A series of mononuclear Ru (II) complexes of the type [Ru (M) 2 (U)] 2+, where M= 2, 2′- bipyridine/1, 10-phenanthroline and U= tpl (Ru1), 4-Cl-tpl (Ru2), 4-CH3-tpl (Ru3), 4-CH3O- tpl (Ru4), and 4-NO2-tpl (Ru5),-pai (Ru6), where tpl= thiopicolinanilide and pai= 2-phenyl- azo-imidazole, have been prepared and characterized by IR, UV–Vis, 1H NMR, 13C-NMR, FAB-Mass spectrophotometer, and elemental analysis. The complexes display metal– ...