Poly[diaqua(μ2-3-carboxypyrazine2-carboxylato)(μ2-pyrazine-2,3-dicarboxylic acid)potassium(I)]

Abstract

The structural unit of the title compound, [K(C6H3N2O4)(C6H4N2O4)(H2O)(2)](n), consists of one potassium cation, one hydrogen pyrazine-2,3-dicarboxylate anion, one pyrazine-2,3dicarboxylic acid molecule and two water molecules; this is twice the asymmetric unit, since the potassium cation lies on an inversion centre. Each anion or acid molecule is linked to two potassium cations, while the potassium cation has contacts to four symmetry-equivalent organic ligands, with two different coordination modes towards this cation. In addition, each potassium cation is coordinated by two water O atoms, raising the coordination number to eight. One of the carboxyl groups of the acid retains its H atom, which forms a hydrogen bond to a coordinated water molecule. The other carboxyl group is deprotonated in half of the ligands and protonated in the other half, taking part in a strong O-H center dot center dot center dot O hydrogen bond disordered over an inversion centre. The stabilization of the crystal structure is further assisted by O-H center dot center dot center dot O and O-H center dot center dot center dot N hydrogen bonds in which water acts as the donor.