Thermal Properties, Crystal Structure, and Phase Transition of Racemic CaC4H4O6•4H2O Single Crystals
T. Fukami *
Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan
S. Hiyajyo
Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan
S. Tahara
Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan
C. Yasuda
Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan
*Author to whom correspondence should be addressed.
Abstract
Single crystals of racemic calcium tartrate tetrahydrate, CaC4H4O6·4H2O, were grown at 308 K by a gel method using silica gel as the medium of growth. Differential scanning calorimetry, thermogravimetric-differential thermal analysis, and X-ray diffraction measurements were performed on the single crystals. The space group symmetry (triclinic, P1(__)) and structural parameters were determined at room temperature. The O–H–O hydrogen-bonding networks formed between adjacent C4H4O6 molecules, and between C4H4O6 and H2O molecules, were found to extend along the c-axis and [01(__)1] directions, respectively. A phase transition, driven by intramolecular proton transfer between three possible positions in the vicinity of O atoms, was found to occur at around 310 K. Weight losses due to thermal decomposition of racemic CaC4H4O6·4H2O occurred in the temperature range of 300–1200 K. The weight losses during decomposition were suggested to be caused by the evaporation of bound water molecules and the evolution of 2H2CO, (1/2)O2, and 2CO gases.
Keywords: Racemic CaC4H4O6•4H2O, phase transition, proton transfer, thermal decomposition, DSC, TG-DTA, X-ray diffraction