Question

The coordination number and oxidation number of the central metal ion in the complex ${\left[ {Pt{{\left( {en} \right)}_2}} \right]^{2 + }}$ is:
A. C.N = 2, O.N = +2
B. C.N = 6, O.N = +4
C. C.N = 4, O.N = +4
D. C.N = 4, O.N = +2

Answer 1

The coordination number of the metal ion is known as the total number of coordinate bonds through which central metal ion is attached with ligands. Also, the oxidation number represents an electric charge which an atom or ion actually has or appears to have when combined with other atoms.

Complete answer:
First, we have to find the coordination number of the central metal. From the definition of coordination number, we understood that it is the total number of coordinate bonds that forms. For that, we have to understand the meaning of ligands. Ligands can be classified based on charge, the number of donor sites and bonding.
Here the ligand is $en$. That is ethyl diamine. The formula for ethyl diamine is as follows
$\ddot N{H_2} - C{H_2} - C{H_2} - \ddot N{H_2}$
From the formula we can see that it has two donor atoms, i.e., the Nitrogen atoms have 2 valence electrons which act as a donor pair. That is why ethyl diamine is known as bidentate ligands.
Therefore, the total number of donor sites is 2×2=4. Which implies the coordination number of the central metal is 4.
Now, for finding the oxidation number. From the formula, we understood that the charge of ethylenediamine is zero. Since there are only donor sites.
The charge of the complex is given as +2.
Let $x$ be the oxidation number of Platinum.
Therefore, $1 \times x + 2 \times 0 = + 2$
i.e., $x = 2$
The oxidation number of the central metal ion is +2.

**Hence option D is correct

Note:**
Apart from bidentate ligands, there are also polydentate ligands which coordinate to a central metal atom or ion through more than two donor atoms are called polydentate ligands. EDTA is an example of this. Also if a polydentate ligand which does not use all its donor atoms to get coordinated to metal atom/ion, the ligand is said to have flexidentate character. EDTA is an example of this also.