Molecular hosts calixarene

Calixarenes, which are macrocyclic compounds, are one of the best building blocks to design molecular hosts in supramolecular chemistry [158]. Synthesis of calix[4]arenes, which have been adamantylated, has been reported [105, 109]. In calix[4]arenes, adamantane or its ester/carboxylic acid derivatives were introduced as substituents (Fig. 29). The purpose of this synthesis was to learn how to employ the flexible chemistry of adamantane in order to construct different kinds of molecular hosts. The X-ray structure analysis of p-(l-adamantyl)thiacalix[4]arene [109] demonstrated that it contained four CHCI3 molecules, one of which was located inside the host molecule cavity, and the host molecule assumed the cone-like conformational shape (Fig. 30). 

The network structures to be discussed will all involved hydrogen bonding as the supramolecular synthon. It should be noted however that other interactions such as coordinate bonds and host-guest interactions may also organise host molecules into network structures. Coordination polymers constructed from molecular hosts may involve functionalised calixarenes [8-11], cyclotriveratrylene [12], or cucurbituril [13]. Calixarenes have also been used to build up network structures via host-guest interactions [14,15]. It is also notable that volatile species may be trapped within the solid state lattice of calix[4] arene with a structure entirely composed of van der Waals interactions [16]. 

Keywords CP/MAS Host-guest chemistry Molecular motion Calixarenes Cyclodextrins Cyclophosphazenes Fullerenes Solid-state NMR... 

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... 

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. 

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. 

C. A. Schalley, R, K. Castellano, M. S. Brody, D. M. Rudkevich, G. Siuzdak, J. Rebek, Jr, Investigating Molecular Recognition by Mass Spectrometry Characterization of Calixarene-Based Self-Assembling Capsule Hosts with Charged Guests , J. Am. Chern Soc, 1999, 121, 4568-4579. 

Cavilaics include crown rnacroring inclusion compounds (coronates), cryptates, podates. cytlophane host inclusion compnunds. calixarene inclusion compounds, cyclodextrin and amylose inclusion compounds, cucurbituril inclusion compounds, molecular deft inclusion compounds, and anionic guest inclusion compounds. 

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