Comer sharing octahedrons

Three-dimensional network with chains of V06 distorted octahedra connected pairwise by an S04 group via comer sharing A V06 octahedron has four S04 tetrahedra in the equatorial plane... 

The bromide system is similar but there is only indirect evidence for VI4 in the vapor phase. VF4 is polymeric with layers of comer-sharing tetragonally compressed VF6 moieties.1 The trihalides have the Bil3 structure in which each metal atom is at the center of a nearly perfect octahedron of halogen atoms. 

These differences may result, in part, from the higher coordination number of aluminum in AIF3. In it, each aluminum atom is surrounded by a distorted octahedron of six fluorine atoms. Each fluorine is two-coordinate, being comer-shared by pairs of octahedra. Thus, the stmcture is similar to ReOs and has a relatively open lattice. As a result, numerous sites exist for water molecules, leading to the occurrence of a wide range of nonstoichiometric and stoichiometric hydrates (AIF3 (H20) n = 1, 3, 9). Quite curiously, no hexahydrate corresponding to [Al(H20)6]Cl3 is known. 

A is absent in the layer compounds of thickness one octahedron. This layer consists of isolated (OD) and comer-sharing octahedra (ID) in the (111) and (100) cuts of... 

Although the stacking sequence of the AO3 layers in these compounds is the same as in the previous materials, in these cation-deficient phases the central octahedron of the triplet groups does not contain any B cations. Because of this the A B jOj structures can be conveniently considered to consist of layers of comer-sharing cubic perovskite sttucture-type (n-1) octahedra in thickness (Figure 3.17a-c). It is seen that on moving from one cubic perovskite layer to the next, the rows in the sheets of apex-linked octahedra are displaced or shifted laterally one relative to the other as in the stoichiometric A B Oj phases in the previous section. 

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