Encapsulated Clusters

For many clusters, the number of valence electrons may be increased as a result of formation of encapsulated compounds containing H, C, N, P, Sb, and S in the interstices between metal atoms (Table 3.12). Recently electron poor clusters containing encapsulated metal atoms such as K and Be and atoms of other elements of the second 

Encapsulated clusters are also significant for the development of the theory of chemical bonds. 

Theories of interstitial compounds assumed either electron shifting from the conductivity band of metals to the nonmetal atom and negative ion formation, or valence electron transfer of the encapsulated atom to the conductivity band leading to positive ion formation. In this case the encapsulated phase is considered as an alloy therefore, metallic properties are retained. Both theories explain some experimental data, such as the decrease of conductivity of encapsulated compounds. 

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Transition-metal nanopartides are of fundamental interest and technological importance because of their applications to catalysis [22,104-107]. Synthetic routes to metal nanopartides include evaporation and condensation, and chemical or electrochemical reduction of metal salts in the presence of stabilizers [104,105,108-110]. The purpose of the stabilizers, which include polymers, ligands, and surfactants, is to control particle size and prevent agglomeration. However, stabilizers also passivate cluster surfaces. For some applications, such as catalysis, it is desirable to prepare small, stable, but not-fully-passivated, particles so that substrates can access the encapsulated clusters. Another promising method for preparing clusters and colloids involves the use of templates, such as reverse micelles [111,112] and porous membranes [106,113,114]. However, even this approach results in at least partial passivation and mass transfer limitations unless the template is removed. Unfortunately, removal of the template may re-... 

The cationic amphiphile RfN + groups induced the self-assembly of the surfactant-encapsulated clusters (RfN + groups capped on Wio0324-) that, during membrane... 

The Sc3N unit s remaining six valence electrons are transferred from the encapsulated cluster to the C80 cage to give a hexa-anion. 

Reactions between azomethine ylides and TNT EMFs have also been reported, and the effect of the size of the encapsulated clusters on the reactivity and selectivity of the cage carbons was observed. Addition of N-ethyl azomethine ylide to Y3N Cso affords exclusively... 

Cai, T., Xu, L., Gibson, H.W. etcd. (2007) Sc3N Cv8 encapsulated cluster regiocontrol of adduct docking on an elUpsoidal metallofullerene sphere. Journal of the American Chemical Society, 129, 10795—10800. lezzi, E.B., Eiuchamp, J.C., Harich, K. etal. (2002) A symmetric derivative of the trimetallic nitride endohedral metallofullerene, SciN Cgo. Journal of the American Chemical Society, 124, 524-525. 

Campanera et al. 2005, 2006 Osuna et al. 2008). Many recent experimental and theoretical studies show that not only the chemical reactivity but also the regioselectivity of TNT EMFs is strongly affected by the encapsulated cluster, metal species, carbon cage size, and symmetry (Akasaka and Nagase 2002 Thilgen and Diederich 2006 Martin 2006 Cardona et al. 2005a liduka et al. 2005). 

Nitride-encapsulated clusters are obtained from compounds containing coordinated NO, Nf, or NCO molecules or ions ... 

Both Br and C1 MAS NMR have been used in the investigation of sodium, silver and halo-sodalite semiconductor supralattices. Useful information is available on the environments of the encapsulated clusters within the sodalite lattice. The Na4X (X = Cl, Br) tetrahedra provide a symmetric environment around the halide and give rise to narrow resonances for specific locations. The spectra are sensitive to the distribution of anion empty cavities or to T containing cavities. 

The literature contains a number of examples of catalysis on active sites qualified as framework defects, for example, on open or uncoordinated carboxyUc acids. The authors cited above [93], who smdied the alkylation reaction in the presence of MOF-5, attribute the catalytic activity to encapsulated clusters of zinc hydroxide, which are formed as an impurity in the rapid synthetic routes, and may also be present in a partially hydrolyzed form of the framework structure, [Zii3(OH)2(bdc)2] [108,109]. 

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