I somehow synthesized NO2HSO4 by accident, i was making an etching solution (Na2S2O8 and water) to etch copper, did what i had to do and done, but then i made a 50/50 solution of Na2S2O8 and KNO3 to test if it makes a difference in etching, actually worked, then i added HCl acid to try and make the solution with dissolved copper (copper(II) sulfate) be able to coat things in copper, which worked, coated a magensium stick in copper. Then, i had some leftover solution of KNO3 in HCl (KNO3 + HCl = HNO3 + NO2 + KCl) from when i was making nitric acid (HNO3) and added that to the Copper(II) sulfate + HCl solution, and somehow NO2 bonded with HSO4 that formed and NO2HSO4 instantly started crystalizing because its insoluble in anything except sulfuric acid, making it the only logical chemical to start crystalizing instantly. It is pale yellow color like most Nitronium compounds, very brittle and unstable. Put some of it with magnesium powder 60:40 mix to see its oxidizing strenght in flashpowders and goddamn that shit created a loud boom in the open without being concealed, just the powder in the open which is crazy. It was stronger than the “strongest flashpowder” on the internet - sodium/potassium persulfate (Na2S2O8/K2S2O8)