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Chemical, structural and electronic properties of graphite fluorosulfate derivatives

University of British Columbia

Emphasis is placed in this dissertation on (a) the development of new synthetic routes to, and (b) the structural characterization of novel graphite intercalation compounds. Chemical conversions such as substitution- , addition - , oxidation - or reduction - reactions as routes to new acceptor intercalation compounds of graphite have been systematically investigated. Suitable starting materials C[sub n]SO₃F, with n~7 as limiting composition, and C[sub n]BrSO₃F, with n~12 for stage 1 intercalation compounds are formed by oxidative intercalation of bis(fluorosulfuryl) peroxide, S₂O₆F₂ , or bromine (I) fluorosulfate, BrSO₃F,respectively. For C₇SO₃F an ionic formulation as C₇₊SO₃F₋ is proposed, however close anion packing causes covalent anion-cation interaction, primarily through oxygen, resulting in backdona-tion of charge and a lowering of the ionic salt limit. Substitution of SO₃F₋ by trifluoromethylsulfate, SO₃CF₃₋, or hexafluoroantimonate (V), SbF₅ , is achieved by solvolysis of C₇SO₃F in excess trifluoromethylsulfuric acid, HSO₃CF₃, or antimony (V) fluoride, SbF₅ to yield C₁₂SO₃CF₃, or C₈SbF₆ respectively. The former is also formed from C₁₂BrSO₃F, and HSO₃CF₃. Add it ion of arsenic (V) fluoride, AsF₅ to C₇SO₃F produces C₁₄+[AsF₅ (SO₃F)] . The same reaction type, or more generally "successive intercalation", is used when f.luoro-sulfuric acid, HSO₃F is added to higher stage binary graphite f uorosulf ates , e.g. C₁₄SO₃F to form acid fluorosulfates, in this case C₁₄SO₃F . HSO₃F[sub 1.05]. Materials similar in composition but with different spectroscopic and electronic properties are formed by "simultaneous intercalation" of controlled amounts of S₂O₆F₂ in HSO₃F solution, and two different packing modes "homogeneous" and "heterogeneous" are suggested. Intercalate Oxidation is found in the reaction of C₁₂BrSO₃F with S₂O₆F₂ to give C₁₆Br(SO₃F)₃, which may in turn undergo intercalate reduction to give C₁₂BrSO₃F. Intercalate disproportion at ion and de composition are encountered when graphite and BrSO₃F are reacted at 10 5 - 110°C to give C₂₀BrF(SO₃F)₂. Structural models are based on X-ray powder diffraction to obtain c axis spacings and the' stage index, Raman spectroscopy (backscattering configuration) to obtain staging information from graphite lattice mode shifts and to observe in rare cases intercalate vibrations, ¹⁹F and where suitable ¹H nuclear magnetic resonance (using Fourier transform techniques) to obtain information on the nature and packing of intercalates, and last but not least on complete quantitative chemical analysis for information on bulk composition and sample purity. Electronic properties of these highly conducting materials are probed occasionally by electron spin resonance spectroscopy and more thoroughly by measuring the basal plane electrical conductivities employing a contactless radio frequency induction method.

Text

2010-06-01

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http://hdl.handle.net/2429/25313

Chemistry

University of British Columbia

Graduate