Recent achievements in the synthesis and characterization of metal hexafluorantimonates and hexafluoroaurates

The efforts to prepare new MSbF₆/MSb₂F₁₁ (A = In, Cu, Au, Hg) compounds were partly successful. Reaction between InBF₄ and excess SbF₅ in anhydrous hydrogen fluoride (aHF) yields a mixture of InF₃·3SbF₅ and unidentified SbF₃·xSbF₅. The attempts to synthesize MSbF₆/MSb₂F₁₁ salts (A = Au, Hg) by controlled reduction of Au(SbF₆)₂ or Hg(SbF₆)₂ solutions in aHF/SbF₅ by elemental hydrogen, resulted in the precipitation of metallic Au or Hg₂(Sb₂F₁₁)₂. In the reaction of metallic Cu and deficit SbF₅, the synthesis of CuSbF₆ was achieved. CuSbF₆, like CuAsF₆, is a rare example of a Cu(I) compound in a pure fluorine environment.Vibrational spectra of M(II) hexafluoroantimonates (M = Ni, Fe, Co, Cu, Cr, Pd, Ag) were reinvestigated. It was found that many of them originally assigned to M(SbF₆)₂ compounds, belong to their mixtures with oxonium salts H₃OM(SbF₆)₃, H₃OSbF₆, and/or H₃OSb₂F₁₁.Reactions were studied between MF₂/2AuF₃ (M = Ni, Cu, Ag, Zn, Cd and Hg) and KrF₂ or UV-irradiated elemental fluorine in aHF as solvent at room temperature. On the basis of mass balances, Raman spectroscopy and X-ray powder diffraction analysis it can be concluded that the isolated solids have structures that can be considered in terms of an M(AuF₆)₂ formulation. Previously reported syntheses and characterization of M(AuF₆)₂ (M = Mg, Ca, Sr, Ba) were reinvestigated. In the case of M = Ba two different Au⁻F₆ salts were isolated.Raman spectra of the majority of synthesized metal hexafluoroaurates (M = Ni, Cu, Ag, Zn, Cd, Hg, Mg and Ca) show more bands than expected for regular Au⁻F₆ anion, indicating that the salts obtained exhibit relatively strong cation-anion interactions. The Raman spectra of the remaining Sr and Ba salts show the presence of more regular Au⁻F₆ octahedra, indicating weak cation-anion interactions.     

X-ray single crystal structures of Hg(AuF6)2 and AgFAuF6

Hg(AuF₆)₂ crystallizes at 200 K in the orthorhombic space group Pbcn (No. 60) with a = 917.67(7) pm, b = 971.59(8) pm, c = 962.04(8) pm, and Z = 4. Mercury atoms are coordinated by eight fluorine atoms with six short and two long Hg-F contacts. HgF₈ polyhedra share their four vertices and two edges with six AuF₆ units forming a tridimensional framework.The results of X-ray diffraction analysis on single crystals of AgFAuF₆ are in agreement with previously known powder X-ray diffraction data (Casteel et al, J. Solid State Chem. 96 (1992) 84-96). AgFAuF₆ crystallizes orthorhombic in the space group Pnma (No. 62), a = 717.06(7) pm, b = 761.67(7) pm, c = 1013.61(10) pm at 200 K, Z = 4.