Structural characterization of pyridazine (pydz) adducts of MX2(M = Mn, Fe, Co, Ni, Cu or Zn; X = Cl or Br). Ab-initio X-ray powder diffraction determination of polymeric [NiX2(pydz) complexes

Abstract

The pyridazine (pydz) complexes of metal halides MX₂(M = Mn, Fe, Co, Ni, Cu or Zn; X = Cl or Br) have been prepared, using a reagent molar ratio of 1 : 1, and investigated by X-ray powder diffraction methods. The crystal structures (orthorhombic, space group Imma, Z= 4) of [NiCl₂(pydz)] and [NiBr₂(pydz)]; have been determined, ab initio. from laboratory X-ray powder diffraction data only: [NiCl₂(pydz)], a= 7.3758(4), b= 6.6069(3) and c= 1 2.7292(7)Å, [NiBr₂(pydz)], a= 7.5598(9), b= 6.8029(8) and c = 1 2.905(2) A. The structures have been solved by direct methods, and refined by the Rietveld technique down to R_profilevalues of 0.062 and 0.078, respectively, for 4400 data points collected at room temperature in the range 17 < 2θ < 105°. Both compounds consist of infinite polymeric chains of nickel atoms, bridged by X (Cl or Br) and pyridazine ligands, showing an octahedral arrangement and trans-DH_4h, NiX₄N₂ chromophores. The Ni–Cl and Ni–Br distances are 2.422(1) and 2.560(2)Å, respectively. Analyses of the other species have shown that the analogues of Mn, Fe and Co are isomorphous with the nickel compounds, while those of Cu and Zn display different diffraction patterns.