Encapsulated atoms

Metallofullerenes are commonly found witli [74], [76], [80] and [82] fullerene and span composites tliat have a single (Mf2 Cg2), two or even tliree metal atoms encapsulated. The first type of... 

More recently N has been encapsulated in [Rhu(N)2(CO)25] and [Rh23(N)4(CO)38]3-. The latter is the largest Rh cluster so far characterized. It consists of an irregular polyhedron of 21 Rh atoms encapsulating a pair of particularly close (257.1 pm) Rh atoms as well as 4 N atoms each of which is located in a semi octahedral site. 

Metallofullerenes will also become an important nanostructured material for future nanoscale electronic devices, because the band gaps of endohedral metallofullerenes, for example, can be varied between 1.0 and 0.2 eV depending on the fullerene size, the kind of metal atom(s) as well as the number of metal atoms encapsulated. 

The endohedral fullerenes U C28 and U C6o have been reported to be sufficiently stable to allow chemical isolation. Endohedral complexes of the smaller fullerenes (C2 , 2n < 60) are conunonly observed in molecular beam experiments (Section 4.1), but this stabilization of C28 by uranium atom encapsulation is remarkable. A theoretical study of [7i-C28]" and Td-C2iiU (25) indicate that they are stable molecules, and that the laboratory preparation of their derivatives may be viable. ... 

Peyser-Capadona and coworkers have gone further, suggesting that the CT enhancement mechanism may, in some cases, be strong enough to allow singlemolecule observation - even in the absence of an EM contribution [71]. Their claims were based on experimental measurements on clusters of only a few Ag atoms encapsulated within peptide scaffolding which are unable to support plasmon resonances due to their small size. 

We note in passing that the recent transmission electron microscopy pictures of Cgo films by Wang and Buseck show evidence of Cjo-Cgo coalescence to form cylindrical bucky tubes in the solid Film, presumably triggered by the 400-keV electron beam. We wonder if metal atom encapsulation events would occur under similar circumstances with metal-doped fullerene films. 

The Co4(CO),2 cluster, which possesses a tetrahedron of cobalt atoms encapsulated inside an icosahedron of carbonyl ligands, also displays variable-temjjerature NMR sjjectra in the solid state which are consistent with the metal cluster rotating inside a fixed cage of carbonyl ligands. That such might be the case had been predicted several years earlier. ... 

It consists of a pentagonal antiprism of nickel atoms encapsulating a germanium atom. Each nickel atom possesses one terminal and one edgebridging (along the pentagons) carbonyl. 

For xenon atoms encapsulated in the individual cavities of zeolite NaA [44], Tjn,ra is equal to infinity and relation (9) is clearly fulfilled. In general, however, when used as a probe particle, xenon will not remain at a fixed position, and so relation (11) must be applied to estimate the range over which discrimination of concentration differences of the adsorbate molecules is possible. 

The clusters [RugP(CO)i9( - 7 / -CHjCsHs)], " [Rh9P(CO)2i] - (Fig. 8b), and [RhioP(CO)22] , provide examples of P-atoms encapsulated in un-, mono-and Z /-capped square antiprismatic geometries, respectively. The replacement of phosphorus by arsenic in the cluster [RhioAs(CO)22] (Fig. 8c),I shows the capacity of the basic square antiprismatic cluster polyhedron to accommodate interstitial atoms of this size. Elongation of the interplanar Rh-Rh contacts results, however, suggesting that the increase in the steric demands of the central atom is accommodated, at least in part, by expansion of the metal polyhedron. 

Ab-initio quantum chemical calculations at the HF/3-21G level of theory were applied to consider the nature of the active sites of sodalite P-cage of the LTA type zeolite and faujasite structures. Especially, the nature of sodium, potassium and silicon atoms encapsulated within the sodalitic P-cage, and their structural and molecular parameters have been described. We have shown that up to four sodium and four potassium atoms as well as five silicon atoms could be encapsulated within the sodalite P-cage. The unique properties of these nano-size materials relate directly to the encapsulated guest atom containing fragments stabilized within the sodalite P-cage of the LTA type zeolite or faujasite structures. 

This branch of metallophosphorus chemistry has expanded particularly rapidly over the past two decades. It includes single P atoms encapsulated in cages of metal atoms (cf. metal phosphides (Sections 8.1 through 8.7), and various P groups where n = 2 to at least 8. These P groups can be chains, rings or fragments which are structurally related to the crystalline forms of the element itself The element is in fact used in many cases for the preparation of these compounds. 

Fullerenes can also form compounds with atoms encapsulated within the cage structure, termed endohedral compounds and designated M C , where the symbol signifies that the M atom is encapsulated within the C cage, e.g., U C2g, Y Cgo, Y2 Cg2, La2 Cgo, La Cg2- Fullerene aggregates are bonded by van der Waals forces (c.f. graphite) and will permit the entrapment of alkali metal ions such as Li, Na, K, Rb and Cs [87]. 

Compoimds of the ZR4 X4 type have been observed for OsR4 Br4 with R = Y, Er as well as for OsSc4 CLi and the higher symmetric ReGd4 Br4. " In all compounds, square antiprisms of R atoms, encapsulating a Re/Os atom, share common faces to chains ZR8/2, which are surrounded by and connected through halide anions, see Figure 38. These compounds have 15/16 clnster-based electrons, scaled per one Z. 

The rare-earth elements, R, may form clusters of six to eight R atoms encapsulating an endohedral transition metal atom T to compensate for the low number of valence electrons of the R atoms (only three). These heteroatomic clusters, TR,, are surrounded by halide ligands, X, to build cluster complexes, TR ... 

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