Pseudo-polymorphism in the tri(o-tolyl)phosphinegoid(I) 2-mercaptobenzoates: Crystallographic, thermal decomposition, and luminescence studies

Abstract

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis of four crystallographically characterized pseudo-polymorphs of tri(o-tolyl)3PAu(2-mercaptobenzoate)•solvent, (o-tol)3PAu(2-mbaH)•solvent, featuring linear P−Au−S entities and different modes of supramolecular association depending on the nature of the included solvent molecule, have been performed. Whereas the thermal decomposition mechanisms of the four pseudo-polymorphs do not differ significantly from each other, the enthalpies of phase change do vary somewhat, indicating influence of solvent upon coherence of the crystal lattice. Crystals of (o-tol)3PAu(2-mbaH)•solvent are very luminescent. UV excitation produced three emission bands for (o-tol)3PAu-(2-mbaH)•solvent. Contrary to the free ligands, (o-tol)3P and 2-HmbaH, the emission shapes of the Au compounds are very dependent on the excitation energy. The single excitation configuration interaction (CIS) post-Hartree−Fock (HF) calculations were performed to model the electronic structures of the free ligands and (o-tol)3PAu(2-mbaH). The configurational interaction supports the notion that the observed electronic transitions of the complex are strongly associated with the charge transfer from S to Au. The assignment of the emission bands is presented in terms of the relaxed excited states responsible for the charge-transfer transitions, in which the crystal field and the vibronic interactions are taken into account as additional perturbations.