Colour 🖌 🌈

  • Electronic spectra UV Vis - we will be looking at 2 different spectra. this will be in the UV and Visible regions.
  • one thing to remember is that we work with complimentary colors.

2 different spectra

Charge transfer spectra

🕑Ligand field spectra

Colour Vs Intensity

Intensity is how bright a colour is, not what the colour is. Energy is the same but the intensity is different.
Intensity is goverened by different things.

  • intensity has to do with the alowed-ness of the electronic transition

colour is colour (red vs blue)

  • these are intense absorptions (see bright colour)
  • use extinction coefficient (Beer Landa Law) equation - basically to use to determine the allowed-ness
  • tends to be in UV but tails off in the visible region.
  • [MnO4]- a d0 thus we see charges transfer between metal and ligand

LMCT

  • corresponds to the reduction (gain) of electrons
  • common in metals that can be reduced or in ligands that can be oxidised.
  • example: TiI4

MLCT

  • corresponds to the oxidation of a metal and the reduction of a ligand
  • typically found in complexes where the ligands have low lying empty pie-acceptor orbitals.
  • example Ti(bippy)3
  • close to "non-innocent" behavior
    Annotate the transitions
  • involves the charge transferee between d-orbitals

Quantum numbers

Recap: n L ML s

microstates (look at 2p2 example drawn below)

  • microstates only have the same energy if repulsions are negligable (but atoms & molecules are compact thus we can not ignore)
  • group all of the same energy states together
  • end up with Terms a spectroscopically distinguishable energy levels and we look at the transitions between these Terms
  • for 3d series (lightest series) we need to consider: the spin of the electron and the orrientation of the anguar momentum
  • when we get down to the heavier d series wee see the coupling (just need to know)
  • can group all the spins to get the Total spin quantum number
  • Total orbital angular momentum
  • Russel Saundres coupling

Russel Saundres scheme

  • we neek to know what values of L and S can arrise in atom
  • apply the Clebsch Gordan series
    Spin coupling:
  • S = (s1 + s2+ s3...)+(s1+s2+s3..-1)+ (s1+s2+s3...-2)+...
  • S must be positive or 0
    Orbit-Orbit coupling
  • same idea for L
  • The value of L determins an energy state for a system of electrons defined by term letters:
    L(orbital A) l 0 l 1 l 2 l 3 l 4 l 5 l
    Term letter l S l P l D l F l G l H l

Quantum no. ML and Ms

  • these quantum no gives the orientation of of the angular momentum relative to arbitrary axis
  • actual values of ML and MS for given microstates found easily by adding values of ml and ms for individual electrons
    Equation to find microstates

Spin-spin coupling > Orbit-orbit coupling > Spin-orbit coupling

Spin selection rule

Can be relaxed by spin-orbit coupling

Orbit (laport) selection rule

Add diagram

L = +/- 1

  • in a central semetric molecule/ ion the only allowed transition are those that are accompaniede by a change in party. (it has a center of inversion)

Spin & Laport values