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

Abstract

Four new d¹⁰ metal–organic coordination polymers tuned by the “V”-shaped tri-pyridyl–bis-amide ligands with different spacers, namely, [Zn(L₁)(BDC)]·H₂O (1), [Cd(L₁)(BDC)]·H₂O (2), [Zn(L₂)(BDC)] (3) and [Cd(L₂)(BDC)] (4) (L₁ = N,N′-bis(pyridine-3-yl)pyridine-2,6-dicarboxamide, L₂ = 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 L₁ to form left- and right-helical Zn/Cd–L₁ chains, which are further extended into two-dimensional (2D) wave-like layers by BDC anions. In 3, two L₂ ligands link two Zn^II ions forming the Zn₂(L₂)₂ loops, which are connected by BDC anions to form a (2·6⁵) topological 2D network. In addition, the large Zn₂(L₂)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 L₂ ligands to generate 1D double chain ribbons with Cd₂(L₂)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.