Question

What is the coordination number of $Fe$ in $\left[ FeC{{l}_{2}}{{\left( en \right)}_{2}} \right]Cl$ ?

Answer 1

We know that the coordination number of an element is the total number of atoms, molecules or ligands the central metal atom can carry in a coordination compound or complex. The coordination number is usually referred to as that of the central metal atom.

Complete answer:
The name of the given coordination compound $\left[ FeC{{l}_{2}}{{\left( en \right)}_{2}} \right]Cl$ is Dichloride bis(ethylenediamine) ferric (III) Chloride.
The central metal atom in this coordination compound is Fe. We can see that Fe has 2 chlorine atoms and two ethylene diamine atoms.
Ethylenediamine (en) is a bidentate ligand as it is attached to two atoms. On the other hand, chlorine is a monodentate ligand. Thus, 2 Ethylenediamine (en) will have 4 coordination sites and 2 chlorine atoms will have 2 coordination sites.
$Coordination\text{ }number\text{ }of\text{ }Fe\text{ }=\text{ 2 }\times \text{ (No}\text{. of en atoms) + 2 }\times \text{ (No}\text{. of Cl atoms) }$
$=\text{ 2 }\times \text{ (2) + 2 }\times \text{ (1) }$
$=\text{ 4 + 2 }$
$=\text{ 6}$
Therefore, the coordination number of Fe in the complex is 6.

Additional information:
The coordination number of the central metal atom is often termed legacy.
The oxidation state of the central metal atom Fe in the coordination complex $\left[ FeC{{l}_{2}}{{\left( en \right)}_{2}} \right]Cl$ is +2.
To find the coordination number, always count the number of atoms attached to the central atom and not the chemical bonds between ligands and the central metal atom. Although to find the oxidation number you have to look into the charge on the atom.

Note:
The coordination number of the central metal atom varies according to the ligands attached to it. The coordination number can differ from the charge present on the central metal atom. Also, the Coordination number for a cation and anion can be calculated.