Question

The coordination number of Pt in the complex ion ${{[Pt{{(en)}_{2}}C{{l}_{2}}]}^{2+}}$ is:
A. 3
B. 4
C. 5
D. 6

Answer 1

Hint: The Coordination number of an atom in a given molecule or a crystal refers to the total number of atoms, ions or molecules bonded with the given atom. Coordination number is also known by the other name called ligancy.

Complete Solution :The atoms, ions, or molecules that are bonded with the central atom, molecule or ion are termed as ligands. In the case of polyatomic ions and molecules coordination number of any given atom can be calculated by counting the total number of atoms bonded to it and it may be a single bond, double or triple bond. With the help of coordination numbers we can easily predict the geometry of the given compound.
- In the given compound ${{[Pt{{(en)}_{2}}C{{l}_{2}}]}^{2+}}$ coordination sphere has 2 monodentate ligands. In which each chloride ions contains two negative charges and 2 neutral bidentate ligands i.e. ethylene diamine is present. Since a bidentate and monodentate ligand form a coordinate bond through two and one atoms respectively so the coordination number here is given by
$2\times 2+2\times 1= 6$
- Here 2 chloride ions give 2 negative charges and two ethylene diamine contains charge equal to one in this we calculate the coordination number.
- Hence we can say that coordinate number of Pt in ${{[Pt{{(en)}_{2}}C{{l}_{2}}]}^{2+}}$ is 6.
So, the correct answer is “Option D”.

Note: Generally the coordination number is the number of donor atoms attached to the central ion. These generally lie in the range 2 - 9. The number of bonds depends on the size, charge and electronic configuration of the metal ion and the donor atom.