## 1 Introduction  
Ionic liquids (ILs) are molten salts comprised entirely of cations and anions with a melting point below 100 \({}^{\circ}\)C. Generally, cations are organic, such as alkyl-substituted imidazolium, pyridinium, pyrrolinium, tetraalkylammonium, and tetraalkylphosphonium. Anions can be organic or inorganic, such as halide, tetrafluoroborate, hexafluorophosphate, and bistrifilimide. In earlier studies, ethylpyridinium cation was reported as an IL in the 1950s [1], N-butylpyridinium cation was reported as an IL in the 1970s [2], and 1-ethyl-3-methyl-imidazolium cation was reported as an IL in the 1980s [3]. Subsequently, ILs received increasing attention due to their extraordinary physicochemical properties including low melting point, low vapor pressure, high conductivity, and wide potential window. In recent decades in particular, ILs have been considered a promising, green medium for reactive metal electrodeposition, replacing high-temperature molten salts [4; 5; 6; 7; 8; 9; 10]. Numerous studies have focused on designing new ILs and on the relationship between the phase behavior and molecular structure, in order to clarify the nature of ILs and expand their applications [11; 12; 13; 14; 15]. Fundamental data on physical and chemical properties are very important for IL design and for the exploration of new applications. So far, many experimental or simulated studies on the density,viscosity, conductivity, thermal behavior, and solubility of pure ILs and their mixtures have appeared in the literature [16; 17; 18; 19; 20]. [PERSON] and co-workers [21; 22; 23] systematically studied the effect of ionic structures, including anionic species, cationic species, and alkyl chain, in imidazolium cation on the physicochemical characteristics of ILs. Alkyl-substituted imidazolium cation-based ILs have been studied extensively due to their advantages in terms of superior fluidity and conductivity. The generic structure of alkyl-substituted imidazolium-based ILs is shown in Figure 1.  
For the molecular structure of alkyl-substituted imidazolium-based ILs, as shown in Figure 1, R\({}_{1}\) is typically methyl and R\({}_{2}\) can generally be butyl [24; 25; 26; 27; 28; 29; 30; 31], ethyl [32; 33; 34; 35], or octyl [36]. Common anionic species include halide, tetrafluoroborate (BF\({}_{4}\)\({}^{-}\)), tetrafluorophosphate (PF\({}_{6}\)\({}^{-}\)), bis(trifluoromethylsulfonyl)imide (Tf\({}_{2}\)N\({}^{-}\)), dicyanamide (DCA), ethylsulfate (EtSO\({}_{4}\)), etc. Among them, ILs with a single fluoride anion are rarely reported because the syntheses of such ILs are challenging, unlike those of other halide ILs. As is known, the enhanced basicity of metal fluorides can lead to Hoffman elimination on side chains of the cationic part of the system. However, anion metathesis from other halides is accessible. [PERSON] and co-workers [37] prepared 1-ethyl-3-methyl imidazolium fluoride (EMIF:2.3 HF) via the reaction of hydrogen fluoride and homologous chloride. [PERSON] et al. [38] reported a method that included putting a strongly hydrogen bonded organic material in contact with an ionic liquid having a fluoride anion for the solubilization of the strongly hydrogen bonded organic material. [EMIm]F and other similar imidazolium fluoride ionic liquids could be prepared using imidazolium chloride and silver fluoride as raw materials. [PERSON] et al. [39] synthesized a series of 1-alkyl-3-methylimidazolium fluorides via the reaction of silver fluoride with the corresponding imidazolium iodides; weak interactions between the fluoride anion and sp3-hybridized C-H groups were observed. So far, few studies exist on the synthesis of [EMIm]F ionic liquid, and knowledge of its physical properties is lacking. We therefore prepared [EMIm]F ionic liquid via an anion metathesis process. It could potentially be used as fluoride source for nanoparticle synthesis [40; 41], as an electrolyte for metal deposition, and as a solvent for chemical processing [42].