Ligand-directed bottom-up synthesis of trivacant lacunary polyoxomolybdates in organic media

Abstract Lacunary polyoxometalates (POMs), characterized by their highly reactive vacant sites, serve as versatile and valuable building units for the rational design of functional materials with broad applications. Despite the significant potential of lacunary polyoxomolybdates as a promising subclass of POMs, their synthesis, isolation, and practical utilization remain formidable challenges. In this study, we present a “ligand-directed bottom-up synthetic approach” for the preparation of trivacant lacunary Keggin-type polyoxomolybdates in organic solvents. The reaction of tetra-n-butylammonium salts of [MoO4]2− and [H2XO4]− (X = P, As) with acid, such as acetic acid and perchloric acid, in the presence of 4-methoxypyridine (pyOMe), as a protecting ligand in acetonitrile led to the selective formation of pyOMe-protected trivacant lacunary polyoxomolybdates, [XMo9O31(pyOMe)3]3−.