The Crystal Structure of Nickel Ethylenedibiguanide Chloride Monohydrate

Abstract

The crystal structure of nickel ethylenedibiguanide has been determined from three-dimensional, x-ray diffractometer data (3087 reflections). The compound, Ni(C6H16N10)Cl2·H2O, crystallizes in the centrosymmetric monoclinic space group P21/c. The unit cell contains four molecules and has dimensions: a = 6.911 ± 0.001, b = 11.678 ± 0.001, c = 18.055 ± 0.002 Å, β = 101.39 ± 0.01° An initial structure was obtained from the nickel-nickel, nickel-chlorine, and chlorine-chlorine vectors on a three-dimensional Patterson map. The trial structure was refined by the method of least squares until a reliability factor of R = 4.85% and a goodness-of-fit of 1.11 was obtained. Hydrogen positions and isotropic temperature factors as well as positions and anisotropic temperature factors of the heavy atoms were allowed to refine in the final stages. The organic ligand molecule complexes in a square planar array about the central nickel atom. The entire molecule is planar, except for the two ethylene carbons, and has point group symmetry c2. The chemically equivalent bonds differ in length by the order of magnitude of the standard deviations of the positions of the bonding atoms. All bond distances have been correlated with both molecular orbital and valence bond descriptions of the molecule, with very satisfactory results. The hydrogen atoms on the nitrogens all participate in hydrogen bonding to the chlorines and to the oxygen of the water molecule. Likewise, the hydrogens on the oxygen are hydrogenbonded to chlorines. It appears that, because of hydrogen bonding to chlorines, the animo hydrogens are distorted from sp2planarity with the nitrogen, so that the nitrogen is almost tetrahedral. Nevertheless, the carbon-nitrogen bond distance clearly reflects double-bond character.