title: 2-Amino-5-(4-carboxyl-atophen-yl)-pyridinium monohydrate.
abstract: The title compound, C(12)H(10)N(2)O(2)·H(2)O, crystallizes as a zwitterion in which the pyridine N atom is protonated and the carb-oxy -OH group is deprotonated. The benzene and pyridinium rings are inclined with a dihedral angle of 6.63 (5)° between them. In the crystal, inter-molecular O-H⋯O and N-H⋯O hydrogen-bonding inter-actions link adjacent mol-ecules into a two-dimensional double layered supra-molecular network.
authors.affiliation: College of Mechanical and Materials Engineering, China Three Gorges University, Yichang 443002,  People's Republic of China.
authors.forename: Xiao-Hong
authors.initials: XH
authors.lastname: Wei
authors.forename: Hong
authors.initials: H
authors.lastname: Yan
authors.forename: Wei-Gong
authors.initials: WG
authors.lastname: Lin