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Ionic liquids (ILs) have emerged as a new class of materials, displaying a unique capability to self-assemble into micelles, liposomes, liquid crystals, and microemulsions. 

Cocrystallization of long-chain bromoalkanes and lipid-like ionic liquids, revealing distinctive host–guest complex structures reminiscent of biomembranes. 

A series of 1,2-dimethylimidazolium ionic liquids bearing a hexadecyl alkyl chain are thoroughly examined via X-ray crystallography. The crystal structures reveal several key variations in the non-covalent interactions in the lipid-like salts. Specifically, distinct cation–cation π interactions are observed when comparing the bromide and iodide structures. Changing the anion to bis(trifluoromethane)sulfonimide (Tf 2 N − ) changes these cation–cation π interactions with anion⋯π interactions. Additionally, several well-defined geometries of the cations are noted based on torsion and core-plane angles of the alkyl chains. Hirshfeld surface analysis is used to distinguish the interactions and geometries in the solid state, helping to reveal characteristic structural fingerprints for the compounds. The solid-state structures of the ionic liquids are correlated with the solution-state structures through UV-vis spectroscopic studies, further emphasizing the importance of the π interactions in the formation of aggregates. Finally, we investigated the thermal properties of the ionic liquids, revealing complex phase transitions for the iodide-containing species. These phase transitions are further rationalized via the analysis of the data gathered from the structures of the other crystallized salts. 

The title salt, C 4 H 6 N 3 O 2 + ·Cl − , exhibits multiple hydrogen-bonding interactions involving the nitroimidazolium cation and the chloride anion. Strong hydrogen bonds between the amine hydrogen atom and the chloride anion link the ionic moieties. Of note, with respect to H...Cl interactions, the central aromatic hydrogen atom displays a shorter interaction than the other aromatic hydrogen atom. Finally, interactions are observed between the nitro moiety and methyl H atoms. While no π–π stacking is observed, anion-π interactions are present. The crystal was refined as a two-component twin.