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

Two novel BCo9-based polyoxometalates, Cs3Na5H10BO (OH) 2Co9O (OH) (H2O) 3SiW6O26 (B-α-SiW9O34) 2·11H2O (1) and Cs13Na4H15BO (OH) 2Co9O (OH) (H2O) 32Co (H2O) GeW6O262 (B-α-SiW9O34) 4·16H2O (2), were synthesized under hydrothermal conditions. 1 contains a boron-modified V-shaped Co9 cluster, which is encapsulated by two SiW9O34 fragments and one SiW6O26 fragment. 2 is composed of two banana-shaped subunits linked by two CoO6 groups, and the configuration of the subunit is similar to the polyoxoanion of 1, where GeW6O26 fragment replaces the SiW6O26 fragment. Catalytic investigations indicate that compounds 1 and 2 can efficiently accelerate the Knoevenagel condensation reactions of various aldehydes with malononitrile.