Question

Which of the following complexes is not expected to exhibit isomerism?
(a) ${{[Ni{{(N{{H}_{3}})}_{4}}{{({{H}_{2}}O)}_{2}}]}^{2+}}$
(b) $[Pt{{(N{{H}_{3}})}_{2}}C{{l}_{2}}]$
(c) $[Ni{{(N{{H}_{3}})}_{2}}C{{l}_{2}}]$
(d) ${{[Ni{{(en)}_{3}}]}^{2+}}$

Answer 1

Hint: The isomerism exhibited by such coordination compounds is the optical isomerism in which the mirror images are non-superimposable and in such compounds the coordination number is 6. Now identify the compounds.

Complete step by step solution:
- First of all, we should know what is isomerism. By the term isomerism we mean the existence of the compounds which have the same molecular formula but different properties and such compounds which show this type of isomerism, is known as the isomers.
- The above given all the complexes will show or not show the isomerism; the optical isomerism and by the optical isomerism we means, those stereoisomers( i.e. the different arrangement of the atoms in space) in which the compounds resemble one another in their chemical reactions and ,most of the physical properties but differ in their effect on polarized light and have non-superimposable mirror images i.e. their mirror images are not superimposed on one another. If it rotates the plane polarized light towards left , it is called as laevorotatory; if it rotates the plane polarized light towards right ,it is called dextrorotatory.
- Optical isomerism is given by only those compounds which form octahedral complexes and has bidentate ligands i.e. their coordination number=6 and are not shown by the tetrahedral complexes have the coordination number as 4 because of the presence of symmetry of elements in them.
- So ,from above all the given complexes only $[Ni{{(N{{H}_{3}})}_{2}}C{{l}_{2}}]$ is a tetrahedral complex and all others are the octahedral complex and will not show optical isomerism.

Hence, option (c) is correct.

Note: the necessary and important condition for a compound to be optically active is not asymmetry but dissymmetry. Asymmetric molecule is that in which the central atom is asymmetric and is linked to four different atoms or groups. On the other hand, a molecule is said to be dissymmetric if it has no plane of symmetry i.e. no plane should divide the molecule in two equal halves and mirror images are non-superimposable.