| Summary: | Records of methanesulfonate acid in ice cores play an important role in reconstruction of the past history of marine productivity, sea ice extent, and major El Ni~no event activities related to climate changes. Considering the lack of thermodynamic and crystal structure data, crystallization conditions below zero degrees Celsius were mimicked in the laboratory, and magnesium methanesulfonic hydrate crystals, Mg(CH3SO3)2 3 12H2O(i.e., [Mg(H2O)6](CH3SO3)2 3 6H2O) were grown from solution by cooling crystallization and by eutectic freeze crystallization. The solubility lines between-5 andþ21 C and between 0 and 25 wt%are presented. The eutectic point of the system is detected at-5 Cand 14 wt %. 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 trigonal with space group R3 (no. 148). The crystal is a colorless block with the following parameters: a=b=9.27150(8)A ° , c=21.1298(4)A ° , V=1572.99(4)A ° 3, Z=3, andDcalc= 1.364 g/cm3. The Raman spectrum of Mg(CH3SO3)2 3 12H2O salt has been recorded and the principal absorption modes identified. Thermogravimetric analysis confirmed the stochiometry of the Mg(CH3SO3)2 3 12H2O salt.
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