Inorganic I - 8 Coordinate Complexes

1. Sep 18, 2011

Nezva

Main question: What is the name of the 8 coordinate complex pointgroup? Or does it even exist?

I've been exposed to octahedrons and icosohedrons, however, the 8 coordinate high symmetry complexes appear to have been skipped. I'm aware that these complexes would be rare but I think that they do exist. I was able to find this image of a XeF8 2- anion:
http://ce.sysu.edu.cn/echemi/inocbx/ic3/Xe/images/XeF8_2-.jpg

Another visual representation is the f-orbital (xyz)... if the lobes were treated as not having spins (all the same "ligand").
http://en.wikipedia.org/wiki/File:F4M2.png

2. Sep 18, 2011

mcbud

For a coordination number of 8, either a square antiprism (like the XeF82- and IF8- anions) or a dodecahedron (ZrO8) can be formed.

3. Sep 20, 2011

Nezva

In square antiprism the squares to not overlay each other, they are staggered 45 degrees. But thank you for showing me antiprisms, very neat structures to try to do molecular symmetry on.
A dodecahedron has too many coordinates from what I see but also an interesting structure.

The pointgroup is Oh, which confused me because there is a 6 coordinate version of the Oh pointgroup. For anyone having the problem I had... The 6 coordinate Oh complex has 3 sigma-h along 5 atoms (4 ligands and center), while the 8 coordinate has 3 sigma-h in between bonds (only intersecting the center atom). Visually, I had a lot of trouble believing they were both the same pointgroup.

4. Sep 21, 2011

DrDu

So you don't seem to be interested in all 8 fold coordinate complexes but in those with a cubic arrangement of the ligands.
The cubic and the octahedral coordination have the same symmetry because they are dual to each other: an octahedron can be inscribed into a cube so that the corners of the octahedron coincide with the centers of the faces of the cube. This works also the other way round. The same relation holds for an icosahedron and a dodecahedron which have both symmetry group I_h. The tetrahedron is dual to itself.