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Transcript
Chapter 24: 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 d0 or d10 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 = hc/
OR = hc/ E
• We see the color which is NOT absorbed, but which was reflected or transmitted.
• We see the complementary color of what was absorbed.
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
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-<H2 O<NH3<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