Question

Which of the following complex ions is not optically active?

• A. \([ \text{Co}(ox)_3 ]^{3-}\)
• B. \(\text{cis}-[\text{Co}(en)_2\text{Cl}_2]^+\)
• C. \(\text{trans}-[\text{Co}(en)_2\text{Cl}_2]^+\)
• D. \([ \text{Co}(en)_3 ]^{3+}\)

Hint:

When dealing with optical activity, remember that symmetry leads to optical inactivity, as in the case of \(\text{trans}\)-complexes.

Answer 1

The Correct Option is C

Optical activity in a coordination compound arises when the compound is non-superimposable on its mirror image, i.e., it lacks symmetry. The \(\text{cis}-[\text{Co}(en)_2\text{Cl}_2]^+\) complex is optically active because of its asymmetric structure. However, the \(\text{trans}-[\text{Co}(en)_2\text{Cl}_2]^+\) complex is optically inactive because of its symmetry (the opposite chloride ions are opposite each other, making it symmetrical). Therefore, the correct answer is (C).