An experimental and theoretical study of the electronic spectra of tetraethylammonium [bis(1,3-dithiole-2-thione-4,5-dithiolato)zincate(II)], [NEt 4] 2[Zn(dmit) 2], and tetraethylammonium [bis(1,3-dithiole-2-one-4,5-dithiolato)zincate(II)], [NEt 4] 2[Zn(dmio) 2

Abstract

Metal-dmit complexes and related compounds have been the object of intense study in the last decade. Despite such efforts on the study of its structural properties, very few attempts have been made to the spectroscopic study of these metal complexes. Experimental reports of its infrared, Raman and UV–Vis spectra present the main spectroscopic features, however, many details of the electronic structure have still to be fully investigated and inconsistent assignments are found in the literature. This work presents a detailed analysis of the UV–Vis spectra of the zinc-dmit, [Zn(dmit) 2] −2, and the zinc-dmio complex, [Zn(dmio) 2] −2. The experimental spectrum was deconvoluted and analysed with several theoretical methodologies including ab initio CI calculations, ab initio TD and zindo semi-empirical methods. The results confirm the multi-configuration nature of several excited states and the calculated results were concordant for several transitions. The results lead to a new assignment of the 457 nm band in the [Zn(dmit) 2] −2 as π(pS m) → π*C S band. In the metal-dmio, the sulfur substitution by oxygen results in a larger HOMO–LUMO gap and a change in the nature of the frontier orbitals. As the first transition we found, for the dmit compound, a high-intensity π → π*C S while for the zinc-dmio, a low-intensity π → σ*C–S transition.