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Transcript
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
nonsuperimposable
mirror images
1
Linkage Isomers
Geometric Isomers
2
Optical Isomers
IntraIntra-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.
3
[M(H2O)6]n+ Complex ions
M
MO6 Octahedron
Crystal Field Splitting (Octahedron)
dz2 & dx
dx2-y2 orbitals (e
(eg)
Energy
H2O
• Point directly at the ligands
• Stronger (repulsive) interaction
with the ligands
dxy,
xy, dyz & dxz orbitals (t2g)
dz2
dx2-y2
dyz
dxz
• Point between the ligands
• Weaker (repulsive) interaction
with the ligands
dxy
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.
4
Energy Levels of d-orbitals in an
octahedron
Energy
dz2
Δ
dxy
dyz
dxz
dz2
dx2x2-y2
Cr3+ ion with a
spherical crystal
field
dxy
dx2x2-y2
dyz
dxz
dz2
dxy
dyz dxz
Cr3+ ion in an
octahedral crystal
field
dx2x2-y2
Free Cr3+ ion
Energy
Electronic Excitation
dx2-y2
dz2
dx2-y2
dz2
eg
Δ = Crystal Field
Splitting Energy
light
(photon)
t2g
dxy
dyz
dxz
dxy
dyz
dxz
5
[Cr3+(H2O)6]3+ Absorption Spectra
Antibonding (σ*)
Metal-Ligand MO’s
0.6
0.5
Absorbance
0.4
Δoct
0.3
0.2
Nonbonding
Metal d MO’s
0.1
0.0
250
300
350
400
450
500
550
600
650
700
750
Wavelength (nm)
6