Further crystal structures for the substituted aspirin family of molecules: the first aspirin carboxylate catemer and a detailed assessment of the subtle influences of weak intermolecular interactions

Structural data on further examples of substituted acetylsalicylic acid (aspirin) derivatives have revealed additional recurring sub-structure relationships, and have enabled a detailed comparative assessment of the significant involvement of weak intermolecular interactions and shape-related packing features in the crystal structure assembly. Amongst the new structures reported, that of the 6-fluoroacetylysalicylic acid provides the first example of a carboxylate catemer structure in this series of compounds. The catemers are linked together by a number of C-H center dot center dot center dot O interactions and a C-H center dot center dot center dot F interaction. The former set includes the centrosymmetric acetyl dimer, first recognized in the structure of aspirin polymorph I.