Outline. Absorption spectroscopySelection rulesCharge transfer bandsJahn-Teller distortions. 2. 3. Colors given by transition metals. Prussian blueapprox. KFe2Fe(CN)6. emeraldCr(III) into Be3Al2(SiO3)6. amethystFe(II), Fe(III), and Ti(IV)into SiO2. rubyCr(III) into Al2O3. 4. Absorption of light.
1. Electronic spectra of coordination complexes MT chapter 11, 10.5
2. Outline Absorption spectroscopy
Charge transfer bands
Jahn-Teller distortions 2
3. 3 Colors given by transition metals
4. 4 Absorption of light
5. Beer-Lambert absorption law 5
6. Selection rules Laporte selection rule: transitions between states of the same parity (symmetry with respect to a center of inversion) are forbidden.
Spin selection rule: transitions between states with different spin multiplicities are forbidden. 6
7. Mechanisms to relax the selection rules Vibronic coupling: because of vibrations, the symmetry is temporarily changed (i.e. no inversion center in Oh complexes).
Orbital mixing: Td complexes absorb more strongly than Oh complexes because p and d orbitals mix more readily in Td than in Oh.
Spin-orbit coupling: the spin and orbital angular momenta couple with each other. It is less important for 1st row complexes, more important for 2nd and 3rd row complexes. 7
9. Charge transfer bands LMCT (ligand-to-metal charge transfer): electrons from the ligands are excited to metal orbitals (usually from p donors).
MLCT (metal-to-ligand charge transfer): electrons from the metal are excited to ligand orbitals (usually to p acceptors). The metal gets oxidized. 9
10. Jahn-Teller distortions Jahn-Teller effect: there cannot be unequal occupation of orbitals with identical energies. 10
11. Jahn-Teller distortions and spectra 11