[Il Divo]

Just a question that's been giving me a bit of confusiong regarding the Ligand Field Energy of a Coordination Complex.

General trends in a given complex show that larger orbitals (4d and 5d) result in greater overlap between ligand and Metal Orbitals leading to a larger stabilization energy. And the same can be said for more highly positive metals and ligands which give strong field splitting. But I've read that apparently these factor for only about 10% of the overall stability of the Complex.

Specifically, does the Ligand Field Energy give any indication of the overall stability of the Coordination Compound? Or does it simply give insight into shape, MO Diagrams, etc.

How do factors such as Lewis Acidity/Basicity come into play for the overall stability of the compound?

Thanks in advance.

[Corribus]

LFE is useful for more than just predicting shape. It can predict a lot of the electronic and optical properties of a metal complex: for example, the spin state of the iron in hermoglobin or the luminescence (or lack thereof) in metal polypyridyl complexes.

But this is a very broad question and I suggest you consult a good quality inorganic or physical chemistry textbook unless you have something more specific you want to know.

[Il Divo]

LFE is useful for more than just predicting shape. It can predict a lot of the electronic and optical properties of a metal complex: for example, the spin state of the iron in hermoglobin or the luminescence (or lack thereof) in metal polypyridyl complexes.

But this is a very broad question and I suggest you consult a good quality inorganic or physical chemistry textbook unless you have something more specific you want to know.

Fair point.

Could you recommend a good starting point to search for what factors ultimately determine the stability of a Coordination Compound?

[Corribus]

Well, what do you mean by "stability"?

[Il Divo]

Well, what do you mean by "stability"?

Is there a way to easily determine what coordination complexes will result in either a ligand displacing another ligand or attaching to a completely different metal?

To use an Organic Chemistry reaction, if someone gave me CH3-I and Hydroxide Anion, I would assume we would have an Sn2 substitution where the Hydroxide would replace the Iodine, which functions as a better leaving group.

Are there similar trends by which I could determine whether ligands preferentially bind to a specific metal?

Sorry if I'm still being unclear.

[Corribus]

Ah, I see. You want to know whether LF theory can be used to predict reactions, yes?

I'm afraid it usually isn't used this way.  Like MO theory, it's primarily used to determine structure and predict some electronic properties. I suppose in principle it might be used to predict thermodynamic favorability in a general sense, but even here it would be tough.  MO theory and LF theory are both fairly qualitative.  Even more quantitative versions like Huckel theory only give crude approximations.  For anything really coming close to predicting real bond energies, you need a more sophisticated model, typically some kind of ab initio approach.  And even these do a somewhat poor job with transition metal complexes (or did, back when I was more involved in this area) because a lot of the better approximations break down for heavy nuclei (relativistic effects, spin orbit coupling, etc.). And even if you could use LF theory to predict bond energies with precision, you still would have to deal with kinetics, a whole different ball game.

So, while LF theory can generally predict what structures are likely to be more stable than others (i.e., planar vs. tetrahedral for an iron center), predicting the products of reactions is going to be far more challenging.

[Il Divo]

Ah, I see. You want to know whether LF theory can be used to predict reactions, yes?

I'm afraid it usually isn't used this way.  Like MO theory, it's primarily used to determine structure and predict some electronic properties. I suppose in principle it might be used to predict thermodynamic favorability in a general sense, but even here it would be tough.  MO theory and LF theory are both fairly qualitative.  Even more quantitative versions like Huckel theory only give crude approximations.  For anything really coming close to predicting real bond energies, you need a more sophisticated model, typically some kind of ab initio approach.  And even these do a somewhat poor job with transition metal complexes (or did, back when I was more involved in this area) because a lot of the better approximations break down for heavy nuclei (relativistic effects, spin orbit coupling, etc.). And even if you could use LF theory to predict bond energies with precision, you still would have to deal with kinetics, a whole different ball game.

So, while LF theory can generally predict what structures are likely to be more stable than others (i.e., planar vs. tetrahedral for an iron center), predicting the products of reactions is going to be far more challenging.

Yes, that was exactly what I was looking for. Sorry for the delayed response, but I appreciate the post nonetheless.