Structure of 2,3-naphthalenedicarboxylic acid.

C12H8O4, M(r) = 216.20, monoclinic, C2/c, a = 5.087 (2), b = 19.222 (3), c = 9.552 (2) A, beta = 93.81 (3) degrees, V = 932.0 (5) A3, Z = 4, Dx = 1.54 g cm-3, lambda = 0.71073 A, mu = 1.09 cm-1, F(000) = 488, T = 295 K, R = 0.037 for 687 unique reflections having I > 3 sigma (I). In the structure reported here, a twofold axis lies in the plane of the molecule and bisects the three central ring bonds. The average C--C bond distance in the naphthalene core is 1.401 (27) A and the average interior angle 120.0 (14) degrees. The average deviation of the C atoms comprising the naphthalene rings from the best least-squares plane describing the rings is 0.021 (8) A. The plane of the single unique carboxylic acid group makes a dihedral angle of 33.1 (1) degrees with the least-squares plane of the naphthalene core. The carboxylic acid group, in which the observed O--H distance is 1.00 (3) A, forms a cyclic-dimer hydrogen bond across a center of inversion with the H...O(acceptor) distance 1.68 (3) A, the O...O-(acceptor) distance 2.676 (2) A and the O--H...O-(acceptor) angle 174 (3) degrees. The C--O bond lengths indicate no disorder in the carboxylic acid dimers. The molecules are arranged in stacks with the naphthalene cores parallel to the (102) plane and with the hydrogen bonds of the acid groups linking adjacent stacks. This structure of 2,3-naphthalenedicarboxylic acid is essentially the same as that of o-phthalic acid, but with the b cell edge correspondingly larger to accommodate the additional aromatic ring.