ligandidega

Ligands are molecules or ions that bind to a central atom, typically a transition metal, in a coordination complex. The binding occurs when a ligand donates one or more pairs of electrons to the metal, forming coordinate covalent bonds. Ligands can be neutral or anionic; common donors include nitrogen, oxygen, sulfur, and phosphorus. Donor atoms can be monodentate (binding through a single site), bidentate (two sites), or polydentate; multidentate ligands are called chelating ligands.

Ligands influence the properties of the metal center: coordination number, geometry, electronic structure, and reactivity. The overall stability of the complex is described by formation constants and can be affected by ligand denticity, sterics, and electronic effects. The spectrochemical series orders ligands by their field strength, affecting spin states in octahedral and other geometries.

Examples include ammonia, water, chloride, cyanide, and carbon monoxide; bidentate ligands such as ethylenediamine or bipyridine; and hexadentate EDTA. Ligand binding is central to catalysis, bioinorganic chemistry (for example hemoglobin and nitrogenase), and medicine (metal-based drugs such as cisplatin). Ligand substitution reactions describe how ligands exchange positions, via associative or dissociative mechanisms.

Understanding ligand associations aids in designing catalysts, sensors, and therapeutic agents.