5 5 Colour in
Coordination
Compounds
Coordinaton
entity
Wavelength of light
absorbed (nm)
Colour of light
absorbed
Colour of coordination
entity
Table 5 3: Relationship between the Wavelength of Light absorbed and the
Colour observed in some Coordination Entities
[CoCl(NH3)5]
2+
535
Yellow
Violet
[Co(NH3)5(H2O)]
3+
500
Blue Green
Red
[Co(NH3)6]
3+
475
Blue
Yellow Orange
[Co(CN)6]
3–
310
Ultraviolet
Pale Yellow
[Cu(H2O)4]
2+
600
Red
Blue
[Ti(H2O)6]
3+
498
Blue Green
Violet
The colour in the coordination compounds can be readily explained
in terms of the crystal field theory Consider, for example, the complex
[Ti(H2O)6]
3+, which is violet in colour