Solvation effect of guest, supramolecular host, and host-guest compounds on the thermodynamic selectivity of calix(4)arene derivatives and soft metal cations.

This paper reports thermodynamic data for the transfer of calixarene derivatives and their metal-ion complexes in dipolar aprotic solvents. These data are used to assess the effect of solvation of these compounds on the selective complexation shown by these macrocycles for soft metal cations in different media. Thus, solubilities and derived Gibbs energies of solution of 5,11,17,23-tetra-tert-butyl[25,27-bis(hydroxyl)-26,28-bis(ethylthioethoxy)]calix(4)arene, 1, and 5,11,17,23-tetra-tert-butyl-[25,27-bis(ethylenethanoate)-26,28-bis(ethylthioethoxy)]-calix(4)arene, 2, in various solvents at 298.15 K are reported. Solvation of these ligands in one medium relative to another is analyzed from their standard transfer Gibbs energies using acetonitrile as the reference solvent. These data are combined with transfer enthalpies (derived from standard solution enthalpies obtained calorimetrically) to calculate the corresponding entropies of transfer of these calix(4)arene derivatives from acetonitrile to methanol and N,N-dimethylformamide. As far as the metal-ion salts (silver and mercury) in their free and complex forms are concerned, standard solution enthalpies were determined in acetonitrile, methanol, and N,N-dimethylformamide. These data are used to derive their transfer enthalpies from one medium to another. It is concluded that the extent of complexation of these macrocycles with soft metal cations is controlled by not only the solvation changes that the free cation undergoes in moving from one medium to another but also those for the ligand and its complex cation in these solvents.