2-(2-Pyridy1)-4-methylthiazole carboxylic acid (PMT-H) and rhenium tricarbonyl chloride react to form the red crystalline compoundfac-Re(PMT-H)(CO)(3)Cl, I, which is an analog of the well-known Re(bpy)(CO)(3)Cl molecule, where bpy is 2,2'-bipyridine. The acids PMT-H (2 equiv) and Re(PMT-H)(CO)(3)Cl (2 equiv) also react with Mo-2((TPB)-P-i)(4) ((TPB)-P-i = 2,4,6-triisopropylbenzoate) in toluene to give the red compound trans-Mo-2((TPB)-P-i)(2)(PMT)(2), II, and the royal blue compound trans-Mo-2((TPB)-P-i)(2)[(PMT)Re(CO)(3)Cl](2), III, respectively. The X-ray and spectroscopic characterization of I confirms its close relationship with Re(bpy)(CO)(3)Cl, as does the spectroscopic characterization of compounds II and III as analogs of other compounds of the form trans-M-2(TiPB)(2)L-2, where L is a pi-acceptor ligand. Electronic structure calculations on model compounds II' and III', where formate ligands substitute for (TPB)-P-i, show that the highest occupied molecular orbital (HOMO) in II is Mo-2 delta. When the Re(CO)(3)Cl unit is attached to the PMT ligand to form III, this orbital is stabilized significantly and now becomes associated with a close in energy band of Re d(6), t(2g) type orbitals. Oxidation of Ill is shown to be Mo-2-based, as evident by EPR spectroscopy, and the lowest-energy electronic absorption corresponds to a Mo-2 delta-to-PMT pi* transition. The S-1 states in both II and III are metal-to-ligand charge-transfer (MLCT), and the lowest-energy triplet sate, T-1 is (MoMo)-Mo-3 delta delta*, as evidenced by its steady state emission spectral features. The excited states of compounds I (T-1) and III (S-1 and T-1) have been investigated by time-resolved infrared spectroscopy (TRIR). The spectral features of I parallel those for Re(bpy)(CO)(3)Cl, with the lowest-energy T-1 state corresponding to Re cbr to PMT-H pi* charge transfer, producing higherenergy CO stretching vibrations relative to the ground state. For III, the CO vibrations are shifted to lower energy, consistent with charge being located on the PMT ligand, which enhances Re-to-CO backbonding. In the MoMo delta delta* T-1 state, however, the backbonding is reduced to the PMT ligand, and the CO stretches are at slightly higher energy relative to the ground state.