AN EXAFS SPECTROSCOPIC STUDY OF AQUEOUS ANTIMONY(III)-CHLORIDE COMPLEXATION AT TEMPERATURES FROM 25 TO 250°C

Abstract

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 #9 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.