8-FeOOH crystal structure

In a recent publication (190), these techniques were applied to elucidate the crystal structure of low-dimensional compounds such as iron oxychloride, FeOCl, and its alkoxy substituents, FeOCl (OR), where R is Me or Et. It was shown that the local symmetry around the iron atom becomes higher for methoxy substituents compared to that for FeOCl. In fact, it is similar to that for y-FeOOH. Similarity of the one-dimensional electron density map along the c axis, obtained separately from X-ray crystallographic studies and from EXAFS fitting, reflects the reliability of the EXAFS fit and indicates its applicability to other two-dimensional systems with poor crystallinity. 

The presence of a hydrated film (FeOOH) was found to depend on the concentration of iron cations at the passive layer-solution interface [64]. In situ surface X-ray diffraction studies indicated that the film consists of a spinel crystal structure [65]. 

Magnetite, Fe304, is a crystalline phase that contains an equal number of Fe and Fe " ions. Its crystal structure is that of an inverse spinel with an oxygen anion lattice containing octahedral and tetrahedral sites that are occupied by metal ions. The Fe " ions occupy the tetrahedral sites and half of the octahedral sites, whereas Fe " is found exclusively on octahedral sites. In contrast to FeOOH phases, magnetite conducts electricity. In addition, it is magnetic. 

Precipitation of ferric chloride in solution (at an iron concentration higher than 4 x 10" mol 1 ) by the addition of a base or thermohydrolysis leads to the oxyhydroxide /3-FeOOH (akaganeite) [58-6la]. Its structure is a parent of goethite. Double chains of octahedra are present in both structures, but they connect differently (Figure 5.16). /3-FeOOH has much wider channels containing variable amounts of chloride ions [58,62]. Unlike basic salts where polydentate ions are usually incorporated in the crystal structure, they are not part of the structure here, and can be exchanged with other ions [63-65]. 

The orange coloured lepidocrocite, y-FeOOH, is named after its platy crystal shape (lepidos scale) and its orange colour (krokus = saffron). It occurs in rocks, soils, biota and rust and is often an oxidation product of Fe ". It has the boehmite (y-AlOOH) structure which is based on cubic close packing (ccp) of anions. 

Maeda, H. Maeda,Y. (1996) Atomic force microscopy studies for investigating the smecti-tic structures of colloidal crystals of P-FeOOH. Langmuir 12 1446-1452... 

Watson, I. (1979) Iron oxide pigments. Colour-frd competitors between natural and synthetic. Minerals in Industry, Aug., 43—51 Watson, J.H.L., Cardell, R.R.Jr. Heller, W. (1962) The internal structure of colloidal crystals of P-FeOOH and remarks on their assemblies in Schiller layers. J. Phys. Chem. 66 1757-1763... 

Anisometric forms of Fe304 with the spinel structure or y-Fe203 with a tetragonal superlattice structure do not crystallize directly. They are obtained from iron compounds that form needle-shaped crystals (usually a- and y-FeOOH, see Section... 

Okamoto et al. [34] studied the crystallization of iron(m) hydroxide gel, containing 15 to 22% water, precipitated from aqueous solution, using X-ray diffraction and Mossbauer spectra. The structure of this material is identified as a hexagonal close-packed lattice of oxygen in which the iron(III) ions are distributed in an almost random manner amongst the available octahedral voids. The kinetics of recrystallization to a-FeOOH were measured from Mossbauer spectra and shown... 

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