Coordination Compounds - Result Question 42
####45. Correct increasing order for the wavelengths of absorption in the visible region the complexes of $Co^{3+}$ is :-
[2017]
(a) $[Co(H_2 O)_6]^{3+},[Co(en)_3]^{3+},[Co(NH_3)_6]^{3+}$
(b) $[Co(H_2 O)_6]^{3+},[Co(NH_3)_6]^{3+},[Co(en)_3]^{3+}$
(c) $[Co(NH_3)_6]^{3+},[Co(en)_3]^{3+},[Co(H_2 O)_6]^{3+}$
(d) $[Co(en)_3]^{3+},[Co(NH_3)_6]^{3+},[Co(H_2 O)_6]^{3+}$
Show Answer
Solution:
- (d) The order of strength of ligand is
en $>NH_3>H_2 O$
For strong ligand, the value of $\Delta_0$ for the complex is higher.
Hence, the increasing order of wavelengths of absorption is:
$[Co(\text{ en })_3]^{3+}<[Co(NH_3)_6]^{3+}<[Co(H_2 O)_6]^{3+}$
Higher value of $\Delta_0$ means higher stability, which means it will absorb high energy photons. High energy photons have low value of wavelength.
