This unit introduces two different models that, most of the time, can be used to reach similar conclusions. Each of these models has its advantages and disadvantages. I'd like you to know both theories and to be able to pull pieces of each model when appropriate.
- Crystal Field Theory (CFT) is one of the simplest models for explaining the structures and properties of transition metal complexes. The theory is based on simple electrostatics of the metal-ligand interaction, and some of the assumptions behind the theory are inaccurate. It was developed to explain spectroscopic (colors) and magnetic properties of coordination complexes, and does not describe bonding. Although it is primitive, does not describe bonding, and is based on naive ideas, it is still useful. Because the model makes effective use of molecular symmetry, it can be surprisingly accurate in describing the magnetism, colors, structure, and relative stability of metal complexes. The major advantage of CFT is that it is simple.
- Ligand Field Theory (LFT) is more advanced in that it is rooted in molecular orbital theory. It is more complex, but it is also more correct. LFT will not only get you to the correct answer more often, but it is also based on accurate ideas (as far as we know).
We will start by examining how each theory treats the most common type of metal complex geometry: the octahedral geometry.
Additional resources: The Organometallic reader, Ligand Field Theory & Froteir MO Theory.