Guest Atoms

Fig. 27. Packing relations in the crystal structure of 47 benzene (1 1) 64>. Stereo drawing of complementary stick style and space filling representations of host and guest molecules, respectively (atomic radii of the corresponding guest atoms in the space filling style are set to about half of their common van der Waals values the H atoms of the host molecules are omitted)...

These investigations focused for the first time on a new aspect of topicity that takes into account the influence of the shape of a bent structure on its reactivity. The remarkable inertness of the inner surface contrasts with the pronounced reactivity of the outer concave surface of Cjq. Almost unperturbed, atomic species or reactive molecules can be studied at ambient conditions once they are encapsulated by CgQ. Moreover, the wavefunction of the guest atom can be influenced by a permanent distortion of the Cjq cage. This was demonstrated by exohedral derivatization of N Cgo, leading to a lowering of the f symmetry, which influences the ESR spectra of the paramagnetic guest [99-103]. 

Fig. 17 The host-guest composite structure of the tll9 phase of Na shown in projection down the c-axis. The host atoms are shown in light grey and guest atoms in dark grey. The monoclinic guest component unit cell is outlined with dashed lines, and a separate perspective view of the guest structure is shown...

The brief overview of intercalation chemistry presented above shows that the subject encompasses a fascinating variety of solid state reactions between two- or three-dimensional host materials and guest atoms and molecules. Not all host material that... 

Bielinska et al. define DNCs as hybrid nanoparticles formed by the dispersion and immobilization of guest atoms or small clusters in dendritic polymer matrices. These authors describe the synthesis of 5-25 nm DNCs of Au NPs and G5-PAMAM dendrimers through UV decomposition of the PAMAM-HAuCf precursor. These nanoparticles have been imaged by in both in vitro and in vivo conditions [135]. 

It is only practical to calculate the interaction between the guest atoms and a partial cage, typically five or ten water molecules, and then apply some configurational procedure to account for the remainder,... 

Insertion electrodes — insertion electrodes the electrochemical activity of which relates to insertion processes. Insertion involves two types of materials host materials and guest materials. Host materials provide a framework (lattice) of atoms/molecules, with specific sites such octahedral, tetrahedral, trigonal, or prismatic sites. The guest atoms or ions are inserted electrochemically (by applying an electrical field) and occupy these sites. Insertion can be in most cases reversible, thus leaving most host materials invariant in their physical and chemical properties after an insertion-deinsertion cycle. 

Figure 4.50. Crystal structures of an unfilled lrSb3 skutterudite (top - Sb atoms shown in black) and Type I/Type II clathrates (bottom). In the skutterudite structure, a void is present in the center of the unit cell, surrounded by 12 Sb atoms. For the clathrate structures, tetrahedrally bound framework atoms (e.g., Ge, Sn, Si) are illustrated in blue, and guest atoms within the various cages are shown in orange and pink. Reproduced with permission from (i) Nolas, G. S. Poon, J. Kanatzidis, M. MRS Bull. 2006, 31, 199, Copyright 2006 Materials Research Society and (ii) Chem. Mater. 2000, 12, 697. Copyright 2000 American Chemical Society.

Finally, a guest atom or molecule may react directly with an exchangeable cation to give produces), including product cation(s). 

Exchangeable cations and guest atoms of the same element... 

Recent calculations predict that carbon tubules of different diameters and helicities have striking variations in electronic transport, from metallic to semiconducting (4-7). Also, such tubules ate expected to shield guest atoms from external electric and magnetic fields (8). Besides tubular structures, other low-energy configurations... 

One popular class of potentials is formed by the embedded-atom approaches.70 75 Here, the basis idea is that each atom is considered as being a guest embedded into the host formed by all the other atoms. The other atoms provide an extra electron density, into which the guest atom is placed. The energy costs related to this is described in forms of a function that depends on the electron density due to the host but at the site of the guest atom. This energy contribution is augmented with pair potentials. 

Figure 2. Successive snapshots of a cluster A47B20 in the course of time evolution. The upper left is the initial configuration, and the elapsed time are imposed for each snapshot. Guest atoms are shown by black circles, while host atoms are denoted by white circles. Gray circles indicate host atoms that are initially located in the center of the cluster. In 1 ps the cluster is in alloyed state. Gray atoms are gradually moves toward the cluster surface. On the other hand, guest atoms diffuse into the inside.

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