Which component of a complex ion is usually responsible for its charge?

In a complex ion, the charge is primarily determined by the central metal ion. The central metal ion is often a transition metal, which can have multiple oxidation states. This variety allows the metal ion to either donate or accept electrons in its interactions with the ligands surrounding it. As a result, the charge of the complex ion reflects the charge of the central metal ion along with any contributions from the ligands.

Ligands, which are the molecules or ions attached to the metal ion, can influence the overall charge of the complex but typically do not dictate it. Many ligands are neutral, while others have their own charges. The charge of the complex is not derived from the solvent molecules, as they serve mainly as a medium in which the complex forms, and coordinating bonds are simply the interactions holding the ligands to the metal ion. Thus, the central metal ion is the crucial component that sets the overall charge of the complex ion.