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The Electronic Spectra of Coordination Compounds

The Electronic Spectra of Coordination Compounds. Charge Transfer Spectra.

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The Electronic Spectra of Coordination Compounds

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  1. The Electronic Spectra of Coordination Compounds

  2. Charge Transfer Spectra Many transition metal complexes exhibit strong charge-transfer absorptions in the UV or visible range. These are much more intense than dd transitions, with extinction coefficients ≥ 50,000 L/mol-cm (as compared to 20 L/mol-cm for dd transitions).

  3. Charge Transfer Spectra Examples of these intense absorptions can be seen in the permanganate ion, MnO4-. They result from electron transfer between the metal and the ligands.

  4. Charge Transfer Spectra In charge transfer absorptions, electrons from molecular orbitals that reside primarily on the ligands are promoted to molecular orbitals that lie primarily on the metal. This is known as a charge transfer to metal (CTTM) or ligand to metal charge transfer (LMCT). The metal is reduced as a result of the transfer.

  5. Charge Transfer Spectra _ _ eg d _ _ _ _ _ _ _ _ t2g _ _ _ _ _ _ _ _ _ _ _ _ free metaloctahedral complex ligand σ orbitals Ligand to metal charge transfer

  6. Ligand to Metal Charge Transfer LMCT occurs in the permangate ion, MnO41-. Electrons from the filled p orbitals on the oxygens are promoted to empty orbitals on the manganese. The result is the intense purple color of the complex.

  7. Ligand to Metal Charge Transfer LMCT typically occurs in complexes with the metal in a fairly high oxidation state. It is the cause of the intense color of complexes in which the metal, at least formally, has no d electrons (CrO42-, MnO41-).

  8. Metal to Ligand Charge Transfer MLCT typically occurs in complexes with π acceptor ligands. The empty π* orbitals on the ligands accept electrons from the metal upon absorption of light. The result is oxidation of the metal.

  9. Charge Transfer Spectra _ _ _ _ _ _ _ _ _ _ _ _ π* _ _ eg d _ _ _ _ _ _ _ _ t2g free metal octahedral complex ligand π* orbitals Metal to ligand charge transfer

  10. Metal to Ligand Charge Transfer Examples of LMCT include iron(III) with acceptor ligands such as CN- or SCN1-. The complex absorbs light and oxidizes the iron to a +4 oxidation state.

  11. Metal to Ligand Charge Transfer The metal may be in a low oxidation state (0) with carbon monoxide as the ligand. Many of these complexes are brightly colored, and some appear to exhibit both types of electron transfer.

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