Two three-dimensional porous frameworks built from metal-organic coordination polymer sheets pillared by polyoxometalate clusters

摘要

Two new porous frameworks [Ni(bix)_2][VW_(12)O _(40)]·(H_2bix)·H_2O (1) and [Co(bix)_2][VW_(12)O_(40)]·(H _2bix)·2H_2O (2) (bix = 1,4-bis(imidazol-1-ylmethyl)- benzene) composed of Keggin polyoxometalates (POMs) and metal-organic coordination polymer sheets have been successfully obtained, and characterized by elemental analysis, IR spectra, thermal gravimetric analysis, and single crystal X-ray diffraction. Structural analysis reveals that the 2D metal-organic coordination polymer sheets in the two compounds are constructed from the transition-metal (TM) cations and the flexible N-donor ligand bix, which are further pillared by POM clusters into the 3D porous frameworks. Powder X-ray diffraction (PXRD) patterns of 1 indicate the structural integrity of the framework in aqueous solution with a wide pH range of 1 to 11, and in common organic solvents (methanol, ethanol and DMF). Photocatalytic studies indicate that compounds 1 and 2 are not only active photocatalysts for degradation of rhodamine B (RB), but very stable and easily separated from the photocatalytic system for reuse as well.