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The interaction of lower rim calix(4)arene derivatives containing ester (1) and ketone (2) functional groups and bivalent (alkaline-earth, transition- and heavy-metal) cations has been investigated in various solvents (methanol, N,N-dimethylformamide, acetonitrile, and benzonitrile). Thus, 1H NMR studies in CD3OD, C3D7NO, and CD3CN show that the interaction of these ligands with bivalent cations (Mg2+, Ca2+, Sr2+, Ba2+, Hg2+, Pb2+, Cd2+) is only observed in CD3CN. These findings are corroborated by conductance measurements in these solvents including benzonitrile, where changes upon the addition of the appropriate ligand (1 or 2) to the metal-ion salt only occur in acetonitrile. Thus, in this solvent, plots of molar conductance against the ligand/metal cation ratio reveal the formation of 1:1 complexes between these ligands and bivalent cations. Four metal-ion complex salts resulting from the interaction of 1 and 2 with cadmium and lead, respectively, were isolated and characterized by X-ray crystallography. All four structures show an acetonitrile molecule sitting in the hydrophobic cavity of the ligand. The mode of interaction of the neutral guest in the cadmium(II) complexes differs from each other and from that found in the lead(II) complexes and provides evidence of the versatile behavior of acetonitrile in binding processes involving calix(4)arene derivatives. The thermodynamics of complexation of these ligands and bivalent cations in acetonitrile is reported. Thus, the selective behavior of 1 and 2 for bivalent cations is for the first time demonstrated. The role of acetonitrile in the complexation process in solution is discussed on the basis of 1H NMR and X-ray crystallographic studies. It is suggested that the complexation of 1 and 2 with bivalent cations is likely to involve the ligand-solvent adducts rather than the free ligand. Plots of complexation Gibbs energies against the corresponding data for cation hydration show a selectivity peak which is explained in terms of the predominant role played by cation desolvation and ligand binding energy in complex formation involving metal cations and macrocycles in solution. A similar peak is found in terms of enthalpy suggesting that for most cations (except Mg2+) the selectivity is enthalpically controlled. The ligand effect on the complexation process is quantitatively assessed. Final conclusions are given highlighting the role of the solvent in complexation processes involving calix(4)arene derivatives and metal cations.

Several analytical techniques ( 1 H NMR, conductance measurements, and titration calorimetry) have been used to assess the interaction of calix [4]pyrrole and halide anions in dipolar aprotic solvents (acetonitrile and N,N-dimethylformamide). Solubility data for calix [4]pyrrole in various solvents at 298.15 K were determined. These data were used to calculate the standard Gibbs energies of solution. Taking acetonitrile as the reference solvent, the transfer Gibbs energies of this ligand to various solvents were calculated. Chemical shift changes (∆δ) of the pyrrole proton relative to the free ligand resulting from the addition of the anion salts to the ligand in CD 3 CN at 298 K follow the sequence F -> Cl -> Br -> I -. Conductance measurements were performed (i) to establish the stoichiometry of the anionic calix[4]pyrrole complexes and (ii) to assess the range of concentration at which the free and complex anion salts are predominantly in their ionic forms in acetonitrile and N,N-dimethylformamide at 298.15 K. Titration calorimetry was used to determine the stability constant, K s , (hence the standard Gibbs energy) and the enthalpy. Combination of Gibbs energy and enthalpy data yields the entropy of complexation. A linear correlation is found between the log K s and the ∆δ values. The results show that calix [4]pyrrole is able to recognize selectively the halide anions in these solvents. The selectivity of the ligand for one anion relative to another is quantitatively evaluated through the calculation of the selectivity factor. It is shown that the ligand behavior is representative of flexible ligands in which calix[4]pyrrole compete successfully with the solvent for the anion to an extent that the higher selectivity of the ligand is for the smallest anion (fluoride). The thermodynamics of complexation is discussed in terms of the solvation properties of the reactants and the products in acetonitrile and N,N-dimethylformamide.

A double-cavity calix[4]pyrrole derivative, meso-tetramethyl-tetra[N-(2-phenoxyethyl)-N'-phenylurea]calix[4]pyrrole, 1, with enhanced hosting ability for the fluoride anion has been designed and characterized. Its interaction with anions (fluoride, chloride, bromide, iodide, dihydrogen phosphate, hydrogen sulfate, perchlorate, nitrate, and trifluoromethane sulfonate) was qualitatively and quantitatively assessed through 1H NMR, conductance, and calorimetric studies. The outcome of these investigations demonstrates that 1 interacts only with fluoride and dihydrogen phosphate anions in dipolar aprotic media. However, the composition of these complexes differs in that two units of fluoride are taken per unit of 1, while a 1:1 anion/ligand complex is formed with the dihydrogen phosphate anion. Results from the 1H NMR studies are striking in that these not only provide information about the active sites of the ligand-anion interaction but also allow the establishment of the sequence of events taking place during fluoride complexation. Thus, hydrogen-bond formation between the pyrrolic hydrogen and the fluoride anion is followed by the uptake of a second anion through the same type of interaction, but with the phenyl urea. It is also the latter group that is responsible for the interaction of 1 with the dihydrogen phosphate anion. Finally, this paper illustrates the importance of structural information for the interpretation of the thermodynamics associated with these systems.

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The complexing properties of two lower rim calix(4)arene derivatives, namely, 5,11,17,23-tetrakis(1,1dimethylethyl)-25,27-bis[2-(methylthio)ethoxy]-26,28-bis[2-(diethylamine)ethoxy]calix(4)arene (1a) and p-tertbutylcalix(4)arene tetradiisopropylethanoamide (1b) toward lanthanide(III), scandium, and yttrium cations in acetonitrile and in N,N-dimethylformamide at 298.15 K were investigated. 1 H NMR complexation experiments established the presence of interactions between the hydrophilic cavity of these macrocycles and these metal cations and revealed the active sites of complexation of these ligands. Conductance measurements were used to (i) establish the concentrations at which the lanthanide trifluoromethanesulfonate salts are fully dissociated 3:1 electrolytes in these solvents and (ii) determine the composition of the metal-ion complex in these solvents. Titration microcalorimetry was used to derive the thermodynamics of complexation of these macrocycles and lanthanide(III) cations in acetonitrile and N,N-dimethylformamide at 298.15 K. No reliable thermodynamic data could be obtained from classical calorimetry due to the slow kinetics observed in the complexation of these calixarene derivatives and these cations in these solvents. Stability constants of 1a were also determined by the competitive potentiometric method using the silver electrodes. Excellent agreement was found between the data derived from calorimetry and those derived by potentiometry. For all the systems investigated, the complexation process between these cations and these ligands was enthalpically controlled. Enthalpy-entropy compensation effects were observed in the complexation of 1a and the different lanthanide(III) cations in acetonitrile and in N,N-dimethylformamide, as suggested by the absence of significant variations in the Gibbs energies of complexation in each case. As far 1b is concerned, a selective behavior was observed for this ligand and the various cations in acetonitrile with the highest stabilities found for gadolinium and europium. The enthalpic and entropic contributions to the Gibbs energy associated with these processes are analyzed. Final conclusions are given.

The solubility of 27 1 : 1 electrolytes in 1,Zdichloroethane and 25 1 : 1 electrolytes in 1,l-dichloroethane has been determined. Combination of the solubility values with association constants, and correction for activity coefficients by the extended Debye-Huckel theory, yields standard free energies of solution of the ionic species (M++X-). From like data in water, free energies of transfer from water to the dichloroethanes have been calculated and have been split into single-ion values through the assumption that AGt(Ph4P+, Ph4As+) = AGt"(Ph4B-). It is shown that the free energy of anions (Cl-, Br-, Iand C10:) in the dichloroethanes is much higher in value than in water and in dipolar aprotic solvents (DMSO, DMF and MeCN). The free energy of most cations (Na+, K+, Rb+, Cs+, Me4N+, Et4N+, Pr4N+ and Bu4N+) is also higher in value in the dichloroethanes than in the dipolar aprotic solvents. Both anions and cations are invariably higher in free energy by -1 kcalmol-l in 1,l-dichloroethane than in 1,Zdichloroethane. It is concluded that the (Ph4P+, Ph4As+) = (Ph4B-) assumption yields single-ion free energies of transfer to or from the dichloroethanes that are chemically reasonable.

A new calix[4]arene derivative containing mixed pendant arms in its lower rim, 5,11,17,23-tetra-tert-butyl[25,27-bis(ethylethanoate)oxy-26,28-bis(ethylthioethoxy)]-calix[4]arene, 1, has been synthesized and characterized by 1H and 13C NMR. 1H NMR data carried out in CDCl3, CD3CN, CD3OD, and C3D7NO suggest that as far as acetonitrile is concerned, the hydrophobic cavity is likely to embrace a solvent molecule. It is shown that the hosting capacity of 1 toward metal cations is greater in acetonitrile than in N,N-dimethylformamide and in methanol. Thus, in the former solvent, complexation with various cations (Li+, Na+, Ag+, Ca2+, Cu2+, Hg2+, and Pb2+) occurs while in the latter media, 1 interacts only with Ag+ and Hg2+. This statement is corroborated by 1H NMR, conductance, calorimetric and potentiometric measurements. It is concluded that through molecular inclusion of acetonitrile in the hydrophobic cavity of 1, the hydrophilic cavity of the resulting adduct becomes more receptive to host metal cations than that of the free ligand. In propylene carbonate, the results show that the ligand loses its ability to interact with metal cations. Thus in acetonitrile, selective recognition of 1 for Hg2+ is demonstrated to an extent that the selectivity for this cation is greater by factors of 1.8 × 103, 1.9 × 103, 6.9 × 103, 1.8 × 104, 4.1 × 104 and 4.5 × 104, relative to Pb2+, Na+, Li+, Cu2+, Ag+, and Ca2+, respectively. This statement is supported by the thermodynamic characterization of the complexation process involving these systems in acetonitrile, N,N-dimethylformamide and in methanol. Thus, the medium effect on the binding process is carefully assessed. The results show that replacement of two ester groups in two alternate pendant arms of the tetraester calix[4]arene derivative by thioethyl moieties has altered significantly the binding capacity and the selective behavior of the latter relative to the former. Final conclusions are given.