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

The X-ray adsorption fine structure (EXAFS) spectroscopy of antimony(I II)-chloride solutions were obtained at temperatures from 25 to 250 de grees C at pressures corresponding to the liquid-vapor equilibrium cur ve for H2O. Two solution compositions were considered: solution A cons isted of 0.042 M SbCl3 + 2.9 M HCl and solution B consisted of 0.1 M S bCl3 + 2.29 M HCl. Interpretation of resulting spectra indicates the p resence of aqueous Sb-CI inner sphere complexes at all investigated te mperatures. The average number of chlorine ions in these complexes inc reases with increasing temperature over the range 25 to 250 degrees C from similar to 3.0 to similar to 3.4 and from similar to 2.6 to simil ar to 2.9 for solutions A and B, respectively. These results also indi cate an increasing average number of chloride ions per complex with in creasing aqueous chloride concentration. The Sb-Cl interatomic distanc es for the two solutions are approximately equal and decrease from 2.4 2 to 2.38 Angstrom with increasing temperature over this range. This l atter observation is consistent with theoretical models of aqueous com plexation that predict decreasing aqueous species electrostatic radii with increasing temperature. (C) 1998 Elsevier Science B.V. All rights reserved.