JEE Chemistry 2023 Question with Solution

Step-by-step solution

Standard Method

Given: The complex is $fac-\left[Co(NH_3)_3Cl_3\right]$.

Find: The value of the $\text{Cl} - \text{Co} - \text{Cl}$ bond angle.

The correct answer is B : $90^\circ$.

In the given octahedral complex, the three Cl ligands in the fac isomer occupy positions on the same face of the octahedron. Therefore, every $\text{Cl} - \text{Co} - \text{Cl}$ angle is a cis angle.

Hence, the bond angle is $90^\circ$.

Therefore, the correct option is B.

Common mistakes

• Confusing fac with mer. In the fac isomer, the three identical ligands are all mutually cis, so the $\text{Cl} - \text{Co} - \text{Cl}$ angle is $90^\circ$. The mer isomer would include a trans relationship.

• Assuming an octahedral complex always has both $90^\circ$ and $180^\circ$ angles for any chosen pair of identical ligands. Octahedral geometry allows both cis and trans positions, but in this specific fac arrangement the Cl ligands are only cis to one another.