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Isomerism & Crystal Field Theory Chapter 24 – Lecture 3. Chemistry 123 Spring 2008 Dr. Woodward. 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. - PowerPoint PPT Presentation
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Isomerism & Crystal Field Isomerism & Crystal Field TheoryTheory
Chapter 24 – Lecture 3Chapter 24 – Lecture 3
Chemistry 123Spring 2008
Dr. Woodward
IsomersIsomers
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
Intra-atomic (d to d) excitationsIntra-atomic (d to d) excitations
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.
CuSO4NiSO4CoSO4FeSO4MnSO4 ZnSO4
ddzz22 & d & dxx22-y-y22 orbitals (e orbitals (egg))• Point directly at the ligands • Stronger (repulsive) interaction with the ligands
Crystal Field Splitting Crystal Field Splitting (Octahedron)(Octahedron)
ddzz22 ddxx22-y-y22
ddxyxy ddyzyz ddxzxz
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.
En
erg
y
ddxyxy, d, dyzyz & d & dxzxz orbitals orbitals (t(t2g2g))• Point between the ligands • Weaker (repulsive) interaction with the ligands
Energy Levels of d-orbitals in an Energy Levels of d-orbitals in an octahedronoctahedron
ddxyxyddyzyz ddxzxz ddz2z2 ddx2-y2x2-y2
ddxyxy ddyzyz ddxzxz ddz2z2 ddx2-y2x2-y2
Free Cr3+ ion
Cr3+ ion with a spherical crystal
field
Cr3+ ion in an octahedral crystal field
En
erg
y
ddxyxy ddyzyz ddxzxz
ddz2z2 ddx2-y2x2-y2
Electronic ExcitationElectronic Excitation
ddxyxy ddyzyz ddxzxz
ddzz22ddxx22-y-y22
t2g
eg
= Crystal Field Splitting Energy
En
erg
y
ddxyxy ddyzyz ddxzxz
light (photon)
ddzz22ddxx22-y-y22
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