The fluorosulfates or fluorosulfonates are a set of salts of fluorosulfuric acid with an ion formula SO3F−. The flurosulfate anion can be teated as though it was a hydrogen sulfate anion with hydroxyl substituted with fluorine. The fluorosulfate ion has a low propensity for form complexes with the metal cation. Since fluorine is similar in size to oxygen the fluorosulfate ion is roughly tetrahedral and forms salts similar to those of perchlorate. When an organic group is substituted for the anions, organic fluorosulfonates are formed.
In solution the fluorosulfate anion is completely ionised. The volume is 47.8 cm3/mol. Nearly every metal ion and quaternary ammonium ions can form a salt with flourosulfate. Different ways to make these salts include treating a metal chloride with anhydrous fluorosulfuric acid which releases hydrogen chloride gas. Double decomposition methods with a metal sulfate with barium fluorosulfate, or a metal chloride with silver fluorosulfate, leave the metal salt in solution.
Related ionic compounds are the fluoroselenites SeO3F− and the fluorosulfites SO2F−.