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Silver(II) fluoride



Silver(II) fluoride
General
Systematic name silver(II) fluoride
Other names silver difluoride
Molecular formula AgF2
Molar mass 145.865 g/mol
Appearance white or grey crystalline powder, hygroscopic
CAS number 7775-41-9
Properties
Density and phase 4.58 g/cm3
Solubility in water Decomposes, violently
Melting point 690 °C (963 K)
Boiling point decomposes at 700 °C (973 K)
Structure
Molecular shape linear
Coordination
geometry
tetragonally elongated
octahedral coordination
Crystal structure orthorhombic
Hazards
MSDS MSDS
Main hazards toxic, reacts violently
with water, powerful oxidizer
Related compounds
Other silver(II) halides no other AgX2 stable
at room temp.
Related compounds Silver(I) fluoride, AgF
Silver subfluoride, Ag2F
Silver(II) oxide, AgO
Silver(I) oxide, Ag2O
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and 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.

Additional recommended knowledge

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, a passivated metal container, or a quartz tube. 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

References

  1. ^  Priest, H. F. “Anhydrous Metal Fluorides” Inorganic Syntheses McGraw-Hill: New York, 1950; Vol. 3, pages 171-183.
  2. ^  Encyclopedia of Chemical Technology. Kirk-Othermer. Vol.11, 4th Ed. (1991)
  3. ^  J.T. Wolan, G.B. Hoflund. "Surface Characterization Study of AgF and AgF2 Powders Using XPS and ISS," Applied Surface Science. 125, (1998).
  4. ^  Hans-Christian Miller, Axel Schultz, and Magdolna Hargittai. "Structure and Bonding in Silver Halides: A Quantum...X=F, Cl, Br, I," Journal of the American Chemical Society 127(22), (2005).
  5. ^  Rausch, D.; Davis, r.; Osborne, D. W. "The Addition of Fluorine to Halogenated Olefins by Means of Metal Fluorides," Journal of Organic Chemistry volume 28, pp. 494-497, Jul. (1962).
  6. ^  Zweig, A.; Fischer, R. G.; Lancaster, J. "New Methods for Selective Monofluorination of Aromatics Using Silver Difluoride," Journal of Organic Chemistry volume 45, (1980).
  7. ^  Levec, J.; Slivnik, J.; Zemva, B. "On the Reaction Between Xenon and Fluorine," Journal of Inorganic Nuclear Chemistry Volume 36, (1974).
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Silver(II)_fluoride". A list of authors is available in Wikipedia.
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