Crystallisation of inorganic salts containing 18-crown-6 from ionic liquids

Reaction of the zwitterionic imidazolium salt [(CH2COOH)(CH2COO)i.m.] with K2CO3 or BaO in the presence of 18-crown-6 affords the salts [(CH2COO)2i.m.][K(18-crown-6)] and [(CH2COO)2i.m.]2[Ba(18-crown-6)]. Recrystn. of these crown complexes from the ionic liq. 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [emim][Tf2N], at a water interface, results in the formation of new salts in which the original anion is replaced by Tf2N-. Single crystal X-ray diffraction has been performed on two of the salts. The potassium structure contg. 18-crown-6 and Tf2N- forms a linear chain coordination polymer that can be regarded as metal org. frameworks (MOFs). The study provides insights into the sepn. of group I and II metal ions using crown ethers in combination with ionic liqs.