Synthesis and X-ray powder structures of nickel(II) and copper(II) coordination polymers with 2,5-bis(2-pyridyl)pyrazine

The reaction of 2,5-bis(2-pyridyl)pyrazine (bppz) with nickel(II) sulfate in aqueous solution yielded a binuclear complex, [Ni-2(bppz)(H2O)(8)](SO4)(2) . 2H(2)O (1), whose structure was solved by single-crystal methods. The compound crystallizes in the monoclinic space group P2(1)/n with a = 8.372(2) Angstrom, b = 18.301(2) Angstrom, c = 17.197(2) Angstrom, beta = 97.54(2)degrees, and Z = 4. The bppz ligand chelates the two octahedrally coordinated nickel atoms through its nitrogen donors. The four remaining coordination sites are occupied by water oxygen atoms. The binuclear [Ni-2(bppz)(H2O)(8)](4+) cations are held together by hydrogen bonds involving sulfate anions and water molecules. Similar reactions with nickel(II) or copper(II) chloride in less polar solvents resulted in the formation of two new coordination polymers, {[Ni2Cl2(bppz)(H2O)(2)(CH3OH)(2)]Cl-2}(n) (2) and [Cu2Cl4(bppz)](n) (3). These polymers could be obtained only in microcrystalline form. Their structures were determined ab initio from X-ray powder diffraction data. The complex {(Ni2Cl2(bppz)(H2O)(2)(CH3OH)(2)]Cl-2}(2) (2) belongs to the triclinic space group P (1) over bar with a = 8.7014(4) Angstrom, b = 10.1465(5) Angstrom, c = 8.0303(3) Angstrom, alpha = 116.095(2)degrees, beta = 112.713(3)degrees, gamma = 64.056(3)degrees, and Z = 1. The octahedral coordination of the nickel atom is achieved by two nitrogens of the ligand bppz, two chloride ions, and two oxygens from the solvent molecules. The bridging nature of the chloride ions and the bis-bidentate ligands (bppz) leads to a one-dimensional polymer. The compound [Cu2Cl4(bppz)](n) (3) crystallizes in the monoclinic space group C2/m with a = 13.9124(5) Angstrom, b = 6.1844(2) Angstrom, c = 10.1572(3) Angstrom, beta = 112.952(3)degrees, and Z = 2. The copper atoms display a distorted octahedral geometry where four of the coordination sites are occupied by chloride ions and the remaining two by nitrogen atoms of bppz. The metal atoms are bridged by two chlorine atoms and the bppz ligands, forming a two-dimensional coordination polymer.