ja9b04533_si_009.cif (1.84 MB)

Anisotropic Polyoxometalate Cages Assembled via Layers of Heteroanion Templates

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posted on 14.08.2019, 15:34 by Qi Zheng, Manuel Kupper, Weimin Xuan, Hirofumi Oki, Ryo Tsunashima, De-Liang Long, Leroy Cronin
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 [W16Mo2O54(XO3)]n, [W21Mo3O75/76(XO3)2]m, and [W26Mo4O93(XO3)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 (WVI/MoV) 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 WVI/MoV metal centers, demonstrating their potential use for electronic materials.