Poly[aqua(μ-pyrazine-2-carboxylato-κ3 N,O:O)(μ-pyrazine-2-carboxylato-κ3 N,O:O′)lead(II)]

The polymeric structure of the title compound, [Pb(C5H3N2O2)2(H2O)]n, is built up from centrosymmetric [Pb(C5H3N2O2)2(H2O)]2 dimers, which are bridged by ligand carboxylate O atoms. The PbII ion adopts an irregular PbN2O5 coordination polyhedron; it is chelated by one N,O-bidentate ligand and also bonds to a water O atom. A second N,O-bidentate ligand forms the dimer bridge and another bridging O atom from a nearby dimer also bonds to the PbII ion, leading to layers propagating in (100). A network of O—H⋯O hydrogen bonds operates between water O atoms (donors) and carboxylate O atoms (acceptors).

The polymeric structure of the title compound, [Pb(C 5

Experimental
The title compound was synthetized by reacting boiling aqueous solution of pyrazine-2-carboxylic acid dihydrate (Aldrich) with some excess of lead(II) hydroxide. The mixture was boiled under reflux for three hours and after cooling to room temperature, filtered and left for crystallization. Few days later, colourless blocks of (I) were found after evaporation to dryness. They were extracted, washed with cold ethanol and dried in the air.

Refinement
Water hydrogen atoms were found from Fourier maps and restrained geometrically to form hydrogen bonds. H atoms attached to pyrazine -ring C atoms were positioned geometrically and refined with a riding model. A maximum peak of 6.450 e Å 3 (at 0.83 Å) and a deepest hole of -5.858 e Å 3 (at 0.80 Å) were found on the final electron density map close to the Pb1 atom.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 Rfactors(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.