[CuCl3]− and [CuCl4]2− Hydrates in Concentrated Aqueous Solution

ARTICLE pubs.acs.org/JPCA

[CuCl3]
and [CuCl4]2
Hydrates in Concentrated Aqueous Solution: A Density Functional Theory and ab Initio Study Hai-Bo Yi,*,† Fei-Fei Xia,† Quanbao Zhou,† and Dewen Zeng*,‡ † ‡

College of Chemistry and Chemical Engineering, Hunan University, Changsha, Hunan 410082, China College of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083, China

bS Supporting Information ABSTRACT: 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 g 1) clusters, it seems that four-coordinated SSIP structures are slightly more favorable than CIP structures. Our calculations suggest that Cu2þ 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 3 kg
1) þ LiCl (>10 mol 3 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.

1. INTRODUCTION Knowledge of the local coordination environment around Cu(II) in aqueous solutions is essential for understanding the structures and properties of Cu complexes for metal hydrometallurgical and sedimentary deposit processes.1
3 Detailed information on the ligand arrangement around the Cu(II) ion is available only in the solid state, whereas structural information in the aqueous phase is less definitive and available only for a few Cu2þ complexes. Generally, it is assumed that cupric ion is not completely in a complex form:4
8 At lower chloride ion concentrations, Cu2þ cannot form copper(II)
chloro complexes, but can form copper(II)
water complexes; at high Cl
concentrations, [CuCl]þ(aq), [CuCl2]0(aq), [CuCl3]
(aq), and [CuCl4]2
(aq) species can be present. In addition, it is wellknown that the color of CuCl2 solution is light blue at low Cl
concentrations, but yellow-green at high Cl
concentrations, which is observed macroscopically. This phenomenon also indicates that the microstructure in CuCl2 solution changes with different Cl
concentrations and that there must be a ligand r 2011 American Chemical Society

competition between H2O and Cl
coordinating with Cu2þ. However, the relationship among the structures of copper
water
chloro complexes in CuCl2 solution at different Cl
concentrations is still unknown. Although scientists have investigated copper(II) chloride aqueous solution with UV
vis spectroscopy4
8 to understand the formation process of CuClx complexes, they assumed that complexes in the statistical ratios [Cu]2þ(aq), [CuCl]þ(aq), [CuCl2]0(aq), [CuCl3]
(aq), and [CuCl4]2
(aq) are present in the solution, and by resolution of experimental UV
vis spectra, they obtained the concentration distribution of these species under specific conditions, as well as the absorption spectra of each assigned species. However, it is unclear whether the resolved absorption spectra correspond to the species assigned, exactly how the structures of the species are Received: October 10, 2010 Revised: March 16, 2011 Published: April 04, 2011 4416

dx.doi.org/10.1021/jp109723v | J. Phys. Chem. A 2011, 115, 4416–4426

The Journal of Physical Chemistry A assumed, and whether [CuCl3]
(aq) and [CuCl4]2
(aq) species in aqueous solution are bound with water molecules. One way of approaching the structure and properties of aqueous salt solutions involves using a quantum chemical method to examine hydrated clusters of a salt. Recently, the hydrations of alkali metal
halide salts and also alkali-metal hydroxides and hydrogen
halide acids were intensively investigated using ab initio method and density functional theory (DFT).9
16 Kim et al.’s11
13 calculations suggested the presence of contact ion pair (CIP) and solvent-shared ion pair (SSIP) structures in the alkali metal
halide salt aqueous solutions. Their results showed the possibility of using a quantum chemical method to investigate the structures and properties of electrolytes in aqueous solution. In previous works,17,18 we concluded that [Cu]2þ(aq) species with a five-coordinated hydration structure exist in infinite-dilute CuCl2 solution, that [CuCl]þ(aq) probably exists as five-coordinated CIP structures of [CuCl(H2O)n]þ (n = 8 and 9) or a fivecoordinated SSIP/s (SSIP with one chloride atom dissociated) structure of CuCl2(H2O)n (n > 8), and that [CuCl2]0(aq) exists in four-coordinated CIP conformers of CuCl2(H2O)n for n = 4
7. However, it is unclear whether the number of Cl
ions coordinating directly to Cu2þ continues to increase in aqueous solution with abundant Cl
-donating salt or whether the electronic absorption spectra of hydrated [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters correspond to the spectra of [CuCl3]
(aq) and [CuCl4]2
(aq) species resolved by Brugger et al.4 The answers to these questions will enable a more complete understanding of the structure of hydrated cupric chloride complex, as well as the influence of the water activity on the association constant of the complex [CuClx]2
x and the interaction of CuCl2 with Cl
-donating salt in aqueous solution. In our previous works,17,18 we carried out a series of quantum calculations on the structures of [CuClx(H2O)n]2
x (x = 0, 1, 2) clusters in aqueous solution. As a continuation of this series of research,17,18 in this work, we investigate the structures and properties of [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters. In their work,4 Brugger et al. assigned the absorption peaks at ∼284 and ∼384 nm to [CuCl3]
(aq) species in CuCl2 (ca. 10
4 mol 3 kg
1) þ LiCl (>10 mol 3 kg
1) solution and those at ∼270 and ∼370 nm to [CuCl4]2
(aq) species. However, Khan et al.7 reported that [CuCl3]
(aq) species have only one absorption band around 270 nm, whereas [CuCl4]2
(aq) species have three peaks at ∼240, ∼265
270, and ∼370
380 nm. Determining the characteristic absorption peaks of [CuCl3]
(aq) and [CuCl4]2
(aq) species is an interesting problem. Therefore, in this work, we calculated the electronic absorption spectra of [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters using longrange-corrected time-dependent density functional theory (LRCTDDFT).19
21 In addition, we performed natural bond orbital22
24 (NBO) charge population analyses to study the changes in the charges on the copper and chloride atoms in [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters as the hydration process proceeds.

2. CALCULATIONS AND METHODS To generate the initial hydrated structures, namely, contact ion pair (CIP) and solvent-shared ion pair (SSIP) clusters, various coordination numbers and hydrogen bonds (HBs) were considered, followed by geometry optimization to obtain local minimum-energy structures. Calculations were performed at the DFT level with the Perdew
Burke
Ernzerhof (PBE) functional and Becke’s three-parameter exchange potential with the

ARTICLE

Lee
Yang
Parr correlation functional (B3LYP), Møller
Plesset second-order perturbation theory (MP2), and coupled cluster with single and double excitations (CCSD) levels of theory. For Cu, the relativistic effective core potentials (RECPs) developed by the Stuttgart group were used in conjunction with the basis set to describe the metal valence electrons, and a set of f and g polarization functions was added.25 The valence space was described by the corresponding (6s5p3d) basis sets. For O, H, and Cl, Dunning’s correlation-consistent basis sets,26 aug-ccpVDZ (abbreviated here as aVDZ), were employed. In addition, single-point calculations were performed at the B3LYP level with Dunning’s correlation-consistent basis sets,26 aug-cc-pVTZ (abbreviated here as aVTZ), for O, H, and Cl elements. The CCSD/aVDZ results for [CuClx]2
x (x = 1
4) clusters were obtained from the single-point calculations on the optimized geometries at the MP2/aVDZ level. The basis set superposition error27(BSSE) correction was taken into account for all calculations and done with the counterpoise method.28 TDDFT is one of the most popular approaches for the calculation of excitation energies in quantum chemistry because of its efficiency and accuracy.29,30 It has also been used to study electron spectra of open-shell systems and even molecules containing transition metals.31
34 Because conventional TDDFT calculations underestimate Rydberg excitation energies, oscillator strengths, and charge-transfer excitation energies, Tawada et al.19 supposed that this problem might also come from the lack of a long-range exchange interaction and applied the long-range-corrected (LRC) scheme to TDDFT calculations. The electronic excited-state calculations of typical [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters at the LRC-TDDFT/aVDZ level were carried out using the Q-Chem software package.19
21,35 All geometry optimization, stabilization energy, and NBO calculations were performed with the Gaussian 03 software package.36 The stabilities of different [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters can be compared using stabilization energies (ΔEs,c) ΔEs, c ¼ E½CuCl3 ðH2 OÞn 

ECu2þ
3ECl

EðH2 OÞn

ð1aÞ

ΔEs, c ¼ E½CuCl4 ðH2 OÞn 2

ECu2þ
4ECl

EðH2 OÞn

ð1bÞ

which correspond to the processes Cu2þ þ 3Cl
þ ðH2 OÞn f ½CuCl3 ðH2 OÞn 
Cu2þ þ 4Cl
þ ðH2 OÞn f ½CuCl4 ðH2 OÞn 2
In the hydration of ions or ion pairs, one can consider that there is an approximate boundary between the inner solvation shell, which should be considered using a quantum mechanics method, and the outer solvation shell mainly having a long-range electrostatic effect on ions or ion pairs, which can be considered as a continuum medium. However, such an approximation might not be valid for concentrated or supersaturated solutions, because there are few free water molecules in the outer solvation shell and most of the water molecules might be in the inner solvation shell, and the long-range electrostatic effect of the solvent usually can be neglected in concentrated or supersaturated solutions. Therefore, we neglected the long-range electrostatic effect of solvent in the calculations of the hydrated structures, thermodynamic properties, and electronic spectra of [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters in aqueous solution. 4417

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3.2. Structures and Energetics. As in our previous works,17,18

3. RESULTS AND DISCUSSION

CIP and SSIP structures were both taken into account when we carried out an extensive search for the low-lying conformers of [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters. For SSIP conformers, SSIP/s, SSIP/d, SSIP/t, and SSIP/te (one, two, three, and four Cl
ions separated by solvation-shell water molecules) structures were all considered. An extensive conformation searching of hydrated [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters was performed to obtain plausible local minimumenergy structures with different coordination numbers and numbers of hydrogen bonds (HBs) formed among solvationshell water molecules and between chloride atoms and water molecules [namely, ion hydrogen bonds (IHBs)]. Our objectives were to analyze their stability as a function of the metal coordination number and hydrated cluster size and to understand the dominant structures of hydrated clusters for copper(II) chloride complex in aqueous solution with trace CuCl2 and abundant Cl
-donating salt. 3.2.1. [CuCl3(H2O)n]
Clusters. The typical low-lying [CuCl3(H2O)n]
(n = 1
5) clusters obtained using the B3LYP/aVDZ method are shown in Figure 2. Table 2 lists different B3LYP/aVDZ structural parameters and energy parameters at the B3LYP/aVTZ//B3LYP/aVDZ, PBE/aVDZ, and MP2/ aVDZ levels for these low-lying energy conformers. The works of Morokuma et al. indicated that NBO calculations can probably leave the p orbitals in the Rydberg space and those orbitals can contribute significantly to the overall charge.39 Our NBO charge population analyses just showed that the p orbitals are obviously involved in CT or coordination bonding, such as the orbital configuration of Cu2þ in the [CuCl3]
cluster (4s0.443d9.384p0.46) and the W3A (4s0.393d9.364p0.51) and W4A (4s0.383d9.334p0.51) conformers of [CuCl3(H2O)n]
. The stabilization energies calculated with different methods show that three-coordinated CIP conformer is more stable than its four-coordinated CIP conformer for [CuCl3(H2O)]
cluster. As shown in Table 2, in the case of the [CuCl3(H2O)2]
cluster, B3LYP/aVDZ stabilization energies showed that the threecoordinated CIP conformer, W2A, is iso-energetic with its four-coordinated SSIP/s conformer, W2C, whereas B3LYP/ aVTZ//B3LYP/aVDZ, PBE/aVDZ and MP2/aVDZ stabilization energies show that the SSIP/s conformer is more stable than the three-coordinated CIP conformer. For the [CuCl3(H2O)3]
cluster, all B3LYP/aVDZ, PBE/aVDZ, and MP2/aVDZ stabilization energies show that the four-coordinated CIP (W3A) conformer is more stable than its SSIP conformers. B3LYP/aVDZ

3.1. Binding Energies of [CuCl x]2
x (x = 1
4) Clusters. All

of the optimized low-lying energy [CuClx]2
x (x = 1
4) clusters are presented in Figure 1, and their B3LYP/aVDZ structural parameters, binding energies, and relative energies computed by different methods are listed in Table 1. Our B3LYP/aVDZ calculations show that the binding energies of [CuClx]2
x for x = 1
3 increase as the number of attached Cl
ions increases, but they decrease for the [CuCl4]2
clusters. The relative energies (ΔEr) of [CuCl4]2
cluster are 51.6 and 55.8 kcal/mol for its two conformers (tetrahedral and square-planar structures, respectively). As shown in Figure 1, two conformers of [CuCl4]2
clusters in the gas phase were obtained: one tetrahedral (td) and the other square-planar (sp). The binding energies show that the td conformer is more stable than the sp one, and the Cu
Cl distance of the td conformer is 2.2 pm shorter than that of sp one (as shown in Table 1), which agrees well with the results calculated by Szilagyi et al.37 It should be noted that the PBE/aVDZ, MP2/aVDZ, and CCSD/aVDZ binding energies of [CuClx]2
x (x = 1
4) clusters led to conclusions on the structure and dissociation behaviors similar to those obtained from the B3LYP/aVDZ calculations. In addition, the bond parameters suggest that the Cu
Cl distances and the negative charges on Cl
increase as the number of attached Cl
ions increases, whereas the positive charges on Cu2þ decrease. Compared with the charge population of the [CuCl2]0 cluster, the total negative charge on the chloride atoms increases by 0.95 for the [CuCl3]
cluster and by 1.96 for the [CuCl4]2
cluster. This phenomenon means that charge transfer (CT) between copper and chloride atoms for [CuCl3]
and [CuCl4]2
clusters becomes negligible as the number of the attached redundant Cl
ions increases and the coordination ability of Cl
in [CuClx]2
x is weakened as x increases.

Figure 1. Optimized structures of [CuClx]2
x (x = 1
4) clusters at the B3LYP/aVDZ level. td and sp are abbreviations for tetrahedron and square-planar, respectively.

Table 1. B3LYP/aVDZ Structural Parametersa and B3LYP/aVDZ, PBE/aVDZ, MP2/aVDZ, and CCSD/aVDZ Binding Energies (ΔEb) of [CuClx]2
x (x = 1
4) Clustersb structural parametersc cluster þ

energy parametersb

RCu
Cl

qCu2þ

qCl


B3LYP

PBE

MP2

CCSD

[CuCl]

209.3

1.05


0.05


425.0 (
425.0)


444.6 (
444.6)


430.2 (
430.2)


402.5 (
402.5)

[CuCl2]0

208.9

0.75


0.38


629.5 (
204.6)


663.0 (
218.4)


601.2 (
171.0)


602.1 (
199.6)

[CuCl3]


220.6

0.71


0.57


686.4 (
56.9)


718.5 (
55.5)


666.2 (
65.0)


665.4 (
63.3)

[CuCl4]2
-td [CuCl4]2
-sp

235.2 236.9

0.72 0.72


0.68
0.68


633.8 (52.6)
627.8 (58.6)


666.6 (51.6)
662.7 (55.8)


620.2 (46.0)
609.4 (56.8)


617.7 (47.7)
608.3 (57.1)

a

RCu
Cl is the Cu
Cl distance in picometers for [CuClx]2
x (x = 1
4), qCu2þ is the charge on the copper atom, and qCl
is the average charge on the chloride atoms. NBO charges given in au/e. b ΔEb is given in kcal/mol and was calculated at room temperature (298 K and 1 atm) using the equation ΔEb = E[CuClx]2
x
ECu2þ
xECl
. The energies in parentheses are relative energies (ΔEr) of [CuClx]2
x (x = 1
4) clusters calculated using the equation ΔEr = E[CuClx]2
x
E[CuClx
1]3
x
ECl
. c The Cu
Cl distances of [CuCl4]2
-td and [CuCl4]2
-sp in the gas phase37 are 234.7 and 236.8 pm, respectively, whereas those in the solid phase38 are 220.9 and 226.4 pm, respectively. 4418

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Figure 2. Typical optimized structures of [CuCl3(H2O)n]
clusters for n = 1
5 at the B3LYP/aVDZ level. Other optimized structures are quite unstable and were not collected. W is an abbreviation for water.

and PBE/aVDZ stabilization energies of [CuCl3(H2O)4]
cluster indicate that the four-coordinated CIP conformer, W4A, is iso-energetic with its five-coordinated SSIP/d conformer (W4F), whereas the MP2/aVDZ hydration energies show that W4F is the most stable conformer. All B3LYP/ aVDZ, PBE/aVDZ and MP2/aVDZ stabilization energies of [CuCl3(H2O)5]
cluster show that four-coordinated SSIP/s conformer is more stable than its CIP conformers, which suggests that the chloride atom tends to dissociate for n = 5. It should be noted that for n g 5, CIP conformers is slightly unstable compared to its SSIP conformers of [CuCl3(H2O)n]
clusters, as shown in Table 2 and Table S1 in the Supporting Information. The B3LYP/aVDZ-optimized [CuCl3]
cluster is a planar triangle geometry, and its Cu
Cl distance is 220.6 pm. The Cu
Cl distance of W1A is also 220.6 pm, whereas that of W1B is 227.0 pm, which indicates that the direct-coordinated water molecule lengthens the Cu
Cl distance obviously. The Cu
Cl distance of four-coordinated CIP conformer, W3B (a regular tetrahedron geometry with two HBs and four IHBs), is 226.1 pm, and that of W4A is 227.3 pm, all these are shorter than that of W2B. As n = 5, the Cu
Cl distance of the four-coordinated conformer (W5A) becomes 230.7 pm, and one Cu
Cl distance increases to 383.2 pm in W5C, which indicates that the chloride atom tends to dissociate. As a whole, it can be noted that the more stable CIP conformers of [CuCl3(H2O)3]
and [CuCl3(H2O)4]
clusters are four-coordinated structures with one water molecule coordinating directly with copper atom, whereas SSIP conformers tends to be more favorable than its CIP conformers as hydration proceeds.

3.2.2. [CuCl4(H2O)n]2
Clusters. The typical local minimumenergy [CuCl4(H2O)n]2
(n = 1
4) clusters obtained using B3LYP/aVDZ method are shown in Figure 3. Table 3 lists different B3LYP/aVDZ structural parameters and energy parameters at the B3LYP/aVTZ//B3LYP/aVDZ, PBE/aVDZ, and MP2/aVDZ levels for these low-lying energy conformers. Similar to the case of [CuCl3(H2O)n]
clusters, our NBO charge population analyses also show that the p orbitals are obviously involved in CT or coordination bonding, such as the orbital configuration of Cu2þ in [CuCl4]2
-td (4s0.393d9.354p0.52) and [CuCl4]2
-sp (4s0.403d9.414p0.46) conformers and the W1B (4s0.373d9.344p0.48), W2E (4s0.353d9.314p0.42) conformers of [CuCl4(H2O)n]2
. As shown in Table 1, the [CuCl4]2
cluster with the td structure is more stable than the sp conformer. All B3LYP/ aVTZ//B3LYP/aVDZ, PBE/aVDZ, and MP2/aVDZ calculations of [CuCl4(H2O)n]2
clusters for n = 1
4 showed that SSIP conformers are more stable than its CIP conformers and that the chloride atom tends to dissociate and form a fourcoordinated SSIP structure in the hydrates of the [CuCl4]2
cluster. In our calculations, only four-coordinated CIP conformers of [CuCl4(H2O)n]2
clusters are preferred; no five-coordinated CIP conformers were obtained. The Cu
Cl distance of W1A, where four chloride atoms coordinate directly with the central copper atom and the water molecule forms IHBs with one of the chloride atoms, is shortened in comparison to that of the td conformer of the [CuCl4]2
cluster. However, the four-coordinated CIP conformer, W1A, is less stable than the four-coordinated SSIP conformer with one chloride atom dissociated (W1B). For n = 2, generally, SSIP conformers are also more stable than the CIP isomers, and among SSIP conformers, W2E 4419

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Table 2. B3LYP/aVDZ Structural Parameters and B3LYP/aVTZ//B3LYP/aVDZ, PBE/aVDZ, and MP2/aVDZ Energy Parameters of [CuCl3(H2O)n]
Clusters for n = 1
5d energy parametersb,c structural parametersa geometry


CN RCu
O RCu
Cl RCu
Cl(d) qCu2þ

B3LYP/aVDZ qCl


qCl
-d

ΔEs,c

ΔHs,c

B3LYP/aVTZ

ΔGs,c

ΔEs,c

PBE/aVDZ ΔEs,c

MP2/aVDZ ΔEs,c

3

220.6

0.71


0.57


685.5
684.6
666.0


711.5


709.2


660.9

W1A

CIP

3

220.6

0.72


0.58


694.7
692.3
665.3


720.5


719.6


671.9

W1B W2A

CIP CIP

4 3

227.0 220.9

0.73 0.72


0.60
0.60
689.5
687.1
658.0
0.56
698.3
696.1
668.5


714.5
669.9


715.1
722.3


669.7
679.6

[CuCl3]

220.4

0.72


0.58


694.1
662.1


668.2


722.7


679.6

0.87


0.60
0.80
698.5
696.4
662.7


670.3


724.6


681.1

220.4

0.72


0.56


694.3


692.7
668.4


714.4


719.5


680.4

226.1

0.73


0.59


698.8
696.3
664.1


722.4


724.7


684.6

W2B

CIP

4

243.1

226.1

W2C

SSIP/s

4

202.6

225.3

W3A

CIP

3

W3B

CIP

4

226.9

394.7


696.6

W3C

CIP

5

211.0

219.8

0.72


0.62


690.9


688.6
657.1


715.6


716.3


677.3

W3D

SSIP/s

4

201.2

228.9

398.1

0.89


0.59
0.80
698.1


696.2
663.7


716.7


723.9


681.1

W3E W3F

SSIP/s SSIP/d

5 4

206.6 196.8

227.1 225.7

386.6 391.7

0.86 1.03


0.61
0.81
696.4
0.62
0.78
696.5


694.4
661.4
695.6
661.7


715.8
718.0


722.0
722.6


683.6
681.4

W4A

CIP

4

218.0

227.3

0.76


0.60


697.0
694.5
662.5


722.1


721.4


684.8

W4B

CIP

5

220.3

234.3

0.74


0.62


691.9


715.9


718.5


680.9


689.5
657.0

W4C

SSIP/s

4

203.7

226.1

396.9

0.91


0.61
0.79
694.7


692.5
659.7


719.3


720.5


683.1

W4D

SSIP/s

5

205.8

228.7

387.9

0.87


0.60
0.82
694.1


692.2
659.4


718.2


718.9


682.2

W4E

SSIP/d

4

197.5

224.9

393.7

1.03


0.62
0.80
693.8


692.5
659.4


718.8


719.9


681.6

W4F

SSIP/d

5

201.2

227.4

379.4

0.99


0.61
0.79
696.6
694.8
659.9


721.4


718.8


687.9

W4G W5A

SSIP/t CIP

4 4

195.3 205.2

391.2 230.7

1.18 0.78


0.76
0.60


683.0
683.5
649.0
700.4
697.6
662.6


707.7
724.4


715.5
728.4


681.9
688.2

0.80


0.63


692.9


691.4
657.3


716.4


717.4


683.5

383.2

0.88


0.60
0.79
701.5
699.4
663.8


725.8


728.7


691.0

W5B

CIP

5

219.4

235.8

W5C

SSIP/s

4

201.8

226.7

W5D

SSIP/s

5

204.9

230.7

386.4

0.90


0.60
0.82
694.2


692.2
658.1


718.9


719.6


685.9

W5E

SSIP/d

4

198.3

227.8

383.2

1.03


0.62
0.80
694.6


692.6
657.3


719.3


721.7


685.4

W5F

SSIP/d

5

200.9

231.7

380.3

1.02


0.63
0.80
697.1


695.3
659.0


721.5


722.6


689.8

RCu
O and RCu
Cl are the Cu
O and Cu
Cl distances in picometers for [CuCl3(H2O)n]
clusters, and RCu
Cl(d) is the distance between the dissociated Cl
and Cu2þ ions, also in pm. CN is coordination number of copper atom. qCl- is the charge on the copper atom, qCl- is the average charge on the Cl
ion, and qCl
-d is the charge on the dissociated Cl
ion. NBO charges are given in au/e. b ΔEs,c, ΔHs,c, and ΔGs,c are the stabilization energies, thermal enthalpies, and thermal free energies, respectively, of the [CuCl3(H2O)n]
clusters calculated at room temperature (298 K and 1 atm), and all the energy parameters are given in kcal/mol. c B3LYP/aVTZ stabilization energies were obtained using B3LYP/aVDZoptimized geometries. d For [CuCl3(H2O)n]
clusters, the most stable CIP and SSIP conformers are marked in bold. a

is the most stable conformer. A six-coordinated CIP conformer (W2B), with two water molecules coordinating directly to the central copper atom in axial positions, was obtained, although it is even far more unstable than the four-coordinated CIP conformer (W2A). This phenomenon suggests that the SSIP structure becomes increasingly favorable as water molecules are involved in [CuCl4(H2O)n]2
clusters. Generally, it seems that the fourcoordinated CIP structure with four chloride atoms coordinated directly to the central copper atom of [CuCl4(H2O)n]2
clusters might be unfavorable for n g 1. Because of the Jahn
Teller effect for the d9 cation Cu2þ, there is still an ongoing debate about the coordination environment for hydrated Cu(II) complexes existing in both the gas and aqueous phases.40
45 It seems that both five- and six-coordinated Cu(II) ions in crystalline compounds are competitive.40 The theoretical calculations of Sukrat et al.41 and the experimental results of Pasquarello et al.42 showed that copper(II)
water complexes prefer the five-coordinated conformer in the gas phase, whereas the results of Bryantsev et al.43 favored Cu(II) complexes in the gas phase that have a very

open four-coordinated structure. In our previous works,17,18 we found that all Cu2þ, CuClþ, and CuCl2 hydrates generally prefer a four-coordinated structure in the gas phase, with the exception of [CuCl(H2O)n]þ (n > 8) clusters, which prefer a five-coordinated structure. As for the hydrated species of Cu2þ in the aqueous phase, the results of both Bryantsev et al.43 and Benfatto et al.44 showed that the more compact five-coordinated square-pyramidal geometry is more stable than either the four- or six-coordinated clusters. However, Pasquarello et al.42 proposed that Cu2þ hydrates are square-pyramidal and trigonal-bipyramidal conformers with five equal Cu
O distances, whereas the work of Benfatto et al.44 supported a distorted fivecoordinated conformer. Our previous work18 showed that [Cu]2þ(aq) and [CuCl]þ(aq) species prefer five-coordinated structures in the aqueous phase, which is in agreement with recent combined EXAFS and XANES studies of aqueous solutions of Cu(II).45 However, the theoretical calculations of the present work suggest that [CuCl3]
(aq) and [CuCl4]2
(aq) prefer four-coordinated structures, similar to that of [CuCl2]0(aq) species.17 4420

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Figure 3. Typical optimized structures of [CuCl4(H2O)n]2
clusters for n = 1
4 at the B3LYP/aVDZ level. Other optimized structures are quite unstable and were not collected. W, sp, and td are abbreviations for water, square-planar, and tetrahedron, respectively.

3.3. Electronic Spectra. Electronic absorption spectra of hydrated [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters were performed at the LRC-TDDFT/aVDZ level as in our previous works,17,18 and the calculated excitation energies and oscillatory strengths of the conformers are listed in Tables 4 and 5. The experimental absorption spectra of CuCl2,46 [CuCl3]
(aq), and [CuCl4]2
(aq) species4 are also included in the tables for comparison. Figures 4 and 5 present the electronic absorption spectra of the typical conformers for [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters. It can be noted that there are three obvious absorption peaks around 189, 317, and 450 nm and a shoulder at ∼240 nm for the [CuCl3]
cluster, and the absorption around 240 nm can be attributed to d
d (t f e) electron transition, whereas the peak at ∼450 nm owing to CT transitions from an electron of chloride to a singly occupied d orbital of copper. With one water molecule involved, the d
d electron transition and CT bands are both blue-shifted to 180, 310, and 430 nm in comparison to those of the [CuCl3]
cluster. In the case of the dihydrated cluster, the d
d electron transition and CT bands of the three-coordinated CIP conformer (W2A) are further blue-shifted to ∼179, ∼237
310, and ∼421 nm, whereas those of the four-coordinated CIP conformer (W2B) are at ∼184, ∼297, and ∼409
410 nm, and the CT bands are more approximate to the resolved experimental spectra (∼284 and ∼384 nm) of the [CuCl3]
(aq) species.4 However, the structure W2B is less stable than its other isomer, W2A, so the [CuCl3]
(aq) species in aqueous solution might not exist as the W2B structure. As n increases to 3, the d
d electron transition band of W3A (four-coordinated CIP conformer) is around 180 nm, whereas the CT bands are around

∼293 and ∼387 nm, which are coincident with the absorption spectra (∼284 and 384 nm) of the [CuCl3]
(aq) species assigned from the experimental spectra in CuCl2 (ca. 10
4 mol 3 kg
1) þ LiCl (>10 mol 3 kg
1) solution.4 The CT absorption bands of the four-coordinated CIP conformer (W4A) are also coincident with the spectra of the [CuCl3]
(aq) species.4 Because the results for stabilization energies show that the fourcoordinated CIP conformer of [CuCl3(H2O)n]
clusters for n = 3 and 4 is the most stable structure among their isomers, the resolved [CuCl3]
(aq) species in CuCl2 (ca. 10
4 mol 3 kg
1) þ LiCl (>10 mol 3 kg
1) solution4 probably exists as the fourcoordinated CIP conformer of [CuCl3(H2O)n]
(n = 3 and 4). As the number of attached water molecules increases to 5, there is only one peak (∼265 nm) attributed to CT for the fourcoordinated CIP conformer (W5A). In addition, the more stable four-coordinated SSIP conformer with one chloride atom dissociated for n = 5 has only one peak at ∼245 nm, which indicates that the CT band at higher wavelength will probably disappear upon the dissociation of Cl
. Our calculated electronic spectra of [CuCl4]2
clusters exhibit two obvious absorption peaks at ∼269 and ∼373 nm for the square-planar (sp) conformer and at ∼287 and ∼382 nm for the tetrahedral (td) conformer, which are both coincident with the absorption spectra (∼270 and 370 nm) of the [CuCl4]2
(aq) species assigned from the experimental spectra in CuCl2 (ca. 10
4 mol 3 kg
1) þ LiCl (>10 mol 3 kg
1) solution.4 Because the sp structure is less stable than the td one, the resolved [CuCl4]2
(aq) species in CuCl2 þ LiCl (>10 mol 3 kg
1) aqueous solution probably corresponds to the [CuCl4]2
cluster with a tetrahedral structure. With one water molecule involved, 4421

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Table 3. B3LYP/aVDZ Structural Parameters and B3LYP/aVTZ//B3LYP/aVDZ, PBE/aVDZ, and MP2/aVDZ Energy Parameters of [CuCl4(H2O)n]2
Clusters for n = 1
4d energy parametersb,c structural parametersa geometry

CN RCu
O RCu
Cl RCu
Cl(d) qCu2þ

B3LYP/aVDZ qCl


qCl
-d

ΔEs,c

ΔHs,c

B3LYP/aVTZ

ΔGs,c

ΔEsp

PBE/aVDZ ΔEs,c

MP2/aVDZ ΔEs,c

sp

4

237.4

0.72


0.68


622.6
622.0
599.4


648.6


652.6


603.6

[CuCl4]2
td

4

235.2

0.73


0.68


632.2
631.1
605.3


657.6


656.4


613.9

W1A W1B

4 4

207.7

0.73 0.80


0.67
648.2
645.6
610.6
0.65
0.93
652.4
649.9
614.7


671.3
677.1


670.4
677.7


631.7
635.3

188.6

2


[CuCl4]

CIP SSIP/s

W1C

SSIP/d

3

W2A

CIP

4

234.8 223.7

496.8

221.4

423.2

234.5

0.94


0.60
0.89
647.2
645.5
610.5


671.6


674.0


627.1

0.72


0.66


658.7
656.2
618.8


679.6


683.3


643.5
600.0

W2B

CIP

6

251.4

242.4

0.78


0.71


599.6
600.8
561.4


623.7


622.2

W2C

SSIP/s

4

205.1

230.8

486.3

0.81


0.63
0.66
661.8
659.5
622.5


685.6


685.8


646.1

W2D

SSIP/d

3

188.3

221.2

420.1

0.93


0.59
0.87
657.0
655.4
618.4


686.2


684.1


643.2

W2E

SSIP/d

4

198.9

228.9

481.2

0.91


0.64
0.89
663.0
661.0
623.0


687.1


689.2


646.2

W3A W3B

CIP SSIP/s

4 4

203.9

234.4 230.9

574.8

0.73 0.80


0.65
662.2
660.2
625.1
0.65
0.91
670.6
667.9
628.8


686.4
695.3


686.6
694.2


648.0
656.7

W3C

SSIP/s

5

222.5

236.8

442.7

0.82


0.66
0.89
659.3
656.7
619.3


683.5


686.0


649.0

W3D

SSIP/d

4

199.3

229.5

469.0

0.92


0.64
0.89
666.3
664.1
626.0


691.3


693.1


651.3

W3E

SSIP/d

5

205.6

242.0

422.7

0.96


0.72
0.87
663.7
661.4
621.8


688.5


687.9


654.2

197.7

228.4

412.9

W3F

SSIP/t

4

W4A

CIP

4

233.6

1.07


0.64
0.85
665.5
664.1
624.2


690.3


692.2


652.0

0.70


0.65


685.3


688.2


650.6


663.5
661.7
629.1

W4B

SSIP/s

4

203.5

230.5

562.0

0.79


0.64
0.90
670.4
667.8
628.7


694.8


693.3


659.0

W4C W4D

SSIP/s SSIP/d

5 4

226.8 199.8

235.6 228.4

444.1 479.3

0.82 0.92


0.65
0.88
660.4
658.1
621.2
0.63
0.90
667.2
664.7
626.7


685.0
692.3


687.0
693.6


653.5
654.4

W4E

SSIP/d

5

216.6

231.2

477.5

0.90


0.63
0.87
664.2
661.8
621.6


688.6


692.0


657.0

W4F

SSIP/t

4

201.8

227.6

388.1

1.01


0.61
0.85
664.9
663.5
624.6


686.6


689.0


652.9

232.6

402.6

1.02


0.66
0.86
667.9
665.5
623.9


692.8


693.8


660.8

402.7

1.19


0.84
676.7
675.4
633.5


701.3


702.1


666.2

W4G

SSIP/t

5

208.9

W4H

SSIP/te

4

194.7

RCu
O and RCu
Cl are Cu
O and Cu
Cl distances in picometers for [CuCl4(H2O)n]2
clusters, and RCu
Cl(d) is the distance between the dissociated Cl
and Cu2þ also in picometers. CN is coordination number of copper atom. qCl
is the charge on the copper atom, qCl
is the average charge on Cl
, and qCl
--d is the charge on the dissociated Cl
. NBO charge is given in au/e. b ΔEs,c, ΔHs,c, and ΔGs,c are stabilization energies, thermal enthalpies, and thermal free energies of the [CuCl4(H2O)n]2
clusters calculated at room temperature (298 K and 1 atm), respectively, and all the energy parameters are given in kcal/mol. c B3LYP/aVTZ stabilization energies were obtained using B3LYP/aVDZ-optimized geometries. d For [CuCl4(H2O)n]2
clusters, the most stable CIP and SSIP conformers are marked in bold. a

there are also two CT bands at ∼284 and 370 nm for the fourcoordinated CIP conformer with four chloride atoms coordinating directly to the central copper atom and water molecules forming ion hydrogen bonds (IHBs) with the chloride atoms, but this conformer is quite unstable and easily changes to another more stable fourcoordinated SSIP conformer, W1B, which has only one CT band at ∼233 nm. For n = 2 and 3, the four-coordinated CIP conformers also have CT bands at 270 and 370 nm; in particular, the six-coordinated CIP conformer, W2B, with two water molecules coordinating to the copper atom in the axial position also has two absorption peaks at ∼276 and 361 nm. These electronic absorption spectra of CIP conformers for [CuCl4(H2O)n]2
(n = 1
3) clusters all correspond to the resolved spectra of the [CuCl4]2
(aq) species, but these CIP conformers are quite unstable compared to the corresponding SSIP conformers with water molecules involved. Therefore, it can be assumed that the [CuCl4]2
cluster with a tetrahedral structure might be the dominant conformer corresponding to the [CuCl4]2
(aq) species assigned from the experimental spectra in CuCl2 (ca. 10
4 mol 3 kg
1) þ LiCl (>10 mol 3 kg
1) solution.4 Brugger et al.4 measured the spectra of trace CuCl2 in LiCl solutions and resolved the measured spectra assuming that

hydrated [CuClx]2
x (x = 0
4) species exist in it. According to our theoretical investigations, the assumed [CuCl3]
(aq) species having resolved absorption peaks at ∼284 and 384 nm is likely to be the four-coordinated CIP conformer of [CuCl3(H2O)n]
clusters for n = 3 or 4, whereas the [CuCl4]2
(aq) species having the resolved absorption peaks at ∼270 and 370 nm might be the [CuCl4]2
cluster with a tetrahedral structure. In our previous works,17,18 we concluded that four-coordinated CIP conformers of CuCl2(H2O)n clusters might be predominant structures for [CuCl2]0(aq) species, whereas five-coordinated CIP conformers of [CuCl(H2O)n]þ clusters (n = 8 and 9) and [Cu(H2O)n]2þ clusters probably correspond to [CuCl]þ(aq) and [Cu]2þ(aq) species, respectively, assigned from experimental spectra.4 From all of the calculated electronic absorption spectra of [Cu(H2O)n]2þ, [CuCl(H2O)n]þ, CuCl2(H2O)n, [CuCl3(H2O)n]
, and [CuCl4(H2O)n]2
clusters, it can be noted that the five-coordinated conformer of [Cu(H2O)n]2þ, the five-coordinated SSIP or CIP/h conformers of [CuCl(H2O)n]þ, and the SSIP/d conformer of CuCl2(H2O)n are all probably predominant structures abbreviated by [Cu]2þ(aq) species in infinite-dilute CuCl2 solution and that 4422

dx.doi.org/10.1021/jp109723v |J. Phys. Chem. A 2011, 115, 4416–4426

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Table 4. Excitation Energies and Oscillatory Strengths of the CuCl2 Molecule, the [CuCl3]
Cluster, and Some Typical [CuCl3(H2O)n]
Clusters for n = 1
5 Using the LRC-TDDFT/aVDZ Method (298 K and 1 atm) geometry

excitation energies (nm)a

CN

CuCl2b

2

∼222, ∼525
588

CuCl2 [CuCl3]
(aq)c

2 unknown

5560.16, 1800.02, 1580.10, 1560.07 ∼284, ∼385

[CuCl3]


CIP

3

4510.02, 3380.01, 3250.06, 3080.05, 2930.01, 2390.06, 1860.07, 1860.03

W1A

CIP

3

4350.03, 3400.01, 3200.05, 3050.04, 2930.01, 2390.06, 1820.02, 1810.05

W1B

CIP

4

4040.01, 3170.01, 2950.02, 2900.03, 2830.05, 2460.07, 1910.05, 1890.02, 1860.04

W2A

CIP

3

4220.03, 3160.05, 3020.04, 2380.06, 1780.07

W2B

CIP

4

4090.02, 3010.05, 2970.02, 2910.02, 2440.04, 1840.03, 1810.02

W3A

CIP

4

3870.02, 3240.01, 2950.03, 2920.03, 2470.03, 2180.01, 1810.02, 1770.01

W3B W3C

CIP SSIP/s

5 4

3540.01, 3010.01, 2860.02, 2760.02, 2640.04, 2410.07, 1870.04, 1850.05, 1840.01 2750.02, 2550.04, 2360.05, 2300.01, 2280.02, 1980.02, 1900.05, 1880.03, 1860.03

W3D

SSIP/s

5

2800.01, 2620.04, 2470.11, 1860.05, 1860.03, 1850.01

W4A

CIP

4

3810.02, 3080.02, 2930.02, 2870.02, 2840.03, 2440.03, 1790.02

W4B

CIP

5

3400.01, 2970.01, 2900.02, 2730.03, 2630.01, 2590.04, 2380.06, 1840.03, 1840.03

W4C

SSIP/s

4

3190.01, 2770.02, 2560.05, 2560.02, 2170.02, 1820.07

W4D

SSIP/s

5

2730.04, 2550.02, 2360.19, 1900.03, 1860.01, 1850.04

W4E

SSIP/d

4

2480.05, 2360.02, 1950.06, 1850.02, 1800.03

W4F W4G

SSIP/d SSIP/t

5 4

2470.09, 1850.04, 1850.01 2530.01, 2290.01, 2110.05, 2050.02, 1910.07

W5A

CIP

4

3580.02, 3170.01, 2870.06, 2760.02, 2570.02, 2540.04, 2280.05, 1850.03, 1810.03

W5B

CIP

5

3390.01, 2970.02, 2760.04, 2640.01, 2560.04, 2500.02, 2320.05, 2030.01, 1830.03, 1820.03

W5C

SSIP/s

4

2580.03, 2420.09, 2030.02, 1860.02, 1810.01, 1780.05

W5D

SSIP/s

5

2670.03, 2530.04, 2310.09, 1990.03, 1820.05

W5E

SSIP/d

4

2470.04, 2430.01, 2020.07, 2010.01

W5F

SSIP/d

5

2440.08, 2220.04, 1860.05, 1860.01

a

Oscillator strength presented as a subscript. b Peaks observed by DeKock and Gruen in experiments at 1076 K.46 c Absorption spectra resolved by Brugger et al. in CuCl2 (ca. 10
4 mol 3 kg
1) þ LiCl (>10 mol 3 kg
1) solution.4

Table 5. Excitation Energies and Oscillator Strengths of [CuCl4]2
Clusters and Some Typical [CuCl4(H2O)n]2
Clusters for n = 1
3 Using the LRC-TDDFT/aVDZ Method (298 K and 1 atm) geometry

excitation energies (nm)a

CN

[CuCl4]
(aq)b

unknown

∼270, ∼370

[CuCl4]2


td

4

3810.02, 3810.02, 2890.06, 2890.06, 2350.01, 2350.01, 2340.03

[CuCl4]2
W1A

sp CIP

4 4

3720.05, 3720.05, 2700.12, 2700.12, 2460.01, 2460.01 3780.02, 3600.01, 2920.02, 2920.04, 2800.04, 2310.04, 2260.02, 2190.04

W1B

SSIP/s

4

3940.01, 3510.01, 3010.01, 2900.01, 2800.04, 2780.04, 2460.05, 2310.03, 2200.05, 2190.05

W1C

SSIP/d

3

4090.02, 3150.01, 2930.05, 2650.05, 2520.05

W2A

CIP

4

3730.02, 3650.02, 2820.06, 2790.07, 2290.04, 2120.01, 2110.02, 2090.02

W2B

CIP

6

3640.04, 3580.05, 2760.10, 2740.05, 2700.03

W2D

SSIP/t

3

4010.02, 3070.02, 2900.04, 2650.05, 2460.04, 2230.04

W2E

SSIP/t

4

3020.01, 2840.05, 2720.09, 2410.02, 2400.04, 2380.02

W3A W3B

CIP SSIP/s

4 4

3640.02, 3530.01, 2880.01, 2810.05, 2770.04, 2730.02, 2270.03, 2040.03, 2020.01 3430.02, 3100.01, 2840.02, 2760.02, 2730.05, 2410.07, 2090.06, 2090.02

W3C

SSIP/s

5

3480.01, 3200.01, 2940.02, 2800.03, 2620.02, 2570.04, 2370.06, 2140.01, 2120.03

W3D

SSIP/d

4

3010.01, 2900.04, 2720.08, 2460.01, 2440.02, 2320.01, 2170.05, 2160.05

W3E

SSIP/d

5

2740.04, 2680.03, 2450.01, 2130.01

Oscillator strength presented as a subscript. b The absorption spectra were resolved by Brugger et al. in trace CuCl2 (ca. 10
4 mol 3 kg
1) þ LiCl (>10 mol 3 kg
1) solution.4 a

the absorption bands of the five-coordinated CIP conformers of [CuCl(H2O)n]þ (n = 8 and 9) and the five-coordinated SSIP/s structure of CuCl2(H2O)n (n g 8) correspond to the observed

absorption spectra of the [CuCl]þ(aq) species.17,18 In addition, the four-coordinated CIP conformers of CuCl2(H2O)n (n = 4
7) clusters might be the predominant structures for [CuCl2]0(aq) 4423

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ARTICLE

Figure 4. Calculated electronic absorption spectra of [CuCl3]
and [CuCl3(H2O)n]
clusters for n = 1
5 using the LRC-TDDFT/aVDZ method (298 K and 1 atm).

Figure 5. Calculated electronic absorption spectra of [CuCl4]2
and [CuCl4(H2O)n]2
clusters for n = 1
3 using the LRC-TDDFT/aVDZ method (298 K and 1 atm).

species,17 whereas the four-coordinated CIP conformers of [CuCl3(H2O)n]
clusters for n = 3 and 4 and the [CuCl4]2
cluster with a tetrahedral structure correspond to [CuCl3]
(aq) and [CuCl4]2
(aq) species, respectively.

4. CONCLUSIONS The B3LYP, PBE, MP2, and CCSD methods were applied to investigate the structures and thermodynamic properties of [CuCl3]
and [CuCl4]2
clusters in aqueous solution. Our calculations suggest that [CuCl3(H2O)n]
clusters for n = 3 or 4 in aqueous solution perhaps prefer four-coordinated CIP structures with one water molecule coordinating directly to the copper atom in the equatorial position, whereas it seems that the four-coordinated SSIP structure with one chloride atom

dissociated becomes slightly more favorable as n increases to 5. However, the calculated stabilization energies of [CuCl4(H2O)n]2
clusters show that the chloride atom tends to dissociate when n g 1, which suggests that [CuCl4]2
(aq) species possibly exist in environments where the water molecule activity is quite low. All structural parameters of [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters suggest that [CuCl3]
(aq) and [CuCl4]2
(aq) species perhaps prefer four-coordinated structures, which is similar to [CuCl2]0(aq) species, whereas the [Cu]2þ(aq) and [CuCl]þ(aq) species prefer five-coordinated structure as shown in our previous works.17,18 In addition, NBO analyses of [CuClx]2
x (x = 1
4) clusters indicate that, in comparison to the charge population of the [CuCl2]0 cluster, CT between copper and chloride atoms for [CuCl3]
and [CuCl4]2
clusters is negligible, and thus the coordination ability of Cl
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The Journal of Physical Chemistry A with Cu2þ is greatly weakened for [CuCl3]
and [CuCl4]2
clusters. Our calculated electronic absorption spectra obtained using the LRC-TDDFT/aVDZ method show that the CT bands at ∼290 and 385 nm for the four-coordinated CIP structure of [CuCl3(H2O)n]
clusters for n = 3 and 4 are coincident with the absorption of the [CuCl3]
(aq) species (∼284 and 384 nm) assigned from the spectra obtained in trace CuCl2 (ca. 10
4 mol 3 kg
1) þ LiCl (>10 mol 3 kg
1) solution, whereas those of the [CuCl4]2
cluster with a tetrahedral structure around 287 and 382 nm correspond to the absorption spectra of the [CuCl4]2
(aq) species (∼270 and 370 nm).

’ ASSOCIATED CONTENT

bS

Supporting Information. More optimized local minimum-energy structures and structural and energy parameters of [CuCl3(H2O)n]
and [CuCl4(H2O)n]2
clusters for n = 1
8 at the B3LYP/aVDZ level. This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected] (H.-B.Y.), [email protected] (D.Z.).

’ ACKNOWLEDGMENT This work was financially supported by the National Natural Science Foundation of China under Contracts 20773036 and 21073056. H.-B.Y. acknowledges the support of the “985” Foundation of the Ministry of Education of China. The authors also thank the reviewers for their constructive suggestions, which helped us improve this work. ’ REFERENCES (1) McDonald, R. G.; Muir, D. M. Hydrometallurgy 2007, 86, 206–220. (2) Senanayake, G. Min. Eng. 2007, 20, 1075–1088. (3) Park, K.-H.; Mohapatra, D.; Kim, H.-I.; Guo, X. Sep. Purif. Technol. 2007, 56, 303–310. (4) Brugger, J.; Mcphail, D. C.; Black, J.; Spiccia, L. Geochim. Cosmochim. Acta 2001, 65, 2691–2708. (5) Libus, Z. Inorg. Chem. 1973, 12, 2972–2977. (6) Mcconnell, H.; Davidson, N. J. Am. Chem. Soc. 1950, 72, 3164–3167. (7) Khan, M. A.; Schwing-Weill, M. J. Inorg. Chem. 1976, 15, 2202–2205. (8) Scholz, B.; L€udemann., H. D.; Franck, E. U. Ber. Bunsen-Ges. Phys. Chem. 1972, 76, 406–409. (9) Petersen, C. P.; Gordon, M. S. J. Phys. Chem. A 1999, 103, 4162–4166. (10) Yang, Y.; Meng, Sh.; Xu, L. F.; Wang, E. G. Phys. Rev. 2005, 72, 012602-1–012602-4. (11) Olleta, A. C.; Lee, H. M.; Kim, K. S. J. Chem. Phys. 2006, 124, 024321-1–024321-12. (12) Singh, N. J.; Yi, H.-B.; Min, S. K.; Park, M.; Kim, K. S. J. Phys. Chem. B 2007, 110, 3808–3815. (13) Olleta, A. C.; Lee, H. M.; Kim, K. S. J. Chem. Phys. 2007, 126, 144311-1–144311-11. (14) Kumar, A.; Park, M.; Huh, J. Y.; Lee, H. M.; Kim, K. S. J. Phys. Chem. A 2006, 110, 12484–12493. (15) Odde, S.; Mhin, B. J.; Lee, K. H.; Lee, H. M.; Tarakeshwar, P.; Kim, K. S. J. Phys. Chem. A 2006, 110, 7918–7924.

ARTICLE

(16) Petit, L.; Vuilleumier, R.; Maldivi, P.; Adamo, C. J. Chem. Theory Comput. 2008, 4, 1040–1048. (17) Xia, F. F.; Yi, H. B.; Zeng, D. W. J. Phys. Chem. A 2009, 113, 14029–14038. (18) Xia, F. F.; Yi, H. B.; Zeng, D. W. J. Phys. Chem. A 2010, 114, 8406–8416. (19) Iikura, H.; Tsuneda, T.; Yanai, T.; Hirao, K. J. Chem. Phys. 2001, 115, 3540–3544. (20) Tawada, Y.; Tsuneda, T.; Yanagisawa, S.; Yanai, T.; Hirao, K. J. Chem. Phys. 2004, 120, 8425–8433. (21) Mary, A.; Rohrdanz, K. M.; Martins.; Herbert, J. M. J. Chem. Phys. 2009, 130, 054112-11–054112-8. (22) Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F. NBO, version 3.1; Theoretical Chemistry Institute, University of Wisconsin: Madison, WI, 1993. (23) (a) Foster, J. P.; Weinhold, F. J. Am. Chem. Soc. 1980, 102, 7211–7218. (b) Reed, A. E.; Weinhold, F. J. Chem. Phys. 1983, 78, 4066–4073. (c) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899–926. (24) Goodman, L; Sauers, R. J. Chem. Theory Comput. 2005, 1, 1185–1192. (25) Dolg, M.; Wedig, U.; Stoll, H.; Preu, H. J. Chem. Phys. 1987, 86, 866–872. (26) Dunning, T. H., Jr. J. Chem. Phys. 1989, 90, 1007–1023. (27) Boys, S. F.; Bernardi, F. Mol. Phys. 1970, 19, 553–566. (28) Pushie, M. J.; Rauk, A. J. Biol. Inorg. Chem. 2003, 8, 53–65. (29) Runge, E.; Gross, E. K. U. Phys. Rev. Lett. 1984, 52, 997–1000. (30) Gross, E. K. U.; Kohn, W. Adv. Quantum Chem. 1990, 21, 255–291. (31) Lange, A. W.; Rohrdanz, M. A.; Herbert, J. M. J. Phys. Chem. B 2008, 112, 6304–6308. (32) Rajapakse, G. V. N.; Soldatova, A. V.; J. Rodgers, M. A. J. Phys. Chem. B 2010, 114, 14205–14213. (33) Seth, M.; Ziegler, T. J. Chem. Phys. 2005, 123, 1441051–144105-14. (34) Ruzankin, S. F.; Anufrienko, V. F.; Yashnik, S. A.; Ismagilov, Z. R. J. Struct. Chem. 2006, 47, 404–412. (35) Dombroski., J.; Head-Gordon., M.; Gilbert., A. Q-Chem, Revision 3.2; Pittsburgh PA, 2009. (36) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, revision E.01; Gaussian, Inc.: Pittsburgh PA, 2003. (37) Szilagyi, R. K.; Metz, M.; Solomon, E. I. J. Phys. Chem. A 2002, 106, 2994–3007. (38) Harlow, R. L.; Wells, W. J., III; Watt, G. W.; Simonsen, S. H. Inorg. Chem. 1974, 13, 2106–2111. (39) Dunn, K. M.; Morokuma, K. J. Phys. Chem. 1996, 100, 123–129. (40) Hathaway, B. J. Comprehensive Coordination Chemistry; Wilkinson, G.; Ed.; Pergamon: Oxford, U.K., 1987; Vol. 5, pp 533
774. (41) Sukart, K.; Parasuk, V. Chem. Phys. Lett. 2007, 447, 58–64. (42) Pasquarello, A.; Petri, I.; Salmon, P. S.; Parisel, O.; Car, R.; .; Powell, D. H.; Fisher, H. E.; Helm, L.; Merbach, A. E. Science Toth, E 2001, 291, 856–859. 4425

dx.doi.org/10.1021/jp109723v |J. Phys. Chem. A 2011, 115, 4416–4426

The Journal of Physical Chemistry A

ARTICLE

(43) Bryantsev, V. S.; Diallo, M. S.; Goddard, W. A., III. J. Phys. Chem. B 2008, 112, 9709–9719. (44) Benfatto, M.; D’Angelo, P.; Longa, S. D.; Pavel, N. V. Phys. Rev. B 2002, 65, 174205-1–174205-5. (45) Chaboy, J.; Mun~oz-Paez, A.; Merkling, P. J.; Marcos, E. S. J. Chem. Phys. 2006, 124, 064509-1–064509-9. (46) DeKock, C. W.; Gruen, D. M. J. Chem. Phys. 1966, 44, 4387–4398.

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