STRUCTURES OF 1,2,3,4-BENZENETETRACARBOXYLIC ACID AND 1,2,3,5-BENZENETETRACARBOXYLIC ACID DIHYDRATE

1,2,3,4-Benzenetetracarboxylic acid (compound A): C10H6O8, M(r) = 254.2, triclinic, P1BAR, a = 9.5616 (1), b = 8.4696 (1), c = 7.0568 (1) angstrom, alpha = 106.806 (1), beta = 100.192 (1), gamma = 69.557 (1)degrees, V = 510.77 (1) angstrom3, Z = 2, D(x) = 1.65 g cm-3, lambda(Mo Kalpha) = 0.71073 angstrom, mu = 1.39 cm-1, F(000) = 260, T = 293 K, final conventional R = 0.036, wR = 0.039 for 1699 'observed' reflections and 187 variables. 1,2,3,5-Benzenetetracarboxylic acid dihydrate (compound B), C10H6O8.2H2O, M(r) = 290.2, triclinic, P1BAR, a = 5.845 (4), b = 7.828 (6), c = 13.31 (1) angstrom, alpha = 94.8 (1), beta = 100.6 (1), gamma = 93.63 (9)degrees, V = 594.6 (9) angstrom3, Z = 2, D(x) = 1.62 g cm-3, lambda(Mo Kalpha) = 0.71073 angstrom, mu = 1.41 cm-1, F(000) = 300, T = 293 K, final conventional R = 0.070, wR = 0.072 for 2354 'observed' reflections and 221 variables. The molecules in both structures are associated through their carboxylic groups forming a network of hydrogen bonds including water molecules in B. The molecules, O atoms excluded, are essentially planar in both compounds. The benzene rings show a week distortion towards a half-chair conformation for compound A and towards a slightly twisted boat conformation for B. The angles between the planes of the carboxyl groups and the least-squares plane of the C atoms of the ring are respectively 2.5 (2), 82.8 (1), 72.7 (1) and 14.7 (1)degrees for compound A, and 6.6 (3), 85.6 (3), 4.0 (3) and 5.8 (3)degrees for B.