Octahedra capped

Figure 55 Stereochemistries corresponding to the locations marked on the upper left-hand side of Figure 54. (P) Pentagonal bipyramids (O) capped octahedra (T) capped trigonal prisms...

Figure 58 Projection of the potential energy surface for [M(unidentate A)6(unidentate B)] on to the 4>B (t>c plane (in degrees) with retention of a mirror plane. The five faint contour lines are for successive 0.02 increments in X above the minima, and the five heavy contour lines are for successive 0.2 increments above the minima, at O. R = 0.1. The locations of the pentagonal bipyramid (P ), and capped octahedra (O) are indicated...

A close approximation to a capped trigonal prism is observed for [Mo(CNBn)7](PF6)2- However, the closely related compounds [Cr(CNBu)7](PF6)2, [Mo(CNPh)7](PF6)2, [Mo(CNMe)7](BF4)2, and [W(CNBn)7](W60i9) lie further towards capped octahedra than capped trigonal prisms. Solutions of [Mo(CNBu)7] + yield only a single NMR signal even down to — 135°C, confirming the expected stereochemical nonrigidity. ... 

Alternatively, one might explore close-packed structures of boranes. Consider, for example, the difference between deltahedral and tetra-capped octahedral BioHio structures (Fig. 4). The former is stable as the dianion (11 cluster pairs) while, based on Extended Htickel calculations (60), the latter is slightly more stable for the +6 cation (7 cluster pairs). The capping principle predicts 7 cluster pairs for capped octahedra (61). A structurally characterized transition metal analogue of the tetra-... 

In the families of heptanuclear clusters, two geometries are found the capped octahedron that is typical for 98-valence electrons, and the vertex-sharing open tetrahedral (butterfly) stmctures typical for 106-valence electrons. An example of the former is Osy(CO)22 (51) an example of the latter is [H2AuOsg(CO)2Q] (52). In the AuOs cluster anion, the gold atom is at the vertex-sharing position. 

Figure 25.11 Metal frameworks of some high-nuclearity binary carbonyl and carbonylate clusters of osmium (a) Os5(CO)i6 (trigonal bipyramid) (b) Os6(CO)ig (bicapped tetrahedron, or capped trigonal bipyramid) (c) [Os6(CO)ig] (octahedron) (d) Os7(CO)2i (capped octahedron) (e) [Osg(CO)22] (bicapped octahedron) (f) [Osi7(CO)36] (3 shaded atoms cap an Osu trigonal bipyramid).

Figure 9.23 The three lowest energy arrangements for seven points on the surface of a sphere assuming a I Ir6 repulsion law (a) the capped octahedron, (b) the capped trigonal prism, and (c) the pentagonal bi pyramid.

Capped argon stirring (CAS), 23 264 Capped octahedron, geometry for metal coordination numbers, 7 574, 575t Capped square antiprismatic, geometry for metal coordination numbers, 7 574, 575t... 

Let US consider the repulsive force model. The repulsive force is proportional to the inverse power n) of the distance (r) force l/r . Based on this consideration alone the pentagonal bipyramidal structure seems to be more stable for small values of n, the capped trigonal prism for intermediate values and the capped octahedron for large values of n, upto the limit of hard-sphere model. It is obvious, however, that such analysis cannot be applied for systems where all the hgands are not equal, i. e. MX Y 7- , and the ligands X and Y are very different from each other. 

He, F.-C., Liu, L.-B., and Li, X.-V. (1990). Molecular models constructed in an easy way. Part 1. Models of tetrahedron, trigonal bipyramid, octahedron, pentagonal bipyramid and capped octahedron, y. Chem. Educ. 67,556—558. 

TaCl4(PMe3)3] X-Ray structure, capped octahedron (C symmetry) 2... 

Relations between the pentagonal bipyramid, capped octahedron and capped trigonal prism - 71... 

The stereochemistry at each of these locations is shown in Figure 55. It can be seen that the capped octahedron can be considered as an intermediate between the pentagonal bipyramid and the capped trigonal prism, but it is much closer in energy and stereochemistry to the latter. 

In the calcium polyiodide compound [Ca(H2O)7](I10) the stereochemistry appears to be intermediate between a capped octahedron and a pentagonal bipyramid, whereas [Sr(H20)7](I12) and [Ca(H20)7]2[CdgCl16(H20)2]-H20 contain capped trigonal prismatic cations.246 247... 

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