In chemistry, the pentazenium cation (also known as pentanitrogen) is a positively-charged polyatomic ion with the chemical formula N+5 and structure N−N−N−N−N.

Together with solid nitrogen polymers and the azide anion, it is one of only three poly-nitrogen species obtained in bulk quantities.

Karl O. Christe, then, a senior investigator at AFRL, chose to attempt building linear N+5 out of N2F+ and N−3, based on the proposed bond structure:[1] The reaction succeeded, and [N5]+[AsF6]− was created in sufficient quantities to be fully characterized by NMR, IR and Raman spectroscopy in 1999.

[3] Actually N5+ had been predicted by ab initio calculations as a member of the dicyanamide isoelectronic series by Pyykkö and Runeberg in 1991 and this was quoted as ref.

Reaction of N2F+ and HN3 in dry HF at −78 °C is the only known method so far: N+5 is capable of oxidizing water, NO, NO2 and Br2, but not Cl2 or O2; its electron affinity is 10.44 eV (1018.4 kJ/mol).