Spectroscopic and electrochemical characterizations of ferrocene- and biferrocene-functionalized terpyridine octanethiolate monolayer-protected clusters were investigated and reported. The electrochemical measurements of RU2+ coordinated with 4'-ferrocenyl-2,2':6',2"-terpyridine and 4'-biferrocenyl-2,2':6',2"terpyridine complexes were dominated by the Ru2+/RU3+ redox couple (E-1/2 at similar to1.3 V), Fe2+/Fe3+ redox couples (E-1/2 from similar to0.6 to similar to0.9 V), and terpy/terpy(-)/terpy(2-) redox couples (E-1/2 at ca. -1.2 and ca. -1.4 V). The substantial appreciable variations detected in the Ru2+/Ru3+ and Fe2+/Fe3+ oxidation potentials indicate that there is an interaction between the Ru2+ and Fe2+ metal centers. The coordination of the Ru2+ metal center with 4'-ferrocenyl-2,2':6',2"-terpyridine and 4'-biferrocenyl-2,2':6',2"-terpyridine leads to an intense (1)[(d(pi)(Fe))(6)] --> (1)[d(pi)(Fe))(5)(pi*(Ru)(terpy))(1)] transition in the visible region. The (1)[(d(pi)(Fe))(6)] --> (1)[d(pi)(Fe))(5)(pi*(Ru)(terpy))(1)] transition observed at similar to510 nm revealed that there was a qualitative electronic coupling between metal centers. The coordination of the Ru2+ transition metal center lowers the energy of the pi*(terpy) orbitals, causing this transition.