Density functional and X-ray diffraction studies of bis(isocinchomeronic acid) trihydrated

Crystal structure of bis(isocinchomeronic acid) trihydrated [bis(2,5-pyridinedicarboxylic acid) trihydrated] has been solved by X-ray diffraction. The crystals are monoclinic, space group C2/c, with a = 17.610(5) Å, b = 7.300(4) Å, c = 14.210(2) Å, β = 116.410(13)°, Z = 4 and R = 0.0489. The molecules crystallize in the zwitterionic form, with one of the carboxylic groups deprotonated and the pyridine nitrogen protonated. The molecules are strongly linked in chains by hydrogen bonds, involving the carboxylic/carboxylate groups and the chains are also linked by hydrogen bonds via interchains water molecules. A calculation was performed for the dimer using density functional theory at the B3LYP/631++G(d,p) level. The calculated geometry results in almost planar molecules linked by strong hydrogen bonds. Molecular mechanic studies confirmed the importance of the hydrogen bonds in the maintenance of the crystal structure.