Chemistry
Analysis
What is this?
Three
central
goals
Modeling
How do I explain it?
Synthesis
How do I
make it?
A Chemist’s View- How we
think
Macroscopic
Three
different
perspectives
Symbolic
Microscopic or
Particulate
NaCl
The Period 4 transition metals
Colors of representative compounds of the Period 4 transition metals
nickel(II) nitrate
hexahydrate
sodium chromate
titanium oxide
scandium oxide
vanadyl sulfate
dihydrate
potassium
ferricyanide
manganese(II)
chloride
tetrahydrate
cobalt(II)
chloride
hexahydrate
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zinc sulfate
heptahydrate
copper(II)
sulfate
pentahydrate
Aqueous oxoanions of transition elements
One of the most characteristic
chemical properties of these
elements is the occurrence of
multiple oxidation states.
Mn(II)
Mn(VI)
Mn(VII)
Mn(VII)
Cr(VI)
V(V)
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Effects of the metal oxidation state and of ligand identity on color
[V(H2O)6]3+
[V(H2O)6]2+
[Cr(NH3)6]3+
[Cr(NH3)5Cl ]2+
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Linkage isomers
An artist’s wheel
Splitting of d-orbital energies by an octahedral field of ligands
D is the splitting energy
The effect of ligand on splitting energy
The spectrochemical series
•For a given ligand, the color depends on the oxidation state of the metal ion.
•For a given metal ion, the color depends on the ligand.
I- < Cl- < F- < OH- < H2O < SCN- < NH3 < en < NO2- < CN- < CO
WEAKER FIELD
SMALLER D
LONGER 
STRONGER FIELD
LARGER D
SHORTER 
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The color of [Ti(H2O)6]3+
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
High-spin and low-spin complex ions of Mn2+
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Orbital occupancy for high- and low-spin complexes of d4 through d7 metal ions
high spin:
weak-field
ligand
low spin:
strong-field
ligand
high spin:
weak-field
ligand
low spin:
strong-field
ligand
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What is electronic spectroscopy?
Absorption of radiation leading to electronic transitions within a molecule or complex
Absorption
Absorption
[Ru(bpy)3]2+
104
[Ni(H2O)6]2+
10
200
400
UV
700
visible
 / nm (wavelength)
~14 000
25 000
visible
50 000
UV
n / cm-1 (frequency)
UV
=
higher energy transitions - between ligand orbitals
visible
=
lower energy transitions
- between d-orbitals of transition metals
- between metal and ligand orbitals
Absorption maxima in a visible spectrum have three important characteristics
1.
number (how many there are)
This depends on the electron configuration of the metal centre
2.
position (what wavelength/energy)
This depends on the ligand field splitting parameter, Doct or Dtet and on the degree
of inter-electron repulsion
3.
intensity
This depends on the "allowedness" of the transitions which is described by two
selection rules
The energy of the absorption by [Ti(OH2)6]3+ is the ligand-field splitting, Do
ES
ES
eg
hn
eg
Do
GS
t2g
complex in electronic
Ground State (GS)
[Ti(OH2)6]3+
GS
t2g
complex in electronic
excited state (ES)
d-d transition
max = 510 nm
Do is 
243 kJ mol-1
20 300 cm-1
An electron changes orbital; the ion changes energy state
The Jahn-Teller Distortion: Any non-linear molecule in a degenerate electronic state
will undergo distortion to lower it's symmetry and lift the degeneracy
Degenerate electronic ground state:
T or E
Non-degenerate ground state:
A
2E
g
2B
1g
d3
d5 (high spin)
d6 (low spin)
d8
4A
2g
6A
1g
1A
1g
3A
2g
A
[Ti(H2O)6]3+, d1
2A
1g
2T
2g
10 000
20 000
30 000
n- / cm-1
Limitations of ligand field theory
[Ni(OH2)6]2+ = d8 ion
2+
3 absorption bands
A
eg
Ni
t2g
25 000
n / cm-1
15 000
LFT assumes there is no inter-electron repulsion
Repulsion between electrons in d-orbitals has an effect on the energy of the whole ion
d2 ion
Electron-electron repulsion
x2-y2
z2
eg
z2
x2-y2
t2g
xy
xz
yz
eg
t2g
xy
xz
yz
xy + z2
z
xz + z2
z
y
y
x
x
lobes overlap, large electron repulsion
lobes far apart, small electron repulsion
These two electron configurations do not have the same energy
The Nephelauxetic Effect
cloud expanding
- some covalency in M-L bonds – M and L share electrons
-effective size of metal orbitals increases
-electron-electron repulsion decreases
Nephelauxetic series of ligands
F- < H2O < NH3 < en < [oxalate]2- < [NCS]- < Cl- < Br- < INephelauxetic series of metal ions
Mn(II) < Ni(II) Co(II) < Mo(II) > Re (IV) < Fe(III) < Ir(III) < Co(III) < Mn(IV)
Selection Rules
Transition
e
complexes
Spin forbidden
Laporte forbidden
10-3 – 1
Many d5 Oh cxs
[Mn(OH2)6]2+
1 – 10
Many Oh cxs
[Ni(OH2)6]2+
10 – 100
Some square planar cxs
[PdCl4]2-
100 – 1000
6-coordinate complexes of low symmetry,
many square planar cxs particularly with
organic ligands
102 – 103
Some MLCT bands in cxs with unsaturated ligands
102 – 104
Acentric complexes with ligands such as acac, or
with P donor atoms
103 – 106
Many CT bands, transitions in organic species
Spin allowed
Laporte forbidden
Spin allowed
Laporte allowed