EFFECT OF CRYSTAL FIELD ON THE ELECTRON DENSITY OF THE METAL ION IN HYDRATES OF 3d METAL SALTS;
X-RAY AND NEUTRON DIFFRACTION RESULTS.

H. Ptasiewicz-Bak1, I. Olovsson2 , G.J. McIntyre3

1Institute of Nuclear Chemistry and Technology, Dorodna 16, 03-195 Warsaw, Poland.
E-mail: bptas@orange.ichtj.waw.pl
2Inorganic Chemistry, Angström Laboratory, University of Uppsala, Box 538, S-751 21 Uppsala, Sweden
3Institut Laue-Langevin, BP 156, 38042 Grenoble CEDEX 9, France

To model the aspherical electron distribution, the multipole deformation functions proposed by Hirshfeld were used. The deformation charge densities around 3d-metal ion in different crystallographic environments, will be discussed for : NiSO4. 7H2O [1], NiCl2. 4H2O, Ni(NO3)2. 6H2O, CrCl3. 6H2O, Na2Ni(CN)4. 3H2O[2], NiSO4. 6H2O [3-4].

Significant differences in the electron density features around metal ion, in the planes defined by ligands, at 30K and 295K were observed. These differences are obviously not due to changes in the immediate surroundings of the metal ion, since these are almost the same at both temperatures. An extensive search in other planes has shown that the maxima of density are not in the planes just mentioned, but in certain planes defined by metal and nearest metal neighbours in the cation sublattice. The 'scheme-recipe' for determining the planes of maximum electron density around the metal in the crystal field is proposed. The features of electron density in the planes determined according to the above scheme are very similar at both (30K and 295K) temperatures, if there are no significant differences in the cation network geometry. For NiSO4. 7H2O we observe changes in the directions having maximum electron densities at 30K and 295K, but here there are small, but significant, differences in the metal-metal sublattice distances at the two temperatures. The above scheme was used for qualitative description, not for interpretation of the experimental results. It appears to be the case that in discussing the electron densities around the metal in the crystal, the field from whole environment must be cosidered, instead of limiting it to the nearest ligands.

  1. H.Ptasiewicz-Bak, I. Olovsson, G.J.McIntyre, Acta Cryst. B53 (1997) 325-336
  2. H.Ptasiewicz-Bak, I. Olovsson, G.J.McIntyre, Acta Cryst. Bxx (1997) Submitted
  3. G.J.McIntyre, H.Ptasiewicz-Bak, I. Olovsson, Acta Cryst. B46 (1990) 27-39
  4. H.Ptasiewicz-Bak, I. Olovsson, & G.J.McIntyre, Acta Cryst. B49 (1993) 192-201

Support of this work by the Nobel Institute for Chemistry is gratefully acknowledged.