Correct increasing order for the wavelengths of absorption in the visible region the complexes of $Co^{3+}$ is :

Question

What is the chemical formula of glycerol?

Answer 1

The given question requires us to determine the correct increasing order of the wavelengths of absorption in the visible region for the complexes of Co^{3+}. The options provided are different coordination complexes of cobalt(III) with different ligands.

To solve this, we need to consider the ligand field strength, which influences the d-d transition energies in the metal complexes. According to the spectrochemical series, ligands can be arranged in order of increasing field strength. Common ligands and their relative positions in the series are:

H_2O (water): Weak field ligand
NH_3 (ammonia): Moderate field ligand
en (ethylenediamine): Strong field ligand

Ligands with higher field strength cause a greater splitting of the d-orbitals, resulting in a greater energy difference between the split d-orbitals. Consequently, complexes formed with stronger field ligands absorb light at shorter wavelengths (higher energy).

Now, let's analyze the complexes in the given options:

[Co(H_2O)_6]^{3+}: Contains water, a weak field ligand
[Co(NH_3)_6]^{3+}: Contains ammonia, a moderate field ligand
[Co(en)_3]^{3+}: Contains ethylenediamine, a strong field ligand

Considering the increasing order of ligand field strength from weak to strong:

H_2O < NH_3 < en

This means the wavelength of absorption, which is inversely related to the ligand field strength, should be in the order:

\lambda_{[Co(en)_3]^{3+}} < \lambda_{[Co(NH_3)_6]^{3+}} < \lambda_{[Co(H_2O)_6]^{3+}}

Therefore, the correct increasing order of the wavelengths of absorption in the visible region for the complexes is:

[Co(en)_3]^{3+} ,\, [Co(NH_3)_6]^{3+},\, [Co(H_2O)_6]^{3+}

Answer 2