Molecular autoionization
Molecular autoionization (or self-ionization) is a reaction between molecules of the same substance to produce ions. If a pure liquid partially dissociates into ions, it is said to be self-ionizing. The oxidation number on all atoms in such a reaction remains unchanged. Such autoionization can be protic (H+
transfer), or non-protic. Some examples of each are:
Protic solvents often undergo some autoionization
Autoionization is not restricted to neat liquids or solids. Solutions of metal complexes exhibit this property. For example, compounds of the type FeX2(terpyridine) are unstable with respect to autoionization [Fe(terpyridine)2]2+[FeX4]2−.
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