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Coordination Chemistry:
History and Introduction to Structure
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1. Coordination Compounds
Involves:
 Metal atoms or ions
 One or more ligands (atoms, ions, or molecules) that donate e- to the metal
 Chemistry of the metal d-orbitals
Consist of the formation of coordinate covalent (dative) bonds:
M
+
L
M-L
 Lewis Acid-Base Adduct
Metal is the Lewis Acid
Ligand is the Lewis Base
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2. History
Complimentary Color Wheel
A. A tale as old as time (Prehistoric)
Absorb
B. Formally introduced by Alfred Werner (late 19th Century)
 Introduced new bonding concepts
 The famous Werner Cobalt Compounds
Compound
A
B
C
D
Elemental Formula
CoN6H18Cl3
CoN5H15Cl3
CoN4H12Cl3
CoN3H9Cl3
See
Color
Yellow
Red
Green or Purple
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2. History: Werner Compounds
Compound
A
B
C
D
Elemental Formula
CoN6H18Cl3
CoN5H15Cl3
CoN4H12Cl3
CoN3H9Cl3
Color
Yellow
Red
Green or Purple
 Early bonding theories allowed only three atoms to be attached to cobalt
because of its valence of 3 (Co3+) for charge balance.
 Jørgensen proposed that for the above compounds
• N could form chains because of its valence of 5
• Chloride (Cl-) could be bound to N or to Co3+
 Werner proposed something very radical for the time
• As many as 6 N (as NH3) could bond directly to Co3+
• Cl- could bond to Co3+ or associate loosely; two kinds of Cl-
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2. History: The Werner Titrations
Complex (aq) + AgNO3 (aq)
Compound
If Cl- is N bound,
would dissociate in
water.
Recall: There are
2 Isomers
Note: 0 Cl-?
Jørgensen
AgCl equivs
A
3
B
2
C
1
D
0
n AgCl (s) + Complexn+
Werner
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2. History: Werner’s Theory
[Co(NH3)6]Cl3
A. Primary Bonding


The positive charge of the metal ion is balanced by negative ions.
Does not have to involve direct bonding to the metal ion.
Primary Sphere
• Today when direct bonding is not involved, we refer to it
as the secondary coordination sphere.
Secondary Sphere
B. Secondary Bonding




Ligands (molecules or ions) directly attached to the metal ion.
This interaction constitutes the coordination sphere; the complex ion.
• Today we refer to it as the primary coordination sphere.
Defines the coordination number.
Defines a specific geometry; “directed in space”.
Remember these are older theories
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2. History: Determining the coordination
mode
Which coordination mode would give 2 isomers for complex C?
a
b
c
d
7
8
9
10
trans
cis
Yes!
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2. History: Cis and Trans Isomers
You can have optical isomers.
Another example.
Ethylenediamine (en)
Optical Isomers (Enantiomers)
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