Ammonium bifluoride

Ammonium bifluoride

Names
IUPAC name Ammonium hydrogen fluoride
Other names Ammonium acid fluoride Ammonium hydrofluoride Ammonium difluoride Ammonium hydrogendifluoride Ammonium hydrogen difluoride
Identifiers
CAS Number	1341-49-7 Y
3D model (JSmol)	Interactive image Interactive image
ChemSpider	21241205 N
ECHA InfoCard	100.014.252
EC Number	215-676-4
PubChem CID	14935
UNII	C2M215358O
UN number	1727
CompTox Dashboard (EPA)	DTXSID9029645
show InChI InChI=1S/F2H.H3N/c1-3-2;/h;1H3/q-1;/p+1 N Key: XIONBZYFLSJNBW-UHFFFAOYSA-O N InChI=1/2FH.H3N/h2*1H;1H3 Key: KVBCYCWRDBDGBG-UHFFFAOYAG
show SMILES [NH4+].F[H-]F [F-].F.[NH4+]
Properties
Chemical formula	F2H5N
Molar mass	57.044 g·mol−1
Appearance	White crystals
Density	1.50 g cm−3
Melting point	126 °C (259 °F; 399 K)
Boiling point	240 °C (464 °F; 513 K)(decomposes)
Solubility in water	63g/100ml 20 °C
Solubility in alcohol	slightly soluble
Refractive index (nD)	1.390
Structure
Crystal structure	Cubic, related to the CsCl structure
Coordination geometry	[NH4]+ cation: tetrahedral [HF2]− anion: linear
Hazards
GHS pictograms	[1]
GHS hazard statements	H301, H314[1]
GHS precautionary statements	P280, P301+310, P305+351+338, P310[1]
NFPA 704 (fire diamond)	3 0 0
Related compounds
Other cations	potassium bifluoride
Related compounds	ammonium fluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

Ammonium hydrogen fluoride is the inorganic compound with the formula NH₄HF₂ or NH₄F·HF. It is produced from ammonia and hydrogen fluoride. This colourless salt is a glass-etchant and an intermediate in a once-contemplated route to hydrofluoric acid.

Structure[]

Ammonium bifluoride, as its name indicates, contains an ammonium cation (NH₄⁺) and a bifluoride, or hydrogen(difluoride), anion (HF₂⁻). The centrosymmetric triatomic bifluoride anion features the strongest known hydrogen bond, with a F−H length of 114 pm.^[2] and a bond energy greater than 155 kJ mol⁻¹.^[3]

In solid [NH₄][HF₂], each ammonium cation is surrounded by four fluoride centers in a tetrahedron, with hydrogen-fluorine hydrogen bonds present between the hydrogen atoms of the ammonium ion and the fluorine atoms.^{[citation needed]} Solutions contain tetrahedral [NH₄]⁺ cations and linear [HF₂]⁻ anions.

Production and applications[]

Ammonium bifluoride is a component of some etchants. It attacks silica component of glass:

SiO₂ + 4 [NH₄][HF₂] → SiF₄ + 4 NH₄F + 2 H₂O

Potassium bifluoride is a related more commonly used etchant.

Ammonium bifluoride has been considered as an intermediate in the production of hydrofluoric acid from hexafluorosilicic acid. Thus, hexafluorosilicic acid is hydrolyzed to give ammonium fluoride, which thermally decomposes to give the bifluoride:

H₂SiF₆ + 6 NH₃ + 2 H₂O → SiO₂ + 6 NH₄F

2 NH₄F → NH₃ + [NH₄]HF₂

The resulting ammonium bifluoride is converted to sodium bifluoride, which thermally decomposes to release HF.^[4]

Ammonium bifluoride is also used as an additive in tin-nickel plating processes as the fluoride ion acts as a complexing agent with the tin, allowing for greater control over the resulting composition and finish.

Toxicity[]

Ammonium bifluoride is toxic to consume and a skin corrosion agent. Upon exposure to skin, rinsing with water followed by a treatment of calcium gluconate is required.^[1]

References[]