PHOTOLUMINESCENCE AND ELECTRONIC-STRUCTURE OF TL[AU(CN)2] - EVIDENCE FOR RELATIVISTIC EFFECTS IN THALLIUM GOLD AND GOLD GOLD INTERACTIONS

Experimental results of a study of the photoluminescence of microcrystalline Tl[Au(CN)2] as a function of temperature (1.7-400 K) and magnetic field (0-6 T) are described. These results, along with relativistically modified extended Huckel calculations, provide evidence that covalent Tl-Au interactions alter its spectroscopic properties in comparison with isostructural Cs[Au(CN)2]. Specifically, the absorption and luminescence of Tl[Au(CN)2] appear at lower energies than for Cs[Au(CN)2], and a comparison of the luminescence spectra and lifetimes for the two compounds reveals evidence for an increased rate of intersystem crossing in Tl[Au(CN)2] relative to Cs[Au(CN)2]. Both effects are reflective of covalent Tl-Au interactions in Tl[Au(CN)2]. The electronic structure calculations clearly demonstrate the covalency of both the Tl-Au and Au-Au interactions in Tl[Au(CN)2] and reveal specific orbital contributions responsible for these interactions. Relativistic effects are shown to play an important role in the Tl-Au and Au-Au bonding.