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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Ilaria on December 28, 2014, 07:18:21 AM

Title: DMSO as a ligand
Post by: Ilaria on December 28, 2014, 07:18:21 AM

I am studying the complex cis,fac-[RuCl₂(DMSO)₄], which has 3 DMSO molecules coordinated by the S atom and one by the O atom. Why is there π backdonation when DMSO is coordinated via S, while there isn't when the coordination is via O? In other words, why is DMSO-κS a π-acceptor ligand and why isn't DMSO-κO a π-acceptor ligand?

Title: Re: DMSO as a ligand
Post by: kriggy on December 28, 2014, 11:30:02 AM

I suggest comparing electron configurations of oxygen and sulphur

Title: Re: DMSO as a ligand
Post by: critzz on December 28, 2014, 02:31:31 PM

I think it can be explained in different ways, but here is one explanation involving electronegativity.
Since oxygen is more electronegative than sulfur, it likes to have a negative charge on oxygen rather than on the sulfur atom.
By π-back donation (or accepting electrons from the metal), the S-coordinated DMSO can delocalize electron density on the oxygen atom. (see picture)

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi58.tinypic.com%2F15e92m1.gif&hash=e16db52d84336df3585e9b2f4ea764343bfbb4a6)

Title: Re: DMSO as a ligand
Post by: Ilaria on December 29, 2014, 02:28:31 AM

Thank you for the explanation!
Now I have another question regarding the same complex: I've found in literature that the cis isomer is the facial one, but why couldn't it be the meridional?

Title: Re: DMSO as a ligand
Post by: critzz on December 29, 2014, 12:05:56 PM

From what I've read, the meridional product does exist; however, the facial product is the thermodynamic stable one.
The -S-DMSO is more steric demanding than the O-DMSO, so probably it has to do with sterics.

Here is the synthesis from what i've found.

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi58.tinypic.com%2F20qb53a.jpg&hash=909df445952d6ea748fbafc8776fc1419a17cde2)

DOI: 10.1021/cr0307291

Title: Re: DMSO as a ligand
Post by: Ilaria on December 30, 2014, 05:47:58 AM

Thank you, particularly for the article. I didn't know about it, even if the author is my teacher!