Speciation of chromium aqua and chloro complexes in hydrochloric acid solutions at 298 K.

The distribution of metal aqua and chloro complexes is fundamental information for analysis of a chemical reaction involving these complexes. The present study investigated the speciation and structures of chromium aqua and chloro complexes using the thermodynamic model fitting analysis of UV-vis/X-ray absorption spectra. The existence of a negatively charged species was examined by adsorbability of chromium species on a strong base anion exchanger. In the results, a planar square [Cr III (H 2 O) 4 ] 3+ , a planar square or distorted tetrahedral [Cr III Cl(H 2 O) 3 ] 2+ , a trigonal bipyramidal [Cr III Cl 3 (H 2 O) 2 ] 0 , and a distorted octahedral [Cr III Cl 4 (H 2 O) 2 ] - were confirmed and the thermodynamic parameters of complexation reactions were quantitatively determined. Investigation of the evolution of speciation of chromium aqua and chloro complexes in a pH 1 solution suggested the existence of [Cr III Cl 2 (H 2 O) m ] + ( m = 2 or 3) during the hydration process, which diminished in the equilibrium state. The kinetic analysis deserves further investigation to understand the speciation process quantitatively.