title: 4-Amino-pyridinium-3-sulfonate monohydrate.
abstract: The reaction of 4-amino-pyridine and oleum yielded the title hydrated zwitterion, C(5)H(6)N(2)O(3)S·H(2)O. There are two formula units in the asymmetric unit. The H and non-H atoms of both zwitterions lie on a mirror plane except for one sulfonate O atom. The water mol-ecules are also situated on a mirror plane. In the crystal, the zwitterions and water mol-ecules are linked by O-H⋯O and N-H⋯O hydrogen bonds, generating a three-dimensional network.
authors.forename: Zhi-Biao
authors.initials: ZB
authors.lastname: Zhu
authors.forename: Shan
authors.initials: S
authors.lastname: Gao
authors.forename: Seik Weng
authors.initials: SW
authors.lastname: Ng