Anisotropic Polyoxometalate Cages Assembled via Layers of Heteroanion Templates

[Image: see text] The synthesis of anisotropic redox-active polyoxometalates (POMs) that can switch between multiple states is critical for understanding the mechanism of assembly of structures with a high aspect ratio, as well as for their application in electronic devices. However, a synthetic methodology for the controlled growth of such clusters is lacking. Here we describe a strategy, using the heteroanion-directed assembly, to produce a family of 10 multi-layered, anisotropic POM cages templated by redox-active pyramidal heteroanions with the composition [W(16)Mo(2)O(54)(XO(3))](n−), [W(21)Mo(3)O(75/76)(XO(3))(2)](m−), and [W(26)Mo(4)O(93)(XO(3))(3)](o−) for the double, triple, and quadruple layered clusters, respectively. It was found that the introduction of reduced molybdate is essential for self-assembly and results in mixed-metal (W/Mo) and mixed-valence (W(VI)/Mo(V)) POM cages, as confirmed by an array of analytical techniques. To probe the archetype in detail, a tetrabutyl ammonium (TBA) salt derivative of a fully oxidized two-layered cage is produced as a model structure to confirm that all the cages are a statistical mixture of isostructures with variable ratios of W/Mo. Finally, it was found that multilayered POM cages exhibit dipolar relaxations due to the presence of the mixed valence W(VI)/Mo(V) metal centers, demonstrating their potential use for electronic materials.