Face-centered octahedral geometries

Thus far, dimensional reduction has not been applied in this way to any of the other parent solids listed in Table I. Of particular interest are systems that straddle the divide between the edge-bridged and face-centered octahedral geometries. Will reduced niobium-molybdenum halide mixtures simply disproportionate or will they lead to new mixed-metal clusters If the latter, then where does the crossover in cluster geometries occur An important factor in applying dimensional reduction is recognizing the variability in the stable electron counts within a particular cluster system. An extreme case occurs... 

For r lower than 0.59 simple structures, such as face-centered cubic (fee), hexagonal close-packed (hep), and simple hexagonal (hex), are predicted. Nonmetal ions are placed in the interstitial sites of octahedral or cubic prismatic geometry. For r larger than 0.59 the metallic arrangement becomes distorted and more complex structures are formed (Fig. 5.1). 

Figure 12.2 shows two types of holes, or vacancies, in a face-centered cubic unit cell where the smaller types of ions in an ionic solid might fit As shown in Figure 12.2(a), the vacancy in the exact body center of a face-centered cubic unit cell has an octahedral coordination geometry with six equidistant nearest neighbors. Therefore, this type of hole is called an octahedral hole or o-hole. The diagram in the... 

Octahedral geometry the geometry of a molecule in which six atoms occupy the vertices of a regular octahedron (a figure with eight faces and six vertices) with the central atom at the center of the octahedron. (10.1)... 

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