Calixarenes molecular complexation

Stibor, I. and Lhotak, P. Calixarenes and their Analogues molecular complexation , in Encyclopedia of Supramolecular Chemistry, Atwood, J. L., Steed, J. W., eds. Marcel Dekker New York, 2004 vol. 1, pp. 628-635. 

Selective functionalization of calixarenes is of central importance for the construction of compounds to serve in various capacities such as polyfunctional ion binders, molecular complexing agents, and enzyme mimics. Many examples of selective functionalization have already been included in the preceding sections, and only a few additional ones are presented in this section as representative of the present state of the art. 

Syntheses, Structures and Interactions of Heterocalixarenes written by S. Kumar, D. Paul and H. Singh (Guru Nanak Dev University, India) describes the recent significant progress in our understanding of heterocyclic derivatives of calixarenes and in particular their role as receptors in molecular complexes. 

For a time one managed by choosing new descriptions and used intricate contractions and modifications of the available terms Some examples being clathrate complex, clathrate hydrate, hydrocarbon clathrate, gas hydrate, interlamellar sorbent, molecular compoimd, addition compound, loose addition complex, cascade complex, lock-and-key complex, super molecular complex, molecular complex associate, tweezer molecule complex, soccer molecule complex, hexapus molecule complex, octopus molecule complex as well as complexes or inclusion compounds of spherands, sepulchrands, coronands, cyclidenes, cryptands, cryptophanes, calixarenes, cucurbit-uril, annelides etc. 

This entry deals with various facets of molecular complexation by calixarenes. Most studies published on this subject are connected with cone conformation of calixar-ene skeleton. 

No conclusion can adequately summarize the developments in the topic of this article. Host-guest chemistry is still in its infancy as a typical multidisciplinary subject. The progress in all basic disciplines will immediately provoke progress in the level of our knowledge on molecular complex formation by calixarenes. The synthesis of many new ligands and their thorough study will definitely be required to better understand the multifaceted problem of molecular recognition and complex formation. 

Calixarenes and Their Analogues Molecular Complex- ation, p. 145... 

The simultaneous binding of cations and neutral molecules can be achieved by different types of molecular hosts or assemblies. Traditional host molecules such as crown ethers and calixarenes can complex both a cation and neutral molecule within different receptor sites. Metallohosts, where a metal cation is an intrinsic part of the host assembly, can complex neutral molecules within... 

It took 8 years to publish another structure. In 1976 K. J. Palmer et al. reported two conformers of another resorcin[4] arene derivative, i.e. cis- and trans-C-para-bromophenyl-4,6,10,12,16,18,22,24-0-octaacetylcalix[4]resorcinarene [3]. Than in next 3 years G. D. Andreetti et al. published the first crystal structure of inclusion compound formed by para-ferf-butylcalix[4] arene with toluene [4]. The calixarene molecule was found in cone conformation and the guest molecule could not be located within the host cavity due to its disorder (the molecular complex was located on a crystallographic fourfold axis). The Authors also noticed that the structure undergoes the order-disorder phase transition at 248 K. In 1996 the disorder high temperature phase was resolved with the aid of solid-state NMR data by E. B. Brouwer et al. [5] (unfortunately, the atoms coordinates are not deposited in CSD) and in 1998 the low temperature ordered phase was reported by A. Arduini et al. [6] (Fig. 38.2). The inclusion complex is stabilized by week interaction. The crystal and molecular structure of this... 

In a study of mixed monolayers of C60 and p-iert-butylcalix[8]arene, different isotherm behavior was obtained [256]. The surface pressure was observed to rise at a lower molecular area (1.00 nm molecule vs. 2.30 mn molecule in the prior study). Similar isotherms were observed whether a 1 1 mixture or a solution prepared by dissolving the preformed 1 1 complex was spread. The UV spectra of the transferred LB films appeared different than that of bulk C60. It was concluded that a stable 1 1 complex could be formed by spreading the solution either of the mixture or of the complex. This was confirmed in a later study by the same group that included separate spreading of the calixarene and the C60... 

Heteroaryl groups are present in the 4-pyridyl-ethynyl compounds81,99,100 and their extended variants with C=C-C6H4-C=C-pyr-4 ligands.81,99 These compounds can be quaternized with Mel or coordinated to a metal complex at their terminal pyridyl functions to give species addressed as molecular rods or molecular wires.81,99 Similar reactions were carried out with 3-phenanthrolinyl-ethynyl complexes,62 and special examples are also known with R based on calixarenes.51... 

Metalated container molecules can be viewed as a class of compounds that have one or more active metal coordination sites anchored within or next to a molecular cavity (Fig. 2). A range of host systems is capable of forming such structures. The majority of these compounds represent macrocyclic molecules and steri-cally demanding tripod ligands, as for instance calixarenes (42), cyclodextrins (43,44), and trispyrazolylborates (45-48), respectively. In the following, selected types of metalated container molecules and their properties are briefly discussed and where appropriate the foundation papers from relevant earlier work are included. Porphyrin-based hosts and coordination cages with encapsulated metal complexes have been reviewed previously (49-53) and, therefore, only the most recent examples will be described. Thereafter, our work in this field is reported. 

Recently, it has been found that the outcome of some cycloadditions can be altered remarkably when performed inside the cavity of cyclodextrins (288), self-assembled molecular capsules (289), or coordination cages (290). This fact intrigued us greatly and stimulated our interest in the Diels-Alder reactivity of the calixarene-like [M2(L19)(L )]+ complexes bearing unsaturated carboxylate coligands L (215). 

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