title: Piperazine-1,4-diium bis-(hydrogen 2-propyl-1H-imidazole-4,5-dicarbox-ylate) monohydrate.
abstract: The title compound, C(4)H(12)N(2) (2+)·2C(8)H(9)N(2)O(4) (-)·H(2)O, is a hydrated proton-transfer compound obtained from 2-propyl-1H-imidazole-4,5-dicarb-oxy-lic acid and piperazine. The asymmetric unit contains one half-cation, one anion and half a water mol-ecule. There is a centre of inversion at the centre of the cation ring and the water molecule O atom lies on a twofold rotation axis. In the crystal, inter-molecular N-H⋯O and N-H⋯N hydrogen bonds help to construct a three-dimensional framework. Almost symmetrical, intramolecular O-H⋯O inter-actions are also observed.
authors.forename: Zhu-Qing
authors.initials: ZQ
authors.lastname: Gao
authors.forename: Jin-Zhong
authors.initials: JZ
authors.lastname: Gu