As a part of our structural studies of 1,8-dibenzoylnaphthalene compounds, one of the highly congested aromatic-rings-accumulated
molecules, 2,7-dibenzyloxy-1,8-bis(4-fluorobenzoyl)naphthalene is designed and determined the crystal structure by X-ray crystallography.
Through comparison of the single molecular structure and the molecular packing structure with the homologues bearing alkoxy/aryloxy
groups (methoxy, ethoxy, butoxy, and phenoxy groups) at the 2,7-positions, the contribution of the non-bonding molecular interactions to
stabilization of the molecular packing is estimated. As a common feature of single molecular structure in the series of the compounds, two
aroyl groups are attached to the naphthalene ring in a nearly perpendicular fashion. In the crystal packing of these compounds, aromatic
hydrogen interacts with carbonyl oxygen to stabilize the spatial organization of non-coplanarly accumulated aromatic rings replacing …
stacking interaction of benzene rings. Especially, intermolecular (Ar)C–H…O=C interactions between the benzene rings of the aroyl groups
and the carbonyl groups of the neighbouring molecules are influential. The pile superposing the naphthalene ring planes constructed
mainly by this intermolecular interaction probably plays the most important role for stabilizing the crystal structure of these compounds. In
addition to the (Ar)C–H…O=C interactions, butoxy-, phenoxy- and benzyloxy-bearing compounds have intermolecular (sp3)C–H…
interactions between the methylene moieties (benzene rings for phenoxy-bearing homologue) of the 2,7-substituents and the aromatic rings
of the neighbouring molecules (aromatic ring: the naphthalene ring for butoxy-bearing homologue; the benzene rings for phenoxy-bearing
homologue; the benzene ring of the benzyloxy group for benzyloxy-bearing homologue). Furthermore, the effective contribution of (Ar)C–
H…O=C interaction depends on the kind of the 2,7-substituents. The existence of intermolecular (sp3)C–H… interactions by 2,7-
substituents is plausible to weaken the contribution of intermolecular (Ar)C–H…O=C interactions to the molecular packing. The stability of
the molecular accumulation in the crystal is rationally interpreted from the viewpoint of the complementary combination of (Ar)C–H…O=C
and (sp3)C–H… interactions. The order of the total stability of the crystals of these compounds estimated on the basis of melting point and
density is in good agreement of the number of these superior interactions, (Ar)C–H…O=C and (sp3)C–H… interactions
Key words: Non-coplanarly aromatic-rings-accumulating molecules, Crystal structure, Spatial organization, Non-bonding molecular
interactions, C–H…O=C interaction, C–H… interaction
|
