Chirality recognition in solvent‐free solid‐state crystallization: Chiral adduct formation by bis‐β‐naphthol derivatives and benzoquinone crystals

Abstract

New adduct crystals were obtained by simply mixing/grinding component crystals of bis-beta-naphthol (BN) derivatives with benzoquinone (BQ) under solvent-free conditions. Chiral recognition was found to operate during this process and either a racemic or a chiral crystal of a BN derivative produced an adduct crystal with BQ by solid-state crystallization. The chirality preference changed subtly according to the molecular structure of the BN derivative. Even in circumstances in which no adduct was formed, addition of a third component, such as crystals of naphthalene, to the grinding mixture yielded an adduct crystal. Remarkably, these adduct crystals were found to decompose spontaneously with time and revert to the starting crystal of the BN derivative by losing BQ molecules from the crystal lattice. Local melting of crystals by the grinding pressure was found unlikely to be the mechanism of adduct formation. Overall, these results demonstrate that molecules in the solid state could change their relative location and hydrogen bonding partners, thereby exerting chiral discrimination.

Molecular recognition in solid‐state crystallization: Colored chiral adduct formations of 1,1′‐Bi‐2‐naphthol derivatives and benzoquinone with a third component

“…Cluster 2a has 16 excited states in the plotted energy range; eight locally excited states of diBr-BN due to the p ® p à transitions (marked with + in the figure), two locally excited states of BQ due to the n ® p à transitions (marked with à ), and six excited states of a CT type due to electronic transitions from the p orbitals on the diBr-BN to the p à orbital on the BQ (marked with #). As suggested from the experimental observation, low-lying CT states are created in cluster 2a; indeed, electrons transfer from diBr-BN(l) or diBr-BN (2) to the BQ in the ®rst (3.19 eV) and second (3.37 eV) CT states, respectively. Their energy difference is understandable from the fact that diBr-BN(l) stacks with BQ more closely than diBr-BN(2) (Fig.…”

“…We have obtained the same adduct crystal from a (1:1) ether/hexane solution and reported the crystal structure. 2 In contrast, when white crystals of biphenyl were ground with a mixture of (R)-BN and BQ in an agate mortar the color of the powder changed only slightly, to gray. Its X-ray powder diffraction patterns recorded, after 60-min grinding, did not reveal the formation of a new crystal.…”

“…A triplet structure similar to this is often observed in adduct crystals containing BN and BQ. 2,3 These three aromatic planes are quite parallel to each other (with the dihedral angles between the BQ and the stacking 6-membered ring of a 6,6¢-diBr-BN in the triplet structure being 3.1 and 2.3°) and the overlaps of aromatic rings are substantial. The distances between the stacking aromatic planes are 3.528 and 3.404 A Ê .…”

“…1 We have recently reported an interesting colorful adduct crystal formation by simple mixing/grinding of 1,1¢-bi-2-naphthol (BN) or its derivatives with benzoquinone (BQ). 2,3 The adduct of racemic BN and BQ displayed an interesting polymorphism: crystals obtained from solution, solid grinding, and melt are all different. Chirality plays an important role in adduct formation and only the racemic BN crystals, but not its enantiopure crystals, form adduct crystals.…”

Benefits of cocrystallisation in pharmaceutical materials science: an update

“…(naphthalene) 3 cocrystal. The direction of propagation of the helical chain is indicated by the arrow [85,86] …”