Crystallization and Characterization of a New Magnesium Sulfate Hydrate MgSO<sub>4</sub>·11H<sub>2</sub>O

The MgSO<sub>4</sub> crystal hydrate formed below approximately 0 °C was proven to be the undecahydrate, MgSO<sub>4</sub>·11H<sub>2</sub>O (meridianiite) instead of the reported dodecahydrate MgSO<sub>4</sub>·12H<sub>2</sub>O. The crystals were grown from solution by eutectic freeze and by cooling crystallization. The crystal structure analysis and the molecular arrangement of these crystals were determined using single crystal X-ray diffraction (XRD). Reflections were measured at a temperature of 110(2) K. The structure is triclinic with space group <i>P</i>1̅ (No. 2). The crystal is a colorless block with the following parameters F.W. = 318.55, 0.54 × 0.24 × 0.18 mm<sup>3</sup>, <i>a</i> = 6.72548(7) Å, <i>b</i> = 6.77937(14) Å, <i>c</i> = 17.2898(5) Å, α = 88.255(1)°, β = 89.478(2)°, γ = 62.598(1)°, <i>V</i> = 699.54(3) Å<sup>3</sup>, <i>Z</i> = 2, <i>D</i><sub>calc</sub> = 1.512 g/cm<sup>3</sup>, μ = 0.343 mm<sup>−1</sup>. Raman spectroscopy was used for characterizing MgSO<sub>4</sub>·11H<sub>2</sub>O and for comparing the vibrational spectra with the MgSO<sub>4</sub>·7H<sub>2</sub>O salt. Between the two salts, there are significant differences mainly in the type of interactions of water with sulfate groups in the lattice, in view of the different O−H stretching vibrations, as well as sulfate, O−H···O (sulfate) and O−Mg−O bands vibrational modes. Thermogravimetric analysis confirmed the stochiometry of the MgSO<sub>4</sub>·11H<sub>2</sub>O salt. Additionally, the Miller indices of the major faces of MgSO<sub>4</sub>·11H<sub>2</sub>O crystals were defined.