Lewisbase

A Lewis base is a chemical species that donates an electron pair to form a covalent bond with a Lewis acid. In Lewis acid–base theory, the interaction creates a Lewis adduct in which the donor electron pair is shared with the electron-poor center of the acid. The concept emphasizes electron pair donation rather than proton transfer.

Lewis bases are typically species with lone pairs or π-electrons capable of donating to an electron-deficient center. They commonly act as ligands in coordination chemistry, binding to metal centers to form coordination complexes. The resulting bond is often described as a coordinate covalent bond, where both electrons in the bond originate from the base.

Common examples of Lewis bases include ammonia and amines, water, hydroxide ion, halide ions (such as fluoride and chloride under suitable conditions), cyanide, carbon monoxide, phosphines, ethers, and many organometallic ligands like bipyridine. Inorganic and organic substrates with lone pairs or π-systems frequently serve as Lewis bases.

The Lewis base concept is broader than the Brønsted–Lowry framework. Many Lewis bases also act as Brønsted–Lowry bases (proton acceptors), but a species can be a Lewis base without acting as a Brønsted–Lowry base in certain reactions. The hard–soft acid–base (HSAB) perspective classifies bases as hard or soft, influencing their preference for different acids and affecting the stability of resulting complexes (hard bases with hard acids, soft bases with soft acids).

Overall, the term describes electron-pair donors that enable diverse applications in synthesis, catalysis, and materials science through formation of Lewis adducts with Lewis acids.