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-CPhH₂IDC²⁻ 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.