Question

A metal complex of coordination number six having three types of ligands a,b and c of composition $M{{a}_{2}}{{b}_{2}}{{c}_{2}}$ can exist in several geometrical isomeric forms; the total number of such isomers is:
(A) 3
(B) 5
(C) 7
(D) 9

Answer 1

Isomers are compounds having the same molecular formula and have different spatial arrangement. The ligands are arranged in different forms and in cis-trans form. Cis is when same type of ligands are adjacent to each other and trans is when same type are placed opposite to each other.

Complete answer:
A coordination complex consists of a central atom or ion, which is usually metallic and is known as coordination centre, and surrounding bound molecules or ions are known ligands or complexing agents. Many metals containing compounds, especially transition metals, are coordination complexes.
For a coordination compound of coordination number six, that means that the central metal ion is surrounded with six ligands. The shape of a coordination compound with six ligands is known as Octahedral. There are several types of isomers. Geometric Isomer is one of them, having cis-trans and E-Z nomenclature. For, coordination compound having composition $M{{a}_{2}}{{b}_{2}}{{c}_{2}}$ , there will 5 geometric isomers present. All are given as follows.

This is a trans isomer, with all the same groups placed opposite to each other.

In this isomer, only c type ligands are trans to each other,rest of the two are placed randomly.

In this isomer, only a type of ligands are trans to each other,rest of the two are placed randomly.

In this isomer, all type of ligands are cis to each other.

In this iomer, b types ligand is trans to each other, and a and c type ligand are cis to each other.

So, the correct answer is “Option B”.

Note: E-Z type of isomerism is used when the same type of ligands are not present. The ligands are ranked as per their priority rule and when two same priority groups are placed on the same side then it is named as Z and when same priority groups are placed opposite side, then it is named E.