Construction of {BCo 9 }-Based Polyoxometalates with Banana- and Peanut-Shaped Structures: Catalytic Activity in Knoevenagel Condensation Reactions

Two novel {BCo 9 }-based polyoxometalates, Cs 3 Na 5 H 10 [BO(OH) 2 Co 9 O(OH)(H 2 O) 3 SiW 6 O 26 (B-α-SiW 9 O 34 ) 2 ]·11H 2 O ( 1 ) and Cs 13 Na 4 H 15 [{BO(OH) 2 Co 9 O(OH)(H 2 O) 3 } 2 {Co(H 2 O)GeW 6 O 26 } 2 (B-α-SiW 9 O 34 ) 4 ]·16H 2 O ( 2 ), were synthesized under hydrothermal conditions. 1 contains a boron-modified V-shaped {Co 9 } cluster, which is encapsulated by two SiW 9 O 34 fragments and one SiW 6 O 26 fragment. 2 is composed of two banana-shaped subunits linked by two CoO 6 groups, and the configuration of the subunit is similar to the polyoxoanion of 1, where GeW 6 O 26 fragment replaces the SiW 6 O 26 fragment. Catalytic investigations indicate that compounds 1 and 2 can efficiently accelerate the Knoevenagel condensation reactions of various aldehydes with malononitrile.