THERMODYNAMICS OF LITHIUM-CROWN ETHER (12-CROWN-4 AND 1-BENZYL-1-AZA-12-CROWN-4) INTERACTIONS IN ACETONITRILE AND PROPYLENE CARBONATE - THEANION EFFECT ON THE COORDINATION PROCESS

Titration microcalorimetry in nonaqueous media (acetonitrile and propy lene carbonate) has been used for the determination of stability const ants (log K-s) and enthalpies of complexation of lithium and crown eth ers (12-crown-4 and 1-benzyl-1-aza-12-crown-4 at 298.15 K. To ensure t hat the data are referred exclusively to the complexation process, sal ts containing highly polarizable anions (hexafluoroasenate, tetrafluor oborate, trifluoromethanesulfonate, and perchlorate) are used as sourc es for lithium. From stability constants and standard enthalpies, stan dard Gibbs energies and standard entropies are calculated. In propylen e carbonate, a correlation is found between the stability of the lithi um crown complex and the increase in conductance of the complexed rela tive to the free cation. Eight new lithium coronand salts of 12-crown- 4 and 1-benzyl-1-aza-12-crown-4 were isolated. Standard enthalpies of these salts and crown ethers in acetonitrile and propylene carbonate a t 298.15 K measured calorimetrically are used to explain (i) the highe r molar ionic conductivities, observed for lithium coronand relative t o lithium electrolytes, and (ii) the effect of the solution properties of ligand, free, and complexed cation in the binding of these ligands with lithium in these solvents. Enthalpies of coordination first repo rted show the anion effect in the process involving reactants and prod uct in their pure physical state. The strength of cation-anion interac tion follows the sequence ClO4- > CF3SO3- > AsF6- > BF4-.