Find the magnetic property of complex

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.