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  4. NiCl2 P(C2H5)2(C6H5) 2 exhibits temperature dependent magnetic behaviour (paramagnetic/diamagnetic) the coordination geometries of Ni2+ in the paramagnetic and diamagnetic states respectively, are

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Q. $NiCl_2 \{ P(C_2H_5)_2(C_6H_5)\}_2$ exhibits temperature dependent magnetic behaviour (paramagnetic/diamagnetic) the coordination geometries of $Ni^{2+} $ in the paramagnetic and diamagnetic states respectively, are

IIT JEEIIT JEE 2012Coordination Compounds

Solution:

In the given complex $NiCl_2 \{P(C_2H_5)_2(C_6H_5) \}_2 $ nickel is in + 2 oxidation state and the ground state electronic configuration of $Ni^{2+} $ ions in free gaseous state is
image
For the given four coordinated complex to be paramagnetic, it must possess unpaired electrons in the valence shell. To satisfy this condition, four lone pairs from the four ligands occupies the four $sp^3-$ hybrid orbitals as :
image
Therefore, geometry of paramagnetic complex must be tetrahedral. On the otherhand, for complex to be diamagnetic, there should not be any unpaired electrons in the valence shell.
This condition can be fulfilled by pairing electrons of 3r/-orbitals against Hund's rule as
image
The above electronic arrangement gives $dsp^2- $ hybridisation and therefore, square planar geometry to the complex.

Solution Image