In a complex ion, which component acts as the Lewis acid?

In the context of a complex ion, the metal ion acts as the Lewis acid. This is because a Lewis acid is defined as a substance that can accept an electron pair from a Lewis base during the formation of a coordinate covalent bond. In a complex ion, the metal ion, typically a transition metal, has empty orbitals that can accommodate additional electron pairs.

The ligands, which are the molecules or ions that donate electron pairs, function as the Lewis bases in this scenario. They interact with the metal ion by donating their lone pair of electrons, resulting in the formation of coordinate bonds. The solvent can play a role in stabilizing the complex but does not act as a Lewis acid in this context. Similarly, the term "base" in this instance is more appropriately applied to the ligands rather than being a standalone option.

Therefore, the correct identification of the metal ion as the Lewis acid in complex ions is essential for understanding the interactions within coordination chemistry, as it highlights the fundamental role that the metal center plays in coordinating with ligands to form stable complexes.