Question for chemists about lanthanide-carboxyl structures and their formation

[Juche]

In a lab I work at at school we are trying to create aggregates of the lanthanide gadalinium along with carboxyl groups which are attached to a long (20 or so) carbon chain. The problem is we are getting polymers of lanthanides with carboxyls instead of a large number of universally sized aggregates of a single gadolinium atom bonded to three carboxyl groups, which is what we want.

Does anyone have any advice, input or can you point me in the direction of any books or scientific articles on carboxyl/lanthanide structures and their formation? I would appreciate it as right now I'm trying to learn about the nature of what's going on and how to create gadolinium with 3 carboxyls on it instead of a massive polymer.

We are trying to create gadolinium 3+ atoms with metalloligand bonds to three carboxyl groups in the hope that this will fulfill the f-shell of the Gd.

My inorganic chemistry is a bit rusty though, and I learned more about S and P shells, not F shells. I know lanthanides have 7 electron shells (s=1, p=3, d=5, f=7) and I'm pretty sure that a gadolinium 3+ atom would have 6 electrons in its shell. From what I remember you want as many electrons to be unpaired as possible, but I thought that a 2+ charge was considered the de facto number of electrons which woudl mean that Gadolinium 3+ already has 6 unpaired electrons, and would prefer to only make one bond. Some Gd-ligand complexed like Gd-DTPA
or Gd-DOTA
show 8 bonds. You'd assume that would happen as Gd in a 3+ state has room for 8 electrons.

However some pictures of Gd-DTPA or Gd-DOTA show the Gd bonded to a water molecule as well, making 9 ligands. Where do the extra water electrons go? Where do they fit?

In my view, maybe we are going about this all wrong for a few reasons.

1. Gadolinium 3+ will only accept 1 electron to gain stability since it'll have 7 unpaired electrons. it can hold up to 8. Trying to add 3 ligands (the professor thinks that Gd 0 is the most stable form) may be unwise as we'll have 2 sets of paired electrons and 5 unpaired electrons. I don't have any idea how to draw up the MO for an f shell bond though. I barely understand how to do it for S and P shells.
2. Gadolinium can bond with up to 8 things, I don't understand F block inorganic chemistry nearly well enough to know what happens to encourage metalloligand bonding, but I just don't see how it is realistic to have only 3 bonds. Either we'd have 1 bond or 8 bonds.


Would we be better off trying 1+ Neodymium, 2+Promethium, 3+ Samarium or 4+ Europium instead of 3+ Gadolinium? Are any of these molecules stable or affordable? Are things like 5+ Gadolinium stable or existant? Is having a charge of 0 more important than having the maximum number of unpaired electrons?

Would doing the synthesis in an acidic environment help any? From what I've gathered by talking to the other professors there is resonance in the carboxyl oxygens, making 2 possible ligands on one molecule. If we left the hydrogen on and had a carboxylic acid would that still be able to metaolligand bond with the Gd?

Keep in mind that my chemistry isn't great, so there can be problems with my view on this subject of f shells and how they relate to metalloligand bonding but any info is helpful.

 

[Valerie Park]

Any advice, input or sources you can point me in the direction of for more reading would be greatly appreciated!

 

[ravenprp]

Hi there,

Thank you for your question about lanthanide-carboxyl structures and their formation. As a chemist, I can provide some insight and resources that may be helpful to you in your research.

Firstly, it's important to understand that the formation of lanthanide-carboxyl structures is a complex and multifaceted process. There are many factors that can influence the formation of these structures, including the choice of ligands, solvent, temperature, and pH. Therefore, it's difficult to pinpoint exactly why you are getting polymers instead of the desired aggregates without more information about your experimental conditions.

That being said, I can offer some general advice and suggestions based on my understanding of lanthanide chemistry. Firstly, it's important to carefully choose your ligands. Carboxyl groups are known to form strong bonds with lanthanides, but the length and flexibility of the carbon chain can also play a role in the formation of aggregates. Additionally, the choice of solvent can greatly affect the formation of aggregates. For example, polar solvents like water tend to favor the formation of polymers, while nonpolar solvents may promote the formation of aggregates.

In terms of resources, I would recommend looking into the work of Prof. Peter Comba at the University of Heidelberg. He has published extensively on lanthanide carboxyl structures and their formation, and his research may provide some insights into your own experiments. Additionally, there are many textbooks on lanthanide chemistry that may be helpful in understanding the nature of lanthanide complexes and their bonding.

Regarding your question about the number of bonds that a lanthanide can form, it's important to note that the number of bonds a lanthanide can form varies depending on its coordination geometry and the nature of the ligands. In general, lanthanides are known to form up to 12 coordination bonds, but this can vary depending on the specific compound. As for your question about the stability of different lanthanide ions, it's difficult to say without more information about your specific compounds and experimental conditions. Generally, the stability of a compound depends on a variety of factors, including its structure, solvent, and pH.

In conclusion, I would recommend carefully considering your choice of ligands and experimental conditions when attempting to form lanthanide-carboxyl structures. Additionally, consulting with a more experienced chemist or seeking out additional resources may also be beneficial in understanding the nature of these structures and