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.