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Terephthalic acid (H2TPA) solubility in several ionic liquids (ILs) at multiple concentrations is higher than for any other known solvents at lower temperatures and pressures which suggests low energy purification of H2TPA from its major impurity, 4-carboxybenzaldehyde (4-CBA) might be possible. To understand the mechanism several strategies were explored to purify H2TPA by taking advantage of this high solubilizing power of ILs for H2TPA in the crystallization of unique salts and cocrystals. Using either zwitterionic carboxylate IL-precursors or direct salt formation with carboxylate ILs or amines, a series of salts of mono, dibasic and two ionic cocrystals were obtained including monobasic, [C1C1im][HTPA], [N4441][HTPA], [C4C1im][HTPA]•0.5H2TPA (a cocrystal), and [C1Him][HTPA] ([C1C1im]+ = 1,3-dimethylimidazolium, [N4441]+ = tribuytlmethylammonium, [C1Him]+ = 1-methyl-3-H-imidazolium), dibasic [C1C1im]2[TPA], [C4C1im]2[TPA], [N4444]2[TPA], [C1Him]2[TPA], [H2N22]2[TPA], [H3N6]2[TPA], and [HN(CH2CH2OH)3]2[TPA] ([C4C1im]+ = 1-butyl-3-methylimidazolium, [N4444]+ = tetrabuylammonium, [H3N6]+ = hexylammonium, [HN(CH2CH2OH)3]+ = triethanolammonium, [H2N22]+= diethylammonium), and a second cocrystal [C2C1im]Cl•0.5H2TPA. The formation of these salts suggest a viable method to purify H2TPA because of preferred salt formation at low energy conditions. One elegant route using 1-ethyl-3-methylimidazolium chloride ([C2C1im]Cl) could be especially promising because the cocrystal [C2C1im]Cl•0.5H2TPA was readily isolated and is easily dissociated when exposed to ambient conditions into crystalline H2TPA and a liquid of hydrated [C2C1im]Cl.

Traditional synthesis of metal–organic frameworks (MOFs) involves the reaction of a metal-containing precursor with an organic linker in an organic solvent at an elevated temperature, in what is termed a `solvothermal' reaction. More recently, many examples have been reported of MOF synthesis in ionic liquids (ILs), rather than an organic solvent, in `ionothermal' reactions. The high concentration of both cations and anions in an ionic liquid allows for the formation of new MOF structures in which the IL cation or anion or both are incorporated into the MOF. Most commonly, the IL cation is included in the open cavities of the MOF, countering the anionic charge of the MOF framework itself and acting as a template around which the MOF structure forms. Ionic liquids can also serve other structure-directing roles, for example, when an IL containing a single enantiomer of a chiral anion leads to a homochiral MOF, even though the IL anion is not itself incorporated into the MOF. A comprehensive review of ionothermal syntheses of MOFs, and the structure-directing effects of the ILs, is given.