The first example of a mixed valence ternary compound of silver with random distribution of Ag(I) and Ag(II) cations.

The reaction between colourless AgSbF6 and sky-blue Ag(SbF6)2 (molar ratio 2 : 1) in gaseous HF at 323 K yields green Ag3(SbF6)4, a new mixed-valence ternary fluoride of silver. Unlike in all other Ag(I)/Ag(II) systems known to date, the Ag(+) and Ag(2+) cations are randomly distributed on a single 12b Wyckoff position at the 4̄ axis of the I4̄3d cell. Each silver forms four short (4 × 2.316(7) Å) and four long (4 × 2.764(6) Å) contacts with the neighbouring fluorine atoms. The valence bond sum analysis suggests that such coordination would correspond to a severely overbonded Ag(I) and strongly underbonded Ag(II). Thorough inspection of thermal ellipsoids of the fluorine atoms closest to Ag centres reveals their unusual shape, indicating that silver atoms must in fact have different local coordination spheres; this is not immediately apparent from the crystal structure due to static disorder of fluorine atoms. The Ag K-edge XANES analysis confirmed that the average oxidation state of silver is indeed close to +1⅓. The optical absorption spectra lack features typical of a metal thus pointing out to the semiconducting nature of Ag3(SbF6)4. Ag3(SbF6)4 is magnetically diluted and paramagnetic (µ(eff) = 1.9 µ(B)) down to 20 K with a very weak temperature independent paramagnetism. Below 20 K weak antiferromagnetism is observed (Θ = -4.1 K). Replacement of Ag(I) with potassium gives K(I)2Ag(II)(SbF6)4 which is isostructural to Ag(I)2Ag(II)(SbF6)4. Ag3(SbF6)4 is a genuine mixed-valence Ag(I)/Ag(II) compound, i.e. Robin and Day Class I system (localized valences), despite Ag(I) and Ag(II) adopting the same crystallographic position.

Crystal and electronic structure, lattice dynamics and thermal properties of Ag(I)(SO3)R (R = F, CF3) Lewis acids in the solid state.

Trifluoromethansulfonate of silver(I), AgSO(3)CF(3) (abbreviated AgOTf), extensively used in organic chemistry, and its fluorosulfate homologue, AgSO(3)F, have been structurally characterized for the first time. The crystal structures of both homologues differ substantially from each other. AgOTf crystallizes in a hexagonal system (R3 space group, No.148) with a = b = 5.312(3) Å and c = 32.66(2) Å, while AgSO(3)F crystallizes in a monoclinic system in the centrosymmetric P2(1)/m space group (No.11) with a = 5.4128(10) Å, b = 8.1739(14) Å, c = 7.5436(17) Å, and ß = 94.599(18)°, adopting a unique structure type (100 K data). There are two types of fluorosulfate anions in the structure; in one type the F atom is engaged in chemical bonding to Ag(I) and in the other type the F atom is terminal; accordingly, two resonances are seen in the (19)F NMR spectrum of AgSO(3)F. Theoretical analysis of the electronic band structure and electronic density of states, as well as assignment of the mid- and far-infrared absorption and Raman scattering spectra for both compounds, have been performed based on the periodic DFT calculations. AgSO(3)F exhibits an unusually low melting temperature of 156 °C and anomalously low value of melting heat (ca. 1 kJ mol(-1)), which we associate with (i) disorder of its anionic sublattice and (ii) the presence of 2D sheets in the crystal structure, which are weakly bonded with each other via long Ag-O(F) contacts. AgSO(3)F decomposes thermally above 250 °C, yielding mostly Ag(2)SO(4) and liberating SO(2)F(2). AgOTf is much more thermally stable than AgSO(3)F; it undergoes two consecutive crystallographic phase transitions at 284 °C and 326 °C followed by melting at 383 °C; its thermal decomposition commences above 400 °C leading at 500 °C to crystalline Ag(2)SO(4) and an unidentified phase as major products of decomposition in the solid state.