![]() ![]() Bjerrum, 18 in which four chromium aqua and chloro complexes in an octahedral configuration were reported. Most of the investigations were based on the reports by N. 10–21 Table 1 shows a list of investigations. The speciation of chromium aqua and chloro complexes in an equilibrium state has been investigated for over a century. 8 Reactivity, such as hydrolysis, solubility, and so on can be used for understanding the thermodynamic properties. 7 Raman spectroscopy besides electromagnetic radiation is also a useful technique. Therefore, X-ray absorption spectra (XAS) as well as UV-vis absorption spectroscopy is employed to analyse chemical properties of species. 5,6 Specifically, absorption of electromagnetic radiation including light depends on electron orbitals of chemical species. The chemical properties of various beautiful colours have attracted many researchers and it is one of the key factors to consider when investigating metal aqua and chloro complexes. Changes in colour reflect changes in the coordination number of Cl and/or the geometric configuration. 4Ī metal aqua and chloro complex exhibits a beautiful transparent colour depending on the elements and the concentration of Cl in aqueous solutions. 1–3 The distribution of chloride complexes in brines is also significant information in the geochemistry field, used to simulate the flow of metal resources in the deep sea. 1 Introduction Metal aqua and chloro complexes play an important role in hydrometallurgical processes, especially involving the adsorption/desorption process on/from ion exchangers, organic solvents, or ionic liquids. The kinetic analysis deserves further investigation to understand the speciation process quantitatively. Investigation of the evolution of speciation of chromium aqua and chloro complexes in a pH 1 solution suggested the existence of + ( m = 2 or 3) during the hydration process, which diminished in the equilibrium state. In the results, a planar square 3+, a planar square or distorted tetrahedral 2+, a trigonal bipyramidal 0, and a distorted octahedral − were confirmed and the thermodynamic parameters of complexation reactions were quantitatively determined. The existence of a negatively charged species was examined by adsorbability of chromium species on a strong base anion exchanger. 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 distribution of metal aqua and chloro complexes is fundamental information for analysis of a chemical reaction involving these complexes. ![]()
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