Metal complexes are chemical structures formed when metal ions bond with molecules or ions called ligands. These ligands can be simple ions, like chloride or nitrate, or larger molecules, such as ammonia or ethylenediamine. The metal ion acts as a central atom, and the ligands surround it, creating a stable arrangement. The properties of metal complexes vary widely depending on the type of metal and ligands involved. They play essential roles in various fields, including catalysis, biochemistry, and materials science. For example, hemoglobin, a metal complex containing iron, is crucial for transporting oxygen in the blood.