Three-dimensional supramolecular architecture based on 4,4′-methylene-bis(benzenamine) and aromatic carboxylic acid guests: Synthons cooperation, robust motifs and structural diversity

Abstract

The two-component solid forms involving 4,4′-methylene-bis(benzenamine) included both salts and co-crystals, while 4,4′-methylene-bis(benzenamine) crystallized exclusively as a salt, in agreement with the differences in the pKa values. Many of the crystal structures displayed either the neutral or the ionic form of the carboxylic acid-amino heterosynthon, and the similarity in crystal structures between the neutral and the ionized molecules makes the visual distinction between a salt and co-crystal dependent on the experimental location of the acidic proton. A variety of supramolecular hydrogen bonded motifs involving interactions between the aza molecules and carboxylic acid groups are observed rather than just the O-H…N/O-H…O motif. The motifs are identical in all the two compounds analyzed showing the robustness of these supramolecular synthons. In all adducts, recognition between the constituents is established through either N-H…O and/or O-H…O/O-H…N pairwise hydrogen bonds. In all adducts, COOH functional groups available on 1 and 2 interact with the N-donor compounds. The COOH moieties in 1 forms only single N-H…O hydrogen bonds, whereas in 2, it forms pairwise O-H…N/N-H…O hydrogen bonds. The supramolecular architectures are elegant and simple, with stacking of networks in 2, but a rather complex network with a threefold interpenetration pattern was found in 1. Thermal stability of these compounds has been investigated by thermogravimetric analysis (TGA) of mass loss.