Question

What are the facial and meridional isomers ? Explain with one example .

Answer 1

Hint : In chemistry, isomers are molecules or polyatomic ions with identical molecular formulas — that is, same number of atoms of each element — but distinct arrangements of atoms in space.Isomerism is existence or possibility of isomers.Isomers do not necessarily share similar chemical or physical properties. Two main forms of isomerism are structural or constitutional isomerism, in which bonds between the atoms differ; and stereoisomerism or spatial isomerism, in which the bonds are the same but the relative positions of the atoms differ.Facial and meridional isomerism is shown by the octahedral complexes of type . Here, M is the metal, a and b are monodentate ligands.

Complete Step By Step Answer:
Isomers are different compounds that have the same molecular formula but the atoms are attached in different ways. In chemistry, octahedral molecular geometry describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The octahedron has eight faces, hence the prefix octa. The octahedron is one of the Platonic solids, although octahedral molecules typically have an atom in their centre and no bonds between the ligand atoms. A perfect octahedron belongs to the point group Oh. Examples of octahedral compounds are sulfur hexafluoride $S{F_6}$ and molybdenum hexacarbonyl $Mo{\left( {CO} \right)_6}$ . The term "octahedral" is used somewhat loosely by chemists, focusing on the geometry of the bonds to the central atom and not considering differences among the ligands themselves. For example, ${[CO{(N{H_3})_6}]^{3 + }}$ which is not octahedral in the mathematical sense due to the orientation of the N−H bonds, is referred to as octahedral. When two or more types of ligands (La, Lb, ...) are coordinated to an octahedral metal centre (M), the complex can exist as isomers. The naming system for these isomers depends upon the number and arrangement of different ligands.When three identical ligands occupy one face of an octahedron, the isomer is said to be facial, or fac. In a fac isomer, any two identical ligands are adjacent or cis to each other. If these three ligands and the metal ion are in one plane, the isomer is said to be meridional, or mer. A mer isomer can be considered as a combination of a trans and a cis, since it contains both trans and cis pairs of identical ligands. $[CO{(N{H_3})_3}C{l_3}]$ an octahedral complex having two different types of ligands. Ammonia and chlorine are two different types of ligands. Three molecules of ammonia and three molecules of chlorine are present in this complex. In the facial isomer, three chlorine ligands are on one face of a regular octahedron. Three ammonia ligands are present on the opposite face of the octahedron. In the meridional isomer, the ammonia ligands are present on different faces of octahedrons. Similarly chloride ligands are present on different faces of octahedrons.

Note :
In facial isomers, three ligands of the same type are present on one face of a regular octahedron. The remaining three ligands of other types are present on the opposite face of the octahedron. In the meridional isomer, the three ligands of the same type are present on different faces of regular octahedrons.