6.2.3 Shapes of Complex Ions

Shapes of Complex Ions

Transition metal ions form complex ions with characteristic shapes based on the size and type of ligands bonded to the metal. These shapes influence the properties, stability, and stereochemistry of the complex ions.

Octahedral Complexes

Typical Ligands:

Small ligands like water ($\text{H}_2\text{O}$) and ammonia ($\text{NH}_3$) often form octahedral complexes with transition metals.

Isomerism in Octahedral Complexes:

Cis–Trans Isomerism:

• Occurs when two identical ligands are adjacent (cis) or opposite (trans) to each other.

• This is a special form of E–Z isomerism. Optical Isomerism:

• When three bidentate ligands form a chiral complex that cannot be superimposed on its mirror image, creating optical isomers.

Example Complex:

Tetrahedral Complexes

Typical Ligands:

Larger ligands, such as chloride ions ($\text{Cl}^-$), commonly lead to tetrahedral coordination due to steric effects.

Isomerism in Tetrahedral Complexes:

Tetrahedral complexes do not exhibit cis–trans or optical isomerism due to their symmetrical structure.

Example Complex:

Square Planar Complexes

Isomerism in Square Planar Complexes:

Cis–Trans Isomerism:

• Just like octahedral complexes, square planar complexes with two pairs of identical ligands exhibit cis–trans isomerism.

Linear Complexes

Example Complex:

Stereoisomerism in Complex Ions

Stereoisomerism arises when complexes have the same formula but different spatial arrangements.

There are two main types of stereoisomerism:

1. Cis–Trans Isomerism: Present in octahedral and square planar complexes where identical ligands can either be adjacent (cis) or opposite (trans).
2. Optical Isomerism: Seen in chiral octahedral complexes with bidentate ligands. Optical isomers are non-superimposable mirror images, similar to left and right hands, and rotate plane-polarized light in opposite directions.