SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES OF CYCLOMETALATED PLATINUM(II) COMPOUNDS CONTAINING CIS-1,2-DICYANO-1,2-DITHIOLATOETHENE

Spectroscopic and electrochemical properties of Bu(4)N(+) salts of two [Pt < N-C >mnt](-) ions are reported. < N-C > represents cyclometalat ed 2-phenylpyridinate, ppy, or 2-(2'-thienyl)pyridinate, tpy, while mn t represents cis-1,2-dicyano-1,2-dithiolatoethene. Bu(4)N[Pt(tpy)mnt] is luminescent in fluid solutions with an emission lifetime in DMF of 1.4 mu s, whereas Bu(4)N[Pt(ppy)mnt] luminesces detectably only in the solid state at room temperature. The electrochemical and spectroscopi c results have been compared with available data for a series of Pt(di imine)mnt complexes. The compounds exhibit a dithiolate-centered quasi reversible one-electron oxidation wave at ca. 0.4 V and a reversible one-electron reduction wave, centered on the cyclometalated ligand, at -2.4 V vs. Fc(+)/Fc. The highly solvatochromic absorption bands are a ssigned to spin-allowed ligand-to-ligand charge transfer transitions. The energies of these bands show good correlation with the energy gap (Delta E(1/2)) between the HOMO and LUMO redox orbitals. The lowest-en ergy spin-forbidden transitions observed in the absorption and emissio n spectra of the [Pt < N-C >mnt](-) complex ions are attributed to pre dominantly dithiolate intraligand transitions.