Determining if ligands can be polydentate

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Matt Jacobs 3H
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Joined: Fri Sep 25, 2015 3:00 am

Determining if ligands can be polydentate

Postby Matt Jacobs 3H » Sun Nov 08, 2015 1:01 pm

How does one know how many lone pairs are on an atom? For example, on the ligand HN(CH2CH2NH2)2, I am aware that this ligand can be polydentate because it has three nitrogens each with a lone pair that are available for bonding to a metal center. But how do we know that each nitrogen has that lone pair? Is it determined from the Lewis Structure?

A similar question can be asked for the oxygen atoms in Oxalato (C2O42-), why is it that only two of the oxygens can bind to the central metal ion and not all four?

Kaitlin Ross 3E
Posts: 25
Joined: Fri Sep 25, 2015 3:00 am

Re: Determining if ligands can be polydentate

Postby Kaitlin Ross 3E » Sun Nov 08, 2015 4:15 pm

The number of lone pairs present on each nitrogen atom can be determined by drawing out the Lewis structure for the ligand:
Link to diagram of the Lewis structure: https://docs.google.com/document/d/1xxtNVzFpruKS51Ya52gijr0SXVZl5POTZda4wvuXi2M/edit?usp=sharing
For Oxalato, only two of the four oxygen atoms are willing to donate an electron pair because they have a formal charge of -1. The other two oxygen atoms are double bonded to the carbon atoms giving them a formal charge of 0. If the two oxygen atoms with a formal charge of 0 were to bond with a transition metal, then they'd acquire a formal charge of +1 making the structure less stable.


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