Peroxynitrate (or peroxonitrate) refers to salts of the unstable peroxynitric acid, HNO4. Peroxynitrate is unstable and decomposes to nitrate and dioxygen.
No solid peroxynitrate salts are known. However, there is a report that the chemist Sebastian Moiseevich Tanatar produced sodium peroxynitrate octahydrate (NaNO3·H2O2·8H2O) by evaporating a solution of sodium nitrate and hydrogen peroxide until crystallisation begins and then mixing with alcohol to form crystals of the octahydrate.
References
Miyamoto, Sayuri; Ronsein, Graziella E.; Corrêa, Thaís C.; Martinez, Glaucia R.; Medeiros, Marisa H. G.; Di Mascio, Paolo (2009). "Direct evidence of singlet molecular oxygen generation from peroxynitrate, a decomposition product of peroxynitrite". Dalton Transactions (29): 5720–5729. doi:10.1039/b905560f. ISSN 1477-9226. PMID 20449086. https://dx.doi.org/10.1039/b905560f ↩
Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. 978-0-08-037941-8 ↩
Mellor, Joseph William (1922). A Comprehensive Treatise on Inorganic and Theoretical Chemistry, Volume 2. New York: Longmans, Green and Co. p. 816. /wiki/Joseph_Mellor ↩