M.Sc I Chemistry

1. Magnetochemistry Part I
Lecture by Prof. G.M.Dongare
Dept. of Chemistry,
Shri Shivaji College Of Arts, Commerce and
Science, Akola (Maharashtra) India
Academic year 2021-22
Class B.Sc and M.Sc I

2. Magnetic Properties of lanthanides
• Magnetic moment of a J-state is expressed by:
J = L+S, L+S-1,……L-S
• For the calculation of g value, we use minimum value of J for
the configurations up to half-filled; i.e. J = L−S for f0-f7
configurations
• maximum value of J for configurations more than half-filled;
i.e. J = L+S for f8-f14 configurations
• For f0, f7, and f14, L = 0, hence μJ becomes μS

3. Magnetic Exchange (coupling of unpaired
electrons):
There are three types:
1.Anti-ferromagnetic interactions:
•This will occur if the spins of unpaired electrons from an antiparallel arrangement in a
magnetic field. (-J, coupling constant)
•Spins are aligned in an antiparallel arrangement.
•In this case the effective magnetic moment is expected to be lower than what spin-
only magnetism would predict. The spins cancel.

9. TN

11. Magnetic Exchange (coupling of unpaired
electrons):
2.Ferromagnetic interactions (less common):
•This occurs is the spins of the Unpaired electrons (upe) on neighbouring metal atoms
align in the same direction. (+J coupling)
• In this case, we expect μeff to be higher than spin only magnetism would predict.

12. Magnetic Exchange (coupling of unpaired
electrons):
3.Ferrimagnetic interactions (note the spelling with an “i” and not an “o”)
•Similar to anti-ferromagnetic interaction but with different metals
• In this case, different metals with different number of upe.

13. Spin Crossover (SCO)
• Spin Crossover (SCO), sometimes referred to as spin transition or spin
equilibrium behavior, is a phenomenon that occurs in some metal complexes
wherein the spin state of the complex changes due to external stimuli such as
a variation of temperature, pressure, light irradiation or an influence of a
magnetic field.
• With regard to a ligand field and ligand field theory, the change in spin state is
a transition from a low spin (LS) ground state electron configuration to a high
spin (HS) ground state electron configuration of the metal’s d atomic orbitals
(AOs), or vice versa. The magnitude of the ligand field splitting along with the
pairing energy of the complex determines whether it will have a LS or HS
electron configuration. A LS state occurs because the ligand field splitting (Δ) is
greater than the pairing energy of the complex (which is an unfavorable
process).
• Conversely, a HS state occurs with weaker ligand fields and smaller orbital
splitting. In this case the energy required to populate the higher levels is
substantially less than the pairing energy and the electrons fill the orbitals
according to Hund’s Rule by populating the higher energy orbitals before
pairing with electrons in the lower lying orbitals. An example of a metal ion
that can exist in either a LS or HS state is Fe3+ in an octahedral ligand field.
Depending on the ligands that are coordinated to this complex the Fe3+ can
attain a LS or a HS state

14. Spin Crossover (SCO)
Spin crossover refers to the transitions between high to low, or low to high, spin
states. This phenomenon is commonly observed with some first row transition
metal complexes with a d4 – d7 electron configuration in an octahedral ligand
geometry.

15. Spin Crossover (SCO)
Octahedral complexes with between 4 and 7 d electrons can be either high-spin or low-spin
depending on the size of Δ When the ligand field splitting has an intermediate value such
that the two states have similar energies, then the two states can coexist in measurable
amounts at equilibrium. Many "crossover" systems of this type have been studied,
particularly for iron complexes.
In the d6 case of Fe(phen)2(NCS)2, the crossover involves going from S=2 to S=0. At the higher
temperature the ground state is 5T2g while at low temperatures it changes to 1A1g. The
changeover is found at about 174K.