Directional Bonding in Decaniobate Inorganic Frameworks

Metal-oxo clusters offer an opportunity to assemble inorganic and metal-organic frameworks (MOFs) by a controlled building-block approach, which led to the revolutionary discoveries of zeolites and MOFs. Polyoxometalate clusters are soluble in water, but more challenging to link into frameworks; the inert oxo-caps that provide solubility are resistant to replacement or further connectivity. We demonstrate how the unique directional bonding and varying basicity of the decaniobate ([Nb-10]) oxo-caps can be exploited to build 1D, 2D, and 3D inorganic frameworks. In nine structures, A(+) (A=Li, Na, K, Rb and Cs), AE(2+) (AE=Ca, Sr, Ba) and Mn2+ demonstrate that the dimensionality of the obtained material is controlled by cation charge and size. Increased cation charge decreases selectivity for oxo-site bonding, leading to higher dimensional linking. Larger cation radii also decreases bonding selectivity, yielding higher dimensional materials. Ion-exchange studies of the A(+)-Nb-10 family shows exclusive selectivity for Cs+ over other alkalis, which is important for radioactive Cs removal and sequestration.

Automated summary

Metal-oxo clusters, specifically decaniobate clusters, can be exploited to construct 1D, 2D, and 3D inorganic frameworks by utilizing their unique directional bonding and varying basicity. The dimensionality of the resulting material is controlled by the charge and size of cations, with higher dimensional materials being achieved through increased cation charge and larger cation radii. Selective ion-exchange studies show exclusive preference for Cs+ over other alkalis in the A(+)-Nb-10 family, highlighting its potential for radioactive Cs removal and sequestration.