About the degree of hydration in potassiumtrisoxalatochromate hydrate

Abstract

Abstract Data obtained from single crystal X-ray and neutron diffraction experiments have been combined with results from thermogravimetry in order to derive an improved structure model for potassium tris(oxalato)chromate hydrate. The degree of hydration for this compound has been reinvestigated: Earlier work assumed a trihydrate stoichiometry and had to accept an unusually short K···O distance of 2.3 Å. Our neutron data reveal the position of the hydrogen atoms in the water molecules; they prove that abnormally short separations between a cation and atoms of a water molecule can only occur between sites of mutually exclusive occupancy and hence remain without chemical relevance. Closest K···O distances in our revised hydration model amount to 2.6 Å, in good agreement with expectation. Both diffraction experiments and thermogravimetric data agree with the stoichiometry K3[Cr(ox)3] · 2.7 H2O for the title compound.