Crystal Structure Determination of 1,2-Cyclohexanedionedioxime-Nickel(II) by Powder Diffraction

E. Horn and M. Kurahashi
[Adv. X-ray Chem. Anal., Vol.26, pp.181-188, 1995]

The reaction of 1,2-cyclohexanedionedioxime, C₆H₁₀N₂O₂ (Hcdd) with nickel chloride results in the very insoluble title complex (Ni(cdd)₂). The nickel complex crystallizes in the orthorhombic space group Ibam with a=20.569(7), b=10.124(3) and c=6.493(2) Å. Data sets were collected by both the Bragg-Brentano and Guinier methods. The former data exhibits a high degree of preferred orientation. The high intensities of the reflections 200, 110 and 002 as well as the space group requirement confine the nickel atom to the special positions (0,0,0) and (1/2,1/2,1/2). The rest of the molecule was modelled by careful space group symmetry, a 2-dimensional Patterson map, molecular packing, bonding considerations. The structure was refined by Rietveld method. The nickel atom is involved in a square planar coordination with two ligands. The crystal lattice consists of columns of Ni(cdd)₂ molecules making Ni-Ni contacts with two neighboring molecules at a distance of 3.247 Å (Fig. 1). The refinement using the Guinier data converged with the final agreement factors R_wp = 0.105 and R_F = 0.041.

Fig. 1. Crystal structure of Ni(cdd)₂