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chelating ligands

Posted: Sat Nov 30, 2019 3:41 am
by Matthew Chan 1B
How would you determine whether a ligand can bind at multiple sites (or be chelating?) Is there a certain angle threshold? For example like in 9C.7 (I've attached an image of the isomers of diaminobenzene that the book uses). Note that B and C should be switched around to represent what the textbook actually depicts. I just got this image from google.Image

Re: chelating ligands  [ENDORSED]

Posted: Sat Nov 30, 2019 11:01 am
by Chem_Mod
As discussed in class, a chelating ligand has more than one bond to the same transition metal cation.

I also discussed in class that the best chelating binding structure/motif was:

atom with lone pair --- spacer atom --- spacer atom --- atom with lone pair
***And the ligand must have sigma bonds to allow rotation and therefore correct positioning of the lone pair atoms to bind to the same transition metal cation.***

I pointed out several chelating examples of this:
ethylenediamine
diethylenetriamine
EDTA

In the diagram above, all the ligands are rigid planar structures.
Ligand A has the N atoms pointing away from each other.
Ligand B, the N atoms are still pointing too far away from each other to bind to the same transition metal cation.

Only ligand C has the structure I discussed in class:

atom with lone pair --- spacer atom --- spacer atom --- atom with lone pair

Since the structure is planar, the N atoms, each with a lone pair, are already in the correct position and therefore do not need to rotate.
Therefore ligand C is the answer.

Re: chelating ligands

Posted: Tue Dec 03, 2019 8:43 pm
by chari_maya 3B
How do you draw diethylenetriammine chelating?

Re: chelating ligands

Posted: Sat Dec 07, 2019 11:52 am
by Elizabeth Harty 1A
How do you know if there are sigma bonds available for rotation?

Re: chelating ligands

Posted: Sat Dec 07, 2019 1:07 pm
by Matthew Chan 1B
Elizabeth Harty 3A wrote:How do you know if there are sigma bonds available for rotation?

dont sigma bonds already have the ability to rotate? so if its just a single sigma bond then it can rotate but if theres pi bonds then you cant rotate. did i answer your question?

Re: chelating ligands

Posted: Sat Dec 07, 2019 6:43 pm
by Angela Prince 1J
Elizabeth Harty 3A wrote:How do you know if there are sigma bonds available for rotation?


all sigma bonds can rotate, but pi bonds cannot

Re: chelating ligands

Posted: Sat Dec 07, 2019 8:26 pm
by chrisleung-2J
Would it be correct, then, to say that “Ligand C is capable of chelating due to its atoms with lone pairs having an Ortho arrangement”?

Re: chelating ligands

Posted: Sat Dec 07, 2019 8:36 pm
by Nick Lewis 4F
Does anyone know what Dr. Lavelle means when he says:
atom with lone pair --- spacer atom --- spacer atom --- atom with lone pair
The only part i dont understand is spacer atom. What does spacer atom mean? Conceptually I see why C is the correct answer i am just unfamiliar with this terminology

Re: chelating ligands

Posted: Sat Dec 07, 2019 9:06 pm
by Ashley Nguyen 2L
Nick Lewis 3D wrote:Does anyone know what Dr. Lavelle means when he says:
atom with lone pair --- spacer atom --- spacer atom --- atom with lone pair
The only part i dont understand is spacer atom. What does spacer atom mean? Conceptually I see why C is the correct answer i am just unfamiliar with this terminology


Spacer atom refers to the two carbons in the benzene that are connecting the amine groups.

Re: chelating ligands

Posted: Sat Dec 07, 2019 9:31 pm
by 005321227
sigma bonds are able to rotate already!

Re: chelating ligands

Posted: Sat Dec 07, 2019 9:47 pm
by Alan Cornejo 1a
Angela Prince 3B wrote:
Elizabeth Harty 3A wrote:How do you know if there are sigma bonds available for rotation?


all sigma bonds can rotate, but pi bonds cannot


Thank you for the clarification .

Re: chelating ligands

Posted: Sat Dec 07, 2019 10:45 pm
by Adelpha Chan 1B
Elizabeth Harty 3A wrote:How do you know if there are sigma bonds available for rotation?

all sigma bonds able to rotate freely along the axis

Re: chelating ligands

Posted: Sun Dec 08, 2019 1:07 am
by Kyle Thorin
Sigma bonds have the ability to rotate already.

Re: chelating ligands

Posted: Sun Dec 08, 2019 2:23 am
by ATingin_3I
Chem_Mod wrote:As discussed in class, a chelating ligand has more than one bond to the same transition metal cation.

I also discussed in class that the best chelating binding structure/motif was:

atom with lone pair --- spacer atom --- spacer atom --- atom with lone pair
***And the ligand must have sigma bonds to allow rotation and therefore correct positioning of the lone pair atoms to bind to the same transition metal cation.***

I pointed out several chelating examples of this:
ethylenediamine
diethylenetriamine
EDTA

In the diagram above, all the ligands are rigid planar structures.
Ligand A has the N atoms pointing away from each other.
Ligand B, the N atoms are still pointing too far away from each other to bind to the same transition metal cation.

Only ligand C has the structure I discussed in class:

atom with lone pair --- spacer atom --- spacer atom --- atom with lone pair

Since the structure is planar, the N atoms, each with a lone pair, are already in the correct position and therefore do not need to rotate.
Therefore ligand C is the answer.

should we memorize the structure of edta?

Re: chelating ligands

Posted: Sun Dec 08, 2019 10:22 am
by Chem_Mod
You will not be asked to draw the entire structure of EDTA. However it may be helpful to know which atoms/lone pairs are involved in forming coordinate covalent bonds

Re: chelating ligands

Posted: Sun Dec 08, 2019 11:18 am
by ASetlur_1G
Just to clarify, polydentate ligands are chelating right?

Re: chelating ligands

Posted: Sun Dec 08, 2019 3:46 pm
by Ami_Pant_4G
ASetlur_3I wrote:Just to clarify, polydentate ligands are chelating right?


yes all polydentates are chelating

Re: chelating ligands

Posted: Sun Dec 08, 2019 4:54 pm
by Natalie Benitez 1E
What exactly is a chelating ligand? Can you also provide an example for it?

Re: chelating ligands

Posted: Sun Dec 08, 2019 5:26 pm
by Chem_Mod
A chelating ligand is a ligand that forms more than one bond to the same transition metal.
Results in a ring of atoms that includes the transition metal atom.

See lecture notes and textbook for multiple examples.

Re: chelating ligands

Posted: Sun Dec 08, 2019 8:03 pm
by Kennedi2J
An example would be ethylenediamine (en) which binds to a transition metal at 2 sites.

Re: chelating ligands

Posted: Sun Dec 08, 2019 9:49 pm
by AnayaArnold_3L
Elizabeth Harty 3A wrote:How do you know if there are sigma bonds available for rotation?


Sigma bonds can rotate,but pi bonds can't because of the p-shaped orbitals interlocking side by side.

Re: chelating ligands

Posted: Mon Dec 09, 2019 1:37 am
by ZevMarx-Kahn3C
Is this a topic that will be relevant in 14B?