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| Names | |
|---|---|
| IUPAC name Silver(I) fluoride | |
| Other names Argentous fluoride Silver monofluoride | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider | |
| ECHA InfoCard | 100.028.996 |
| EC Number |
|
| 122625 | |
| RTECS number |
|
| UNII | |
| |
| |
| Properties | |
| AgF | |
| Molar mass | 126.8666 g·mol−1 |
| Appearance | yellow-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) |
| 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)[1] | |
| Solubility | 83g/100 g (11.9 °C) inhydrogen fluoride 1.5g/100 mL inmethanol(25 °C)[2] |
| −36.5·10−6 cm3/mol | |
| Structure | |
| cubic | |
| Thermochemistry | |
| 48.1 J/mol·K[1] | |
Std molar entropy(S⦵298) | 83.7 J/mol·K[1] |
Std enthalpy of formation(ΔfH⦵298) | −206 kJ/mol[1] |
Gibbs free energy(ΔfG⦵) | −187.9 kJ/mol[1] |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Corrosive |
| GHS labelling:[3] | |
 | |
| Danger | |
| H314 | |
| P260,P280,P303+P361+P353,P304+P340,P305+P351+P338,P310 | |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Otheranions | Silver(I) oxide Silver(I) chloride |
Othercations | Copper(I) fluoride Gold(I) fluoride |
Related compounds | Silver subfluoride Silver(II) fluoride |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Silver(I) fluoride is theinorganic compound with the formula AgF. It is one of the three mainfluorides of silver, the others beingsilver subfluoride andsilver(II) fluoride. AgF has relatively few niche applications; it has been employed as afluorination anddesilylationreagent inorganic synthesis and inaqueous solution as atopical caries treatment indentistry.
Thehydrates of AgF present as colorless, while pureanhydrous samples are yellow.[4]: 150
High-purity silver(I) fluoride can be produced by the heating ofsilver carbonate to 310 °C (590 °F) under ahydrogen fluoride environment, in aplatinum tube:[5]: 9
Laboratory routes to the compound typically avoid the use of gaseous hydrogen fluoride. One method is thethermal decomposition ofsilver tetrafluoroborate:
In an alternative route,silver(I) oxide is dissolved in concentrated aqueoushydrofluoric acid, and the silver fluoride is precipitated out of the resulting solution byacetone.[5]: 10
The structure of AgF has been determined byX-ray diffraction.[6][7]: 3736 [8] At ambient temperature and pressure, silver(I) fluoride exists as the polymorph AgF-I, which adopts acubic crystal system with space groupFm3m in theHermann–Mauguin notation. Therock salt structure is adopted by the other silver monohalides. The lattice parameter is 4.936(1)Å, significantly lower than those of AgCl and AgBr.[9]: 562 Neutron and X-ray diffraction studies have further shown that at 2.70(2) GPa, a structural transition occurs to a second polymorph (AgF-II) with thecaesium chloride structure, and lattice parameter 2.945 Å.[10]: 7945 [11]: 770 The associated decrease in volume is approximately ten percent.[10]: 7946 A third polymorph, AgF-III, forms on reducing the pressure to 2.59(2) GPa, and has an inversenickel arsenide structure. The lattice parameters are a = 3.244(2) Å and c = 6.24(1) Å; the rock salt structure is regained only on reduction of the pressure to 0.9(1) GPa.Non-stochiometric behaviour is exhibited by all three polymorphs under extreme pressures.[12]: 939 [10]: 7947
Silver(I) fluoride exhibits unusual optical properties. Simpleelectronic band theory predicts that the fundamentalexcitonabsorption for AgF would lie higher than that of AgCl (5.10 eV) and would correspond to a transition from an anionic valence band as for the other silver halides. Experimentally, the fundamental exciton for AgF lies at 4.63 eV.[13]: 2604 This discrepancy can be explained by positing transition from a valence band with largely silver 4d-orbital character.[9]: 563 The high frequencyrefractive index is 1.73(2).[7]: 3737
In contrast with the othersilver halides, anhydrous silver(I) fluoride is not appreciablyphotosensitive, although thedihydrate is.[14]: 286 [4]: 150 With this and the material's solubility in water considered, it is unsurprising that it has found little application inphotography but may have been one of the salts used byLevi Hill in his "heliochromy",[15] although a US patent for an experimental AgF-based method was granted in 1970.[16]
Unlike the other silver halides, AgF is highlysoluble in water (1800 g/L), and it even has some solubility inacetonitrile. It is also unique among silver(I) compounds and the silver halides in that it forms the hydrates AgF·(H2O)2 and AgF·(H2O)4 on precipitation from aqueous solution.[17]: 1185 [18] Like thealkali metal fluorides, it dissolves in hydrogen fluoride to give a conducting solution.[19]
Silver(I) fluoride finds application inorganofluorine chemistry for addition offluoride across multiple bonds. For example, AgF adds to perfluoroalkenes in acetonitrile to give perfluoroalkylsilver(I) derivatives.[20]: 7367 It can also be used as a desulfuration-fluorination reagent onthiourea derived substrates.[18]: 562 Due to its high solubility in water and organic solvents, it is a convenient source offluoride ions, and can be used to fluorinatealkyl halides under mild conditions.[2] An example is given by the following reaction:[21]
Another organic synthetic method using silver(I) fluoride is theBINAP-AgF complex catalyzedenantioselective protonation ofsilyl enol ethers:[22]: 1546
The reaction ofsilver acetylide with a concentrated solution of silver(I) fluoride results in the formation of achandelier-like [Ag10]2+ cluster with endohedral acetylenediide.[23]
Tetralkylammonium fluorides can be conveniently prepared in the laboratory by the reaction of the tetralkylammonium bromide with an aqueous AgF solution.[24]: 430
It is possible to coat a silicon surface with a uniform silver microlayer (0.1 to 1 μm thickness) by passing AgF vapour over it at 60–800 °C.[25] The relevant reaction is:
Multiple studies have shown silver(I) fluoride to be an effectiveanti-caries agent, although the mechanism is the subject of current research.[26] Treatment is typically by the "atraumatic" method, in which 40% by mass aqueous silver(I) fluoride solution is applied to carious lesions, followed by sealing of the dentine withglass ionomer cement.[27] Although the treatment is generally recognised to be safe,fluoride toxicity has been a significant clinical concern inpaediatric applications, especially as some commercial preparations have had considerablesilver(II) fluoride contamination in the past.[27][28][29] Due to the instability of concentrated AgF solutions,silver diammine fluoride (Ag(NH3)2F) is now more commonly used.[29]: 26 Preparation is by the addition of ammonia to aqueous silver fluoride solution or by the dissolution of silver fluoride in aqueous ammonia.[30]
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