Room temperature syntheses of AuF₆^- and PtF₆^- salts, Ag⁺AuF₆^-, Ag²⁺PtF₆^2-, and Ag²⁺pdF₆^2-, and an estimate for E(MF₆^-) [M = Pt, Pd]

Solutions of AuF₄^- or PtF₆^2- salts, prepared from the metals at ∼20 °C, in liquid anhydrous hydrogen fluoride (aHF), made basic with alkali fluorides, are further oxidized by photodissociated F₂ (visible or near-UV light) to give AuF₆^- or PtF₆^- salts, including O²⁺AuF₆^- (with O₂ in the F₂). Similar photochemical oxidation of PdF₆^2- salts does not occur. This new synthetic approach has provided LiAuF₆ and LiPtF₆ for the first time, each of which has the LiSbF₆ type (R3̄) structure with (hexagonal cell): LiAuF₆, a = 4.9953(9) Å, c = 13.704(3) Å, V/Z = 98.71(6) ų; LiPtF₆, a = 5.0236(7) Å, c = 13.623(2) Å, V/Z = 99.25(5) ų. Interaction of AuF₆^- with Ag⁺ gives Ag⁺AuF₆^- (R3̄, a = 5.283(3) Å, c = 15.053(6) Å, V/Z = 121.3(2) ų), whereas PtF₆^2- or PdF₆^2- stabilize Ag²⁺ as Ag²⁺Pt(Pd)F₆^2- (R3̄; AgPtF⁶: a = 5.049(8) Å, c = 14.46(2) Å, V/Z = 106.4(5) ų; and AgPdF₆, a = 5.00(4) Å, c = 14.6(2) Å, V/Z -105(3) ų). New cubic modifications (probable space group Ia3) have been found for AgMF₆ (M, a value, Å): Ru, 9.653(10); Os, 9.7318(9); Ir, 9.704(2). The preference for Ag²⁺Pt(Pd)F₆^2- over Ag⁺Pt(Pd)F₆^- is attributed to a second electron affinity of Pt(Pd)F₆, E(Pt(Pd)F₆^-)> 60 kcal mol^-1.