The System NaF-HF-H₂O at 0 and -15°¹

Metal Hydrogen Fluorides

“…The formation of the hydrogen difluoride LiF.HF in the HF-LiF-H 2 O system (investigated up to 75% HF) was established, but, because of the slowness of the reaction LiF -> LiF.HF in the solid phase, it was recommended that lithium hydrogen difluoride be obtained by crystallisation from a saturated solution of LiF in hydrofluoric acid 65 . In a subsequent reinvestigation of the HF-NaF-H 2 O system 68 and part of the HF-NaF system 69 , metal hydrogen fluorides were obtained whose composition was similar to that established previously 66 . Further investigations of systems of the type HF-MF-H a O were undertaken by the authors of this review.…”

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

“…These systems have been also excellent subjects to investigate strong hydrogen bonds. Thermochemical, spectroscopic, and diffraction studies of the solid-state alkali fluorides have revealed the presence of (FH)F - ( D ∞ h symmetry), (FH) 2 F - ( C 2 v symmetry), and (FH) 3 F - ( D 3 h symmetry) anions, which are formed by strong hydrogen bonding. − Mootz et al determined the crystal structures of solid (CH 3 ) 4 NF· m HF ( m = 2.0, 3.0, and 5.0) and found (FH) 2 F - , (FH) 3 F - , and (FH) 5 F - anions by single-crystal X-ray diffraction measurements at low temperatures (−80 to −160 °C) . Shenderovich et al confirmed the presence of (FH) 2 F - and (FH) 3 F - anions in solid ( n C 4 H 9 ) 4 NF· m HF ( m = 2, 3) dispersed in CDF 3 /CDF 2 Cl by NMR measurements at low temperatures (110−130 K) .…”

A Symmetric F−H−F Hydrogen Bond in Strontium Bifluoride, Sr[HF2]2

“…Additionally, salts with higher HF contents contain more complex anions that exhibit strong hydrogen bonding, for example Na[H 2 F 3 ], Na[H 3 F 4 ], and Na[H 4 F 5 ]. [1][2][3][4][5][6] Na[HF 2 ] is widely applied in pH adjustment, metal plating, surface pretreatment, and glass etching. [7] It has been characterized extensively using X-ray [8,9] and neutron diffraction [10] (including high pressure experiments [11] ), IR, [12,13] Raman, [11] and NMR spectroscopy, [14] as well as quantum chemical calculations.…”

“…The alkali metal fluorides A F ( A =Li−Cs) are able to form adducts with HF, [1] the simplest being the bifluorides containing the [HF 2 ] − anion. Additionally, salts with higher HF contents contain more complex anions that exhibit strong hydrogen bonding, for example Na[H 2 F 3 ], Na[H 3 F 4 ], and Na[H 4 F 5 ] [1–6] . Na[HF 2 ] is widely applied in pH adjustment, metal plating, surface pretreatment, and glass etching [7] .…”