title: 3,3'-(Piperazine-1,4-diium-1,4-di-yl)di-propionate dihydrate.
abstract: During the recrystallization of 3-[4-(2-carb-oxy-eth-yl)piperazin-1-yl]propionic acid, the carb-oxy-lic acid H atoms were transferred to the piperazine N atoms, forming the title compound, C(10)H(18)N(2)O(4)·2H(2)O, in which the zwitterion lies about an inversion center. In the crystal, bifurcated N-H⋯(O,O) hydrogen bonds connect the zwitterions into a two-dimensional framework parallel to (-102) forming R(4) (4)(30) rings. O-H⋯O hydrogen bonds involving the solvent water mol-ecules connect the two-dimensional framework into a three-dimensional network. In addition, weak C-H⋯O hydrogen bonds are observed.
authors.affiliation: Tianmu College of ZheJiang A & F University, Lin'An 311300,  People's Republic of China.
authors.forename: Shouwen
authors.initials: S
authors.lastname: Jin
authors.forename: Yanfei
authors.initials: Y
authors.lastname: Huang
authors.forename: Hao
authors.initials: H
authors.lastname: Fang
authors.forename: Tianyi
authors.initials: T
authors.lastname: Wang
authors.forename: Liangliang
authors.initials: L
authors.lastname: Ding