Jahn - Teller effect

[NTUchemist]

please help with homework...

 

 

Discuss each of the following observation:

() the [CoCl4]2- ion is a regular tetrahedron but [CuCl4]2- has a flattened tetrahedral structure.

[mississippichem]

Ah, a chance to talk about coordination chemistry...awesome!

 

You should construct a CFT diagram for both complexes. These complexes are tetrahedral and "pseudo-tetrahedral" so the [math]e_g[/math] energy level (doubly degenerate) should be lower in energy that the [math] t_{2g}[/math] level (triply degenerate).

 

Then determine the oxidation state of your metal centers and fill electrons accordingly. Remember, chloride ions are weak field ligands and the geometries are tetrahedral so the crystal field [math] \Delta[/math] splitting energy should be low or less than the pairing energy to bind an electron pair in the [math] e_g[/math] level.

 

So you should notice you are dealing with two high spin complexes. Now you could do this the long and cumbersome way and determine which crystal field has the largest number of micro-states with a non-zero S total quantum number, or you could take the less rigorous way and just eyeball it. Which of the two crystal field diagrams shows an electron in the [math]t_{2g}[/math] level that could be moved around that energy level without changing the global spin multiplicity? Think about how this might cause distortion in the coordination geometry.

 

Hope this helps

Edited November 23, 2010 by mississippichem