ike the other noble gases, krypton is highly chemically unreactive. However, following the first successful synthesis of xenon compounds in 1962, synthesis of krypton difluoride (KrF
2) was reported in 1963. In fact, before the 1960s, no noble gas compounds had been discovered.[19] Under extreme conditions, krypton reacts with fluorine to form KrF2 according to the following equation:
Kr + F2 → KrF2
In the same year, KrF
4 was reported by Grosse, et al.,[20] but was subsequently shown to be a mistaken identification.[21] There are also unverified reports of a barium salt of a krypton oxoacid.[22] ArKr+ and KrH+ polyatomic ions have been investigated and there is evidence for KrXe or KrXe+.[23]
Compounds with krypton bonded to atoms other than fluorine have also been discovered. The reaction of KrF
2 with B(OTeF
5)
3 produces an unstable compound, Kr(OTeF
5)
2, that contains a krypton-oxygen bond. A krypton-nitrogen bond is found in the cation [HC≡N–Kr–F]+
, produced by the reaction of KrF
2 with [HC≡NH]+
[AsF−
6] below −50 °C.[24][25] HKrCN and HKrC≡CH (krypton hydride-cyanide and hydrokryptoacetylene) were reported to be stable up to 40 K.[19]