New nonpolymeric diruthenium (II, III) carboxylates of the type [Ru 2 (l-O 2 CR) 4 Cl] [R = 9-methyl-9H-carbazole, 9-phenyl-9H-carbazole, 9-(4-vinylphenyl)-9H-carbazole] were obtained by reaction of HO 2 CR with [Ru 2 (l-O 2 CCH 3 ) 4 Cl] in MeOH-H 2 O. All complexes were characterized by TG, electron spectroscopy, cyclic voltammetry, and ESR spectra. The solvent influence on fluorescence was also discussed. Simultaneously, the electrochemical properties of these complexes were discussed in terms of the most probable electronic configuration of the complexes in solution. The frozen-solution e.s.r. spectra at 110 K give g = 1.94, 1.99, 1.95 for Ru 2 (L 0 ) 4 Cl, Ru 2 (L 1 ) 4 Cl and Ru 2 (L 2 ) 4 Cl, respectively. The complexes in DMF solution exhibited strong two-photon absorption (t.p.a.) at 532 nm nanosecond laser pulse. Their t.p.a. coefficient b, t.p.a. cross-section d have been determined by the Z-scan technique.