Involvement of the -C(O)-CH=CH- linker chain in different π interactions in crystalline chalcones, (2E)-phenyl-C(=O)-CH=CH-benzene derivatives. Importance of anti-parallel layered motifs in benzyloxy substituted compounds

Abstract

X-ray crystallographic, Hirshfeld surface and PIXEL study is reported on five benzyloxy substituted compounds, namely (E)-3-[2 methoxy‑5-benzyloxyphenyl]-1-(2‑hydroxy-4-methoxyphenyl)-2-ene-1-one, compound 1, (E)-3-[2,5-bis(benzyloxy)phenyl]-1-(2-hydroxyphenyl)-2-ene-1-one, compound 2, (E)-3-[2,5-bis(benzyloxy)phenyl]-1-(2‑hydroxy-4-methoxyphenyl)-2-ene-1-one, compound 3, (E)-3-[2,5-bis(benzyloxy)phenyl]-1-(2‑hydroxy-3,4-dimethoxyphenyl)-2-ene-1-one, compound 4, and (E)-3-[2,5-bis(benzyloxy)phenyl]-1-(2‑hydroxy-4,5-dimethoxyphenyl)-2-ene-1-one, compound 5. All five compounds exhibit intramolecular O—H(hydroxyl)···O(carbonyl) classical hydrogen bonds, (E)-arrangements about the olefinic bond and near planar chalcone cores, with the interplanar angles between chalcone rings A and B all less than 10°. The phenyl groups in the benzyloxy substituents make much greater interplanar angles with the chalcone core rings, A and B. The linker units, -C(O)-CH=CH-, between the terminal phenyl rings in the chalcone cores, exhibit electronic delocalization as indicated by the bond lengths being between single and double bonds. Motifs having molecules aligned in antiparallel arrangements in layers, with perpendicular distances between the two layers of ca.3.5 Å are amongst the most important motifs. The molecular slippage of the antiparallel molecules in these motifs varies significantly, which results in different functionality, e.g., the terminal phenyl rings, or segments in the linker unit, such as the carbonyl or the olefinic groups, in one layer being suitably placed to interact with functionality in the other. This series of motifs illustrate a great range of slippage distances which is reflected in the variety of interactions present in the motifs, including off-set, face-to-face π···π, π(CO)···π, π(CO)···π(CO) and π(C=C)···π(C=C) interactions. PIXEL calculations reveal the important motifs and their energies, and generally indicate the much greater importance of the dispersive contribution than Coulombic and polarization contributions to the overall energies of these molecules.