Thermal dehydration in lithium croconate dihydrate (Li2C5O5 center dot 2H(2)O) studied by vibrational and thermoanalytical techniques

This work reports the thermal dehydration of the oxocarbonic salt Li2C5O5. 2H(2)O studied by IR and Raman spectroscopy, by ex situ and in situ techniq ues. The loss of the crystallization water is not only reflected by the dis appearing of the pertinent bands, but also by the change in the crystalline phase, as evidenced by the alteration in the splitting pattern of the oxoc arbon modes and by differential scanning calorimetry. In the anhydrous salt spectra, a great number of overtones and combination bands appear in the 2 000-4000 cm(-1) region, indicating an increased anharmonicity. The enhanced splitting suggests that the anhydrous phase belongs to a less symmetric un it cell. The tetrahedral environment around the lithium ion is preserved, a s suggested by the shifts of some modes in the 300-600 cm(-1) region on iso topic substitution from Li-7 to Li-6. Raman and thermoanalytical data seem to indicate that the crystallization water is released in a single-step pro cess. (C) 2001 Elsevier Science B.V. All rights reserved.