Five mononuclear ruthenium complexes of the general type trans-[Ru II (L)(Azo)Cl 2 ] {(Azo=C 6 H 5 NNC(COCH 3 )NC 6 H 4 Y, Y=H (1), CH 3 (2), OCH 3 (3), Cl (4), Br (5)} and L is 2-(1,2,3-thiadiazol-4-yl)pyridine have been synthesized and their structures investigated by elemental analyses, spectroscopic (IR, UV/–Vis, and NMR) and electrochemical (cyclic voltammetry) techniques. In addition, complex (3) has been further characterized by X-ray diffraction analysis. The absorption spectrum of 3 in acetonitrile has been modeled by time-dependent density functional theory (TD-DFT) using mixed basis set, LanL2DZ/6–-31+g(d,p), in acetonitrile as a solvent.