Kation '''pentazolium''' siklik ({{chem|N|5|+}}) tidak diketahui karena kemungkinan sifat antiaromatiknya;
sedangkan kation [[pentazenium]] yang berantai terbuka ({{chem|N|5|+}}) diketahui. Butler dkk. pertama membuktikan adanya siklik {{chem|N|5|-}} dalam larutan melalui penguraian aril pentazol tersubstitusi pada suhu rendah. Kehadiran {{chem|N|5|H|}} dan {{chem|N|5|-}} (ditahan dalam larutan melalui interaksi dengan ion seng) terbukti terutama menggunakan teknik produk penguraiandekomposisi <sup>15</sup>N NMR.<ref>{{Cite journal| url = http://www.rsc.org/delivery/_ArticleLinking/DisplayHTMLArticleforfree.cfm?JournalCode=CC&Year=2003&ManuscriptID=b301491f&Iss=8 | doi = 10.1039/b301491f| title = First generation of pentazole (HN5, pentazolic acid), the final azole, and a zinc pentazolate salt in solution: A new N-dearylation of 1-(p-methoxyphenyl) pyrazoles, a 2-(p-methoxyphenyl) tetrazole and application of the methodology to 1-(p-methoxyphenyl) pentazole | journal = Chemical Communications| issue = 8| pages = 1016| year = 2003| last1 = Butler| first1 = R. N.| last2 = Stephens| first2 = John C.| last3 = Burke| first3 = Luke A.}}</ref> Hasil ini awalnya ditantang oleh beberapa penulis,<ref>{{cite journal|vauthors=Schroer T, HaigesR, Schneider S, Christe KO|title=The race for the first generation of the pentazolate anion in solution is far from over|journal=Chemical Communications|date=2004-12-31|issue=12|pages=1607|doi=10.1039/B417010E}}</ref> namun percobaan-percobaan selanjutnya yang melibatkan analisis terperinci mengenai produk dekomposisi, yang dilengkapi dengan studi komputasi, menyokong kesimpulan awal.<ref>{{cite journal|vauthors=Butler RN, Hanniffy JM, Stephens JC, Burke LA |title=A Ceric Ammonium Nitrate N-Dearylation of N-p-Anisylazoles Applied to Pyrazole, Triazole, Tetrazole, and Pentazole Rings: Release of Parent Azoles. Generation of Unstable Pentazole, HN5/N5-, in Solution|journal=The Journal of Organic Chemistry|date=2008-01-31|volume=73|issue=4|pages=1354–1364|doi=10.1021/jo702423z|pmid=18198892}}</ref><ref>{{cite journal|vauthors=Perera SA, Gregusová A, Bartlett RJ |title=First Calculations of 15N−15N J Values and New Calculations of Chemical Shifts for High Nitrogen Systems: A Comment on the Long Search for HN5 and Its Pentazole Anion|journal=The Journal of Physical Chemistry A|date=2009-04-01|volume=113|issue=13|pages=3197–3201|doi=10.1021/jp809267y|pmid=19271757}}</ref><ref>{{cite news | url = http://www.irishtimes.com/news/science/galway-discovery-ahead-of-the-world-1.718468 | title = Galway discovery ahead of the world | publisher = The Irish Times | date = Aug 13, 2009}}</ref>
