Pseudopolymorphs of 3,5-dinitrosalicylic acid

Seven pseudopolymorphs of 3,5-dinitrosalicylic acid are studied. Four of these (A-D) are obtained from dioxane and their formation is rationalised on the basis of simultaneous O-H … O and C-H … O bond formation between the donor-rich solute molecule and the multiple-acceptor solvent. A fifth (E) is a previously reported centrosymmetric hydrate. The sixth and seventh (F and G) are a non-centrosymmetric hydrate and a tert-butyl alcoholate whose structures are related to that of form E, in that hydrogen bonds are both donated and accepted between solute and solvent. The formation of this rich diversity of pseudopolymorphs with hydrogen bonding solvents follows from the nature of the title acid while the similarities between the structures of the pseudopolymorphs may be accounted for in terms of a permutation of a small number of solute-solvent supramolecular synthons. All this indicates that this interesting phenomenon may be both anticipated and also studied systematically. The scope of the term pseudopolymorph has been extended a little, in the expectation that such a definition would be of more general utility

Crystal structures and packing of 4-cyanocubanecarboxylic acid, its methyl ester, and the solid solution of 1,4-dicyanocubane and 1,4-dibromocubane

The crystal structure of 4-cyanocubanecarboxylic acid contains the same syn-anti carboxyl group catemer that is found in other cubane monocarboxylic acids. The cyano groups are arranged according to the type-II geometry, in that they are 21 screw-axis related. Curiously, there is a 5% orientational disorder of the cyano and anti carboxyl groups. The ester of the title acid packs isostructurally with the corresponding chloro and fluoro analogs because of the importance of the C-H…O hydrogen bond patterns. 1,4-Dicyanocubane forms solid solutions with 1,4-dibromocubane, but, interestingly, the crystal structure of the solid solution is distinct from that of either component. The formation of these solid solutions seems to be governed by shape and size factors

Cubanecarboxylic acids. crystal engineering considerations and the role of C-H···O hydrogen bonds in determining O-H···O networks

A family of 4-substituted-1-cubanecarboxylic acids have been synthesized and their X-ray crystal structures analyzed. The rare syn-anti O-H...O catemer 6 is a recurring pattern in this series of compounds. Catemer 6 is observed in the crystal structures of 4-chloro-1-cubanecarboxylic acid (10), 4-bromo-1-cubanecarboxylic acid (11), 4-iodo-1-cubanecarboxylic acid (12), and 4-(methoxycarbonyl)-1-cubanecarboxylic acid (13). The ready occurrence of catemer 6 in this family is ascribed to its stabilization by auxiliary C-H···O hydrogen bonds formed by the relatively acidic cubyl C-H groups. The frequency of occurrence of 6 also facilitates its definition as a useful supramolecular synthon. As is true in many catemers, the formation of 6 is sensitive to steric factors. Therefore, the robustness of this synthon may be assessed by analyzing the crystal structures of molecules wherein the 4-substituent is too small (R = H, 14), too large (R = Ph, 15), or has a specific hydrogen bonding preference of its own (R = CONH2, 16). In these structures, either dimer 3 (in 14 and 15) or heterodimer 22 (in 16) is observed. Powder diffraction shows that the previously noted structure of 1,4-cubanedicarboxylic acid (7) that contains catemer 6 is characteristic of the bulk material. In summary, the syn-anti catemer is the dominant supramolecular synthon in this family of cubanecarboxylic acids