Hydrates of Cu²⁺ and CuCl⁺ in Dilute Aqueous Solution: A Density Functional Theory and Polarized Continuum Model Investigation

Abstract

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)](2+) 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)](2+) 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)](2+) 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](2+)(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](2+)(aq), [CuCl](+)(aq), and [CuCl(2)](0)(aq) species, the central Cu(II) atom prefers five-coordination.

Origins of contrasting copper coordination geometries in crystalline copper sulfate pentahydrate

“…However, the electronic interactions between the copper and coordinated waters must play a central role in governing the absolute orientations of the molecules in the structure. In fact, a gas-phase geometry optimization of an isolated CuSO 4 Á5H 2 O results in a totally planar arrangement of the coordinated water molecules (in agreement with some previous gas and solution-phase studies 7,14,16,30 ), demonstrating that the crystalline environment causes the observed tilting of the waters. Any structural deviations from the isolated-molecule calculation can be viewed as a strain, which results in a weakened copper-water bent bond, but this strain penalty must be offset by favorable cohesive interactions of the bulk solid for crystallization to occur.…”

“…[10][11][12][13] One such species is hexaaqua-copper(II), whose solvent phase structure has been a subject of controversy, specifically regarding the orientation of the coordinated water molecules. 7,9,[14][15][16][17] While not a direct probe of the solvated aqueous copper(II) cation, X-ray diffraction (XRD) studies of crystallized copper(II) hydrates can provide useful geometry information regarding the local environment around the metal cations with atomic precision. Investigation of crystalline solid-state samples enables rigorous study of both geometry and underlying electronic structure, leading to deeper understanding of their relationship.…”

“…[26][27][28][29] The coordination of one copper cation is almost identical to the solution-phase structure, while the other is markedly different. 7,[14][15][16]30 This has led to a detailed investigation of the copper-water interaction in the solid state, ultimately helping to clarify the origins of the dissimilar metal-water coordination configurations. While evaluation of quantum mechanical phenomena, such as chemical bond strengths and electron occupations, may be possible using experimental techniques, the roots of these properties (i.e.…”

High-order Cu(II) chloro-complexes in LiCl brines: Insights from density function theory and molecular dynamics

“…The hybrid DFT method, Becke's three-parameter exchange potential and Lee-Yang-Parr correlation functional (B3LYP) (Becke, 1993), for calculating the hydration of alkali mental halides and [CuCl x -(H 2 O) n ] 2Àx (x = 0-4) clusters, has shown a reasonable success (Lee et al, 2005;Olleta et al, 2006Olleta et al, , 2007Xia et al, 2009Xia et al, , 2010Xu et al, 2014;Yi et al, 2009Yi et al, , 2011 (Oolg et al, 1987) (RECPs), added a set of two f and one g polarization functions, used for Cu (jointly abbreviated here as aVDZ). 50% basis set superposition error (BSSE) correction was done (Kim et al, 2000).…”

“…So quantum mechanical calculations and molecular simulations for the Cu-Cl complexes in CuCl 2 -MCl (M = Na, Li)-H 2 O systems can be used to explain and predict experimental observations. A series of [CuCl x ] 2Àx (x = 0-4) hydration clusters have been studied through density functional theory (DFT) calculations (Xia et al, 2009(Xia et al, , 2010Yi et al, 2011) 8,10) clusters, in which one of three Cl À in the second or third complexing layer, are considered as solvent separated ion pair (1SSIP or 2SSIP) conformers of [CuCl 3 ] À aq species in the following context. Hydration energies and electronic absorption spectra are employed to analyze structural characteristics and UV-Vis spectra of CIP and 1SSIP/2SSIP conformers.…”