Metalladichalcogenolate cluster complexes [{CpCo(S2C6H4)}(2)MO(CO)(2)] (CP = eta(5)-C5H5) (3), [{CPCO(S2C6H4)}(2)W-(CO)(2)] (4), [CpCo(S2C6H4)Fe(CO)(3)] (5), [CpCo(S2C6H4)Ru(CO)(2)((PBU3)-B-t)] (6), [{CpCo(Se2C6H4)}(2)MO(CO)(2)] (7), and [{CpCo(Se2C6H4)}(Se2C6H4)W(CO)(2)] (8) were synthesized by the reaction of [CpCo(E2C6H4)] (E = S, Se) with [M(CO)(3)(py)(3)] (M = Mo, W), [Fe(CO)(5)], or [Ru(CO)(3)((PBu3)-Bu-t)(2)], and their crystal structures and physical properties were investigated. In the series of trinuclear group 6 metal-Co complexes, 3, 4, and 7 have similar structures, but the W-Se complex, 8, eliminates one cobalt atom and one cyclopentadienyl group from the sulfur analogue, 4, and does not satisfy the 18-electron rule. H-1 NMR observation suggested that the CoW dinuclear complex 8 was generated via a trinuclear Co2W complex, with a structure comparable to 7. The trinuclear cluster complexes, 3, 4, and 7, undergo quasi-reversible two-step one-electron reduction, indicating the formation of mixed-valence complexes (CoMCoII)-M-III-Co-0 (M = Mo, W). The thermodynamic stability of the mixed-valence state increases in the order 4 < 3 < 7. In the dinuclear group 8 metal-Co complexes, 5 and 6, the CPCO(S2C6H4) moiety and the metal carbonyl moiety act as a Lewis acid character and a base character, respectively, as determined by their spectrochemical and redox properties. Complex 5 undergoes reversible two-step one-electron reduction, and an electron paramagnetic resonance (EPR) study indicates the stepwise reduction process from (CoFe0)-Fe-III to form (CoFe-I)-Fe-III and (CoFe-I)-Fe-II.