Lanthanides Actinides 1 st Row Transition M 2 nd Row Transition M 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 4f z 3 4f z 3 4f xz 2 4f yz 2 4f y(3x 2 -y 2 ) 4f x(x 2 -3y 2 ) 4f xyz 4f z(x 2 -y 2 )4f xz 2 4f yz 24f y(3x 2 -y 2 ) 4f x(x 2 -3y 2 )4f xyz 4f z(x 2 -y 2 ) Cubic set 4f x 3, 4f y 3, 4f z 3 4f x 3, 4f y 3, 4f z 3 4f x(z 2 -y 2 ), 4f y(z 2 -x 2 ), 4f z(x 2 -y 2 ), 4f xyz4f x(z 2 -y 2 ), 4f y(z 2 -x 2 ), 4f z(x 2 -y 2 ), 4f xyz 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

Symbol Idealized Observed La 5d 1 6s 2 5d 1 6s 2 Tb 4f 8 5d 1 6s 2 4f9 6s2 Ce 4f 1 5d 1 6s 2 4f 1 5d 1 6s 2 Dy 4f 9 5d 1 6s 2 4f10 6s2 Pr 4f 2 5d 1 6s 2 4f3 6s2 Ho 4f 10 5d 1 6s 2 4f11 6s2 Nd 4f 3 5d 1 6s 2 4f4 6s2 Er 4f 11 5d 1 6s 2 4f12 6s2 Pm 4f 4 5d 1 6s 2 4f5 6s2 Tm 4f 12 5d 1 6s 2 4f13 6s2 Sm 4f 5 5d 1 6s 2 4f6 6s2 Yb 4f 13 5d 1 6s 2 4f14 6s2 Eu 4f 6 5d 1 6s 2 4f7 6s2 Lu 4f 14 5d 1 6s 2 4f145d16s2 Gd 4f 7 5d 1 6s 2 4f75d16s2 The diamagnetic ions are: La3+, Lu3+, Yb2+ and Ce4+. The rest are paramagnetic. Lanthanide Electron Configurations Ion Unpaired e-Color La3+ 0 Colorless Tb3+ 6 Pale Pink Ce3+ 1 Colorless Dy3+ 5 Yellow Pr3+ 2 Green Ho3+ 4 Pink; yellow Nd3+ 3 Reddish Er3+ 3 Reddish Pm3+ 4 Pink; yellow Tm3+ 2 Green Sm3+ 5 Yellow Yb3+ 1 Colorless Eu3+ 6 Pale Pink Lu3+ 0 Colorless Gd3+ 7 Colorless

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(NO 3 ) 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 Ground state electron configuration: [Xe] 4f 7 6s 2 Term Symbol: 8 S 7/2 how many unpaired e-? EuFOD :also called Eu(fod) 3. Eu(OCC(CH 3 ) 3 CHCOC 3 F 7 ) 3

NMR Paramagnetic Shift Reagents: Eu vs Pr Using Eu(fod) 3  Using Pr(fod) 3  With NO Shift rgt  Hmmm, not so pretty oooh! Lovely!! Huh? – signals shifted upfield with Pr

Gadoteric acid Effect of contrast agent on images: Defect of the blood–brain barrier after stroke shown in MRI. T 1 -weighted images, left image without, right image with contrast medium administration. 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.gadolinium MRI contrast agents are used as oral or intravenous administration.intravenous administration

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, MRI Contrast agents: most bind H 2 O

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. SmI 2 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)

the first metal site in the molecule is always occupied by a rare earth atom. rare earth superconductors YPd2B2C 23 K LuNi2B2C 16.6 K YNi2B2C 15.5 K TmNi2B2C 11 K ErNi2B2C 10.5 K (ferromagnetic) HoNi2B2C 7.5 K

Parent structure LaCuO 3 (related to perovskite, CaTiO 3 ) Rare earth doped material YBa 2 Cu 3 O 7 : “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.