Silver(II) fluoride

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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 has the formula AgF₂. It is currently the only silver(II) compound that is known to be stable at room temperature (25 °C). Silver is usually present in its +1 oxidation state, making the formation of AgF₂ unusual.

1 Preparation
2 Composition and structure
3 Uses
4 References
5 External links
6 Suppliers

[edit] 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.

[edit] 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 Ag^I[Ag^IIIF₄], which would be similar to silver oxide. Neutron diffraction studies, however, confirmed its description as silver(II). The Ag^I[Ag^IIIF₄] 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).

[edit] 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.

Fluorination]]s 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.

[edit] References

↑ Priest, H. F. “Anhydrous Metal Fluorides” Inorganic Syntheses McGraw-Hill: New York, 1950; Vol. 3, pages 171-183.
↑ Encyclopedia of Chemical Technology. Kirk-Othermer. Vol.11, 4th Ed. (1991)
↑ J.T. Wolan, G.B. Hoflund. "Surface Characterization Study of AgF and AgF₂ Powders Using XPS and ISS," Applied Surface Science. 125, (1998).
↑ 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).
↑ 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).
↑ Zweig, A.; Fischer, R. G.; Lancaster, J. "New Methods for Selective Monofluorination of Aromatics Using Silver Difluoride," Journal of Organic Chemistry volume 45, (1980).
↑ Levec, J.; Slivnik, J.; Zemva, B. "On the Reaction Between Xenon and Fluorine," Journal of Inorganic Nuclear Chemistry Volume 36, (1974).