From Platonic Templates to Archimedean Solids: Successive Construction of Nanoscopic {V16As8}, {V16As10}, {V20As8}, and {V24As8} Polyoxovanadate Cages

Supramolecular coordination cages provide unique restricted inner cavities that can be exploited for molecular recognition purposes and catalysis. Their syntheses often involve complex self-organization processes and rely on the identification of preorganized, kinetically stable building units that provide ligand-accessible coordination sites. Here we report a highly effective protocol for the successive buildup of symmetrical nanoscopic polyoxometalate (POM) cages. Our methodology takes advantage of a supramolecular templating effect and utilizes the structure-directing influence of octahedral {Xx(H2O)6–x} (X = Br–, Cl–; x = 2, 4, 6) assemblies that reside inside the hollow cluster shells and determine the arrangement of di- and tetranuclear vanadate units. The approach allows the preparation of a series of high-nuclearity POM cages that are characterized by {V16As8}, {V16As10}, {V20As8}, and {V24As8} core structures. In the latter cluster cage, the vanadium centers adopt a truncated octahedral topology. The formation of this Archimedean body is the direct result of the assembly of six square {V4O8} units that cap the vertices of the encapsulated Platonic {Cl6} octahedron. To the best of our knowledge, this {V24As8} cage is the largest hybrid vanadate cluster reported to date.