catena-Poly[[lithium-μ(2)-(di­hydrogen pyrazine-2,3,5,6-tetra­carboxyl­ato)-κ(6) O (2),N (1),O (6);O (3),N (4),O (5)-lithium-di-μ-aqua-κ(4) O:O] 2.5-hydrate]

The title coordination polymer, {[Li(2)(C(8)H(2)N(2)O(8))(H(2)O)(2)]·2.5H(2)O}(n), is built up from mol­ecular ribbons propagating in the c-axis direction of the ortho­rhom­bic unit cell; the ligand bridges two Li(+) ions using both its N,O,O′-bonding sites and adjacent Li(+) ions are bridged by pairs of water mol­ecules. The coordination geometry of the metal ion is distorted trigonal bipyramidal, with the ligand O atoms in the axial sites. Two of the carboxyl­ate groups of the ligand remain protonated and form short symmetric O—H⋯O hydrogen bonds. In the crystal, the ribbons inter­act via a network of O—H⋯O hydrogen bonds in which coordinating water mol­ecules act as donors and carboxyl­ate O atoms within adjacent ribbons act as acceptors, giving rise to a three-dimensional framework. O—H⋯N inter­actions are also observed. The asymmetric unit contains quarter of the ligand and the complete ligand has 2/m symmetry; the Li(+) ion lies on a special position with m.. site symmetry. Both bridging water mol­ecules have m2m site symmetry and both lattice water mol­ecules have m.. site symmetry; one of the latter was modelled with a site occupancy of 0.25.