LEWIS acids and bases--no conjugates here!

Gilbert N. Lewis is famous for many things, among them is his definition of acid/base chemistry. A Lewis acid is electron deficient. Generally, transition metal cations are considered good Lewis acids. A Lewis base is electron-rich and after collision, can stick to a Lewis acid through sharing an unbonded pair of electrons. When talking about transition metal chemistry, Lewis bases are the ligands that coordinate (bond or stick) with the metal cation. Electron-pair suppliers can come from molecules that contain an atom with a nonbonded lone pair -- such as N in NH3, N in en, O in H2O. Electron-pair suppliers can also come from anions in solution -- such as O in ox, Cl-, N in CN-. Chelating ligands are long and flexible enough to be polydentate. Both en and ox are both important examples of bidentate ligands. They act as Lewis bases and coordinate to a metal in two positions. When Lewis acid/base chemistry happens between a transition metal cation and ligands in aqueous solution, the result is a complex ion, often with a beautiful color. The formation of complex ions is reversible and so a K value (Kf) can describe the equilibrium composition of the mixture of Lewis acid, Lewis base, and the complex ion.