Several new mono- and dinuclear eta(5)-pentamethylcyclopentadienyl (Cp*) iridium(III) complexes bearing 5-methyltetrazolate (MeCN4-) have been synthesized and their molecular and crystal structures have been determined. For complexes incorporating 2,2'-bipyridine (bpy) or 1,10-phenanthroline (phen), both mononuclear kappa N-2-coordinated and dinuclear mu-kappa N-1:kappa N-3-bridging MeCN4 Complexes were obtained: [Cp*Ir(bpy or phen)(MeCN4-kappa N-2)]PF6 (1 or 3) and [{Cp*Ir(bpy or phen)}(2)(mu-MeCN4-kappa N-1:kappa N-3)](PF6)(3) (2 or 4), respectively. It was confirmed by X-ray analysis that the dinuclear complex in 2 has a characteristic structure with a pyramidal pocket constructed from a mu-kappa N-1:kappa N-3-bridging MeCN4- and two bpy ligands. In the case of analogous complexes with N,N-dimethyldithiocarbamate (Me(2)dtc(-)), yellow platelet crystals of mononuclear kappa N-1-coordinated complex, [Cp*Ir(Me(2)dtc)(MeCN4-kappa N-1)]center dot HN4CMe (5 center dot HN4CMe), and yellow prismatic crystals of dinuclear mu-kappa N-1:kappa N-4-bridging one, [{Cp*Ir(Me(2)dtc)}(2)(mu-MeCN4-kappa N-1: kappa N-4)]PF6 (6), were deposited. The kappa N-1- and kappa N-1:kappa N-4-bonding modes of MeCN4- in these complexes presumably arise from the compactness of the Me(2)dtc(-) coligand. 6 is the first example in which tetrazolates act as a mu-kappa N-1: kappa N-4-bridging ligand. Furthermore, the molecular and crystal structures of dinuclear complexes having mu-kappa S-2,N:kappa S-bridging 2-pyridinethiolate (2-Spy(-)) or 8-quinolinethiolate (8-Sqn(-)) ligands have been determined: [(Cp*Ir)(2)(mu-2-Spy or 8-Sqn-kappa S-2,N:kappa S)(2)] (7 or 8). These thiolato-bridging complexes were stable toward the addition of 5-methyltetrazole (HN4CMe), owing to the characteristic intramolecular stacking interaction between the pyridine or the quinoline rings. The 2-Spy complex of 7, however, reacted with an excess amount of Na(N4CMe), resulting in cleavage of the Ir-N(py) bond and coordination of MeCN4- in the mu-kappa N-2:kappa N-3-bridging mode: [(Cp*Ir)(2)(mu-2-Spy-kappa S:kappa S)(2)(mu-MeCN4-kappa N-2:kappa N-3)]PF6 (9). This bridging mode of MeCN4- was also observed in the triply bridging MeCN4 complex: [(Cp*Ir)(2)(mu-MeCN4-kappa N-2:kappa N-3)(3)]PF6 (10). In these various MeCN4 complexes, the structural parameters of the MeCN4 moiety were not perturbed by the difference in the bonding modes.