Syntheses, crystal structures and anion-exchange properties of copper(ii) and cadmium(ii) complexes containing a novel tripodal ligand

Abstract

Four novel metal-organic frameworks (MOFs), [Cu(3)₂](ClO₄)₂·0.67H₂O (4), [Cu(3)₂][Cu(mal)₂]·6H₂O (mal²⁻ = ⁻OCOCH₂COO⁻) (5), [Cd(3)₂](NO₃)₂·H₂O, (6) and [Cd(3)(OAc)₂]·6H₂O (7), were obtained by self-assembly of the corresponding metal salts with a novel flexible tripodal ligand, 1-(1-imidazolyl)-3,5-bis(imidazol-1-ylmethyl)benzene (3), and their structures were determined by single crystal X-ray diffraction analyses. Complex 4 has a 2D network structure in which 3 shows two different coordination modes, one kind of 3 acts as a three-connecting ligand and the other one serves as a two-connecting (bridging) ligand using its two flexible arms. Complex 5 has an infinite 1D hinged chain structure in which only two of three imidazole groups of 3 are coordinated with the metal atoms while the last one is uncoordinated. In complexes 6 and 7, the metal centers are all six-coordinated; 6 has a 2D honeycomb and 7 has a 2D grid network structure, respectively. Ligand 3 has a trans conformation in 7, which is different from that in complexes 4 (cis and L-shaped), 5 (cis) and 6 (cis). The anion-exchange properties of complex 6 were investigated.