chelating ligands [ENDORSED]
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chelating ligands
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.
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Re: chelating ligands [ENDORSED]
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.
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.
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Re: chelating ligands
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?
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Re: chelating ligands
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
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Re: chelating ligands
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”?
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Re: chelating ligands
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
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
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Re: chelating ligands
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.
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Re: chelating ligands
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 .
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Re: chelating ligands
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
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Re: chelating ligands
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?
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Re: chelating ligands
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
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Re: chelating ligands
ASetlur_3I wrote:Just to clarify, polydentate ligands are chelating right?
yes all polydentates are chelating
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Re: chelating ligands
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.
Results in a ring of atoms that includes the transition metal atom.
See lecture notes and textbook for multiple examples.
Re: chelating ligands
An example would be ethylenediamine (en) which binds to a transition metal at 2 sites.
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Re: chelating ligands
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.
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Re: chelating ligands
ZevMarx-Kahn3C wrote:Is this a topic that will be relevant in 14B?
I think that it will, but I think this would be more relevant for a biochem/Ochem class. Hope this helps!
Re: chelating ligands
Wait I thought that the whole concept of a ligand was a biology term, since when is it in chemestry and what is its definition when it comes to the field of chemistry.
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Re: chelating ligands
Hi!
Perhaps someone else has already asked this but I was wondering, what exactly is a chelating ligand? :(
Perhaps someone else has already asked this but I was wondering, what exactly is a chelating ligand? :(
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Re: chelating ligands
Lorena_Morales_3D wrote:Hi!
Perhaps someone else has already asked this but I was wondering, what exactly is a chelating ligand? :(
Hi! Chelating ligands are basically polydentate ligands that can attach to two or more positions to a metal atom. Hope this helps!
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Re: chelating ligands
Hi! This is just a clarification statement I wanted to type out to be sure I'm understanding resonance/chelating ligands properly. In today's review session with C2O42-, it doesn't matter when we draw the 2 Os that share lone pairs opposite one another (a structure that, on paper, looks as if the lone pairs are opposite one another and does not appear able to bond to the same TM) because really the C2O42- ion has delocalized e-, so each O has an equal ability to form a chelate. Hopefully that makes sense and someone can tell me that I'm thinking about it the right way. Thank you :)
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Re: chelating ligands
Renny_kim_2G wrote:Does this mean polydentate ligands and chelating ligands are the same thing?
not always. A ligand can be polydentate but bind to two different transition metals. The result wouldn't be a ring, so the compound wouldn't be a chelate. A ligand that does this would be called a bridging ligand instead.
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Re: chelating ligands
Then to clarify, a ring is what is a chelate? and that forms when it's a ligand-spare atom-spare atom-same ligand?
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Re: chelating ligands
Jessica Hu 3L wrote:Then to clarify, a ring is what is a chelate? and that forms when it's a ligand-spare atom-spare atom-same ligand?
I am also confused on this. Could someone clarify?
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Re: chelating ligands
Are there any exceptions to the atom-spacer-spacer-atom condition for chelation or can this be considered absolute?
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Re: chelating ligands
Renny_kim_2G wrote:Does this mean polydentate ligands and chelating ligands are the same thing?
Remember that a chelate must have ligands that form a ring-like structure around the central atom
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Re: chelating ligands
Nick Lewis 4F 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
The spacer atoms are atoms that do not have lone pairs. There must be exactly two of these "regular" atoms in between two atoms that each have a lone pair. This "formula" will allow the ligand to be chelating or bind in multiple places on the metal cation, so a ring structure is formed.
Re: chelating ligands
Is there a limit to how many ligands can be in a compound ? Or if there is one molecule that is a ligand can there be another cation acting as one as well?
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Re: chelating ligands
I think that six is the maximum number of ligands because electron pairs repel each other and can't really form a bond angle less than 90 degrees. However, I am not sure if our textbook just does not go into whether it is possible to have more than 6 but I think for now that is all we have to recognize.
Re: chelating ligands
Tony Chen 3D wrote:Renny_kim_2G wrote:Does this mean polydentate ligands and chelating ligands are the same thing?
Remember that a chelate must have ligands that form a ring-like structure around the central atom
Polydentate ligands are range in the number of atoms used to bond to a central metal atom or ion. Meanwhile Chelating ligands are attached to a central metal ion by bonds that are from two or more donor atoms. So no they are not the same thing.
Re: chelating ligands
405566265 wrote:Is there a limit to how many ligands can be in a compound ? Or if there is one molecule that is a ligand can there be another cation acting as one as well?
There is a limit to how many ligands can be in a compound and it is 6. If there is a molecule that acts like a ligand then there can be another acting as a cation.
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Re: chelating ligands
Lorena_Morales_1K wrote:Hi!
Perhaps someone else has already asked this but I was wondering, what exactly is a chelating ligand? :(
Hi!
a ligand is a neutral molecule or an ion that binds to a central metal atom to form complex coordination compounds. They are lewis bases because they contain at least one pair of electrons to donate to the central metal atom. A chelating ligand is a polydentate ligand meaning that it has more than one donor site (lone pair) and it forms a ring structure with the central metal ion.
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Re: chelating ligands
Elizabeth Harty 1A wrote:How do you know if there are sigma bonds available for rotation?
pi bonds don't/can't rotate, but sigma bonds can.
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Re: chelating ligands
Levon_Avedian_2H wrote:What are some examples of chelating ligands and their bond angles?
Common textbook examples: Hemoglobin, chlorophyll, Oxalic acid, EDTA
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Re: chelating ligands
Hi, So a chelating ligand is a ligand that has two or three coordination sites allowing for the formation of a ring-link structure. Some examples of chelating ligands include: Chlorophyll, EDTA (Ethylenediamine tetraacetate) ,hemoglobin, Oxalic acid, and various other less common ones.
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Re: chelating ligands
Renny_kim_2G wrote:Does this mean polydentate ligands and chelating ligands are the same thing?
Not quite. We can think of chelating ligands as a sort of subset of polydentate ligands because we know that it must bind more than once to the same metal atom. For example, Hemoglobin (protein+iron complex), pictured below, exemplifies this and you can clearly see the ring structure.
On the other hand, a polydentate ligand doesn't ligate to the same metal atom, so it isn't always chelating.
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Re: chelating ligands
Elizabeth Harty 1A wrote:How do you know if there are sigma bonds available for rotation?
pi bonds are the bonds that are not able to rotate, but sigma bonds do have that ability
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Re: chelating ligands
For these type of problems do we need to label all different types of bonds or does it not have to do with that necessarily?
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Re: chelating ligands
LianaHernandez1F wrote:For these type of problems do we need to label all different types of bonds or does it not have to do with that necessarily?
To answer your question, I am sure that is we need to know a bond then we will have to write it down and identify the bond as it will help us answer the question.
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