Construction of a series of coordination polymers from three imidazole-based multi-carboxylate ligands

Abstract

2-Carboxylphenyl, 3-carboxylphenyl and 4-carboxylphenyl groups were introduced into the 2-position of imidazole-4,5-dicarboxylate system, respectively, obtaining three multi-functional ligands 2-(2-carboxylphenyl)-1H-imidazole-4,5-dicarboxylic acid (o-CPhH4IDC), 2-(3-carboxylphenyl)-1H-imidazole-4,5-dicarboxylic acid (m-CPhH4IDC) and 2-(4-carboxylphenyl)-1H-imidazole-4,5-dicarboxylic acid (p-CPhH4IDC). Then the three organic ligands are employed to react with Sr(II) and Cd(II) ions. Subsequently, five 3D or 2D polymers, [Sr(o-CPhH2IDC)]n (1), [Sr3(m-CPhHIDC)2(H2O)3]n (2), [Sr(p-CPhH2IDC)(H2O)]n (3), [Cd(o-CPhH2IDC)(H2O)2]n (4) and {[Cd3(m-CPhHIDC)2(H2O)8]·2H2O}n (5), have been hydro(solvo)thermally synthesized and structurally characterized. Compound 1 is a (5,5)-connected 3D structure with unique “H-shape” channels. Three kinds of coordination environments around the Sr atoms are exhibited in compound 2. Both compounds 1 and 2 contain unusual irregular cages. Compound 3 displays a (4,6)-connected 3D porous framework composed of right-handed helices connected by p-CPhH2IDC(2−) anions. Both compounds 4 and 5 present net-like layer structures. These various architectures demonstrate the versatile coordination abilities of the three imidazole-based multi-carboxylate ligands.