Microwave-Assisted Solvothermal Synthesis of a Dynamic Porous Metal-Carboxylate Framework

By treating Cu(NO3)2·3H2O with a V-shaped ligand 4,4ʼ-oxydibenzoic acid (H2oba), a dynamic metal-carboxylate framework [Cu2(oba)2(DMF)2]·5.25DMF (MCF-23) was synthesized, which features a wavelike layer with rhombic grids based on the paddle-wheel secondary building units. These layers stack via strong offset π-π stacking of the phenyl groups of oba ligands to give three-dimensional porosity. MCF-23 synthesized by conventional solvothermal methods always contains considerable and intractable impurities. In contrast, a microwave-assisted solvothermal method was proven to be a faster and greener approach to synthesize phase-pure MCF-23 in high yield. More interestingly, larger crystals suitable for single-crystal diffraction could be obtained by the multistep microwave heating mode. A powder X-ray diffraction study of MCF-23 reveals the dynamic structural transformation accompanying the release and reabsorption of the guest molecules. The N2 (77 K) and CO2 (195 K) gas sorption isotherms of the guest-free phase MCF-23a were measured.