Structure–Property Correlation of a New Family of Organogelators Based on Organic Salts and Their Selective Gelation of Oil from Oil/Water Mixtures

Abstract

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 π–π interactions is not a contributing factor in the gelation process.