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

Abstract Owing to the unique lone-pair effect and pronounced hydrolytic tendency, the controllable synthesis of SbIII-containing polyoxometalates (POMs) remains a significant challenge. Rather than being confined as internal heterogroup, the employment of SbIII as an accessible metal center that cooperates with the POM framework represents an emerging research frontier. In this work, a series of SbIII-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 SbIII 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 SbIII centers might serve as a promising strategy for the optimization of catalytic performance.