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Nitronium ion
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<h2 id="structure">Structure</h2> <p>The nitronium ion is <a href="/facts/Isoelectronicity/SbzuaI05">isoelectronic</a> with <a href="/facts/Carbon_dioxide/xGzpppEp">carbon dioxide</a> and has the same linear structure and bond angle of 180°. For this reason it has a similar vibrational spectrum to carbon dioxide. Historically, the nitronium ion was detected by <a href="/facts/Raman_spectroscopy/XY063k29">Raman spectroscopy</a>, because its symmetric stretch is Raman-active but infrared-inactive. The Raman-active symmetrical stretch was first used to identify the ion in nitrating mixtures.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p> <h2 id="salts">Salts</h2> <p>A few stable nitronium salts with anions of weak <a href="/facts/Nucleophile/xYccoaJQ">nucleophilicity</a> can be isolated. These include <a href="/facts/Nitronium_perchlorate/0rbP8S2I">nitronium perchlorate</a> [NO2]+[ClO4]−, <a href="/facts/Nitronium_tetrafluoroborate/jRGRlxxm">nitronium tetrafluoroborate</a> [NO2]+[BF4]−, nitronium <a href="/facts/Hexafluorophosphate/mXYXC2Bf">hexafluorophosphate</a> [NO2]+[PF6]−, nitronium <a href="/facts/Hexafluoroarsenate/ukLLApQv">hexafluoroarsenate</a> [NO2]+[AsF6]−, and nitronium <a href="/facts/Fluoroantimonic_acid/HfSxCACr">hexafluoroantimonate</a> [NO2]+[SbF6]−. These are all very <a href="/facts/Hygroscopic/1NBGewXv">hygroscopic</a> compounds.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p><p>The solid form of <a href="/facts/Dinitrogen_pentoxide/2uAxoRpM">dinitrogen pentoxide</a>, N2O5, actually consists of nitronium and <a href="/facts/Nitrate/5AnVlYnL">nitrate</a> ions, so it is an <a href="/facts/Ionic_compound/jB9nMfrE">ionic compound</a>, nitronium nitrate [NO2]+[NO3]−, not a <a href="/facts/Molecular_solid/X952jWbq">molecular solid</a>. However, dinitrogen pentoxide in <a href="/facts/Liquid/t9GkLWzt">liquid</a> or <a href="/facts/Gas/hVVAoodV">gaseous</a> state is <a href="/facts/Molecule/N9ljSfFq">molecular</a> and does not contain nitronium ions.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a><a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p> <h2 id="related-species">Related species</h2> <p>The compounds <a href="/facts/Nitryl_fluoride/q7xYXaGm">nitryl fluoride</a>, NO2F, and <a href="/facts/Nitryl_chloride/Y1XbBTdf">nitryl chloride</a>, NO2Cl, are not nitronium salts but molecular compounds, as shown by their low boiling points (−72 °C and −6 °C respectively) and short nitrogen–halogen bond lengths (N–F 135 pm, N–Cl 184 pm).<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p><p>Addition of one electron forms the neutral <a href="/facts/Nitryl/WxMpo3zm">nitryl</a> <a href="/facts/Radical_(chemistry)/qFymuVoT">radical</a>, NO2•; in fact, this is fairly stable and known as the compound <a href="/facts/Nitrogen_dioxide/FoLvApPI">nitrogen dioxide</a>. </p><p>The related negatively charged species is NO−2, the <a href="/facts/Nitrite/qkz2XScK">nitrite</a> ion. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Nitrosonium/zmRlEu1k">Nitrosonium</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="978-0-08-037941-8" target="_blank">978-0-08-037941-8</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Ingold, C. K.; Millen, D. J.; Poole, H. G. (1946). "Spectroscopic Identification of the Nitronium Ion". Nature. 158 (4014): 480–481. Bibcode:1946Natur.158..480I. doi:10.1038/158480c0. S2CID 4106964. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Kenneth Schofield (1980). Aromatic nitration. CUP Archive. p. 88. ISBN 0-521-23362-3. <a href="0-521-23362-3" target="_blank">0-521-23362-3</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. <a href="978-0-08-037941-8" target="_blank">978-0-08-037941-8</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Cantrell, C. A.; Davidson, J. A.; McDaniel, A. H.; Shetter, R. E.; Calvert, J. G. (1988). "The equilibrium constant for N2O5⇄NO2+NO3: Absolute determination by direct measurement from 243 to 397 K". The Journal of Chemical Physics. 88 (8): 4997–5006. doi:10.1063/1.454679. <a href="https://aip.scitation.org/doi/10.1063/1.454679" target="_blank">https://aip.scitation.org/doi/10.1063/1.454679</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>F. A. Cotton and G.Wilkinson, Advanced Inorganic Chemistry, 5th edition (1988), Wiley, p.333 <a href="/wiki/F._Albert_Cotton" target="_blank">/wiki/F._Albert_Cotton</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> </ol>