Talk:Complex (chemistry)

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[edit] Hemoglobin

I'm perplexed as to why there is no mention of the importance/function of metal complexes in hemoglobin in this article whatsoever. Could someone please expand this article in that specific area? Ajaxkroon 11:02, 29 March 2006 (UTC)

I've done something about it. --Dirk Beetstra 08:40, 16 May 2006 (UTC)

[edit] Um...

Non-covalent bond? Aren't the bonds considered to be covalent since they are sharing? Olin 17:28, 31 March 2006 (UTC)

Are they not covalent once they are formed? I know they call them coordinate covalent bonds. This is what the article on CCBs has to say:

"A coordinate covalent bond...is a special type of covalent bond in which the shared electrons come from one of the atoms only." Expert needed. JohnJohn 17:16, 21 April 2006 (UTC)

I don't think the term applies to that, I'm not sure though. A coordinate covalent bond would be like the one between the extra H and N in NH4+, because both electrons come from the electron pair on N. Since complexes are often, if not mostly or always, composed of a central metal ion (which is positively charged), it'd be hard for that to donate electrons. They might come from the ligands though, although I'd still say there's a largely electrostatic attraction. I'd have to look it up to be sure. Jack the Stripper 14:57, 22 September 2007 (UTC)

Ligands (L:) in complexes use their lone pairs (if they have them) to form dative covalent bonds with the central metal atom.

Ben 15:24, 22 September 2007 (UTC)

[edit] Statements in Atomic structure of coordination compounds

I am removing some ambiguous statements in the Atomic structure of coordination compounds section of the article. Some are not untrue, but I think it is better to give real reasons (which have already been explained) instead of 'rule of thumb'-like statements. (As an example, the reason why late transition metals tend to have lower coordination numbers, is that (for a given oxidation state) late transition metal ions are smaller than the early transition metal ions (Sc3+ is much bigger than Co3+), so less ligands tend to fit around late transition metal ions. But, coordination is governed by overlap between orbitals (a thing also true for main group elements). --Dirk Beetstra 15:44, 16 May 2006 (UTC)

[edit] Assessment

I just took another look at this for the Wikipedia:WikiProject_Chemistry/Worklist, and it's certainly come a long way (it was only a "Start"), thanks a lot for adding all this content Smokefoot and Beetstra! I wanted to ask a few questions:

  • I formatted a ref and noticed after doing so that it had was the same as an external link. Can you clarify which it is? (Wikipedia defines refs as actually used in the writing of the article, whereas ext links are just nice pages folks might find helpful).
No clue .. ref was there already, did not have a look .. --Dirk Beetstra 07:34, 22 May 2006 (UTC)
  • Can you make sure you add in any refs that you have used? The list seems rather short considering the amount of work.
The most I did was reorganising some pages, moving the info to the page where I thought it belonged, a lot of info is coming from Ligand (which does not contain any references as well ..). The article surely needs some references, but I must confess, most of my chemistry-books are back in NL, I (re)write info that (to me) is common knowledge or logic. I may have to have a dive into the library for some things. --Dirk Beetstra 07:34, 22 May 2006 (UTC)
  • Do you think a section on chelation, crown ethers and cryptands would be appropriate? If so, should I write it, or would one of you like to?
Chelation gets quite some space in ligand (in the section denticity, it might need some attention there). I think that it is more appropriate there, chelation is a property of a ligand, not of a complex (IMHO, it should only be noted here that complexes with chelating ligands tend to be more stable in terms of ligand dissociation).. By the way, it still lacks the thermodynamic rationale behind the concept of chelation. --Dirk Beetstra 07:34, 22 May 2006 (UTC)
  • Are there any other sections that need writing? If not, then with the above modifications we could get this article to A-Class, which would be nice! Walkerma 04:14, 22 May 2006 (UTC)
I am quite (I'd like to say: very) unhappy with the isomerism section, that needs a decent rewrite, trans-effects are completely missing, and optical isomers need to be explained here (the concept with 6-coordinate atoms is more difficult than with 4-coordinate atoms C, N (,S, P)!! Though the concepts of that should be explained in some page like chirality (chemistry) (I did not have a look on that page, yet, one moment .. OK, inorganic complexes do have a section there, but that section is a plain stub). I think important here are the effects of isomerism: cis-platin, trans-effect, orientation of reactive sites (in general cis to each other). --Dirk Beetstra 07:34, 22 May 2006 (UTC)
OK, rewrote this section to a readable and more or less correct state, still there is info missing, some linking needs to be done, and see if the concepts in this section are explained sufficiently in the pages linked to. --Dirk Beetstra 21:12, 22 May 2006 (UTC)
It is good to hear that the page is getting where it should be, after shuffling ligand and complex I already found that it was a better article, thanks for the assesment and the compliments. I think when we have these pages (ligand and complex) on a good level, they serve as a decent background for other (inorganic) chemistry concepts that need explaining. --Dirk Beetstra 07:34, 22 May 2006 (UTC)

[edit] 9-coordination - help

Is what has been described as Tri-capped trigonal prismatic actually a Triaugmented triangular prism ??? --Dirk Beetstra 21:44, 22 May 2006 (UTC)

I dont think so, but I am checking with a math person. The tricapped trigonal prism is deltahedral but there are no "mu5-vertices", because the square faces are capped. --Smokefoot 23:09, 22 May 2006 (UTC) My topology friend tells me that Tri-capped trigonal prismatic and Triaugmented triangular prism are the same.--Smokefoot 18:28, 23 May 2006 (UTC)
Great, thanks. I have corrected the link in the article. Cheers! --Dirk Beetstra 18:32, 23 May 2006 (UTC)
P.S. does it make sense to your friend to make a redirect from Tri-capped trigonal prismatic to Triaugmented triangular prism as well? --Dirk Beetstra 18:32, 23 May 2006 (UTC)

[edit] Problems with this article

Reading this article I think that there are some changes required, which I think need some discussion as so many folk have contributed.For example:-

Metal complexes The definition as it stands does not include e.g Aluminium etc. Poor or post transition metals need adding to the definition for completeness.
Why is there no link to the Ligand article?
Geometry The point "the idealised descriptions of 5,7,8...etc" When a square pyramid is so distorted that it becomes an idealised tbp then it really IS a tbp. Perhaps the point to be made is that it is impossible to tell the difference sometimes between e.g a distorted sp and a distoretd tbp.
Color The reference to Tanabe-Sugano diagrams is fine but simple CFT does quite well for the less competent amongst us, and the CFT article is pretty good and deals with the colors of transition metal complexes quite well whereas the T-S article is not very helpful.
Magnetism "Metal complexes that have unpaired electrons are magnetic". This should read paramagnetic. Magnetic is misleading- as it usually understood to refer to ferromagnetism.

Axiosaurus 11:08, 27 February 2007 (UTC)