Electronic spectra  of coordination complexes

Electronic spectra of coordination complexes PowerPoint PPT Presentation


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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.

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Electronic spectra of coordination complexes

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1. Electronic spectra of coordination complexes MT chapter 11, 10.5

2. Outline Absorption spectroscopy Selection rules 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

8. 8

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

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