Coordination complexes are special chemical structures formed when a central metal atom, often a transition metal like copper or iron, bonds with surrounding molecules or ions called ligands. These ligands can be simple ions, like chloride, or larger molecules, such as ammonia. The arrangement of these ligands around the metal creates a unique three-dimensional shape, influencing the complex's properties and reactivity. These complexes play a crucial role in various fields, including biochemistry and materials science. For example, the hemoglobin in our blood is a coordination complex that helps transport oxygen. Understanding these structures helps scientists design new materials and drugs.