Talk:Ligand field theory

so their σ-symmetrical orbitals form bonding orbitals with the d_z² and d_x²-y² orbitals.

Is the hyphen in the subscript above supposed to be a minus sign? If so, it should say

d_x²−y²

since the stubby little hyphen is hard to see. Michael Hardy 18:09, 10 May 2005 (UTC)

I noticed this a little late (I'm not a faithful pagewatcher I must admit) but you are right. I changed the hyphen into a minus sign and will continue to use the minus sign if I get to expansion of this article. Thanks!

--tijmz 4 July 2005 14:28 (UTC)

Can I just say that this is a really good explanation of ligand field theory given that there are no diagrams! Well done, whoever wrote most of it (although the last section isn't quite so good - I might have a crack at that later).--Brichcja 18:25, 24 May 2006 (UTC)

LFSE

I feel the last section, on LFSE, is very confusing. Furthermore, I think it's wrong. What is described here is Crystal Field Stabilisation Energy (CFSE), because it is assuming that the Barycentre rule applies: (i.e. that the t_2g go down by 2/5 Δ_o and the e_g go up by 3/5 Δ_o). If you look at the MO diagram, this plainly isn't true beacuse the t_2g are often non-bonding (they don't go down at all), and if they do go down, the amount is not related to how far the e_g have gone up, it's related to the amount of π-bonding.

Any thoughts?

Chris 21:30, 26 December 2006 (UTC)

You are probably correct and should proceed with editing as you seem to be inclined. In general, much confusion exists between LF and CF theories and sometimes I feel we should just drop CFT because it is more primitive than LFT and it simply confuses more than it clarifies. Part of the problem may be that texts propagate the concept of LFSE being related to multiples of Δ_o, as you mention. If you had time, it might be worth checking a modern inorganic text. Regarding one details of your comments, t_2g can be pushed up with pi-donor ligands, the case of h.s. [CoF₆]^3- being the famous example.--Smokefoot 02:02, 27 December 2006 (UTC)

OK, I removed the LFSE section for the reasons given above. I wrote a section on CFSE and put it on the crystal field theory page to replace it. Chris 19:50, 31 December 2006 (UTC)

Spectrochemical series

I added some stuff about the spectrochemical series, because LFT explains it and the spectrochemical series is empirical evidence for LFT. There is a page for the spectrochemical series, but it doesn't really say anything other than give the same list of ligands. There's no explanation there for it, and I would be tempted to blank it and turn it into a redirect to here. Equally, there's a bit on the spectrochemical series on the CFT page, which I am going to remove. It's got nothing to doo with CFT, and everything to do with LFT.... Chris 22:12, 31 December 2006 (UTC)

What the heck?

What in the world does this sentence mean in the first paragraph:

For first row transition metals, n = 3; for second and third row metals, n = 4 and 5, respectively.

OK - now I see that these are the principal quantum numbers - well that wasn't at all clear, so I am rewriting this sentence.

As I read further, there are a lot of unexplained or outright unclear sections in this article. In the figure, for example, what is "M-L sigma"??? I suspect what is going on is d2sp3 hybridization, with a single electron remaining in the 3 unhybridized orbitals, but I'm reading this because I really don't know this subject, so someone else had better undertake the rewriting.

A day later ...

Hey Brichcja! I understand what you saw a need to correct, but you don't define "n" at any point, and what the heck are "five nd"??? The following sentence in the version you just created just makes no sense:

"A transition metal ion has nine atomic orbitals of appropriate energy to engage its ligands, which are five nd, one (n+1)s, and three (n+1)p orbitals. For first row transition metals, n = 3; for second and third row metals, n = 4 and 5, respectively." —Preceding unsigned comment added by 67.190.157.17 (talk) 01:20, 9 January 2009 (UTC)

Ligand-field theory versus molecular-orbital theory

Everything under the main title LFT is properly described as MO theory of transition-metal complexes. LFT is a FIELD theory (like Crystal-field theory). It seeks (pretty successfully) to represent certain TM properties by a pseudo-potential approach in which the environment of the TM ion/atom by an effective ONE-electron operator (a potential). Mo theory does no such thing but is a many-electron theory. MO theory and field theories are like chalk and cheese. This is not an academic point but a crucial point which was very well understood all those years ago by Van Vleck. Unfortunately, he has been little read on this issue and frequently misunderstood.

I'm afraid, therefore, that Wikipedia's whole entry for Ligand-field theory is just silly. —Preceding unsigned comment added by Gerloch (talk • contribs) 09:42, 9 February 2009 (UTC)

The intro basically fits with the conventional understanding of LFT presented in places like Misessler and Tarr's Inorganic Chemistry. Most references say that LFT is a combination of a field theory with a bonding theory based on Mullikan's MO theory. This works out to a chalky cheese or a heterogeneous mixture of chalk and cheese. This relationship is the origin of the terms symbols for the t_2g and e_g orbitals; derived using group theory and a linear combination of orbitals according to methods outlined by molecular orbital theory.

As I understand it Van Vleck was a supporter/innovator of crystal field theory. The historic interpretation I know is that CFT was largely replaced by LFT, since LFT incorporated a reasonable explanation for bonding interactions which CFT, a pure field theory did not. I would expect Van Vleck to have criticized LFT as a competing theory to his CFT. The Van Vleck text would probably be best considered a valid criticism but would not necessarily be representative of today's conventional or mainstream thinking on the subject. Its important to remember that Wikipedia doesn't strive to present the true material it attempts to present mainstream theory supported by citation even if it will be corrected in the future (undoubtably it will be).

I hate to say it but I don't know what the specific meanings of "ONE-electron operator" or "pseudo-potential approach"? Are they describing a valence bond model interaction and some form of non-bonding interaction. I'm not a theoretician and that's probably why I don't understand your terminology but I doubt I'm the only one. Clarification would be appreciated. I recognize that this area is one of your specialties so any effort to clean it up would be greatly appreciated. But, we are forbidden from presenting original research which shouldn't be a problem since most of your ideas are probably published. The only thing to remember is that as Wikipedia editors we have to represent mainstream understandings so if some of your ideas are part of a dissenting minority they will have to be presented as such. --OMCV (talk) 13:16, 9 February 2009 (UTC)

Well, I'm sorry. I should have added that LFT involves a one-electron operator acting within a PURE d or f electron basis. So, within applications to the d block, calculations explicitly make no mention of orbitals (one-electron wavefunctions) other than d. Furthermore, no mention is made of the radial part of those d functions for that is wrapped up in the LF parameters. It is simply not possible to calculate such radial functions without enormously difficult computations of an entirely different sort and those are not especially successful anyway.

As to your other point about sticking to 'conventional wisdom' (my words, I admit): why bother if that old-fashioned wisdom is simply wrong? It would be nice if this new medium (Wikipedia) could provide something more up to date and correct than that of the past 40 years. Anyway, I'm off! —Preceding unsigned comment added by Gerloch (talk • contribs) 07:30, 4 March 2009 (UTC)

When it comes to Ligand Field Theory I am essentially an end user (like many others). To me LFT is a tool to explain why bonding energies, reduction potentials, and electronic spectra change with perturbations in complex geometry and ligand field. My interested are in the reactivity of transition metal complexes and how the reactivity can be modified by ligand environments. I don't ever plan to publish anything challenging or modifying LFT; its just a useful model if a better one comes along I'll use that. You clearly know more about this subject than I ever will. It would be extremely valuable if you shared your knowledge. My comments above were just to inform you of wikipedia's self imposed limitations. There is actually specific recommendation that states wikipeida is not the place to right wrongs. I hope you can see the value of wikipedia attempt to present a NPOV knowledge baseline. If folks like me can get good, well established, fundamental information for free, we might one day be able to fully appreciate your critique of LFT.--OMCV (talk) 23:47, 4 March 2009 (UTC)

Can you explain the spectrochemical series through a visual aide? --Guacamole21 (talk) 18:26, 6 January 2020 (UTC)