Thermodynamic and electrochemical aspects of lithium-macrocycle interactions in dipolar aprotic media

• Main Author: Tanco, Margot Anabell Llosa
• Published: University of Surrey 1996
• Subjects: 541; Lithium batteries
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318695

In the introduction of this thesis thermodynamic and electrochemical studies on macrocyclic ligands related to those ligands investigated in this thesis are reviewed. A brief account on the progress made and the problems encountered in lithium battery technology are also presented. Thermodynamic parameters of complexation (Gibbs energies, DeltacG°, enthalpies, DeltacH°, and entropies, DeltacS° of lithium (hexafluoroarsenate, tetrafluoroborate and trifluoromethanesulfonate) and crown ethers (1-aza-12-crown-4 and 15-crown-5) in acetonitrile and propylene carbonate and (4'-aminobenzo-15-crown-5 and 4'-nitrobenzo-15-crown-5) in acetonitrile at 298.15 K derived from calorimetric studies are presented. As far as 1-aza-12-crown-4 and 15-crown-5 are concerned the complexation processes are found to be enthalpy controlled. However, the stability (in enthalpic terms) of 15-crown-5 and lithium is slightly higher than that observed for the same cation and 1-aza-12-crown-4 in both solvents. Based on the stability of lithium-crown ether complexes, six lithium coronand salts were isolated and their thermochemical behaviour in dipolar aprotic media investigated. Comparison of solution enthalpies of these salts relative to those containing the free cation shows that while the former are endothermic, the latter are exothermic. This was taken as an indication that the lithium coronand cation is less solvated than the free cation. This statement was corroborated by the significant increase on the conductivity observed by the addition of crown ethers to lithium salts in propylene carbonate. From complexation and solution data for 15-crown-5 and 1-aza-12-crown-4 and lithium, enthalpies for the coordination, process in which the reactants and the product are in their pure physical state were calculated. These data combined with solution enthalpies for 15-crown-5, the un-complexed and complexed lithium salts were used to derive the enthalpy of complexation of 15-crown-5 and lithium in tetrahydrofuran, a solvent of low permittivity.