Structure-directing roles of auxiliary polycarboxylate ligands in the formation of Zn(II) and Cd(II) coordination polymers based on a flexible N,N′-di(3-pyridyl)dodecanediamide

Reactions of the flexible N,N'-di(3-pyridyl)dodecanediamide (L) with Zn(II) and Cd(II) metal salts in the presence of different polycarboxylic acids under hydrothermal conditions afforded five new coordination polymers, [Zn(2,4-PDC)(L)(H2O)](infinity) (2,4-H2PDC = 2,4-pyridinedicarboxylic acid), 1, {[Zn(1,3,5-HBTC)(L)]center dot 2H(2)O}(infinity) (1,3,5-H3BTC = 1,3,5-benzenetricarboxylic acid), 2, {[Zn(3,4-PDC)(L)]center dot 0.5L}(infinity) (3,4-H2PDC = 3,4-pyridinedicarboxylic acid), 3, {[Cd(1,2-BDC)(L)(H2O)]center dot 0.5L}(infinity) (1,2-H2BDC = 1,2-benzenedicarboxylic acid), 4, and {[Cd(1,3,5-HBTC)(L)(1.5)]center dot 2H(2)O}(infinity), 5, which have been structurally characterized by X-ray crystallography. Complexes 1 and 2 manifest quintuple and double helices formed by zinc ions and L ligands, which are supported by 2,4-PDC2- and 1,3,5-HBTC2- anions, respectively, to construct the rare single-walled metal-organic nanotubes. Complex 3 shows 1D fish-bone chains and complexes 4 and 5 display 2D pleated grids with helical and looped carboxylate chains, respectively, supported by the L ligands. Complexes 1-3 represent a unique example of the polycarboxylate ligands showing a significant effect on folding and unfolding of the Zn(II) helical coordination polymers, and they are also important in determining the number of helices. The L ligands in 1, 2 and 4 adopt a bidentate bonding mode, and a unique monodentate bonding mode for the dipyridyl amide ligand is found in 3 and 5, resulting in various types of ligand conformations.