Access to Sb^III-containing polyoxotungstates with structure-dependent catalytic enhancement toward Knoevenagel condensation

Owing to the unique lone-pair effect and pronounced hydrolytic tendency, the controllable synthesis of Sb^III-containing polyoxometalates (POMs) remains a significant challenge. Rather than being confined as internal heterogroup, the employment of Sb^III as an accessible metal center that cooperates with the POM framework represents an emerging research frontier. In this work, a series of Sb^III-containing polyoxotungstates were successfully prepared, displaying a systematic structural evolution from dimeric to trimeric assemblies with tunable Sb content. Benefiting from the introduction of strongly Lewis acidic Sb^III centers, the obtained POMs, serving as Lewis acid-base catalysts, exhibited significantly enhanced catalytic activity, broad substrate scope, and excellent recyclability in the Knoevenagel condensation reaction. Based on the structure-activity relationship analysis, it is believed that modulation of the coordination environment around the Sb^III centers might serve as a promising strategy for the optimization of catalytic performance.