Electronic (UV-visible)
Spectroscopy
｜
Electronic ｜
XPS UPS UV-visible
1
UV-visible spectroscopy
ligand p*
(1) metal-metal (d-d) transition
(2) charge transfer
s*
metal d
metal-ligand
(MLCT)
ligand-metal
(LMCT)
n
metal d
n
ligand p
(3) ligand-centered transition
s
instrument
energy
source
sample
energy
selector
energy
analyzer
output
computer
electric connection
light path
absorbance
Io
A = log ―― = ecl
I
e: extinction coefficient
c: concentration mol/L (M)
l: path length (cm)
2
selection rules
1. only one electron is involved in any transition
2. there must be no net change of spin DS = 0
3. it must involve an overall change in orbital
angular momentum of one unit DL = ±1
4. Laporte (or parity) selection rule
only g →u and u →g transitions are allowed
vibronic coupling – interaction between electronic
and vibrational modes
electronic transition
Laporte allowed (charge transfer)
e
10000
(1000—50000)
Laporte forbidden (d-d transition)
spin allowed; noncentrosymmetiric 100—200
(200—250)
spin allowed; centrosymmetric
5—100
(20—100)
spin forbidden
0.01—1
(< 1)
3
[CoCl4]2-
[Co(H2O)6]2+
[Mn(H2O)6]2+
4
d-d transition
crystal field splitting
Do size and charge of the metal ion and ligands
4d metal ~50% larger than 3d metal
5d metal ~25% larger than 4d metal
5d > 4d > 3d
crystal field stabilization energy (CFSE)
spin-pairing energy
high-spin/low spin configuration d4 ~ d7
d4
5
other shapes
tetrahedral
Dt = 4/9 Do
tetrahedron
octahedron elongated
square
octahedron planar
6
d1
[Ti(H2O)6]3+
hu = D o
hole formalism
d2
possible electron
possible arrangements of electrons
transitions
7
Russell-Saunders term symbols
2S+1L
for free atoms and ions
J
S: total spin quantum number Sms
L: total orbital angular quantum number Sml
L = 0, 1, 2, 3, 4, …………..
S P D F G
1
3
5
7
9
J: total angular quantum number L+S, ……,│L-S│
d2 configuration
S
10!
———— = 45 microstates
8! 2!
+1
0
-1
L
(2+ 2-)
4
(2+ 1+)
(2+ 1-) (2- 1+)
(2- 1-)
2
(2+ 0+)
(1+ 1-)
(2+ 0-) (2- 0+)
(2- 0-)
1
(1+ 0+)
(2+ -1+)
(1+ 0-) (1- 0+)
(2+ -1-) (2- -1+)
(1- 0-)
(2- -1-)
(1+ -1+)
(2+ -2+)
(0+ 0-)
(1+ -1-) (1- -1+)
(2+ -2-) (2- -2+)
(1- -1-)
(2- -2-)
3
0
1G
9
3F
1D
+ 21 + 5
ground term
3P
+
9
1S
+
1 = 45
8
states for dn systems in Russell-Saunders coupling
splitting of terms in various chemical
environments
d orbitals in Oh environment
consider pure rotational O subgroup
rotation by angle a ==> R(r), Q(q), ψs invariant
only F(f) will be altered
F(f) = eimf ==> F(f + a) = eim(f + a)
m = 2, 1, 0, -1, -2
e2if
e2i(f + a)
eif
ei(f + a)
e0
======>
e0
e-if
e-i(f + a)
9
e-2if
e-2i(f + a)
transformation matrix
e2ia
0
0
0
0
ei a
0
0
0
0
e0
0
0
0
0
e-ia
0
0
0
0
sum of the diagonal elements
sin(l + 1/2)a
c (a) = ———————
sin(a/2)
0
0
0
0
e-2ia
for d orbitals
c (E ) = 5
sin(5p/2)
c (C2) = ————— = 1
sin(p/2)
sin(5p/3)
sin(5p/4)
c (C3) = ————— = -1 c (C4) = ————— = -1
sin(p/3)
sin(p/4)
==> G = eg + t2g
10
splitting of one-electron levels in an Oh environment
splitting of one-electron levels in various symmetries
11
determine the spin multiplicity of each term
d2 configuration in Oh environment
aA + bE + cT + dT
(i) t2g2
1g
g
1g
2g
total degeneracy 15
a
b
c
I
1
1
1
II
1
1
3
III
3
3
1
d
3
1
1
a T + bT
(ii) t2g1eg1
1g
2g
total degeneracy 24
only possibility 1T1g 1T2g 3T1g 3T2g
aA + bA + cE
(iii) eg2
1g
2g
g
total degeneracy 6
a
b
c
I
1
3
1
II
3
1
1
1S
1A
1g
1G
1A
1g
3P
3T
1g
1 E 1T
g
2g
3A
3
3
1g T1g T2g
1D
3F
1E 1T
1
g
1g T2g
12
method of descending symmetry
consider d2 ion in Oh environment
from correlation table for group Oh
(i) t2g2
A1g Eg T1g T2g
lowering the symmetry to C2h
1A
1E
t2g × t2g =
1g
g
possible spin
1
1
multiplicity
1
1
3
3
1A
corresponding 1Ag
g
1B
representations
g
in C2h
ag × ag
Ag ====>
ag × ag’
Ag ====>
a g × bg
Bg
====>
ag’ × ag’
Ag
====>
a g ’ × bg
Bg
====>
bg × bg
Ag
====>
t2g
3T
1g
1
3
1
3A
g
3B
g
3B
g
1A
g
1A 3A
g
g
1B 3B
g
g
1A
g
1B 3B
g
g
1A
g
===> total 41Ag + 3Ag + 21Bg + 23Bg
a g + a g + bg
1T
2g
3
1 ˇ
1
1A
g
1A
g
1B
g
13
(ii) eg2
A1g A2g Eg
lowering the symmetry to D4h eg
a1g + b1g
a1g2
A1g possible spin multiplicity 1A1g
a1gb1g
B1g possible spin multiplicity 1B1g 3B1g
b1g2
A1g possible spin multiplicity 1A1g
==>
D4h
Oh
1A
1A
1g
1g
3B
3A
2g
1g
1 A 1B
1E
1g
1g
g
(iii) t2g1eg1
????
consider d2 ion in Td environment
from splitting of energy level in Td symmetry
3F
3A 3T 3T
2
1
2
1D
1E 1T
2
3P
3T
1
1G
1A 1E 1T 1 T
1
1
2
1S
1A
1
electron configurations
e2
A1 A2 E
total degeneracy 6
et2
T1 T2
total degeneracy 24
t22
A1 E T1 T2 total degeneracy 15
assign the correct spin multiplicity ???
14
splitting of the terms for d2 ion in several point
groups
15
correlation diagram for a d2 ion in Oh
environment
16
correlation diagram for a d2 ion in Td
environment
17
Orgel diagrams
d1, d6/d4, d9
d1, d6 tetrahedral
d4, d9 octahedral
d1, d6 octahedral
d4, d9 tetrahedral
u = 10 Dq
E
Eg
T2
T2 g
T2g
T2
Eg
E
18
d2, d7/d3, d8
cm-1
d2, d7 tetrahedral
d3, d8 octahedral
Dq
d2, d7 octahedral
d3, d8 tetrahedral
A2→T2 u1 = 10Dq
T1→T2
u1 = 8Dq + c
A2→T1(F) u2 = 18Dq - c
T1(F)→T1(P) u2 = 18Dq + c
A2→T1(P) u1 = 15B + 12Dq + c T1→A2
u3 = 15B + 6Dq + 2c
19
20
Tanabe-Sugano diagrams
21
22
simplified Tanabe-Sugano diagrams
d2
d5
d3
d6
d4
d7
d8
23
magnitude of Do
Mn(II) < Ni(II) <Co(II) < Fe(II) < V(II) < Fe(III)
< Cr(III) < V(III) < Co(III) < Mn(IV) < Mo(III)
< Rh(III) < Pd(IV) < Ir(III) < Re(IV) < Pt(IV)
Do values for octahedral [M(H2O)6]n+ complexes
Do (cm-1)
Ti3+ 20400
Mn3+ 21000
Co3+ 19000
V3+ 19000
Mn2+ 7500
Co2+ 9750
Cr3+ 17700
Fe3+ 21000
Ni2+
8500
Cr2+ 12500
Fe2+ 10500
Cu2+ 12600
spectrochemical series
I- < Br- < -SCN- < Cl- < F- < urea < OH- < CH3COO< C2O4- < H2O < -NCS- < glycine < pyridine ~ NH3
< en < SO32- < o-phenanthroline < NO2- < CN- < PR3
< CO
ex. [Co(H2O)6]3+
Do = 19000 cm-1
[Co(NH3)6]3+
Do = 22900 cm-1
[Co(H2O)3(NH3)3]3+ Do = ?
3/6 × 19000 + 3/6 × 22900 = 20950 cm-1
24
Jørgensen prediction of 10Dq and B
10Dq = f · g (cm-1 × 10-3)
B = Bo (1 － h · k)
Bo : free ion interelectronic repulsion parameter
Jahn-Teller distortions
distortion will occur whenever the resulting splitting
energy levels yields additional stabilization
__ dx2-y2
__ dz2
eg __ __
__ dz2
__ dx2-y2
or
__ dxy
__ __dxz, dyz
t2g __ __ __
__ __ dxz, dyz
__ dxy
25
[M(H2O)6]n+
Ti3+ (d1)
Mn2+ (d5)
V3+ (d2)
Fe2+ (d6)
Cr3+
Co2+ (d7)
(d3)
Ni2+ (d8)
Cu2+ (d9)
Cr2+ (d4)
26
d1
d2
27
d3
28
d3
29
d4
d5
30
d6
31
d6
32
d6
33
d7
34
d8
d9
35