Resorcarenes structure

Cavitand 6.29 has a vase-shaped cavity that is large enough to accommodate Me2NCHO in the solid state. In solution, the most effective host is the dimethylsilyl derivative (6.28e), which has a tall, narrow cavity suitable for inclusion of linear guests such as those listed above. Compound 6.28e is prepared readily from the octol [4] resorcarene 6.3 by treatment with SiMe2Cl2. The X-ray crystal structure of the CS2 complex of 6.28e is shown in Figure 6.7, indicating clearly the neat fit of the linear... 

Work by Paul Beer et al. in Oxford on dithiocarbamate-functionalised resorcarenes has resulted in resorcarene trimers termed molecular loops and molecular tetrahedra composed of four resorcarene units. The molecular loops (pyridine-capped Cd(II) and Zn(II) complexes) can bind C60 which fits neatly into the 16.4 A wide central cavity.35 The slightly larger tetrahedral tetramer which has a 19.4 A edge length, compared to 19.1 A for the loop, is bridged by square planar copper(III) ions, a very unusual oxidation state of copper that is obtained from iodine oxidation of an intermediate copper(II) complex. The solid-state structures of examples of the loop and tetrahedron are shown in Figure 10.35. 

Figure 10.44 X-ray crystal structure of the capsular, propan-2-ol linked Ms([4] resorcarene) portion of the co-crystal of 6.3 (R = CH2CH2Ph) with C60.48...

Atwood et al. have gone on to prepare a truly enormous molecular capsule along these principles, which conforms to the geometry of a snub cube (structure (1) in Figure 10.47). Reaction of six equivalents of the octol [4] resorcarene (with either methyl or undecyl feet ) with eight water molecules results in... 

Figure 11.17 Model showing the FRET process between pyrenyl donor and perylenyl acceptor in hexameric [4]resorcarene capsules containing benzene guests (reproduced from Reference 16) along with the structure of the fluorescent guest 11.26. 

In this chapter we present an overview of chiral structures realized on the basis of calixarenes and resorcarenes.8 Clearly this cannot be an exhaustive survey, due to the enormous development calixarene chemistry has experienced during the last decade (mainly the last 5 years). Rather, it is a survey of the potential possibilities that are offered by this class of macrocyclic molecules—illustrated by selected examples of what has been done and indicating what might be done in the future. 

The three structures shown at the right of the second line represent important families of receptor molecules that have been extensively studied in their own right. The aromatic spherand grew out of crown ether chemistry while calixarene chemistry developed on a separate evolutionary pathway. Still, their similarity is apparent. The structures of calixarenes and resorcarenes (also resorcinarenes) are included here because they have often been fused to macrocycles to form complex receptor systems. A few examples of fused receptor systems are discussed below. 

The synergistic effect was only found in mixed stationary phases that have a special selectivity. Those stationary phases were CD, crown ether, liquid crystal-hne, resorcarene, calixarene, AgNOs, and others. Crown ether, CD, cahxarene, and resorcarene possess cyclic moieties with cavity-like structures that are able to form inclusion complexes with metal ions and organic molecules. Liquid crystalhne stationary phases have temperature-dependent ordered structures and the retention is governed by the solute s length-to-breadth ratio. AgNOs retards olefins by the formation of loose adducts. Together with the above special selectivity stationary phases, they have already been the focal point of sup-ramolecular chemistry. 

Calixarenes are macrocyclic molecules synthesized with high yield by condensation of appropriate arenes and aldehyde derivatives. Calix means bowF in Latin and Greek, and this phrase reflects the shape of the tetramer, which usually adopts a bowl or beaker-like conformation. Gutsche first introduced the name calixarene for this class of compounds [38]. Several authors have exhaustively reviewed the chemistry and synthetic procedures, which lead to different structural modifications of calixarenes [39-42]. In general, three types of calixarenes derivatives are known first, metacyclophanes (type 1) second, those obtained by condensation of formaldehyde with phenol (type 11), and third, those obtained by reaction with resorcinol (type III) (Scheme 6). The latter modifications are also called resorcarenes to distinguish calixarenes of type III from those of type II. 

This last example demonstrates already one of the future lines. As the chemistry of calixarenes and resorcarenes is more and more understood, these fascinating molecules lend themselves as building blocks for the construction of increasingly larger and more and more sophisticated structures. It is hoped that this fascination could be transferred at least in part to the reader. 

Figure 10.48 (a) Space-filling view of the structure of the snub cube (f) formed from six [4]resorcarenes and eight water molecules. (b) Crystal structure of the analogous pyrogaUol[4]arene hexameric capsule containing two molecules of pyrene butyric acid (reproduced with permission from [54]). 

A wider synthetic flexibility is foimd in resorcarene-based materials to stabilize Cgo within their framework. Several metal ions, in conjunction with multiple units of a dithiocarbamate-resorcarene ligand, are the starting point for resorcarene-based nanostructures. In principle, the structures can be varied by the choice of metal ions and their... 

Very recently. Beer and co-workers (325) reported the synthesis and structure of the resorcarene-based complex [Cu8(Li)4][l3]7[I].6H20 (Fig. 230), which is... 

Figure 230. Structural representations of the resorcarene-based complex [Cu8(Li)4][l3]7[I].6H20.

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