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 D3h symmetry with three equal Fe-F bonds, each of length 176.3 pm. At very high temperatures, it decomposes to give FeF2 and F2.
Two crystalline forms - or more technically, polymorphs - of FeF3·3H2O are known, the α and β forms. These are prepared by evaporation of an HF solution containing Fe3+ at room temperature (α form) and above 50°C (β form). The space group of the β form is P4/m, and the α form maintains a P4/m space group with a J6 substructure. The solid α form is unstable and converts to the β form within days. The two forms are distinguished by their difference in quadrupole splitting from their Mössbauer spectra.
Read more about this topic: Iron(III) Fluoride
Famous quotes containing the word structure:
“It is difficult even to choose the adjective
For this blank cold, this sadness without cause.
The great structure has become a minor house.
No turban walks across the lessened floors.
The greenhouse never so badly needed paint.”
—Wallace Stevens (1879–1955)
“Just as a new scientific discovery manifests something that was already latent in the order of nature, and at the same time is logically related to the total structure of the existing science, so the new poem manifests something that was already latent in the order of words.”
—Northrop Frye (b. 1912)
“Who says that fictions only and false hair
Become a verse? Is there in truth no beauty?
Is all good structure in a winding stair?
May no lines pass, except they do their duty
Not to a true, but painted chair?”
—George Herbert (1593–1633)