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

Abstract

The MgSO 4 crystal hydrate formed below approximately 0 °C was proven to be the undecahydrate, MgSO 4 ·11H 2 O (meridianiite) instead of the reported dodecahydrate MgSO 4 ·12H 2 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 P 1̅ (No. 2). The crystal is a colorless block with the following parameters F.W. = 318.55, 0.54 × 0.24 × 0.18 mm 3, 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) Å 3, Z = 2, D calc = 1.512 g/cm 3, μ = 0.343 mm −1 . Raman spectroscopy was used for characterizing MgSO 4 ·11H 2 O and for comparing the vibrational spectra with the MgSO 4 ·7H 2 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 4 ·11H 2 O salt. Additionally, the Miller indices of the major faces of MgSO 4 ·11H 2 O crystals were defined.