Tetrafluoroammonium ion

Exception The name ammonium is retained for the NHf ion similarly for substituted ammonium ions for example, NFJ, tetrafluoroammonium ion. 

The terms tetrafluoroammonium, perfluoroammonium, tetra-fluoronitrogen(V), and tetrafluoronitronium have been used to describe NF4+. Most authors prefer to call this the tetrafluoroammonium ion. The polarity of the bond is NF4+ is different from that in NH4+ for NF4+ the nitrogen atom has a formal oxidation state of +5. NF4+ salts are important for solid propellant NF3-F2 gas generators or reagents for the electrophilic fluorination of aromatic compounds. 

Two independent groups were responsible for the original discovery of tetrafluoroammonium salts, both basing the synthesis on the reaction of NFj with fluorine in the presence of a strong Lewis acid, which acts as a fluoride ion acceptor ... 

The same principle was used in preparing the compounds NF4UF7 and NF4WF7 from the hexafluorides UF6 and WF6, both of which are weak Lewis acids with only a moderate tendency to form the MF7 ion. It is for this reason that the two tetrafluoroammonium salts cannot be made by direct synthesis from NF3, F2, and the Lewis acid, or indirectly by a metathetical reaction in AHF solution. Repeated treatment of NH4HF2 with the hexafluoride, accompanied by removal of the AHF set free, as in the synthesis of (NF4)2SiF6, did, however, give the required compounds (297) (where X = U, W) ... 

---