In chemistry, an ate complex is a salt formed by the reaction of a Lewis acid with a Lewis base whereby the central atom (from the Lewis acid) increases its valence and gains a negative formal charge. (In this definition, the meaning of valence is equivalent to coordination number).
Often in chemical nomenclature the term ate is suffixed to the element in question. For example, the ate complex of a boron compound is called a borate. Thus trimethylborane and methyllithium react to form the ate compound , lithium tetramethylborate(1-). This concept was introduced by Georg Wittig in 1958. Ate complexes are common for metals, including the transition metals (groups 3-11), as well as the metallic or semi-metallic elements of group 2, 12, and 13. They are also well-established for third-period or heavier elements of groups 14–18 in their higher oxidation states.
Ate complexes are a counterpart to onium ions.
Lewis acids form ate ions when the central atom reacts with a donor ( X-type ligand), gaining one more bond and becoming a negative-charged anion.
Lewis bases form onium ions when the central atom reacts with an acceptor ( Z-type ligand), gaining one more bond and becoming a positive-charged cation.