NOVELTY - Ionic liquid (I) with a melting point of less than 100 degrees C, is claimed.    USE - (I) is useful as solvent, which is useful for: performing chemical reactions; dissolving natural and synthetic polymers; electrochemical process; and production and stabilization of nanoparticles. (I) is useful as: an extracting agent for the liquid-liquid-extraction; electrolyte or electrolyte non-aqueous component in energy storage systems and energy conversion systems; a high temperature lubricant (all claimed); heat carrier; and electrolyte in batteries, in double-layer-condensators, in solar cells or in extraction- or separation processes and in the printed circuit board production.    ADVANTAGE - (I) exhibits high temperature stability, electrochemical stability, redox stability, wide area of tension and good dissolving capability for non-polar substances. (I) is free of solvent and toxic components. The melting point of (I) is relatively low when compared to other salts with similar cations.    DETAILED DESCRIPTION - Ionic liquid of formula (1/n(Xn+) (Y1-)) (I) with a melting point of less than 100 degrees C, is claimed.    Xn+ = cation containing metal ions, which are quaternary ammonium-, oxonium-, sulfonium- or phosphonium-ion;    Y1- = anion of ester group of formula (R6O-(R7-O-)x-R8-COO-);    n = 1-3;    x = 2-8;    R6 = 1-3C-hydrocarbon;    R7 = 2-4C alkylene; and    R8 = 1-4C alkylene.    Where the hydrogen atoms in R6-R8 are completely or partially substituted by F. An INDEPENDENT CLAIM is included for the preparation of (I) comprising reacting a polyoxyalkylenemonoalkylether compound of formula (R6O-(R7-O-)x-H) with a halocarboxylic acid compound of formula (Hal-R8-COOH) to give carboxylic acid compound of formula (R6O-(R7-O-)x-R8-COOH) (II), and neutralizing (II) with a base of formula (X(OH)n) or (XnH) to give an ionic liquid of formula (1/n(Xn+))(R6O-(R7-O-)x-R8-COO-), where the solvents and/or the solvents formed during the reaction are completely separated.    Hal = F, Cl, Br or I.