XAFS measurements on zinc chloride aqueous solutions from ambient to supercritical conditions using the diamond anvil cell

Abstract

The structure and bonding properties of metal complexes in subcritical and supercritical fluids are still largely unknown. Conventional high pressure and temperature cell designs impose considerable limitations on the pressure, temperature, and concentration of metal salts required for measurements on solutions under supercritical conditions. In this study, we demonstrate the first application of the diamond anvil cell, specially designed for x-ray absorption studies of fn'st-row transition metal ions in supercritical fluids. Zn K-edge XAFS spectra were measured from aqueous solutions of 1-2m ZnC12 and up to 6m NaC1, at temperatures ranging from 25-660 C and pressures up to 800 MPa. Our results indicate that the ZnC142complex is predominant in the lm ZnC12/6m NaC1 solution, while ZnC12(H20)2 is similarly predominant in the 2m ZnC12 solution, at all temperatures and pressures. The Zn-C1 bond length of both types of chlorozinc(II) complexes was found to decrease at a rate of about 0.01 A/100 C.