Access to Sb^III-containing polyoxotungstates with enhanced structure-dependent catalytic performance in Knoevenagel condensation

Owing to the unique lone-pair effect and pronounced hydrolytic tendency of Sb^III, the controllable synthesis of Sb^III-containing polyoxometalates (POMs) remains a great challenge. Rather than being confined as an internal heterogroup, using 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 displaying a systematic structural evolution from dimeric to trimeric assemblies with tuning of Sb content were successfully prepared. Benefiting from the introduction of strongly Lewis acidic Sb^III centers, the resulting polyoxotungstates functioned as Lewis acid–base catalysts with enhanced catalytic activity, broad substrate scope, and excellent recyclability in the Knoevenagel condensation reaction. Elucidation of the structure–activity relationship revealed that modulating the coordination environment around the Sb^III centers is a promising strategy for optimizing the catalytic performance of POMs.