Question

The coordination number of cobalt in [Co(NH$_3$)$_6$]Cl$_3$ is:

• A. 3
• B. 4
• C. 6
• D. 8

Hint:

Do not confuse coordination number with the oxidation state of the metal.
In $[\text{Co}(\text{NH}_3)_6]\text{Cl}_3$, the coordination number is 6, while the oxidation state of cobalt is $+3$.
Only count the ligands inside the square brackets; counter-ions outside the brackets do not contribute to the coordination number.

Answer 1

The Correct Option is C

Step 1: Count donor atoms.
Six NH$_3$ directly bonded to Co (Cl$^-$ are outer-sphere counter ions). Coordination number = 6.
Answer: 6