f block Flashcards
why are f block elements not really effected by crystal field theory?
orbitals tend to be core like and unavailable therefore are largely unaffected by the ligands attached to them
what is the bonding like between f block elements and ligands?
no overlap of orbitals between f and the ligands thus the f orbitals do not participate in bonding
what determines the structure of the metal complexes in lanthanides? what is the bonding between lanthanides and ligands?
sterics of the ligands
-> not effected as much by orientation of orbitals due to its core like (spherical) structure
electrostatics (negative electrons from the ligands and the positive metal ion)
can you measure the NMR of lanthanides and why?
difficult because most of them are paramagnetic
it is difficult to record the NMR of paramagnetic species due to:
Broadened NMR signals: In paramagnetic species, unpaired electrons create additional magnetic fields that can influence the local electronic environment of nearby atomic nuclei. This results in a broadening of the NMR signals, making it difficult to obtain well-resolved peaks. The broadening effect can obscure the fine details of the NMR spectrum and make it harder to interpret.
Relaxation effects: Paramagnetic species often exhibit faster nuclear relaxation times compared to diamagnetic species (substances without unpaired electrons). The presence of unpaired electrons enhances the relaxation processes, reducing the signal intensity and making it more challenging to detect and analyze the NMR signals.
Line shape distortions: The broadening and relaxation effects mentioned above can result in distorted line shapes in the NMR spectrum. The lines may become asymmetric, overlapping, or featureless, making it difficult to extract meaningful information about the molecule’s structure and dynamics.
Paramagnetic interference: The paramagnetic properties of the species being studied can interfere with the magnetic field homogeneity required for precise NMR measurements. The presence of paramagnetic species in the vicinity can lead to field distortions and cause artifacts in the NMR spectrum.
what are the 3 elements that like the 2+ oxidation state for lanthanides?
Eu, Sm, Yb
due to almost half filled, half filled and full orbital
which element prefers to be in the 4+ oxidation state in the lanthanides and why?
Ce due to achieving Xenon configuration which is highly stable
which oxidation state is most common with lanthanides and why?
3+ oxidation state due to having the most thermodynamic stability
the 3+ lanthanide ions have a relatively high charge density and can readily form stable complexes due to their favorable size and electronic properties.
what are the 2 anomalies in the metallic radii of lanthanides and why?
Eu and Yb both prefer a 2+ oxidation state which is larger than the 3+ oxidation state for the rest of the lanthanides (thus appear to have a larger metallic radii)
why do f-block elements have large coordination numbers?
- larger size means that they can accommodate more ligands
- ionic bonding is non directional (lack of need for orbital overlap) means that more likely to have more ligands around f block ion
what is the gadolinium break and what is the cause of this?
trend does not increase in stability due to the change in water coordination from 9->8 (logK decreases because there is a slight loss of entropic drive)
what are the significant differences between colouring/intensity of lanthanide and transition metal complexes?
4f does not react strongly with ligands thus crystal field effects and vibronic coupling is insignificant (no covalency for lanthanides)
less intense colouring for lanthanides (lower energy transitions and ionic point charge bonding means that they are normally laporte forbidden)
are f-f absorption bands sharper or broader than d-d? why?
are they dependent on its environment?
sharper because for d-d there is vibronic coupling which involves changing electronic and vibrational states leading to a wider range of absorption values
for f block it is independent of gas/solution/solid but not for d block because the solution can bind to the metal as well
which electrons are lost first in d complexes?
s electrons are lost before the d electrons
what are the additional differences between the 4f and 5f orbitals?
5f has an additional radial node
5f also has a greater extension thus have a greater covalent contribution to bonding
what are uses of uranium and why?
nuclear power, nuclear weapons
submarines (no refuelling requires)
ice breaking vessels
