ligandos

Ligands are atoms, ions, or molecules that donate electron pairs to a central metal atom or ion, forming coordination complexes. The ligand acts as a Lewis base, while the metal center is a Lewis acid. Ligands bind through donor atoms such as oxygen, nitrogen, sulfur, phosphorus, or carbon, and can be neutral or anionic.

Based on denticity, ligands are monodentate (binding through one donor atom), bidentate (two), or polydentate (multiple) such as chelating ligands that wrap around the metal. Common examples include water and ammonia (monodentate), ethylenediamine (two donor sites), and oxalate (multiple).

Coordination chemistry studies several features of ligands, including binding strength, geometry, and electron donation. The coordination number describes how many donor atoms are bound to the metal, with common values of 4, 5, or 6 for transition metals. Ligand metal complexes can be biologically important, as in the heme group of hemoglobin or other metalloenzymes, or used as catalysts in chemical transformations, such as hydrogenation or hydroformylation. Stability is influenced by the chelate effect, whereby multidentate ligands often form more stable complexes than equivalent collections of monodentate ligands.

Terminology varies by language; in chemistry literature, ligands are sometimes categorized as neutral or anionic, and chelating ligands are highly valued for complex stability. Ligands play a central role across chemistry, biochemistry, and materials science.