Monday, May 12, 2014

Symmetry and Group Theory- Point Group Tips and Practice 7 (K2ReH9)

Time to add another example to point group practice problems. I got this complex from the publication below:
S. C. Abrahams, A. P. Ginsberg, K. Knox
Inorg. Chem., 1964, 3 (4), pp 558–567
Publication Date: April 1, 196


Dr. Frank Hoffmann was very kind enough to contact me and "make the threecapped trigonal prism  visible through the polyhedral representation in VESTA.." So, he sent me the Vesta file and I just changed the color of the atoms so that it looks clear on my blog's template. You can see the screenshots below.  As I mentioned in my other posts, there is a free online course named "The Fascination of Crystals and Symmetry" on . The course has started three weeks ago. So, you are not late to register and start enjoying the symmetry. Just check it out:

 Hydrogens are black, potassium ions are blue and rhenium ions are shown as pink.


I tried to draw and show the geometry, but I really couldn't figure out how I am supposed to show it using a software. I think you can see one of my unsuccessful attempts on Avogadro below.

  an unsuccessful drawing attempt!

Anyway, you can see the metal complex here:

So, the principal axis goes through the center of the "triangles." Then it is very easy to see that there is a C3 rotation axis. Now it is time to look for a perpendicular C2. You can see it (actually three of them) going along one of those equatorial atoms (7, 8, 9). Obviously, we are assuming that this is a perfect geometry with equal angles and bond lengths. This says that our point group will be D3. 

There is a mirror plane going through atoms #7, #8 and #9. This means there is a perpendicular mirror plane divides complex into two equal "parts." Finally, this mirror plane tells us that the point group is D3h.

If you had difficulty to follow how I found out the point group, you can look at the very simple "flowchart" I made here

Actually, this is a  really nice paper with a molecular orbital diagram too. I feel like it is an inorganic chemistry lecture. Also, this complex was one of the first ones that helped chemists think as "M-H bond as a normal covalency." [1].

Reference :

1. Crabtree, H.R. The Organometallic Chemistry of the Transition Metals , John Wiley and Sons, 2001. Print.


  1. Dear chemraven,

    I would like to send you a certain file. To contact me, you can send me an email to:

    best regards

  2. Thank you. I edited and updated the post. I hope you like it.