Cages, encapsulating

The final section of the volume contains three complementary review articles on carbon nanoparticles. The first by Y. Saito reviews the state of knowledge about carbon cages encapsulating metal and carbide phases. The structure of onion-like graphite particles, the spherical analog of the cylindrical carbon nanotubes, is reviewed by D. Ugarte, the dominant researcher in this area. The volume concludes with a review of metal-coated fullerenes by T. P. Martin and co-workers, who pioneered studies on this topic. 

Fullerenes can encapsulate various atoms within the cages, and these compounds have been referred to as endohedral fullerenes. For example, the symbolic representations La C6o and La2 Cso indicate that the fullerene cage encapsulates one and two lanthanum atom(s), respectively. The IUPAC description refers to these fullerenes species as incar-fullerenes, and the formulas are written as t LaCeo and tl Cso, (i is derived from incarcerane). Some metal endohedral fullerenes are listed in Table 14.2.1. The endohedral fullerenes are expected to have interesting and potentially very useful bulk properties as well as a fascinating chemistry. Some non-metallic elements, such as N, P, and noble gases, can be incarcerated into fullerenes to form N 0,0, P C6o, N C o, Sc3N C80, Ar Oo, etc. 

Zuo, T.M., Olmstead, M.M., Beavers, C.M. etal. (2008) Preparation and structural characterization of the 7h and the Dsh isomers of the endohedral fullerenes TmsNOCgo icosahedral Cgo cage encapsulation of a trimetallic nitride magnetic cluster with three uncoupled Tm + ions. Inorganic Chemistry, 47, 5234-5244. 

In this context, [Ga4Lg] coordination cage was used for encapsulation and stabilization of aromatic diazonium cations and tropylium cations (Fig. 9.7) [19], The results indicated that only 4-(diethylamino) benzenediazonium cation, 1, and aromatic tropylium cation, 4, could be encapsulated within a [Ga4L5] coordination cage. Encapsulation protected reactive cations and resulted in deceleration of their decomposition [19]. 

As encapsulation of the guest depends on shape and size, tetrahedral lacton, which can better fit the cavity of the coordination cage, encapsulated and stabilized more than quinone. This can shift the equilibrium of two forms toward lactonization and disappearance of pink color. In this way, cavity-directed (and not pH-dependent) chromism can be obtained. Therefore, phthalein dyes remain colorless, even in a basic solution. Upon release of phthalein dyes by the addition of a competitive guest, the pink color will be recovered. The authors believed that this procedure could be used to control the responsiveness of target compounds to external stimuli without any chemical modification [46]. 

Campanera, J. M., Bo, C., 8c Poblet, 1. M. (2005). General rule for the stabilization of fullerene cages encapsulating trimetallic nitride templates. Angewandte Chemie-International Edition, 44(44), 7230-7233. 

The classification of caging (encapsulating) Ugands (capsules) used here is based on the nature of chemical bonds between the ligand syntones and the nature of these syntones belonging to different classes of organic and coordination compounds and supramolecular systems as well. 

Chand DK, Biradha K, Eujita M (2001) Self-assembly of a novel macrotricyclic Pd(II) mettillo-cage encapsulating a nitrate ion. Chem Commun 1652-1653... 

Custelcean and Wu groups independently reported tripodal tris(3-pyridylurea) receptor 38e, which assembled with metal sulfate salts MSO4 (M = Mn, Zn, Co, Mg, etc.) to afford supramolecular cages encapsulating S04 anion via multiple H-bonds in a 3D structure held by second-sphere coordination (Fig. 5.30) [82, 83]. 

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