Different molecular frameworks of zinc(II) and cadmium(II) coordination polymers constructed by flexible double betaine ligands

A series of six novel Zn(Cd)-double betaine coordination polymers have been obtained by the mild reactions of the respective metal nitrate with three flexible double betaine ligands. Single-crystal X-ray structural analyses reveal that the six complexes possess different molecular frameworks derived from various coordination modes and flexibilities of double betaine ligands, which indicates that the nature of the ligands has a great influence on the structural topologies of the metal-organic molecular architectures. Extensive hydrogen bonds play important roles in crystal packing and supramolecular frameworks. It is noteworthy that the different one-dimensional water chains with "arm-chair" and "zigzag" characteristics are presented in the complexes Zn(L-2)(H2O)(NO3)]NO3)center dot 2H(2)O (3) and [Cd(L-2)(H2O)(NO3)]NO3 center dot 3H(2)O (4) [L-2 = 1,3-bis(pyridinio-4-acetato)-propane], respectively.