[CuCl₃]⁻ and [CuCl₄]²⁻ Hydrates in Concentrated Aqueous Solution: A Density Functional Theory and ab Initio Study

In this work, structures and thermodynamic properties of [CuCl3]− and [CuCl4]2− hydrates in aqueous solution were investigated using density functional theory and ab initio methods. Contact ion pair (CIP) and solvent-shared ion pair (SSIP) structures were both taken into account. Our calculations suggest that [CuCl3(H2O)n]− clusters might favor a four-coordinated CIP structure with a water molecule coordinating with the copper atom in the equatorial position for n = 3 and 4 in aqueous solution, whereas the four-coordinated SSIP structure with one chloride atom dissociated becomes more stable as n increases to 5. For the [CuCl4]2− cluster, the four-coordinated tetrahedron structure is more stable than the square-planar one, whereas for [CuCl4(H2O)n]2− (n ≥ 1) clusters, it seems that four-coordinated SSIP structures are slightly more favorable than CIP structures. Our calculations suggest that Cu2+ perhaps prefers a coordination number of 4 in CuCl2 aqueous solution with high Cl− concentrations. In addition, natural bond orbital (NBO) calculations suggest that there is obvious charge transfer (CT) between copper and chloride atoms in [CuClx]2−x (x = 1−4) clusters. However, compared with that in the [CuCl2]0 cluster, the CT between the copper and chloride atoms in [CuCl3]− and [CuCl4]2− clusters becomes negligible as the number of attached redundant Cl− ions increases. This implies that the coordination ability of Cl− is greatly weakened for [CuCl3]− and [CuCl4]2− clusters. Electronic absorption spectra of these different hydrates were obtained using long-range-corrected time-dependent density functional theory. The calculated electronic transition bands of the four-coordinated CIP conformer of [CuCl3(H2O)n]− for n = 3 and 4 are coincident with the absorption of [CuCl3]−(aq) species (∼284 and 384 nm) resolved from UV spectra obtained in CuCl2 (ca. 10−4 mol·kg−1) + LiCl (>10 mol·kg−1) solutions, whereas the calculated bands of [CuCl3(H2O)n]− in their most stable configurations are not when n = 0 − 2 or n > 4, which means that the species [CuCl3]−(aq) exists in those CuCl2 aqueous solutions in which the water activity is neither too low nor too high. The calculated bands of [CuCl4(H2O)n]2− clusters correspond to the absorption spectra (∼270 and 370 nm) derived from UV measurements only when n = 0, which suggests that [CuCl4]2−(aq) species probably exist in environments in which the water activity is quite low

Isopiestic Measurements on Aqueous Solutions of Heavy Metal Sulfates: MSO₄ + H₂O (M = Mn, Co, Ni, Cu, Zn). 2. <i>T</i> = 373.15 K

The water activities of the systems MSO₄ + H₂O (M = Mn, Co, Ni, Cu, Zn) are essential data needed for simulating the hydrometallurgical process of these metals. In our previous work (J. Chem. Eng. Data, 2014, 59, 97–102), the experimental data of water activity for these binary systems have been reported at 323.15 K. As one part of this series of work, the experimental data of water activity for these systems are reported at 373.15 K. The reliability of the apparatus at 373.15 K was verified by measuring and comparing the water activities of the two reference systems, CaCl₂ + H₂O and LiCl + H₂O. The results showed that the maximal relative deviation of the water activities between the reference systems was 0.054%. The water activities for the concerned five systems were found to be approximately the same at a certain salt molality below 1 M. The water activities of these systems decrease at a certain salt molality more than 1 M in the following sequence: <i>a</i>_MnSO₄ > <i>a</i>_CuSO₄(∼<i>a</i>_ZnSO₄) > <i>a</i>_CoSO₄(∼<i>a</i>_NiSO₄). Furthermore, the experiment data obtained in this work were compared with the model values reported in the literature