Coordination Polymers with a Pyrazine-2,5-diyldimethanol Linker: Supramolecular Networks through Hydrogen and Halogen Bonds

Abstract

In this paper, the synthesis and crystal structure of pyrazine-2,5-diyldimethanol (pyzdmH2, C6H8N2O2), a new symmetric water-soluble N,O-chelating tetra-dentate organic ligand, is reported and an environmentally friendly method is used to synthesize coordination compounds in water under ambient conditions, from the reaction of pyzdmH2 with the halide salts of Cu(II), Zn(II), Hg(II) and Cd(II): {[Cu(pyzdmH2)0.5(µ-Br)(Br)(H2O)]·H2O}n 1, {[Zn2(pyzdmH2)(µ-Cl)(Cl)3(H2O)]·H2O}n 2, [Hg2(pyzdmH2)0.5(µ-Cl)2(Cl)2]n 3, {[Cd2(pyzdmH2)(µ-Cl)4]·H2O}n 4, and {[Cd2(pyzdmH2)(µ-Br)4]·H2O}n 5. Single-crystal X-ray diffraction analysis reveals that 1–3 are 1D coordination polymers and 4 and 5 are 3D coordination networks, all constructed by bridging pyrazine-2,5-diyldimethanol and halogen ions. The hydroxyl groups in the organic linker extend the 1D chains to non-covalent 3D networks. In all non-covalent and covalent 3D networks, water molecules are trapped by strong hydrogen bond interactions. Supramolecular analysis reveals strong O-H···O, O-H···N, O-H···X, and weak C-H···O, C-H···X (X = Cl, Br) hydrogen bonds, as well as π-π(pyrazine ring), metal-halogen···π(pyrazine ring), and O-H···ring(5-membered chelate ring) interactions. In addition, X···O weak halogen bonds are present in 1–5 (X = Cl and Br).