C401Ch20LN2 - between the metal’s d-electrons and the...

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Chapter 20: Transition Metals Coordination Compounds Part 2 Transition Metals The transition metals include the d-block, Groups 3-12. The inner transition metals include the f-block elements. Many transition metals form beautifully colored solids and solutions. Why are so many transition metal complexes colored? Usually only metals with d 0 or d 10 form colorless compounds (Zn, Ag). Colors in metal complexes (or any compound) is due to their absorption spectrum. When a metal complex absorbs light, an electron undergoes an electronic transition from a ground state to an excited state. Remember: ± E = h c/ ² OR ² = h c/ ± E We see the color which is NOT absorbed, but which was reflected or transmitted. We see the complementary color of what was absorbed.
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Crystal Field Theory Why do metal complexes absorb light in the Vis light spectrum? Crystal Field Theory tries to explain this. When a ligand approaches a free metal atom or ion in order to form a bond, e-e repulsions occur
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Unformatted text preview: between the metal’s d-electrons and the ligands electrons. • This causes the metal’s 5 degenerate d-orbitals to increase in energy AND to split. • So they are no longer degenerate. • Different ligands cause more of an energy split in the d-orbitals. • Ligands which cause the d-orbitals to split more with a higher ± E are called strong-field ligands. • Ligands which cause the d-orbitals to split less with a lower ± E are called weak-field ligands. • Ligand Series from Weak to Strong: I-<Br-<Cl-<F-<H 2 O<NH 3 <en<CN- • Ligand splitting of a metal’s d-orbitals also explains why some complexes are highly paramagnetic and others are diamagnetic or weakly paramagnetic. • Highly Paramagnetic: These are weak field complexes with a low ± E, so the d-e are easily promoted. The result is a complex with many unpaired electrons, or a high-spin complex. Octahedral Complexes Tetrahedral & Square Planar Complexes...
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This note was uploaded on 06/25/2008 for the course CHEM 400-401 taught by Professor Dr.samples during the Fall '06 term at American River.

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C401Ch20LN2 - between the metal’s d-electrons and the...

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