Poly[μ2-aqua-μ2-(pyrazine-2-carboxylato)-lithium]

The structure of the title compound, [Li(C5H3N2O2)(H2O)]n, contains an LiI ion with a distorted trigonal–bipyramidal coordination environment involving the N and O atoms of pyrazine-2-carboxylate ligands with a bridging carboxylate group, and two aqua O atoms also in a bridging mode. The symmetry-related LiI ions bridged by a carboxylate O atom and a coordinating water O atom form an Li2O2 unit with an Li⋯Li distance of 3.052 (4) Å, which generates molecular ribbons propagating in the c-axis direction. The ribbons are held together by a network of O—H⋯O hydrogen bonds in which the coordinating water molecules act as donors and the carboxylate O atoms as acceptors.

The structure of the title compound, [Li(C 5 H 3 N 2 O 2 )(H 2 O)] n , contains an Li I ion with a distorted trigonal-bipyramidal coordination environment involving the N and O atoms of pyrazine-2-carboxylate ligands with a bridging carboxylate group, and two aqua O atoms also in a bridging mode. The symmetry-related Li I ions bridged by a carboxylate O atom and a coordinating water O atom form an Li 2 O 2 unit with an LiÁ Á ÁLi distance of 3.052 (4) Å , which generates molecular ribbons propagating in the c-axis direction. The ribbons are held together by a network of O-HÁ Á ÁO hydrogen bonds in which the coordinating water molecules act as donors and the carboxylate O atoms as acceptors.
Experimental 50 mL of a solution containing 1 mmol of LiNO 3 and an excess of pyrazine-2-carboxylic acid dihydrate to mantain pH ca 5.1 was boiled under reflux with stirring for 10 h, then left to crystallise at room temperature. After a couple of days single-crystal blocks of the title compound were detected among polycrystalline material. They were washed with methanol and dried in the air.

Refinement
Water hydrogen atoms were located in a difference map and refined isotropically while H atoms attached to pyrazine-ring C atoms were positioned at calculated positions and were treated as riding on the parent atoms, with C-H=0.93 Å and U iso (H)=1.2U eq (C).

Figure 2
Packing diagram of the structure viewed along the c axis.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1 0.28627 (