Abstract: A new rare earth complex La(C15H12N5O2)( C15H11N5O2)•2.5H2O has been synthesized. Attempts have been made to ascertain its probable structure on the basis of elemental analyzes, molar conductivities, IR, 1H NMR and TG-DTG. It is suggested that the complex has a eight-coordinated configuration. The enthalpies of solution in DMF for the complex were measured by means of a micro calorimeter. The data of standard molar enthalpy of solution (ΔsolHmΘ=－135.62 kJ•mol－1) and the empirical formulae of enthalpy of solution (ΔsolH=－135.62－11633b＋3761.5b1/2) for the complex at different concentration b (mol•kg－1) were obtained. And relative apparent molar enthalpy (Li),relative partial molar enthalpy (Li)) and enthalpy of dilution (ΔdilH1,2) were drawn up respectively by the data of enthalpies of solution of the complex: Li=－11633b＋2761.5b1/2, Li=－23266b＋5642.2b1/2 and ΔdilH1,2=－11633(b21/2－b11/2)＋3761.5(b2－b1).The second-stage decomposition reaction for the complex was studied and the apparent activation energy was obtained by the Kissinger's formulae.

Key words: Salicylaldehyde-1H-benzotriazol-1-aceylhydrazone, Rare earth, 　Enthalpy of solution, Thermal decomposition, Activation energy