Onium ion
In chemistry, an onium ion is a cation formally obtained by the protonation of mononuclear parent hydride of a pnictogen, chalcogen, or halogen. The oldest-known onium ion, and the namesake for the class, is ammonium,, the protonated derivative of ammonia,.
The name onium is also used for cations that would result from the substitution of hydrogen atoms in those ions by other groups, such as organic groups, or halogens; such as tetraphenylphosphonium,. The substituent groups may be divalent or trivalent, yielding ions such as iminium and nitrilium.
A simple onium ion has a charge of +1. A larger ion that has two onium ion subgroups is called a double onium ion, and has a charge of +2. A triple onium ion has a charge of +3, and so on.
Compounds of an onium cation and some other anion are known as onium compounds or onium salts.
Onium ions and onium compounds are inversely analogous to ions and ate complexes:
- Lewis bases form onium ions when the central atom gains one more bond and becomes a positive cation.
- Lewis acids form ions when the central atom gains one more bond and becomes a negative anion.
Simple onium cations (hydrides with no substitutions)
Group 13">Boron group">Group 13 (boron group) onium cations
Group 14">Carbon group">Group 14 (carbon group) onium cations
- carbonium ions have a pentacoordinated carbon atom with a +1 charge.
- *alkanium cations,
- **methanium,
- **ethanium,
- **propanium,
- ***propylium, or propan-1-ylium
- ***propan-2-ylium
- **butanium,
- ***n-butanium
- ****n-butylium, or n-butan-1-ylium
- ****n-butan-2-ylium
- ***isobutanium
- ****isobutylium, or isobutan-1-ylium
- ****isobutan-2-ylium
- **octonium or octanium,
- silanium,
- *disilanium,
- *further silanium cations,
- germonium,
- stannonium,
- plumbonium,
- flerovonium,
Group 15">Pnictogen">Group 15 (pnictogen) onium cations
Group 16">Chalcogen">Group 16 (chalcogen) onium cations
Hydrogen onium cation
- hydrogenonium, better known as trihydrogen cation,, found in ionized hydrogen and interstellar space
Group 17">Halogen">Group 17 (halogen) onium cations, [halonium ion]s, (protonated [hydrogen halide]s)
[Pseudohalogen] onium cations
- aminodiazonium,
- methylidyneammonium and hydrocyanonium,, isomers
Group 18">Noble gas">Group 18 (noble gas) onium cations
- hydrohelium or helonium, better known as helium hydride ion,
- neonium,
- argonium,
- kryptonium,
- xenonium,
- radonium,
- oganessonium
Onium cations with monovalent substitutions
- primary ammonium cations, or
- *hydroxylammonium,
- *methylammonium,
- *ethylammonium,
- *hydrazinium, or diazanium,
- *anilinium,
- secondary ammonium cations,
- *dimethylammonium,
- *diethylammonium,
- *ethylmethylammonium,
- *diethanolammonium,
- tertiary ammonium cations,
- *trimethylammonium
- *triethylammonium
- quaternary ammonium cations, or
- *tetrafluoroammonium,
- *tetramethylammonium,
- *tetraethylammonium,
- *tetrapropylammonium,
- *tetrabutylammonium, or abbreviated
- *trimethyl ammonium compounds,
- *didecyldimethylammonium,
- *pentamethylhydrazinium,
- quaternary phosphonium cations, or
- *tetraphenylphosphonium,
- quaternary arsonium cations, or
- *tetraphenylarsonium,
- quaternary stibonium cations, or
- *tetraphenylstibonium,
- primary oxonium cations,
- *alkyloxonium cations
- **methyloxonium,
- **ethyloxonium,
- *dioxidanonium,
- secondary oxonium cations,
- *dialkyloxonium cations
- **dimethyloxonium,
- tertiary oxonium cations,
- *trifluorooxonium,
- *trimethyloxonium,
- *triethyloxonium,
- *oxatriquinacene,
- *oxatriquinane,
- primary sulfonium cations,
- secondary sulfonium cations,
- *dimethylsulfonium,
- tertiary sulfonium cations,
- *trimethylsulfonium,
- tertiary selenonium cations,
- *triphenylselenonium,
- tertiary telluronium cations,
- *triphenyltelluronium,
- primary fluoronium cations,
- secondary fluoronium cations,
- *dichlorofluoronium,
- secondary iodonium cations,
- *diphenyliodonium,
Onium cations with polyvalent substitutions
- secondary ammonium cations having one double-bonded substitution,
- *diazenium,
- *guanidinium,
- tertiary ammonium cations having one triple-bonded substitution, R≡NH+
- *nitrilium,
- *diazonium or diazynium,
- cyclic tertiary ammonium cations where nitrogen is a member of a ring,
- *pyridinium,
- quaternary ammonium cations having one double-bonded substitution and two single-bonded substitutions,
- *iminium,
- *diazenium,
- *thiazolium,
- quaternary ammonium cations having two double-bonded substitutions,
- *nitronium,
- *bis(triphenylphosphine)iminium,
- quaternary ammonium cations having one triple-bonded substitution and one single-bonded substitution,
- *diazonium,
- *nitrilium,
- tertiary oxonium cations having one triple-bonded substitution,
- *acylium ions,
- *nitrosonium,
- cyclic tertiary oxonium cations where oxygen is a member of a ring,
- *pyrylium,
- tertiary sulfonium cations having one triple-bonded substitution,
- *thionitrosyl,
- dihydroxyoxoammonium,
- trihydroxyoxosulfonium,
Double onium dications
- hydrazinediium or hydrazinium dication,
- diazenediium cation,
- diazynediium cation,
Enium cations
The extra bond is added to a less-common parent hydride, a carbene analog, typically named -ene or -ylene, which is neutral with 2 fewer bonds than the more-common hydride, typically named -ane or -ine.- borenium cations,
- carbenium cations, have a tricoordinated carbon atom with a +1 charge.
- *alkenium cations,
- **methenium cation,
- **ethenium,
- *benzenium,
- *tropylium,
- silylium cations,
- nitrenium cations,
- phosphinidenium cations,
- mercurinium cations,
Substituted eniums
- diphenylcarbenium,
- triphenylcarbenium,
Ynium cations
- carbynium ions have a carbon atom with a +1 charge.
- *alkynium cations,
- **methynium cation,
- **ethynium,