Bis(3-azoniapentane-1,5-diaminium) cyclo­hexa­phosphate dihydrate: a monoclinic polymorph

In the title hydrated mol­ecular salt, 2C(4)H(16)N(3) (3+)·P(6)O(18) (6−)·2H(2)O, the complete cyclo­hexa­phosphate anion is generated by crystallographic inversion symmetry. The six P atoms of the P(6)O(18) (6−) anion form a chair conformation and the organic cation has a corrugated linear geometry. In the crystal, the cations and the anions are connected by N—H⋯O hydrogen bonds into slabs propagating in the ac plane. The water mol­ecules link the slabs by accepting N—H⋯O links and forming O—H⋯O links. The triclinic polymorph was reported by Gharbi et al. [(1995). J. Solid State Chem. 114, 42–51].