Chemical speciation in concentrated aqueous solutions of CuCl2 using thin-film UV–visible spectroscopy combined with DFT calculations

Abstract

In this work, a thin-film UV–visible spectroscopic technique has been developed and combined with time-dependent density functional theory (TD-DFT) calculations for the study of the chemical speciation in concentrated aqueous solutions of Cu(II)+Cl−. When the CuCl2 concentration changed from 0.05mol·kg−1 to 5mol·kg−1, the UV peak shifted from ~250nm to ~262nm. Similar shifts were recorded for CuCl2 solutions containing up to 5mol·kg−1 NaCl. Combination of the spectral data with our previous TD-DFT calculations provided a consistent model of the chemical speciation in the Cu(II)/Cl− system up to high concentrations of both components. The results obtained indicate that many of the previous conclusions regarding these solutions, drawn from a variety of techniques are unreliable. Under the present conditions, the only species detected were innersphere complexes with one or two Cl− ions bound to the aquated Cu(II) ion. For all the solutions, no remarkable peaks at ~280nm or 380nm, indicative of CuCl3− (aq) and CuCl42− (aq) respectively, were observed.