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Fluorosulfates of the noble metals, and their use in novel superacid systems

University of British Columbia

This study was initiated by the search for novel superacid systems based on HSO₃F, the strongest simple protonic acid. Therefore, the synthesis of binary metal fluorosulfates, M(SO₃F)n, was investigated, with special emphasis on compounds where M is in a medium or high oxidation state and formally coordinatively unsaturated, i.e., n = 3,4 or 5. Preferably, the resulting fluoro-sulfate would also display a sufficiently high thermal stability with respect to dissociations giving rise to SO₃ or S₂O₅F₂, and reasonable solubility in HSO₃F. In order to obtain suitable binary fluorosulfates, a new, generally applicable synthetic method was developed, involving the oxidation of a metal with S₂O₆F₂. In presence of HSO₃F: M+ n/2 S₂O₆F₂ -- HSO₃F M(SO₃F)[sub= n], where M is primarily a 4d or 5d transition metal, in particular, palladium, platinum, gold and iridium. This fluorosulfonation mixture combines the strong oxidizing ability of S₂O₆F₂ with the good solvating property of HSO₃F towards ionic solutes. The ability of these binary fluorosulfates to act as fluorosulfate ion acceptors was established by the synthesis of anionic complexes of the type [M(SO₃F)[sub= n+m][sup= m-], where m = 1,2. Both Au(SO₃F)₃ and Pt(SO₃F)₄ were found to act as ansolvo-acids in H SO₃F by the removal of fluorosulfate ions from the solvent ionization equilibrium: 2H SO₃F > H₂SO₃F⁺ + SO₃F⁻, to form [Au(SO₃F)₄]⁻ or [Pt(SO₃F)₆]²⁻ . Results from conductivity measurements indicate the resulting superacids have acid strengths comparable to that of the HSO₃F-SbF₅-SO₃ system and definitely superior to the HSO₃F –SbF₅ system. In both cases, the variety of ternary fluorosulfates synthesized included unusual cations such as Br₃⁺ and Br₅⁺. In the case of platinum, evidence for poly-nuclear oligomeric anions of the type of [Pt(SO₃F)₅][sub= n][sup= n-] were obtained; similar observations were also made in the tin system. The oxidation of palladium yielded Pd(SO₃F)₂ and a mixed valency compound, Pd(II)[Pd(IV)(SO₃F)₆], both containing Pd(II) in a rather uncommon octahedral coordination sphere and a ³A₂₉ electronic ground state. These magnetically dilute compounds allowed meaningful magnetic results and ligand field parameters to be interpreted. Both Ir(S0₃F)₃ and Ir(SO₃F)₃ could be synthesized, along with some tenary fluorosulfate complexes. Some preliminary results were also obtained on the fluorosulfates of germanium, molybdenum, niobium and tantalum.

Text

2010-03-26

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http://hdl.handle.net/2429/22630

Chemistry

University of British Columbia

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