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Some Coordination Compounds of Cobalt
Studied by Werner
Werner’s Data*
Total Free
Ions
Cl-
Traditional
Formula
.
CoCl . 5 NH
CoCl . 4 NH
CoCl . 3 NH
CoCl3 6 NH3
Modern
Formula
Charge of
Complex Ion
4
3
[Co(NH3)6]Cl3
3+
3
3
3
2
[Co(NH3)5Cl]Cl2
2+
3
3
2
1
[Co(NH3)4Cl2]Cl
1+
3
3
0
0
[Co(NH3)3Cl3]
---
Table 23.10 (p. 1020)
Valence Bond Theory
Hybrid Orbitals and Bonding in the Octahedral
[Cr(NH3)6]3+ Ion
Fig. 23.13
Valence Bond Theory
Hybrid Orbitals and Bonding in the Square Planar
[Ni(CN)4]2- Ion
Fig. 23.14
Valence Bond Theory
Hybrid Orbitals and Bonding in the
Tetrahedral [Zn(OH)4]2- ion
Fig. 23.15
Isomerism
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Isomerism
• Isomers: two compounds with the same formulas
but different arrangements of atoms.
• Coordination-sphere isomers and linkage isomers:
have different structures (i.e. different bonds).
• Geometrical isomers and optical isomers are
stereoisomers (i.e. have the same bonds, but
different spatial arrangements of atoms).
• Structural isomers have different connectivity of
atoms.
• Stereoisomers have the same connectivity but
different spatial arrangements of atoms.
Isomerism
Diastereomers Enantiomers
(Chiral:
Non-superimposable
Mirror Images)
Isomerism
Structural Isomerism
Fig. 23.11
Stereoisomerism
Fig. 23.12
Stereoisomerism
• Enantiomers are chiral: I.e. They are non-superimposable
mirror images.
• Enantiomers are “optical isomers.” eg. (+) and (-)
carvone
• Most physical and chemical properties of enantiomers are
identical.
• Therefore, enantiomers are very difficult to separate eg.
Tartaric acid…ask Louis Pasteur.
• Enzymes are catalysts that are very specific, acting on
only one enantiomer.
• Enantiomers can have very different physiological
effects: eg. (+) and (-) carvone
Chirality
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Optical Activity
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Optical Activity
(+) dextrorotatory
(-) levorotatory
The mirror image of an enantiomer will rotate the plane of polarized
light by the same amount in the opposite direction. Eg (+) d-carvone
+62o and (-) l-carvone -62o…. What about a 50:50 (racemic)
mixture?
Color and Magnetism
• Color of a complex depends on: (i) the metal and
(ii) its oxidation state.
• Pale blue [Cu(H2O)6]2+ can be converted into dark
blue [Cu(NH3)6]2+ by adding NH3(aq).
• A partially filled d orbital is usually required for a
complex to be colored.
• So, d 0 metal ions are usually colorless.
Exceptions: MnO4- and CrO42-.
• Colored compounds absorb visible light.
• The color our eye perceives is the sum of the light
not absorbed by the complex.
Color and Magnetism
Color
An Artist’s
Wheel
Fig. 23.16
Relation Between Absorbed and
Observed Colors
Absorbed
Color
 (nm)
Violet
Blue
Blue-green
Yellow-green
Yellow
Orange
Red
400
450
490
570
580
600
650
Table 23.11 (p. 1027)
Observed
Color
 (nm)
Green-yellow
Yellow
Red
Violet
Dark blue
Blue
Green
560
600
620
410
430
450
520
Color & Visible Spectra
Color& Spectra
• The plot of absorbance versus wavelength is the
absorption spectrum.
• For example, the absorption spectrum for [Ti(H2O)6]3+
has a maximum absorption occurs at 510 nm (green and
yellow).
• So, the complex transmits all light except green and
yellow.
• Therefore, the complex appears to be purple.
Color and Magnetism
Magnetism
• Many transition metal complexes are
paramagnetic (i.e. they have unpaired electrons).
• There are some interesting observations.
Consider a d6 metal ion:
– [Co(NH3)6]3+ has no unpaired electrons, but [CoF6]3has four unpaired electrons per ion.
• We need to develop a bonding theory to account
for both color and magnetism in transition metal
complexes.
Crystal-Field Theory
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