A Tetranuclear Thorium-Containing Hexameric Antimonotungstate: Synthesis, Structure, and Catalysis of the Knoevenagel Condensation

A novel hexameric thorium−antimony-tungstate compound, [NH 2 (CH 3 ) 2 ] 16 Na 10 -{[(SbW 9 O 32 )(OH)(SbW 9 O 31 )(OH) 2 (SbW 9 O 33 )(Th 2 WSb 9 O 13 )(OH) 4 (H 2 O)] 2 }·57H 2 O ( Th 4 Sb 24 ), has been synthesized. It represents the first tetranuclear thorium-containing polyoxometalates (POMs) cluster, consisting of a [{(Th 2 WSb 9 O 29 )(OH) 5 (H 2 O)} 2 ] 22− ({Th 4 Sb 18 W 2 }) heterometallic cluster and six {SbW 9 } units, and it exhibits the highest Th and Sb nuclearity in POM chemistry. Th 4 Sb 24 serves as an efficient heterogeneous catalyst for the Knoevenagel condensation under mild conditions, achieving 93% yield, a turnover number (TON) of 1860, and a turnover frequency (TOF) of 3720 h −1, while showing good recyclability and scalability. Mechanistic studies indicate a synergistic effect where the Lewis-acidic Th centers activate benzaldehyde, while the {SbW 9 } units facilitate proton abstraction. This work offers a viable strategy for designing high-nuclearity actinide POMs with practical catalytic utility.