PHOTOREACTIVITY OF THE (2,2'-BIPYRIDYL)HEXACYANOTUNGSTATE(IV) ION IN AQUEOUS-SOLUTION

The electronic spectrum of the W(bpy)(CN)62- ion (bpy, 2,2'-bipyridyl) in the visible region is dominated by metal-to-ligand charge transfer (MLCT) transitions. The complex undergoes photosubstitution with the preferential loss of the bpy ligand. The wavelength-independent quantum yields PHI increase from 3.1 X 10(-3) (at pH 1) to 7.2 X 10(-3) (in the range pH 8.12-10.85). The photoreaction occurs from a short-lived, low-lying ligand field (LF) state. The lower reactivity in acidic medium suggests that the formation of the intermediate W(CN)6(OH)24- is more efficient than the formation of the aqua-substituted analogue. A scheme of photoreactions and thermal reactions based on the experimental observations is presented.