Coordination Number: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | higher

Coordination Number 7

Like in the case of five-coordination, there is no single structure that is clearly preferred by a variety of compounds. Instead, there are 3 structure types that predominate, Pentagonal Bipyramidal, Capped Trigonal Prismatic and Capped Octahedral.

-Pentagonal Bipyramidal AB7 pentagonal bipyramidal

There are 2 different ligand positions in this structure, 2 axial and 5 equatorial positions. This structure type is adopted in many cases, where there is a macrocyclic pentadentate ligand, that occupies the equatorial positions.

Pentagonal Bipyramidal PicturePentagonal Bipyramidal 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.
Pentagonal Bipyramidal Picture Pentagonal Bipyramidal Picture Pentagonal Bipyramidal Picture

 

Complex with a macrocyclic ligand

 

 

-Capped Trigonal Prismatic AB7 capped trigonal prismatic

The trigonal prismatic structure is only rarely adopted. The few examples known include hexamethyl complexes with d0 configuration, such as hexamethyltungsten and [Zr(CH3)6]2-. Like all capped structures, in this case the base of the structure is a known polyhedron. The additional ligand is added on top of a face of the trigonal prism. Slight distortions can occur to accomodate the additional ligand, which is shown in blue in the following picture.

Capped Trigonal Prismatic

Capped Trigonal Prismatic Picture Capped Trigonal Prismatic 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.
Capped Trigonal Prismatic Picture Capped Trigonal Prismatic Picture Capped Trigonal Prismatic Picture
[NbF7]2-

 

-Capped Octahedral AB7 capped octahedral

In case of 6 monoatomic ligands, an undistorted octahedron also has the high octahedral symmetry and belongs to the point group Oh.

Capped Octahedral PictureCapped Octahedral Picture

Capped Octahedral Picture Capped Octahedral Picture Capped Octahedral 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.
[W(CO)4Br3]-

 

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