110330 - observed Strong field ligand Weak field ligand...

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1 CHM3400 - Lecture 31 Mar 30 Coordination compounds (Chapter 12 469- 483) Coordination complexes Hard and soft ligands Crystal field splitting Octahedral, tetrahedral, square planar Protein examples
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2 Coordination complexes Coordination complex = metal ion with ligands forming a complex Metal (=acid) in center surrounded by ligands Coordination number = number of ligands
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3 Hard and soft acids and bases
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4 Crystal field theory Splitting of degenerate d orbitals on metal due to repulsion of valence electrons on metal and lone pair on ligands Energy of orbital is raised due to head-on ligand interaction
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5 Octahedral complexes Crystal field splitting Δ Lowering of d(xy), d(yz), d(xz) Raising of d(x 2 -y 2 ) and d(z 2 ) Crystal field stabilization energy ( CFSE ) = n(e g )(0.6 Δ ) - n(t 2g )(0.4 Δ )
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6 Crystal field splitting magnitude I - < Br - < SCN - < Cl - < F - < OH - < H 2 O < NH 3 < en < NO 2 - < CN - < CO Energy of photon corresponds to energy level splitting Predict energy from λ
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7 High spin – low spin Depending on the crystal field splitting, high or low-spin complex is
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Unformatted text preview: observed Strong field ligand Weak field ligand What rule predicts high spin? 8 Other symmetries Can you rationalize the different energy splittings? Splitting for tetrahedral complexes smaller . spin complexes 9 Molecular orbital theory Crystal field theory is easy to understand, but it completely neglects the covalent character of metal-ligand bonds. Non-bonding orbitals Anti-bonding orbitals 10 Coordination compounds in biological systems Iron in hemoglobin Why not possible? 11 High- and low-spin Fe 2+ Fe 2+ : d 6 O 2 binding No O 2 binding Remember cooperative binding for hemoglobin Low-spin more compact complex fits into heme group 12 CO binding to hemoglobin Why is CO binding to hemoglobin much stronger than O 2 binding (200x stronger)? 13 Zn affinity for tetrahedral binding Zn 2+ d 10 configuration What is the crystal field stabilization energy? Why is tetrahedral ligand chelation favored?...
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This note was uploaded on 05/29/2011 for the course CHM 3400 taught by Professor Seabra during the Spring '08 term at University of Florida.

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110330 - observed Strong field ligand Weak field ligand...

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