Sulfate-modified Ti IV -Zr IV -heterometallic germanotungstate used for catalyzing Knoevenagel condensation reaction

Abstract

The synthesis of novel heterometallic polyoxometalates not only represents a significant advancement in structural chemistry but also serves as a bridge connecting fundamental research to practical applications. Herein, a novel sulfate-modified TiIV−ZrIV-heterometallic germanotungstate [H2N(CH3)2]18.5K4.5Na[Ti6Zr2O9(OH)2 (SO4)2(A-α-GeW9O34)2]2·CH3 COOH·47H2O (1) has been synthesized and structurally characterized. The asymmetric structural unit of 1 contains two crystallographically independent dimeric [Ti6Zr2O9(OH)2(SO4)2(A-α-GeW9O34)2]12− subunits. Notably, each [Ti6Zr2O9(OH)2(SO4)2(A-α-GeW9O34)2]12− subunit consists of a sulfate-modified TiIV−ZrIV-heterometallic [Ti6Zr2O9(OH)2(SO4)2]8+ core bridging two [A-α-GeW9O34]10− fragments. To the best of our knowledge, 1 represents the first example of a sulfate-modified TiIV−ZrIV-heterometallic polyoxotungstate. Furthermore, 1 exhibits excellent catalytic performance as a heterogeneous catalyst for the Knoevenagel condensation reaction at room temperature, achieving high yields and exceptional cycling stability. The significance of this work lies not only in the first successful synthesis of a sulfate-modified TiIV−ZrIV-heterometallic polyoxometalate but also in providing an experimental foundation for the development of high-valence 3d−4d-heterometallic polyoxometalates with potential catalytic applications.