Geometrical isomerism in six coordination compound

Geometrical Isomerism in Six-Coordination Compounds

In coordination chemistry, geometrical isomerism is an important type of stereoisomerism observed in coordination compounds. It occurs because ligands can be arranged in different positions around the central metal ion in space.

Occurrence in Six-Coordination Compounds

Six-coordination compounds generally adopt an octahedral geometry. In such structures, geometrical isomerism occurs when ligands can occupy different positions relative to each other—either adjacent (cis) or opposite (trans) to one another.

Types of Ligand Arrangements

• Ma₄b₂ type: Two geometrical isomers are possible:
  • Cis-isomer: The two b ligands are adjacent to each other.
  • Trans-isomer: The two b ligands are opposite each other.

  Example: [Co(NH₃)₄Cl₂]⁺

• Ma₃b₃ type: Two isomers are possible:
  • Facial (fac): The three identical ligands are positioned on the same triangular face of the octahedral structure.
  • Meridional (mer): The three similar ligands are arranged in a single plane that includes the central metal ion, forming a 90° and 180° angle pattern.

  Example: [Co(NH₃)₃NO₂₃]

Important Notes

• Geometrical isomerism is not possible in all six-coordinate complexes—it depends on the types and positions of ligands.
• Octahedral complexes with three or more different ligands may have more than two isomers.

Significance in JEE Main

Questions on geometrical isomerism often appear in JEE Main, particularly involving recognition of cis/trans or fac/mer isomers, and drawing their structures.