Question

How many number of unpaired electrons is present in the complex \[Hg\left[ {Co{{\left( {SCN} \right)}_4}} \right]\]

Answer 1

Hint: In a coordination complex, there are metal, coordination complexes and ligands attached to it. The metal, ligands and counterions together form a coordination complex. Bidentate ligands are the one in which two atoms coordinate directly to the central atom forming a coordination complex.

Complete answer:
Before starting this question we need to know what coordination number and oxidation state is?
Coordination number is derived for the central atom present in any complex, that central atom is bonded to many ligands around it. So the number of atoms, molecules or ions which are bonded to central atoms defines the coordination number of any complex.
For example: A complex \[[CuC{l_2}]\]- has a coordination number two since it has two chlorine atoms.
Now, what is the oxidation state? Oxidation state can be defined on the basis of gaining and losing an electron. When an atom loses or gains an electron so as to form a chemical bond with another atom in a molecule, it defines oxidation state.
For example: A complex \[Mn{O_2}\]has \[ + 2\] oxidation state.
Now let’s start the question to find the number of unpaired electrons in \[Hg\left[ {Co{{\left( {SCN} \right)}_4}} \right]\]
Let oxidation number of Cobalt be x, therefore
$x + 4\left( { - 1} \right) = - 2$
$x = - 2 + 4$
$x = 2$
Cobalt in plus two oxidation states will have $3$unpaired electrons.
Electronic configuration of Co= \[\left[ {Ar} \right]3{d^7}4{s^2}\]
Electronic configuration of \[C{o^{2 + }}\]= \[\left[ {Ar} \right]3{d^7}\]
Thus in $ + 2$ oxidation state it will have $3$unpaired electrons.
Answer- There are three unpaired electrons is present in the complex \[Hg\left[ {Co{{\left( {SCN} \right)}_4}} \right]\]

Note:
We have to remember that \[SCN\] in this complex is a thiocyanate ion which has a molecular name thiocyanate ion. When an atom loses or gains an electron so as to form a chemical bond with another atom in a molecule defines oxidation state.