[SiNb_(12)O_(40)]~(16-) and [GeNb_(12)O_(40)]~(16-): Highly Charged Keggin Ions with Sticky Surfaces

摘要

Heteropolyanions are negatively charged clusters of corner-sharing and edge-sharing early transition-metal MO_6 octahedra and heteroatom XO_4 tetrahedra, in which the tetrahedra are usually located in the interior of the cluster. The geometry, composition, and charge of these clusters are varied through synthesis parameters, and cluster properties are highly tunable as a function of these characteristics. Heteropolyanions have been employed in a range of applications that include virus-binding inorganic drugs, homogeneous and heterogeneous catalysts, electro-optic and electrochromic materials, metal and protein binding, and as building blocks for nanostructuring of materials. The α-Keggin geometry, which was first structurally characterized in 1933 by J. F. Keggin for the phosphotungstic acid (H_3PW_(12)O_(40)) is one of the most widely recognized and thoroughly studied heteropolyanion geometries.