The wavelengths of light absorbed by the complexes \(\left[\mathrm{Ni}\left(\mathrm{H}_2…
The wavelengths of light absorbed by the complexes \(\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+},\left[\mathrm{Ni}(\mathrm{en})_3\right]^{2+},\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_4 \mathrm{en}\right]^{2+}\) are \(\lambda_1, \lambda_2, \lambda_3\) respectively. The correct order of wavelengths is
\(\lambda_1 > \lambda_2 > \lambda_3\)
\(\lambda_3 > \lambda_2 > \lambda_1\)
\(\lambda_1 > \lambda_3 > \lambda_2\)
\(\lambda_2 > \lambda_3 > \lambda_1\)
Solution
The wavelength of the light absorbed by the complexes \(\propto \frac{1}{\text { strength of ligands }}\).
Strength of ligand is en \( > \mathrm{H}_2 \mathrm{O}\).
Hence, energy absorbed would be in order of \(\left[\mathrm{Ni}(\mathrm{en})_3\right]^{2+} > \left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_4 \mathrm{en}\right]^{2+} > \left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}\)
Hence, wavelength order would be
\(\underset{\left(\lambda_1\right)}{\left[\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_6\right]^{2+}} > \underset{\left(\lambda_3\right)}{\left[\left(\mathrm{Ni}\left(\mathrm{H}_2 \mathrm{O}\right)_4 \mathrm{en}\right)\right]}^{2+} > \underset{\left(\lambda_2\right)}{\left[\mathrm{Ni}(\mathrm{en})_3\right]}^{2+}\)
Hence, \(\left(\lambda_1 > \lambda_3 > \lambda_2\right)\).