Ionic liquid

An ionic liquid (IL) is a <a href="/facts/Salt_(chemistry)/lsSKwGpn">salt</a> in the <a href="/facts/Liquid/t9GkLWzt">liquid</a> state at ambient conditions. In some contexts, the term has been restricted to salts whose <a href="/facts/Melting_point/MY0w0h0k">melting point</a> is below a specific temperature, such as 100 °C (212 °F). While ordinary liquids such as <a href="/facts/Water/0lkXnJPK">water</a> and <a href="/facts/Gasoline/lcnxq5BS">gasoline</a> are predominantly made of <a href="/facts/Electric_charge/xxsBfmlB">electrically neutral</a> <a href="/facts/Molecule/N9ljSfFq">molecules</a>, ionic liquids are largely made of <a href="/facts/Ion/3bePpDna">ions</a>. These substances are variously called liquid electrolytes, ionic melts, ionic fluids, fused salts, liquid salts, or ionic glasses.
Ionic liquids have many potential applications. They are powerful <a href="/facts/Solvent/LoMPMz8S">solvents</a> and can be used as <a href="/facts/Electrolyte/4YE8bIVa">electrolytes</a>. Salts that are liquid at near-ambient temperature are important for <a href="/facts/Electric_battery/bqEpm4ue">electric battery</a> applications, and have been considered as <a href="/facts/Sealant/WY22bcvE">sealants</a> due to their very low <a href="/facts/Vapor_pressure/whrEr96T">vapor pressure</a>.
Any salt that melts without <a href="/facts/Pyrolysis/h1cEegI7">decomposing</a> or vaporizing usually yields an ionic liquid. <a href="/facts/Sodium_chloride/MWcXl3Mb">Sodium chloride</a> (NaCl), for example, melts at 801 °C (1,474 °F) into a liquid that consists largely of <a href="/facts/Sodium/eYuSPu2V">sodium</a> cations (Na+) and chloride anions (Cl−). Conversely, when an ionic liquid is cooled, it often forms an <a href="/facts/Ionic_solid/jB9nMfrE">ionic solid</a>—which may be either <a href="/facts/Crystal/e2R2mk3E">crystalline</a> or <a href="/facts/Glass/hezRsAGf">glassy</a>.
The <a href="/facts/Ionic_bond/R6nUJI5u">ionic bond</a> is usually stronger than the <a href="/facts/Van_der_Waals_force/jyGU8Vh9">Van der Waals forces</a> between the molecules of ordinary liquids. Because of these strong interactions, salts tend to have high <a href="/facts/Lattice_energy/MRVJpWfk">lattice energies</a>, manifested in high melting points. Some salts, especially those with organic cations, have low lattice energies and thus are liquid at or below <a href="/facts/Room_temperature/YHwUIUTE">room temperature</a>. Examples include compounds based on the 1-ethyl-3-methylimidazolium (EMIM) cation and include: <a href="/facts/1-Ethyl-3-methylimidazolium_chloride/nCeC0aIx">EMIM:Cl</a>, EMIMAc (acetate anion), EMIM <a href="/facts/Dicyanamide/laMq7kMK">dicyanamide</a>, (C2H5)(CH3)C3H3N+2·N(CN)−2, that melts at −21 °C (−6 °F); and 1-butyl-3,5-dimethylpyridinium bromide which becomes a glass below −24 °C (−11 °F).
Low-temperature ionic liquids can be compared to <a href="/facts/Ionic_solution/4YE8bIVa">ionic solutions</a>, liquids that contain both ions and neutral molecules, and in particular to the so-called <a href="/facts/Deep_eutectic_solvent/nQLlxhkd">deep eutectic solvents</a>, mixtures of ionic and non-ionic solid substances which have much lower melting points than the pure compounds. Certain mixtures of nitrate salts can have melting points below 100 °C.

Ionic liquid open-in-new

Ionic liquid