The solubilities of the ternary Dy(NO3)3.3H2O-(benzo-15-crown-5)-Me2CO system at 18?were studied through the study of phase equilibrium using the modified semimicro method. The results indicated that the solubility curve of this system consists of 2 branch lines, the long branch corresponds to solid Dy(NO3)3.benzo-15-crown-5.3H2O.2Me2CO; the short one to solid benzo-15-crown-5. The curve of refractive indexes for saturated solns. also consists of 2 branch lines, which corresponds to the 2 branch lines of solubility curve. No complex species with different Dy/crown ratio was found. The behavior of water in the equilibrium system has been examined The results indicate that the mole ratio, H2O/Dy(NO3)3, is always 3:1 either in liquid or solid phase. Dy(NO3)3.benzo-15-crown-5.3H2O.0.65Me2CO was isolated. The properties of this complex were examined by IR spectra, DTA, TG and DSC. The enthalpies of desolvation and thermal decomposition were determine by DSC. The apparent activation energy of the thermal decomposition was 117.46 kJ/mol from DSC curves using Kissinger method.

Key words: INFRARED SPECTROPHOTOMETRY, THERMODYNAMIC PROPERTIES, CROWN ETHER COMPOUNDS, NITRATE, ACETONE, RARE EARTH METAL COMPLEX, DYSPROSIUM COMPLEX