Ligand

A ligand is an atom, ion, or molecule that donates an electron pair to a central atom in a coordination complex, forming a coordinate bond.

Coordinate covalent bond: A covalent bond in which both shared electrons originate from one atom. A ligand forms this bond by donating an electron pair to a central atom.
Lewis base: A species that donates an electron pair to form a bond. Ligands are Lewis bases when they donate electron pairs to central atoms.
Organometallic chemistry: The study of compounds containing bonds between carbon atoms and metals. Many organometallic compounds use organic groups as ligands that tune metal reactivity.
Counterion: An ion whose charge balances that of another ion in a compound or solution. A counterion may balance a complex’s charge without being coordinated to its central atom.
Coordination number: The number of donor atoms directly bonded to a central atom in a coordination complex. Ligand donor atoms determine how many direct bonds surround the metal center.
Donor atom: An atom in a ligand that supplies an electron pair to a central atom. The donor atom is the specific site through which a ligand forms a coordination bond.
Homogeneous catalysis: Catalysis in which the catalyst and reactants occupy the same phase. Ligands tune soluble metal catalysts’ activity, selectivity, and stability.
Solvent: A substance that dissolves a solute to form a solution. Solvent molecules can become ligands when they coordinate to a dissolved metal center.
Chelation: Binding of a metal ion by a ligand attached through multiple donor atoms, often forming rings. Multidentate ligands bind through several sites and can stabilize complexes through ring formation.
Denticity: The number of donor atoms in a ligand that can bind simultaneously to one central atom. Denticity distinguishes ligands that bind through one site from those with several.

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