The coordination reactions of benzo-15-crown-5 with fifteen rare earth (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y) perchlorates in acetonitrile were studied at 298.15 K by calorimetric titration The stability constants of coordination compounds and enthalpies of coordination reaction were calculated The values of free energy and entropy of coordination reactions were also obtained. The rare earth ions (III) can coordinate with benzo-15-crown-5 and all the enthalpy changes are endothermic. The coordination compound of La3+ is the most stable, followed by the Ce3+ compound The other compounds do not show distinct differences in stability; a sudden change was observed at Tb. These coordination compounds are stabilized by entropic effects.

Key words: COMPUTER APPLICATIONS, STABILITY CONSTANT, CROWN ETHER COMPOUNDS, BENZENE P, THERMODYNAMIC FUNCTION, RARE EARTH METAL COMPLEX, ENTROPY, ENTHALPY, PERCHLORATE, ACETONITRILE