Search

The interaction of calix[3]thieno[1]pyrrole, 1, and halide and dihydrogen phosphate anions in a variety of solvents (acetonitrile, propylene carbonate, N,N-dimethylformamide, and dimethyl sulfoxide) has been investigated through 1H NMR, conductance measurements, and titration calorimetry. 1H NMR measurements reveal the sites of interaction of the ligand with the anions in CD3CN while the composition of the complex was determined through conductance measurements. A quantitative assessment of anion-ligand interactions is provided. Thus the thermodynamics of complexation of 1 with halide and dihydrogen phosphate anions in dipolar aprotic media at 298.15 K is reported. These data are interpreted in terms of the thermodynamics of transfer of reactants and product from a reference solvent (acetonitrile) to other solvents. The crucial role played by the solvent on the ability of the ligand to interact with anions and on the composition of the complex is demonstrated.

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.

The solvent control on the ability of a partially substituted lower rim calix(4)arene derivative 5,11,17,23,tetra-tert-butyl[25,27-bis(hydroxy)-26,28-bis(ethylthioethoxy)]-calix(4)arene, 1 to host soft metal cations (Hg(II) and Ag(I)) is demonstrated through 1H NMR, electrochemical (conductance measurements), and thermodynamic characterization of the complexation process in a wide variety of solvents. Solvent-ligand interactions were assessed from 1H NMR measurements involving 1 and various solvents in CDCl3. Thus, the formation of a 1:1 1-CH3CN adduct is reported. As far as metal cations are concerned, depending on the medium their complexation with 1 was only observed for Hg(II) and Ag(I). Thus, in acetonitrile, 1 is more selective for Hg(II) relative to Ag(I) by a factor of 2.2 x 10(3). In methanol the selectivity is reversed to an extent that the affinity of 1 for Ag(I) is 1.4 x 10(3) higher than that for Hg(II). However, 1 is unable to recognize selectively these cations in N,N-dimethylformamide while in propylene carbonate the ability of 1 to interact with these cations is lost. An outstanding feature of thermodynamics emerges when an assessment is made of the ligand effect on the complexation of these cations and analogues calix(4)arene derivatives. Thus, in acetonitrile the thermodynamics of cation complexation by the hydrophilic cavity of a calix(4)arene containing mixed pendant groups is built up from thermodynamic data for the same process involving derivatives with common functionalities at the narrow rim. This is a unique example of the additive contribution of pendant arms in the field of thermodynamics of calixarene chemistry.