Lecture 4

Question 1

General features of lanthanide coordination chemistry

Answer 1

• Ln ions behave as hard Lewis acids with high affinity for Lewis bases
• bonding is largely electrostatic with geometries determined by shape and size
• large cations formed therefore have high coordination numbers
• across group there are higher charge densities and stronger ionic bonds

Question 2

Stability constants

Answer 2

• higher for hard ions than softer ones
• values for Lu 3+ are higher than for La 3+
• chelating ions have highest values

Question 3

Hydrated lanthanide structures

Answer 3

• tricapped trigonal prismatic
• 8-9 coordinate
• Early Ln are 9 coordinate and late ones are 8 coordinate
• gadolinium break

Question 4

What is the gadolinium break?

Answer 4

• reason why after Gd K(h2o) is reduced

- reduction in entropy change as only 5 water molecules are liberated

Question 5

Complexes with water

Answer 5

• acidic
• h2o easily ionised due to highly polar Ln3+
• H20 exchange rapid
• acidity increases along group

Question 6

Chelate complexes

Answer 6

• high K

- kinetically stable due to polydentate nature

Question 7

What range of coordination number has been observed?

Answer 7

3-12 depending on steric bulk

- the lower the L-M-L angle the more ligands can fit around the metal

Question 8

Ln Shift reagents

Answer 8

- added to diamagnetic complexes
to induce a chemical shift change
- through space interactions
- most systems involve Eu 3+ and Pr 3+ (with short relaxation times) coordinated to acac-
- used to analyse overlapping peaks

Question 9

Chiral shift reagents

Answer 9

• still in use
• each enantiomer interacts differently with an NMR shift reagent
• ee can then be calculated

Question 10

Lanthanides in MRI

Answer 10

• used as a proton relaxing agent
• enhances signals by reducing relaxation times
• can become concentrated in tumors and give signal enhancement to the water in the surrounding area

Question 11

General features of Actinide Coordination Chemistry

Answer 11

• more covelant
• some ligand orbital overlap
• due to 5f orbitals being more accessible
• later in the group there is more lanthanide like behaviour
• stronger bonds along the group

Question 12

Actinide Coordination numbers

Answer 12

• normally large
• 3-14 viewed
• determined by steric and size

Question 13

Aqueous actinide complexes and actinyl ions

Answer 13

• From U-Am actinyl ions form AnO 2+ and AnO2 2+
• Th and Pr resemble group 4/5 TM
• late actinides act like lanthinides

Question 14

Actinyl Ion geometry

Answer 14

• linear units
• ligands are always in the equatorial plane
• give octahedral, pentagonal bipyramidal and hexagonal
  bipyramidal structures
• oxygen groups are trans due to 5f orbital participation

Question 15

Actinyl ions in the gas phase

Answer 15

• not always linear

- due to the relative energies of the 6s and 5f orbitals

Question 16

How are traps used with aqueous uranium?

Answer 16

• paceman ligands bind to the the UO2 group in the transition metal
• additional metals interact with the U=O weakening them and allowing bonds to be activated