Capped octahedron geometry

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... 

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. 

Fig. 8.4. Coordination geometries for seven- and eight-coordination (a) pentagonal bipyramid, (b) capped trigonal prism, (c) capped octahedron, (d) cube, (e) square antiprism and (/) triangulated dodecahedron. Central atom-ligand bonds are shown by full lines dashed lines indicate the edges of the polyhedral figure.

When the number of metal atoms in a cluster increases, the geometries of the clusters become more complex, and some are often structurally better described in terms of capped or decapped polyhedra and condensed polyhedra. For example, the first and second clusters listed in Table 19.4.3 are a capped octahedron and a bicapped octahedron, respectively. Consequently, capping or decapping with a transition-metal fragment to a deltapolyhedral cluster leads to an increase or decrease in the cluster valence electron count of 12. When a transition-metal atom caps a triangular face of the cluster, it forms three M-M bonds with the vertex atoms, so according to the 18-electron rule, the cluster needs an additional 18 - 6 = 12 electrons. The parent octahedron of [Os6(CO)is]2- has g = 86, the monocapped octahedron Osy(CO)2i has g = 98, and the bicapped octahedron [Oss(CO)22]2- hasg = 110. 

Figure 1-3 The three important geometries for seven coordination (a) Pentagonal bipyramid ( >5A) (b) Capped octahedron (C3 ) (c)...

Routes to homoleptic isocyanide complexes have been defined in thf (Scheme 46).616 [M L7]+ (L = xylyl isocyanide) are fluxional in solution but do not exchange ligand with free L. The cation in [ML7][BF4] is very crowded with the shortest Me- -Me contact being 4.59 A. The TaC7 core has a geometry intermediate between the capped octahedron (Cjv) and capped trigonal prism (C2v). 

The rearrangement which retains a mirror plane passes a geometry which is close to, but not identical to, the capped octahedron. This pathway can be separated into 2 separate sections,... 

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