Static and dynamic structure of Au2Cl6, AuAlCl6 and AuFeCl6 clusters

Abstract

Fourfold coordination of trivalent metal ions by chlorines in molecular dimers changes from tetrahedral in Al2Cl6 and Fe2Cl6 to planar in Au2Cl6. Within an ionic model we interpret this transition in the stable molecular shape as due to the quadrupolar polarizability of the gold(III) ion. We also demonstrate within the same model that a mixed tetrahedral-planar coordination is stable in AuAlCl6 and AuFeCl6 clusters. Quantitative comparisons are presented for the calculated molecular structures and vibrational frequencies against the available experimental data from crystalline diffraction and from Raman spectra of the crystal and of vapours.