NEW CYANO COMPLEX OF W(V), (ASPH4)[W(BPY)(CN)6] - REVERSIBLE REDOX SYSTEM W(BPY)(CN)6(-)/W(BPY)(CN)6(2-)

The preparation and spectroscopic characterization of the new cyano complex of W(V), (AsPh4)[W(bpy)(CN)6], is reported. While the light yellow crystalline salt is thermally stable in the solid state and in aqueous solution, in light it undergoes photoreduction to the W(IV) analogue with the initial quantum yield PHI365(0) = 0.17 in H2O. The electronic absorption spectrum in the visible part shows ligand-to-metal charge-transfer (LMCT) bands which are solvent dependent. Linear correlations between nu(max) versus Reichardt E(T) parameter were found. The ESR spectrum at 77 K shows characteristic g tensors with g1 = 1.9352, g2 = 1.9523 and g3 = 1.9726 (g(av) = 1.9486 at 293 K). Cyclic voltammetry measurements indicate a reversible one-electron, reduction leading to W(bpy)(CN)62- with formal redox potential E0 = 0.845 V (in 0.1 M aqueous KCl), dependent on the nature of the solvent. A new synthetic route to (AsPh4)2[W(bpy)(CN)6]-5H2O is also presented.