|Themes > Science > Chemistry > Miscellenous > Help file Index > Complex Ions > Crystal field theory: complex color|
The energy difference D in many complexes is about equal to the energy of a photon of visible light. When a complex is struck by a photon of the correct energy, it is absorbed and the electron jumps from the lower energy d orbitals to the higher ones. Since the complex absorbs light of that frequency and reflects the rest, we see the complementary color of light. To get the complement of a color, look at the color wheel below. Find the color that is absorbed, then move directly across the wheel to the other side to get the complement.
For example, the complex [Co(NH3]6]+3 absorbs light with a wavelength of 437 nm. This is in the blue-violet region of the spectrum. If we look directly across the color wheel from blue-violet, we see yellow: this complex appears yellow.
The magnitude of the splitting energy D can be gotten from the color of light absorbed. Remember that the energy of a photon of light is E = hc/l, where h is Planck's constant, c is the speed of light and l is the wavelength of light.
Example: The complex [Co(NH3]6]+3 absorbs light with a wavelength of 437 nm. What is the splitting energy D?
Solution: The complex absorbs light at this frequency, so D must be equal to this energy. We know that E = hc/l. h = 6.626*10-34 J*s and c = 3.00*108 m/s. The light wavelength is 437 nm, or 4.37*10-7 m. Thus, the energy of the light is