What characterizes coordination complexes?

Coordination complexes are characterized by a central metal atom or ion that is surrounded by molecules or ions known as ligands. The correct choice highlights that a central metal atom, which is often a transition metal due to its ability to form various oxidation states and complex geometries, is coordinated by ligands. Ligands can be neutral molecules or charged ions and typically possess lone pairs of electrons that they can donate to the metal, forming coordinate covalent bonds.

The ability of a metal ion to form complex structures with ligands significantly influences the properties of the resulting coordination complex, including its color, reactivity, and solubility in different solvents. The nature of the ligands and their arrangement around the metal greatly impact these characteristics, making the interactions within coordination complexes quite intricate and important in chemistry.

In contrast, other options do not accurately describe coordination complexes. For instance, coordination complexes can contain multiple types of ligands rather than just one, and while metal ions can play a significant role in solubility, asserting that they have no effect would be misleading. Additionally, ligands do indeed connect to metal ions through coordinate bonds, specifically by sharing their lone pairs of electrons, making the statement indicating that they do not connect incorrect.