Sipos Pál, Zeller Dalma, Kuzmann Erno, Vértes Attila, Homonnay Zoltán, Walczak Monika, Canton Sophie E
University of Szeged, Department of Inorganic and Analytical Chemistry, PO Box 440, H-6701, Szeged, Hungary.
Dalton Trans. 2008 Nov 7(41):5603-11. doi: 10.1039/b806937a. Epub 2008 Aug 27.
To establish the structure of ferric ions in strongly alkaline (pH > 13) environments, aqueous NaOH solutions supersaturated with respect to Fe(III) and the solid ferric-hydroxo complex salts precipitating from them have been characterized with a variety of experimental techniques. From UV measurements, in solutions of pH > 13, only one kind of Fe(III)-hydroxo complex species was found to be present. The micro crystals obtained from such solutions were proven to be a new, so far unidentified solid phase. Mössbauer spectra of the quick-frozen solution and that of the complex salt indicated a highly symmetrical ferric environment in both systems From the EXAFS and XANES spectra, the environment of the ferric ion in these solutions (both native and quick-frozen) and in the complex salt was found to be different. In the complex salt, the bond lengths are consistent with an octahedral coordination around the ferric centres. In solution, the coordination geometry of Fe(III) is most probably tetrahedral. Our results demonstrate that in strongly alkaline aqueous solutions, ferric ions behave very similarly to other structurally related tervalent ions, like Al(III) or Ga(III).
为确定强碱性（pH > 13）环境中铁离子的结构，对相对于Fe(III)过饱和的NaOH水溶液以及从中沉淀出的固态铁羟基络合物盐，采用了多种实验技术进行表征。通过紫外测量发现，在pH > 13的溶液中，仅存在一种Fe(III) - 羟基络合物物种。从这类溶液中获得的微晶被证明是一种新的、迄今尚未鉴定的固相。速冻溶液和络合物盐的穆斯堡尔光谱表明，两个体系中铁环境都具有高度对称性。从扩展X射线吸收精细结构（EXAFS）和X射线吸收近边结构（XANES）光谱可知，这些溶液（天然的和速冻的）以及络合物盐中铁离子的环境有所不同。在络合物盐中，键长与铁中心周围的八面体配位一致。在溶液中，Fe(III)的配位几何结构很可能是四面体。我们的结果表明，在强碱性水溶液中，铁离子的行为与其他结构相关的三价离子（如Al(III)或Ga(III)）非常相似。
