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

摘要

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)pentyl-oxy]biphenyl (BBO6-Me), C_26H_34O_6, and 4,4'-bis[5-(ethoxycarbonyl)pentyl-oxy]biphenyl (BBO6-Et), C_28H_38O_6, 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.