Question
Explain the following:
Cobalt metal complex is pink when it is octahedral [Co(H2O)6]2+ and it is blue when tetrahedral [CoCl4]2–
Solution
[CoCl4]2– is blue in colour as lower energy (red regions) light is absorbed by the CO2+ metal ion for d-d transition. Also tetrahedral complex does not possess centre of symmetry.