Silver(II) fluoride

Silver(II) fluoride
Silver(II) Fluoride Structure
General
Systematic name	silver(II) fluoride
Other names	silver difluoride
Molecular formula	AgF₂
Molar mass	145.865 g/mol
Appearance	white or grey crystaline 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 (973K)
Structure
Molecular shape	linear
Coordination geometry	tetragonally elongated octahedral coordination
Crystal structure	orthorombic
Hazards
MSDS	MSDS
Main hazards	toxic, reacts violently with water, powerful oxidizer
Related compounds
Other Ag(II) halides	no other AgX₂ stable at room temp.
Related compounds	Silver(I) fluoride (AgF), Ag₂F, AgO, Ag₂O
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Chemical infobox

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.

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.

Silver(II) fluoride should be stored in Teflon, a passivated metal container, or a quartz tube. AgF₂ is light sensitive.

AgF₂ can be purchased from various suppliers, the demand being less than 100kg/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 dollar per kg.

Composition and structure

Pure AgF₂ is a white crystalline powder, but it is usually black/brown-colored due to contaminates. The F/Ag ratio for most samples is < 2, typically approaching 1.75 due to contamination with Ag and oxides and carbon.

For some time, it was doubted silver was actually in the 2+ oxidation state rather in some combination of states such as Ag(I)which would be similar to silver oxide. However, neutron diffraction studies confirm the description as silver(II). The Ag(I)[Ag(III)F₄ was found to be present at high temperatures, but it was unstable with respect to AgF₂.

AgF₂ is believed to have D_∞h symmetry.

Approximately 14 kcal/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

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.

Selective monofluorination of aromatics

Substitutive fluorinations of aromatic compounds are readily achieved, but selective monofluorinations are more difficult.

C₆H₆ + 2 AgF₂ → C₆H₅F + 2 AgF + HF

Oxidation of xenon . This reaction, which can be explosive, proceeds in homogeneous anhydrous HF solutions producing XeF₂.

AgF₂ oxidizes carbon monoxide to carbonyl fluoride.

References

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," J. Am. Chem. Soc. 127(22), (2005).
Douglas Rausch, Ralph Davis, and D. Wendell Osborne. "The Addition of Fluorine to Halogenated Olefins by Means of Metal Fluorides," J. Org. Chem. 28, pp. 494-497, Jul. (1962).
Arnold Zweig, Robert G. Fischer, and John Lancaster. "New Methods for Selective Monofluorination of Aromatics Using Silver Difluoride," J. Org. Chem. 45, (1980).
J. Levec, J. Slivnik, and B. Zemva. "On the Reaction Between Xenon and Fluorine," J. Inorg. Nucl. Chem. Vol. 36, (1974).

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