Identifying Polydentates?  [ENDORSED]

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Mimi Lec 2H
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Joined: Fri Jul 22, 2016 3:00 am

Identifying Polydentates?

Postby Mimi Lec 2H » Mon Nov 14, 2016 10:01 pm

I'm having trouble with the homework problem 17.33 where you're given some ligands and are told to identify which ones are mono/bi/polydentates. I know that polydentate signifies that the ligand can attach to more than one binding site simultaneously, but identifying them is a little confusing for me. How come CO3^2- can be either a mono or bidentate ligand? Does it have to do with the number of lone pairs on the atoms? I've seen some "Number of Nitrogens" shortcut to determine them..can someone explain that?

Thank you in advance!

Anika_Desar_3N
Posts: 21
Joined: Sat Jul 09, 2016 3:00 am

Re: Identifying Polydentates?

Postby Anika_Desar_3N » Mon Nov 14, 2016 10:58 pm

I am still having trouble identifying which molecules are polydente and then using that to find the coordination number of the molecule. Any help will be great! Thanks (:

Kiara Quinn 3B
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Joined: Sat Jul 09, 2016 3:00 am

Re: Identifying Polydentates?

Postby Kiara Quinn 3B » Wed Nov 16, 2016 1:03 am

Why is H2O always monodenate?

Julia Hwang 3G
Posts: 22
Joined: Wed Sep 21, 2016 3:00 pm

Re: Identifying Polydentates?

Postby Julia Hwang 3G » Wed Nov 16, 2016 9:53 am

I also have trouble with this, but I know looking at the lewis structure helps a lot. In the example of ethylenediamine, once you draw the structure you can see that the two "N's" in the NH2 have a lone pair that can form a bond, hence en is bidentate. Dien is tridendate because the 3 "N's" and their lone pairs form bonds with the central atom. I'm not sure how to tell if a molecule is polydentate without drawing the structure. For the list of ligands we were given, you could even remember which ones are bidentate, etc. I'm far from an expert on this topic but hope this helped!

Julia Hwang 3G
Posts: 22
Joined: Wed Sep 21, 2016 3:00 pm

Re: Identifying Polydentates?

Postby Julia Hwang 3G » Wed Nov 16, 2016 9:55 am

In regards to the coordination number, if a molecule is bidentate, then it can bond with the central atom in 2 places, so you consider that as a 2 when adding up the coordination number of the compound. If it's tridentate, then it would be 3, and so on. If it's written like (en)2 then you would multiply 2 x 2 since there are 2 en molecules and en is bidentate, so it would be 4.

Patrick Ricaflanca 2H
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Joined: Sat Jul 09, 2016 3:00 am

Re: Identifying Polydentates?

Postby Patrick Ricaflanca 2H » Wed Nov 16, 2016 11:48 am

Is there a way to identify whether something is mono-, bi-, try-, etc. dentate just by looking at the compound given? Or do we always have to draw the structure?

Mimi Lec 2H
Posts: 29
Joined: Fri Jul 22, 2016 3:00 am

Re: Identifying Polydentates?

Postby Mimi Lec 2H » Wed Nov 16, 2016 12:28 pm

So can you determine it by the number of atoms with lone pairs?

Jose_Arambulo_2I
Posts: 35
Joined: Wed Sep 21, 2016 2:59 pm

Re: Identifying Polydentates?

Postby Jose_Arambulo_2I » Wed Nov 16, 2016 8:47 pm

It's not just the number of atoms with lone pairs, it also considers shape and type of bond. For example, if the lone pair atom is bonded with a double or triple bond, then they won't have the ability to bend to form chelates, preventing them from being polydentate. Single bonds, however, allow this bending to take place. Also the "atom with a lone pair, spacer, spacer, atom with a lone pair" thing Lavelle says is a good guideline. Hope this helps a bit!!

Janice Kim 3I
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Joined: Wed Sep 21, 2016 2:56 pm

Re: Identifying Polydentates?  [ENDORSED]

Postby Janice Kim 3I » Thu Nov 17, 2016 11:06 am

Identifying a ligand as polydentate has two criteria.
1) The ligand must have at least 2 atoms that have lone pairs. This can be found through simply drawing the Lewis structure.
2) The atoms must be in the correct geometry to bind to the Transition metal cation in more than one place at the same time. For example, the ligand EDTA has multiple atoms (N) that have lone pairs, and these N are in good geometry. There are spacers(ethylene) that gives EDTA good geometry to bind in more than one place.

There are some molecules that can be considered either monodentate or some form of polydentate. These molecules depend on whether the Transition metal is small enough so that the molecule is able to get closer and bind to in different places depending on its geometry.


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