IC Study Set 4

Are these transitions localized or delocalized?

• These are localized transitions (hence the term charge transfer).

• These are delocalized transitions (hence the term resonance transfer).

• These are neither localized nor delocalized transitions.

• These are partially localized transitions.

What characteristic of the metal atom will give a strong CT band?

• A metal ion in a high oxidation state.

• A metal ion with a large atomic radius.

• A metal ion in a low oxidation state.

• A metal ion with a filled d-subshell.

What characteristic of the complex makes a MLCT likely to occur?

• If a complex has ligands with low lying π* orbitals, especially with aromatics, a MLCT is likely to occur.

• If a complex has ligands with high energy σ orbitals, a MLCT is likely to occur.

• If a complex contains only alkali metal ligands, a MLCT is likely to occur.

• If a complex has ligands with no available π* orbitals, a MLCT is likely to occur.

Describe the relative proximity of ligand and metal orbitals in a MLCT.

• The metal d orbitals are low in energy, lying very close to the empty ligand orbitals.

• The ligand orbitals are much lower in energy than the metal d orbitals, making transfer impossible.

• The metal d orbitals are much higher in energy than the ligand orbitals, preventing overlap.

• The metal and ligand orbitals are at the same energy level, resulting in no charge transfer.

What are the most common ligands to result in MLCT?

• Diimines are the most common ligands to result in a MLCT.

• Phosphines are the most common ligands to result in a MLCT.

• Carboxylates are the most common ligands to result in a MLCT.

• Halides are the most common ligands to result in a MLCT.

What is Emax?

• It is a measure of the absorption strength for ligand field transitions.

• It is the maximum wavelength of light absorbed by a compound.

• It is the energy difference between two electronic states.

• It is the rate constant for a chemical reaction.

What is the approximate Emax for octahedral complexes? Tetrahedral? Square planar?

• For both octahedral (and almost octahedral) and square planar complexes, it is about 100 dm³/mol*cm. Tetrahedral complexes have Emax of about 250 dm³/mol*cm.

• For octahedral complexes, it is about 250 dm³/mol*cm; for tetrahedral, about 100 dm³/mol*cm; for square planar, about 300 dm³/mol*cm.

• For octahedral and tetrahedral complexes, it is about 300 dm³/mol*cm; for square planar, about 100 dm³/mol*cm.

• For octahedral complexes, it is about 1000 dm³/mol*cm; for tetrahedral, about 500 dm³/mol*cm; for square planar, about 250 dm³/mol*cm.

What is a transition dipole moment?

• The transition dipole moment is the impulse of a transition on an electromagnetic field, which is a measure of the strength of transition.

• It is the energy difference between two quantum states.

• It is the time taken for a molecule to transition between energy levels.

• It is the frequency of light absorbed during a transition.

What is the transition dipole moment for an allowed transition? Forbidden?

• The transition dipole moment for an allowed transition is nonzero, whereas forbidden transitions have a dipole moment of zero.

• Both allowed and forbidden transitions have nonzero dipole moments.

• Allowed transitions have zero dipole moment, forbidden transitions have nonzero dipole moment.

• Both allowed and forbidden transitions have zero dipole moments.

Describe spin allowed transitions in terms of singlet to triplet transition, and the value of ΔS.

• A singlet (s=0) cannot undergo a transition to a triplet (s=1), it is a forbidden transition.

• A singlet (s=0) can freely transition to a triplet (s=1), it is an allowed transition.

• A singlet (s=0) always transitions to a triplet (s=1) with ΔS = 0.

• A singlet (s=0) can transition to a triplet (s=1) only if ΔS = 2.