An experimental and theoretical study of the electronic spectra of tetraethylammonium [bis(1,3-dithiole-2-thione-4,5-dithiolato)M(III)] and tetraethylammonium [bis(1,3-dithiole-2-one-4,5-dithiolato)M(III)] (M = Sb or Bi)

This work presents a detailed analysis of the UV–vis spectra of [M(dmit) 2] −1 and [M(dmio) 2] −1 (M = Sb or Bi). The experimental spectrum was deconvoluted and analysed using several theoretical methodologies including ab initio CI calculations. The results confirm the multi-configuration nature of several excited states. ▪ Metal complexes of dmit and related ligands, such as dmio, have been studied extensively over the last few decades: [dmit] 2− = bis(1,3-dithiole-2-thione-4,5-dithiolato); [dmio] 2− = bis(1,3-dithiole-2-one-4,5-dithiolato). While much effort has been placed on determining structural properties, very few vigorous spectroscopic studies of these metal complexes have been undertaken. The spectroscopic features of the infrared, Raman and UV–vis spectra, previously reported, have largely been used to characterize compounds. In particular, many details of the electronic structure are still to be revealed. We now report a detailed analysis of the UV–vis spectra of the [M(dmit)] −1 and [M(dmio)] −1 anions, where M = Sb(III) or Bi(III). Experimental spectra were deconvoluted and analysed by several theoretical methodologies, including ab initio CI, TD and CISD calculations. The results led to the assignments of several MLCT/LMCT bands, occurring between 390 and 300 nm, and the confirmation of metal orbital contributions to the HOMO–LUMO boundary.