An EXAFS spectroscopic study of aqueous antimony(III)-chloride complexation at temperatures from 25 to 250°C

The X-ray adsorption fine structure (EXAFS) spectroscopy of antimony(III)-chloride solutions were obtained at temperatures from 25 to 250°C at pressures corresponding to the liquid–vapor equilibrium curve for H2O. Two solution compositions were considered: solution A consisted of 0.042 M SbCl3+2.9 M HCl and solution B consisted of 0.1 M SbCl3+2.29 M HCl. Interpretation of resulting spectra indicates the presence of aqueous Sb–Cl inner sphere complexes at all investigated temperatures. The average number of chlorine ions in these complexes increases with increasing temperature over the range 25 to 250°C from ∼3.0 to ∼3.4 and from ∼2.6 to ∼2.9 for solutions A and B, respectively. These results also indicate an increasing average number of chloride ions per complex with increasing aqueous chloride concentration. The Sb–Cl interatomic distances for the two solutions are approximately equal and decrease from 2.42 to 2.38 Å with increasing temperature over this range. This latter observation is consistent with theoretical models of aqueous complexation that predict decreasing aqueous species electrostatic radii with increasing temperature.