Effect of flexibility of organic dicarboxylates anions on the four 3D metal-organic frameworks constructed from flexible benzimidazolyl-based ligand

Four new polymeric frameworks, [Co(bbbi)(L1)] (1), [Cu(bbbi)(L1)] (2), [Co(bbbi)(L2)] (3) and [Ni(bbbi) (L2)] (4), (bbbi = 1,1-(1,4-butanediyl)bis-1H-benzimidazole, H(2)L1 = 5-nitroisophthalic acid and H(2)L2 = itaconic acid) have been hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction. Complexes 1 and 2 are isomorphous, and they can be described as CsCl-type net utilizing bimetal cores as eight-connected nodes, the bridging bbbi ligands and L1 serve as spacers to yield a unique eight-connected net with 4(24)6(4) topology. Complexes 3 and 4 are isomorphous. It is interesting that 3D frameworks containing meso-helical chains (left-and right helical chains) have been observed in 3 and 4, in which meso-helical chains are alternately linked by bbbi ligands coordinating to Co1(Ni1) cations with the zigzag shaped conformation to generate a 3D binodal (4,4)-connected net with {5(3)center dot 6 center dot 8(2)}{5(2)center dot 6(4)} topology structure. The bbbi ligands adopt three conformations, namely, the completely "M" shaped conformation in 1 and 2, the zigzag shaped conformation and "Omega" shaped conformation in 3 and 4. The influence of carboxylate anions with different flexibility on the construction of different network topology in the self-assembly process has been discussed. Moreover, the thermal stabilities and the voltammetric behavior of complexes 1-4 have been reported. (C) 2011 Elsevier B.V. All rights reserved.