Assembly and property of four 2D layer-like coordination polymers with different structural features derived from bis(3-pyridylformyl)piperazineligand and aromatic dicarboxylic acids with nitro group

Abstract

Using the mixed ligands bis(3-pyridylformyl)piperazine (3-bpfp) and 5-nitroisophthalic acid (H₂NIPH) or 3-nitrophthalic acid (H₂NPH), four two dimensional (2D) copper or cadmium coordination polymers with different structural features formulated as [Cu(3-bpfp)(NIPH)(H₂O)] (1), [Cu(3-bpfp)_0.5(NPH)(H₂O)₂] (2), [Cd(3-bpfp)_0.5(NIPH)] (3), and [Cd(3-bpfp)(NPH)(H₂O)]·H₂O (4) have been hydrothermally synthesized and structurally characterized. Single-crystal X-ray diffraction analyses indicate that complex 1 displays a new contorted 2D layer consisting of two kinds of tetranuclear cycles with different dimensions: A-cycle of 20.53 × 9.57 Å and B-cycle of 19.17 × 12.07 Å, in which Cu^II ions are knitted by the 3-bpfp ligands with μ₂-bridging coordination mode (via ligation of nitrogen atoms in pyridyl rings) and NIPH. In complex 2, Cu^II centers are connected by the ligands NPH to form one dimensional (1D) Cu^II-NPH left- and right-handed helical chains, and these chains are extended into 2D layer network by the 3-bpfp ligands with μ₂-bridging coordination mode. Only one hexanuclear cycle with dimension of 16.86 × 11.10 Å was included in the 2D structure of 2. Complex 3 contains two types of 1D ladder-like chains composed of Cd^II ion, the 3-bpfp ligand with μ₄-bridging coordination mode (via ligation of nitrogen atoms in pyridyl rings and oxygen atoms in carbonyl groups) and bridging NIPH ligand with two coordination modes (chelate-monodentate mode and chelate mode), forming a double layer 2D network with the (4²·6)(4²·8⁴)(4⁷·6³) topology. Complex 4 possesses 2D sheet based on the 1D right-handed helical chains constructed from the Cd^II ions and the NPH ligands with bis-chelating coordination mode, and the 3-bpfp ligands with μ₂-bridging coordination mode. Moreover, the 2D structures of complexes 1–4 are ultimately packed into three dimensional (3D) supramolecular frameworks through the hydrogen bonding or the π–π stacking interactions. In addition, the fluorescent properties of the title complexes and the electrochemical behaviors of 1–2 at room temperature have been investigated.