Why water is a weak field ligand whereas oxalate ion is strong?

Dear Ankit

 

In my opinion both are weak field ligands. 

 

Please check

 

Explanation for water

 

water is a weak field ligand becaz in it oxygen has 2 lone pair of electrons first it donate its electrons to eg orbiatal and second pair of electrons it cannot donate becaz it already donated one pair of electrons.The second pair of electrons cases repulsion with eg electrons which water’s oxygen already donated to metal centre therefore the energy gap b/w eg and t2g decrease due to the repulsion b/w electrons and delta value becomes smaller eg and t2g comes close to each other due to the electrinic repulsion and hence it becomes weak field ligand.