colour and the d block l.
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Colour and the d block. 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. .

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Colour and the d block


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Presentation Transcript
slide2
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.
d block metal complexes
d – block metal complexes
  • These have unusually close energy levels due to the splitting of the 3d orbitals in a non spherical environment.
slide5

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

3d orbitals in complex
3d orbitals in complex

Energy

Closer to ligands

Further from ligands

slide7

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

3d orbitals in ti 3 complex9
3d orbitals in Ti3+ complex

Absorbs a photon of yellow light

Energy

slide10

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+

slide12

Different ligands cause different degrees of splitting of the d orbital energies.

Ligand exchange therefore usually causes a change of

colour

3d orbitals in ni 2 complexes
3d orbitals in Ni2+ complexes

Absorbs orange appears blue

Absorbs red appears green

Ni(H2O)62+

Ni(NH3)62+