How do
the
electrons
fill for
Rare
Earths?
The shape of the seven 4f orbitals (cubic set). From left to right: (top row)
4fy3, 4fx3, 4fz3, (middle row) 4fx(z2-y2), 4fy(z2-x2), 4fz(x2-y2), and (bottom
row) 4fxyz. For each, the copper zones are where the wave functions have
negative values and the gold zones denote positive values.
Rare Earth Concepts
1. Electron configurations— Lanthanides fill 4f orbitals; Actinides fill 5f orbitals
F-orbitals are 7-fold degenerate. **More than one way to depict them!!
General set
4fz3 4fxz2 4fyz2 4fy(3x2-y2) 4fx(x2-3y2) 4fxyz 4fz(x2-y2)
Cubic set
4fx3, 4fy3, 4fz3 4fx(z2-y2), 4fy(z2-x2), 4fz(x2-y2), 4fxyz
Lanthanides: 4f orbitals are buried, feel increasing nuclear charge Z
 Causes Lanthanide contraction
 no covalent bonding with 4f, ionic and hard ions
 mainly 3+ ions
Actinides: 5f orbitals are somewhat shielded
 increasing amount of covalency
 more oxidation states available, because energies of the
5f, 6d, 7s and 7p are similar and can participate in covalent bonds
 oxidation states from 2+ to 7+ (U:3+ to 6+, Pu 3+ to 7+, Am:2+ to 6+ )
“Rare Earths” are not rare!! Difficult to separate: nearly same size
Lanthanide Electron Configurations
Symbol
Idealized
Observed
Symbol
Idealized
Observed
La
Ce
Pr
Nd
Pm
Sm
Eu
Gd
5d16s2
4f15d16s2
4f25d16s2
4f35d16s2
4f45d16s2
4f55d16s2
4f65d16s2
4f75d16s2
5d16s2
4f15d16s2
4f3 6s2
4f4 6s2
4f5 6s2
4f6 6s2
4f7 6s2
4f75d16s2
Tb
Dy
Ho
Er
Tm
Yb
Lu
4f85d16s2
4f95d16s2
4f105d16s2
4f115d16s2
4f125d16s2
4f135d16s2
4f145d16s2
4f9
6s2
4f10 6s2
4f11 6s2
4f12 6s2
4f13 6s2
4f14 6s2
4f145d16s2
Ion
La3+
Ce3+
Pr3+
Nd3+
Pm3+
Sm3+
Eu3+
Gd3+
Unpaired e0
1
2
3
4
5
6
7
Color
Colorless
Colorless
Green
Reddish
Pink; yellow
Yellow
Pale Pink
Colorless
Ion
Tb3+
Dy3+
Ho3+
Er3+
Tm3+
Yb3+
Lu3+
Unpaired eColor
6
Pale Pink
5
Yellow
4
Pink; yellow
3
Reddish
2
Green
1
Colorless
0
Colorless
The diamagnetic ions are: La3+, Lu3+, Yb2+ and Ce4+. The rest are paramagnetic.
Lanthanides share many similar characteristics, key ones include the following:
Similarity in physical properties throughout the series
Adoption mainly of the +3 oxidation state, and +2 or +4 for some
A preference for more electronegative elements (such as O or F) binding
Very small crystal-field effects
Little dependence on ligands
Ionic complexes undergo rapid ligand-exchange
High coordination numbers (usually 8-9), tends to decrease C. N. across the series
Like a supersized Na+ ???
[Ln(NO3)6]3-
Lanthanides have strong fluorescence
Visible emission (from left to right) of complexes with
Tb(III), Eu(III), Dy(III) and Sm(III).
NMR Paramagnetic Shift Reagents
EuFOD :also called Eu(fod)3.
Eu(OCC(CH3)3CHCOC3F7)3
Ground state electron configuration: [Xe] 4f7 6s2
Term Symbol: 8S7/2 how many unpaired e-?
NMR Paramagnetic Shift Reagents: Eu vs Pr
Using
Eu(fod)3
oooh! Lovely!!
With NO
Shift rgt 
Hmmm, not so pretty
Using
Pr(fod)3
Huh? – signals
shifted upfield
with Pr
MRI Contrast agents: same principles, applied to medicine
•
•
•
•
•
MRI Contrast Agents: observes differential magnetization of
protons in different types of molecules that predominate in
different tissues. The different magnetization signal
intensities produce the contrast between tissues.
The nuclear magnetization is produced by the pulse sequence
applied, by the density of nuclear spins sub-fractions (water vs
fat protons) and by the spin-lattice relaxation time T1 and
phase relaxation time T2 in each nuclear spin sub-fraction. T1
and T2 depend on tissues type.
MRI Contrast Agents interact with one sub-fraction type
(usually that easily exchangeable protons, like water) to
increase the T1 spin-lattice relaxation times.
The most commonly used compounds for contrast
enhancement are gadolinium-based.
MRI contrast agents are used as oral or intravenous
administration.
Gadoteric acid
Effect of contrast agent on images: Defect of
the blood–brain barrier after stroke shown in
MRI. T1-weighted images, left image without,
right image with contrast medium
administration.
MRI Contrast agents: most bind H2O
MRI scan of mouse injected with Gd-TREN-bis-(1-Me)3,2-HOPO-TAM-PEG.
Thompson, M. K.; Misselwitz, B.; Tso, L. S.; Doble, D. M. J.;
Schmitt-Willich, H.; Raymond, K. N. J. Med. Chem. 2005,
48, 3874-3877.
New Contrast Agents: multi-armed octopi model
Ken Raymond labs, Berkely
Lanthanides in Organic Synthesis
• Lanthanide metals are useful for reduction of functional groups and for carbon-carbon bond
forming reactions
• Eu, Sm, and Yb can form relatively stable 2+ states. Eu exists in water.
• SmI2 is the most widely employed Ln(II) and is used for one electron reductive reactions
• Trivalent lanthanides are hard Lewis acids with high oxophilicity and as such are employed in
several highly selective reactions (Luche reduction, hetero-Diels-Alder)
rare earth superconductors
the first metal site in the molecule is always occupied by a rare earth atom.
YPd2B2C
LuNi2B2C
YNi2B2C
TmNi2B2C
ErNi2B2C
HoNi2B2C
23 K
16.6 K
15.5 K
11 K
10.5 K
7.5 K
(ferromagnetic)
Parent structure
LaCuO3
(related to perovskite, CaTiO3)
Rare earth doped material
YBa2Cu3O7 :
“1-2-3 type” superconductor
The Meissner effect
The Meissner effect in superconductors like this black ceramic yttrium based superconductor acts to exclude magnetic
fields from the material. Since the electrical resistance is zero, supercurrents are generated in the material to exclude
the magnetic fields from a magnet brought near it. The currents which cancel the external field produce magnetic poles
which mirror the poles of the permanent magnet, repelling them to provide the lift to levitate the magnet.
The levitation process is quite remarkable. Since the levitating currents in the superconductor meet no resistance, they
can adjust almost instantly to maintain the levitation. The suspended magnet can be moved, put into oscillation, or even
spun rapidly and the levitation currents will adjust to keep it in suspension.