Synthesis, X-ray structure, spectroscopic and DFT study of cis-[Ru(PPh3)(L)X2] complexes (X = Cl−, Br−, I− and NCS−) (L = 1-methyl-2-{(o-thiomethyl)phenylazo}imidazole)

The complex cis-[Ru(PPh3)(L)Cl2] (1) has been synthesized by the reaction between Ru(PPh3)3Cl2 and thioether containing azo ligand (L) (L = 1-methyl-2-{(o-thiomethyl)phenylazo}imidazole). The Cl atoms have been exchanged with Br−, I− and NCS− leading to the formation of cis-[Ru(PPh3)(L)Br2] (2), cis-[Ru(PPh3)(L)I2] (3) and cis-[Ru(PPh3)(L)(NCS)2] (4), respectively. The complexes have been characterized by spectroscopic techniques (IR, NMR and UV–Vis) and geometries have been confirmed by X-ray crystal structures of 1 and 3. The electronic spectra of the complexes show moderately intense MLCT band along with intense ILCT transitions. Cyclic voltammetric studies show one quasi reversible Ru(III)/Ru(II) oxidation couple and two successive one electron reductions leading to the formation of L− and L2−, respectively. The electronic structure, redox and absorption properties of the complexes have been explained based on DFT and TDDFT results.