Silver(II) fluoride is a chemical compound with the formula AgF2. It is a rare example of a silver(II) compound - silver usually exists in its +1 oxidation state. It is used as a fluorinating agent.
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. For some time, it was doubted that silver was actually in the +2 oxidation state, rather than some combination of states such as AgI[AgIIIF4], which would be similar to silver(I,III) 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. In the gas phase, AgF2 is believed to have D∞h symmetry. Per single-crystal X-ray diffraction, the silver atoms are square planar-coordinated in the solid state. Approximately 14 kcal/mol (59 kJ/mol; 0.61 eV/f.u.) separate the ground and first excited states. The compound is paramagnetic, but it becomes ferromagnetic at temperatures below −110 °C (163 K).
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.
Uses AgF2 is a strong fluorinating and oxidising agent. It is formed as an intermediate in the catalysis of gaseous reactions with fluorine by silver. With fluoride ions, it forms complex ions such as AgF−3, the blue-violet AgF2−4, and AgF4−6. It is used in the fluorination 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):
CZ3H + 2 AgF2 → CZ3F + HF + 2 AgF CZ3X + 2AgF2 → CZ3F + X2 + 2 AgF 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. AgF2 is also used in the fluorination of aromatic compounds, although selective monofluorinations are more difficult:
C6H6 + 2 AgF2 → C6H5F + 2 AgF + HF AgF2 oxidises xenon to xenon difluoride in anhydrous HF solutions.
2 AgF2 + Xe → 2 AgF + XeF2 It also oxidises carbon monoxide to carbonyl fluoride.
2 AgF2 + CO → 2 AgF + COF2 It reacts with water to form oxygen gas:
4 AgF2 + 4 H2O → 2 Ag2O + 8 HF + O2 AgF2 can be used to selectively fluorinate pyridine at the ortho position under mild conditions.
Safety AgF2 is a very strong oxidizer that reacts violently with water, reacts with dilute acids to produce ozone, oxidizes iodide to iodine, and upon contact with acetylene forms the contact explosive silver acetylide. It is light-sensitive, very hygroscopic and corrosive. It decomposes violently on contact with hydrogen peroxide, releasing oxygen gas. It also liberates HF, F2, and elemental silver.
References
External links
National Pollutant Inventory Fluoride and compounds fact sheet WebElements Silver(II) Fluoride Structure graphic Archived 2016-03-03 at the Wayback Machine
