catena-Poly[[lithium-μ2-(di-hydrogen pyrazine-2,3,5,6-tetra-carboxyl-ato)-κ(6) O (2),N (1),O (6);O (3),N (4),O...

The title coordination polymer, {[Li2(C8H2N2O8)(H2O)2]·2.5H2O} n , is built up from mol-ecular ribbons propagating in the c-axis direction of the ortho-rhom-bic 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 mol-ecules. The coordination geometry of the metal ion is distorted trigonal bipyramidal, with the ligand O atoms in the axial sites. Two of the carboxyl-ate groups of the ligand remain protonated and form short symmetric O-H⋯O hydrogen bonds. In the crystal, the ribbons inter-act via a network of O-H⋯O hydrogen bonds in which coordinating water mol-ecules act as donors and carboxyl-ate O atoms within adjacent ribbons act as acceptors, giving rise to a three-dimensional framework. O-H⋯N inter-actions 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 mol-ecules have m2m site symmetry and both lattice water mol-ecules have m.. site symmetry; one of the latter was modelled with a site occupancy of 0.25.