Crystal Structure of Anthracen-9-yl(3,6-dimethoxynaphthalen-2-yl)methanone: Decisive Factors for Formation of Two-Fold Helical Molecular Assemblies in Three Directions Affording Chiral Crystal

Abstract

Anthracen-9-yl(3,6-dimethoxynaphthalen-2-yl)methanone (III), affords chiral crystals belonging to P2₁2₁2₁ space group. To investigate the decisive factors of chiral supramolecular crystallisation, the crystal structural characteristics of compound III were compared with the those of two 3-aroylated 2,7-dimethoxynaphthalene homologues, the 3-benzoylated (I) and 3-(1-naphthoylated) (II) derivatives, and those of their mother skeleton molecule, 2,7-dimethoxynaphthalene. The two homologues yielded achiral crystals in P2₁/c space group and the mother skeleton afforded chiral crystal in P2₁2₁2₁ space group. The spatial features of the single molecular structure, molecular accumulation, non-covalent bonding interactions, and proximity of molecules in crystal were analysed for the four compounds. In the crystalline single molecular structure of compound III, the connection between the 2,7-dimethoxynaphthalene ring and the ketonic carbonyl moiety is nearly coplanar and the anthracene ring connects to the ketonic carbonyl moiety almost perpendicularly. In the crystalline single molecular structures of homologues I and II, the 2,7-dimethoxynaphthalene rings are bonded with larger twists to the ketonic carbonyl groups than the arene rings. In crystal packings of homologues I and II, the centrosymmetric dimeric aggregations with pairs of complementary non-classical hydrogen bonds are observed. Compound III forms two-fold helical molecular assemblies with C–H…π non-classical hydrogen bonds along the a-axis. Hirshfeld surface analysis has emphasised that these packing motifs affect molecular packing distinctively. Compound III has the largest number of molecules in close proximity. The crystal structures of the four compounds, including non-aroylated 2,7-dimethoxynaphthalene, are interpreted in terms of their potential for chiral crystal formation by considering the transition in the types and ratios of effective non-classical hydrogen bonds functioning as inter- and intramolecular modes, under the primary influence of ketonic carbonyl group participating interactions.

Graphical Abstract

The crystal structures of the 3-(9-anthroylated) 2,7-dimethoxynaphthalene and its homologues having smaller sized-aromatic ring substituents, including non-aroylated 2,7-dimethoxynaphthalene, have been interpreted in terms of their potential for chiral crystal formation by considering the transition in the types and ratios of effective non-classical hydrogen bonds functioning as inter- and intramolecular modes.