We report absorption and luminescence data for a series of d8 complexes with the formula [Pt(trpy)X]+ where trpy denotes 2,2':6/,2"-terpyridine and X = Cl, NCS, OMe, or OH. Each complex exhibits three or four relatively low-energy absorption maxima in the near-UV and visible regions with extinction coefficients on the order of 1000 M-1 cm-1. Since these energies are well below those of the 'ir-ir* transitions of the coordinated trpy ligand, we assign the bands as metal-to-ligand transfer (CT) transitions. At room temperature in deoxygenated acetonitrile each complex, save the chloride derivative, exhibits a broad, unstructured emission signal. The corrected emission maxima (and lifetimes) are 588 nm (3.5 ns), 654 nm (180 ns), and 621 nm (170 ns) for X = NCS, OMe, and OH, respectively. The thiocyanate and hydroxide derivatives also give stable, emissive solutions and significantly enhanced emission lifetimes in methylene chloride. The emissions are assigned to 3d-ir* CT excited states. Efficient radiationless decay via a low-lying 3d-d state may explain the fact that there is no detectable emission from the chloride derivative. To obtain additional information about these systems, we have solved the crystal structure of [Pt(trpy)OMe] (BPh4). The crystal symmetry is P\. The important lattice information includes: Z = 2, a = 10.656(2) Á, b = 11.830(5) A,c= 14.240(3) A, a = 110.47(2)°, ß = 92.52(2)°, and y = 105.62(3)°. In the final stage of refinement, R = 0.056. The coordination geometry is more-or-less rhombic with slightly shorter bonds to the methoxide oxygen and the central nitrogen of the trpy ligand.

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