Synthesis and structures of copper coordination polymers incorporating a bis-pyridyl-bis-amine ligand

Abstract

A new bis-pyridyl-bis-amine ligand, namely N,Nʹ-bis(pyridin-3-ylmethyl)-1,2-ethylenediamine (bpmen), has assembled with Cu(II) salts of sulfate and nitrate to yield corresponding Cu coordination polymers {[Cu(H2bpmen)(H2O)4](SO4)2∙2H2O}n (1) and {[Cu(bpmen)](NO3)}n (2). Compound 1 has a cationic simple coordination chain structure, where the Cu(II) center has an octahedral geometry consisting of N2O4 donors and the protonated H2bpmen2+ ligand suits a bis-monodentate coordination mode with the –CH2NHCH2CH2NHCH2- backbone in a GGTGG conformation, where G and T devoted as gauche and trans conformations, respectively. Numerous hydrogen-bonding interactions make 1 to form a three-dimensional neutral supramolecular hydrogen-bonded net. For synthesizing 2, the starting Cu(II) cations are reduced to Cu(I) cations by bpmen ligands during the assembly process. Compound 2 has a cationic double-stranded zigzag chain structure, where the Cu(I) center has a tetrahedral geometry composing of N4 donors and the bpmen ligand adopts a chelating-bridging mode with the –CH2NHCH2CH2NHCH2- backbone in a TGGTT conformation. A variety of framework … nitrate hydrogen-bonding interactions results in a two-dimensional neutral supramolecular hydrogen-bonded layer. Thermogravimetric (TG) analysis showed that the coordination frameworks of 1 and 2 after releasing lattice and coordination water molecules are thermally stable up to approaching 252 and 210 ​°C, respectively. Solid-state emission spectra of 1 and 2 exhibited no and weak luminescence emission bands, respectively, upon irradiation.