Wikipedia
Thiophosphoric acid
Thiophosphoric acid is a chemical compound. Structurally, it is the acid derived from phosphoric acid with one extra sulfur atom, although it cannot be prepared from phosphoric acid. It is a colorless compound that is rarely isolated in pure form, but rather as a solution. The structure of the compound has not been reported, but two tautomers are reasonable: SP(OH) and OP(OH)SH.