Anionic Species (FH)_xF^- in Room-Temperature Molten Fluorides (CH₃)₄NF·mHF

Abstract

Ionic and nonionic species in (CH3)4NF·mHF melts (m = 3.0−5.0) were investigated by 1H NMR, IR spectroscopy, Raman spectroscopy, and high-energy X-ray diffraction measurements. Three types of anions, (FH)F-, (FH)2F-, and (FH)3F-, were identified in these melts. The (FH)2F- anion was thermodynamically the most stable of the complex anions in the (CH3)4NF·mHF (3.0 ≤ m ≤ 5.0), and its concentration was the highest. (FH) x F- anions with x = 4 and 5 were not present at room temperature though the presence of (FH) x F- (x = 1−5) has been known in the solid-state crystals. In the (CH3)4NF·mHF melts with m = 3.0−5.0, the number of HF combined with F- is three or less, and excess HF exists as molecular HF.

Cesium fluorohydrogenate, Cs(FH)2.3F

“…Structural characteristics of EMImFHF at both the liquid and solid states and RMIm(FH) 2.3 F in the liquid state were studied using X-ray diffraction techniques [23][24][25]. Some spectroscopic data are also available for TMA(FH) n F (TMA = tetramethylammonium, n = 3.0-5.0) salts that show some HF dissociation pressures at ambient temperatures [26]. Cs(FH) 2.3 F is also a potential electrolyte for electrochemical energy conversion devices like other fluorohydrogenate salts.…”

Unique solvent effects on selective electrochemical fluorination of organic compounds

“…In a solution such as DME, Et 4 NFÁ4HF may dissociate to Et 4 N + , F(HF)n À (n = 1-3), and HF [30][31][32][33]. Moreover, it was also found that DME was oxidized simultaneously during the electrolysis of substrates, which can suppress overoxidation of both the substrates and products, particularly at a later stage of the electrolysis [27].…”

Fluorohydrogenate Ionic Liquids, Liquid Crystals, and Plastic Crystals

“…The (FH) n F − anions are regarded as an ion where F − is bound to one or more HF molecules. The H−F bond in (FH) n F − is known as "strong hydrogen bond" [9] and has been a target of theoretical and computational studies [10][11][12][13] as well as X-ray diffractional and vibrational spectroscopic studies. The smallest fluorohydrogenate ion is FHF − with D ∞h symmetry which is determined in a number of crystal structures ( Figure 5.2 (a)) [5,[14][15][16][17][18][19][20][21][22].…”