A series of new iridium(III) complexes containing pentamethylcyclopentadienyl (Cp* = eta(5)-C5Me5) and 1,8-naphthyridine (napy) have been prepared. X-ray crystallography revealed that napy acted as a monodentate, a didentate chelating, and a bridging ligand in complexes of [Cp*IrCl2(napy)] (1), [Cp*IrCl(napy)]PF6 (2), and [(Cp*IrC])(2)(H)(napy)]PF6 (4), respectively. The crystal structure of [Cp*Ir(napy)(2)]-(PF6)(2) (3) has also been determined; the dicationic complex bore both monodentate and chelating napy ligands. Dinuclear Cp*Ir-III complex bridged by napy was only isolable if two Ir-III centers were supported by a hydride (H-) bridge. In complexes 2 and 3, the four-membered chelate rings formed by napy exhibited a large steric strain; in the rings the N-Ir-N bond angles were only 60.5(2)-61.0(4)degrees and the Ir-N-C angles were 94.7(8)-96.7(8)degrees. The bridging coordination of napy in complex 4 also afforded a large strain, i.e., the Ir-III centers were displaced by 0.84(3) angstrom from the napy plane, due to the steric interaction between two Cp*IrCl moieties. The monodentate napy complex I in CDCl3 or CD2Cl2 at ambient temperature showed a rapid coordination-site exchange reaction, which gave two N sites of napy equivalent; at temperatures below -40 degrees C, the H-1 NMR spectra corresponded to the molecular structure of [Cp*IrCl2(napy-KN)]. The analogous diazido complex of [Cp*Ir(N-3)(2)(napy)] (5) has also been prepared, and the crystal structure has been determined. In contrast to the dichloro complex 1, the diazido complex 5 exhibited a dissociation equilibrium of coordinated napy in solution. (c) 2006 Elsevier B.V. All rights reserved.