One-dimensional coordination polymer [Co(H2O)4(pyz)](NO3)2•2H2O (pyz = pyrazine) with intra- and inter-chain H-bonds:: structure, electronic spectral studies and magnetic properties

The synthesis, structure and magnetic properties of the cobalt(II) complex (1) [Co(H2O)(4)(pyz)](NO3)(2) . 2H(2)O is reported. The compound crystallizes in the triclinic system, space group P (l) over bar, with cell constants: a = 7.0328(15) Angstrom, b = 7.1255(16) Angstrom, c = 8.4198(19) Angstrom, alpha = 107.226(4)degrees, beta = 114.242(4)degrees, gamma = 90.487(4)degrees, Z = 1 and V = 363.35(14) Angstrom(3). The structure of 1 consists of elongated octahedral CoO4N2, chromophores with bridging pyrazine ligands forming a one-dimensional coordination polymer along the crystallographic b-axis. The nitrate ions hydrogen-bond to the water ligands (L) and guest water (G), and form H2O(L) ... H2O(G) ... NO3- ... H2O(G) ... H2O(L) chains which flank either side of the coordination polymer chains. Hydrogen-bonding is extended to neighboring chains forming a two-dimensional network. The solvent effect on the electronic spectra of pyrazin and pyrazine cobalt complex 1 has been investigated. The magnetic susceptibility of complex 1 versus temperature data showed a strong antiferromagnetic coupling between Co ions. The best fitting parameters were obtained for J(1)/k(B) = -26.4 K, J(2)/k(B) = 2.2 K and g = 2.3. (C) 2004 Elsevier Ltd. All rights reserved.