1 MSc: f-Elements, Prof. J.-C. Bünzli, 2008 f - Elements Section of chemistry and chemical...

1MSc: f-Elements, Prof. J.-C. Bünzli, 2008

f - Elementsf - Elements

Section of chemistry and chemical engineeringLaboratory of lanthanide supramolecular

chemistry

Jean-Claude Bünzli2008

4fz3

Gd

GdEu

Master degree course, SCGC


Table of contentsTable of contents

Pedagogical objective 3Chapter 1 f-Atoms and ions 4Chapter 2 Physico-chemical properties 52Chapter 3 Coordination chemistry 121Chapter 4 Organometallics 205Chapter 5 Selected applications 247

Appendices


Pedagogical objective

FF4f4f

5f5f

1 21 2 3 4 5 6 7 83 4 5 6 7 8

SS PPDD

3d3d

4d4d5d5d

6d6d

11223344556677

• Overview of f-elements properties, with reference to their uses in daily life and high technology applications

• Mainly focused on 4f-elements

Pre-requisitesCoordination chemistryQuantum chemistry


1.1 Definitions and discovery

1.2 Occurrence of 4f elements

1.3 Basic properties

1.3.1Electronic configuration

1.3.2Oxidation states of 4f elements

1.3.3Oxidation states of 5f elements

1.4 Radioactivity of 5f elements

Table of ContentsTable of Contents

Nuclear fuelrod assembly

Particle filterfor Diesel exhaustgases

Chapter 1 f-Atoms and Ions


Chapter 1. f-Atoms and IonsChapter 1. f-Atoms and Ions

1.1 Definitions and discovery

Lanthanides: 58-71 LnActinides: 90-103 An

Parent elements La and Ac often included in Ln and AnRare earths: Sc, Y, La + Ce-Lu

Discovery of rare earths

1794 (Y) – 1947 (Pm)

Discovery of actinides

1789 (U) – 1971 (Lr)

Naturally occurring: Ac, Th, Pa, U, (Np, Pu)



1.1 The discovery of 4f-elements

rare earthsrare earths

actinidesactinides

Yttrium was discovered in 1794 by Johan Gadolin, in Åbo (Turku)

4f4f

5f5f

lanthanides: Ce-Lulanthanoids: La-Lu



1787 Carl Axel Arrhenius, an artillery lieutenant and amateur geologist, finds a black mineral in a quarry near Ytterby, 30 km from Stockholm.

1788 B. R. Geijer (Stockholm) describes the mineral (d = 4.2) and names it ytterbite, presently known as gadolinite, with formula Be2FeY2SiO10.

1792 J. Gadolin (1760-1852) studies the mineral and publishes a 19-page report in 1794 in the Proceedings of the Royal Swedish Academy of Sciences, concluding to the presence of a new “earth”, which he names yttrium.

Discovery of yttrium (1794)

Subsequent work revealed that yttrium contained the oxides of 10other elements.



HNO3 / HCl

SiO2Fe3+, Be2+, Y3+

K2CO3, pH = 4-5

O2, H2O

Fe(OH)3

Y3+

NH3, pH = 7-8

Y(OH)3

Be2FeY2SiO10

Johan Gadolin, 1794

Chemical separationof yttrium

Be(OH)2,FeCO3

taken as Al



1751 The mineralogist Cronstedt finds a peculiar heavy stone near Batnäs.

1803 W. Hisinger and J. J. Berzelius analyse this stone and find it contains an unknown “earth” they name ceria

after the recently discovered planet Ceres. Their finding is published in 1804 in a 24-page report and confirmed by the German chemist Klaproth.

The silicate material has a variable composition close

to (Ce,La)3MIIH3Si3O13 and is presently named cerite

(M = Ca, Fe).

Discovery of cerium (1804)



Most of the other rare earths have been discovered by furtheranalysing the two initial minerals, gadolinite and cerite.

The main techniques were fractional precipitation andcrystallisation, as well as flame spectroscopy (absorption andemission).

These operations were tedious: for instance, 20 tons wereneeded to produce 82 g of element 61 by ion-exchangeseparation techniques (61 = radioactive promethium), that is afraction equal to 4x10-12 !)

Other rare earths (1839-1947)



1.2 Occurrence of4f elements Abundance in cosmosAbundance in cosmos

relative to silicon:relative to silicon:

Si = 10 Si = 1066

La-Lu

The elements are “rare”but not rarer than manyothers, such as Au, Pt,Pd, Rh, for instance



Natural abundance

Abundance in earth’s crustexpressed in ppm (g/ton)

La

Ce

Nd

Pr

Sm Gd

Eu Tb

Dy Er

Ho Tm

Yb

Lu

Odd/even effect

56 58 60 62 64 66 68 70 72

0

10

20

30

40

50

0

10

20

30

40

50

Atomic number



Cerium group (lighter elements)

Bastnasite Ln(CO3)F 65-70%

Monazite LnPO4 50-75%

Cerite (Ce,La)3MIIH3Si3O13 50-70%

Yttrium group (heavier elements)

Xenotime LnPO4 55-65%

Gadolinite Ln2M3Si2O10 35-50%

Euxenite Ln(Nb,Ta)TiO6xH2O 15-35%

Main resources (4f elements)



Main resources

World resources are estimated to 83 million metric tons

for a present usage of about 40’000 metric tons a year

China 50 % (?)

Russia 25 % (?)

USA 10 %

Australia 5 %

Other 10 %

Baotou (InnerMongolia)



Applications of 4f-elements

• Catalysts- cracking of hydrocarbons- conversion of exhaust gases (gasoline and diesel)

• Metallurgy- Steel production (removal of O, S)- Nodular graphite- Hardener (e.g. in magnesium)

• Materials- High temperature superconducting ceramics- Electronic devices (capacitors, O2-sensors)- Magnets (Sm5Co, Nd5Fe)- Neutron moderators in nuclear reactors- Hydrogen storage with metal hydrides



CeO2

Gazfiltrés

Gas produced by

the engine

Gas filtration

Sootparticles

CeO2

EOLYS® Soot emission of Dieselengines reduced by 99.9 %



• Optics and lighting- Polishing powders- Protection against sun (sunglasses)- Lasers, particularly Nd YAG- Phosphors for displays (incl. electrolumin. displays)- Fluorescent lamps

• Medicine- Seasickness (Ce oxalate), thromboses (Nd oxalate)- Renal insufficiency (La2(CO3)3

.4H2O) - X-ray intensifying screens- NMR imaging- Cancer radio- and photo-therapy- Laser surgery (Nd YAG laser)- Luminescent immunoassays

• Science- Shift reagents, luminescent and magnetic probes- Catalysts for organic chemistry



fluorescent lamps

Er amplifierfor optical fibers rechargeable batteries



pigments

Re-inforcedcast Al pistons

MRI images



1.3 Basic properties

1.3.1Electronic configuration

4f-orbitals x(x2–3y2)

y(3x2–y2) z(x2–y2)xyz

xz2 yz2 z3



4f-orbitals (in octahedral symmetry)

xy

z

z3 y3 x3

xyz

z(x2-y2) y(z2-x2) x(z2-y2)

T2u

T1u

A2u



• Sc, Y and La introduce the 3d, 4d and 5d transitionseries: nd1(n+1)s2 n=3 (Sc), 4 (Y) and 5 (La)

• The energy of the 4f orbitals decreases abruptly beyond La: -0.95 eV for La, -5 eV for Nd ! which leads to the filling of the 4f shell

• The 4f orbitals lie outside the Xe electronic structure for La, but inside the Xe electronic structure for the other Ln elements

Lanthanides

Actinides• Similarly, the 5f orbitals are also “inner orbitals”



inner nature of4f (Nd3+) and5f (U3+) orbitals



Ln0 4fN-1 5d1 6s2

La, Ce, Gd, Lu 4fN 6s2

Pr-Eu,Tb-Yb

1.3.2 Oxidation states of 4f elements

LnII 4fN-1 5d1

La, Gd4fN

Ce-Eu, Tb-Yb4fN-1 6s1

Lu

LnIII 4fN-1 (no exception)


Slide 210


55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73-2.2

-2.3

-2.4

-2.5

-2.6

-2.7

atomic number

Eored : Ln3+(aq) + 3 e- Ln(s)

La

Tb

Lu

• The more stable oxidation state of Ln is +3Oxidation states of 4f elements

Y (Z = 39)Sc (Z = 21, E o

red = -2.08 V )



Explanation:Upon ionization, all of the valence orbitals (4f, 5d, 6s)are stabilized, but to variable degrees.4f orbitals are stabilized most and 6s least.After removal of three electrons, the remaining are verytightly bound

Main reason: the fourth ionization energy is larger than the sum of the first three ones; this extra energy cannot, in most cases, be compensated by bond formation

Main reason: the fourth ionization energy is larger than the sum of the first three ones; this extra energy cannot, in most cases, be compensated by bond formation





• Ce, Pr, Nd and Tb may have +4 oxidation state E 0

red for Ln4+(aq) + e- Ln3+(aq) in acidic solutions: +1.72 V for Ce4+, stable in water +3.20 V for Pr4+, oxidizes water +3.10 V for Tb4+, oxidizes water

• Sm, Eu, and Yb have a relatively stable +2 state

E 0red for Ln3+(aq) + e- Ln2+(aq) in acidic solutions:

-0.35 V for Eu2+, stable in water

-1.15 V for Yb2+, reduces water

-1.56 V for Sm2+, reduces water

Oxidation states of 4f elements



Ln3+ + e- Ln2+ In waterIn thfCalculated

-0.83



LuII 4f145d1

YbII 4f14

GdII 4f75d1

EuII 4f7



Ionic radii: lanthanide contraction



Ionic radii: variation with coordination number CN

6 7 8 9 10 11 120.8

0.9

1.0

1.1

1.2

1.3

1.4

CaII

EuIII

YbIII

LaIII

CN

ri / Å



56 58 60 62 64 66 68 70 721.70

1.75

1.80

1.85

1.90

1.95

2.00

2.05

2.10

La

CePr NdPmSm

Eu

GdTb Dy HoEr Tm

Yb

Lu

atomic number

Oxidation states in the 4f metals

Atomic radii / Åfor CN = 12

+3

+2



1.3.3 Oxidation states of 5f elements An

commonothersolid state only



• The stability of AnIV decreases along the series Quite stable for Th, Pa, U, Np. Only found in solution with fluoride for Am, Cm, Bk The drop in E 0 (An4+/An3+) at Bk reflects the stability of [Rn]5f7 (BkIV).

• The trend in E 0 (An3+/An2+) parallels the one in E 0 (An4+/An3+). The stability of AnII increases across the series. Note that the discontinuity appears at Cm, reflecting the stability of [Rn]5f7 (CmIII).

• The greater range of oxidation numbers of An elements compared with Ln is due to the nature of 5f orbitals



I4

I3

I2

I1



Reduction potentials of 5f elements

E 0 / V8

6

4

2

0

-2

-4

-6

An3+ / An2+

An4+ / An3+

Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

[Rn]4f7



Influence of relativity on f-orbitals

=−

0

21 ( )

mm

vc

mass of a particle movingwith velocity v

For U(1s) : m = 1.35m0, leads to contraction of 1s

On the contrary d and f orbitals are expanded and destabilized.

5f orbitals are more destabilized than 4f; they are more weaklybound and more chemically active, henceforth the larger range of oxidation numbers (and, also, larger covalency of the bonds)

Effects are important for heavy elements



Ionic radii: actinide contraction

An3+

An4+

An5+


r / pm


1.4 Radioactivity of the actinides

All of the An isotopes are radioactive, mostly emitters.

Z El. A t1/2 (* -, EC) Z El. A t1/2

90 Th 232 1.401010 y 96 Cm 244 18.11 y

91 Pa 231 3.25104 y 97 Bk 247 1.38103 y

92 U 235 7.04108 y 98 Cf 249 351 y

238 4.47109 y 99 Es 252 472 d

93 Np 236 1.55105 y* 100 Fm 257 100.5 d

94 Pu 239 2.41104 y 101 Md 258 56 d

244 8.26107 y 102 No 259 1 h ( + EC) 95 Am 241 4.32102 y 103 Lr 262 3.6 h



Nuclear fission

23592U

10n

9136Kr

14236Ba

A large nucleus is split into two smaller (and more stable)ones by collision with a thermal neutron.The process releases several neutrons, which in turncollide with other nuclei, initiating “chain reaction”,provided a “critical mass” exists, i.e. a minimum amount ofthe fissile product.

thermal neutronca. 2 kJmol-1



The nucleus mass is smaller than the sum of the masses of itsconstituting particles (neutrons, protons), due to the nuclear forces.Henceforth the concept of “cohesion energy”, usually given pernucleon:

1 MeV =1.610-13 J

KrBa

fission

fusion



Nuclear power generation

Control rods

Fuel rods

Best natural isotope: 235UNatural abundance: 0.72 %,henceforth the need forenrichment.

Fuel: UO2 enriched to 2-3% 235U, under the form ofpellets stuffed into Zr tubes

Cooling fluid(H2O, D2O)

Steam

Control rods: boron nitride orgraphite (absorb neutrons)

The cooling fluid also acts asmoderator, slowing down theproduced neutrons (boric acidadded).



• Gaseous diffusion of UF6 through Al or Ni membranes (pore size 10-25 nm). Graham’s law:

3000 passes needed (large and expensive fluorine- resistant chemical plants) for 90% enrichment

Isotope separation

1

MWdiffv ∝

• Centrifugation of UF6 (238UF6 concentrates near the walls)

• Laser separation (now abandoned) Ionization energy of 235U slightly different from 238U Laser with wavelength tuned for ionizing 235U produces 235U+ which is collected on an electrode

2356

2386

( UF ) 3521 0043

( UF ) 349diff

diff

v.

v = = =



Fuel reprocessing and treatment

1st stage: extraction of U and Pu

238 1 239 239 0 -92 0 92 93 - 1 1/2

239 0 -93 - 1 1

399 /2

24

U + n U Np + e ( , t 24min)

Np + e (Pu , t 2 4days).

→ → =

→ =

238U produces 239Pu, which can also be used as fuel

TBP extractionin kerosene (PUREX)

HNO3 7 Mnitrates

Other fissionproducts + AnOther fissionproducts + An

[UO2(NO3)2(TBP)2][Pu(NO3)4(TBP)2

[UO2(NO3)2(TBP)2][Pu(NO3)4(TBP)2

Np



[UO2(NO3)2(TBP)2]

[Pu(NO3)4(TBP)2

FeII

PuIII(aq)[UO2(NO3)2(TBP)2]

UO3

UO2

H2

PUREX Plutonium-UraniumRefining by EXtraction

HNO2

PuIV(aq)

oxalic acid

300 oC

PuO2



2nd stage: separation of radioactive wastes

1000 kg irradiated fuel1000 kg irradiated fuel

957 kg U

10 kg Pu957 kg U

10 kg Pu

0.8 kg minoractinides

0.8 kg minoractinides

33 kg fissionproducts

33 kg fissionproducts

Np, Am, Cm Zr 3.6 kgCs 2.7 kgTc 0.8 kgSm 0.8 kgSe, Sn, I 0.3 kgRadioactive Xe, 3H2

Other non radioactive 24.8 kg

of which2 kgradioactive320 g

420 g 30 g



Other fissionproducts

Other fissionproducts DIAMEX

Am, Cm, LnAm, Cm, Ln

AmIII, CmIIIAmIII, CmIII

LnIII(aq)

Glass

SANEX

Selective ActinideEXtraction

Am Cm

N

N

N

N

NN



Some extraction molecules for An/Ln separation

tptz Cyanex 301 CMPO

N

N

N

N

NN

P

S

SH P

O O

N

exploiting the difference in hard/soft behavior



Some extraction molecules for selective separation

calix[4]arene-CMPO

4

CH2

OR

N

HO

PO

R = C3H7

H3COOCH3

OCH3

O OO

OO

calix-crown for 137Csseparation



Future developments

Grouped separation allowing separation of all An which are then inserted into a matrix and irradiated by high- velocity neutrons (breeder reactor) – if politically accepted.

Reprocessingplant in La Hague

Ionic liquids

N N

X-


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