catena-Poly[[diaquarubidium(I)](mu(2)-3-carboxypyrazine-2-carboxylato)(mu(2)-pyrazine-2,3-dicarboxylic acid)]

Abstract

The structural unit of the title compound, [Rb(C6H3N2O4)-(C6H4N2O4)(H2O)(2)](n), consists of one rubidium cation, one hydrogen pyrazine-2,3-dicarboxylate anion, one pyrazine-2,3-dicarboxylic acid molecule and two water molecules. This formulation is repeated twice in the asymmetric unit as the rubidium cation lies on an inversion centre. Each anion or acid molecule is linked to two rubidium cations, while the rubidium cation has close contacts to four symmetry-equivalent organic ligands, with two different coordination modes towards this cation. In addition, each rubidium cation is coordinated by two water O atoms, raising the coordination number to eight. One of the carboxyl groups of the acid holds 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-bonding interactions involving the water molecules and carboxylate O atoms.