New estertin derivatives based on trivacant Keggin-type [β-SbW9O33]9− cluster

Two new polyoxometalate-based estertin derivatives, Na6K4[{Sn(C3H4O2)}2{Sn(C3H4O2)(H2O)}2·(B-β-SbW9O33)2]·14H2O (1) and Na4K6[{Sn(C4H6O2)(H2O)}2(WO2)2(B-β-SbW9O33)2]·19H2O (2), have been synthesized by the reaction of Na9[B-α-SbW9O33]∙19.5H2O with Cl3Sn(CH2)2COOCH3 or Cl3SnCH2CH(CH3)COOCH3 in an aqueous KCl solution. Both compounds exhibit the sandwich-type structural feature, in which the carboxyethyltin fragments are sandwiched by two B-β-[SbW9O33]9− units. Structural analyses reveal that the reaction process involves α → β isomerization of [SbW9O33]9− unit and the hydrolysis of estertin into carboxyethyltin group. Both compounds display good electrocatalytic activities toward the reduction of hydrogen peroxide, and compound 1 also shows good anti-tumoral activities in vitro.