Polyoxometalate-Induced Preorganization of Halogenated Ligands in Supramolecular Assemblies

Research on polyoxometalates (POMs) with the Keggin structure has been ongoing for several decades. However, the trilacunary phosphomolybdate derivative was difficult to obtain until recently. By using pyridine in nonaqueous media, stabilization of the trilacunary phosphomolybdate was achieved, and the six terminal ligand sites within the structural vacancy alternated between oxido and pyridyl ligands. Through ligand exchange experiments, we were able to control the intramolecular spatial separation of coordinated halogenated ligands as well as intermolecular halogen-halogen interactions in the crystalline state. Our results reveal a new X-6 synthon (where X = Cl, Br, and I) and a desolvation-induced single-crystal to single-crystal transition.