Theoretical Study Of Structures And Electronic Absorption Spectra Of Copper(â…¡)-chloride Brine Solution

Cu2+ exists in many biosystems and plays an essential role in some important biological processes.Meanwhile,the study of structures of Cu2+ in brine solution also plays an essential role in chemical engineering and hydrometallurgy processes.So far, there are some debates that Cu2+ hydrates exist in which form (four-,five-,or six-fold) in aqueous solution after all,which owing to the Jahn-Teller effect.In addition, the competition between water molecule and chloride ion for coordination with Cu2+ in copper(Ⅱ)-chloride solution makes the strutures and properties of this Cl-donating brine solution very complicated, which leads to its strutures and properties are difficult to be determined directly by experimental methods.To describe the thermodynamic properties of the CuCln complexes from dilute to concentrated copper(Ⅱ)-chloride solution(such as what's the species in this brine solution, how do these existed species assign and so on) accurately, and understand the properties of the ions in the aqueous solution distinctly, it is necessary to systematically study the micro-structures of the copper(Ⅱ)-chloride solution using quantum chemistry calculation methods.We have investigated hydrated structures of main species in copper(Ⅱ)-chloride solution system under hydrated cluster model approximation.Firstly, a series of hydrated [CuCln(H2O)m]2-n(n=0-4) clusters were optimized using B3LYP/aVDZ method.Secondly, on the basis of cluster/polarizable continuum model and approximate complete solvation of central ions,the most stable structures of [Cu]aq2+, [CuCl]aq+,and[CuCl2]aq0 species in dilute CuCl2 solution were analysed, and various possible dominant species were investigated in the process of competition between the hydration and chloridation of Cu2+.In addition, the possible hydrated structures of [CuCl3]aq- and [CuCl4]aq2- species in aqueous solution were studied under hydrated cluster model.Then, the excited energy and electronic absorption spectra of some typical optimized [CuCln(H2O)m]2-n(n=0-4) clusters were calculated using LRC-TDDFT/aVDZ method.With the structure analyses of the hydrated [CuCln(H2O)m]2-n(n=0-4) clusters, the structures of possible species in CuCl2 solution were resolved as the Cl" concentration increases under theoretical calculations.Five-fold conformer of [Cu(H2O)n]2+ clusters for n=5-12 is more stable in the aqueous solution, while five-fold CIP(contact ion pair) conformer of [CuCl(H2O)n]+ clusters for n=8-10 is more stable,and five-fold CIP/h conformer(CIP conformer with axial position Cl- tending to dissociate) becomes more stable than its other conformers as n increases to 11.An approximate complete solvation shell of Cu2+ in the aqueous solution needs more than 12 water molecules, while that of CuCl+ needs only about 8 water molecules.In the aqueous solution,five-fold SSIP/s(solvent-shared ion pair with one chloride ion dissociated) conformer of CuCl2(H2O)n clusters is more stable for n=8,and 9,and 7 water molecules can form an approximate complete solvation shell for CuCl2.Four-fold CIP conformer of [CuCl3(H2O)n]- clusters is the most stable structure for n≤4 in the aqueous solution.As n increases to 5,four-fold SSIP/s conformer becomes more stable than its CIP conformers.However, the Cl-tends to dissociate to form an stable SSIP conformer even though there is only one free water molecule in [CuCl4(H2O)n]2- clusters,and the calculated hydration energy suggest that the CuCl42- monomer with tetrahedral structure is more stable than its square planar structure.The calculated electronic spectra indicate that experimental assumed[Cu]2+aq species are likely to be five-fold structure of [Cu(H2O)n]2+(n≥8),five-fold SSIP or CIP/h structure of [CuCl(H2O)n]+(n≥10),or four-fold SSIP/d structure of CuCl2(H2O)10 in trace CuCl2(ca.10-5 mol/kg)+LiCl(0-18 mol/kg) aqueous solution, and [CuCl]+aq species are likely to be five-fold CIP structure of [CuCl(H2O)n]+(n=8, and 9) and five-fold SSIP/s structure of CuCl2(H2O)n(n>8),while [CuCl2]0aq species are likely to be four-fold CIP structure of CuCl2(H2O)n(n=3-7).In addition, [CuCl3]-aq species is probably a four-fold CIP structure of [CuCl3(H2O)n]-(n=3,and 4) in aqueous solution,while [CuCl4]2- species is probably a tetrahedral structure of CuCl42-.Meanwhile,our calculated electronic spectra also indicate Cu2+ tends to form a five-fold conformer in dilute CuCl2 solution.The typical absorption spectra appear at-180,-250,and-270 nm as the number of Cl- that coordinated directly with Cu2+ from 0 to 2 as the Cl- concentration increases(from infinite dilute solution).However,in concentrated or supersaturated CuCl2 solution, the number of Cl- that coordinated directly with Cu2+ may be 3 and 4, and the typical absorption spectra appear at -290,-385 nm and -287,-382 nm, respectively, which agrees well with Brugger et al.' resolved experimental spectra.