The correct order of the complexes [Co(NH3)5(H2O)]3+ (A), [Co(NH3)6]3+ (B), [Co(CN)6]3- (C) and [CoCl(NH3)5]2+ (D) in terms of wavelength of light absorbed is
- D > C > B > A
- C > B > A > D
- D > A > B > C
- C > B > D > A
Answer
(3) D > A > B > C
Solution
All four are octahedral Co3+ complexes; they differ only in the ligands.
Spectrochemical series: Cl- < H2O < NH3 < CN-
Crystal field splitting: o (C) > o (B) > o (A) > o (D)
(B has six NH3; A has one NH3 replaced by the weaker H2O; D has one NH3 replaced by the still weaker Cl-.)
o = hc 1 o
Wavelength of light absorbed: D > A > B > C
Answer: (3)