Abstract
The synthesis of a bipyridine ligand with a flexible spacer and a noncoordinating amine group N,N-(2-pyridyl)-(4-pyridylmethyl)amine, L2, and its coordination chemistry with cadmium have been investigated. Two-dimensional (2D) coordination polymers of L2 with empirical formulas [Cd(L2)2(ClO4)2]∞, 1, or [Cd(L2)2(NO3)2]∞, 2, were prepared by hydro(solvo)thermal reactions of L2 and Cd(ClO4)2·6H2O or Cd(NO3)2·4H2O in mixtures of water and ethanol, respectively. Single-crystal X-ray diffraction studies reveal that 1 and 2 have similar structures in which each L2 ligand bridges two cadmium centers with both the 4-pyridyl and 2-pyridyl nitrogen atoms to result in 2D rhombohedral polymeric grids. The two rings of L2 are essentially perpendicular to each other, likely to accommodate the coordination of both pyridyl nitrogen atoms to the Cd centers as well as the “intramolecular” hydrogen bonds between the amine group in the flexible spacer and the coordinated anion group. When the hydro(solvo)thermal reaction was carried out between L2 and CdSO4·6H2O, a 3D Cd coordination polymer [Cd2(L2)4(H2O)2(SO4)2]∞, 3, resulted. Two distinct Cd centers reside in the asymmetric unit in 3. One Cd center coordinates to four 4-pyridyl nitrogen atoms of L2 ligands and two sulfate groups, while the other Cd center binds to two 2-pyridyl nitrogen atoms, two sulfate groups, and two water molecules. The two distinct cadmium centers are bridged by both L2 ligands and sulfate groups to result in an unusual 3D polymeric structure. Crystal data for 1: monoclinic space group C2/c, a = 8.4931(6) Å, b = 17.264(1) Å, c = 16.699(1) Å, β = 99.517(6)°, V = 2559.4(1) Å3, Z = 4, R = 0.034, Rw = 0.039. Crystal data for 2: monoclinic space group C2/c, a = 8.6231(5) Å, b = 17.288(1) Å, c = 16.1675(7) Å, β = 94.730(2)°, V = 2401.9(1) Å3, Z = 4, R = 0.050, Rw = 0.058. Crystal data for 3: monoclinic, space group P21/n, a = 11.7188(2) Å, b = 15.7525(3) Å, c = 12.8528(1) Å, β = 93.064(1)°, V = 2369.2(1) Å3, Z = 2, R = 0.042, Rw = 0.047.