Face-sharing clusters

A fascinating variety of discrete (or occasionally polymeric) polynuclear halogeno complexes of As, Sb and Bi have recently been characterized. A detailed discussion would be inappropriate here, but structural motifs include face-shared and edge-shared distorted (MXe) octahedral units fused into cubane-like and other related clusters or cluster fragments. Examples (see also preceding paragraph) are ... 

The discovery of a cluster of six face-sharing [M6N] octahedra, shown in Figure 3.1-7, in a compound that contained 14 additional Na atoms per cluster, seemed to violate the validity of Miedema s rule, because the central atom refined perfectly as K in the X-ray structure determination. 

Figure 4.28. Schemes of octahedral cluster condensation, (a) Vertex-sharing, (b) edge-sharing and (c) face-sharing. In these examples octahedra centred by interstitial atoms are shown.

Edge-sharing and face-sharing poly-condensed clusters. Polyhedra... 

Li" ion enters the adjacent, face-sharing site. It is clear that, in these materials, Li ions do not move by means of isolated, random hops in the LISICONS there is clear evidence for clustering of lithium ions and indeed, migration may involve a process of continual reorganisation of the clusters (Bruce and Abrahams, 1991). 

The metal cluster of [Rh 11 (CO)23]3 is composed of three face-sharing octa-hedra, as shown in Fig. 19.4.1(e). The metal cluster of [Rhi2Sb(CO)27l3 consists of an icosahedron with an encapsulated Sb atom at its center. 

The absorption bands at 18,450 cm-1 and 20,300 cm-1 (fig. 4.16c) represent crystal field transitions within Ti3+ ions, and the weaker band near 12,500 cm-1 may represent a Ti3+ - Ti4+ IVCT transition between cations in face-shared octahedra. The peaks in the spectra of the yellow and blue sapphires clustered at 22,200 cm-1 and near 26,000 cm-1 represent spin-forbidden 6A, - 4AxfE G) and 6A[ — 4A2,4E(D) transitions in octahedrally coordinated Fe3+ ions (fig. 3.10), intensified by exchange interactions between adjacent Fe3+ ion pairs in the corundum structure ( 3.7.3). Other spin-forbidden Fe3+ bands occur at... 

Figure 8-11 The three face-sharing tetrahedra of Pb atoms in the Pb60(0H) + cluster. The middle tetrahedron has an O atom at its center. The end tetrahedra have OH groups.

Face sharing of two such octahedra results in the cluster Rb902 three equivalent octahedra form the cluster CS11O3. 

A study of many different iron hydroxyphosphates exhibiting clusters of face sharing FeOe octahedra of different sizes has been carried out. It turned out that all catalysts were belonging after catalytic testing to the same solid solution of the type Fe VxFe 3x(P04)3(OH)3-... 

Fig. 5. Distorted G 2 polyhedra, connected through cl face-sharing, in the Mo3S7C16 clusters of the M03S7CI4 framework (projection in an arbitrary direction)...

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