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.

In the present paper, a novel lithium-conducting polymer electrolyte, based on the low molecular weight dimethoxy poly(ethylene oxide) matrix as well as high molecular weight poly(ethylene oxide), is studied. New calixarene derivatives have been designed, synthesized, and successfully applied as neutral anion-binding receptors in the electrolytes, what could be of interest in the search for new sensors as well as for enhancing electrolytic functionality in energy-storage devices. Herein, details regarding synthesis and structural properties of all compounds incorporated in the polyether system are presented and discussed. The effect of supramolecular additives on physical (e.g., the charge-carriers transport mechanism, mechanical and thermal properties, or degree of crystallinity) and chemical (e.g., ion-receptor ion-matrix interactions) characteristics of polymer electrolyte is investigated in terms of differential scanning calorimetry, Fourier-transform IR spectroscopy, and impedance spectroscopy result...

Anion-Binding Calixarene Receptors: Synthesis, Microstructure, and Effect on Properties of Polyether Electrolytes

Spacer directed metallo-supramolecular assemblies of pyridine carboxylates

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

A new efficient and highly selective fluorescent chemosensor for determination of Pb (2+) has been obtained by covalent attachment of two pendent proton-ionizable dansylcarboxamide groups to the calix[4]arene preorganized in the partial cone conformation. This geometry of the calixarene moiety was chosen on the basis of the prior (1)H NMR study of conformations adopted by the flexible dansyl-containing prototype upon complexation with lead ion. In acidic MeCN-H2O (1:1 v/v) solutions, the partial cone fluoroionophore allowed for detection of Pb (2+) at the levels as low as 2.5 ppb, which is totally compatible with the regulations of the U.S. Environmental Protection Agency and the World Health Organization on the limiting content of this hazardous pollutant in drinking water.

New fluorogenic dansyl-containing calix[4]arene in the partial cone conformation for highly sensitive and selective recognition of lead(II).

The solubility and derived standard Gibbs energies of solution of three geometrical isomers of pyridinocalix(4)arenes {5,11,17,23-tert-butyl-[25,26,27,28-tetrakis-(n-pyridylmethyl) oxy]-p-tert-butylcalix(4)arene, with n=2, 3, 4} in a variety of solvents at 298.15 K are reported. Solvation effects are assessed from the standard transfer Gibbs energies of these ligands, using acetonitrile as the reference solvent. For the 2-pyridyl derivative in alcohols as the aliphatic chain length of the alcohol increases, the extent of solvent–ligand interaction increases, whereas for the 3- and the 4-pyridyl derivatives the opposite is observed. The protonation constants for the 4-pyridyl derivative in methanol at 298.15 K are reported. The results, compared with corresponding values for the 3-pyridyl derivative show that the basic character of these ligands follows the sequence; 4-pyridyl>3-pyridyl>2-pyridyl calix(4)arene. Thermodynamic parameters for the complexation of these macrocycles (2 and 4-pyridyl derivatives) and the silver cation in acetonitrile show that, as the distance between the phenolic oxygens and the pyridyl nitrogens increases, the strength of complexation decreases. Thermodynamic data for the complexation of silver and the 2-pyridylcalix(4)arene derivative are compared with corresponding values for sodium and this ligand in the same solvent. The results suggest that the 2-pyridyl derivative provides phenolic oxygens and pyridyl nitrogens as the active sites for complexation with silver. This is corroborated by 1H NMR measurements of this ligand and silver in CD3CN at 298 K.The crystal structure of a 1:1 monoacetonitrile and silver complex of the 2-pyridyl derivative with perchlorate as the counter-ion has been determined from XRD data. The substance crystallises in the tetragonal space group P4/n with a=15.580(2) A, c=13.082(2) A, and z=2. The macrocycle is sited on a fourfold symmetry axis and consists of two conical parts, one hydrophobic, filled with an acetonitrile molecule, the other hydrophilic, encapsulating the Ag+ ion through the ethereal oxygen [d(Ag···O)=2.923(3) A] and pyridine nitrogen atoms [d(Ag···N)=2.483(5) A]. The coordination around the Ag+ ion has the form of a distorted Archimedean square antiprism. The ability of the macrocycle to complex the silver cation in its hydrophilic cavity is demonstrated.

Solution thermodynamics of geometrical isomers of pyridino calix(4)arenes and their interaction with the silver cation. The X-ray structure of a 1:1 complex of silver perchlorate and acetonitrile with 5,11,17,23-tetra-tert-butyl-[25,26,27,28-tetrakis(2- pyridylmethyl)oxy]calix(4)arene

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

The interaction of 5,11,17,23-tetra-tert-butyl [25,26,27,28-tetrakis(2-pyridylmethyl)oxy]calix(4)arene 1a with alkali-metal cations in dipolar aprotic media (acetonitrile and benzonitrile) has been investigated. 1H NMR experiments were carried out by adding to the ligand an excess amount of the appropriate metal cation (Li+, Na+, K+) in CD3CN at 298 K. Measurements were taken at different time intervals ranging from 30 min to 10 days. It was found that the kinetics of the process in this solvent is fast. Conductance measurements demonstrated that 1:1 metal cation:ligand stoichiometries are found with these cations in these solvents. Thermodynamic parameters of complexation for this ligand and alkali-metal cations in acetonitrile and in benzonitrile at 298.15 K were derived from titration microcalorimetry. Stability constants were also determined by the competitive potentiometric method using silver electrodes. Excellent agreement is found between the data derived from calorimetry and those derived by potentiometry. The highest stability is found for lithium with this ligand. The results are compared with data previously reported for systems involving a calix(4)arene ester derivative and these cations in the same solvents. The implications of stability constant data on the selective behaviour of this ligand for metal cations in these solvents are discussed. It is shown that this ligand in these solvents is able to discriminate between the smaller cations (Li+ and Na+) and the larger ones (K+ and Rb+). The sodium perchlorate complex of 1a was synthesised and the molecular structure of this complex has been determined from X-ray diffraction data. The substance crystallises in the tetragonal group P4cc with a=21.791(2), c=26.958(3) A and z=8. There are three different complexes in the lattice, two sited on fourfold axes and a third one on a twofold axis. All ligands exhibit a ‘cone’ conformation and the Na+ ion is encapsulated in their hydrophilic pockets with an acetonitrile molecule filling their hydrophobic cavities. Based on 1H NMR, conductimetric, microcalorimetric and X-ray diffraction studies final conclusions are given.

Thermodynamics of cation (alkali-metal) complexation by 5,11,17,23-tetra- tert -butyl[25,26,27,28-tetrakis(2-pyridylmethyl)oxy]- calix(4)arene and the crystal structure–superstructure of its 1:1 complex with sodium and acetonitrile

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.

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

Lupe E. Pulcha Salazar

Papers

Solution thermodynamics of geometrical isomers of pyridino calix(4)arenes and their interaction with the silver cation. The X-ray structure of a 1:1 complex of silver perchlorate and acetonitrile with 5,11,17,23-tetra-tert-butyl-[25,26,27,28-tetrakis(2- pyridylmethyl)oxy]calix(4)arene

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

Thermodynamics of cation (alkali-metal) complexation by 5,11,17,23-tetra- tert -butyl[25,26,27,28-tetrakis(2-pyridylmethyl)oxy]- calix(4)arene and the crystal structure–superstructure of its 1:1 complex with sodium and acetonitrile

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