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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 AB8 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.

Cubic PictureCubic Picture

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.
Cubic Picture Cubic Picture Cubic Picture

 

CsCl
La(bpyO2)4+

 

 

-Square Antiprismatic AB8 square antiprismatic

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

 

Square Antiprismatic Picture Square Antiprismatic Picture

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 Picture Square Antiprismatic Picture Square Antiprismatic Picture

 

Zr(ox)4

Picture with the antiprism

 

-Dodecahedral AB8 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 ....

Dodecahedral PictureDodecahedral Picture

Dodecahedral PictureDodecahedral Picture

Dodecahedral Picturedodecahedron

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.
Dodecahedral Picture Dodecahedral Picture Dodecahedral Picture
[Mo(CN)8]3-

Picture with the dodecahedron

 

©2005 Paul Kiprof, All Rights Reserved
Comments: pkiprof@d.umn.edu
Updated: December 2005