Question

What is the coordination number of Co in the complex \( K_3[Co(C_2O_4)_3] \)?

• A. 3
• B. 4
• C. 5
• D. 6

Hint:

Oxalate is bidentate; three oxalate ligands each occupy two sites.

Answer 1

The Correct Option is D

Step 1: The coordination number is the number of ligand donor atoms directly bonded (coordinated) to the central metal ion.
Step 2: The ligand here is oxalate \( (C_2O_4)^{2-} \), which is a bidentate ligand: each oxalate binds the metal through two oxygen donor atoms.
Step 3: There are three oxalate ligands. Donor atoms = \( 3 \times 2 = 6 \).
Step 4: Hence the coordination number of Co is 6, so option (iv) is correct. The number of ligand molecules (3) is not the coordination number, which is why option (i) is wrong.