Octahedra sharing faces and vertices

An interesting structure of a quite different type is that of Cs4Mg3F1 g, in which groups of three face-sharing MgFs octahedra are linked by four of their terminal vertices to form layers (Fig. 5.40), between which Cs ions occupy positions of 10- and 11-coordination. Inasmuch as all the bonds in this crystal are presumably essentially ionic in character, the description of the structure in terms of the coordination groups around the smaller cations is not intended to imply that this is 186 

Close-packed ABX3 structures in which octahedral coordination groups share faces 

Face-sharing groups Structure Other examples 

Pairs + single Hexagonal BaTiOa CsMnFj, RbNiFs 

Infinite chains High-BaNiOs CsNiCl3, CsCuCl3 

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