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The correct order of the wavelength of light absorbed by the following complexes is:
A. $[\text{Co(NH}_3)_6]^{3+}$
B. $[\text{Co(CN)}_6]^{3-}$
C. $[\text{Cu(H}_2\text{O)}_4]^{2+}$
D. $[\text{Ti(H}_2\text{O)}_6]^{3+}$
Choose the correct answer from the options given below:
A. $[\text{Co(NH}_3)_6]^{3+}$
B. $[\text{Co(CN)}_6]^{3-}$
C. $[\text{Cu(H}_2\text{O)}_4]^{2+}$
D. $[\text{Ti(H}_2\text{O)}_6]^{3+}$
Choose the correct answer from the options given below:
A
B < D < A < C
B
B < A < D < C
C
C < D < A < B
D
C < A < D < B
Explanation
Crystal field splitting follows $\Delta_o \propto \text{charge on metal} \times \text{ligand strength}$: $\text{CN}^- > \text{NH}_3 > \text{H}_2\text{O}$. Since $\lambda_{\text{abs}} \propto 1/\Delta_o$, the absorbed wavelength order is $\text{B} < \text{A} < \text{D} < \text{C}$.
Detailed Solution
According to spectrochemical series, ligand field strength is $\text{CN}^- > \text{NH}_3 > \text{H}_2\text{O}$. Higher oxidation state on metal and stronger ligand increase crystal field splitting: $\Delta_o([\text{Co(CN)}_6]^{3-}) > \Delta_o([\text{Co(NH}_3)_6]^{3-}) > \Delta_o([\text{Ti(H}_2\text{O)}_6]^{3+}) > \Delta_o([\text{Cu(H}_2\text{O)}_4]^{2+})$. Since absorbed photon wavelength is inversely related to splitting ($\lambda = \frac{hc}{\Delta}$), the order of absorbed wavelength is $B < A < D < C$.