Question: Which of the following complexes are
diamagnetic in nature?
a)
K3[Fe(CN)6]
b)
[Co(NH3)6]Cl3
c)
Na3[Co(Oxalate)3]
d)
[NiCl4]-2
Solution:
Magnetic property of a complex
depends upon the number of unpaired electrons present in the orbital of its
metal.
·
If
unpaired electron present in the complex then it is paramagnetic in nature.
·
If
there is no unpaired electron then the complex is diamagnetic in nature.
Now let us
start with each option and find out its magnetic property.
a)
K3[Fe(CN)6]
It is a anionic
complex because it carries negative charge on complex ion.
(Complex Ion)
In this
complex ion Fe is central metal and CN is ligand. To calculate number of
electron in Fe we have to know its oxidation state. Since the whole complex ion
show (-3) charge so the oxidation number of Fe will be:
Charge
number of [Fe(CN)6]3- = charge on Fe + charge on CN
-3 = x + 6 (-1) (CN has -1 charge)
X = +3
Now let us find
out number of electrons in the central atom Fe3+
Fe (26) = 2,
8, 14, 2
= 3s2, 3p6, 3d6,
4s2
Fe3+
= 3s2, 3p6, 3d5, 4s0
In the
presence of CN as ligand, the electrons present in 3d get shifted and undergoes
d2sp3 hybridisation.
But this makes one electron unpaired in 3d.
Due to
presence of this unpaired electron, K3[Fe(CN)6] shows
paramagnetic.
b)
[Co(NH3)6]Cl3
It is a
cationic complex because it carries positive charge on complex ion.
In this
complex ion Co is central metal and NH3 is ligand. Now let us know
the oxidation number of Co:
Charge
number of [Co(NH3)6]3+ = charge on Co + charge on NH3
+3 =
x + 6 (0) (NH3 is neutral)
X = +3
Now let us
find out number of electrons in the central atom Co3+
Co (27) = 3s2,
3p6, 3d7, 4s2
Co3+
= 3s2, 3p6, 3d6, 4s0
In the
presence of NH3 as ligand, the electrons present in 3d get shifted
and undergoes d2sp3 hybridisation. But this makes all electron paired in 3d.
Hence, [Co(NH3)6]Cl3
shows diamagnetic.
c)
Na3[Co(Oxalate)3]
It is an
anionic complex because it carries negative charge on complex ion.
In this
complex ion Co is central metal and oxalate is ligand. Now let us know the
oxidation number of Co:
Charge
number of [Co(oxalate)3]3- = charge on Co + charge on NH3
-3 = x + 6 (-1) (oxalate, C2O4, has
-1 charge)
X = +3
Now let us
find out number of electrons in the central atom Co3+
Co (27) = 3s2,
3p6, 3d7, 4s2
Co3+
= 3s2, 3p6, 3d6, 4s0
In the
presence of oxalate (C2O4) as ligand, the electrons
present in 3d get shifted and undergoes d2sp3
hybridisation. But this makes all
electron paired in 3d.
Hence, Na3[Co(oxalate)3]
shows diamagnetic.
d)
[NiCl4]-2
In this
complex ion Ni is central metal and Cl is ligand. Now let us know the oxidation
number of Ni:
Charge
number of [NiCl4]2- = charge on Ni + charge on H2O
-2 = x + 4 (-1) (Cl has -1
oxidation number)
X = +2
Now let us
find out number of electrons in the central atom Ni2+
Ni (28) = 3s2,
3p6, 3d8, 4s2
Ni2+
= 3s2, 3p6, 3d8, 4s0
In the
presence of Cl as ligand, one 4s and three 4p orbitals undergo sp3
hybridisation. Each Cl- ion donates a
pair of electrons. But this makes two electrons unpaired in 3d.
Hence, [NiCl4]
2- shows paramagnetic nature.
Thus,
options b and c are diamagnetic in nature.