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Isomerism & Crystal Field Theory Chapter 24 – Lecture 3
Chemistry 123 Spring 2008 Dr. Woodward
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Isomers Different ligands make bonds to the metal
Ligands bond to the metal through different atoms Ligands have different (ligand) neighbors Molecules are non-superimposable mirror images
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Linkage Isomers
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Geometric Isomers
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Optical Isomers
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Intra-atomic (d to d) excitations
MnSO4 FeSO4 CoSO4 NiSO4 CuSO4 ZnSO4 In these complexes the color comes from absorption of light that leads to excitation of an electron from one d-orbital to a different d-orbital on the same metal cation.
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[M(H2O)6]n+ Complex ions
MO6 Octahedron H2O
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Crystal Field Splitting (Octahedron)
Energy dz2 & dx2-y2 orbitals (eg) Point directly at the ligands Stronger (repulsive) interaction with the ligands dz2 dx2-y2 dxy, dyz & dxz orbitals (t2g) Point between the ligands Weaker (repulsive) interaction with the ligands Figure: 24-30a-f dxy dyz dxz Electrons in d-orbitals are repelled from the electrons in the ligands. The repulsion is stronger for electrons in d-orbitals pointing directly at the ligands.
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Energy Levels of d-orbitals in an octahedron
dz2 D dx2-y2 dxy dyz dxz dz2 dx2-y2 Cr3+ ion with a spherical crystal field dxy dyz dxz dxy dyz dxz dz2 dx2-y2 Cr3+ ion in an octahedral crystal field Free Cr3+ ion
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Electronic Excitation
dx2-y2 dz2 Energy dx2-y2 dz2 eg light (photon) D = Crystal Field Splitting Energy t2g dxy dyz dxz Figure: 24-30a-f dxy dyz dxz
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Antibonding (s*) Metal-Ligand MO’s Nonbonding Metal d MO’s
[Cr3+(H2O)6]3+ Absorption Spectra Antibonding (s*) Metal-Ligand MO’s Doct Nonbonding Metal d MO’s
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