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