Vibrational and Thermal Evidence of Coordinated Water and Carboxylate Groups in Crystalline Calcium Malonate Dihydrate

Revision of the crystal structure of calcium malonate dihydrate, [Ca(mal)(H2O)2], has shown that it belongs to the monoclinic system, space groupC2/m, witha=13.857(6),b=6.8072 (8),c=6.806(5) ?,beta=106.31(7)°,Z=4, andV=616.2(5) ?3. This is in agreement with one of the previous structural determinations, and nonequivalent water molecules and chelating and bridging carboxylate groups in the crystal lattice are evidenced. The infrared and Raman spectra were recorded and discussed in relation to the structural properties. Librational modes of water have been clearly identified and an assignment for all the internal modes is proposed. The thermal dehydration and decomposition processes were investigated using TG/DTA measurements. The structural model is consistent with the vibrational behavior and the two different temperatures observed in the dehydration process.