Pseudosymmetry in ammonium [(carboxymethyl)sulfanyl]acetate

The structure of the title compound, NH₄⁺·C₄H₅O₄S⁻, is composed of mono­carboxyl­ate anions of [(carboxymethyl)sulfanyl]acetic acid linked into infinite chains via strong O—H⋯O⁻ hydrogen bonds. The three‐dimensional structure is completed by the ammonium cations, which interlink neighbouring chains via N—H⋯O hydrogen bonds. Solution and refinement in the true space group Pn led to an unambiguous position for the single carboxyl H atom. In the higher symmetry space group P2/n, the carboxylate anion would be located on a twofold axis.