Question

a. Draw the geometrical isomer of complex $\left[ {{\text{Pt}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{2}}}{\text{C}}{{\text{l}}_{\text{2}}}} \right]$.
b. On the basis of crystal field theory, write the electronic configuration for ${{\text{d}}^{\text{4}}}$ ion if ${\Delta _0} < {\text{P}}$.
c. Write the hybridisation and magnetic behaviour of the complex $\left[ {{\text{Ni}}{{\left( {{\text{CO}}} \right)}_{\text{4}}}} \right]$. (At. no. of ${\text{Ni}} = 28$).

Answer 1

The complex $\left[ {{\text{Pt}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{2}}}{\text{C}}{{\text{l}}_{\text{2}}}} \right]$ is a $\left[ {{\text{M}}{{\text{a}}_2}{{\text{b}}_2}} \right]$ type of complex. ${\Delta _0}$ is the crystal field splitting energy and ${\text{P}}$ is the pairing energy. When ${\Delta _0} < {\text{P}}$, it is a weak field ligand. The outer electronic configuration of nickel is $1{s^2}\,2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^8}$.

Complete step by step solution:
a. The complex $\left[ {{\text{Pt}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{2}}}{\text{C}}{{\text{l}}_{\text{2}}}} \right]$ is a $\left[ {{\text{M}}{{\text{a}}_2}{{\text{b}}_2}} \right]$ type of complex. These kind of complexes have two types of geometrical isomers.
The cis isomer is obtained when the same ligands are adjacent to each other.
The trans isomer is obtained when the same ligands are opposite to each other.
Thus, the geometrical isomers of the complex $\left[ {{\text{Pt}}{{\left( {{\text{N}}{{\text{H}}_{\text{3}}}} \right)}_{\text{2}}}{\text{C}}{{\text{l}}_{\text{2}}}} \right]$ are as follows:

b. When the ligand bonds to the metal ion, the energy of the degenerate d-orbitals increases. As the energy of the degenerate d-orbitals increases, the degenerate orbitals split into ${{\text{t}}_{{\text{2g}}}}$ and ${{\text{e}}_{\text{g}}}$ orbitals.
The difference in the energies of the ${{\text{t}}_{{\text{2g}}}}$ and ${{\text{e}}_{\text{g}}}$ orbitals is known as the crystal field splitting energy (CFSE). It is denoted by ${\Delta _0}$.
When ${\Delta _0} < {\text{P}}$ i.e. crystal field splitting energy is smaller than the pairing energy, the ligand is a weak field ligand. When the ligand is a weak field ligand, the fourth electron jumps in the ${{\text{e}}_{\text{g}}}$ orbital.
Thus, the electronic configuration for ${{\text{d}}^{\text{4}}}$ ion is as follows:

Thus, on the basis of crystal field theory, the electronic configuration for ${{\text{d}}^{\text{4}}}$ ion if ${\Delta _0} < {\text{P}}$ is ${\text{t}}_{{\text{2g}}}^3\,{\text{e}}_{\text{g}}^1$.

c. The electronic configuration of nickel is $1{s^2}\,2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^8}$.
The outer electronic configuration is $3{d^8}4{s^2}4{p^0}$.

In the complex $\left[ {{\text{Ni}}{{\left( {{\text{CO}}} \right)}_{\text{4}}}} \right]$, ${\text{C}}{{\text{O}} }$ is a strong ligand. Thus, it will cause the pairing of electrons.

Thus, the hybridisation of the complex $\left[ {{\text{Ni}}{{\left( {{\text{CO}}} \right)}_{\text{4}}}} \right]$ is $s{p^3}$.
The complex $\left[ {{\text{Ni}}{{\left( {{\text{CO}}} \right)}_{\text{4}}}} \right]$ does not have any unpaired electron. Thus, the complex $\left[ {{\text{Ni}}{{\left( {{\text{CO}}} \right)}_{\text{4}}}} \right]$ is a diamagnetic complex.

Note:
Strong field ligands form low spin complexes. The examples of strong field ligands are ${\text{C}}{{\text{O}} }$, ${\text{C}}{{\text{N}}^ - }$. Weak field ligands form high spin complexes. The examples of weak field ligands are ${{\text{F}}^ - }$, ${\text{C}}{{\text{l}}^ - }$. The complexes having unpaired electrons are paramagnetic in nature and those having no unpaired electrons are diamagnetic in nature.