Dual-Ligand-Regulated Tb-Containing Antimonotungstate for the Heterogeneous Catalytic Synthesis of N-Heterocycles in Ethanol.

A novel Tb3+-containing antimonotungstate, [(CH3)2NH2]3Na18[Tb4(mal)2(OAc)(W6O13)(SbW9O33)4(H2O)15]·47H2O, regulated by dl-malic acid and acetic acid (Tb4mal2, H3mal = malic acid; HOAc = acetic acid), has been successfully synthesized. The structural analysis reveals that the polyanion of Tb4mal2 consists of four {B-α-SbW9O33} units interconnected by a decanuclear metal cluster {Tb4W6(mal)2(OAc)}. The flexible malic acid ligands involved in the coordinating process create a certain torsion angle, resulting in a twisted rectangular structure of polyanion Tb4mal2. In addition, Tb4mal2 exhibits excellent heterogeneous catalytic activity for the synthesis of 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxides through the condensation reaction of 2-aminobenzenesulfonamide and benzaldehydes under environmentally benign reaction conditions.