Applications of 4f chemistry

Question 1

Most stable oxidation state of Ce

Answer 1

Ce3+

Question 2

Formula of ceria

Answer 2

CeO2

Question 3

CeO2 as a catalyst in self-cleaning ovens.

Answer 3

2CeO2 + R2CH2 ---> Ce2O3 + H2O + "R2C"
4CeO2 + "R2C" ---> 2Ce2O3 + CO2 + "R2"
3Ce2O3 + 11/2O2 ---> 6CeO2
OVERALL:
R2CH2 + 11/2O2 ---> "R2" + H2O + CO2

Question 4

CeO2 in catalytic converters

Answer 4

2CeO2 + CO —> 2Ce2O3 + CO2

Ce2O3 + NO —> 2CeO2 + 1/2N2

Question 5

Application of Eu3+

Answer 5

Produces very narrow, single wavelength emissions which can be used to spot counterfeit banknotes

Question 6

Application of Nd

Answer 6

‘Single wavelength emissions’ can be used to create lasers that emit narrow wavelength, coherent light
Nd:YAG (neodymium:yttrium aluminium garnet) is the most well-known class - consist of an ‘yttrium aluminium garnet doped with 1% Nd3+ ions (Ndx:Y3-xAl5O12)
Pumping at 800nm occupies high energy levels that decay to a metastable state that then emits infrared (1064 nm)
(can be frequency doubled with certain compounds to give green laser pointers - 532 nm)

Question 7

Lanthanide shift reagents

Answer 7

= added to diamagnetic samples to induce changes in chemical shifts via ‘through-space’ interactions
This leads to separation of closely-clustered peaks

Question 8

Lanthanides used as lanthanide shift reagents

Answer 8

Eu3+ or Pr3+ with beta-diketonate ligands (for solubility)

These lanthanides are chosen for their short relaxation times which decreases broadening

Question 9

Lanthanides as MRI imaging agents

Answer 9

Gd3+ complexes are widely used as ‘contrast agents’ to enhance the contrast in MRI images
Gd3+ complexes shorter the relaxation times of coordinated H2O molecules which leads to brighter images
Common ligand = DTPA (water stable, blood soluble)

Question 10

Paramagnetic compounds

Answer 10

Align their spins with an applied field, but do not retain magnetism when the field is removed

Question 11

Ferromagnetic compounds

Answer 11

Align their spins with an applied field, and retain their magnetic moment when the field is removed up until their Curie temperature

Question 12

Curie temperature

Answer 12

The temperature at which the spins in a ferromagnetic compound re-randomise and lose their magnetism

Question 13

Magnetic field strength depends on…

Answer 13

…the magnetic moment of the ions in the material

Question 14

Why do lanthanides have strong magnetic fields?

Answer 14

They have large numbers of unpaired electrons and large spin-orbit coupling.

Question 15

Example of a magnetic lanthanide.

Answer 15

Nd alloys (e.g. Nd2Fe14B), which has widespread uses and a Curie temperature of 600K!