Crystal structure and characterization of magnesium carbonate chloride hepta­hydrate

MgCO(3)·MgCl(2)·7H(2)O is the only known neutral magnesium carbonate con­taining chloride ions at ambient conditions. According to the literature, only small and twinned crystals of this double salt could be synthesised in a concentrated solution of MgCl(2). For the crystal structure solution, single-crystal diffraction was carried out at a synchrotron radiation source. The monoclinic crystal structure (space group Cc) exhibits double chains of MgO octa­hedra linked by corners, connected by carbonate units and water mol­ecules. The chloride ions are positioned between these double chains parallel to the (100) plane. Dry MgCO(3)·MgCl(2)·7H(2)O decom­poses in the air to chlorartinite, Mg(2)(OH)Cl(CO(3))·nH(2)O (n = 2 or 3). This work includes an extensive char­acterization of the title com­pound by powder X-ray diffraction, thermal analysis, SEM and vibrational spectroscopy.