Rhenium(I) complexes with NNS donor thioarylazoimidazole ligands with the cis-{Re(CO)2}+ core: Synthesis, characterization, electrochemical study and DFT calculation

New rhenium(I) dicarbonyl complexes containing cis-{Re(CO)2}+ fragment with redox non-innocent NNS donor ligands L1/L2 (L1, 1-methyl-2-{(o-thiomethyl)phenylazo}imidazole and L2, 1-ethyl-2-{(o-thioethyl)phenylazo}imidazole) having general formula cis-[ReX(CO)3(L1/L2)] (1/2) (X = Cl (1) and Br (2)) have been synthesized and characterized by both experimental and theoretical studies. The structural confirmation has been carried out for 1b. The complexes show quasireversible ReI/ReII oxidation and ligand based reduction in the cyclic voltammetric studies. The electronic structure and the nature of ReCO bonding has been explained by means of DFT and NBO calculations. The spin allowed singlet–singlet electronic transitions of 1b and 2b have been calculated with TDDFT method, and the experimental spectra of the complexes have been discussed on this basis.