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					                f - Elements


Gd
                                                        Eu
     Gd




                            4fz3
          Master degree course, SCGC
               Jean-Claude Bünzli
                             2008

     Section of chemistry and chemical engineering
       Laboratory of lanthanide supramolecular
                       chemistry
            MSc: f-Elements, Prof. J.-C. Bünzli, 2008        1
                  Table of contents


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

Appendices




             MSc: f-Elements, Prof. J.-C. Bünzli, 2008   2
Pedagogical objective

                                          1 2                           3 4 5 6 7 8
• Overview of f-elements             1
                                                S                 P
  properties, with                   2
                                                             D
  reference to their uses            3
  in daily life and high             4               3d
  technology applications            5                       4d
                                     6               5d
                                     7                       6d
• Mainly focused on
  4f-elements                                                                  F
                                                                   4f
Pre-requisites                                                    5f
      Coordination chemistry
      Quantum chemistry

                 MSc: f-Elements, Prof. J.-C. Bünzli, 2008                         3
           Chapter 1             f-Atoms and Ions


                   Table of Contents

   1.1    Definitions and discovery
   1.2    Occurrence of 4f elements
   1.3    Basic properties
          1.3.1 Electronic configuration
          1.3.2 Oxidation states of 4f elements
          1.3.3 Oxidation states of 5f elements
   1.4    Radioactivity of 5f elements


Nuclear fuel                     Particle filter
rod assembly                     for Diesel exhaust
                                 gases
               MSc: f-Elements, Prof. J.-C. Bünzli, 2008   4
               Chapter 1          f-Atoms and Ions

          Chapter 1.            f-Atoms and Ions
1.1 Definitions and discovery
Lanthanides: 58-71          Ln
Actinides:   90-103         An
Parent elements La and      Ac often included in Ln and An
Rare 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)

                MSc: f-Elements, Prof. J.-C. Bünzli, 2008    5
                     Chapter 1          f-Atoms and Ions

1.1     The discovery of 4f-elements


                                                     lanthanides: Ce-Lu
                                                     lanthanoids: La-Lu


                                              4f                  rare earths




                                               5f                 actinides
      Yttrium was discovered in 1794 by Johan Gadolin, in Åbo (Turku)
                      MSc: f-Elements, Prof. J.-C. Bünzli, 2008                 6
                  Chapter 1          f-Atoms and Ions

Discovery of yttrium (1794)
    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.

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

                   MSc: f-Elements, Prof. J.-C. Bünzli, 2008       7
                   Chapter 1          f-Atoms and Ions

Chemical separation
of yttrium
                               Be2FeY2SiO10
                                           HNO3 / HCl

        Fe3+, Be2+, Y3+                                     SiO2

               K2CO3, pH = 4-5

                                  Be(OH)2,FeCO3

             Y3+             taken as Al

               NH3, pH = 7-8                                       Fe(OH)3
                                                    O2, H2O
           Y(OH)3
                                        Johan Gadolin, 1794

                    MSc: f-Elements, Prof. J.-C. Bünzli, 2008                8
                  Chapter 1          f-Atoms and Ions


Discovery of cerium (1804)

  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).



                   MSc: f-Elements, Prof. J.-C. Bünzli, 2008       9
                   Chapter 1          f-Atoms and Ions

Other rare earths (1839-1947)

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

  The main techniques were fractional precipitation and
  crystallisation, as well as flame spectroscopy (absorption and
  emission).
  These operations were tedious: for instance, 20 tons were
  needed to produce 82 mg of element 61 by ion-exchange
  separation techniques (61 = radioactive promethium), that is a
  fraction equal to 4x10-12 !)




                    MSc: f-Elements, Prof. J.-C. Bünzli, 2008      10
                  Chapter 1          f-Atoms and Ions

1.2   Occurrence of
      4f elements                                Abundance in cosmos
                                                 relative to silicon:
The elements are “rare”                                        Si = 106
but not rarer than many
others, such as Au, Pt,
Pd, Rh, for instance




                                                                     La-Lu




                   MSc: f-Elements, Prof. J.-C. Bünzli, 2008                 11
                     Chapter 1          f-Atoms and Ions

Natural abundance
     50         Ce                                                               50
                              Abundance in earth’s crust
     40                       expressed in ppm (g/ton)                           40

     30                  Nd                                                      30
                                           Odd/even effect
     20                                                                          20
               La                Sm Gd
     10                                            Dy       Er    Yb             10

      0             Pr                                                           0
                                     Eu       Tb       Ho Tm           Lu
          56    58       60      62 64 66 68                      70        72
                                 Atomic number
                      MSc: f-Elements, Prof. J.-C. Bünzli, 2008                       12
                    Chapter 1          f-Atoms and Ions

Main resources (4f elements)

   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%


                     MSc: f-Elements, Prof. J.-C. Bünzli, 2008            13
                      Chapter 1          f-Atoms and Ions

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 (Inner
                                                                   Mongolia)


                       MSc: f-Elements, Prof. J.-C. Bünzli, 2008                   14
                 Chapter 1          f-Atoms and Ions

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

                  MSc: f-Elements, Prof. J.-C. Bünzli, 2008   15
Chapter 1          f-Atoms and Ions




              CeO2




                          EOLYS®
                          Soot emission of Diesel
                          engines reduced by 99.9 %




 MSc: f-Elements, Prof. J.-C. Bünzli, 2008       16
                  Chapter 1          f-Atoms and Ions

• 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
                   MSc: f-Elements, Prof. J.-C. Bünzli, 2008   17
      Chapter 1          f-Atoms and Ions




fluorescent lamps




     Er amplifier
     for optical fibers                     rechargeable batteries
       MSc: f-Elements, Prof. J.-C. Bünzli, 2008                 18
           Chapter 1          f-Atoms and Ions




                                                        Re-inforced
pigments                                                cast Al pistons



                                                   MRI images


            MSc: f-Elements, Prof. J.-C. Bünzli, 2008                19
                 Chapter 1          f-Atoms and Ions

1.3   Basic properties
1.3.1 Electronic configuration
4f-orbitals
                                                        x(x2–3y2)


           y(3x2–y2)                      xyz                       z(x2–y2)




          xz2                 yz2                                   z3



                  MSc: f-Elements, Prof. J.-C. Bünzli, 2008                    20
                 Chapter 1          f-Atoms and Ions

4f-orbitals (in octahedral symmetry)

                                                          T2u
                                                                    A2u


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


                                                                    xyz
                                                          T1u
                                                                      z

                                                                y         x
    z3          y3                        x3
                  MSc: f-Elements, Prof. J.-C. Bünzli, 2008                   21
                 Chapter 1          f-Atoms and Ions

Lanthanides
• Sc, Y and La introduce the 3d, 4d and 5d transition
      series: 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
Actinides
• Similarly, the 5f orbitals are also “inner orbitals”

                  MSc: f-Elements, Prof. J.-C. Bünzli, 2008   22
Chapter 1          f-Atoms and Ions




                                        inner nature of
                                        4f (Nd3+) and
                                        5f (U3+) orbitals




 MSc: f-Elements, Prof. J.-C. Bünzli, 2008                  23
                      Chapter 1          f-Atoms and Ions

1.3.2    Oxidation states
         of 4f elements

Ln0     4fN-1 5d1 6s2
        La, Ce, Gd, Lu
        4fN 6s2
        Pr-Eu,Tb-Yb

LnII    4fN-1 5d1
        La, Gd
        4fN
        Ce-Eu, Tb-Yb
        4fN-1 6s1
        Lu
LnIII 4fN-1 (no exception)
          Slide 210    MSc: f-Elements, Prof. J.-C. Bünzli, 2008   24
                  Chapter 1          f-Atoms and Ions

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



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


                                                Tb


           Y (Z = 39)
                                                               Lu
           Sc (Z = 21, E ored = -2.08 V )



                   MSc: f-Elements, Prof. J.-C. Bünzli, 2008        25
               Chapter 1          f-Atoms and Ions

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


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 very
tightly bound




                MSc: f-Elements, Prof. J.-C. Bünzli, 2008   26
Chapter 1          f-Atoms and Ions




 MSc: f-Elements, Prof. J.-C. Bünzli, 2008   27
                 Chapter 1          f-Atoms and Ions

Oxidation states of 4f elements

• Ce, Pr, Nd and Tb may have +4 oxidation state
  E 0red for Ln4+(aq) + e- D 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- D 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

                  MSc: f-Elements, Prof. J.-C. Bünzli, 2008   28
             Chapter 1          f-Atoms and Ions

Ln3+ + e- D Ln2+                                           In water
                                                           In thf
                                                           Calculated
                                                          -0.83




              MSc: f-Elements, Prof. J.-C. Bünzli, 2008                 29
 Chapter 1          f-Atoms and Ions




                                YbII 4f14
EuII 4f7




 GdII    4f75d1                    LuII 4f145d1




  MSc: f-Elements, Prof. J.-C. Bünzli, 2008       30
                 Chapter 1          f-Atoms and Ions

Ionic radii: lanthanide contraction




                  MSc: f-Elements, Prof. J.-C. Bünzli, 2008   31
                Chapter 1            f-Atoms and Ions

Ionic radii: variation with coordination number CN
                                                                         III
   1.4 r / Å                                                        La
        i
                                   II
                               Ca
   1.3                                                              Eu
                                                                         III



   1.2
                                                                          III
   1.1                                                              Yb

   1.0

   0.9
                                                                          CN
   0.8
         6     7           8            9       10             11         12
                   MSc: f-Elements, Prof. J.-C. Bünzli, 2008                    32
                Chapter 1          f-Atoms and Ions

Oxidation states in the 4f metals

                                                 Atomic radii / Å
                                                 for CN = 12
                 +2




         +3



                 MSc: f-Elements, Prof. J.-C. Bünzli, 2008          33
                Chapter 1          f-Atoms and Ions

1.3.3   Oxidation states of 5f elements An


                                                       common
                                                       other
                                                       solid state only




                 MSc: f-Elements, Prof. J.-C. Bünzli, 2008                34
                Chapter 1          f-Atoms and Ions

• 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

                 MSc: f-Elements, Prof. J.-C. Bünzli, 2008   35
Chapter 1          f-Atoms and Ions




                                             I4


                                             I3



                                             I2

                                             I1




 MSc: f-Elements, Prof. J.-C. Bünzli, 2008        36
                     Chapter 1          f-Atoms and Ions

Reduction potentials of 5f elements

  8        E0 / V
                                                   [Rn]4f7
  6
  4                   An4+ / An3+

  2                                                           An3+ / An2+

  0
 -2
 -4
 -6
      Th    Pa   U   Np   Pu Am Cm Bk                 Cf      Es   Fm Md No Lr


                      MSc: f-Elements, Prof. J.-C. Bünzli, 2008              37
                  Chapter 1           f-Atoms and Ions

Influence of relativity on f-orbitals

                             mass of a particle moving
                             with velocity v



Effects are important for heavy elements

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 weakly
bound and more chemically active, henceforth the larger range of
oxidation numbers (and, also, larger covalency of the bonds)




                    MSc: f-Elements, Prof. J.-C. Bünzli, 2008      38
                    Chapter 1          f-Atoms and Ions

Ionic radii: actinide contraction

           r / pm

                                                           An3+



                                                           An4+



                                                           An5+




                     MSc: f-Elements, Prof. J.-C. Bünzli, 2008    39
                    Chapter 1          f-Atoms and Ions

1.4   Radioactivity of the actinides
All of the An isotopes are radioactive, mostly a emitters.

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

 90   Th    232   1.401010 y              96       Cm      244   18.11 y
 91   Pa    231   3.25104 y               97       Bk      247   1.38103 y
 92   U     235   7.04108 y               98       Cf      249   351 y
            238   4.47109 y               99       Es      252   472 d
 93   Np    236   1.55105 y*              100      Fm      257   100.5 d
 94   Pu    239   2.41104 y               101      Md      258   56 d
            244   8.26107 y               102      No      259   1 h (a + EC)
 95   Am    241   4.32102 y               103      Lr      262   3.6 h

                     MSc: f-Elements, Prof. J.-C. Bünzli, 2008                   40
                  Chapter 1          f-Atoms and Ions

Nuclear fission




thermal neutron
ca. 2 kJmol-1


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 turn
collide with other nuclei, initiating “chain reaction”,
provided a “critical mass” exists, i.e. a minimum amount of
the fissile product.
                   MSc: f-Elements, Prof. J.-C. Bünzli, 2008   41
                    Chapter 1          f-Atoms and Ions

The nucleus mass is smaller than the sum of the masses of its
constituting particles (neutrons, protons), due to the nuclear forces.
Henceforth the concept of “cohesion energy”, usually given per
nucleon:
                                      Kr
1 MeV =                                         Ba
1.6´10-13 J

    fission

    fusion




                     MSc: f-Elements, Prof. J.-C. Bünzli, 2008       42
                   Chapter 1          f-Atoms and Ions

Nuclear power generation
   Control rods                         Best natural isotope: 235U
                   Steam                Natural abundance: 0.72 %,
                                        henceforth the need for
                                        enrichment.
                                        Fuel: UO2 enriched to 2-3%
                                        235U, under the form of
               Fuel rods
                                        pellets stuffed into Zr tubes
                                        Control rods: boron nitride or
                                        graphite (absorb neutrons)
                                        The cooling fluid also acts as
                                        moderator, slowing down the
   Cooling fluid                        produced neutrons (boric acid
   (H2O, D2O)                           added).
                    MSc: f-Elements, Prof. J.-C. Bünzli, 2008       43
                Chapter 1          f-Atoms and Ions

Isotope separation
• 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

• 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

                 MSc: f-Elements, Prof. J.-C. Bünzli, 2008   44
                 Chapter 1          f-Atoms and Ions

Fuel reprocessing and treatment
238U produces 239Pu, which can also be used as fuel




1st stage: extraction of U and Pu
                                                   Other fission
                                                   products + An
      HNO3 7 M
                  nitrates                        Np

                                                   [UO2(NO3)2(TBP)2]
                                                   [Pu(NO3)4(TBP)2
                           TBP extraction
                           in kerosene (PUREX)
                  MSc: f-Elements, Prof. J.-C. Bünzli, 2008            45
              Chapter 1          f-Atoms and Ions

              [UO2(NO3)2(TBP)2]
               [Pu(NO3)4(TBP)2                             Plutonium-Uranium
PUREX
                                                           Refining by EXtraction
                            FeII


[UO2(NO3)2(TBP)2]                                   PuIII(aq)
                                                                HNO2

                                                    PuIV(aq)
        UO3                                                oxalic acid
   H2                                                            300 oC

        UO2                                                PuO2

               MSc: f-Elements, Prof. J.-C. Bünzli, 2008                      46
                    Chapter 1          f-Atoms and Ions

2nd stage: separation of radioactive wastes

                 1000 kg irradiated fuel



  0.8 kg minor              957 kg U                             33 kg fission
    actinides                10 kg Pu                              products
 Np, Am, Cm                                             Zr     3.6 kg
420 g        30 g             of which                  Cs     2.7 kg
                              2 kg                      Tc     0.8 kg
     320 g                    radioactive               Sm     0.8 kg
                                                        Se, Sn, I 0.3 kg
                                                        Radioactive Xe, 3H2
                                                        Other non radioactive
                                                               24.8 kg
                     MSc: f-Elements, Prof. J.-C. Bünzli, 2008                   47
                  Chapter 1             f-Atoms and Ions


                            Other fission
                              products                            DIAMEX



Glass                        Am, Cm, Ln

                  LnIII(aq)                    SANEX

                            AmIII, CmIII
 Selective Actinide
 EXtraction
                       Am                       Cm


                      MSc: f-Elements, Prof. J.-C. Bünzli, 2008            48
                    Chapter 1          f-Atoms and Ions

Some extraction molecules for An/Ln separation
exploiting the difference in hard/soft behavior


             tptz                     Cyanex 301                 CMPO




                     MSc: f-Elements, Prof. J.-C. Bünzli, 2008          49
                 Chapter 1          f-Atoms and Ions

Some extraction molecules for selective separation

                      calix[4]arene-CMPO




                                                                      OCH3
                                                              O               O
                                                                  O       O
                                                                      O
                                                                  OCH3
                                                                    H3CO




                                                   calix-crown for                137Cs

                                                   separation

                  MSc: f-Elements, Prof. J.-C. Bünzli, 2008                               50
                   Chapter 1          f-Atoms and Ions

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.

Ionic liquids



                Reprocessing
                plant in La Hague

                    MSc: f-Elements, Prof. J.-C. Bünzli, 2008   51

				
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