Hydrates of Cu2+ and CuCl+ in dilute aqueous solution: a density functional theory and polarized continuum model investigation.

In this work, structures, and properties of Cu(2+) and CuCl(+) hydrates in the gas and aqueous phases have been investigated using the B3LYP method. Contact ion pair (CIP) and solvent-shared ion pair (SSIP) were both taken into account for CuCl(+) hydrates. Our calculations show that Cu(H(2)O)(n) clusters favor a very open four-coordinated structure for n = 5-12 in the gas phase, while a five-coordinated conformer is favored for n > or = 8 in the aqueous phase. An approximate complete solvation shell of Cu(2+) in the aqueous phase needs more than 12 water molecules, while that of CuCl(+) in the aqueous phase needs only about eight water molecules. For CuCl(H(2)O)(n) clusters, the most stable structure is a four-coordinated CIP conformer for n = 4-7 in the gas phase and a five-coordinated CIP conformer for n = 8-10 in the aqueous phase. However, the five-coordinated CIP/h conformer (CIP conformer that the axial chloride atom tends to dissociate) of CuCl(H(2)O)(n) clusters becomes more favorable as n increases to 11. As the hydration process proceeds, the charges on the copper atom of Cu(H(2)O)(n) clusters decrease, while those of CuCl(H(2)O)(n) clusters increase (probably due to the dissociation of Cl(-)). The d-d electron transition and partial charge transition band around 160 nm of the five-coordinated conformer of Cu(H(2)O)(n) clusters and those bands (approximately 170 and approximately 160 nm) of SSIP or five-coordinated CIP/h conformers of CuCl(H(2)O)(n) clusters are coincident with the absorption of Cu(aq) species (approximately 180 nm) resolved from the spectra obtained in trace CuCl(2) (ca. 10(-5) mol x kg(-1)) + LiCl (0-18 mol x kg(-1)) aqueous solution, while those of five-coordinated CIP conformers of CuCl(H(2)O)(n) clusters (n = 8 and 9) around 261 and 247 nm correspond to the absorption of CuCl(aq) species (approximately 250 nm). Our calculated electronic spectra indicate that the typical peak of copper(II)-chloride complexes changes from 180 to 250 nm, and 275 nm, as the process of Cl(-) coordination. For Cu(aq), CuCl(aq), and CuCl(2)(aq) species, the central Cu(II) atom prefers five-coordination.