Organic salts based on dicyclohexylamine and substituted/unsubstituted cinnamic acid exhibit efficient gelation of organic fluids, including selective gelation of oil from an oil/water mixture. Among the cinnamate salts, dicyclohexylammonium 4-chlorocinnamate (1), 3-chlorocinnamate (2), 4-bromocinnamate (3), 3-bromocinnamate (4), 4-methylcinnamate (5) and the parent cinnamate (6) are gelators, whereas 2-chlorocinnamate (7), 2-bromocinnamate (8), 3-methylcinnamate (9), 2-methylcinnamate (10) and hydrocinnamate (11) are non-gelators. Non-gelation behaviour of 11 and various benzoate derivatives 12-18 indicate the significance of an unsaturated backbone in the gelation behaviour of the cinnamate salts. A structure-property correlation based on the single-crystal structures of most of the gelators (1, 3, 5 and 6) and non-gelators, such as 7, 8, 10-18, indicates that the prerequisite for the one-dimensional (1D) growth of the gel fibrils is mainly governed by the 1D hydrogen-bonded network involving the ion pair. All the non-gelators show either two- (2D) or zero-dimensional (0D) hydrogen-bonded assemblies involving the ion pair. The molecular packing of the fibres in the xerogels of 1, 3, 5 and 6 has also been established on the basis of their simulated powder diffraction patterns, XRPD of bulk solids and xerogels. Ab initio quantum chemical calculations suggests that pi-pi interactions is not a contributing factor in the gelation process.
A series of easy to prepare organic salt based on imidazole derivatives and cyclobutane-1,1-dicarboxylic acid have been studied for their gelation behavior after it was found that
imidazolium hydrogen cyclobutane-1,1-dicarboxylate (1) can harden few organic liquids. 1
forms remarkably stable gel (remains intact for several months in an open container, gel
dissociation temp T
Gel = 66 °C) with nitrobenzene at a very low concentration of 0.137 wt %,
whereas bis-imidazolium cyclobutane-1,1-dicarboxylate (2) resulted in a weak and unstable
gel with nitrobenzene, indicating the importance of the free COOH group in 1 in gel
formation. Molecular packing in the primary assembly unit (fibers) of xerogel of 1/nitrobenzene is successfully established based on single-crystal X-ray and X-ray powder diffraction
data. The morph responsible for gel formation of 1 with nitrobenzene is found to be different
from that of its xerogel. Substitution on the imidazole moiety results in nongelators.
Besides its capability to gelate various organic solvents, dicyclohexyl ammonium 4-chlorocinnamate 1 is shown to perform selective gelation of oil from oil/water mixtures. While the corresponding 3-chloro derivative 2 is an excellent gelator of nonpolar organic solvents, 2-chloro derivative 3 turned out to be a nongelator.
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