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 Hückel 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. © 1991, American Chemical Society. All rights reserved.