yang, L.-W.; Liu, S.; Wong, E.; Rettig, S. J.; Orvig, C. Inorg. Chem. 1995, 34,2164.(2) Atkins, T. J.; Richman, J. E. Org. Syn. 1978, 58, 86.(3) Tabushi, I.; Taniguchi, Y.; Kato, H. Tetrahetron Lett. 1977, 1049.(4) Yatsunami, T.; Sakonaka, A.; Kimura, E. AnaL Chem. 1981, 53,477.(5) Machida, R.; Kimura, E.; Kodama, M. Inorg. Chem. 1983, 22, 2055.(6) Drain, C. M.; Sable, D. B.; Corden, B. B. Inorg. Chem. 1990, 29, 1428.(7) Kimura, E.; Machida, R.; Kodama, M. J, Am. Chem. Soc. 1984, 106, 5497.137AppendicesAppendices138AppendicesTable A.1. Selected Crystallographic Dataa for [Pr(H3(3-MeOaea))2](N03)3•5.56H200.44C3Hcomplex [Pr(H3(3-MeOaea))2](N0)•5.56H00.44CHformula C60 44H96 88N11026.9Prfw 1549.92cryst syst monoclinicspace group C2/ca, A 25.260 (2)b, A 14.927 (3)c, A 21.402 (2)13,deg 112.912 (7)v, A 7433 (2)Z 4pc,g/cm3 1.385T,°C 21radiation (2, A) Cu (1.54 178)I.t(CuKct) (cm1 58.64transm factors 0.90 - 1.00R 0.033Rw 0.040a R = ZIIF0l-IF I/ZLF,R = (w(IFI-IFI)2/Zw)”NB: For atomic fractional coordinates, please refer to Inorg. Chem. 1993, 32, 2773.139AppendicesTable A.2. Selected Crystallographic Dataa for [Gd(H3(3-Meoaea))21(N0)•5.96H0O 66CH3H.complex Gd(H3(3-MeOaeaD2](N0)5.96H20 0.66CH3Hformula C60 66H9856GdN11027.62fw 1581.15cryst syst monoclinicspace group C2/ca,A 25.131(2)b, A 14.990 (4)c,A 21.459 3)13,deg 112.615 (7)v, A 7462 (2)Z 4Pc g/cm3 1.407T,°C 21radiation (X, A) Mo (0.7 1069)i(CuKcL) (cnr1 9.73transm factors 0.91 - 1.00R 0.0330.036a R = EIIF0I-IFIt 1LF,R = (Zw(IFI-IFcI)2/E I)112NB: For atomic fractional coordinates, please refer to Inorg. Chem. 1993, 32, 2773.140AppendicesTable A.3. Selected Crystallographic Data’1 forH3api.Compound H3apiFormula C27H30N40fw 458.56Crystal system MonoclinicSpace group P2 i/aa,A 19.281(2)b, A 5.774(3)21.999(2)ct,deg 903,deg 97.85(1)7 deg 90v,A3 2426(1)Z 4Pcalc’ g/cm3 1.255T,°C 21Radiation Cu1.54 178j.t, cm4 6.32Transmission factors (rel) 0.96-1.00R(F) 0.034Rw(F) 0.031‘1R = ZIIF0IIFcII/ELF,R = (Ew(IFoIiFcb2/ZwIFoI)”141AppendicesTable A.4. Final Atomic Coordinates (Fractional) and Beq (A2)* forH3api.z Beqatom x y0(1) 0.59586(10) 0.7311(3) 0.30925(8) 5.6(1)0(2) 0.61047(10) —0.0030(3) —0.05235(8) 6.2(1)0(3) 0.38588(10) —0.3197(3) 0.38012(8) 6.1(1)N(1) 0.54495(8) 0.4799(3) 0.16849(7) 4.01(9)N(2) 0.49180(8) 0.4673(3) 0.25698(7) 3.82(8)14(3) 0.60758(10) 0.3547(4) 0.01883(8) 4.8(1)N(4) 0.45621(9) 0.0579(4) 0.37952(8) 4.7(1)C(1) 0.54741(10) 0.3537(4) 0.22681(9) 3.6(1)C(2) 0.47069(12) 0.5225(5) 0.14938(10) 5.6(1)C(3) 0.44522(12) 0.5892(5) 0.20821(11) 5.6(1)C(4) 0.57795(11) 0.3509(5) 0.12309(9) 4.6(1)C(S) 0.57817(12) 0.4924(5) 0.06501(10) 5.5(1)C(6) 0.45404(11) 0.3064(4) 0.29188(10) 4.3(1)CU) 0.49784(11) 0.2224(5) 0.34965(10) 4.8(1)C(8) 0.61923(10) 0.3662(4) 0.26356(9) 3.3(1)C(9) 0.64120(12) 0.5579(4) 0.29957(10) 4.1(1)C(10) 0.71008(13) 0.5748(5) 0.32714(10) 5.0(1)C(11) 0.75650(12) 0.3988(6) 0.32070(11) 5.4(1)C(12) 0.73535(13) 0.2026(5) 0.28783(11) 4.9(1)C(13) 0.66647(12) 0.1887(4) 0.25978(9) 4.1(1).C(14) 0.65639(12) 0.4428(4) —0.00701(10) 4.4(1)CUB) 0.68576(12) 0.3257(4) —0.05580(9) 4.0(1)C(16) 0.66107(12) 0.1108(5) —0.07774(10) 4.5(1)C(17) 0.68740(14) 0.0106(5) —0.12737(11) 5.7(1)142AppendicesatomCC 18)C(19)C( 20)C(21)CC 22)C(23)CC 24)C(25)CC 26)CC 27)0.7379(2)0.76365(14)0.73763(13)0.44132(11)0.39879(11)0.37254 C 12)0.33123 C 13)0.31695(14)0.34278(13)0.38320(11)y0.1219(6)0.3324(6)0.4324(4)0.1035 C 4)—0.0528(5)—0.2572(5)—0.4026 CS)—0.3462(6)—0.1461(6)0.0016(5)—0.15420(11)—0.13242(12)—0.08381(10)0.43304(10)0.46440(10)0.43692(11)0.46694(12)0.52445(13)0.55312(11)0.52310(10)Beg6.3(2)6.4(2)5.1(1)4.4(1)4.1(1)4.5(1)5.6(1)6.1(2)5.8(1)5.0(1)— (8/3)nEtU..a.*a.*(a..a.)eqx 2143AppendicesTable A.5. Selected Crystallographic Data’ for Yb(1,2,4-btt)•0.5MeOH.Compound Yb( 1 ,2,4-btt)•0.5MeOHFormula C27 5Ybfw 650.64Crystal system MonoclinicSpace group P21na, A 12.798(2)b,A 19.671(6)c,A 21.129(2)cx, deg 903,deg 91.895(9)c deg 90v,A3 5316(1)Z 8Pcalc’ g/cm3 1.626T,°C 21Radiation Mo0.7 1069p, cm-’ 35.43Transmission factors (rel) 0.46-1.00R(F) 0.031R(F) 0.025a R = EIIFo(IFcIIfEWoI, R = (Zw(IFoI{FeI)/I LFo)”144AppendicesatomYb C 1)0(1)0(2)0(3)N(1)NC 2)N(3)N( 4)C(1)C(2)CC 3)C( 4)C(S)C(6)CC 7)C(8)CC 9)CC10)CU1)CC 12)C(13)C(14)C(1S)C(16)C(17)x0.21564(2)0.0712(2)0.3482(3)0.2098(3)0.2745(3)0.3214(3)0.1684(3)0.0822(3)0.3350(4)0.3091(4)0.2835(4)0.1725(4)0.0661(4)0.0682(4)0.1830(4)0.1031(4)0.0482(4)—0.0314(4)—0.0527(5)0. 0033(5)0. 0806 (4)0.4353(4)0.4587(4)0.4159(4)0.4480(4)0.198249(11)0.1521(2)0.2408(2)0.2897(2)0.1492(2)0.0904(2)0.1445(2)0.2675(2)0.0856(3)0.0473(3)0.0516(3)0.0698(3)0.1695(3)0.2456(3)0.1438(3)0.0920(3)0.1009(3)0.0556(3)0.0005(3)—0.0108(3)0.0361(3)0.1089(3)0.1524(3)0.2174(3)0.2599(3)1450.241504(10)0.20773(14)0.2920(2)0.1841(2)0.1403(2)0.2637(2)0.3422(2)0.2949(2)0.1460(2)0.2062(2)0.3193(2)0.3337(2)0.3629(2)0.3607(2)0.0942(2)0.1131(2)0.1692(2)0.1818(2)0.1424(3)0. 0896(3)0.0746(2)0.2741(2)0.3318(2)0.3366(2)0.3878(3)3.31(1)3.8(2)4.8(2)4.5(2)3.7(2)3.3(2)3.8(2)3.9(2)4.0(3)4.0(2)4.2(3)4.2(3)4.7(3)5.3(3)4.3(3)3.6(2)3.5(2)4.7(3)5.9(4)6.2(4)5.1(3)4.0(3)4.0(3)4.2(3)5.3(3)Table A.6. Final Atomic Coordinates (Fractional) and B (A2)* forYb(1 ,2,4-btQO.SMeOH.y z B eqAppendicesatomC( 18)C( 19)C( 20)C(21)C(22)C(23)C(24)C( 25)C( 26)C(27)Yb ( 10(1’)0(2’)0(31)N(1’)N(2’N(3’N(4’)CU’)C(2’C(3’C(4’)C(5’)C(6’CU’C(8’x0.5207(5)0.5605(4)0.5307(4)0.0977(4)0.0769(4)0.1343(4)0.1107(5)0.0331(5)—0.0236(5)—0.0005(5)0.87440(2)0.8160(3)0.8915(2)1.0343(2)0.9503(3)0.7631(3)0.6927(3)0.8552(3)0.8897(5)0.7758(5)0.6498(4)0.6234(4)0.6695(4)0.7549(4)0.9752(4)0.8782(4)0.2355(4)0.1727(4)0.1307(3)0.3417(3)0.3637(3)0.3354(3)0.3561(3)0.4025(3)0.4296(3)0.4109(3)0.716253(11)0.7845(2)0.6396(2)0.7016(2)0.8249(2)0.7660(2)0.6745(2)0.6319(2)0.8621(3)0.8406(3)0.7497(3)0.7306(3)0.6457(3)0.5958(3)0.8678(3)0.8967(3)0.4321(3)0.4285(3)0.3784(3)0.2881(3)0.2204(3)0.1718(3)0.1094(3)0.0958(3)0.1437(4)0.2055(3)0.411653(10)0.48281(15)0.33996(15)0.44532(14)0.3787(2)0.3207(2)0.4120(2)0.4970(2)0.3274(3)0.3255(2)0.3262(3)0.3924(3)0.4741(3)0.4920(3)0.4356(2)0.4649(2)Beq6.0(4)5.9(4)5.0(3)5.1(3)4.4(3)4.1(3)5.4(3)6.3(4)6.5(4)5.5(3)3.03(1)3.8(2)3.7(2)4.0(2)4.2(2)3.7(2)3.4(2)3.2(2)5.4(3)5.0(3)4.4(3)4.1(3)4.5(3)4.7(3)4.8(3)4.3(3)y z146AppendicesatomC(9’c(10’C(11’C(12’C(13’ )C(14’C(15’C(16’C(17’CC 18’)C(19’C(20’C(21’C(22’C(23’C(24’C(25’C(26’C(27’0(4)0(4A)C( 28)0.8030(4)0.7122(4)0.6972(5)0.7729(7)0.8619(5)0.8041(4)0.7871(4)0.8339(4)0.8179(4)0.7614(4)0.7172(4)0.7299(4)0.9463(4)1.0414(4)1.0801(4)1.1669(4)1.2158(4)1.1793(5)1.0923(4)0.3730(6)0.427(2)0.3845(9)0.8514(3)0.8795(3)0.9487(4)0.9924(3)0.9669(3)0.7417(3)0.6663(3)0.6195(3)0.5503(3)0.5286(3)0.5745(3)0.6433(3)0.5849(2)0.6196(3)0.6780(3)0.7108(3)0.6849(4)0.6270(4)0.5950(3)0.3785(5)0.3466(14)0.4036(5)0.4865(2)0.5110(2)0.5137(3)0.4925(3)0.4681(3)0.2591(2)0.2481(2)0.2901(2)0.2786(3)0.2255(3)0.1837(3)0.1950(2)0.5014(2)0.5288(2)0.4981(2)0.5272(2)0.5814(3)0.6093(3)0.5830(2)0.1955(4)0.2447(13)0.2550(6)Beg4.1(3)4.9(3)6.2(4)7.0(4)5.5(3)4.3(3)3.7(2)3.5(2)4.3(3)5.2(3)5.2(3)4.8(3)4.0(3)3.6(2)3.6(2)4.5(3)5.5(3)5.9(4)4.7(3)11.3(6)11.4(7)12.5(8)= (8/3)n2EEUaeq .*a.*(a.x y z147AppendicesTable A.7. Selected Crystallographic Dataa for [La(Brapi)]2•2CHC13Compound [La(Brapi)]2•2CHC13Formula 56H0Br6C1aN8Ofw 1901.01Crystal system MonoclinicSpace group C’2/ca, A 22.336(1)b, A 14.770(2)c, A 22.647(2)a, deg 90j3,deg 116.855(5)‘y deg 90v, A 6665.7(9)Z 4Pcalc’ g/cm3 1.894T,°C 21Radiation Cu1.54 178j.i, cm’ 166.28Transmission factors (rel) 0.59-1.00R(F) 0.042Rw(F) 0.036a R = ZIlF0-IF I/EIF,R = (Ew(IF0I-IF )2/ I)”.148AppendicesTable AS. Final Atomic Coordinates (Fractional) and B (A2)* for[La(Brapi)j2•2CHC13atom X y z BegLa(1) 0.15492(3) 0.28999(5) -0.02795(3) 3.310)Br(1) 0.31773(9) 0.2239(1) 0.34675(6) 8.46(5)Br(2) -0.17378(6) 0.2075(1) 0.01239(8) 7.92(5)Br(3) 0.63909(9)-0.12110) 0.24502(9) 9.67(6)C1(1) -0.1395(2) 0.1223(3) 0.2221(2) 12.3(2)C1(2) -0.0087(2) 0.1253(4) 0.3280(2) 12.9(2)Cl(S) -0.1096(2) 0.0118(3) 0.3361(2) 11.7(2)00) 0.2521(3) 0.2127(5) 0.0584(3) 3.20)0(2) 0.0940(3) 0.1989(5) 0.0104(3) 4.5(2)0(3) 0.3805(4) 0.0828(5) 0.0954(3) 4.7(2)NO) 0.2396(4) 0.4157(5) 0.0721(4) 3.3(2)N(2) 0.3505(4) 0.3708(5) 0.1038(4) 3.0(2)N(S) 0.0959(4) 0.3887(6) 0.0264(5) 4.3(3)N(4) 9.4593(5) 0.2395(6) 0.1315(5) 4.3(3)C(l) .0.3008(5) 0.3802(7) 0.1297(5) 3.3(3)C(2) 0.3369(6) 0.4483(7) 0.0577(6) 4.7(3)C(3) 0.2651(6) 0.4786(7) 0.0385(6) 5.1(3)C(4) 0.1986(5) 0.4636(7) 0.0984(5) 4.5(3)C(S) 0.1269(6) 0.4771(7) 0.0477(6) 4.6(3)C(6) 0.4184(6) 0.3741(7) 0.1607(6) 4.5(3)C(7) 0.4726(6) 0.3365(9) 0.1447(6) 4.8(3)0(8) 0.2887(5) 0.2946(8) 0.1587(5) 3.4(2)C(9) 0.2665(4) 0.2158(8) 0.1223(5) 3.2(2)COO) 0.2575(5) 0.1390(7) 0.1537(6) 4.3(3)149Appendicesatom x y z BeqC(11) 0.2721(6) 0.1415(8) 0.2204(6) 5.0(3)C(12) 0.2944(5) 0.2204(9) 0.2544(5) 4.7(3)C(13) 0.3031(5) 0.2964(9) 0.2252(5) 4.3(3)C(14) 0.0438(6) 0.3699(8) 0.0343(5) 4.2(3)C(15) 0.0086(5) 0.2844(9) 0.0208(5) 3.7(3)C(16) 0.0356(5) 0.2043(10) 0.0099(5) 4.2(3)C(17) -0.0041(6) 0.1256(8) -0.0030(6) 5.2(4)C(18) -0.0664(6) 0.1265(9) -0.0037(6) 5.2(4)C(19) -0.0904(5) 0.2075(9) 0.0095(5) 4.7(3)C(20) -0.0542(5) 0.2855(9) 0.0218(5) 4.8(3)C(21) 0.5063(6) 0.1835(9) 0.1662(8) 5.1(4)C(22) 0.4996(7) 0.0853(9) 0.1627(6) 4.6(3)C(23) 0.4366(7) 0.0406(9) 0.1301(6) 4.4(3)C(24) 0.4389(7) -0.0546(9) 0.1391(6) 5.7(4)C(25) 0.4978(8) -0.0999(9) 0.1721(7) 6.5(5)C(26) 0.5585(7) -0.056(1) 0.2011(7) 6.3(5)C(27) 0.5595(6) 0.0363(10) 0.1980(6) 5.4(4)C(28) -0.0923(8) 0.115(1) 0.3075(8) 9.9(6)Dec = 8y2(U (aa)2 +U22(bb*) +U33(cc’)2+ 2Uiaabb C087 + 2Uj3aacc cosfl+ 2U365’cc cosa)150AppendicesTable A.9. Selected Crystallographic Dataa for(H3dha2tren)(N0)•0.Compound (H3dha2tren)(N0).0Formulafw 527.53Crystal system TriclinicSpace group PTa, A 11.483(2)b,A 11.775(3)9.691(4)cx, deg 98.70(3)I, deg 97.90(2)y, deg 77.22(2)v, A 1255.8(7)Z 2pj,g/cm3 1.395T,°C 21Radiation Cu1.54 178i, cm1 8.97Transmission factors 0.91-1.00R(F) 0.054R (F) 0.048a R = Z11F01-1/11,R = (Ew(IF0I-TF )2/ [)”.151AppendicesTable A.1O Final Atomic Coordinates (Fractional) and Beg (A2)* for(H3d1la2tren)(N03).H20.atom0(1)0(2)0(3)0(4)0(5)0(6)N(1)14(2)N(3)N(4)CUC(2C(3)C(4)C(S)C(6)CU)C(8)C( 9)C(10)CU1)C(12)C(13)C(14)CUE)x0.3643(3)0.3002(4)0.4587(3)0.1023(3)0.1578(3)0.09S2( 3)0.2446(3)0.4125(3)0.1881(3)0.0443(3)0.3753(4)0.4191(4)0.3723(4)0.3198(5)0.3818(4)0.3447(5)0.4079(5)0.4371(4)0.4271(4)0.4209(6)0.2091(4)0.2410(4)0.1875(4)0.2396(5)0.1402(4)y0.2961(4)0.4685(3)0.4288(3)0.2575(3)0.2163(3)0.6049(2)0.7910(3)0.6340(3)0.5672(3)0.8561(3)0.7803(4)0.7547(4)0.5919(4)0.6752(4)0.4683(4)0.4196(5)0.2256(5)0.2702(4)0.3926(4)0.0988(5)0.7564(4)0.6246(4)0.4555(4)0.3750(4)0.4168(4)152z0.4486(4)0.5647(4)0.1296(3)0.1865(4)—0.0240(4)0.2113(3)0.0745(4)0.2656(4)—0.0224(4)0.2593(4)0.1046(5)0.2524(5)0.3630(5)0.4821(5)0.3518(5)0.4614(6)0.3342(6)0.2307(5)0.2314(5)0.3459(7)—0.0756(5)—0.1153(5)—0.0306(5)—0.1516(5)0.0793(5)Beg6.5(2)7.7(3)4.7(2)4.9(2)6.6(2)4.2(2)3.6(2)4.0(2)3.8(2)4.6(2)4.1(3)4.4(3)3.8(2)5.7(3)4.0(3)5.1(3)5.6(3)4.5(3)4.0(3)9.7(5)4.4(3)4.4(3)3.7(2)5.4(3)3.3(2)Appendicesatom x y z Beg=eqC(16) 0.1354(4) 0.2954(4) 0.0696(5) 4.1(3)C(17) 0.0697(5) 0.3329(5) 0.3023(5) 4.9(3)C(18) 0.0639(5) 0.4463(4) 0.3072(5) 4.7(3)C(19) 0.0988(4) 0.4965(4) 0.1971(5) 3.5(2)C(20) 0.0447(6) 0.2687(5) 0.4138(6) 7.9(4)C(21) 0.1837(4) 0.9116(4) 0.1202(5) 4.3(3)C(22) 0.0553(4) 0.9226(4) 0.1465(5) 4.6(3)0(7) —0.2336(5) 1.0334(3) 0.5293(5) 10.8(3)0(8) —0.1156(5) 1.0662(4) 0.4140(7) 13.1(4)0(9) —0.1934(4) 0.9225(4) 0.3395(4) 9.2(3)N(5) —0.1834(5) 1.0078(4) 0.4267(6) 6.5(3)0(10) —0.3794(6) 0.9579(6) 0.0943(7) 18.8(6)153AppendicesTable All. Selected Crystallographic Dataa for [Nd(NO3)(Hdhatren)].Compound [Nd(NO3)(Hdhatren)]Formula C30H67NdO18fw 926.89Crystal system MonoclinicSpace group P21/na, A 10.488(3)b, A 20.047(4)c, A 18.587(4)ccdeg 90j3,deg 96.17(2),deg 90v, A 3885(1)Z 4pj,gIcm3 1.584T,°C 21Radiation Mo0.71069p,cm1 14.19Transmission factors 0.58-1.00R(F) 0.052R (F) 0.044a R = ZIIF0I-IFI /EF,R = (Zw(IF0I-IF )2/E li)112.154AppendicesTable A.12. Final Atomic Coordinates (Fractional) and B (A2)* for[Nd(H3dha3tren)(N0 )31n.atom x y z BeqNd(1) 1.04323(6) 0.40741(3) 0.53966(4) 2.60(1)0(1) 1.1130(9) 0.1360(4) 0.6703(5) 5.5(3)0(2) 0.9292(9) 0.1118(4) 0.7081(7) 8.1(3)0(3) 1.0292(6) 0.3324(3) 0.6447(5) 3.4(2)0(4) 0.2523(8) 0.3643(4) 1.0156(5) 5.9(3)0(5) 0.3968(9) 0.4389(4) 0.9924(6) 5,4(3)0(6) 0.4906(6) 0.2075(4) 0.9957(4) 3.3(2)0(7) 0.0718(8) 0.2283(5) 0.8644(5) 5.3(3)0(8) 0.0007(8) 0.3301(5) 0.8568(6) 6.7(3)0(9) 0.4173(8) 0.2729(4) 0.8000(5) 4.8(3)0(10) 1.0212(8) 0.4090(5) 0.4121(5) 5.6(3)0(11) 0.9766(8) 0.5126(4) 0.3648(5) 4.3(2)0(12) 1.054(1) 0.4300(6) 0.2852(7) 11.5(5)0(13) 0.8605(6) 0.4907(3) 0.4986(4) 3.1(2)0(14) 0.8105(6) 04029(4) 0.5657(4) 3.5(2)0(15) 0.657400) 0.4955(6) 0.5540(8) 11.6(5)0(16) 1.2692(7) 0.4153(5) 0.6123(5) 5.4(3)0(17) 1.2567(7) 0.3562(4) 0.5157(6) 5.5(3)0(18) 1.4385(8) 0.3683(5) 0.5796(6) 7.9(3)NO) 0.6283(8) 0.4262(4) 0.7991(5) 2.8(2)N(2) 0.8053(8) 0.3083(4) 0.6915(5) 3.1(2)N(3) 0.6177(8) 0.4032(5) 0.9576(5) 3.7(2)N(4) 0.3557(8) 0.3964(5) 0.7956(5) 3.8(3)N(S) 1.0130) 0.4508(7) 0.3638(8) 6.0(4)155Appendicesatom x y zN(6) 0.7846(10) 0.4590(6) 0.5406(7) 5.8(4)N(7) 1.325(1) 0.3786(5) 0.5679(7) 4.5(3)CU) 0.7344(9) 0.4004(6) 0.7622(6) 3.3(3)C(2) 0.692(1) 0.3429(6) 0.7113(7) 3.8(3)C(3) 0.8430) 0.2492(6) 0.7072(7) 3.5(3)C(4) 0.767(1) 0.2065(7) 0.7529(9) 7.0(5)C(S) 0.994(1) 0.1564(6) 0.6907(8) 4.8(4)C(6) 0.966(1) 0.2270(6) 0.6864(7) 3.2(3)C(7) 1.053(1) 0.2712(6) 0.6574(6) 2.8(3)C(S) 1.174(1) 0.2447(6) 0.6423(7) 4.1(4)C(9) 1.199(1) 0.1812(8) 0.6502(7) 5.0(4)COO) 1.3190) 0.1447(8) 0.6349(9) 8.6(6)C01) 0.680(1) 0.4706(6) 0.8572(7) 4.0(3)C(12) 0.727(1) 0.4331(6) 0.9262(7) 4.0(3)C(13) 0.581(1) 0.3414(5) 0.9595(7) 3.4(3)C(14) 0.663(1) 0.2874(6) 0.9332(7) 4.4(4)C(15) 0.377(1) 0.3785(7) 0.9970(8) 4.0(4)COG) 0.461(1) 0.3249(5) 0.9853(6) 2.6(3)C(17) 0.4210) 0.2572(6) 0.9984(6) 3.5(3)C(18) . 0.2948(10) 0.2490(5) 1.0159(6) 2.5(3)COO) 0.2160) 0.2993(7) 1.0239(7) 4.5(4)C(20) 0.0820) 0.2941(8) 1.0428(9) 8.1(5)C(21) 0.530(1) 0.4577(5) 0.7483(7) 3.7(3)C(22) 0.4030) 0.4638(6) 0.7809(7) 4.3(4)156Appendicesatom x Y Z BegC(23) 0.2420) 0.3810(6) 0.8129(7) 3.9(3)C(24) 0.1500) 0.4377(6) 0.8189(8) 6.0(4)C(25) 0.092(1) 0.2944(7) 0.8494(8) 4.7(4)C(26) 0.2170) 0.3129(6) 0.8277(6) 3.3(3)C(27) 0.312(1) 0.2622(6) 0.8196(7) 4.1(4)C(28) 0.274(1) 0.1959(6) 0.8382(7) 3.9(3)C(29) 0.163(2) 0.1799(7) 0.8591(8) 5.3(4)C(30) 0.1210) 0.1139(7) 0.8816(8) 7.3(5)Beg = 2(Uii(aas)2 +U22(bb)33(cc*)+2Uaaa*bb*cos7+2Ul*c cosfl+2U366’cc cosa)157

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