STUDIES OF THE ROOM-TEMPERATURE ABSORPTION AND EMISSION-SPECTRA OF [PT(TRPY)X]+ SYSTEMS

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 1pi-pi* 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 abroad, 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-pi* 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 P1BAR. The important lattice information includes: Z = 2, a = 10.656(2) angstrom, b = 11.830(5) angstrom, c = 14.240(3) angstrom, alpha = 110.47(2)degrees, beta = 92.52(2)degrees, and gamma = 105.62(3)degrees. 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.