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Coordination Number 8

For eight-coordination, there are 3 main structure types, two of which are preferred for molecules. The Cubic structure, the Square Antiprism andthe Dodecahedron.

-Cubic

The cubic coordination is is observed for ionic compounds because of steric reasons, it is not realized for molecular structures. A prime example is the structure of CsCl.

Here are some different views of the same structure. In the first model, you see the structure with just the bonds that exist between the central atom and the ligand atoms.	The second structure shows the bonds and the connections (which are usually not bonds) between the ligand atoms.	The third picture shows the structure without the bonds but with the connections between the ligand atoms showing the polyhedron formed by the ligand atoms.

-Square Antiprismatic

The square antiprism can be derived from a cube by trurning one of the faces with respect to the opposite face.

Here are some different views of the same structure. In the first model, you see the structure with just the bonds that exist between the central atom and the ligand atoms.	The second structure shows the bonds and the connections (which are usually not bonds) between the ligand atoms.	The third picture shows the structure without the bonds but with the connections between the ligand atoms showing the polyhedron formed by the ligand atoms.

Zr(ox)4	Picture with the antiprism

-Dodecahedral

There are several ways to construct a dodecahedron. One method empoys two trapezoids that are perpendicular to each other in space. The other possibility is to imagine the polyhedron composed of two ....

Here are some different views of the same structure. In the first model, you see the structure with just the bonds that exist between the central atom and the ligand atoms.	The second structure shows the bonds and the connections (which are usually not bonds) between the ligand atoms.	The third picture shows the structure without the bonds but with the connections between the ligand atoms showing the polyhedron formed by the ligand atoms.

[Mo(CN)8]3-	Picture with the dodecahedron