Assembly and spontaneous resolution of the chiral inorganic polyoxometalates-based frameworks via helical chains association

Abstract

Two pairs of enantiomerically pure three-dimensional (3D) chiral polyoxometalate (POM) framework materials L,D-[K(H₂O)]₆·[H₂GeW₁₂O₄₀]₃·35H₂O (1a and 1b) and L,D-[K(H₂O)]₆·[H₂SiW₁₂O₄₀]₃·29H₂O (2a and 2b) based on inorganic achiral building blocks, have been synthesized and characterized by X-ray crystallography, elemental analysis, powder X-ray diffraction (PXRD), UV-Vis spectroscopy, circular dichroism (CD) spectra. Single-crystal X-ray diffraction analyses revealed that 1a and 1b, 2a and 2b are enantiomers, respectively. In 1a and 1b, 2a and 2b, {K(H₂O)}_n link terminal oxygen and μ₂-bridging oxygen of Keggin-type polyanion moieties to generate 1D 3₁ helical infinite chiral chains, which are further connected by the achiral Keggin-type polyoxoanions to form 3D 4,8-connected chiral self-assembly frameworks with {4¹²·6¹⁰·8⁶}{4⁶}₂ topology. 1 and 2 are isostructural. They are obtained by spontaneous resolution upon crystallization in the absence of any chiral source. They represent new examples of chiral self-penetrating pure inorganic frameworks known for POM systems. Compounds 1 and 2 display adsorption activity toward volatile organic compounds (VOCs).