Redetermination of MgCrO₄·5H₂O

Abstract

The CCD-data based redetermination of the crystal structure of the title compound, magnesium chromate(VI) penta-hydrate, confirms in principle the previous study based on precession film data [Bertrand et al. (1971 ▶). C. R. Hebd. Seances Acad. Sci. Serie C, 272, 530-533.], but with all atoms refined with anisotropic displacement parameters and with all H atoms localized. This allowed an unambiguous assignment of the hydrogen-bonding pattern. MgCrO4·5H2O adopts the MgSO4·5H2O structure type. It contains two Mg(2+) sites on special positions with site symmetry -1, one tetra-hedral CrO4 group and five water mol-ecules. Four of them coordinate to the Mg(2+) cation, and one is an uncoordinating lattice water mol-ecule. The octa-hedral environment of the Mg(2+) cation is completed by two axial O atoms of CrO4 tetra-hedra. This arrangement leads to the formation of chains parallel to [011]. Adjacent chains are linked through O-H⋯O hydrogen bonds (one of them bifurcated), involving both the coordi-nating and lattice water mol-ecules, into a three-dimensional network.