A series of coordination polymers constructed from flexible bis(benzimidazole)ether ligands and different carboxylates

Six new coordination polymers constructed from two structurally related ligands, 2,2′-bis(2-methylbenzimidazole) ether (L1) and 2,2′-bis(2-ethylbenzimidazole)ether (L2), have been synthesized. They are [Cu(L1)(bz)2] (1), [Cu(L2)(bz)2] (2), [Zn2(L1)(m-bdc)2] (3), [Cd2(L2)(m-bdc)2(H2O)]2·H2O (4), [Zn(L1)(OH-bdc)-(H2O)] (5) and [Zn2(L2)(btca)] (6), where Hbz = benzoic acid, m-H2bdc = 1,3-benzenedicarboxylic acid, OH-H2bdc = 5-hydroxyisophthalic acid, and H4btca = 1,2,4,5-benzenetetracarboxylic acid. In 1 and 2, the bidentate N-donor ligands (L1 and L2) bridge neighboring metal centers to form 1D single chains. The bz anions are attached on both sides of the chains. In 3 and 4, the N-donor ligands (L1 and L2) in cis conformations bridge two metal centers to generate a [M2(L1)]4+ unit (M = Zn(II) and Cd(II)). The adjacent [M2(L1)]4+ units are further linked via the dicarboxylate anions to form 1D double chain structures. In 5, the Zn(II) cations are bridged by OH-m-bdc anions to form an infinite polymeric chain. The L1 ligands are attached on one side of the chain in a monodentate mode. In 6, two Zn(II) cations are bridged by two L2 ligands to form a [ZnL2]24+ ring, which is further linked by btca anions to generate a 2D layer. The luminescent properties of the ligands and 3–6 in the solid state at room temperature were also studied.