Activation-controlled outer-sphere electron transfer reactions: reduction of heteropoly 11-tungstovanadophosphate and heteropoly 10-tungstodivanado phosphate by thiourea in aqueous acid medium

作者：Sami Ponnusamy; Mariselvi Natarajan; Venkateshwari Kandasamy; Vairalakshmi Murugesan; Sarathi Arunachalam; Rajasekaran Kasi^*

来源：Transition Metal Chemistry, 2010, 35(5): 563-570.

DOI：10.1007/s11243-010-9364-z

The kinetics of reduction of heteropoly 11-tungstovanadophosphate, [PV(V)W(11)O(40)](4-), (HPA1) and heteropoly 10-tungstodivanadophosphate, [PV(V)V(V)W(10)O(40)](5-), (HPA2) by thiourea has been investigated in HClO(4)/phthalate/acetate buffer solutions spectrophotometrically at 25 A degrees C in aqueous medium. The stoichiometry of the reaction is 1:1 in both cases. The HPAs are converted into the corresponding one-electron reduced heteropoly blues, namely, [PV(IV)W(11)O(40)](5-) and [PV(IV)V(V)W(10)O(40)](6-), and thiourea is oxidised to formamidine disulphide. The reaction shows first-order dependence in both [HPA] and [thiourea] at constant pH. The rate-pH profile shows the participation of both the neutral and deprotonated forms of thiourea in the reaction. The reaction proceeds through an outer sphere electron transfer mechanism in which activation-controlled electron transfer is the rate-determining step. Self-exchange rate constants for the couples [PV(V)W(11)O(40)](4-)/[PV(IV)W(11)O(40)](5-), [PV(V)V(V)W(10)O(40)](5-)/[PV(IV)V(V)W(10)O(40)](6-) and H(2)NCSNH(2)/H(2)NCS(center dot+)NH(2) have been evaluated by Marcus theory.

• 出版日期2010-8