how to tell coordination number

[Tiao Tan 3C]

I usually find coordination # directly from the molecular formula by counting the number of ligands in the bracket. Is this always correct? Are there any special cases where we need to draw the lewis structure to find out?

[Megan Hulsy 1A]

When you have (en) --> bidentate, (edta)--> hexadentate, and (ox)--> bidentate as ligands, you need to understand that they're polydentate. So if you have a molecule, for example, [PtCl2(en)2]^2+, the coordination number is 6 since en is bidentate, multiplied by the 2 subscript, and added to the 2 on Cl. Hope this helps!

[Pranav Daggubati 3C]

It is the sum of all the number of binding sites on the ligands as long as the number is or less than 6. For example, [Fe (NH3)2 Cl3] would be 5, 3 from the chloridos and 2 from the ammines.

[annabelchen2a]

I agree with the posts above, you would have to remember the 4 most common polydentate ligands and how many sites they can bond - so en is bidentate, dien is trident ate, oxalate is bidentate, and edit is hexadente. I also have written in my notes that you can identify coordination number by the number of bonds in the coordination sphere. This should work unless you have those polydentate ligands, and then depending on how many of those ligands there are, then you multiply that number by 2, 3, or 6 (depending on how many bonding sites it has).