1,4,5,8-naphthalenetetracarboxylic acid cyclic 1,8-anhydride bis(dimethyl sulfoxide) solvate and 1,4,5,8-naphthalenetetracarboxylic 1,8:4,5-dianhydride.

1,4,5,8-Naphthalenetetracarboxylic acid cyclic 1,8-anhydride crystallized from dimethyl sulfoxide (DMSO) as the solvate, C14H6O7.2C2H6OS, in the centrosymmetric space group P1. Two O-H...O hydrogen bonds with O...O distances of 2.592 (3) and 2.598 (3) A are formed, with the two carboxylic acid OH groups as donors and the O atoms of the two inequivalent DMSO molecules as acceptors. The carboxylic H atoms are ordered, as are the carboxylic O atoms. In addition to the conventional hydrogen bonds, there are numerous C-H...O interactions consistent with the large number of potential CH donors and O-atom acceptors. 1,4,5,8-Naphthalenetetracarboxylic 1,8:4,5-dianhydride, C14H4O6, crystallized in the centrosymmetric space group P2(1)/c with half the molecule as the asymmetric unit. Each molecule is involved in four significant C-H...O interactions as a donor and in an additional four as an acceptor. These eight interactions link each molecule to six neighboring molecules, forming a three-dimensional network. Geometric parameters of both substances are in general agreement with analogous parameters for naphthalic anhydride, monosodium 1,4,5,8-naphthalenetetracarboxylic acid cyclic 1,8-anhydride monohydrate and 1,4,5,8-naphthalenetetracarboxylic 1,8:4,5-dianhydride, as reported previously.