Crystal structures of XeF5+MF4- (M = Ag, Au) and their relevance to the basicity and oxidizability of MF4-

Article abstract of DOI:10.1021/ic00317a014

XeF₅⁺AuF₄^- has been prepared from BrF₃·AuF₃ by displacement of BrF₃ with XeF₆. The salt interacts quantitatively with KrF₂ in anhydrous HF, below 0°C, to yield XeF₅⁺AuF₆^-. XeF₅AuF₄ (I) is isostructural with XeF₅AgF₄ (II), and these compounds crystallize in space group I4/m with the following unit cell dimensions: I, a_o = 5.735 (5) A?, c_o = 20.007 (17) A?, V = 658 (2) A?³, Z = 4; II, a_o = 5.593 (2) A?, c_o = 20.379 (5) A?, V = 637.5 (8) A?³, Z = 4. The structure of II was solved by the Patterson method and refined to conventional R and R_w values of 0.077 and 0.090, respectively. The structure contains double layers of XeF₅⁺ and layers of AgF₄^- ions, all layers being parallel to the ab plane. The XeF₅⁺ ion had C_4v symmetry with Xe-F(axial) = 1.853 (19) A?, Xe-F(equatorial) = 1.826 (9) A?, and F(axial)-Xe-F(equatorial) = 77.7 (3)°. The anion (site symmetry D_2h), which is not significantly different from O_4h symmetry, has Ag-F = 1.902 (11) A?. Differences between the XeF₅AgF₄ and XeF₅AuF₄ structures are attributed to lower ligand charges in the anion of the former, relative to those in the latter, and these in turn are related to observed differences in the basicity and oxidizability of the anions.