Engineering Chemistry S Datta

TRANSITION METAL CHEMISTRY 305
spin ‘s’ is also reduced. So, the complexes formed with strong ligands have minimum
number of unpaired electrons, so the spin value ‘s’ gets lowered. These types of complexes
are known as low spin (L.S.) or spin paired complexes.
• The weak ligands i.e., ∆ 0
when lower, first force the electrons to occupy all the five
d-orbitals singly and then get paired. Thus weak ligands produce higher number of
unpaired electrons and so the higher value of ‘s’. These types of complexes produced by
weak ligands are known as high spin (H.S.) or spin free complexes.
Table 13.1: Distribution of d-electrons in t 2g
and e g
sets in strong octahedral ligand
field (n = number of unpaired electrons, S = resultant spin)
Distribution of d-electrons in
d z ion n S = n/2
t 2g
set
e g
set
d 1 ↑ _ _ – – 1 1/2
d 2 ↑ ↑ _ – – 2 2/2 = 1
d 3 ↑ ↑ ↑ – – 33/2
d 4 ↑ ↑ ↑ – – 2 1
d 5 ↑ ↓ ↑ ↓ ↑ – – 1 1/2
d 6 ↑ ↓ ↑ ↓ ↑ ↓ – – 0 0
d 7 ↑ ↓ ↑ ↓ ↑ ↓ ↑ _ 1 1/2
d 8 ↑ ↓ ↑ ↓ ↑ ↓ ↓ ↑ 2 1
d 9 ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑ 1 1/2
d 10 ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ 0 0
CFT and Magnetic Properties of the Complex Formed
One of the greatest achievements of CFT is: with the help of this theory prediction of the
magnetic properties of the complexes formed is possible. The complexes having no unpaired
electrons should not exhibit any magnetic property, so therefore are diamagnetic. The complexes
having one or more unpaired electrons should show magnetic properties, so they are paramagnetic
complexes. The magnetic moment µ is related to the unpaired electrons n by the relation
µ = nn ( + 2) . Bµ
Table 13.2: Distribution of d-electrons in t 2g
and e g
sets in weak octahedral ligand field
Distribution of d-electrons in
d x ion n S = n/2
t 2g
set
e g
set
3 3
d 1 ↑ _ _ – – 1 1 × 1 2 = 1 2
d 2 ↑ ↑ _ – – 2 1
d 3 ↑ ↑ ↑ – – /2
d 4 ↑ ↑ ↑ ↑ _ 4 2
d 5 ↑ ↑ ↑ ↑ ↑ 5 5/2
d 6 ↑ ↓ ↑ ↑ ↑ ↑ 4 2
d 7 ↑ ↓ ↑ ↓ ↑ ↑ ↑ 33/2
d 8 ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↑ 2 1
d 9 ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑ 1 1/2
d 10 ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ 0 0