Post on 16-Apr-2018
Probing the Solution Speciation and Coordination Environment of f-
Element complexes by NMR and Emission Spectroscopy
Louise Natrajan Karlsruhe, 27th January 2010
Lanthanide Luminescence
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
450 550 650 750 850 950 1050 1150 1250 1350
Wavelength/ nm
Tb
Eu
Nd
Yb
•Emission spectra span the visible and near IR regions
•Choice of sensitising chromophore important
•Lifetimes range nanosecond to millisecond order
Triplet mediated energy transfer mechanism
hv
5D0
7F0
7F1
7F2
7F3
7F4
7F5
7F6
5D1
5D2
S1
T1
S0
Ligand Eu3+
Relative Energy
kisc
ket
kfluorescence kphosphorescence2F5/2
2F7/2
S1
T1
S0
Ligand Yb3+
Relative Energy
kisc
kelectron transfer LMCTYb2+ + 1Ar*
kelectron transfer
Lanthanide Luminescence
LMCT mediated energy transfer mechanismFaulkner et al., Dalton Trans., 2009, 3890.http://int.ch.liv.ac.uk/Lanthanide/Lanthanides
Tetra Picolyl Substituted Cyclen
Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Tm, Er, Yb
Lpy
•Ave. Yb-Ncyclen 2.63 Å
•Ave Yb-Npy 2.52 Å
•Yb-OH2 2.40 Å
Mono-capped SAP (φ = 39°)
[Yb(Lpy)(OH2)][OTf]3
Change in solid state coordination geometry across the series
Nd TSAP (φ = 24°)
Eu TSAP (φ = 25°)
Gd SAP (φ = 36°)
Tb SAP (φ = 37°)
Er SAP (φ = 38°)
N
NN
NN
N
N
N
N
NN
NN
N
N
N
Ln
.
Ln(OTf)3
MeOH .3OTf
Solution Coordination Isomerism
•Four stereoisomers
•Interconversion by pendant arm rotation and ring inversion
•TSAP faster H2O exchange
•Same isomerism for DO3A complexes
Dalton Trans. 2005, 3829.Twisted Square Antiprism Λ(λλλλ)
Square Antiprism Δ(λλλλ)
Arm
Rotation
Arm
Rotation
Ring Inversion Ring Inversion
Square Antiprism Λ(δδδδ)
Twisted Square Antiprism Δ(δδδδ)
N
N
N
NO
O
O
O
OO
O
O
Ln
N
N
N
NO
O
O
O
O O
O
O
Ln
N
N
N
NOO
O
O
OO
O
O
Ln
N
N
N
N OO
O
O
OO
O
O
Ln
Steady state and time resolved luminescence studies:
•Kinetic traces for Yb, Pr and Nd fitted to a bi-exponential decay
•Eu and Tb follow mono-exponential decay kinetics
[Nd(LPy)(OTf)].2OTf/D2O[Tb(LPy)(OTf)].2OTf/H2O
0
5
10
15
20
25
0.00E+00 5.00E-07 1.00E-06 1.50E-06 2.00E-06 2.50E-0
Time (s)
0
2
4
6
8
10
12
14
450 500 550 600 650
Wavelength (nm)
5D4 → 7FJ λem = 1055 nm
Solution Studies
0.34.471.63Yb
0.225402060Tb0.41130720Eu-0.12 33 %--0.08 67 %-Pr
0.40.17 50 %0.09 50 %0.00.35 50 %0.22 50 %NdqH2OτD2O/μsτH2O/μsComplex
q = A(kH2O - kD2O - B) (Eu, Tb)
q = A(kH2O - kD2O) - B (Nd) Number of inner sphere H2O molecules approximates to 0
J. Chem. Soc., Perkin Trans 2., 1999, 493.
Lifetime Measurements
1H NMR Spectrum of Eu(Lpy)/D2O
Solution conformation different to solid state geometry
ppm-15-10-50510
ppm7.42 ppm6.14 ppm4.50
HeqHeq
HaxHax
CH2-py
CH2-py H3
H5H4
H6
Heq HeqHax Hax
CH2-py
NN
Heq
N
HaxH
HH3
H4
H5
H6Δ p i= Di
3cos2θi −1ri
3
Pr . L py Nd. L p y
S m .L pyEu.L py
T b .L py D y . L p y
1H NMR Spectra of Ln(Lpy)/D2O
DFT Calculations of Y(Lpy)
DFT scan through cyclen ring isomerisation pathway
The isomerisation process is a sequence of single-joint inversion pathways
N
N
N
N
OO
O
O
OO
N
N
N
N O
O
O
OO O
O
EuEu
Bimetallic Complexes: 1H NMR
Luminescence Studies
τH2O 0.51 & 1.67 μs
τD2O 1.17 & 4.95 μs
q = 0.3 & 1
τH2O 2.26 ms
τD2O 2.55 ms
q = 0
Differentiated binding sites Non-distinguishable binding sites
Pope et al., Chem. Commun., 2003, 125.Open vs. closed conformation
N
N
N
N O
O
O
OO
O
O
N
N
N
N
OO
O
O
OO
Yb Yb
NN
NN O
O O
O
O
OO
N
N
N
N
O O
O
OOO
Tb Tb
Anisole Derivative
Removal of coordinative ability of phenol
Eu τH2O 0.50 ms, τD2O 1.45 ms, q = 1.3
Tb τH2O 1.31 ms, τD2O 1.87 ms, q = 0.8
Yb τH2O 1.42 μs, τD2O 4.63 μs, q = 0.4
N
N
N
N
O
O
O
O
O
O
N
N
N
NO
O
O
OOO
O
Ln
Ln
pD 3
pD 5
pD 8
N
N
N
NOH
O
O
OO
O
O
O
N
NN
N
O
O
OO
O
O
Eu
Eu
pH Dependence of 1H NMR Spectra
q = 1.3
q = 0.3
1H NMR Spectra Independent of pH
N
N
N
N O
O
O
OO O
O
N
N
N
N
OO
O
O
OO
EuEu
NN
NNO
OO
O
O
O O
N
N
N
N
OO
O
O O O
EuEu
Selective Introduction of Ln3+
Orthogonal protections
NHHN
O O N N
NN
NN
N N
OO
O
OO
OO
O
O
O
OO
Yb Tb
qYb = 0.5 qTb = 0.6
Natrajanet al., Chem. Commun., 2009, 6020.
•Solid state structures of complexes with Lpy do not provide an ideal model for solution behaviour
•Unusual donor sets change the nature of the anisotropy
•In bimetallic systems, solution isomerism is more complicated and NMR spectra are more difficult to interpret
•Emission spectroscopy can be used to study dynamic solution behaviour
•Complementary technique with NMR spectroscopy
Summary
Luminescence Studies of Uranium(IV) Complexes
Kirishima et al., Chem. Commun., 2003, 910.
Uranium(IV) (f2)
Electronic repulsion
Spin-orbit
Ligand field
Oh D4h
U(IV) in 1M HClO4
Uranium(IV) Complexes
Complexes prepared by reaction of K salt of ligand wih UCl4
NN
NN O
O O
O
O
OO
N
N
N
N
O O
O
OOO
U U
N N
N NH
OO
O
O
OO
U
N N
N N
OO
O
O
OO
UO
OMe
N
NN
NN
N
N
N
U
4
N N
N N
OO
O
O
OO
U
O
O
Hydrolysis of U(IV) to UO2(VI) occurs with Lpy
X-ray crystal structure
of [H2Lpy][UO2Cl4]
X-ray Crystal Structures
N N
N NH
HOO
HO
O
OHO
Cl
UCl Cl
Cl
Co-crystallisation of H3DO3A and UCl4 occurs; 1H NMR suggests
equilibrium mixture with complex
Emission Spectra (MeOH and DMF)
0
20
40
60
200 300 400 500 600 700 800
Wavelength (nm)
UCl4_285_emUCl4_405_emUCl4_400_excUCl4_520_exc
λexc= 375 and 405 nm; all lifetimes are ~ 2-10 ns (400 - 900 nm)
UCl4
0
0.2
0.4
0.6
0.8
1
300 400 500 600 700
Emission (285 nm excitation)Emission (400 nm excitation)
0
0.2
0.4
0.6
0.8
200 400 600 800 1000 1200
Wavelength (nm)
NN
NN O
O O
O
O
OO
N
N
N
N
O O
O
OOO
U UN N
N NH
OO
O
O
OO
UN N
N N
OO
O
O
OO
UO
OMe
N N
N N
OO
O
O
OO
U
O
O
NMR Spectra (MeOD)
N N
N N
OO
O
O
OO
U
O
O
U(IV) DOTA
N N
N N
OO
O
O
OO
Pr
O
O
Pr(III) DOTA
Aime et al., Inorg. Chem., 1992, 31, 4291
Tm(III) DOTA
NMR Spectra
NN
NN O
O O
O
O
OO
N
N
N
N
O O
O
OOO
U U
NN
NN O
O O
O
O
OO
N
N
N
N
O O
O
OOO
Pr Pr
Summary
•Several macrocyclic uranium(IV) complexes have been synthesised
•These show long-lived visible emission (ILCT and f-f)
•Intra f-f transitions exhibit charge transfer character
•Emission spectroscopy can be used as a probe for actinide speciation
•1H NMR spectra of symmetric systems are structurally informative
•1H NMR spectra of DO3A systems appear similar to the Ln3+ series
Acknowledgements
Stéphanie Cornet
Mike Redmond
David Collison
Stephen Faulkner
Alan Kenwright
Ilya Kuprov
Ntai Martin Khoabane
Ben Dadds
Simon Pope
Aaron Villaraza
Robin Pritchard
Chris Muryn
Uranyl(VI) Luminescence
U
O
O
OO
O
OO
O
4-
OO
O
UO22+*
Photochemistry
Luminescent Probe
hυ
LMCT
Characteristic green emission
Long lived triplet excited state (μs - s)
5f0
UO22+ LMCT absorption
J. Photochem. Photobiol., 1990, 52, 293.
Uranyl(VI) Complexes
Ligands relevant to the PUREX process
P OPh
NP
Ph
O
Ph
Ph
Ph3P=O Ph3As=O Ph3P=NHL =
[UO2(TPIP)2(thf)] [UO2(OAsPh3)2Cl2]M. Redmond S. Cornet
0
0.2
0.4
0.6
0.8
1
1.2
200 300 400 500 600 700
U
O
O
P OPh
NP
PhO
Ph
Ph
POPh
NP
Ph
O
Ph
Ph
O
Emission Spectra
All complexes show well resolved uranyl LMCT emission
λexc = 360 nm, λem 523 nm (DCM)
L λem
Cl 504 nm
Ph3P=NH 517 nm
Ph3PO 529 nm
Ph3AsO 531 nm
O
U
O
LLCl
Cl
Luminescence Lifetimes
3.46 - 1.097
λexc 405 nm, λem 450 - 550 nm
τ1 (μs) τ2 (μs) χ2
2.00 - 1.008
0.87 (93 %) 0.19 (7 %) 1.063
0.15 (46 %) 0.04 (54 %) 1.520
1.42 (75 %) 0.13 (25 %) 1.001
U
O
O
P OPh
NP
PhO
Ph
Ph
POPh
NP
PhO
Ph
Ph
O
O
U
O
O=AsPh3Ph3As=OCl
Cl
O
U
O
O=PPh3Ph3P=OCl
Cl
O
U
O
thfthfCl
Cl thf
O
U
O
NH=PPh3Ph3P=HNCl
Cl
Cea-Olivers et al., Inorg. Chem. Commun., 2005, 8, 205.
Future Outlook[UO2(TPIP)2]3
Using luminescence as a probe of nuclearity and speciation