Pseudopolymorphs of 3,5-dinitrosalicylic acid

Abstract

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.