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Thermal and Structural Study of the Crystal Phases and Mesophases in the Lithium and Thallium(I) Propanoates and Pentanoates Binary Systems: Formation of Mixed Salts and Stabilization of the Ionic Liquid Crystal Phase

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posted on 12.08.2010, 00:00 by F. J. Martínez Casado, M. Ramos Riesco, I. da Silva, A. Labrador, M. I. Redondo, M. V. García Pérez, S. López-Andrés, J. A. Rodríguez Cheda
The temperature and enthalpy vs composition phase diagrams of the binary systems [xC2H5CO2Li + (1 − x)C2H5CO2Tl], and [x(n-C4H9CO2Li) + (1 − x)n-C4H9CO2Tl], where x is the mole fraction, were determined by DSC. Both binary systems display the formation of one 2:1 mixed salt each (at x = 0.667) that appear as a peritectic (incongruent melting) at Tfus = 512.0 K, and Tfus = 461.1 K, with ΔfusHm = 13.76 and 8.08 kJ·mol−1 for Li−Tl (I) propanoates, and n-pentanoate mixed salts, respectively. The thermotropic liquid crystal of the thallium(I) n-pentanoate transforms into a more stable liquid-crystal phase, which appears in the phase diagram between 380 and 488 K and for x = 0 up to x = 0.56. The crystal structure of thallium(I) propanoate and of the two mixed salts were obtained via X-ray synchrotron radiation diffraction measurements. These compounds present a bilayered structure similar to the two pure lithium salts previously found by our group.