Structural characterization, gelation ability, and energy-framework analysis of two bis(long-chain ester)-substituted 4,4′-biphenyl compounds

There are few examples of single-crystal structure determinations of gelators, as gel formation requires that the dissolved gelator self-assemble into a three-dimensional network structure incorporating solvent via noncovalent interactions rather than self-assembly followed by crystallization. In the solid-state structures of the isostructural compounds 4,4′-bis[5-(methoxycarbonyl)pentyloxy]biphenyl (BBO6-Me), C₂₆H₃₄O₆, and 4,4′-bis[5-(ethoxycarbonyl)pentyloxy]biphenyl (BBO6-Et), C₂₈H₃₈O₆, the molecules sit on a crystallographically imposed center of symmetry, resulting in strictly coplanar phenyl rings. BBO6-Me behaves as an organogelator in various alcohol solvents, whereas BBO6-Et does not. The extended structure reveals bundles of molecules that form a columnar superstructure. Framework-energy calculations reveal much stronger interaction energies within the columns (−52 to −78 kJ mol⁻¹) than between columns (−2 to −16 kJ mol⁻¹). The intracolumnar interactions are dominated by a dispersion component, whereas the intercolumnar interactions have a substantial electrostatic component.