Er‐Bridged Polyoxometalate With Trilayered Pagoda‐Shaped Seleno‐Bismutho‐Tungstate Fragments and Catalysis for Knoevenagel Condensation

A novel Er‐bridged seleno‐bismutho‐tungstate [H 2 N(CH 3 ) 2 ] 4 NaH 18 [Er(H 2 O) 4 (Se 2 BiW 21 O 75 ) 2 ]·20H 2 O ( 1 ) has been successfully synthesized in acidic aqueous solution and systematically characterized by powder X‐ray diffraction, infrared spectroscopy, and thermogravimetric analysis. The polyoxoanion is assembled from two identical trilayered pagoda‐shaped Se 2 BiW 21 O 75 fragments linked by one central Er atom. The Se 2 BiW 21 O 75 can be viewed as being constructed from one BiW 9 O 33 moiety and two SeW 6 O 27 segments, wherein Bi and Se atoms simultaneously function as central heteroatoms. Furthermore, compound 1 , as a heterogeneous catalyst, exhibits good catalytic performance in accelerating the Knoevenagel condensation of various aldehydes with malononitrile under mild reaction conditions.