Cuboctahedra

Figure 4. TEM images of the (a) Pt cubes, (b) Pt cuboctahedra, and (c) Pt octahedra. Inset images are corresponding HRTEM images and ideal structural models [15]. (Reprinted from Ref. [15], 2005, with permission from American Chemical Society.)...

Pt cuboctahedra and octahedra were also deposited on the silica substrate in an identical manner. These 2D model catalysts have the attributes of tunable particle density and the deposition of the different particles changes the relative ratio of exposed [100] and [11 1] surfaces. 

The shape-controlled nanoparticles were incorporated into the silica framework by NE by the procedure outlined in Scheme 2. These catalysts are denoted as Pt(X )/SBA-15-NE where X = cubes, cuboctahedra, and octahedra. 

As an additional point, the f-factors calculated for the four sites of Aujj [25], as well as those for several smaller and larger magic-number and non-magic number cuboctahedra, for most of which no real examples of gold cluster compounds exist, exhibit a linear dependence on the coordination number of each site. Several of these are shown in Fig. 5. Thus, the coordination numbers of... 

Stang, P. J., Olenyuk, B., Whiteford, J. A., Fechtenkotter, A., Self-assembly of nanoscale cuboctahedra by coordination chemistry. Nature 1999, 398, 796-799. 

In total, many different container molecules of various shapes like tetrahedra, octahedra, cubes, triangular bipyramids, dodecahedra, icosahedra, cuboctahedra or various shaped prisms or antiprisms have been described in the literature up to now [6-10]. Altogether they are far too many to be described in detail. Therefore this chapter focuses only on container molecules based on imine type ligands. 

Icosahedra and cuboctahedra are closely related. There is still no satisfactory answer to the question, why M33 clusters are built up icosahedrally in one case and cuboctahed-rally in another case. Possibly the type of ligand or packing effects in the crystal lattice are decisive. The structures, shown in Fig. 8 are all known from the solid state. 

Related structures are found in MB12 borides (M = Sc, Ni, Y, Zr, Hf, W) having B 2 cuboctahedra (5-1) and metal atoms in cubic lattices of the NaCl type. 

Figure 3.22. A zeolite is constructed from linked cuboctahedra, which in turn, are constructed from four-membered squares of tetrahedra.

Before turning to the SFG spectra of adsorbed CO, it is worthwhile to examine the statistics of surface metal atoms (22) by which is meant the exact particle surface structure that eventually governs the particle properties. Figures 21a and b show truncated (perfect) cuboctahedra of the same size (6.2 nm) but with different aspect (height/diameter) ratios, both exhibiting a (1 1 1) top facet, and (111) and (100)... 

Fig. 21. Schematic models of truncated cuboctahedra of various sizes and aspect ratios, exhibiting a (111) top facet and (1 1 1) and (100) side facets. According to HRTEM images of palladium nanoparticles, the terraces may be incomplete, leading to surface facets with steps. For structural characteristics, see Table II.

This preparation is unusual as one would expect PVP to selectively bind to less stable crystal faces of single crystals of silver, such as the 100 face, to generate nanocubes. Indeed, in this reaction silver nanocubes are the initial product as expected, but by continuing the reaction, after nanocubes have already formed, further growth leads to cuboctahedra, truncated octahedra and then finally to octahedra, see Figure 11.36. It is quite uncertain why the growth anisotropy switches in this manner. 

Figure 11.36 By extending the polyol reaction for a ven time period, various polyhedral shapes capped with 100 and 111 faces can be obtained in high yield, a) A schematic of the nucleation and growth process, in which silver continuously deposits onto the 100 faces to eventually result in a completely 111 -bound octahedron, b to f) SEM images of cubes, truncated cubes, cuboctahedra, truncated octahedra, and octahedra, respectively (scale bar 100 nm). Reproduced with permission from reference [91]. (2006) Wiley-VCH Verlag GmbH Co. KGaA.

FIGURE 7-25 An Example of an Aluminosilicate Structure, Illustrated is the space-filling arrangement of truncated octahedra, cubes, and truncated cuboctahedra. (Reproduced with permission from A. F. Wells, Structural Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, 1975, p. 1039.)... 

FIGURE 22.1 The ABO3 perovskite structure (a) AO12 cuboctahedra, (b) BO octahedra. 

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