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] 3d 2 4s 2 So Ti 3+ has the electron configuration [Ar] 3d 1

8. 3d orbitals in Ti 3+ complex Energy

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

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… Zn 2+, 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 Ni 2+ complexes Absorbs red appears green Absorbs orange appears blue Ni(H 2 O) 6 2+ Ni(NH 3 ) 6 2+