Crystallization and Characterization of a New Magnesium Sulfate Hydrate MgSO4·11H2O

The MgSO4 crystal hydrate formed below approximately 0 °C was proven to be the undecahydrate, MgSO4·11H2O (meridianiite) instead of the reported dodecahydrate MgSO4·12H2O. 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 P1̅ (No. 2). The crystal is a colorless block with the following parameters F.W. = 318.55, 0.54 × 0.24 × 0.18 mm3, a = 6.72548(7) Å, b = 6.77937(14) Å, c = 17.2898(5) Å, α = 88.255(1)°, β = 89.478(2)°, γ = 62.598(1)°, V = 699.54(3) Å3, Z = 2, Dcalc = 1.512 g/cm3, μ = 0.343 mm−1. Raman spectroscopy was used for characterizing MgSO4·11H2O and for comparing the vibrational spectra with the MgSO4·7H2O 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 MgSO4·11H2O salt. Additionally, the Miller indices of the major faces of MgSO4·11H2O crystals were defined.