Evolution of the MLCT band following changes in oxidation state for highly coupled mixed
valence complexes
Benjamin Lear and Malcolm Chisholm64th International Symposium on Molecular Spectroscopy
June 23rd 2009
Mixed-valence systems and their classification
Localized electronic
states
Non-adiabatic
Adiabatic
Localized electronic
states
Class I
Fre
e E
ner
gy
XDelocalized electronic
states
Class III
Fre
e E
ner
gy
X
Class II
Fre
e E
ner
gy
X
Solvent dependent IVCT band
Solvent independent IVCT band
WW
O
O
O
O
O O
O
O
WW
O
O
O
O
O O
O
O
1+
M M mixed valence complexes
WW
O
O
O
O
O O
O
O
WW
O
O
O
O
O O
O
O WMo
O
O
O
O
O O
O
O
MoW
O
O
O
O
O O
O
OMo
Mo
O
O
O
O
O O
O
O
MoMo
O
O
O
O
O O
O
O
10000 15000 20000 25000
Re
lativ
e I
nte
nsi
ty
Wavenumbers /cm-1
10000 15000 20000 25000
Re
lativ
e I
nte
nsi
ty
Wavenumbers /cm-1
5000 10000 15000 20000
Re
lativ
e In
ten
sity
Wavenumber /cm-1
MLCT in neutral vs. mixed valence state
IVCT band
WW
O
O
O
O
O O
O
O
WW
O
O
O
O
O O
O
O
A three state model for mixed valence chemistry
Asymmetric coordinate
Symmetric
coordinate
Asymmetric
coordinate
Fre
e en
ergy
WW
O
O
O
O
O O
O
O
WW
O
O
O
O
O O
O
O
IVCT MLCT
Electronic transitions of the mixed valence state
10000 15000 20000 25000
Re
lative
In
ten
sity
Wavenumbers /cm-1
MLCTIVCT
WW
O
O
O
O
O O
O
O
WW
O
O
O
O
O O
O
OW
Mo
O
O
O
O
O O
O
O
MoW
O
O
O
O
O O
O
OMo
Mo
O
O
O
O
O O
O
O
MoMo
O
O
O
O
O O
O
O
1+ 1+ 1+
Class III
T1 T3 T2
Frequency
Inte
nsity
Time
Ove
rlap
1/ 1/ 2/
FourierTransform
Nuclear coordinate
Raman spectra
Compound 1
2
3
MM
1 1411 932 576 3952 1351 933 576 3673 1323 915 582 312
Table 4. Energies (in cm-1) of the Raman modes for 1-3 found for excitation resonant with the MLCT transition.
Wavenumber /cm-1
Inte
nsity
MoMo
O
O
O
O
O O
O
O
MoMo
O
O
O
O
O O
O
O
MLCT simulationN
eutr
al
MoMo
O
O
O
O
O O
O
O
MoMo
O
O
O
O
O O
O
OW
Mo
O
O
O
O
O O
O
O
MoW
O
O
O
O
O O
O
OWW
O
O
O
O
O O
O
O
WW
O
O
O
O
O O
O
O
Mix
ed V
alen
ce
12000 15000 18000 21000
0.0
0.5
1.0
nm
Nor
mal
ized
Inte
nsity
Energy /cm-1
1000 900 800 700 600 500
12000 15000 18000 21000 24000
0.0
0.5
1.0
nm
Nor
mal
ized
Inte
nsity
Energy /cm-1
900 800 700 600 500 400
15000 18000 21000
0.0
0.5
1.0
nm
Nor
mal
ized
Inte
nsity
Energy /cm-1
750 700 650 600 550 500
18000 21000 24000 27000
0.0
0.5
1.0
nm
Nor
mal
ized
Inte
nsity
Energy /cm-1
600 550 500 450 400
12000 15000 18000 21000 24000
0.0
0.5
1.0
nm
Nor
mal
ized
Inte
nsity
Energy /cm-1
900 800 700 600 500 400
12000 15000 18000 21000
0.0
0.5
1.0
nm
Nor
mal
ized
Inte
nsity
Energy /cm-1
900 800 700 600 500
18000 21000 24000 27000
0.0
0.5
1.0
nm
Nor
mal
ized
Inte
nsity
Energy /cm-1
600 550 500 450 400
PES offsetsCompound Raman Band Neutral Mixed valence percent reduction
cm-1
Mo4oxa 1411 1.6 0.5 68.75(MoW)2oxa 1351 1.4 0.4 71.43
W4oxa 1323 1.0 0.3 70.00
Nuclear Coordinate
1
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
Mixed valence
Neutral
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
Mixed valence
Neutral
O
OO
O
W
W
W
W
1+
O
OO
O
W
W
W
W
1+
Mixed-valence systems and their classification
Localized electronic
states
Non-adiabatic
Adiabatic
Localized electronic
states
Class I
Fre
e E
ner
gy
XDelocalized electronic
states
Class III
Fre
e E
ner
gy
X
Class II
Fre
e E
ner
gy
X
Solvent dependent IVCT band
Solvent independent IVCT band
WW
O
O
O
O
O O
O
O
WW
O
O
O
O
O O
O
O
1+
Symmetric coordinate
PES and classification
Asymmetric coordinate
Asymmetric
coordinateSymmetric
coordinate
Class IClass I Class IIClass II Class IIIClass III Strongly Class IIIStrongly Class IIIClass I Class II Class III Class IV
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
Mixed valence
Neutral
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
Mixed valence
Neutral
O
OO
O
W
W
W
W
1+
O
OO
O
W
W
W
W
1+
Conclusions
• MLCT band in mixed valence complexes contains information regarding the underlying states
• Coupling in mixed valence systems tends to make states more similar to one another
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
Mixed valence
Neutral
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
Mixed valence
Neutral
O
OO
O
W
W
W
W
1+
O
OO
O
W
W
W
W
1+
Nuclear CoordinateNuclear Coordinate
AcknowledgmentsMalcolm H. ChisholmThe Chisholm research group
Classification of mixed valence complexes: The “nesting” criterion
View along the symmetric coordinate
Class I Class IVClass III
Theories for absorption profiles
Time dependent pictureFranck-Condon picture
Three-state model: Orbital picture
X
g
g
u
u
u
u
MLCT
IVCT
Redox center combinations Bridge orbital
M'
M''
O
O
O
O
O O
O
O
M'
M''
O
O
O
O
O O
O
O
Concerning the current models
X
g
g
u
u
u
u
MLCT
IVCT
Redox center combinations Bridge orbital
M'
M''
O
O
O
O
O O
O
O
M'
M''
O
O
O
O
O O
O
O
Class IV
IVCT
MLCT
“IVCT”
“MLCT”
Class I
Nuclear coordinate Nuclear coordinate
Conclusions
• MLCT band in mixed valence complexes contains information regarding the underlying states
• Coupling in mixed valence systems tends to make states more similar to one another
• Orbital pictures for describing coupling between states are dangerous
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
Mixed valence
Neutral
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
1.2x104 1.6x104 2.0x104
0
1x104
2x104
3x104
4x104
5x104
(M
-1cm
-1)
Wavenumbers (cm-1)
1
1+
Mixed valence
Neutral
O
OO
O
W
W
W
W
1+
O
OO
O
W
W
W
W
1+
Nuclear CoordinateNuclear Coordinate
X
g
g
u
u
u
u
MLCT
IVCT
Redox center combinations Bridge orbital
M'
M''
O
O
O
O
O O
O
O
M'
M''
O
O
O
O
O O
O
O
≠
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