Coordination CompoundHard

Question

Which one of the following is an outer orbital complex and exhibits paramagnetic behaviour ?

Options

A.[ Ni(NH3)6 ]2+
B.[ Zn(NH3)6 ]2+
C.[ Cr(NH3)6 ]3+
D.[ Co(NH3)6 ]3+

Solution

Outer orbital complex utilises nd orbitals for bonding and exhibit paramagnetic behaviour, only if there present unpaired electrons.
(a) In [ Ni ( NH3)6]2+:
Ni2+ = [Ar] 3d8 4s0 
      
       [Ni(NH3)6]2+ =

So, this is an outer orbital complex having paramagnetic character.
       (b) In [ Zn ( NH3)6]2+ :
       Zn2+ = [ Ar ] 3d10
      
      [Zn(NH3)6]2+ =

Thus, it is also an outer orbital complex but it is dimagnetic as all the electrons are paired.
      (C) In [ Cr(NH3)6]3+ :
      Cr3+ = [Ar]3d3

[Cr( NH3)63+ =
  
Because of the involvement of (n1)d, i.e., 3d orbital in hybridisation, it is an inner orbital complex. Its nature is paramagnetic because of the presence of three unpaired electrons.
(d) In [ Co( NH3)6]3+ :
Co3+ = [ Ar ] 3d6
   
[Co(NH3)6]3+ =

As all the electrons are paired it is dimagnetic complex.

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