Disorder of a Trigonally Planar Coordinated Water Molecule in Cobalt Sulfate Heptahydrate, CoSO4 · 7 D2O (Bieberite)+

Abstract

Cobalt sulfate heptahydrate (d-14), CoSO4·7D2O, Mr = 294.99, monoclinic, P21/c, a = 1404.8(1), b = 649.41(6), c= 1092.5(2) pm, β = 105.232(8), V = 961.66·106 pm3, Z = 4, Dx = 2.073 Mg· m-3, λ(MoKa) = 71.073 pm, [(sin θ)/λ]max = 0.7035· 10-2 pm-1, μ = 20.26 cm-1, F(000) = 580, T = 298 K, R(F) = 0.0264 for 2339 observed unique reflections. CoSO4·7 D2O is shown to be isotypic to FeSO4· 7 H2O (Melanterite). The deuterated compound is stable at ambient conditions in contrast to the normal hydrate. Its structure is built up by [Co(D2O)6]2+ octahedra, SO4 2- tetrahedra, and “lattice” water molecules. One water molecule, which is almost exactly trigonally planar coordinated in its average position, exhibits a distinct oxygen disorder. The “lattice” water molecule accepts two strong hydrogen bonds and donates a linear and a bifurcated one. The hydrogen-bond lengths (O···O distances) are in the range 271-302 pm.