Chromyl fluoride is an inorganic compound

Inorganic compound

Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the formula CrO₂F₂. It is a violet-red colored crystalline solid that melts to an orange-red liquid.

Structure

The liquid and gaseous CrO₂F₂ have a tetrahedral geometry with C_2V symmetry

Symmetry group

The symmetry group of an object is the group of all isometries under which it is invariant with composition as the operation...

, much like chromyl chloride

Chromyl chloride

Chromyl chloride is a chemical compound with the formula CrO2Cl2. This compound is an opaque dark blood-red liquid at room temperature and pressure. It is tetrahedral, somewhat like SO2Cl2. CrO2Cl2 is similar to the most commonly encountered chromium derivative chromate, [CrO4]2−; both are...

. Chromyl fluoride crystallizes in the P2_1/c space group

Space group

In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...

 with Z=4. The Cr=O bond lengths are about 157 pm, and the Cr-F bond lengths are 181.7, 186.7, and 209.4pm. Chromium resides in a distorted octahedral position with a coordination number of six. It dimerizes via fluoride bridges in the solid state.

Reactions

Chromyl fluoride is a strong oxidizing agent

Oxidizing agent

An oxidizing agent can be defined as a substance that removes electrons from another reactant in a redox chemical reaction...

 capable of converting hydrocarbons to ketones and carboxylic acids. It can also be used as a reagent in the preparation of other chromyl compounds. Like some other fluoride compounds, CrO₂F₂ reacts with glass and quartz, so silicon-free plastics or metals must be used when handling the compound.

History and preparation

Pure chromyl fluoride was first isolated in 1952 as reported by Engelbrecht and Grosse. It was first observed as red vapor in the early 19th century upon heating a mixture of fluorspar (CaF₂), chromates, and sulfuric acid. These red vapors were initially thought to be CrF₆, although some chemists assumed a CrO₂F₂ structure analogous to CrO₂Cl₂. The first moderately successful synthesis of chromyl fluoride was reported by Fredenhagen who examined the reaction of hydrogen fluoride

Hydrogen fluoride

Hydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...

 with alkali chromates. A later attempt saw Wartenberg prepared impure CrO₂F₂ by treating CrO₂Cl₂ with elemental fluorine

Fluorine

Fluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...

. Another attempt was made by Wiechert, who treated HF with dichromate, yielding impure liquid CrO2F2 at -40 °C.

Engelbrecht and Grosse’s synthesis of CrO₂F₂, and most successive syntheses, involve treating chromium trioxide

Chromium trioxide

Chromium trioxide is the inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.This compound is a dark-red/orange brown solid, which dissolves in water concomitant with hydrolysis...

 (CrO₃) with a fluorinating agent:

CrO₃ + 2 HF → CrO₂F₂ + H₂O

The reaction is reversible, as water will readily hydrolyze CrO₂F₂ back to CrO₃.
Other methods include treatment with chlorine fluoride, carbonyl fluoride

Carbonyl fluoride

Carbonyl fluoride is the chemical compound with the formula COF2. This gas, like its analog phosgene, is highly toxic. The molecule is planar with C2v symmetry.-Safety:...

, or some metal hexafluorides:

CrO₃ + 2 ClF → CrO₂F₂ + Cl₂ + O₂

CrO₃ + COF₂ → CrO₂F₂ + CO₂

CrO₃ + MF₆ → CrO₂F₂ + MOF₄ (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 CrO₂F₂. They reported 100% yield when the reactions were conducted at 120°C. As expected from the relative reactivities of MoF₆ and WF₆, the MoF₆ reaction proceeded more readily.

Reactions

In addition to being to oxidizing hydrocarbons to ketones and carboxylic acids, CrO₂F₂ participates in a variety of other reactions as reported by Brown, Green, and Gard. Chromyl Fluoride can exchange fluorine atoms with metal oxides.

CrO₂F₂ + MO → MF₂ + CrO₃

Chromyl fluoride will also convert the oxides of boron and silicon to the fluorides.

Chromyl fluoride reacts with alkali and alkaline earth metal fluorides in a perfluoroheptane solvent to produce the orange-colored fluorochromates:

CrO₂F₂ + 2 MF → M₂CrO₂F₄

Chromyl fluoride will react with Lewis acids as well:

CrO₂F₂ + 2(CF₃CO)₂O → CrO₂(CF₃COO)₂ + 2CF₃COF

Chromyl fluoride forms adducts with weak bases NO, NO2, and SO₂.