THERMODYNAMICS OF COMPLEXATION OF LANTHANIDES BY 2-HYDROXYPHENYLHYDRAZOETHYL-ACETOACETATE (2-HPHEAA) - 2-HYDROXYPHENYL-HYDRAZOETHYLCYANOACETATE (2-HPHECA) AND 2-HYDROXYPHENYLHYDRAZOMALONONITRILE (2-HPHMN)

The thermodynamic parameters (DELTAG, DELTAH and DELTAS) for the forma tion of 1:1 and 1:2 complexes between lanthanide cations and 2-HPHMN, 2-HPHECA and 2-HPHEAA were determined by potentiometric titrations in 75% (v/v) methanol-water solutions of 0.10 M KNO3 ionic strength. It e lucidated that the stepwise Gibbs energies of formation of metal compl exes varied in the sequence, DELTAG1 < DELTAG2 and the stepwise enthal pies, DELTAH-1 > DELTAH-2, and thus, the stepwise entropies markedly d ecrease in the order, DELTAS1 > DELTAS2. Both of the enthalpy and entr opy of all complex systems are negative. The non-linear variation of t he thermodynamic parameters as a function of ionic potential of lantha nide elements was discussed.