Question

Absorption maxima values for the most intense peaks are given for the following UV-Visible Spectrum:

for [Co (en)₃] Cl₃ : 465 nm

for [Co(NH₃)₆]³⁺ (aq): 480 nm

for [Co(NO₂)₆]^_3- (aq): 358 nm

for [Co(gly)₃] (aq); 542 nm

for [Co(ox)₃]^3- (aq): 422 nm

for [Co(OH₂)₆]³⁺ (aq): 607 nm

Rank the ligands ( start with the largest energy separation first) in terms of their ability to increase the energy separation between the ground and excited state in the cobalt (III) complexes, and explain why you ranked in that way.

Answer 1

Energy formula is given by

where h is constant and mu is frequency

Now this can also be written as

c is constant

Eneregy is inversely proportional to wavelength

So the complex with largest energy separation will absorb smallest wavelength

So the order is as follows largest energy separation first

[Co(NH3)6]3+ (aq): 341 nm and 480 nm

[Co(NO2)6]3- (aq): 358 nm

[Co(gly)3] (aq); 382 nm and 542 nm

[Co(ox)3]3- (aq): 422 nm

[Co (en)3] Cl3 : 465 nm

[Co(OH2)6]3+ (aq): 607 nm