Question

The sum of Coordination number and oxidation number of metal $M$ in the complex \[\left[ {M{{\left( {en} \right)}_2}\left( {{C_2}{O_4}} \right)} \right]Cl\], where $en$ is ethylenediamine is?
A. 7
B. 8
C. 9
D. 6

Answer 1

Hint: The number of constituent particles such as atoms, molecules, or ions that surround the central metal atom is a complex compound i.e. the atoms, molecules, or ions present in the coordination sphere along with the central metal atom in the coordination compound is called its coordination number.

Complete answer:
Step 1: Calculating the coordination number of the complex compound:
For calculating the coordination number the central metal atom is identified first and then the atoms, molecules, or ions nearest to the central metal atom i.e. the atoms, molecules, or ions present in the coordination sphere are added.
So, in the complex, \[\left[ {M{{\left( {en} \right)}_2}\left( {{C_2}{O_4}} \right)} \right]Cl\] the molecules that surround the metal atom i.e. the constituents present in the coordination sphere are two ions of ethylenediamine and one ion of oxalate. But, in this complex chlorine or Cl-1 ion is outside the coordination sphere and it exists as an anion. Moreover, both ethylenediamine and oxalate are bidentate ligands which means both of them to attach themselves to the metal atom from two sides because of the presence of lone pair. Hence the coordination number is $(2 \times 2) + 2$
\[4 + 2 = 6\;\;\]
Therefore, the coordination number of this complex is $6$.
Step 2: Calculating the oxidation number of the metal atom:
In this complex, the ethylenediamine is a neutral molecule which means its oxidation state is zero, but oxalate is an anion with oxidation number -2. Let the oxidation number of the metal atom be $x$.
$x + (0)(2) + ( - 2) = + 1$
$x + 0 - 2 = + 1$
$x - 2 = + 1$
$x = + 3$
So, the oxidation number of the central metal atom in this complex is +3.
Step 3: Calculating the sum of the coordination number and the oxidation state of the central metal atom:
The coordination number for this complex is $6$ while the oxidation state of the central metal atom in this complex is $ + 3$. So, the sum of the coordination number and oxidation state of the central metal atom is
\[6 + 3 = 9\]
Therefore, the sum of the coordination number and oxidation number of the central metal atom is 9.
So the correct answer is option C.

Note:
Oxidation number which is also known as the oxidation state is defined as the total number of electrons that an atom can gain or lose in order to form chemical bonds with the other atoms. Moreover, the number which is allocated to elements in a chemical combination also describes the oxidation number.