High-Nuclear Ni-Substituted Poly(polyoxometalate) Containing an Anderson-like {Cs7} Cluster

A novel high-nuclear Ni-substituted poly(polyoxometalate) [poly(POM)], [H2N(CH3)2]2Na18Cs2H13[(Cs7(H2O)6)@{(PO4)-@(Ni4(OH)3(WO4))3@(B-α-PW9O34)3}2]·30H2O (1), has been successfully developed and structurally characterized. The polyoxoanion of 1 can be viewed as a unique huge sandwich structure made of an unprecedented Cs7(H2O)6 ({Cs7}) cluster core encapsulated by two trimeric [(PO4)@(Ni4(OH)3(WO4))3@(B-α-PW9O34)3]21- subunits, in which the {Cs7} cluster presents an interesting Anderson-like arrangement and is the first example of a classical POM configuration based on the alkali metal cluster in the POM chemistry. The polyoxoanion can also be described as an unusual [(Cs7(H2O)6)@{(PO4)@(Ni4(OH)3(WO4))3}2]19+ cluster packaged by six {PW9} fragments. Furthermore, investigations on the Knoevenagel condensation reaction reveal that 1 has good catalytic activity for the condensation of various aldehydes and malononitrile into corresponding products with excellent yields.