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.
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