ELECTROCHEMISTRY AND SPECTROELECTROCHEMISTRY (EPR, UV-VIS-NEAR-IR) OF PLATINUM(II) 2,2'-BIPYRIDINE AND RING-METALATED BIPYRIDINE COMPLEXES - PTII(L-) AND PTI(L-) BUT NOT PTI(L)

The Pt(II) complexes [Pt(bpy)(PY)2]2+ (I), [Pt(bpy)(Me2N-PY)2]2+ (II), [Pt(Me2-bpy)(PY)2]2+ (III), [Pt(bpy)-(en)]2+ (IV), [Pt(Mebpy-H)(py)2]2+(V), [Pt(Mebpy-H)(bpy)]2+ (VI), [Pt(phen)(PY)2]2+ (VII), and [Pt(PY)4]2+ (VIII) (bpy, 2,2'-bipyridine; py, pyridine; Mebpy - H, N-methyl-2,2'-bipyridinyl-C(3),N'; Me2-bpy, 4,4'-dimethyl-2,2'-bipyridine; Me2N-py, 4-(dimethylamino)pyridine; en, 1,2-diaminoethane; phen, 1,10-phenanthroline) have been investigated by cyclic voltammetry and where possible by EPR spectroelectrochemistry and by UV-vis-near-IR spectroelectrochemistry. All complexes except VIII show at least two reversible reductive one-electron processes; VI shows three, and VIII shows one chemically irreversible process. In all cases, the doubly reduced species showed the characteristic pi* --> pi* UV-vis-near-IR absorptions of the ligand anion radicals. For the singly reduced species, EPR spectra show the added electron to be localized on the bipyridine-type ligand. However, the UV-vis-near-IR spectra of these species are not typical of ligand-based reduction products, and the potentials are less negative than expected for such a process. We conclude that the singly reduced species are best formulated as containing Pt(II), with tbe semioccupied and/or the lowest unoccupied ligand orbitals (corresponding to the LUMO and SLUMO of the unreduced parent species) being perturbed by the presence of metal orbitals. The doubly reduced species, however, are straightforward anion radical complexes of Pt(I).