The spectrophotometric titrations have been performed in anhydrous acetonitrile at 20.0-35.0℃ to give the constants (logKs) and the thermodynamic parameters (ΔH°and TΔS°) for the intramolecular sandwich complexation of light lanthanoid (III) nitrates (La, Ce, Pr, Nd, Sm, Eu, Gd) with bis (benzo-15-crown-5) (1), and the results were compared with the data reported for the parent benzo-15-crown-5. The stoichiometry of the complex formed is 1 : 1 for all light lanthanoid nitrates complexation with bis (benzo-15-crown-5) (1). The effects of the bis (crown ether)'s size-fit concept, spatial arrangement, intramolecular constitution and other major factors upon complex stability are discussed from a viewpoint of thermodynamics. The thermodynamic parameters obtained indicate that the coordination of Eu^3^+ with bis (benzo-crown ether)(1) shows the strongest complexation ability and selectivity, and Nd^3^+ the second. The stabilities of light lanthanoid nitrates complexation with bis (crown ether) are contributed mainly through the coordination entropy.

Key words: SPECTROPHOTOMETRY, THERMODYNAMIC PROPERTIES, NITRATE, ACETONITRILE, CROWN ETHER