Optical and Conformational Studies on (o-Tolyl)3PAuCl

Abstract

Monoand multi-nuclear phosphinegold(I) complexes show characteristic luminescence in the visible region. Solid Ph3PAuX produce two emission bands with a broad lowenergy shoulder, and some bis(phosphine)gold(I) complexes produce one band. The observed luminescence in these complexes have been discussed in terms of metalcentered transitions or ligand-to-gold charge-transfer transitions. Furthermore, Au...Au (i.e. aurophilic) interactions, sometimes observed in the solid-state structures of phosphinegold(I) complexes, have been proposed to influence the luminescence characteristics. Against this background, it is not surprising that extensive studies of the photophysical properties of Au(I) complexes have been performed, but despite this, the optical processes have yet to be characterized in detail. The present study was undertaken to investigate optical properties of (o-tolyl)3PAuCl in which the Au(I) center is linearly coordinated by P and Cl atoms as revealed by X-ray crystallographic studies on the two polymorphs found for this complex; aurophilic interactions are precluded owing to steric hindrance afforded by the omethyl groups. In this study, the CIS post-HF calculations on the molecular orbitals and excited states of (o-tolyl)3PAuCl are undertaken to determine the nature of the orbitals and the transition probabilities involved in the optical processes. The electronic structures of (o-tolyl)3PAuCl are clearly established and a model for the absorbing and emitting levels presented. This work has importance in delineating the luminescent properties of related mononuclear Au(I) complexes where there is some debate as to the optical processes and their relationship to different structural conformations.