Ligand-Isomerism Controlled Structural Diversity of Zn(II) and Cd(II) Coordination Polymers from Mixed Dipyridyladipoamide and Benzenedicarboxylate Ligands

Abstract

By using isomeric N,N′-di(2-pyridyl)adipoamide (L1), N,N′-di(3-pyridyl)adipoamide (L2) and N,N′-di(4-pyridyl)adipoamide (L3) and isomeric 1,2-benzenedicarboxylic acid (1,2-H2BDC), 1,3-benzenedicarboxylic acid (1,3-H2BDC) and 1,4-benzenedicarboxylic acid (1,4-H2BDC), eight Zn(II) and Cd(II) coordination polymers [Zn(1,2-BDC)(L2)]∞, 1; [Zn2(1,3-BDC)2(L2)(H2O)2]∞, 2; [Zn2(1,4-BDC)2(L1)(H2O)2]∞, 3; {[Zn2(1,2-BDC)2(L3)(H2O)2]·2H2O}∞, 4; {[Cd(1,2-BDC)(L2)(H2O)]·H2O}∞, 5; [Cd2(1,3-BDC)2(L2)(H2O)4]∞, 6; {[Cd2(1,4-BDC)2(L2)2]·(H2O)3}∞, 7; [Cd2(1,4-BDC)2(L1)(H2O)2]∞, 8, have been synthesized under hydrothermal conditions. Complexes 1, 4, and 5 form 1D double-looped chain, 1D chain with loops and 2D layer with loops, respectively, and complex 6 exhibits a 1D ladder chain. Complex 2 shows rare 3-fold interpenetrated hcb layers, in which each layer interdigitates with other four parallel layers by directing the 1,3-BDC ligands into the windows of the adjacent nets, whereas complexes 3 and 8 forms planar and undulated hcb layers, respectively. Complex 7 shows a 3D self-penetrating net of {424.5.63}-ilc topology with a unique arrangement for the L2 spacer ligands. The L1 ligands in complexes 3 and 8 adopt the new tetradentate bonding mode involving chelation and bridge through two pyridyl nitrogen atoms and two amide oxygen atoms, whereas the L2 and L3 ligands in other complexes show the bidentate bonding mode through the two pyridyl nitrogen atoms. The various bonding modes and the ligand-isomerism of the spacer ligands BDC2– and L1–L3 as well as the identity of the metal center play important roles in determining the structural diversity.