Clusters cubic close packed

Further effects seen with the substitution of Cl for T in the [(Zr6Z)Ii2] type are a reduction of inter-cluster I I repulsions which allows for a reduction in Zr-I inter-cluster bond lengths. The [110] section of this rhombohedral structure is shown in Fig. 5.3 and illustrates that the clusters can be described as a cubic-close-packed array, with the 3 axes running vertically through Z. Phase widths found are 0[Pg.63]

The metal nuclei of the so-called full-shell clusters, also referred to as magic number clusters, generally exhibit hexagonal or cubic close packing (ccp). Figure 6 shows the stepwise formation of the first magic-number clusters built by 13, 55, 147, and 309 atoms. 

The scheme of cluster condensation or cluster fragment condensation leads eventually to structures observed in bulk metals. Particularly through extensive condensation of tetrahedral and octahedral clusters, arrangements closely related to the hexagonal and cubic close-packed structures can be obtained. Condensation also of icosahedral five-fold symmetrical clusters may be related to crystalline and quasicrystalline metallic structures. 

For the beautiful tetracapped octahedral Os cluster, [OsioC(CO)24]2- with an interstitial C atom in the octahedral core, shown in Figure 3.10, the predicted eve count is 14(6) + 2 + 4(12) = 134, which agrees with that of the observed stoichiometry. It s a little bit harder to count the sep but give it a try. Each tetrahedral cap consists of an Os(CO)3 fragment and the other six fragments are Os(CO)2 so we have (4x2 + 6x0 + 4 + 2)/2 = 7 appropriate for an octahedron. If you look ahead in Chapter 6 (Exercise 6.1), you will find that this trigonal bipyramidal ten-atom core can be excised from a cubic close-packed metal lattice (ABC layers). [OsioC(CO)24]2- can be considered a nano-sized metal particle stabilized by the ligands in the same manner as Ni atoms are stabilized when removed from Ni metal by CO as Ni(CO)4 in the Mond process. 

Figure 15 (a) Molecular structure of Al7 N(SiMe3)2 le (methyl groups omitted) (b) view showing the relationship of the AI7 cluster to the cubic close packing in Al metal. (Reprinted from Ref 59. 2002, with permission from Elsevier)... 

Figure 13-27 There are two crystal structures in which atoms are packed together as compactly as possible. The diagrams show the structures expanded to clarify the difference between them, (a) In the hexagonal close-packed structure, the first and third layers are oriented in the same direction, so that each atom in the third layer (A) Ues directly above an atom in the first layer A), (b) In the cubic close-packed structure, the first and third layers are oriented in opposite directions, so that no atom in the third layer (C) is directly above an atom in either of the first two layers A and B). In both cases, every atom is surrounded by 12 other atoms if the strucmre is extended indefinitely, so each atom has a coordination number of 12. Although it is not obvious from this figure, the cubic close-packed structure is face-centered cubic. To see this, we would have to include additional atoms and tilt the resulting cluster of atoms.

Crystallographic studies of [PtCu2(CCPh)4] show this compound can adopt at least three polymorphs. The most singular of these comprises a near linear trimer of trans-Pt2Cu4 octahedra with inter-octahedral Pt Pt distances of 300 pm. The emission spectra are different for each polymorph and are concentration dependent in solution.281 EXAFS shows that [Pt30903oL36] (L = sulfonated phen) has cubic close packed Pt with a 1% contraction in the cluster compared to the pure metal.282... 

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