The solubilities of the ternary system, Pr(ClO4)3.3H2O-18C6- C2H5OH, have been investigated by a semimicro method at 298.15K for study of phase equilibrium and the refractive indexes of saturated solutions have been determined. The results indicate that there are two kinds of coordination compounds formed in the system, their chemical compositions are: Pr(ClO4)3.18C6.3H2O(1) and Pr(ClO4)3.2(18C6).3H2O(2). The two solid coordination compounds have been prepared. The composition and properties of the complexes have been investigated by chemical analysis, IR, TG and DTG. The integral heats of solution of Pr(ClO4)3.3H2O in 18C-C2H5OH solution, the complexes (1) and (2) in C2H5OH, and 18C6 in C2H5OH have been measured calorimetrically at 298.15K. By means of a thermochemical cycle suggested in this paper, the standard molar enthalpies of formation for two complexes were obtained.

Key words: PHASE EQUILIBRIUM, INFRARED SPECTROPHOTOMETRY, TERNARY SYSTEM, CROWN ETHER COMPOUNDS, ENTHALPY OF FORMATION, PERCHLORATE, PRASEODYMIUM COMPLEX