CRYSTAL STRUCTURE OF 2,7-DIBENZYLOXY-1,8-BIS(4-FLUOROBENZOYL)NAPHTHALENE AND THE COMPARISON WITH THE HOMOLOGUES: CONTRIBUTION OF (Ar)C–H…O=C AND (sp3)C–H…pi INTERACTIONS TO THE MOLECULAR PACKING
Crystal structures of 1,8-dibenzoylnaphthalene homologues bearing alkoxy groups (methoxy, ethoxy, butoxy, and benzyloxy groups) at 2,7-positions, one of the highly congested aromatic-rings-accumulated molecules, are studied. 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 p…p 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- and benzyloxy-bearing compounds have intermolecular (sp3)C–H…pi interactions between the methylene moieties of the 2,7-substituents and the aromatic rings of the neighbouring molecules (aromatic ring: the naphthalene ring for butoxy-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…pi 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…pi 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…pi interactions.
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