Polyoxometalate-Based\nMetal–Organic Frameworks\nwith Unique High-Nuclearity Water Clusters

Abstract

The\nmaximum exposure of polyoxometalates (POMs) is of great significance\nto enhance the catalytic performance of HKUST-1 with incorporated\nKeggin-type POMs. Herein, two phosphovanadomolybdates were encapsulated\ninto the HKUST-1 via a hydrothermal method to obtain two polyoxometalate-based\nmetal–organic frameworks, formulated as [Cu₁₂(BTC)₈(H₂O)₁₂]­[H₄PMo₁₁VO₄₀]@(H₂O)₃₀ (<b>1</b>) and\n[Cu₁₂(BTC)₈(H₂O)₁₂]­[H₅PMo₁₀V₂O₄₀]@(H₂O)₄₉ (<b>2</b>). Single-crystal X-ray diffraction\nanalysis indicates that two compounds contain unique high-nuclearity\nwater clusters without organic counter cations. The octahedral-shaped\nwater cluster (H₂O)₃₀ was constructed from square-pyramid-shaped\n(H₂O)₅ for compound <b>1</b>, while the\nhuge cage-shaped water cluster (H₂O)₄₉ of compound <b>2</b> consisted of crown-like (H₂O)₈ and\none water molecule, which substitute the organic counter cations involved\nin the structural construction. More importantly, after removing the\nwater clusters via simple heat treatment, the active sites of the\ntwo compounds were fully exposed, leading to good catalytic activities\nfor both benzene hydroxylation reaction and oxidative desulfurization.\nFurthermore, the catalytic test confirmed that compound <b>2</b> may be a bifunctional heterogeneous catalyst with great promise\nfor both benzene hydroxylation and oxidative desulfurization.