Speciation and crystal chemistry of iron(III) chloride hydrolyzed in the presence of SiO4 ligands. 1. An FeK-edge EXAFS study

The hydrolysis of Fe-Si systems with Si/Fe ratios between 0 and 4 leads to the formation of poorly crystalline or, more frequently, of long-range diso rganized precipitates. The increase of Si/Fe molar ratios results in an dra matic change of Fe polymerization. The formation of double and single corne r-sharing Fe linkages is reduced compared to pure Fe hydrolysis products. T he growth regime depends on the Si concentration in the system. Three-dimen sional and two-dimensional growth of Fe colloids occurs at low and high Si/ Fe ratios, respectively, systems with Si/Fe ratios around 1 representing a crossover between these two regimes. Though Si neighbors cannot be detected unequivocally by Fe K-edge EXAFS, their presence in the close environment of Fe atoms is evident from the change in Fe speciation.