Silver(I) fluoride is an inorganic compound with the formula AgF. It is one of the three main fluorides of silver , the others being silver subfluoride and silver(II) fluoride . AgF has relatively few niche applications; It has been employed in aqueous solutions as a fluorination and desalination reagent in organic synthesis and as a topical caries treatment in dentistry .
The hydrates of AgF are colourless, whereas pure anhydrous samples are yellow.
preparation
High purity silver (I) fluoride can be produced by heating silver carbonate to 310 °C under a hydrogen fluoride atmosphere in a platinum tube :
Ag 2 CO 3 + 2 HF → 2 Agf + H 2 O + CO 2
Laboratory routes for the compound generally avoid the use of gaseous hydrogen fluoride. One method is the thermal decomposition of silver tetrafluoroborate:
AGBF 4 → AGF + BF 3
In an alternative route, silver(I) oxide is dissolved in concentrated aqueous hydrofluoric acid, and silver fluoride is precipitated out of the resulting solution by acetone.
Property
| Property | |
|---|---|
| chemical formula | Ag F |
| molar mass | 126.8666 g·mol −1 |
| appearance | yellowish-brown solid |
| density | 5.852 g/cm3 ( 15 °C) |
| Melting point | 435 °C (815 °F; 708 K) |
| boiling point | 1,159 °C (2,118 °F; 1,432 K) |
| Solubility in water | 85.78 g/100 mL (0 °C) 119.8 g/100 mL (10 °C) 179.1 g/100 mL (25 °C) 213.4 g/100 mL (50 °C) |
| solubility | Hydrogen fluoride 83 g/100 g (11.9 °C) in methanol 1.5 g/100 mL (25 °C) |
| magnetic susceptibility (χ) | −36.5 10 −6 cm 3 /mol |
| related compound | |
|---|---|
| other ions | Silver(I) Oxide Silver(I) Chloride |
| other quotes | Copper (I) Fluoride Gold (I) Fluoride |
| related compound | Silver Subfluoride Silver(II) Fluoride |
structure
The structure of AgF has been determined by X-ray diffraction. [7] [8] : 3735 At ambient temperature and pressure, silver(I) exists as the fluoride polymorph AgF-I, which adopts a cubic crystal system with the space group Fm 3 m in the Hermann–Mougin notation . The rock salt structure is similar to that adopted by other silver monohalides. The lattice parameter is 4.936 (1) , significantly lower than that of AgCl and AgBr. [9] : 562 neutron and X-ray diffraction studies have further shown that at 2.70(2) GPa, a structural transition to a second polymorph (AgF-II) with the cesium chloride structure and lattice parameter 2.945 it happens . [10] : 7945 [11] :The associated reduction in 770 quantities is about ten percent. [10] A third polymorph, AgF III, forms upon reducing pressure to 2.59(2) : 7946 GPa, and has an inverse nickel arsenide structure. The lattice parameters are a = 3.244(2) and c = 6.24(1); The structure of rock salt is obtained only when the pressure is reduced to 0.9(1) GPa. The non-stoichiometric behavior is exhibited by all three polymorphisms under extreme pressure.
spectroscopy
Silver (I) fluoride exhibits unusual optical properties. Simple electronic band theory predicts that the fundamental excitation absorption for AgF will be higher than that for AgCl (5.10 eV) and is consistent with a transition from an ionic valence band for other silver halides. Experimentally, the fundamental levitation for AgF is 4.63 eV. [13] : 2604 This discrepancy can be explained by introducing a transition from a valence band with a largely silver 4d-orbital character. [9] : The refractive index of the 563 high frequency is 1.73(2).
synthesis
Unlike other silver halides, anhydrous silver(I) fluoride is not quite as photosensitive, although the dihydrate is. [14] : 286 [5] : 150 With this and considering the material’s solubility in water, it is not surprising that it has found little use in photography, but the salts used by Levi Hill in his “Heliochromy” However , a US patent for an experimental AGF-based method was granted in 1970. [16]
solubility
Unlike other silver halides, AGF is highly soluble in water (1800 g/L), and it also has some solubility in acetonitrile. It is also unique among silver(I) compounds and silver halides in that it forms AgF(H 2 O) 2 and AgF (H 2 O) 4 hydrates upon precipitation from aqueous solution . [17] : 1185 [18] Like alkali metal fluoride, it dissolves in hydrogen fluoride to give a conducting solution.
Application
organic synthesis
Silver(I) fluoride finds application in organofluorine chemistry for linking fluoride to multiple bonds. For example, AgF gives perfluoroalkylsilver(I) derivatives by adding perfluoro alkanes to acetonitrile. [20] : 7367 It can also be used as a desulfuration-fluorination reagent on thiourea derived substrates. [18] : 562 Because of its high solubility in water and organic solvents, it is a convenient source of fluoride ions, and can be used to fluorinate alkyl halides under mild conditions. [2] An example is given by the following reaction:
Another organic method using synthetic silver (I) fluoride is the BINAP-AgF complex catalyzed enantioselective protonation of silyl enol ether:
inorganic synthesis
The reaction of silver acetylide with a concentrated solution of silver (I) fluoride results in the formation of a chandelier-like [Ag 10 ] 2+ cluster with endohedral acetylenide. [23]
Tetracalammonium fluoride can be easily prepared in the laboratory by the reaction of tetraalkalammonium bromide with aqueous AGF solution. [24] : 430
other
It is possible to coat a silicon surface with a uniform silver microlayer (0.1 to 1 µm thickness) by passing AgF vapor at 60–800 °C. [25] The relevant response is:
4 AgF + Si → 4 Ag + SiF 4
Several studies have shown silver(I) fluoride to be an effective anti-caries agent, although the mechanism is a subject of current research. [26] Treatment is usually by the “atraumatic” method, in which a 40% mass aqueous silver(I) fluoride solution is applied to the carious legions, followed by sealing of the dentine with glass ionomer cement. [27] Although the treatment is generally considered safe, fluoride toxicity has been a significant clinical concern in pediatric applications, particularly as there has been considerable silver(II) fluoride contamination in the past in certain commercial preparations. Because of the instability of concentrated AgF solutions, silver diamine fluoride (Ag( NH3 ) 2f) is now more commonly used. [29] : 26 Preparations are made by adding ammonia to an aqueous solution of silver fluoride or by adding a solution of silver fluoride to aqueous ammonia.
