colour and magnetism

Question 1

what is the conversion betwee KJmol^-1 and wavenumbers (cm^-1)

Answer 1

1KJmol^-1 = 84 cm^-1

Question 2

what are things to be aware of when measuring absorption in vis spectrum?

Answer 2

other d-d transitions, charge transfer band, colour due the ligand itself rather than the metal complex

Question 3

what governs the energy of a transition?

Answer 3

1. ligands
2. metal ion

Question 4

what determines the intensity of a transition?

Answer 4

1. l = +-1 (change of orbital)
2. should have no change in spin (can be any electron from the lower orbitals)
   -> spin forbidden
3. laport selection rule: if has inversion center, g->g or u->u transitions are not allowed

the more rules that the metal complex complies with the more intense the colour

Question 5

what are the 3 origins of colour?

Answer 5

1. d-d transitions
2. ligand to metal electron transfer
3. metal to ligand electron transfer

Question 6

why do some octahedral complexes still have colour even though they do not obey the laport selection rule?

Answer 6

1.vibronic coupling: the vibrational motion (vibration) and electronic motion (electronic states) are coupled or connected together. It describes the interaction between the electronic and vibrational energy levels of a molecule. this motion distorts the molecule (loss of degeneracy of orbitals) causing a relaxation of the laporte selection rule

2. spin-orbit coupling: interactions between orbitals and electron spin creates new non degenerate energy levels which changes the electrons energy
3. jahn-teller distortions
4. MO mixing with pi bonds results in not d-d transitions

Question 7

what are the 2 types of charge transfers?

Answer 7

1. ligand to metal (LMCT): transfer of electron from p (u parity) orbital of ligand to d (g parity) orbital of metal
   -> particularly useful for metal complexes without any d orbital electrons
2. metal to ligand (MLCT): transfer of electrons from d orbital of metal to pi star orbital of ligand (higher energy -> UV transitions)

Question 8

what are the 2 types of magnetism? which one is stronger?

Answer 8

diamagnetic: no unpaired electrons therefore no net magnetic moment

paramagnetic: unpaired electrons result in permanent magnetic moment (when in a magnetic field the atom/molecule experiences attraction)

*usually paramagnetism is stronger

Question 9

what is the spin only magnetic moment equation?

Answer 9

(n(n+2))^1/2 x μB

where n is the number of unpaired electrons

Question 10

what are the 2 contributions to a paramagnetic complex?

Answer 10

spin angular momentum and orbital angular momentum

Question 11

why would the real value deviate from the spin-only formula?

Answer 11

ignored spin-orbital coupling

Question 12

what is the effective magnetic moment equation?

Answer 12

μeff = 2.83 (molar magneitc susceptibility x temp in K)^1/2

Question 13

how would the gouy balance determine the magnetism of a material?

Answer 13

if it repels the magnetic field then the laser will point downwards thus is diamagnetic

if it is attracted to the magnetic field then the laser will point upwards thus is paramagnetic

upwards and downwards relative to no magnetic field

Question 14

which complex has more intense colour (tet or oct) and why?

Answer 14

tet because it always obeys the laporte selection rule as it is not centrosymmetric