Chapter 2 Physico-chemical properties
E / 103 cm-1
10.0
2F
5/2
2F
7/2
0
2.1
2.2
2.3
Electronic levels
Magnetism
Electronic absorption spectra
2.4
Luminescence spectra
2’
1’
0’
3
2
1
0
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
1
Chapter 2
2.1
Physico-chemical properties
Electronic levels
2.1.1 Electronic structure of 4f elements
(Summary from the BSc course “Coordination chemistry”
Russel-Saunders coupling usually works well
(2S+1)
Spectroscopic term
Multiplicity = (2S+1)´(2L+1)
G
S P D F G H I J K …
0 1 2 3 4 5 6 7 8 = L
spin multiplicity
(2S+1)
GJ
J = L+S, L+S-1…, |L-S|
Spectroscopic level, multiplicity = (2J+1)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
2
Chapter 2
Physico-chemical properties
Hund’s rules for ground state:
• Spin multiplicity must be the highest possible (Smax)
• If more than one term have the highest multiplicity,
the term with the highest value of L is the ground
state (Lmax)
• The ground level has Jmin if the subshell is less than
half filled, Jmax if the subshell is more than half
filled
Example: Nd3+, 4f3
Smax = 3´½ = 3/2
Lmax = 6
3 2 1 0 -1 -2-3
J = 15/2……9/2
ml (l = 3)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
4I
9/2
3
Chapter 2
Ln3+
4fn, n
Physico-chemical properties
Ground Color
level
Magnetic moment
exp.
calc.
Ce
1
2F
5/2
colorless
2.3-2.5
2.54
Pr
2
3H
4
green
3.4-3.6
3.58
Nd
3
4I
9/2
lilac
3.5-3.6
3.62
Pm
4
5I
4
pink
n.a.
2.68
Sm
5
6H
5/2
yellow
1.4-1.7
0.85
Eu
6
7F
0
pale pink
3.3-3.5
0
Gd
7
8S
colorless
7.9-8.0
7.94
Tb
8
7F
6
colorless
9.5-9.8
9.72
Dy
9
6H
15/2
yellow
10.4-10.6
10.6
Ho
10
5I
8
yellow
10.4-10.7
10.6
Er
11
4H
15/2
rose
9.4-9.6
9.58
Tm
12
3H
6
pale green 7.1-7.5
7.56
Yb
13
2F
7/2
colorless
4.54
7/2
4.3-4.9
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
4
Chapter 2
Physico-chemical properties
Spin-orbit coupling constants for aqua-ions
LnIII
l4f
z4f
LnIII l4f
z4f
Ce
625
625
Tb
-285
1710
Pr
370
740
Dy
-483
1932
Nd
295
885
Ho
-535
2140
Sm
232
1160
Er
-793
2380
Eu
221
1326
Tm
-1315
2630
Gd
207
1450
Yb
-2940
2940
z
l
2S
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
for S  0
5
Chapter 2
Physico-chemical properties
Some electronic
levels…
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
6
Chapter 2
Physico-chemical properties
Ligand field effects
They are very weak, a few hundreds cm-1 as compared
to a few thousands for spin-orbit coupling, and 104 cm-1
for electron repulsion.
Example: Yb3+ (2F7/2 and 2F5/2) in D3 symmetry
Since J is half-integer, double group D’3 has to be used
a) Determine the reducible representation with rotation formula
b) Use reduction formula
J 
sin(J 
sin
1
)
2

2
1
ai =  gR  r (R)  i (R)
h R
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
7
Chapter 2
C2 ,  = 1800
C2R,  = 5400
C3 ,  = 1200
C32,  = 2400
Physico-chemical properties
J = 5/2
sin(540)/sin(90) = 0
J = 7/2
sin(720)/sin(90) = 0
J = 5/2
sin(1620)/sin(270) = 0
J = 7/2
sin(2160)/sin(270) = 0
J = 5/2
sin(360)/sin(60) = 0
J = 7/2
sin(480)/sin(60) = 1
J = 5/2
sin(720)/sin(120) = 0
J = 7/2
sin(960)/sin(120) = -1
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
8
Chapter 2
D 3’
Physico-chemical properties
E
R
(h=12)
C3
C32
C32R
C3R
3 C2 3 C2R
G1
A1
+1
+1
+1
+1
+1
+1
G2
A2
+1
+1
+1
+1
-1
-1
G3
E
+2
+2
-1
-1
0
0
G4
+2
-2
+1
-1
0
0
G5
+1
-1
-1
+1
+i
-i
G6
+1
-1
-1
+1
-i
+i
J=7/2
J=5/2
+8
+6
-8
-6
+1
0
-1
0
0
0
0
0
J = 7/2: 3G4 + G5,6
J = 5/2: 2G4 + G5,6
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
9
Chapter 2
N
N
N
N
OH
N
O
O
3 H2L + 2 Yb3+  [Yb2L3] + 6 H+
self-assembly process in water
yields triple-stranded helicate
N
H2L
Physico-chemical properties
OH
 D3
symmetry
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
10
Chapter 2
Physico-chemical properties
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
11
Chapter 2
D2O
2F
5/2
3
2F
7/2
Emission
9.0
0' 2'
Physico-chemical properties
Excitation
*
2 0
1‘ ?
10.0
x1010
9.5
10.0 10.5 11.0
E / 103 cm-1
* vibronic components
E / 103 cm-1
2F
5/2
*
11.5
269
cm-1
0
F. Gonçalves e Silva, J.-C. G. Bünzli
et al. J. Chem. Phys. A 2002, 106, 1670.
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
2F
7/2
2’
1’
0’
3
2
1
0
372
cm-1
 D3
symmetry
12
Chapter 2
Physico-chemical properties
(4  2) !
14 !

N !(4  2  N ) ! N !(14-N )!
Number of levels
Number of f Number of Number of
electrons
terms
levels
2S+1L
2S+1L
J
Number of LF
sublevels
2S+1G
x
1
13
1
2
2
12
7
13
91
3
11
17
41
364
4
10
47
107
1001
5
9
73
198
2002
6
8
119
295
3003
119
327
3432
7
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
14
13
Chapter 2
Physico-chemical properties
2.1.2 Electronic structure of 5f elements
An
Atom
[Rn]xxx
An3+
An4+
An
Atom
An3+ An4+
[Rn]xxx
Ac
6d17s2
[Rn]
-
Bk
5f97s2
5f8
5f7
Th
6d27s2
5f1
[Rn]
Cf
5f107s2 5f9
5f8
Pa
5f26d17s2
5f2
5f1
Es
5f117s2 5f10
5f9
U
5f36d17s2
5f3
5f2
Fm
5f127s2 5f11
5f10
Np
5f46d17s2
5f4
5f3
Md
5f137s2 5f12
5f11
Pu
5f67s2
5f5
5f4
No
5f147s2 5f13
5f12
Am
5f77s2
5f6
5f5
Lr
5f13
Cm
5f76d17s2
5f7
5f6
5f146d1 5f14
7s2
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
14
Chapter 2
Physico-chemical properties
Deciphering the electronic structure needs the use of
an adequate scheme for spin-orbit coupling.
The coupling is much greater than for 4f elements, so
that Russel-Saunders scheme does not work.
Interpretation of magnetic and optical data is therefore
more difficult than for 4f elements.
Sometimes, however, Russell-Saunders coupling scheme is
used as a first approach.
Example: UIV, 5f2
Ground level: 3H4
SO levels: 3H4, 3H5, 3H6
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
15
Chapter 2
Physico-chemical properties
UIV, 5f2
Spin-orbit
Note: DE decreases
with increasing
tetragonal distortion
(from Oh)
Ligand field
Oh
D4h
Electronic
repulsion
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
16
Chapter 2
Physico-chemical properties
2.2 Magnetism
When Russell-Saunders scheme for spin-orbit coupling is
valid and when the ground state is pure and well
separated from excited states, the following formulae are
well adapted to predict the effective magnetic moment:
eff 
3RT   M
 2,828  M  T
NA  
eff = gJ (J (J + 1)
J (J + 1) + S (S + 1) - L (L + 1)
gJ = 1 +
2J (J + 1)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
17
Chapter 2
12
Physico-chemical properties
eff
10
Dy Ho
Tb
Gd
Tm
6
Pr Nd
4
10
Er
exceptions
8
12
Ce
Yb
6
4
Pm
Eu
2
8
2
Sm
0
Z
La
56
58
60
62
64
66
Lu
68
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
70
0
72
18
Chapter 2
Physico-chemical properties
Actinides
 More complicated behavior: large z5f (see Table below)
and RS coupling scheme for spin-orbit is not applicable.
 UVI compounds [Rn]5f0 (1S0) should be diamagnetic, but
they often display temperature-independent paramagnetism (TIP) because of the mixing of excited states with
the ground state.
 UIV compounds: [Rn]5f2 (3H4). Predicted
gJ = 1 + (4x5 + 1x2 – 5x6)/2x4x5 = 1-0.2 = 0.8
eff = 0.8x(4x5)1/2 = 3.6
measured for [U(NCS)8]4-: 2.9
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
19
Chapter 2
Physico-chemical properties
Spin-orbit coupling constants for some trivalent ions
fn
LnIII z4f/cm-1 AnIII z5f/cm-1
f3
Nd
885
f4
Pm
f5
U
1666
1070
Np
2070
Sm
1160
Pu
2292
f6
Eu
1326
Am
2548
f7
Gd
1450
Cm
2968
Moreover, interelectronic repulsion is only about 2/3 that
of Ln ions, therefore j-j coupling should be used.
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
20
Chapter 2
2.3
2.3.1
Physico-chemical properties
Electronic absorption spectra
General considerations: selection rules
Laporte’s rule:
Dl = ± 1 (ed)
Dl = ± 0 (md)
Spin rule:
DS = 0
DS = ± 1 (md)
(ed)
Rules on L and J: depend on the specific ion
Symmetry rule:
Gop GixGf
2.3.2 Spectra of AnIII aquo ions
They contain f-f transitions (100-300 M-1cm-1) and
more intense f-d absorptions (1000-3000 M-1cm-1),
(5fN  5fN-16d).
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
21
Chapter 2
e/
300
Physico-chemical properties
4I
15/2
4F
7/2
4G
5/2
4S
3/2
M-1cm-1
5 levels
200
7 levels
4G
100
7/2
4I
13/2
2H
9/2
4F
5/2
4I
11/2
0
24
2000
20
e/
16
M-1cm-1
12
30
40
4
E / 103 cm-1
f-d transitions
1000
20
8
50
103 cm-1
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
U3+
5f3, 4I9/2
22
Chapter 2
Physico-chemical properties
Pu3+
5f5, 6H5/2
28
24
20
16
12
E / 103 cm-1
8
2.3.3 Uranyl spectrum
UVI: main compounds
UF6, UCl6, UOF4, UOMe6, and UO22+ compounds
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
23
Chapter 2
Uranyl :
Physico-chemical properties
Linear molecule
Vibrational frequencies:
920-990 cm-1 nas
850-900 cm-1 ns
240-260 cm-1 ds
z
1.7-1.9 Å
very short!
Bonding, MO model, symmetry Dh:
UVI: [Rn]5f06d0, these a.o. can be implied in bonding
6d
sg (dz2)
pg (dxz, dyz)
dg (dxy,dx2-y2)
5f
su(fz3)
pu(fxz2, fyz2)
du(fxyz, fz(x2-y2))
fu(fx(x2-3y2), fy(3x2-y2)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
24
Chapter 2
Physico-chemical properties
2 S
… s’v
h=
+1
1
…
+1
x2+y2, z2
-1
+1
1
…
-1
Rz
…
0
+2
-2cosf
…
0
Rx,Ry
2cos2f
…
0
+2 +2cos2f …
0
2
2cos3f
…
0
+2
-2cos3f …
0
…
…
…
…
…
…
…
…
…
Su
1
1
…
+1
-1
-1
…
-1
Su
1
1
…
-1
-1
-1
…
+
Pu
2
2cosf
…
0
-2
+2cosf
…
0
Du
2
2cos2f
…
0
-2
-2cos2f …
0
xyz, x(x2-y2)
Fu
2
2cos3f
…
0
-2
+2cos3f …
0
x(x2-3y2), y(3x2-y2)
…
…
…
…
…
…
Dh
E
2 C …
sv
i
Sg
1
1
…
+1
Sg
1
1
…
Pg
2
2cosf
Dg
2
Fg
…
…
xy, xz
x2-y2, xy
z
z3, z(x2+y2)
x, y
xz2, yz2
…
Symmetry-adapted 2p(O) orbitals: sg + su + pg + pu
Therefore dg, du, fu are non bonding orbitals
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
25
Chapter 2
Physico-chemical properties
Some m.o.
sg
2pz
dz2
2pz
su
2pz
fz3
2pz
pg
z
2px
2py
dxz
dyz
2px
2py
z
2px
2py
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
fxz2
fyz2
pu
2px
2py
26
Chapter 2
Physico-chemical properties
pg
UO22+
Approximate
MO diagram
sg
6d pg
dg
su
dg
Ground state:
…(pu)4(su)2 1Sg
su
p
5f fu
u
du
pu
fu
du
sg
No bonding
electron
U6+
su
pg
sg
pu
su
pg
sg
pu
UO22+
2
Excited states:
…(pu)4(su)1(du)1
…(pu)4(su)1(fu)1
2p …(pu)3(su)2(du)1
…(pu)3(su)2(fu)1
etc.
O2-
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
(Level ordering
is somewhat arbitrary)
27
Chapter 2
Physico-chemical properties
UVI : typical uranyl spectrum
e
/
M-1cm-1
[UO2(MeCO2)3
20
]-
av. 670 cm-1
10
0
350
400
450 nm
U-O-U stretch
Ground state (IR/Raman)
850 cm-1 (symmetric)
Excited states:
…(pu)4(su)1(du)1
…(pu)4(su)1(fu)1
…(pu)3(su)2(du)1
…(pu)3(su)2(fu)1
etc.
…(pu)3(su)2(du)1
gives rise to
1F , 1P , 3F , 3P
u
u
g
g
identified as
in Dh
1P  1S
u
g
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
28
Chapter 2
Physico-chemical properties
2.3.4 LnIII ions
f-f transitions
- Narrow bands
e < 10 M-1cm-1
- Barycenters of LF sublevels are not much
dependent on the nature of the LnIII environment
therefore energy of the transitions is more or
less constant (but not LF splitting!)
Electric dipole transitions are forbidden
Magnetic dipole transitions are allowed, but very weak
The number of components for a given (2S’+1)L’J’2S+1)LJ
transition depends on the site symmetry.
Some transitions are hypersensitive, i.e. very sensitive
to small changes in the LnIII environment
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
29
Chapter 2
E / 103 cm-1
0.012
Pr(Tf2N)3 10-2 M in BumimTf2N
2
0.01
absorbance
Physico-chemical properties
0.008
1
0.006
3P
20
J
1I
6
0
0.004
15
1D
2
10
0.002
5
0
400
450
500
550
600
650
l/nm
F3C
N
25
N
N
CF3
S
O
S
O
O
O
Tf2N
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
0
2
1
0
3P
1I
6
1D
2
1G
4
4
3
2 3F
6
5 3H
4
PrIII 4f2, 3H4
30
Chapter 2
Physico-chemical properties
Europium(III), 4f6
Special selection rules (also valid for 4f8, TbIII):
- ED: DL, DJ = 0, 2, 4, 6
0-0
- MD: DL = 0, DJ = 0, ±1
forbidden
2.8 e / M-1cm-1
5L
2.4
6
EuCl3 0.05 M
in H2O
2.0
1.6
1.2
0.8
5G
4
5G 5H
6
3
5F
5K
4
6
6
4
0.4
250
(2S+1)G
5H
J
300
5G
5D
4
3
6
5G
4
7F0,1
5G
2
5D
3
350
J
400
5D
2
450
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
5D
1
500 nm
31
Chapter 2
Physico-chemical properties
Reflectance of solid Eu(Tf2N)3
5D
80
70
80
 7F0 (ED)
79
5D
78
77
400
79
4
5G
500
4
5G
600
80
7
J’  FJ
(MD)
2
79
525
5D
530
2
370
375
380
1
385
535
540
545
7FJ (ED)
J=0, DJ=2
78
0 1 0
365
550
5G
0 1
76
360
450
J=1
%R
350
DJ=0
J=0
520
300
7FJ (MD)
%R
5L
6
DJ=6
%R
%R
7F0
(ED)
1
DJ=1
81
5H
6
7F0 (MD)
5D
82
75
0
J=1, DJ=1
77
390
460
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
465
470
475
480
32
Chapter 2
0.003
0.002
A
Physico-chemical properties
Yb(Tf2N)3 10-2 M
in BuminTf2N
E / 103 cm-1
2F
5/2
10.0
0.001
0
MD transition
950 960 970 980 990 nm
Absorption coefficient:
e
= 0.00203/0.01´0.1 =
2.03 M-1cm-1
0
2F
7/2
YbIII 4f13, 2F7/2
Conclusion: RS scheme O.K. for LnIII ions
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
33
Chapter 2
Physico-chemical properties
Hypersensitivity
Some f-f transitions are particularly sensitive to changes
in symmetry and/or in the inner coordination sphere.
They display shifts of their maxima, splittings, and
intensity variation.
Some examples:
3F  3H
PrIII
5200 cm-1
2
4
2H
4F
4I
-1
NdIII
,

17300
cm
9/2
5/2
9/2
5D 7F , 5D 7F
-1
EuIII
21500,
18700
cm
2
0
1
1
5G 5I , 5H 5I
-1
HoIII
22100,
27700
cm
6
8
6
8
2H
4
ErIII
19200 cm-1
11/2 I15/2
1G 3H
TmIII
21300 cm-1
4
6
The mechanism has been discussed at length: it arises
from the mixing of the 4f states with ligand states
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
34
Chapter 2
Physico-chemical properties
Transitions of NdIII:
103 cm-1
4
4I
9/2
4F
2H
,
5/2
9/2
3
4I
9/2
4F
4
7/2, S3/2
2
4I
9/2
4G
1
4I
9/2
2K
4G
2G
,
,
13/2
7/2
9/2
420
10
5
500
e/M-1cm-1
2
1
5/2,
600
3
750
2G
20
2K
2G
7/2
1000
2H
2000 5000 nm
10
4
4I
0
24 22 20 18 16 14 12 10 8
6
4
4G
4S
4F
15/2
Nd3+(aq)
0
etc !
13/2
11/2
9/2
2 103 cm-1
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
35
Chapter 2
Physico-chemical properties
NdIII hypersensitivity
2H
9/2,
CN =
4F
4
5/2 I9/2
Nd(BrO3)3´9H2O (solid)
9
9
[Nd(H2O)9]3+ 0.05 M / H2O
[Nd(H2O)9]3+ 0.05 M / HCl 11 M
CN =
8
8
8
780
NdCl3´6H2O (solid)
Nd2(SO4)3´8H2O (solid)
800
820
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
36
Chapter 2
Physico-chemical properties
f-d Transitions
Allowed by Laporte’s rule,  100-1000 M-1cm-1
Highly energetic, except for CeIII, PrIII, and TbIII
80
3
-1
E / 10 cm
70
60
50
40
30
Free ions
4f to 5d transition
Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
37
Chapter 2
[Ce(H2O)9]3+,
102 e
8
225
Physico-chemical properties
E / 103 cm-1
D3h symmetry
250
n.obs.
300 nm
6
2D
5/2
44.0
4
2
0
48.0
E / 103 cm-1
48
44
40
36
Ce3+ [Xe]5d1 generates two
levels, 2D3/2 and 2D5/2
40.0
2D
3/2
32
2
2F
7/2
0
2F
5/2
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
38
Chapter 2
Physico-chemical properties
Observed f-d transitions for
LnBr3 in anhydrous EtOH:
Ce
Pr
Tb
312 nm ( 800 M-1cm-1)
228 nm (1500 M-1cm-1)
231 nm ( 500 M-1cm-1)
100
LnIII (aq)
300
e
/ M-1cm-1
Tb
e / M-1cm-1
200
50
100
0
0
49 47 45
E / 103 cm-1
Pr
49
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
47
45
43
E / 103 cm-1
39
Chapter 2
Physico-chemical properties
Charge transfer transitions
Allowed by Laporte’s rule,  200-500 M-1cm-1
48
46
E /103 cm-1
44
42
4
III
O
YP
YO
F
Eu (CT state)
-1
4
O
LaP
38
36
3
Cl
O
a
L
O
La2
34
30
3
Y2O
40
32
3
in 10 cm
Host
2S
Y2O
28
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
40
Chapter 2
Physico-chemical properties
Charge transfer in bimetallic complexes with calix[n]arenes
p-tert-butylcalix[5]arene (b-L’H5)
wider rim (lipophilic)
narrow rim (oxophilic)
Cone conformation
[Eu2(b-L’H2)2(DMSO)4]
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
41
Chapter 2
e / M-1cm-1
3000
Physico-chemical properties
[Eu2(b-L’H2)2(DMSO)4], 7x10-4 M in thf
2500
2000
24 740 cm-1
1500
M-1cm-1
719
LMCT transition
1000
500
0
nm
400
500
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
600
42
Chapter 2
Physico-chemical properties
p-tert-butylcalix[8]arene
“undulated” conformation
[Eu2(b-LH2)(dmf)5]
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
43
Chapter 2
1,9
A
Physico-chemical properties
LMCT: 25’000 cm-1,
e
= 720 M-1cm-1
[Eu2(b-LH2)(DMF)5] in DMF
1,4
3.8x10-3 M
0,9
Eu(NO3)3.4DMSO
0,4
5D0
7F0
-0,1
350
400
450
500
550
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
600
44
Chapter 2
Physico-chemical properties
Intensity stealing
Overlap between LMCT and f-states leads to f-f
transitions with larger intensities, e.g. 5D07F0
Replacing p-tbut by SO3H (s-LH8) and NO2 (n-LH8)
leads to LMCT states with higher energy and to a
reduced intensity stealing
Cmpnd
MLCT/cm-1 0-0/cm-1
e / M-1cm-1
Eu2(b-LH2)
24740
17330
5.0
Eu2(s-LH2)
30300
17322
1.4
Eu2(n-LH2)
not located 17319
0.8
[Eu(H2O)9]3+
-
0.001
17212
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
45
Chapter 2
Physico-chemical properties
2.4
Luminescence spectra
2.4.1 Basics of luminescence
Jablonski’s diagram (organic molecules)
energy
S2
S = singlet
E2
T = triplet
S1
E1
T1
A
F
A = absorption
10-16 s
F = fluorescence
10-12-10-6 s
P = phosphorescence
10-6 – 10s
P
E0 S0
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
non-radiative
de-activation
intersystem
crossing
46
Chapter 2
Physico-chemical properties
e(YO.M. )
e(YO.M. )
intersystem
one electron
changes its spin
crossing
singlet S1
triplet T1
Fluorescence : without spin change
Phosphorescence : with spin change
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
47
Chapter 2
Physico-chemical properties
The states involved
sp* states
s
p*
p
p*
pp* states
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
48
Chapter 2
Physico-chemical properties
np* states
n
p*
Charge transfer states
4fn  4fn+1L-1 (reduction of the metal ion)
4fn  4fn-1L+1 (oxidation of the metal ion)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
49
Chapter 2
Physico-chemical properties
Quantum yield :
Iém
number of emitted photons
Q=
=
 f (T )
Iabs number of absorbed photons
The quantum yield increases when temperature decreases
I0(l)
It(l)
Iem
Q
I 0  It
Iobs(l)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
50
Chapter 2
Physico-chemical properties
What is the relationship between Iobs and concentration ?
Iobs  K  Q  I0  e  b  c  constant  c
if e  b  c  0, 05
The condition on ebc stems from the fact that only the
first term of a series development is retained in
demonstrating this formula.
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
51
Chapter 2
Physico-chemical properties
Example of a calibration curve showing the
inner-filter effect
Iobs
H O
H
NH2
O
O
-O P O CH
2
H
O
H
H
OH
NADH in H2O
N
H
c / mM
OH
0.001
NH2
H
O
-O P O CH
2
O
H
N
N
H
H
OH
OH
0.01
0.1
1.0
N
N
H
H
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
52
Chapter 2
E
Physico-chemical properties
vibrational
levels
(rotations
not shown)
excited
state
Born-Oppenheimer
approximation
Vertical absorption
Vertical emission
Kasha’s rule: emission from
relaxed excited state
Non-radiative
de-activation
ground
state
distance
DE = DEel + DEvibr + DErot
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
53
Chapter 2
Physico-chemical properties
excited states
singlet S1
triplet T1
E
isc
DE < DE , lP > lF
ground
state S0
Fluorescence and
phosphorescence
When vibrational
levels match,
the energy can flow
to the triplet
state: intersystem
crossing isc
Phosphorescence
occurs
distance
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
54
Chapter 2
Physico-chemical properties
Time dependence of the emitted light
If N * is the number of excited molecules at time t:
-dN */dt = kr·N *
kr = radiative rate constant (s-1)
-dN */N * = kr·dt
Integration between {N0*; t0 } and {N *; t } gives
N * = N0*·e-krt
I(t) = It=0·e-krt
The lifetime of the excited level is given by:
t = 1/kobs (s)
During this time, a fraction 1/e of the excited molecules
return to the ground state (e = 2,73)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
55
Chapter 2
Physico-chemical properties
Photons per s
1000
1/e I0
800
600
7
kobs = 7,1.10 s
200
t=t
0
0
H
C
H3CO
-1
400
CH CH2
HO
t = 14 ns
10
9
10 t / s
20
30
40
N
H
SO4-2
Quinine sulfate in water
N
H
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
56
Chapter 2
Physico-chemical properties
In absence of non-radiative de-activation (Q = 1),
kobs = kr
In presence of non-radiative de-activation (Q < 1),
kobs = kr + knr, therefore
tobs
kr
kr
Q =
=
=
kobs
kr + knr
tr
2.4.2 The special case of 4f-elements
In view of the weak f-f oscillator strengths, direct
excitation of LnIII luminescence is not very efficient,
unless powerful lasers are used. Therefore the need
for sensitisation (antenna effect).
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
57
Chapter 2
Physico-chemical properties
Indirect excitation, called sensitisation is achieved through
lattice or attached ligands
hn
hn
hn
hn
light harvesting
Energy transfer
light emision
The excited states of LnIII ions are usually long-lived with
lifetimes in the range s to ms, so that the ligand triplet
state plays a major role in the energy transfer process.
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
58
Chapter 2
Physico-chemical properties
Energy migration paths
Ligand
E
LnIII
Complex
4f*
1S*
3T*
Absorption
F
P
LMCT
ILCT
Absorption
Ground state
> 20 rate
constants !
Non radiative deactivation
Energy transfer
Quenching or back transfer
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
59
Chapter 2
Physico-chemical properties
QLnL = sens ЧQLnLn = isc Чet ЧQLnLn
intrinsic
quantum
yield
In the special case of EuIII, tr may
be estimated from:
жI
1
3
= 14.65 Чn Чззз tot
зиI md
tr
ц
ч
ч
ч
ч
ш
=
tobs
tr
where n is the refractive index, Itot the total emitted
light intensity and Imd the intensity of the purely
magnetic dipole transition 5D07F1.
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
60
Chapter 2
2.4.3
Physico-chemical properties
4f emission spectra
Tb Dy
Gd
40
Ho Er
Tm
Yb
40
3P
0
35
35
Pr
Nd Sm Eu
6P
7/2
30
25
30
1D
2
25
20
3
E / 10 cm
-1
5D
3
15
10
2
3P
0
1
0
4G
5/2
1D
2
1G
4
3F
4
5D
4
5S
2
5F
5
5D
20
1G
4
4F
9/2
4S
3/2
15
4F
3/2
2F
5/2
5
4I
10
5
13/2
0
0
3H
4
4I
9/2
6H
7
8
5/2 F0,1 S7/2
7F
6
6H
15/2
5I
8
4I
15/2
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
3H
6
2F
7/2
61
Chapter 2
Physico-chemical properties
The smaller the gap between excited and ground state,
the larger the contribution of non-radiative de-activation
(particularly through vibrations).
GdIII is the best ion, but emits
in the UV
EuIII, TbIII have often large
intrinsic quantum yields and are
used as luminescent probes.
Tb
Eu
Dy
Sm
500
600
700 nm
PrIII (1.33 m), NdIII (1.06 m), ErIII (1.54 m), and
YbIII (0.98 m) have interesting emission bands in the
NIR range, some of them are in the telecommunication
window (1 – 1.6 m)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
62
Chapter 2
Physico-chemical properties
Cerium(III) in Oh symmetry
Cs2Na(Y:Ce)Cl6
Double group O’h
Emission spectrum at 10 K, exc.
50x103 cm-1
2T (G )
2g 8g
G6u
 2F7/2
E / 103 cm-1
24
25
G7u
2T (G )
2g 8g
26
48.0
30.0
 2F5/2
27
G8g
2E
g
44.0
G8u
G8u
E / 103 cm-1
28
(E.P. Tanner et al. JACS 2003 125, 13225)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
2
0
G7g
G8g
G6u
G8u
G7u
G8u
G7u
2T
2g
2F
7/2
2F
5/2
63
Chapter 2
Physico-chemical properties
Cs2Na(Y:Ce)Cl6
Double group O’h
Emission spectrum at 10 K, exc.
50x103 cm-1
2E (
g G8g)
 2F5/2 G8u
G7u
E / 103 cm-1
48.0
G8g
2E
g
44.0
2E (
g G8g)
 2F7/2
G8u G
7u
44
30.0
45
46
E / 103 cm-1
47
(E.P. Tanner et al. JACS 2003 125, 13225)
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
2
0
G7g
G8g
G6u
G8u
G7u
G8u
G7u
2T
2g
2F
7/2
2F
5/2
64
Chapter 2
Physico-chemical properties
Neodymium(III): Nd(NTf2)3 in BumimNTf2
E / 103 cm-1
4I
11/2
laser line
4I
9/2
800
1000
1200
N
N
S
O
S
O
nm
CF3
O
O
4F
3/2
10
4I
13/2
F3C
N
2G
7/2
4G
5/2
20
Tf2N
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
15/2
5
13/2
11/2
0
9/2
4I
65
Chapter 2
N
N
N
N
OH
Physico-chemical properties
N
N
O
H2L
O
OH
• log23 = 51 for Eu
• pEu = 21 (dota : 25)
Samarium emission spectrum:
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
66
Chapter 2
Physico-chemical properties
Samarium(III): Sm2L3 in H2O
E / 103 cm-1
20
15
4I
J
4F
J
4G
J
7/2
5/2
160
5
6H
 6HJ
9/2
5/2
11/2
11/2
6F
J
0
4G
5/2
120
80
10
7/2
40
1/2
15/2
nm
0
550
600
650
700
750
J
5/2
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
67
Chapter 2
Physico-chemical properties
Europium(III): tris(dipicolinate)
Cs3[Eu(dpa)3]
Solid state
Emission spectrum
dpa
250
300
lexc = 280 nm (L)
Excitation spectrum
5L
6
5D
2
350
400
450
395 nm (f-f)
5D
1
500
550
l / nm
580
600
620
640
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
660
l / nm
680
700
720
68
Chapter 2
Physico-chemical properties
Europium(III): tris(dipicolinate)
Q LEu = 56 ± 2 %
tobs = 1.8 ± 0.1 ms
Q EuEu = 66 ± 4 %
Itot / IMD = 7.4
n = 1.517
trad = 2.74 ms
Q EuEu = 1.8/2.74 = 66 %
Perfect match!
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
69
Chapter 2
Physico-chemical properties
Terbium(III): Tb(NO3)3 in DMSO
E / 103 cm-1
5
30
5D 7F
4
J
0
1
25
3
J=6
4
3
5D
20
2
x6
5D
4
15
10
650
600
550
500 nm
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
5
0
0
6
7F
70
MSc: f-Elements, Prof. J.-C. Bünzli, 2008
71