Assembly of Zn/Cd coordination polymers containing helixes or polycatenane structures tuned by the tri-pyridyl-bis-amide ligands with different spacer: syntheses, structures, photoluminescent and photocatalytic properties

Four new d(10) metal-organic coordination polymers tuned by the V''-shaped tri-pyridyl-bis-amide ligands with different spacers, namely, [Zn(L-1)(BDC)]center dot H2O (1), [Cd(L-1)(BDC)]center dot H2O (2), [Zn(L-2)(BDC)] (3) and [Cd(L-2)(BDC)] (4) (L-1 = N,N'-bis(pyridine-3-yl) pyridine-2,6-dicarboxamide, L-2 = N, N'-bis(pyridine-3-yl) pyridine- 3,5-dicarboxamide, H2BDC = 1,4-benzenedicarboxylic acid) have been synthesized under hydrothermal conditions. In complexes 1 and 2, the metal ions are linked by L-1 to form left-and right-helical Zn/Cd-L-1 chains, which are further extended into two-dimensional (2D) wave-like layers by BDC anions. In 3, two L-2 ligands link two Zn-II ions forming the Zn-2(L-2)(2) loops, which are connected by BDC anions to form a (2 center dot 6(5)) topological 2D network. In addition, the large Zn-2(L-2)(2) loops are threaded by the BDC rods from above and below 2D layers so as to form 2D -> 3D polyrotaxane and polycatenane structures. In 4, the Cd-II ions are linked by L-2 ligands to generate 1D double chain ribbons with Cd-2(L-2)(2) loops, which are further connected by the BDC linkers to form a 3D framework. Two identical 3D frameworks interpenetrate each other in a twofold mode, giving rise to a polyrotaxane and polycatenane array, which is relative limited. The diverse structures of complexes 1-4 demonstrate that the tri-pyridyl-bis-amide ligands and the central metals have significant effect on the final structures. The thermal stability and fluorescent properties of complexes 1-4 have been investigated. In addition, the title complexes exhibit photocatalytic activity for dye methylene blue degradation under UV light.