A wide variety of macrocyclic ligands able to interact with cations, anions, and neutral species are known. These have been isolated from natural resources or are the result of the synthetic developments which have taken place in the last 30 years.1a,b Among the latter, calixarenes (products of the baseinduced condensation of p-substituted phenols and formaldehyde) and their derivatives have received considerable attention in recent years. The chemistry of calixarenes has been extensively discussed in several books2a-c and review articles.2d-g There are several reasons for the current widespread interest in calixarenes. An important one is the remarkably simple way (single-step procedure) used for the synthesis of the parent compounds. In addition, lower and upper rim functionalization of these macrocycles has resulted in a massive expansion in the range of derivatives available.2e,g Within this context, calix(4)arenes are of particular interest. Several conformers (cone, partial cone, 1,2 alternate, and 1,3 alternate) have been isolated. A great deal of efforts have been directed toward calix(4)arene derivatives in “cone” conformation. Their particular molecular architecture with well-defined hydrophobic and hydrophilic regions makes these compounds suitable hosts for neutral and ionic species. Calixarenes are potential building blocks for the design of novel supramolecular systems. This is exemplified in the synthesis of calixarenes bridged across the lower and upper rim or indeed coupled between themselves or to other macrocycles.2g-i Calixarenes have found a wide range of applications. A good account on the industrial uses of these macrocycles prior to 1992 has been given by Perrin and Harris.2j However in the past few years several internationally significant patents have been published.2k-u These patents center mostly on the potential use of calixarenes to sequester metal ions and neutral species, although the ultimate use is fairly broad. The remarkable growth of the field of calixarene chemistry has been greatly motivated by the interest in finding derivatives able to enter into selective complexation with neutral or ionic species. A quantitative measure of the strength of interaction between two chemical species (macrocycle and guest) in a given solvent is provided by the stability constant. Therefore, the role of experimental thermodynamics in understanding the factors contributing to complex stability and selectivity is important and must not be underestimated. It should be explicity stated that the derivation of accurate thermodynamic data requires knowledge of the speciation in the systems under study. A significant point arising from this statement is that a high level of scrutiny and detail regarding the behavior of chemical species in a given medium is required in thermodynamic studies related to solution processes. It is only on the bases of accurate experimental data that the 2495 Chem. Rev. 1998, 98, 2495−2525

Thermodynamics of Calixarene Chemistry.

Using 1H and 13C NMR, FT IR spectroscopy together with quantum mechanical DFT calculations, we show that tetraethyl p-tert-butylcalix[4]arene tetraacetate (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in acetonitrile-d 3. Protons for this complex were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H3O+ adopts a slightly asymmetric conformation, which is distinctly more cone-like than ligand 1. According to spectral evidence, the hydroxonium ion H3O+ is bound mainly to three of the phenoxy oxygen atoms of 1 by strong hydrogen bonds leaving the ester carbonyl groups, which are the usual coordination site for metal cations, free. Theoretical DFT calculations support the bonding to phenoxy oxygen atoms but slightly prefer a structure with one of the carbonyls being involved in the coordination.

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Experimental Evidence for Unusual Protonation of Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate and the Most Probable Structure of the Resulting Complex

Titration microcalorimetry in nonaqueous media (acetonitrile and propylene carbonate) has been used for the determination of stability constants (log Ks) and enthalpies of complexation of lithium and crown ethers (12-crown-4 and 1-benzyl-1-aza-12-crown-4 at 298.15 K. To ensure that the data are referred exclusively to the complexation process, salts containing highly polarizable anions (hexafluoroasenate, tetrafluoroborate, trifluoromethanesulfonate, and perchlorate) are used as sources for lithium. From stability constants and standard enthalpies, standard Gibbs energies and standard entropies are calculated. In propylene carbonate, a correlation is found between the stability of the lithium crown complex and the increase in conductance of the complexed relative to the free cation. Eight new lithium coronand salts of 12-crown-4 and 1-benzyl-1-aza-12-crown-4 were isolated. Standard enthalpies of these salts and crown ethers in acetonitrile and propylene carbonate at 298.15 K measured calorimetrically are ...

Thermodynamics of Lithium−Crown Ether (12-crown-4 and 1-Benzyl-1-aza-12-crown-4) Interactions in Acetonitrile and Propylene Carbonate. The Anion Effect on the Coordination Process

Hartree-Fock, second order Moller-Plesset perturbation theory, and density functional theory calculations were carried out to analyse the complexation of calix[4]arene with cationic species including H + and the alkali metal cations (Li + , Na + , K + , Rb + , and Cs + ). Special emphasis has been placed on conformational binding selectivity, and on the structural characterization of the complexes. Li + and Na + cations are located in the calix[4]arene lower rim. The larger cations (K + , Rb + , and Cs + ) complex preferentially with the calix[4]arene cone conformer, and their endo (inclusive) complexation is driven by cation- ~ interactions, leading in the case of K + to a structure that reflects a preferential interaction with two phenol rings. The endo complexation of Cs + with calix[4]arene is in agreement with X-ray diffraction data.

Complexation of Calix[4]arene With Alkali Metal Cations: Conformational Binding Selectivity and Cation-π Driven Inclusion

Strontium PVC-membrane sensor based on 2-[(2-mercaptophenylimino)methyl]phenol

Thermodynamics of Calix(4)arene Esters. 1. Complexation of Alkyl p-tert-Butylcalix(4)arenetetraethanoates and Alkali-Metal Cations in Acetonitrile and in Benzonitrile

Thermodynamics of Alkyl p-tert-Butylcalix[4]arenetetraethanoates. 2. Solution Studies of Calix[4]arene Esters and Lithium and Sodium Ethylcalix[4]arene Ester Complexes: Coordination Data in the Solid State

Elisabeth Gil

Papers

Thermodynamics of Calix(4)arene Esters. 1. Complexation of Alkyl p-tert-Butylcalix(4)arenetetraethanoates and Alkali-Metal Cations in Acetonitrile and in Benzonitrile

Thermodynamics of Alkyl p-tert-Butylcalix[4]arenetetraethanoates. 2. Solution Studies of Calix[4]arene Esters and Lithium and Sodium Ethylcalix[4]arene Ester Complexes: Coordination Data in the Solid State