Question

What is the coordination number of Cu in ${\left[ {{\mathbf{Cu}}{{\left( {{\mathbf{en}}} \right)}_2}} \right]^{2 + }}$.

Answer 1

We know that the coordination compounds are those compounds in which the central metal atom is linked to a number of ions or neutral molecules by coordinate bonds. The coordination number is known as the total number of coordination bonds through which the central metal atom ion is attached with ligands.

Complete Step by step answer:
We know that we have to find the coordination number of the central metal ion present in the complex ${\left[ {{\text{Cu}}{{\left( {{\text{en}}} \right)}_2}} \right]^{2 + }}$. Let us look into it bit by bit.
The central metal or ion to which the one or more neutral molecules or ions are linked by coordinate bonds is known as the centre of coordination. We have to find the coordination number of this central metal Cu.
So in the complex ${\left[ {{\text{Cu}}{{\left( {{\text{en}}} \right)}_2}} \right]^{2+}}$, where the ligand attached to it is called ethylene diamine and it is written as $en$.

Let us look into its formula, since we have two amine groups present we have two nitrogen with two electron pairs in them. As we said in the definition, In coordination compounds the central atoms are linked to ions and neutral molecules by donation of electron pairs. Here our ligands also have two electron pairs in them. In the complex there are two ethylene diamines, hence a total of 4 electron pairs and we can form 4 coordinate bonds with the ligands.

Therefore, we say the coordination number of Cu in ${\left[ {{\text{Cu}}{{\left( {{\text{en}}} \right)}_2}} \right]^{2 + }}$ is 4.

Note: We can call ethylene diamine has bidentate ligands as they can coordinate to central metal atoms or ions through two donor atoms and form two coordinate bonds. Other types of ligands are monodentate (one coordinate bonds) and polydentate (more than two donor atoms).