HW 9C.5

[Janet Nguy 2C]

Hi!
Problem 9C.5 on the homework is this:

Which of the following ligands can be polydentate? If the
ligand can be polydentate, give the maximum number of places on
the ligand that can bind simultaneously to a single metal center:
(a) HN(CH2CH2NH2)2; (b) CO3
22; (c) H2O; (d) oxalate.

Can someone explain to me how to go about this problem, step by step? Do we draw the lewis structures for all of them and see which atoms have lone pairs and just count the # of atoms that have them? I also don't think I have a very good understanding of what it means to be polydentate...

[kevinchang_4I]

Polydentate means that it is a ligand with multiple donor atoms, or atoms with lone pairs that can bond to the central metal atom. So in order to solve this problem we have to look at which of these molecules has lone pairs. For (a) I googled the structure. Other people can recognize that all the N's have a lone pair but I am not that smart. This means (a) is polydentate, or tridentate to be more specific. For [CO3]2- we again look at the structure of the molecule. This one is hard bc based on resonance structures and the O's it can be mono and bidentate. Sorry but I don't have a great explanation for this. For (c) and H2O it is monodentate bc while the O has two lone pairs, they are facing oppositely from one another and thus only one can bond the a central metal atom. (d) is bidentate bc of the two oxygens that can donate electrons to the central atom. We see this by drawing the lewis structure.

Not the most clear explanation but I hope this helped a bit.

[Janet Nguy 2C]

Thank you so much, that was very helpful!

Does anyone have an explanation for when you deal with resonance?