Structural characterization, gelation ability, and energy-framework analysis of two bis(long-chain ester)-substituted
David K Geiger1, H Cristina Geiger1, Shawn M Moore1
1Department of Chemistry, SUNY College at Geneseo, Geneseo, NY 14454, USA.
Abstract:
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.
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