OBSERVATIONS ON RARE EARTHS .80. THERMODYNAMIC STABILITIES OF ETHYLENEDIAMINE CHELATES OF TRIPOSITIVE LANTHANIDE IONS IN ANHYDROUS ACETONITRILE

Four distinct enthalpy changes characterize the calorimetric titration of a lanthanide (III) perchlorate solution in acetonitrile with ethylenediamine under rigorously anhydrous conditions. The calculated enthalpies of formation of the species Ln(en)n3+ (n= 1-4) demonstrate the remarkable thermodynamic stabilities of these ions in acetonitrile. With nitrate as the anion, only the first two enthalpy changes can be evaluated, and the continuing evolution of heat even beyond a 6:1 ligand to cation mole ratio indicates competition between nitrate ion and ethylenediamine for additional coordination sites. Variations in thermodynamic stability in the lanthanide series are discussed. The ethylenediamine complexes formed under these conditions are enthalpy stabilized. © 1969, American Chemical Society. All rights reserved.