Which of the following complex has highest ∆o value?  (1) [Fe(H2O)6]2+,   (2) [Fe(H2O)6]3+, (3) [Fe(CN)6]3-,        (4) All have equal values.

Asked by patra04011965 | 21st Jul, 2019, 11:40: PM

Expert Answer:

Factors Affecting Δo:

1. Geometry of the Complex:  Δt is approximately 4/9 times of Δ. The lower value of Δt is due to lesser number of ligands in tetrahedral complex. 

Given three complxes are octahedral.

2. Oxidation state of metal ion: It is observed that the higher the charge on the central metal atom (or oxidation state), the higher the CFSE.

e.g., Δo for [Fe(CN)6]3- and [Fe (H2O)6]3+ is greater than [Fe (H2O)6]2+

3. Nature of ligand: The value of Δo depends upon the nature of ligands.

Some ligands in spectro chemical series are given below:

I2– < Cl < N3, F < Urea, OH < Oxalate, O2– < H2O < NCS < EDTA < py, NH3 < en =SO3-2 < bipy, phen < NO2 < CH3 < C6H5 < CN < CO.

For strong field ligands, the order depends on the donor atom and is in the following order:

C-donor > N-donor > O-donor > Halogen donor


In given compounds, [Fe(CN)6]3- and [Fe (H2O)6]3+ , [Fe(CN)6]3-  has strong field ligand CN– hence it has greater Δthan [Fe (H2O)6]3+

Complex [Fe(CN)6]3- have greater Δthan rest of given complexes because the charge on central metal ion is +3 and the central metal ion is bonded to a strong ligand CN– 

Answered by Ramandeep | 22nd Jul, 2019, 03:43: PM

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