SYNTHESIS, STRUCTURE, AND SPECTROSCOPIC PROPERTIES OF ORTHO-METALATEDPLATINUM(II) COMPLEXES

The ortho-metalated Pt(II) complexes Pt(ppy)(CO)Cl (1), Pt(ptpy)(CO)Cl (2), and Pt(ppy)(Hppy)Cl (3) (where ppy and ptpy are respectively the ortho-C-deprotonated forms of 2-phenylpyridine and 2-p-tolylpyridine and Hppy is 2-phenylpyridine) have been prepared. Crystal structure de termination performed on a yellow needle of 2 shows that this compound crystallizes in the orthorhombic system, space group Pna2(1) (No. 33) , with a = 7.2025(14) Angstrom, b = 19.082(5) Angstrom, 8.7393(22) Ang strom, V = 1201.9(5) Angstrom(3), Z = 4 molecules/cell, and R = 0.046 (R, 0.056) for 1747 unique reflections. The CO Ligand is coordinated t rans to the nitrogen atom of the ortho-metalated ligand and exerts a s trong trans effect resulting in a relatively long Pt-N bond [2.114(19) Angstrom]. Characterization of 1 and 2 by IR and H-1 NMR spectra reve als that these complexes have analogous geometries. Complex 3 crystall izes in the monoclinic system, space, group P2(1)/c (No. 14), with a = 12.023(5) Angstrom, b = 9.547(4) Angstrom, c = 16.870(7) Angstrom, be ta = 103.559(5)degrees, V = 1882.5(13) Angstrom(3), Z = 4 molecules/ce ll, and R = 0.044 (R(w) = 0.061) for 2361 unique reflections. This str ucture shows both the bidentate ppy ligand and the monodentate Hppy wi th the nitrogens of these ligands trans to each other. The UV/vis elec tronic absorption spectra of 1-3 have intense bands in the near-UV reg ion (similar to 375 nm) which have been assigned as metal to ligand ch arge transfer (MLCT) transitions, and higher energy bands were assigne d as ligand-centered transitions. Each complex exhibits relatively lon g-lived structured emissions in the solid state at ambient temperature and at 77 K and in 77 K glassy toluene solutions. These emissions are proposed to originate from triplet MLCT states. Notably, in solution both the lifetime and spectrum of 2 proved to be a function of the con centration, a phenomenon interpreted in terms of the propensity of squ are planar d(8) complexes to oligomerize. In contrast, the more steric ally hindered complex d3 displayed no such tendency toward oligomeriza tion.