Question

How can a metal cation be at the centre of a complex anion?

Short answer

A metal cation can be at the centre of a complex anion (in a ligand) so that the lone pairs can be donated to central metal ion.

Step-by-step solution

Introduction

An atom or a collection of atoms with a negative electric charge is known as an anion. An atom or a collection of atoms with a positive electric charge is known as a cation.

Cation at center of complex anion

Observe the ${\text{Pt}}^{\text{4 +}}$metal iongiven below-

The dots around ${\text{Pt}}^{\text{4 +}}$ion represent another atoms or molecules that could be bonded to it with coordinate bonds. These atoms and molecules are called ligands. One thing which all of these ligands have in common are active lone pairs in their outer shells which they can donate to central metal ion (they are acting as Lewis bases). A dative bond is formed between the central metal atom and the ligands.

Therefore, ligands have cation in between the complex anion.