Solution and co-ordination enthalpies (solid state) of lithium and sodium macrocycle (ethyl p-tert-butylcalix(4)arene tetraethanoate, cryptand 222 and crown ethers) systems

A series of lithium and sodium ethyl p-tert-butylcalix(4)arene tetraethanoate and cryptand 222 salts has been isolated and thermochemically characterised in acetonitrile at 298.15 K. Also reported are the standard enthalpies of solution of common sodium salts (tetrafluoroborate, trifluoromethanesulfonate, iodide and bromide) in this solvent at the same temperature. Solution data for the free and the complexed salts and for the ligand are combined with complexation data for the appropriate cation and macrocycle in acetonitrile to derive the enthalpies of co-ordination of these systems for the process where the product and the reactants are in the solid state. Comparison of data involving lithium and the calix(4)arene ester and the cryptand 222 with those for crown ethers reflects considerable weakening of cation–anion interactions in the former ligands relative to crown ethers. It is concluded that for a given ligand and metal cation, the anion effect is reflected in the co-ordination enthalpies. On the other hand, for systems containing the same ligand and anion, there is a decrease in enthalpic stability in moving from lithium to sodium. The need to obtain experimental data on crystal lattice enthalpies of these ligands and their metal ion complex salts is emphasised.