A complex compound, also known as a coordination compound, is a chemical compound that consists of a central metal atom or ion bonded to a group of molecules or ions, known as ligands. These ligands are typically anions or neutral molecules that donate electron pairs to the metal, forming coordinate covalent bonds.
Complex compounds are characterized by their unique structures and properties, which often include distinctive colors, magnetic properties, and reactivity. The central metal atom or ion is usually a transition metal, and the ligands are arranged around it in a specific geometric pattern, such as octahedral, tetrahedral, or square planar.
One of the most well-known examples of a complex compound is [Fe(CN)6]4-, where the central iron ion (Fe2+) is coordinated to six cyanide ions (CN–). This complex ion is part of the compound potassium ferrocyanide, K4[Fe(CN)6].
Complex compounds play a crucial role in various fields, including biochemistry, industrial chemistry, and materials science. For example, hemoglobin, the protein responsible for transporting oxygen in the blood, contains a complex of iron(II) ion coordinated to a porphyrin ring and other ligands.