Determination of the crystal structure of sanderite, MgSO4{middle dot}2H2O, by X-ray powder diffraction and the charge flipping method

The crystal structure of sanderite, MgSO4∙2H2O, was determined from laboratory X-ray powder diffraction data measured from 2-140 °2θ using CuKα radiation. Sanderite is orthorhombic, space group P212121, with unit-cell parameters a = 8.8932(1) Å, b = 8.4881(1) Å, c = 12.4401(2) Å, V = 939.16(3) Å3, Z = 8. The crystal structure model was determined using the charge flipping method and was refined using fundamental parameters Rietveld refinement method to Rwp = 6.52%, Rexp = 1.89%, and χ2 = 3.43. Bond-valence calculations for the refined model show that the structure is chemically reasonable. In the refined structure, Mg2+ cations are coordinated by four O atoms from [SO4]2- groups and by two H2O molecules, forming distorted octahedra. By sharing vertex O atoms, [SO4] tetrahedra and [MgO4(H2O)2] octahedra build up a 3-D framework.