Question

5. The visible absorption spectra of four cobalt complexes are shown in the following figure. Assign, with justification, the spectra curves A, B, C, and D to complexes [CO(NH3)], [CO(NH3)], [Co(H20).], and [CoCl. (4 marks) os in L molem 5 10 30 35 15 20 (103 cm 25 )

please assign, with detailed explanations. thank you!

Answer 1

The visible spectra for these complexes are based on their CFSE vales. The more the CFSE value, the more will be its absorption peak.

1.[Co (NH3)6]2+  ...... Co2+

2. [Co (NH3)6]3+ ...... Co3+

3. [Co(H2O)]2+ ........ Co2+

4. [CoCl4]2- ......... Co2+

According to spectrochemical series, ligand strength is given decreasing order,

NH3 > H2O > Cl- and +3 Oxidation state has higher CFSE then +3 O.S

Therefore, CFSE order is given in decreasing order as,

2> 1>3>4 so, A is 2, B is 1 , C is 3, D is  4.