COMPLEXATION THERMODYNAMICS OF RARE-EARTH (III)-CROWN ETHER .2. CALORIMETRIC TITRATION OF COMPLEXATION OF THE ARM TYPE 15-CROWN-5 AND ARM TYPE 18-CROWN-6 WITH RARE EARTH(III) NITRATES IN ANHYDROUS ACETONITRILE

Calorimetric titrations were performed in anhydrous acetonitrile at 29 8.15 K to give the complex stability constants (K(s)) and the thermody namic parameters for the complexation of rare earth (III) nitrates (La , Ce, Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho, Er, Yb) with N-benzyl-monoaza-15 -crown-5 and of rare earth(III) nitrates (La, Oe) with N-benzyl-monoaz a-18-crown-6. The complexation stoichiometry is 1:1 for all rare earth (III) nitrates. The complex stability constants (K(s)), reaction enth alpies (DELTAH-degrees) and entropies (T DELTAS-degrees) were calculat ed directly by using precision calorimeter connected to an Apple II mi crocomputer. The effects of the crown ether's size-fit concept, spatia l arrangement and other major factors upon complex stability are discu ssed from a viewpoint of thermodynamics.