Optical investigation of the intervalence charge-transfer interactions in the three-dimensional gold mixed-valence compounds Cs2Au2X6(X = Cl, Br or I)

Abstract

The intervalence charge-transfer (i.v.c.t.) transitions between the gold-(I) and -(III) ions in Cs₂Au₂X₆(X = Cl, Br or I) have been investigated. From the polarized reflectance spectra of a single crystal of Cs₂Au₂I₆ and group-theory analysis, the i.v.c.t. bands have been assigned. The strongest reflectance peak was that of lowest energy, which was observed with the electric vector perpendicular to the c axis, and was assigned to the Au^I(5d_x²–y²)→ Au^III(5d_x²–y²) transition in the ab plane. This indicates that a two-dimensional correlation between the gold ions is present in the charge-transfer interaction despite the three-dimensional perovskite structure of the compounds.