The tetrafluoroammonium cation (also known as perfluoroammonium) is a positively charged polyatomic ion with chemical formula NF+4.

These include the bifluoride anion (HF−2), tetrafluorobromate (BrF−4), metal pentafluorides (MF−5 where M is Ge, Sn, or Ti), hexafluorides (MF−6 where M is P, As, Sb, Bi, or Pt), heptafluorides (MF−7 where M is W, U, or Xe), octafluorides (XeF2−8),[2] various oxyfluorides (MF5O− where M is W or U; FSO−3, BrF4O−), and perchlorate (ClO−4).

[4] The geometry of the tetrafluoroammonium ion is tetrahedral, with an estimated nitrogen-fluorine bond length of 124 pm.

[5] Tetrafluoroammonium salts are prepared by oxidising nitrogen trifluoride with fluorine in the presence of a strong Lewis acid which acts as a fluoride ion acceptor.

The original synthesis by Tolberg, Rewick, Stringham, and Hill in 1966 employs antimony pentafluoride as the Lewis acid:[5] The hexafluoroarsenate salt was also prepared by a similar reaction with arsenic pentafluoride at 120 °C:[5] The reaction of nitrogen trifluoride with fluorine and boron trifluoride at 800 °C yields the tetrafluoroborate salt:[6] NF+4 salts can also be prepared by fluorination of NF3 with krypton difluoride (KrF2) and fluorides of the form MFn, where M is Sb, Nb, Pt, Ti, or B.