The preparation of a series of cis-[RuII(L–L)2(CO)L]n+ complexes [L–L-2,2′-bipyridyl (bipy), n= 1, L = H, Cl, or NCS; n= 2, L = H2O, MeCN, CO, pyridine (py), 4-vinylpyridine (vpy), or 4-methylpyridine (Mepy); L–L = 4,4′-dimethyl-2,2′-bipyridyl (Me2bipy), n= 1, L = H or Cl; n= 2, L = H2O or CO] is reported. The CO stretching frequency, the energy of the d–π* metal to ligand charge-transfer absorption bands, and the oxidation and reduction potentials of the complexes are found to depend markedly on the σ- and the π-donor abilities of the ligands. In complexes [Ru(L–L)2(CO)(H2O)]2+ and [Ru(L–L)2(CO)Cl]+ the water and Cl– ligands are thermally substitution labile. On u.v. irradiation all complexes except [Ru(L–L)2(CO)H]+ are efficiently decarbonylated.