silver(I) fluoride

High-purity silver(I) fluoride can be produced by the heating of silver carbonate to {{Convert|310|C|F|abbr=on}} under a hydrogen fluoride environment, in a platinum tube:{{cite book|last=Roesky|first=Herbert W.|title=Efficient Preparation of Fluorine Compounds|date=2012|publisher=Wiley|location=Somerset, New Jersey|isbn=9781118409428}}{{rp|9}}

:{{chem2 | Ag2CO3 + 2 HF -> 2 AgF + H2O + CO2 }}

Laboratory routes to the compound typically avoid the use of gaseous hydrogen fluoride. One method is the thermal decomposition of silver tetrafluoroborate:

:{{chem2 | AgBF4 -> AgF + BF3 }}

In an alternative route, silver(I) oxide is dissolved in concentrated aqueous hydrofluoric acid, and the silver fluoride is precipitated out of the resulting solution by acetone.{{rp|10}}

:{{chem2 | Ag2O + 2 HF -> 2 AgF + H2O }}

The structure of AgF has been determined by X-ray diffraction.{{cite journal|last1=Ott|first1=H.|title=XI. Die Strukturen von MnO, MnS, AgF, NiS, SnJ4, SrCl2, BaF2; Präzisionsmessungen einiger Alkalihalogenide|journal=Z. Kristallogr.|date=1926|volume=63|issue=1–6|pages=222–230|doi=10.1524/zkri.1926.63.1.222|s2cid=102244646}}{{cite journal|last1=Bottger|first1=G.L.|last2=Geddes|first2=A.L.|title=Lattice Vibrations, Crystal Structure, Dielectric Properties, and Elastic Constants of AgF|journal=J. Chem. Phys.|date=1972|volume=56|issue=8|pages=3735–3739|doi=10.1063/1.1677770|bibcode=1972JChPh..56.3735B}}{{rp|3736}}{{cite journal|last1=Lozinšek|first1=Matic|last2=Belak Vivod|first2=Matic|last3=Dragomir|first3=Mirela|title=Crystal structure reinvestigation of silver(I) fluoride, AgF|journal=IUCrData|date=2023|volume=8|issue=Pt 1 |pages=x230018|doi=10.1107/S2414314623000184|pmid=36794053 |pmc=9912324|bibcode=2023IUCrD...830018L }} At ambient temperature and pressure, silver(I) fluoride exists as the polymorph AgF-I, which adopts a cubic crystal system with space group Fm{{overline|3}}m in the Hermann–Mauguin notation. The rock 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.{{cite journal|last1=Birtcher|first1=R.C.|last2=Deutsch|first2=P.W.|last3=Wendelken|first3=J.F.|last4=Kunz|first4=A.B.|title = Valence band structure in silver fluoride|journal=J. Phys. C: Solid State Phys.|date=1972|volume=5|issue=5|pages=562–6|doi=10.1088/0022-3719/5/5/008|bibcode=1972JPhC....5..562B}}{{rp|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 the caesium chloride structure, and lattice parameter 2.945 Å.{{cite journal|last1=Hull|first1=S.|last2=Berastegui|first2=P|title=High-pressure structural behaviour of silver(I) fluoride|journal=J. Phys.: Condens. Matter|date=1998|volume=10|issue=36|pages=7945–7955|doi=10.1088/0953-8984/10/36/005|bibcode=1998JPCM...10.7945H|s2cid=250869196 }}{{rp|7945}}{{cite journal|last1=Halleck|first1=P.M.|last2=Jamieson|first2=J.C.|title=B1 and B2 phase change of AgF at high pressure|journal=J. Phys. Chem. Solids|date=1972|volume=33|issue=4|pages=769–773|doi=10.1016/s0022-3697(72)80093-3|bibcode=1972JPCS...33..769H}}{{rp|770}} The associated decrease in volume is approximately ten percent.{{rp|7946}} A third polymorph, AgF-III, forms on reducing the pressure to 2.59(2) GPa, and has an inverse nickel 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.{{cite journal|last1=Jamieson|first1=J.C.|last2=Halleck|first2=P.M.|last3=Roof|first3=R.B.|last4=Pistorius|first4=C.W.F.T.|title=Additional polymorphism and non-stoichiometry in AgF|journal=Journal of Physics and Chemistry of Solids|date=1975|volume=36|issue=9|pages=939–944|doi=10.1016/0022-3697(75)90172-9|bibcode=1975JPCS...36..939J}}{{rp|939}}{{rp|7947}}

Silver(I) fluoride exhibits unusual optical properties. Simple electronic band theory predicts that the fundamental exciton absorption 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.{{cite journal|last1=Marchetti|first1=A.P.|last2=Bottger|first2=G.L.|title=Optical Absorption Spectrum of AgF|journal=Physical Review B|date=1971|volume=3|issue=8|pages=2604–7|doi=10.1103/physrevb.3.2604|bibcode=1971PhRvB...3.2604M}}{{rp|2604}} This discrepancy can be explained by positing transition from a valence band with largely silver 4d-orbital character.{{rp|563}} The high frequency refractive index is 1.73(2).{{rp|3737}}

In contrast with the other silver halides, anhydrous silver(I) fluoride is not appreciably photosensitive, although the dihydrate is.{{cite book|last1=Slayter|first1=Elizabeth|title=Light and Electron Microscopy|date=1992|publisher=Cambridge University Press|isbn=9780521339483|url=https://books.google.com/books?id=LlePVS9oq7MC}}{{rp|286}}{{cite book|last1=Palmer|first1=William George|title=Experimental Inorganic Chemistry|date=1954|publisher=CUP Archive|isbn=9780521059022}}{{rp|150}} With this and the material's solubility in water considered, it is unsurprising that it has found little application in photography but may have been one of the salts used by Levi Hill in his "heliochromy",{{Cite book|url=https://archive.org/details/treatiseonhelioc00hill|title=A treatise on heliochromy : or, The production of pictures, by means of light, in natural colors. Embracing a full, plain, and unreserved description of the process known as the hillotype, including the author's newly discovered collodio-chrome, or natural colors on collodionized glass ...|last=Hill|first=Levi L.|date=1856|publisher=New York : Robinson & Caswell|others=Getty Research Institute|page=143}} although a US patent for an experimental AgF-based method was granted in 1970.{{cite patent

| country = US

| number = 3537855

| status = patent

| title = Photosensitive silver fluoride element

| pubdate = 1971-11-3

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Unlike the other silver halides, AgF is highly soluble in water (1800 g/L), and it even has some solubility in acetonitrile. 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.{{Greenwood&Earnshaw2nd|page=}}{{rp|1185}}{{cite journal|last1=Tyrra|first1=Wieland|title=Silver(I) fluoride and related compounds in chemical synthesis|journal=Heteroatom Chemistry|year=2002|volume=13|issue=6|pages=561–566|doi=10.1002/hc.10102}} Like the alkali metal fluorides, it dissolves in hydrogen fluoride to give a conducting solution.{{cite book|last1=Schwartz|first1=Mel|title=Encyclopedia of Materials, Parts and Finishes|date=2002|publisher=CRC press|isbn=1420017160|page=305|edition=2nd}}

Silver(I) fluoride finds application in organofluorine chemistry for addition of fluoride across multiple bonds. For example, AgF adds to perfluoroalkenes in acetonitrile to give perfluoroalkylsilver(I) derivatives.{{cite journal | last1 = Miller | first1 = W. T. | last2 = Burnard | first2 = R. J. | year = 1968 | title = Perfluoroalkylsilver compounds" "Title | journal = J. Am. Chem. Soc. | volume = 90 | pages = 7367–7368 | doi=10.1021/ja01028a047}}{{rp|7367}} It can also be used as a desulfuration-fluorination reagent on thiourea derived substrates.{{rp|562}} Due to 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. An example is given by the following reaction:{{cite journal|last1=Muller|first1=Paul|last2=Etienne|first2=Robert|last3=Pfyfer|first3=Jean|last4=Pinenda|first4=Nelson|last5=Schipoff|first5=Michel|title=Allylic Reactions of Benzocyclopropenes. Discrimination of Halogen Substituents in 1,l-Dihalogenobenzocyclopropenes|journal=Helvetica Chimica Acta|date=1978|volume=61|issue=7|pages=2482–8|doi=10.1002/hlca.19780610719 }}

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Another organic synthetic method using silver(I) fluoride is the BINAP-AgF complex catalyzed enantioselective protonation of silyl enol ethers:{{cite journal|last1=Yanagisawa|first1=Akira|last2=Touge|first2=Taichiro|last3=Takayoshi|first3=Arai|title=Enantioselective Protonation of Silyl Enolates Catalyzed by a Binap⋅AgF Complex|journal=Angewandte Chemie International Edition|date=2005|volume=44|issue=10|pages=1546–8|doi=10.1002/anie.200462325|pmid=15645475}}{{rp|1546}}

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The reaction of silver acetylide with a concentrated solution of silver(I) fluoride results in the formation of a chandelier-like [Ag₁₀]²⁺ cluster with endohedral acetylenediide.{{cite journal|last1=Guo|first1=Guo-Cong|last2=Zhou|first2=Gong-Du|last3=Wang|first3=Qi-Guang|last4=Mak|first4=Thomas C.W.|title=A Fully Encapsulated Acetylenediide in Ag₂C₂.8AgF|journal=Angewandte Chemie International Edition|date=1998|volume=37|issue=5|pages=630–2|doi=10.1002/(sici)1521-3773(19980316)37:5<630::aid-anie630>3.0.co;2-k|pmid=29711066 }}

Tetralkylammonium fluorides can be conveniently prepared in the laboratory by the reaction of the tetralkylammonium bromide with an aqueous AgF solution.{{cite journal|last1=Clark|first1=James H.|title=Fluoride ion as a base in organic synthesis|journal=Chemical Reviews|year=1980|volume=80|issue=5|pages=429–452|doi=10.1021/cr60327a004}}{{rp|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.{{cite journal|last1=Voorhoeve|first1=R. J. H.|last2=Merewether|first2=J. W.|title=Selective Deposition of Silver on Silicon by Reaction with Silver Fluoride Vapor|journal=J. Electrochem. Soc.|date=1972|volume=119|issue=3|pages=364–368|doi=10.1149/1.2404203|bibcode=1972JElS..119..364V|doi-access=free}} The relevant reaction is:

:{{chem2 | 4 AgF + Si -> 4 Ag + SiF4 }}

Multiple studies have shown silver(I) fluoride to be an effective anti-caries agent, although the mechanism is the subject of current research.{{cite journal|last1=Peng|first1=J. J-Y.|last2=Botelho|first2=M.G.|last3=Matinlinna|first3=J.P.|title=Silver compounds used in dentistry for caries management: A review|journal=Journal of Dentistry|date=2012|volume=40|issue=7|pages=531–541|doi=10.1016/j.jdent.2012.03.009|pmid=22484380}} Treatment is typically by the "atraumatic" method, in which 40% by mass aqueous silver(I) fluoride solution is applied to carious leisons, followed by sealing of the dentine with glass ionomer cement.{{cite journal|last1=Gotjamanos|first1=Theo|last2=Afonso|first2=Fernando|title=Unacceptably high levels of fluoride in commercial preparations of silver fluoride|journal=Australian Dental Journal|date=1997|volume=42|issue=1|pages=52–3|doi=10.1111/j.1834-7819.1997.tb00097.x|pmid=9078648|doi-access=free}} Although the treatment is generally recognised to be safe, fluoride toxicity has been a significant clinical concern in paediatric applications, especially as some commercial preparations have had considerable silver(II) fluoride contamination in the past.{{cite journal|last1=Gotjamanos|first1=Theo|last2=Orton|first2=Vergil|title=Abnormally high fluoride levels in commercial preparations of 40 per cent silver fluoride solution: Contraindications for use in children|journal=Australian Dental Journal|date=1998|volume=43|issue=6|pages=422–7|doi=10.1111/j.1834-7819.1998.tb00203.x|pmid=9973713}}{{cite journal|last1=Shah|first1=Shalin|last2=Bhaskar|first2=Visjay|last3=Venkatraghavan|first3=Karthik|last4=Choudhary|first4=Prashant|last5=Trivedi|first5=Krishna|last6=M.|first6=Ganesh|title=Silver Diamine Fluoride: A Review and Current Applications|journal=Journal of Advanced Oral Research|date=2014|volume=5|issue=1|pages=25–35|doi=10.1177/2229411220140106|s2cid=56987580|doi-access=free}} Due to the instability of concentrated AgF solutions, silver diammine fluoride (Ag(NH₃)₂F) is now more commonly used.{{rp|26}} Preparation is by the addition of ammonia to aqueous silver fluoride solution or by the dissolution of silver fluoride in aqueous ammonia.{{cite patent

| country = US

| number = 3567823

| status = patent

| title = Silver ammonia fluoride solution and method of its use

| pubdate = 1971-2-12

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| invent1 = Yokomizo Ichiro

| invent2 = Yamaga Reiichi

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{{reflist}}

{{Silver compounds}}

{{Fluorides}}

{{DEFAULTSORT:Silver(I) Fluoride}}

Category:Fluorides

Category:Silver compounds

Category:Metal halides

Category:Fluorinating agents

Category:Rock salt crystal structure