A family of uranium–carboxylic acid hybrid materials: synthesis, structure and mixed-dye selective adsorption

Abstract

Four uranyl complexes (UO₂)₂(pht)₂(Hpac)₂(H₂O)₂ (pht = phthalic acid and Hpac = nicotinic acid) (1), (UO₂)(pac)₂(H₂O)₂ (2), [(UO₂)(CMA)₃]·[H₂N(CH₃)₂] (CMA = cinnamic acid) (3) and (UO₂)₂(C₂O₄)(μ₂-OH)₂(H₂O)₂·H₂O (4) were synthesized by the reaction of UO₂(CH₃COO)₂·2H₂O as the metal source with phthalic acid, nicotinic acid, cinnamic acid or oxalic acid as the ligand. They were characterized by elemental analysis, IR, UV-vis, XRD, single crystal X-ray diffraction and thermal gravimetric analysis. The structural analysis showed that complexes 1, 2 and 3 were discrete structures, and by hydrogen bonding interactions, the adjacent molecular units are connected to form a three-dimensional (3D) supramolecular network structure for complex 1 and one-dimensional (1D) chains for complexes 2 and 3. Meanwhile, in the structure of complex 4, a tetrameric SBU (UO₂)₄(μ₂-OH)₄(H₂O)₄ is linked to a 2D layer through a bridging oxalic acid ligand, and furthermore extends the 2D layer into a 3D supramolecular architecture by hydrogen bonding interactions. In order to extend their functional properties, their photoluminescence, surface photovoltage and mixed-dye selective adsorption properties have been studied for the first time. Through experiments, we found that the adsorption performance of complex 3 was better than others, and the amount of adsorbed RhB was 4.22 mg g⁻¹.