Polydentates: HW 17.33 6th Ed

[Phoebe Chen 4I]

Hi, I am unsure of how to tell if a ligand is a polydentate and specifically what polydentate. Does it have something to do with the number of lone pairs?

[Fayez Kanj]

Hey!

Ligands must have atleast 1 lone pair to be considered a ligand. So to determine whether a ligand is polydentate, you count how many atoms have atleast 1 lone pair

Follow this guide:

Bind at 1 site (donate 1 pair of electrons) → Monodentate
Binds at 2 sites (donates 2 pairs of electrons) → Bidentate
Binds at 3 sites (donates 3 pairs of electrons) → tridentate
Binds at 6 sites (donates 6 pairs of electrons) → hexadentate

In your example, for a), it would be tridentate, since there is a maximum of 3 places in which the ligand can bind to the central metal ion (one on each nitrogen)
b) this would be either mono dentate or bidentate, since there is a maximum of 2 places in which it can bind to the metal center (there are 2 oxygens that have a negative formal charge)
c) monodentate (can only bind to a center metal ion with the Oxygen atom, NOT the hydrogens)
d) bidentate for the same reason as above

Hope this helps :)

[AdityaGuru1H]

A polydented is a ligand that can bond to the transition metal in multiple places. Usually it is the large molecule that are polydente but for the final since we don't need to know that many it may be easier just to memorize them.
ethylenediamine and oxalate are bidentate
diethelynetriamine is tridentate
edta is hexaamine
You can look up all the ligand we need to know on page 742 of the 6th edition