(Mn2O7), which forms by reaction of Mn with pure O2, reacts with water to form permanganic acid (HMnO4), which is as strong as perchloric acid (HCLO4).
All manganese species with oxidation states greater than +2 act as oxidizing agents, but the purple permanganese (MnO4-) ion is particularly powerful. like compounds with chromium in its highest oxidation state, MnO4- is a much stronger oxidizing agent in acidic than in basic solution