Molecular autoionization

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This article is about molecular autoionization in solution chemistry by reaction of two identical molecules. For autoionization of a single atom or molecule (a different process studied in physics), see 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.[1]:163 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:

Examples[edit]

Protic solvents[edit]

Protic solvents often undergo some autoionization

2 H
2
O
H
3
O+
+ OH
The self-ionization of water is particularly well studied, due to its implications for acid-base chemistry of aqueous solutions.
2 NH
3
NH+
4
+ NH
2
[1]:217
3 HFH
2
F+
+ HF
2
[1]:221 Here proton transfer between two HF combines with homoassociation of F
and a third HF to form HF
2
.

Non-protic solvents[edit]

2 PF
5
PF
6
+ PF+
4
2 N
2
O
4
NO+
+ NO
3
[1]:217
2 BrF
3
BrF+
2
+ BrF
4
[1]:224

Coordination chemistry[edit]

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−.[2]

See also[edit]

References[edit]

  1. ^ a b c d e f Housecroft C.E.; Sharpe A.G. (2005). Inorganic Chemistry (2nd ed.). Pearson. ISBN 0130-39913-2. 
  2. ^ Kamata, K.; Suzuki, A.; Nakai, Y.; Nakazawa, H., "Catalytic Hydrosilylation of Alkenes by Iron Complexes Containing Terpyridine Derivatives as Ancillary Ligands", Organometallics 2012, 31, 3825-3828. doi:10.1021/om300279t