FEF

FEF or Fef may refer to:

Other uses

Iron(II) fluoride

Iron(II) fluoride (also ferrous fluoride) is the inorganic compound with formula FeF₂. It is a green high-melting solid. The name iron(II) fluoride also applies to hydrates FeF₂·4H₂O.

Structure and physical properties

Like many difluorides, FeF₂ adopts the TiO₂rutile structure wherein the iron centers are octahedrally and the fluoride ions three coordinate. The Fe-F bond lengths are 2.03 and 2.10 Å.

Low temperature neutron diffraction studies show that the material is antiferromagnetic.Heat capacity measurements reveal an event at 78.3 K corresponding to ordering of antiferromagnetic state.

The vapor species were identified between 965 and 1149 K. Using mass spectrometry the heat of sublimation was experimentally determined and averaged to be 75.56 ± 0.23 kcal. mole⁻¹. The following reaction was proposed in order to calculate the atomization energy for Fe⁺:

Synthesis and reactions

The anhydrous salt can be prepared by combining the elements.

Recrystallization of the anhydrous solid from water yields the colorless tetrahydrate, FeF₂·4H₂O, (CAS Number 13940-89-1). The latter can exists in two structures, or polymorphs. One form is rhombohedral and one is hexagonal, the former having a disordered The tetrahydrate oxidizes in moist air to a hydrate of iron(III) fluoride, 2FeF₃·9H₂O. The hydrate is poorly soluble in water, with a solubility product, K_sp, of 2.36 × 10⁻⁶.

Iron(III) fluoride

Iron(III) fluoride, also known as ferric fluoride, is an inorganic compound. It exists in an anhydrous form (formula FeF₃) as well as two hydrated forms (both formula FeF₃·3H₂O). It is produced commercially mostly for laboratory work and is not as useful as the related compound iron(III) chloride. Anhydrous iron(III) fluoride is white while the hydrated forms are light pink.

Chemical and physical properties

Iron(III) fluoride is a thermally robust, paramagnetic solid, consisting of high spin Fe(III) centers, which is consistent with the pale colors of all forms of this material. Both anhydrous iron(III) fluoride as well as its hydrates are hygroscopic.

Structure

The anhydrous form is adopts a simple structure with octahedral Fe(III)F₆ centres interconnected by linear Fe-F-Fe linkages. In the language of crystallography, the crystals are classified as rhombohedral with an R-3c space group. The structural motif is similar to that seen in ReO₃. Although the solid is nonvolatile, it evaporates at high temperatures, the gas at 987 °C consists of FeF₃, a planar molecule of D_3hsymmetry with three equal Fe-F bonds, each of length 176.3 pm. At very high temperatures, it decomposes to give FeF₂ and F₂.