A ruthenium complex [ruthenium bis(2,2'-bipyridine)(2-mercaptopyridine)(pyridine)](PF6)(2) was crystal lographically characterized from its deprotonated form and was electrochemically investigated. In the deprotonated complex, the 2-mercaptopyridine ligand coordinates to the Ru atom only by the S atom; therefore, the N atom of the 2-mercaptopyridine ligand-can be protonated. In a CH3CN solution, the complex shows a reversible redox couple attributed to Ru-III/II-S. The addition of a base to the CH3CN solution of the complex gives irreversible voltammograms, implying electrochemically induced linkage isomerization between Rull-S and Ru-III-N. Analysis of the observed cyclic voltammograms gave the equilibrium and rate constants for linkage isomerization: K-NS(II) = 1.2 x 10(18), K-NS(III) = 0.64, K-NS(II) = 5 x 10 s(-1), K-SN(II) = 4 x 10(-17) S-1, K-NS(III) = 0.26 s(-1), and k(SN)(III) = 0.40 s(-1).