THE STRUCTURE AND THERMAL-BEHAVIOR OF SOME LONG-CHAIN CERIUM(III) CARBOXYLATES

The even chain length cerium(III) carboxylates from the octanoate to t he octadecanoate have been synthesised by metathesis. Thermogravimetry shows the presence of coordinated water for the short chain homologue s, whereas the longer chain ones only contain adsorbed water. X-Ray di ffraction and IR spectral measurements show that the solid phase has a lamellar, bilayer structure with planes of the cerium(III) ions coord inated to the carboxylate groups. The phase behaviour of the carboxyla tes has been studied by DSC and polarized-light microscopy. One or mor e mesophases are observed over the temperature range 70-120 degrees C and melting occurs between 130 and 150 degrees C. The textures observe d on the polarizing microscope clearly show the anisotropic nature of the mesophases. Although the overall enthalpy and entropy of melting o f these compounds increase with increasing chain length, the values ar e considerably lower than expected for complete fusion of the alkyl ch ains. Competition between melting of the chains and changes in the met al-carboxylate coordination region is the major factor responsible for the differences observed in the phase behaviour between the short and long chain derivatives.