Potassium 1,2,4,5-benzenetetracarboxylate, C6H2(CO2K)4�4H2O; its formation, crystal structure, and hydrogen bonding

From an aqueous mixture of 1,2,4,5-benzenetetracarboxylic acid, C6H2(CO2H)4, and KF we grew crystals first of KHF2 then of the title compound. An X-ray crystallographic determination of this compound shows a network of C6H2(CO 2 − )4 units linked through hydrogen bonds to water molecules. This is the first reported structure of a benzenecarboxylate anion. Two carboxylate groups are coplanar with the benzene ring, whereas the other two are perpendicular to it.