Chlorosulfuric acid is a tetrahedral molecule. The formula is more descriptively written SO(OH)Cl, but HSOCl is traditional. It is an intermediate, chemically and conceptually, between sulfuryl chloride (SOCl) and sulfuric acid (HSO). The compound is rarely obtained pure.  Upon standing with excess sulfur trioxide, it decomposes to pyrosulfuryl chlorides:
:2 ClSOH + SO → HSO + SOCl