Other Cage Structures

Foremost among the elements that pack in icosahedral (and other Ar-chimedeans) structures is boron, its various hydrides (boranes), and related boron compounds (25 pp. 157-185). This topic, which is covered by numerous reviews and books, will not be further discussed in this chapter. Many other cage structures have been discussed in the literature, some of them are briefly discussed in (26). 

Li-Barbier reactions were studied [25] for several other cage-structure bromides with adamantone, another highly sterically hindered reactant, as the carbonyl compound. 

By extending this study to other cage-structured radicals, it was demonstrated that the radical pathway (4) is in competition with the organometallic pathway (3), and that one of the factors that regulate this competition is the stability of the radical. 

Intramolecular carbene cycloadditions have been used in syntheses of prostanoids, diterpenoids, and other caged structures. Although unlikely to be of great synthetic use, the pyrolyses of the sodium salts of the lactone tosylhydrazones (89) give cyclopropane products via the oxycarbene intermediates as reported in preliminary form last year. ... 

In other related studies,186 we determined the structures of mixed water-methanol clusters the intensity distributions of (H20)n(CH30H)JBH+ showed magic numbers at n + m = 21, 0 < m 8 due to the enhanced stabilities of the dodecahedral cage structures in the mixed clusters. Studies of the metastable dissociation of (H20)B(CH30H)mH+ (n + m < 40) provided evidence that the dissociation channels... 

Two approaches have been used in the synthesis of these types of compounds. Small boron-phosphorus ring compounds can serve as building blocks, and addition and elimination reactions with other main group elements can then extend the cage structure (see Schemes 23 and 24, Section 12.12.6.4.5). Alternatively, an unsaturated carbenoid fragment can be added to the bicyclic fragment as illustrated in Scheme 31 <1998IC490>. 

One difficulty with many synthetic preparations of semiconductor NCs that complicates any interpretation of NMR results is the inevitable distribution of sizes (and exact shapes or surface morphologies). Therefore attempts to make semiconductors as a sort of molecular cluster having a well-defined stoichiometry are of interest to learn potentially about size-dependent NMR parameters and other properties. One approach is to confine the semiconductor inside a template, for instance the cuboctahedral cages of the sodalite framework or other zeolite structures, which have been characterized by multinuclear NMR methods [345-347], including the mesoporous channel material MCM-41 [341, 348]. 

Severin and coworkers reported (146) the reaction of tris(2-aminoethyl)amine and 4-formylphenylboronic acid with penta-erythritol to give, via multicomponent assembly, the boronic acid based macrobicyclic cage 35 (Fig. 25). The cage has the form of an ellipsoid with a diameter of 20.5 A and binds two Cud) ions in a fashion similar to the smaller tren-based cryptands. The reversible formation of boronic esters has also been employed to build other hollow structures such as nanotubes (147) and porous covalent organic frameworks (148,149). 

It is convenient to visualize zeolites in terms of secondary building units (SBUs). Several of the SBUs currently recognized by the IZA are depicted in Fig. 3 along with other useful structural units, the sodalite and pentasil cages. The sodalite unit is... 

The structure of UCSB-6 viewed along the 010 direction shown in Fig. 20 is based on a composition Co26Ga26P480192. This 3D channel system has two types of cages where one cage has five 12-MR structures (8 A) and the other cage has three 12-MR structures. The UCSB-6 structure is synthesized using 1,7-diamino-heptane as the template. 

It is to be acknowledged that this species and other cage (bicyclic) peroxides have planar bridgehead nitrogen atoms, J. T. Edward, F. L. Chubb, D. E. Gilson, R. C. Hynes, R. Sauiiol and A. Wiesenthal, Can. J. Chem., 77, 1057 (1999). This structural feature was not incorporated into our thermochemical analysis. 

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