Question
Chemistry Question on coordination compounds
Consider the following complexes:
[CoCl(NH3)5]2+ (A)
[Co(CN)6]3− (B)
[Co(NH3)5(H2O)]3+ (C)
[Cu(H2O)4]2+ (D)
The correct order of A, B, C, and D in terms of wavenumber of light absorbed is:
C < D < A < B
D < A < C < B
A < C < B < D
B < C < A < D
D < A < C < B
Solution
As the ligand field strength increases, the energy of light absorbed by the complex also increases. Since wavenumber νˉ∝ energy of absorbed light, the order of wavenumber depends on the ligand strength.
For [Co(CN)6]3− (B), CN− is a strong field ligand (highest νˉ).
For [Co(NH3)5(H2O)]3+ (C), NH3 and H2O have moderate ligand field strength.
For [Cu(H2O)4]2+ (D), H2O is a weaker field ligand.
For [CoCl(NH3)5]2+ (A), Cl− is the weakest field ligand (lowest νˉ).
Thus, the order is:
D<A<C<B.