High-Nuclear Ni-Substituted Poly(polyoxometalate) Containing an Anderson-like {Cs 7 } Cluster.

A novel high-nuclear Ni-substituted poly(polyoxometalate) [poly(POM)], [H 2 N(CH 3 ) 2 ] 2 Na 18 Cs 2 H 13 [(Cs 7 (H 2 O) 6 )@{(PO 4 )-@(Ni 4 (OH) 3 (WO 4 )) 3 @( B -α-PW 9 O 34 ) 3 } 2 ]·30H 2 O ( 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 Cs 7 (H 2 O) 6 ({Cs 7 }) cluster core encapsulated by two trimeric [(PO 4 )@(Ni 4 (OH) 3 (WO 4 )) 3 @( B -α-PW 9 O 34 ) 3 ] 21- subunits, in which the {Cs 7 } 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 [(Cs 7 (H 2 O) 6 )@{(PO 4 )@(Ni 4 (OH) 3 (WO 4 )) 3 } 2 ] 19+ cluster packaged by six {PW 9 } 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.