Propane-1,3-diammonium bis­[aqua­chlorido(4-hydroxy­pyridine-2,6-di­carboxyl­ato-κ(3) O (2),N,O (6))mercurate(II)] tetra­hydrate

The reaction of mercury(II) chloride dihydrate, propane-1,3-diamine and 4-hydroxy­pyridine-2,6-dicarboxylic acid in a 1:1:1 molar ratio in aqueous solution, resulted in the formation of the title compound, (C(3)H(12)N(2))[Hg(C(7)H(3)NO(5))Cl(H(2)O)](2)·4H(2)O or (pnH(2))[Hg(hypydc)Cl(H(2)O)](2)·4H(2)O (where pn is propane-1,3-diamine and hypydcH(2) is 4-hydroxy­pyridine-2,6-dicarboxylic acid). The metal atom is coordinated by one chloride group, one water mol­ecule cis to the chloride ligand and one (hypydc)(2−) ligand. The coordinated water mol­ecule is almost perpendicular to the plane of the aromatic ring of (hypydc)(2−). The geometry of the resulting HgClNO(3) coordination can be described as distorted square-pyramidal. This structure also contains propane-1,3-diammonium (site symmetry 2) as a counter-ion and four uncoordinated water mol­ecules. There is a wide range of non-covalent inter­actions consisting of hydrogen bonding [of the types O—H⋯O, N—H⋯O and C—H⋯O, with D⋯A ranging from 2.548 (5) to 3.393 (6) Å] and ion pairing.