Extension of the previously used "complexes-as-metals and complexes-as-ligands" synthetic strategy (J. Am. Chem. Sec. 1992, 114, 2944) to cyclometalated Rh(III) and Ir(III) complexes has allowed us to prepare four new tetranuclear bimetallic complexes (as PF6- salts) : [Ru{(mu-2,3-dpp)Rh(ppy)(2)}(3)](5+) (RuRh3), [Ru{(mu-2,3-dpp)Ir(ppy)(2)}(3)](5+) (RuIr3), [Os{(mu-2,3-dpp)Rh(ppy)2}(3)](5+) (OsRh3), and [Os{(mu-2,3-dpp)Ir(ppy)(2)}(3)](5+) (OsIr3); 2,3-dpp = 2,3-bis(2-pyridyl)-pyrazine, ppy = phenylpyridine anion. The absorption spectra, excited state properties, and electrochemical behaviors of the four novel complexes in CH2Cl2 solution have been investigated and compared with those observed for previously studied Ru(II)- and/or Os(II)-based tetranuclear complexes. All the complexes examined exhibit very intense ligand-centered (LC) absorption bands in the UV region and moderately intense metal-to-ligand charge-transfer (MLCT) bands in the visible region. The RuRh3 and OsRh3 complexes show a luminescence emission (at 77 K, lambda(max) = 645 and 789 nm, respectively) that can be assigned to the lowest (3)MLCT level of the Ru-based and Os-based cores. For RuIr3 and OsIr3 complexes, the observed emissions (at 77 K, lambda(max) = 726 and 810 nm, respectively) are likely due to the peripheral Ir-based units in the former compound and to the Os-based core in the latter. All the compounds exhibit luminescence also at room temperature, where mixing of states of different orbital origin is more likely. Cyclic and differential pulse voltammetry experiments carried out in argon-purged dichloromethane solution at room temperature show that the RuRh3, RuIr3, and OsIr3 complexes undergo three reversible reduction processes in the -0.3/-0.7 V (vs SCE) potential range, which correspond to the successive first reduction of the three bridging ligands in each complex. At more negative potentials (-1.1/-1.6 V), three other reduction waves are observed, assigned to the successive second reduction of each bridging ligand. The trend observed for the reduction waves of the various complexes is discussed.The reduction processes observed for OsRh3 are irreversible. For the RuRh3 and RuIr3 complexes, irreversible oxidation waves are observed at +1.25 and +1.40 V, respectively. For the former compound, the process involves one electron and can be attributed to oxidation of the Ru ion, whereas for the RuIr3, the process involves at least three electrons and therefore should concern the Ir peripheral units. For OsIr3, a somehow reversible oxidation wave at +1.00 V, assigned to the one-electron oxidation of the central Os(II) ion, is followed by an irreversible, three-electron wave at +1.40 V, assigned to the one-electron oxidation of the three peripheral Ir-based units. In the case of OsRh3, an irreversible one-electron oxidation at +0.75 V, assigned to the oxidation of the Os ion, is followed by an irreversible oxidation at +1.50 V, which involves more than one electron, and is therefore assigned to the oxidation of the peripheral Rh-based units. The successful synthesis of these new tetranuclear compounds shows that combination of N-N (bipyridine type) and C--N (cyclometalating type) chelating sites is a promising strategy to extend the number and the type of metals and/or ligands that can be incorporated in luminescent and redox-active complexes of high nuclearity.y?