Poly[diammonium [(μ(4)-butane-1,2,3,4-tetra-carboxyl-ato)zincate] tetra-hydrate]

In the title compound, {(NH(4))(2)[Zn(C(8)H(6)O(8))]·4H(2)O}(n), the asymmetric unit contains one ammonium cation, half of a butane-1,2,3,4-tetra-carboxyl-ate anion, one Zn(2+) cation and two water mol-ecules. The butane-1,2,3,4-tetra-carboxyl-ate ligand is located about an inversion centre at the mid-point of the central C-C bond. The Zn(2+) cation is situated on a twofold rotation axis and is surrounded by four O atoms from four symmetry-related butane-1,2,3,4-tetra-carboxyl-ate anions in a distorted tetra-hedral environment. In turn, each anion coordinates to four Zn(2+) cations. The bridging mode of the anions leads to a three-dimensional framework structure with channels extending along [110] and [010] in which the ammonium cations and the water mol-ecules are located. N-H⋯O and O-H⋯O hydrogen bonding between the cations and water mol-ecules and the uncoordinating O atoms of the carboxyl-ate groups consolidates the crystal packing.