Light

1
Light . ITS ENERGY!
The Electromagnetic Spectrum.
absorption
The Artists Colour Wheel.
We can determine the colour of a compound from
the light it absorbs. Complimentary colours are
on opposite sides of the wheel.
apparent colour
2
How many transitions?
t2g1
eg1
The absorption of visible light promotes the t2g
electron to the eg. The energy of the light
corresponds to ?o. This is because there is only
one possible transition.
Do we see only ONE absorption if we have ONE
d-electron?
At first glance this may appear true.but is it?
3
dn Transitions
We must remember that any d ? d transitions
observed are spin-allowed. This means that in
such a dn configuration you will observe as many
E.S.s as is possible as long as the spin of the
electron doesnt change.
E.S.1 is of lower energy than E.S.2
4
Energies of Transitions.
E.S.1 is of lower energy than E.S.2
But there are three absorptions!!! WHY?
The highest energy transition corresponds to the
promotion of both electrons.
5
What about other dn systems?
6
What governs the magnitude of ??

• The identity of the metal.
• CFS of 2nd row TMs is 50 greater than 1st row.
• CFS of 3rd row TMs is 25 greater than 2nd row.
• There is also a small increase in CFS along each
  period.
• The Oxidation State of the metal.
• Generally, the higher the oxidation state of the
  metal the greater the splitting. This explains
  why Co(II) complexes are H.S. and most Co (III)
  complexes are L.S.
• The Number of Ligands.
• This was already hinted at when we looked at
  Tetrahedral vs. Octahedral splitting. In this
  case the ?T 4/9 ?O.
• 4. The nature of the ligands.

7
Invisible Ink
heat
2Co(H2O)6Cl2(s)
CoCoCl4(s) 12 H2O
Why does this happen?