Local structure of ferric hydroxide Fe(OH)₃ in aqueous solution by the anomalous X-ray scattering and EXAFS methods

The atomic structure around ferric ions of the ferric hydroxide Fe(OH)₃ in aqueous solution has been studied by the anomalous X-ray scattering (AXS) and EXAFS methods. It is found that this ferric hydroxide consists of the FeO₆ octahedral unit structure and these octahedral units are connected with the edge and double-corner sharing linkage. On the other hand, the powder of the present ferric hydroxide prepared by freeze-drying the aqueous solution was also studied by the conventional X-ray diffraction method. The atomic structure of ferric hydroxide powder is also found to consist of the FeO₆ octahedra connected with the edge and double-corner sharing linkage. Referring to the crystalline structures of other ferric hydroxides and oxides, it is predicted that the FeO₆ octahedral chains formed by the edge sharing linkage are connected with the double-corner sharing linkage in the present ferric hydroxide Fe(OH)₃ solution and powder. The number of the double-corner sharing linkage in solution is about 60% of that in powder. This implies that the solution structure is characterized by the octahedral chains with a relatively large amount of vacant space.