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Physicochemical properties of LanthanidesPhysicochemical properties of Lanthanides

Electronic levels: Term Symbols (ground state)Electronic absorption spectraLuminescence spectraMagnetism

0123

E / 103 cm-1

10.0

0

2F5/2

2F7/2

2’1’0’

Lecture 22

Swavey, S. J. Chem. Educ., 2010, 87 (7), 727–729

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2.1 Electronic levels

(Summary from the BSc course “Coordination chemistry”2.1.1 Electronic structure of 4f elements

Russel-Saunders coupling usually works well

(2S+1)(2S+1)

S P D F G H I J K …0 1 2 3 4 5 6 7 8 = L

J = L+S, L+S-1…, |L-S|

spin multiplicity

(2S+1)J(2S+1)J

Spectroscopic termMultiplicity = (2S+1)´(2L+1)

Spectroscopic level, multiplicity = (2J+1)

Electronic States/Term symbols

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 groundstate (Lmax)

• The ground level has Jmin if the subshell is less thanhalf filled, Jmax if the subshell is more than halffilled

Example: Nd3+, 4f3

3 2 1 0 -1 -2-3 m ( = 3)

Lmax = 6 J = 15/2……9/2

4I9/24I9/2

Smax = 3´½ = 3/2

Electronic States/Term symbols-Ground state term symbols

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Ground state Term Symbol for Sm3+

Work Out/Solution

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Tb: [Xe]4f96s2

Tb3+: [Xe]4f8

Swavey, S. J. Chem. Educ., 2010, 87 (7), 727–729

Diagram representing the interactions leading to the splitting of the electronic energy levels of a Eu3+ ion

Notice minimal effect of ligand field

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Interpret the Transiitons from the spectra

Ln3+ 4fn, n Groundlevel

Color Magnetic momentexp. calc.

Ce 1 2F5/2 colorless 2.3-2.5 2.54Pr 2 3H4 green 3.4-3.6 3.58Nd 3 4I9/2 lilac 3.5-3.6 3.62Pm 4 5I4 pink n.a. 2.68Sm 5 6H5/2 yellow 1.4-1.7 0.85Eu 6 7F0 pale pink 3.3-3.5 0Gd 7 8S7/2 colorless 7.9-8.0 7.94Tb 8 7F6 colorless 9.5-9.8 9.72Dy 9 6H15/2 yellow 10.4-10.6 10.6Ho 10 5I8 yellow 10.4-10.7 10.6Er 11 4I15/2 rose 9.4-9.6 9.58Tm 12 3H6 pale green 7.1-7.5 7.56Yb 13 2F7/2 colorless 4.3-4.9 4.54

Linking spectral and Magnetic properties

Figure out spectral and magnetic properties from term symbol

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Electronic Absorption Spectra

Observe: Very low molar absorption coefficient (y-axis)Frame a question!!! On why this value is very small.

Pr(Tf2N)3 10-2 M in BumimTf2N

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0.002

0.004

0.006

0.008

0.01

0.012

400 450 500 550 600 650

abso

rban

ce

N NN

SO O

F3CS

O O

CF3 PrIII 4f2, 3H4

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10

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25E / 103 cm-1

1G4

1D2

3H

3F

1I6

3P

456234

012

3PJ

1D2

01

2

1I6

/nm

Tf2N

Absorption spectral properties

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Jablonski diagram

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Luminescence spectra

Basics of luminescence

S1

S2

S0

T1

F PA

S = singlet

T = triplet

E0

E2

E1

energy A = absorption10-16 s

F = fluorescence10-12-10-6 s

P = phosphorescence10-6 – 10s

non-radiativede-activationintersystemcrossing

Jablonski’s diagram (organic molecules)

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singlet S1 triplet T1

intersystem

crossingone electronchanges its spin

Fluorescence : without spin changePhosphorescence : with spin changeFluorescence : without spin changePhosphorescence : with spin change

Indirect excitation, called sensitisation is achieved throughlattice or attached ligands

light harvesting

hn hn

hnhn

Energy transfer light emision

The excited states of LnIII ions are usually long-lived withlifetimes in the range ms to ms, so that the ligand tripletstate plays a major role in the energy transfer process.

Physico-chemical properties of Lanthanides-Indirect Sensitization

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Absorption

LnIII

4f*

Ligand

1S*

Ground state

3T*

Complex

Energy transfer

Non radiative deactivation

Quenching or back transfer

F

P

E

20 rate constants ! Complicated energy transfer

pathways

Energy migration paths

Physico-chemical properties

Many competitive pathways…

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4f emission spectra

Pr Nd Sm Eu

Tb Dy Ho Er Tm Yb

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35

40

E/ 1

03

cm-1

3H4 4I9/2

6H5/27F0,1

8S7/2 7F6

6H15/2 5I8 4I15/2

3H6 2F7/2

1D2

3P0

4F3/2

4G5/25D

01

2

6P7/2

5D4

5D3

4F9/2

5S24S3/2

1D2

1G4

2F5/2

Gd

1G4

4I13/2

3P0

3F4

5F5

Chapter 2 Physico-chemical properties

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Energy level diagrams for lanthanides

Bünzli, J. C. G. et al. Chem. Soc. Rev. 2005, 34, 1048-1077

The main luminescent levels are drawn in red, while the fundamental levels is indicated in blue

Electronic levels: 14!/n!(14 -n)!Eu(III) and Tb(III): 3003 Gd(III): 3432

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