| Silver(II) fluoride | |
|---|---|
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|
| IUPAC name |
silver(II) fluoride
|
| Other names | silver difluoride |
| Identifiers | |
| CAS number | 7775-41-9 |
| Properties | |
| Molecular formula | AgF2 |
| Molar mass | 145.865 g/mol |
| Appearance | white or grey crystalline powder, hygroscopic |
| Density | 4.58 g/cm3 |
| Melting point |
690 °C (963 K) |
| Boiling point |
decomposes at 700 °C (973 K) |
| Solubility in water | Decomposes, violently |
| Structure | |
| Crystal structure | orthorhombic |
| Coordination geometry |
tetragonally elongated octahedral coordination |
| Molecular shape | linear |
| Hazards | |
| MSDS | MSDS |
| Main hazards | toxic, reacts violently with water, powerful oxidizer |
| Related compounds | |
| Other anions | silver(I,III) oxide |
| Other cations | copper(II) fluoride, palladium(II) fluoride, cadmium(II) fluoride |
| Related compounds | silver(I) fluoride |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
| Infobox references | |
Silver(II) fluoride is a chemical compound with the formula AgF2. It is a rare example of a silver(II) compound. Silver is usually present in its +1 oxidation state. It is used as a fluorinating agent.
Contents |
Preparation
AgF2 can be synthesized by fluorinating Ag2O with elemental fluorine. Also, at 200 °C (473 K) elemental fluorine will react with AgF or AgCl to produce AgF2.[1][2]
As a strong fluorinating agent, AgF2 should be stored in Teflon or a passivated metal container. It is light sensitive.
AgF2 can be purchased from various suppliers, the demand being less than 100 kg/year. While laboratory experiments find use for AgF2, it is too expensive for large scale industry use. In 1993, AgF2 cost between 1000-1400 US dollars per kg.
Composition and structure
AgF2 is a white crystalline powder, but it is usually black/brown due to impurities. The F/Ag ratio for most samples is< 2, typically approaching 1.75 due to contamination with Ag and oxides and carbon. [3]
For some time, it was doubted silver was actually in the 2+ oxidation state rather in some combination of states such as AgI[AgIIIF4], which would be similar to silver oxide. Neutron diffraction studies, however, confirmed its description as silver(II). The AgI[AgIIIF4] was found to be present at high temperatures, but it was unstable with respect to AgF2.[4]
In the gas phase, AgF2 is believed to have D∞h symmetry.
Approximately 14 kcal/mol (59 kJ/mol) separate the ground and first states. The compound is paramagnetic, but it becomes ferromagnetic at temperatures below −110 °C (163 K).
Uses
AgF2 is a strong fluorinating and oxidation agent. Illustrative applications are listed below.
- Fluoronation and preparation of organic perfluorocompounds [5]
This type of reaction can occur in three different ways (here Z refers to any element or group attached to carbon, X is a halogen):
- 1) CZ3H + 2 AgF2 → CZ3F +HF + 2 AgF
- 2) CZ3X + 2AgF2 → CZ3F +X2 + 2 AgF
- 3) Z2C=CZ2 + 2 AgF2 → Z2CFCFZ2 + 2 AgF
Similar transformations can also be effected using other high valence metallic fluorides such as CoF3, MnF3, CeF4, and PbF4.
- Fluorinations of aromatic compounds is readily achieved, but selective monofluorinations are more difficult:[6]
- C6H6 + 2 AgF2 → C6H5F + 2 AgF + HF
- Oxidation of xenon [7]. This reaction, which can be explosive, proceeds in anhydrous HF solutions producing XeF2.
- AgF2 oxidizes carbon monoxide to carbonyl fluoride.
References
- ^ Priest, H. F.; Swinehert, Carl F. (1950). "Anhydrous Metal Fluorides". Inorg. Synth. 3: 171–183. doi:.
- ^ Encyclopedia of Chemical Technology. Kirk-Othermer. Vol.11, 4th Ed. (1991)
- ^ J.T. Wolan, G.B. Hoflund (1998). "Surface Characterization Study of AgF and AgF2 Powders Using XPS and ISS". Applied Surface Science 125: 251. doi:.
- ^ Hans-Christian Miller, Axel Schultz, and Magdolna Hargittai (2005). "Structure and Bonding in Silver Halides. A Quantum Chemical Study of the Monomers: Ag2X, AgX, AgX2, and AgX3(X = F, Cl, Br, I)". J. Am. Chem. Soc. 127 (22): 8133. doi:.
- ^ Rausch, D.; Davis, r.; Osborne, D. W. (1962). "The Addition of Fluorine to Halogenated Olefins by Means of Metal Fluorides". J. Org. Chem. 28: 494–497. doi:.
- ^ Zweig, A.; Fischer, R. G.; Lancaster, J. (1980). "New Methods for Selective Monofluorination of Aromatics Using Silver Difluoride". J. Org. Chem. 45: 3597. doi:.
- ^ Levec, J.; Slivnik, J.; Zemva, B. (1974). "On the Reaction Between Xenon and Fluorine". Journal of Inorganic Nuclear Chemistry 36: 997. doi:.
External links
- National Pollutant Inventory Fluoride and compounds fact sheet
- WebElements Silver(II) Fluoride
- Structure graphic
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