Complexes Between 1,1′-Binaphthyl-2,2′-Dicarboxylic Acid and Pyrazoles: A Case of Manual Sorting of Conglomerate Crystals (Triage)

Spontaneous resolution under supramolecular control

“…However, the salt-type complex of 10 with 3,5-dimethylpyrazole (11) spontaneously resolves upon crystallisation. 16 The 1+1 complex is formed by a carboxylate anion and a pyrazolium cation linked by an [ + N-H…O 2 ], [ + N-H…O] and [O-H…O 2 ] hydrogen bonds as well as [C-H…O] interactions in a cyclic arrangement, leading to the formation of chains of the same configuration, i.e., each crystal is formed by only on enantiomer of 10 (Fig. 6).…”

“…The spontaneous resolution of the 1+1 complex of 10 with 11 into a conglomerate constitutes a unique example amongst many complexes reported for the bis-acid. 16 Chiral crystals can also be formed by co-crystallisation of two achiral molecules. For example, self-assembly of an achiral molecule in a chiral conformation and another achiral molecule was achieved through a combination of hydrogen bonding and ionic interactions in a series of 12 carboxylic acids and achiral bases.…”

Stereochemistry and Twisted Crystals

“…While we will see examples of inorganic materials whose chiral growth has been probed using electron microscopy, the situation for organic materials often remains very challenging. For mixtures of enantiomers of molecular compounds, triage of enantiomorphic crystals has been used for their separation [7,8] but easier ways of making chiral materials exist. The separation of enantiomers by other means (such as chromatography) leads to chiral building blocks that can be used to induce homochirality in crystallization, [9] for example in the remarkable Viedma ripening.…”

Protonation-assisted spontaneous resolution: formation of a homochiral 2D interpenetrated hydrogen-bonded network from 4,4′-binicotinic acid under highly acidic conditions

“…8 A different theoretical study, however, predicted significant discrimination energies favoring homochiral interactions between molecules with permanent electric dipoles locked in a crystalline environment. 9 Recent structural studies 10,11 have also indicated that hydrogen bonding, including weak CH … O interactions, 12 may play an important role in the homochiral recognition in supramolecular aggregates. Guest inclusion 13 or cocrystallization 14 were also found to induce spontaneous resolution in some cases.…”