In this work, a thin-film UV–visible spectroscopic technique has been developed and combined with timedependent 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 0.05 mol·kg−1 to 5 mol·kg−1, the UV peak shifted from~250 nmto ~262 nm. Similar shiftswere recorded for CuCl2 solutions containing up to 5 mol·kg−1 NaCl. Combination of the spectral datawith our previous TD-DFT calculations provided a consistentmodel of the chemical speciation in the Cu(II)/Cl− systemup 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 ~280 nm or 380 nm, indicative of CuCl3 − (aq) and CuCl4 2− (aq) respectively, were observed.