Calixarenes solid-state inclusion compounds

A Versatile Class of Macrocyclic Compounds, J. Vicens, V. Bohmer, Eds., Kluwer, Dordrecht, 1991, p. 65 G. D. Andreetti, F. Ugozzoli, Inclusion Properties and Host-Guest Interactions of Calixarenes in the Solid State, ibid., p. 87. 

The complex was characterized by thermogravimetric analysis (TGA) and solid state NMR. Low temperature X-ray crystal structure analysis of the compound indicated the inclusion of CS2 in the calixarene cavity to be highly symmetrically oriented directly on the C4 axis of the host. The CP/MAS experiment showed significant complexation-induced chemical shift (CIS=... 

The calixarenes have a flexible or rigid cavity, resp., which can be shaped to some extent. Some inclusion compounds in the solid state have bren described, but the low solubility in water did not allow applications in respect to an enzyme mimick as yet. Host/guest interactions in solution according to studies of Gutsche et al. seem to occur in some cases, but are weak. Shinkai and coworkers seem recently to have overcome parts of these problems by incorporation of sulfonic add groups in this skeleton (72 and 73). 

In these solid inclusion componnds, the association of host and guest components is strictly a solid state phenomenon, and the examples covered in this chapter focns almost entirely on solid inclnsion componnds of this type. However, it is relevant to note that there is also another class of inclnsion compound in which the host is a molecnle containing an appropriate cavity or binding site that can inclnde gnest molecules. Such molecular host-guest complexes generally exist as associated entities both in the solntion state and in the crystalline state, and thns the incln-sion phenomenon is not exclusively a property of the solid state. Examples of host molecules of this type are crown ethers, cyclodextrins, cryptands, and calixarenes. 

Solid state investigations are of great importance in particular in case of studying calixarene and calix-type compounds due to their great ability to form molecular inclusion complexes, co-crystals and supramolecular assemblies. In CSD (Cambridge Structural Database [1]) over 6000 structures of calix-type compounds are deposited so far. Approximately one-third of the entries are organometallic compounds and two-thirds are classified as organic compounds. 

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... 

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