Is Oxalate C2O42- a storng or weak field ligand? Does it cause pairing?
Oxalate ion (C2O42-) is a weak field ligand. It causes only a small splitting of energy levels due to which it is energetically more favourable for the electrons to occupy the upper eg level rather than pairing up in the t2g level. Example: K3[Fe(oxalate)3] 3H2O is a high spin complex with five d electrons distributed as t2g3 eg2.