1. Colour and the d block

2. UV / Vis frequencies are have photons with energies of the sort of values needed to promote electrons from their ground state energy level to a higher level.
A typical substance will require UV photons so does not absorb Visible light.
Most substances are colourless.

3. d – block metal complexes
These have unusually close energy levels due to the splitting of the 3d orbitals in a non spherical environment.

4. 3d orbitals in gas
Energy

5. But in an octahedral complex two of the orbitals will be closer to ligands than the other three.
But ligands usually have a negative charge…
..so electrons in the d orbitals are repelled. They have a higher energy

6. 3d orbitals in complex
Energy
Further from ligands
Closer to ligands

7. d electrons will tend to go preferentially into the lower energy orbitals further from the ligands.
Ti has the electron configuration
[Ar] 3d2 4s2
So Ti3+ has the electron configuration
[Ar] 3d1

8. 3d orbitals in Ti3+ complex
Energy

9. 3d orbitals in Ti3+ complex
Absorbs a photon of yellow light
Energy

10. So what d block complexes will not be coloured ?
Ones with no d electrons eg……
Sc 3+, Ti 4+
..or those for which the d shell is full so electrons cannot move. Eg…
Zn2+ , Cu+

11. 3d orbitals in Cu+ complex
Energy

12. Different ligands cause different degrees of splitting of the d orbital energies.
Ligand exchange therefore usually causes a change of
colour

13. 3d orbitals in Ni2+ complexes
Absorbs orange appears blue
Absorbs red appears green
Ni(H2O)62+
Ni(NH3)62+