So, I read that an oxalate ion is a bidentate ligand but since I saw that it has 4 oxygen atoms I was confused as to why it isn't a tetradentate ligand instead.
I searched it on Google and found this: Oxalate ion dentiticity - why is it bidentate and not tetradentate?
Now, in the link it's implied that the oxalate ion can donate the 2 pairs of electrons either from the 2 oxygen atoms having negative formal charge or from 1 "double-bonded" O atom and 1 negatively charged O atom.
But why can't the two pairs of electrons be donated from Both the "double-bonded" O atoms? Why isn't this "third" bonding mode possible?
EDIT: From the comment below, I infer that because of resonance, there is no double-bonded or negatively charged O atom in the Oxalate ion; rather all of the O atoms have a partial negative formal charge and double-bond character, is that correct?
So, can electrons be donated from any O atom in the ion?
(And so did the answer in the provided link just ignore this for the sake of simplicity?)