Oxycation

An oxycation, or oxocation, is an ion with the generic formula A
_xO^z+
_y (where A represents a chemical element and O represents an oxygen atom). Their names normally end with the suffix "-ium" or "-yl".^[1]

Isolable oxycations

Structural details of the acetyl cation.^[2]

A few salts of oxycations have been reported. They are all associated with lighter main group elements. The nitrogen-containing cations are NO⁺ and NO⁺
₂. The latter is the active species in nitration reactions.

The Friedel-Crafts reaction is a classical organic reaction for attachment of acyl groups to arenes. The active acylating agent is often an acylium ion, several of which have been isolated..^[2]^[3]

Oxycation nomenclature

Main group species

NO⁺ - example: nitrosyl tetrafluoroborate
NO⁺
₂ - example: nitronium tetrafluoroborate
ClO⁺
₂ - example: chloryl hexafluororuthenate^[4]

More complicated oxycations include species like SOF₃⁺.^[5] Aluminyl, antimonyl, bismuthyl derivatives more closely resemble the situation for transition metal oxy cations in the sense that they are bonded to many Lewis bases. The cation [Bi₆(O)₄(OH)₄]⁶⁺, a face-capped octahedral cluster, is one example.^[6]

Transition metal species

Many transition compounds that contain an oxo ligand can be viewed as salts of a hypothetical "oxycation." In condensed phase, they are always complexed with strong Lewis bases.

TiO²⁺ - example: titanyl sulfate, Ti(O)SO₄(H₂O).^[7]
VO³⁺ - example: vanadyl chloride, VOCl₃
VO²⁺ - example: vanadyl phosphate, VO(HPO₄)
CrO₂²⁺ - example: chromyl chloride, CrO₂Cl₂^[8]
MoO³⁺ - molybdenyl chloride, MoOCl₃.^[9]
FeO²⁺ - examples include many ferryl intermediates

Actinide species

Oxycations in the gas-phase

While species like vanadyl (VO²⁺ and VO³⁺) do not exist in solution, some oxycations can be generated in the vacuum chamber of mass spectrometers. Using ion cyclotron resonance, these oxy cations have been shown to react even with simple hydrocarbons, attesting to the high reactivity.^[12]

References

^ However, the International Union of Pure and Applied Chemistry standard book on nomenclature of inorganic chemistry does not mention "oxycation". Union internationale de chimie pure et appliquée, ed. (2005). Nomenclature of inorganic chemistry: IUPAC recommendations 2005 (PDF). Cambridge: Royal society of chemistry. ISBN 978-0-85404-438-2. Retrieved 2025-05-22.
^ ^a ^b Davlieva, Milya G.; Lindeman, Sergey V.; Neretin, Ivan S.; Kochi, Jay K. (2004). "Structural effects of carbon monoxide coordination to carbon centers. σ and π Bindings in aliphatic acyl versus aromatic aroyl cations". New Journal of Chemistry. 28 (12): 1568. doi:10.1039/B407654K.
^ Boer, F. Peter (1968). "Crystal structure of a Friedel-Crafts intermediate. Methyloxocarbonium hexafluoroantimonate". Journal of the American Chemical Society. 90 (24): 6706–6710. doi:10.1021/ja01026a025.
^ Bougon, R.; Cicha, W. V.; Lance, M.; Meublat, L.; Nierlich, M.; Vigner, J. (1991). "Preparation characterization and crystal structure of chloryl hexafluororuthenate(1-). Crystal structure of [ClF
₂]⁺
[RuF
₆]⁻
". Inorganic Chemistry. 30 (1): 102–109. doi:10.1021/ic00001a019.
^ Brownstein, M.; Dean, P. A. W.; Gillespie, R. J. (1970). "The Trifluorosulphur(VI) Oxide Cation, SOF₃⁺". Journal of the Chemical Society D: Chemical Communications: 9. doi:10.1039/C29700000009.
^ Sundvall, Bengt (1983). "Crystal Structure of Tetraoxotetrahydroxohexabismuth (III) Perchlorate Heptahydrate, Bi₆O₄(HO)₄(ClO₄)6.7H₂O: An X-ray and Neutron Diffraction Study". Inorganic Chemistry. 22 (13): 1906–1912. doi:10.1021/ic00155a017.
^ Gatehouse, B. M.; Platts, S. N.; Williams, T. B. (1993). "Structure of Anhydrous Titanyl Sulfate, Titanyl Sulfate Monohydrate and Prediction of a New Structure". Acta Crystallographica Section B. 49 (3): 428–435. Bibcode:1993AcCrB..49..428G. doi:10.1107/S010876819201320X.
^ Sisler, Harry H. (1946). "Chromyl Chloride [Chromium(VI) Dioxychloride]". Inorganic Syntheses. Vol. 2. pp. 205–207. doi:10.1002/9780470132333.ch63. ISBN 9780470132333. {{cite book}}: ISBN / Date incompatibility (help)
^ Olah, George; Welch, John; Surya Prakash, G.; Ho, Tse-Lok (2002). "Synthetic Methods and Reactions; XXIV¹. Oxidative Cleavage of Hydrazones with Molybdenyl Chloride (MoOCl₃) or Molybdenum Hexafluoride and Reductive Cleavage of Oximes with Molybdenyl Chloride/Zinc". Synthesis. 1976 (12): 808–809. doi:10.1055/s-1976-24211.
^ Österreichische Chemiker-Zeitung (in German). Vol. 66. Springer. 1965. p. 52. Retrieved 21 May 2025.
^ ^a ^b Shanna L. Estes; Baofu Qiao; Geng Bang Jin (4 January 2019). "Ion association with tetra-n-alkylammonium cations stabilizes higher-oxidation-state neptunium dioxocations". Nature Communications. 10 (1): 59. Bibcode:2019NatCo..10...59E. doi:10.1038/S41467-018-07982-5. ISSN 2041-1723. PMC 6320366. PMID 30610189. Wikidata Q60920989.
^ Gunay, Ahmet; Theopold, Klaus H. (2010). "C−H Bond Activations by Metal Oxo Compounds". Chemical Reviews. 110 (2): 1060–1081. doi:10.1021/cr900269x. PMID 20143877.

[1] However, the International Union of Pure and Applied Chemistry standard book on nomenclature of inorganic chemistry does not mention "oxycation". Union internationale de chimie pure et appliquée, ed. (2005). Nomenclature of inorganic chemistry: IUPAC recommendations 2005 (PDF). Cambridge: Royal society of chemistry. ISBN 978-0-85404-438-2. Retrieved 2025-05-22.

[Kochi-2] Davlieva, Milya G.; Lindeman, Sergey V.; Neretin, Ivan S.; Kochi, Jay K. (2004). "Structural effects of carbon monoxide coordination to carbon centers. σ and π Bindings in aliphatic acyl versus aromatic aroyl cations". New Journal of Chemistry. 28 (12): 1568. doi:10.1039/B407654K.

[3] Boer, F. Peter (1968). "Crystal structure of a Friedel-Crafts intermediate. Methyloxocarbonium hexafluoroantimonate". Journal of the American Chemical Society. 90 (24): 6706–6710. doi:10.1021/ja01026a025.

[4] Bougon, R.; Cicha, W. V.; Lance, M.; Meublat, L.; Nierlich, M.; Vigner, J. (1991). "Preparation characterization and crystal structure of chloryl hexafluororuthenate(1-). Crystal structure of [ClF
₂]⁺
[RuF
₆]⁻
". Inorganic Chemistry. 30 (1): 102–109. doi:10.1021/ic00001a019.

[5] Brownstein, M.; Dean, P. A. W.; Gillespie, R. J. (1970). "The Trifluorosulphur(VI) Oxide Cation, SOF₃⁺". Journal of the Chemical Society D: Chemical Communications: 9. doi:10.1039/C29700000009.

[6] Sundvall, Bengt (1983). "Crystal Structure of Tetraoxotetrahydroxohexabismuth (III) Perchlorate Heptahydrate, Bi₆O₄(HO)₄(ClO₄)6.7H₂O: An X-ray and Neutron Diffraction Study". Inorganic Chemistry. 22 (13): 1906–1912. doi:10.1021/ic00155a017.

[7] Gatehouse, B. M.; Platts, S. N.; Williams, T. B. (1993). "Structure of Anhydrous Titanyl Sulfate, Titanyl Sulfate Monohydrate and Prediction of a New Structure". Acta Crystallographica Section B. 49 (3): 428–435. Bibcode:1993AcCrB..49..428G. doi:10.1107/S010876819201320X.

[Sis-8] Sisler, Harry H. (1946). "Chromyl Chloride [Chromium(VI) Dioxychloride]". Inorganic Syntheses. Vol. 2. pp. 205–207. doi:10.1002/9780470132333.ch63. ISBN 9780470132333. {{cite book}}: ISBN / Date incompatibility (help)

[9] Olah, George; Welch, John; Surya Prakash, G.; Ho, Tse-Lok (2002). "Synthetic Methods and Reactions; XXIV¹. Oxidative Cleavage of Hydrazones with Molybdenyl Chloride (MoOCl₃) or Molybdenum Hexafluoride and Reductive Cleavage of Oximes with Molybdenyl Chloride/Zinc". Synthesis. 1976 (12): 808–809. doi:10.1055/s-1976-24211.

[10] Österreichische Chemiker-Zeitung (in German). Vol. 66. Springer. 1965. p. 52. Retrieved 21 May 2025.

[Np-11] Shanna L. Estes; Baofu Qiao; Geng Bang Jin (4 January 2019). "Ion association with tetra-n-alkylammonium cations stabilizes higher-oxidation-state neptunium dioxocations". Nature Communications. 10 (1): 59. Bibcode:2019NatCo..10...59E. doi:10.1038/S41467-018-07982-5. ISSN 2041-1723. PMC 6320366. PMID 30610189. Wikidata Q60920989.

[12] Gunay, Ahmet; Theopold, Klaus H. (2010). "C−H Bond Activations by Metal Oxo Compounds". Chemical Reviews. 110 (2): 1060–1081. doi:10.1021/cr900269x. PMID 20143877.

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