The Nature of the Hexahydrates of Divalent Transition Metal Cations: The Structures of the Hexafluorogermanate Hexahydrates of Iron(II), Cobalt(II) and Nickel(II)

Abstract

The crystal and molecular structures of the room temperature phases of M^II(H₂O)₆GeF₆ (M = Fe, Co, Ni) are reported. In each structure the M(H₂O₆²⁺ and GeF₆^2- octahedra are in approximate CsCl -type packing with hydrogen bonding between the ions. Differences in the structures arise from disorder in the orientations of the octahedra . Fe(H₂O)₆GeF₆ crystallizes in the spate group R3M, with three molecules in the unit cell of dimensions a_hex , 9.728(2), ^Chex 9.796(2) Å. Refinement converged with R 0.0135 and R_w 0.0137, 286 independent observed reflections being used. There is disorder of both fluorine and oxygen atoms between two positions related by a mirror plane, which raises the 3 symmetry within each octahedron to overall 3m symmetry. Ni(H₂O)₆GeF₆ crystallizes in the spate group R3 with three molecules in the unit cell of dimensions a_hex 9.443(1), c_hex 9 .77O(l) Å. Refinement converged with R 0.016 and R, 0.018 for 444 independent observed reflections. There is disorder only of the fluorine atoms between two positions unrelated by any symmetry element. CO(H₂O)₆GeF₆ crystallizes in the space group P2₁/c with two molecules in the unit cell of dimensions a 6.552(2), b 9.577(2), c 8.520(1) Å, ,β 99.74(2)º. Refinement converged with R 0.042 and R, 0.054 for 1232 independent observed reflections. The structure is not disordered and deviates only slightly from rhombohedral symmetry.