STUDIES OF MIXED-VALENCE STATES IN 3-DIMENSIONAL HALOGEN-BRIDGED GOLD COMPOUNDS, CS2AUIAUIIIX6 (X = CL, BR OR I) .3. AU-197 MOSSBAUER SPECTROSCOPIC STUDY

The mixed-valence states in Cs2AuIAuIIIX6 (X = Cl, Br or I) were studied by Mossbauer spectroscopy with the 77.34 keV gamma-ray resonance of Au-197. 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 (perpendicular-to c axis) than in the z direction (parallel-to c axis); (3) for the cubic phase CsAu0.6Br2.6 only a single resonance line having a rather broad half-width was observed.