HYDROGEN-BOND STUDIES .157. THE EXPERIMENTAL ELECTRON-DENSITY IN MONOCLINIC COBALT SULFATE HEXAHYDRATE, COSO4.6D2O, AT 25-K

The electron density in CoSO4.6D2O has been determined at 25 K by mult ipole refinement against single-crystal X-ray intensity data. Hydrogen positional and displacement parameters have been taken from a refinem ent using single-crystal neutron data. The influence of superposition on the total deformation density has been assessed by calculating the densities separately from the deformation functions of the individual constituents of the structure. The deformation density is significantl y distorted from octahedral symmetry for the two crystallographically independent Co2+ ions, although the water O-atom arrangement around th em is close to octahedral in both cases. The individual deformation de nsities for the six water molecules show clear polarization effects in the oxygen lone-pair region, which correspond to the respective coord ination modes, ranging from trigonal planar to tetrahedral. The result s are compared with those of similar studies on both tetragonal and mo noclinic NiSO4.6(H,D)2O. Crystal data: cobalt(II) sulfate hexahydrate (-d12), CoSO4.6D2O, M(r) = 275.15, monoclinic, C2/c, a = 10.006 (5), b = 7.252 (4), c = 24.122 (12) angstrom, beta = 98.96 (4)-degrees, V = 1729.0 (9) angstrom3, Z = 8, D(x) = 2.03 g cm-3; lambda(Mo Kalpha) = 0 .71073 angstrom, mu = 29.90 cm -1, F(000) = 1080, T = 25 K, R(F) = 0.0 1 86 for 4676 observed unique reflections up to [(sintheta)/lambda]ma x = 0.995 angstrom-1 (X-ray); R(F) = 0.0407 for 3963 observed reflecti ons up to [(sin theta)/lambda]max = 0.9 1 0 angstrom-1 (neutron).