Disproportionation of Ag(II) to Ag(I) and Ag(III) in Fluoride Systems and Syntheses and Structures of (AgF⁺)₂AgF₄^-MF₆^- Salts (M = As, Sb, Pt, Au, Ru)

Abstract

Interaction of Ag(+) salts in anhydrous liquid hydrogen fluoride, aHF, with AgF(4)(-) salts gives amorphous red-brown diamagnetic Ag(I)Ag(III)F(4), which transforms exothermally to brown, paramagnetic, microcrystalline Ag(II)F(2) below 0 degrees C. Ag(I)Au(III)F(4) prepared from Ag(+) and AuF(4)(-) in aHF has a tetragonal unit cell and a KBrF(4) type lattice, with a = 5.788(1) Å, c = 10.806(2) Å, and Z = 4. Blue-green Ag(II)FAsF(6) disproportionates in aHF (in the absence of F(-) acceptors) to colorless Ag(I)AsF(6) and a black pseudotrifluoride, (Ag(II)F(+))(2)Ag(III)F(4)(-)AsF(6)(-). The latter and other (AgF)(2)AgF(4)MF(6) salts are also generated by oxidation of AgF(2) or AgF(+) salts in aHF with F(2) or in solutions of O(2)(+)MF(6)(-) salts (M = As, Sb, Pt, Au, Ru). Single crystals of (AgF)(2)AgF(4)AsF(6) were grown from an AgFAsF(6)/AsF(5) solution in aHF standing over AgF(2) or AgFBF(4), with F(2) as the oxidant. They are monoclinic, P2/c, at 20 degrees C, with a = 5.6045(6) Å, b = 5.2567(6) Å, c = 7.8061(8) Å, beta = 96.594(9) degrees, and Z = 1. The structure consists of (AgF)(n)()(n)()(+) chains (F-Ag-F = 180 degrees, Ag-F-Ag = 153.9(11) degrees, Ag-F = 2.003(4) Å), parallel to c, that enclose stacks of alternating AgF(4)(-) and AsF(6)(-), each anion making bridging contact with four Ag(II) cations of the four surrounding chains "caging" them. There is no registry between the ordered array in one "cage" and that in any neighboring "cage". The F-ligand anion bridges between the anions and, with the Ag(II) of the chains, generates a trifluoride-like structure. (AgF)(2)AgF(4)AsF(6) [like other (AgF)(n)()(n)()(+) salts] is a temperature-independent paramagnet except for a Curie "tail" below 50 K.

Theory meets experiment: Gas-phase chemistry of coinage metals

“…Fluorine allows formation of highest oxidation states, and in the case of silver even solid AgF 3 has been isolated [91], although Ag(III) otherwise is an unstable oxidation state [92,93]. Conceptually, the valence state of the metal hence can be adjusted by the number of halido ligands in conjunction with the net charge of the species.…”

Real and Hypothetical Intermediate-Valence AgII/AgIII and AgII/AgI Fluoride Systems as Potential Superconductors

“…Two very short AgÀF bonds of 2.04 (AgÀF (2) and AgÀF (6) There are many ternary fluorides known containing infinite [Ag II ± F À ] chains. [56,57] They belong to three principal types: a) [AgF] [MF 4 ] À , M Au, [29] B [29] b) [AgF] [MF 6 ] À , M Bi, [28] Sb, [28] As, [29,58,59] Au, [29] Ir, [28] Ru [28] [14] Pt, [14] Ru, [14] As, [14] Sb. [14] Infinite [Ag II ± F À ] chains are also found in quaternary fluorides of the formula: Co. [61,62] Properties and structural data for these solids are listed in Table 2.…”

Superconductivity in Copper, Silver, and Gold Compounds

“…Ag II systems are not disproportionated in fluorides at low temperatures 4. 8, 11, 47, 48 Wells' salt, CsAuCl 3 , is probably the first and best‐known example of disproportionation in gold compounds 12–16. At normal pressure the distances of the xy plane are 0.4 Å smaller in Au III Cl than corresponding distances in Au I Cl.…”

“…The spin structure is complicated 4. β‐AgF 2 is stable at a high temperature and has mixed valence with a CDW ground state 47. The two phases are thus very different, but there is a phase transition at elevated temperatures.…”