H2O vs C2O4 2-

[rita_h]

H2O is said to have a ligand that is monodentate (1 site to pair with a metal at the level of the oxygen atom due to presence of the lone pair).
In C2O4 2-, yes the two negative oxygens make up sites for metal bonding therefore serving as ligands- but why don't the lone pairs on the oxygen atoms (that are double bonded to carbon) also serve as ligands?

[Natalie Keung 1D]

I don't know if this is the proper way to view this, but it has worked for me so far. Whenever there are polydentate ligands, I always look for either lone pairs on the N atoms of lone pairs on O with a -1 charge.