Supermolecular complexes of d-metal (Mo, W) anions with polyvinyl alcohol in aqueous solution

The formation of supermolecular complexes between d-metal (Mo, W) polyanion s and polyvinyl alcohol (PVA) in aqueous solution was studied by turbidimet ry and viscosimetry. There are five or more functional groups of the polyme r per metal atom. The number of associated groups per metal atom, n, falls stepwise with increasing the salt concentration, reflecting the decrease in the polyanion charge. Ammonium heptamolybdate and paratungstate, (NH4)(6)M o7O24. 4H(2)O and (NH4)(10)W12O41. nH(2)O, were used as the starting salts. For the molybdate-PVA complexes, the formation constant was estimated spec trophotometrically. Reversible partial photochemical reduction of Mo(VI) in PVA-salt supermolecular complexes was observed for the first time. The mos t likely mechanism of the reaction involves electron phototransfer from the polymeric chain to the d-metal ion. The threshold wavelength and quantum y ield were determined for the reaction, as well as the effective oxidation n umber of molybdenum in its complexes. Rare-earth (La, Y) ions, broadening t he absorption band in the electronic spectrum of Mo, sensitize the molybdat e-PVA complexes. Furthermore, these ions link polymeric molecules into a th ree-dimensional network, promoting the formation of a stable polymer-salt g el.