Question

What is the coordination number of Fe in the complex, K₃[Fe(C₂O₄)₃]?

Answer 1

The coordination complex is [Fe(C₂O₄)₃]³⁻ Potassium ions K⁺ are counter ions and do not affect coordination number. C₂O₄²⁻ is oxalate, a bidentate ligand and each oxalate ion donates two electron pairs to the metal center. 

There are 3 oxalate ligands

3 ligand is bidentate → donates 2 donor atoms

Coordination number of Fe

= 3 ligands × 2 

= 6