Studies of mixed-valence states in three-dimensional halogen-bridged gold compounds, Cs2AuIAuIIIX6(X = Cl, Br or I). Part 3. Gold-197 Mössbauer spectroscopic study

Abstract

The mixed-valence states in Cs₂Au^IAu^IIIX₆(X = Cl, Br or I) were studied by Mössbauer spectroscopy with the 77.34 keV γ-ray resonance of ¹⁹⁷Au. The states Au^I and Au^III could clearly be distinguished for all compounds. From an analysis of the isomer shifts and the quadrupole splittings the following conclusions were drawn: (1) the signs of the electric field gradient at Au^I and Au^III are negative and positive, respectively; (2) the charge-transfer interaction between Au^I and Au^III through the bridging halogen increases in the order X = Cl < Br < I and should be stronger in the xy plane (⊥c axis) than in the z direction (∥c axis); (3) for the cubic phase CsAu_0.6Br_2.6 only a single resonance line having a rather broad half-width was observed.