Spectrochemical Series

Ligand Field Splitting Energy

Both Crystal Field Theory and Ligand Field Theory predict a splitting in the normally degenerate valence-shell d orbitals upon complexation of a metal by a ligand. The magnitude of the splitting, Δ, is an important parameter in characterizing coordination compounds.

What factors affect the magnitude of Δ?

Exercise

This exercise explores the last item in the list: the impact of the chemistry of the ligand on Δ. A set of eleven ligands are shown below in random order. The goal of this exercise is to arrange the ligands in order of increasing Δ, with the ligand producing the smallest Δ on the far left and the ligand producing the largest Δ on the far right. Click on a ligand to select it, and use the <<< and >>> buttons to shift the position of the selected ligand in the list. The vertical status bar at the far left indicates the accuracy of the current order. Look at each ligand and determine whether it is likely to yield a relatively small or relatively large Δ. Then adjust the order of the ligands accordingly.

What characteristics of a ligand are relevant in determining Δ? Here are some properties to consider.

If you would like a little help in establishing the correct order, enable the energy diagram. For the sake of simplicity, the energy diagram shows the splitting for this ligand in an octahedral complex. The semi-quantitative energy diagram separates the effects of σ and π bonding. The rightmost pattern shows both effects.

In completing this exercise, bear in mind the following issues.


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Shift Ligand:                                                    
 
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Δo
d orbitals
Ligand is a σ donor.
Ligand is a π donor.



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© Copyright 2009 David N. Blauch