Ligand Field Theory

1
Ligand Field Theory

• Provides an improved theory of coordination
  chemistry because this theory utilizes a
  molecular orbital approach
• Why is CO a strong field ligand while Cl- is a
  weak field ligand?

2
Formation of Molecular Orbitals
Constructive interference
Destructive interference
Antibonding molecular orbital
Bonding molecular orbital
3
Molecular Orbitals
4
Merging Orbitals for Octahedral
5
Molecular Orbitals in an Octahedral
6
Why is CO a Strong Field Ligand?
7
Why is Cl- a Weak Field Ligand?
8
Production of Fe
9
Transition Metals in Steel
10
Nonferrous Alloys
11
Chapter 16, The d-Block Metals in Transition
12
Transition Elements

• Characteristic properties of transition elements
• Most of the elemental metal forms have high
  melting metals
• Except for group IIIB, they all have two or more
  stable oxidation states.
• Most of their compounds are colored.
• Magnetic properties

13
Atomic Radius
Decreases across period
Atomic radius decreases due to an increase in
Zeff
14
Lanthanide Contraction
The 5th and 6th periods are very similar in
atomic radii
Compare the following pairs Zr with Hf Y with Lu
Due to increased Zeff
Similar chemical properties
Different physical properties density
15
Comparison of Densities
16

• Ionization Energy

Increases from across period because of
increasing Zeff
17
Transition Metal Oxidation States

• Have positive formal oxidation states, like all
  metals.
• Tend to lose their outer s-electrons before the
  d-electrons. Even though the d-electrons were
  added last.
• Fe Ar 3d64s2
• Fe2 Ar 3d6
• Most positive oxidation state corresponds to
  losing all s and d electrons (noble gas config.).
• Ti Ar 3d24s2
• Ti4 Ar

18
Stable Oxidation States Fourth Period

• Most common oxidation states are in black

2 corresponds to losing the s-electrons
all s- and d-electrons are lost
19
Stable Oxidation States Fifth Period
Most common oxidation states are in black
all s- and d-electrons are lost
20
Stable Oxidation States Sixth Period
Most common oxidation states are in black
all s- and d-electrons are lost
21
For all rows, one of most common oxidation states
for the first 6 elements is losing all s- and d-
electrons. Only for the 4th row is losing just
the s-electrons often the most stable. Rows 5 and
6 - have higher oxidation states. Most positive
oxidation states occur when the metal is combined
with the most electronegative elements (e.g. F, O)
22
Oxidation State vs Oxiding Agent
MnO4- 8H 5e- Mn2 4H2O Ered 1.51 V
Cr2O72-14H 6e- 2Cr3 7H2O Ered 1.33 V
MnO2 4H 2e- Mn2 2H2O Ered 1.23 V
ClO4- 2H 2e- ClO3- H2O Ered 1.23 V
NO3- 4H 3e- NO 2H2O Ered 0.96 V
2H(aq) 2e- H2(g) Ered 0.00 V
The higher the oxidation state, the better the
oxidizing agent.
23
Chapter 15

• Soft Materials

• Luminesence