Chromyl fluoride

Structure

The liquid and gaseous have a tetrahedral geometry with C2v symmetry, much like chromyl chloride. Chromyl fluoride dimerizes via fluoride bridges (as ) in the solid state, crystallizing in the P21/c space group with Z = 4. The Cr=O bond lengths are about 157 pm, and the Cr–F bond lengths are 181.7, 186.7, and 209.4 pm. Chromium resides in a distorted octahedral position with a coordination number of 6.

History and preparation

Pure chromyl fluoride was first isolated in 1952 as reported by Alfred Engelbrecht and Aristid von Grosse. It was first observed as red vapor in the early 19th century upon heating a mixture of fluorspar (), chromates, and sulfuric acid. These red vapors were initially thought to be , although some chemists assumed a structure analogous to . Another attempt was made by Wiechert, who treated HF with dichromate, yielding impure liquid at −40 °C.

Engelbrecht and von Grosse's synthesis of , and most successive syntheses, involve treating chromium trioxide with a fluorinating agent: : The reaction is reversible, as water will readily hydrolyze back to .

The approach published by Georg Brauer in the Handbook of Preparative Inorganic Chemistry drew on von Wartenberg's approach of direct fluoridation: :

Other methods include treatment with chlorine fluoride, carbonyl fluoride, or some metal hexafluorides: : : : (M = Mo, W)

The last method involving the fluorides of tungsten and molybdenum are reported by Green and Gard to be very simple and effective routes to large quantities of pure .

Reactions

Chromyl fluoride is a strong oxidizing agent capable of converting hydrocarbons to ketones and carboxylic acids. It can also be used as a reagent in the preparation of other chromyl compounds. Chromyl fluoride can exchange fluorine atoms with metal oxides.

:

where M is a metal. Chromyl fluoride also converts the oxides of boron and silicon to their fluorides.

Chromyl fluoride reacts with alkali and alkaline earth metal fluorides in perfluoroheptane (solvent) to produce orange-colored tetrafluorodioxochromates(VI): : Chromyl fluoride also reacts with Lewis acids, drawing carboxylate ligands from organic acid anhydrides and producing an acyl fluoride byproduct: : Chromyl fluoride forms adducts with weak Lewis bases NO, , and .

Chromium oxytetrafluoride is prepared by fluorination of chromyl fluoride with krypton difluoride: :

References

References

1. Brauer, Georg. (1963). "Handbook of Preparative Inorganic Chemistry, Volume 1". [[Ferdinand Enke Verlag]]; [[Academic Press, Inc.]].
2. (1986). "Inorganic Syntheses".
3. (1958). "Infrared Absorption Spectra of Chromyl Fluoride and Chromyl Chloride". The Journal of Chemical Physics.
4. (2007). "Technetium Fluoride Trioxide, TcO₃F, Preparation and Properties". Inorganic Chemistry.
5. (1952). "Pure Chromyl Fluoride¹". Journal of the American Chemical Society.
6. (1941). "Über höhere Chromfluoride (CRF₄, CRF₅ und CrO₂F₂)". Zeitschrift für Anorganische und Allgemeine Chemie.
7. (1977). "Chemistry of chromyl fluoride. 5. New preparative routes to chromyl fluoride". Inorganic Chemistry.
8. (1986). "Synthesis and characterization of CrF4O, KrF2.CrF4O, and NO+CrF5O-". Inorganic Chemistry.