Speciation in Aqueous Zinc Chloride. An <i>ab Initio</i> Hybrid Microsolvation/Continuum Approach

A series of geometry, frequency, and energy calculations of chloroaquazinc(II) complexes were carried out at up to the MP2/6-31+G* level. A thorough examination of all species up to and including hexacoordinate species, and with up to six chlorides, was carried out. The structures of the complexes are compared with experimental data where available. The solution chemistry of zinc(II) in the presence of chloride is discussed, and Raman spectra of zinc perchlorate with increasing amount of chloride are presented.

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“…Using an ECP gave a more comparable value of 2.41 A ˚. 40 The value of Hillier 41 is identical to ours.…”

Section: àsupporting

confidence: 84%

An ab initio investigation of zinc chloro complexes

Pye

Corbeil

Rudolph

2006

Phys. Chem. Chem. Phys.

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“…For ions with well defined coordination numbers, like Ca 2+ and Zn 2+ , the optimum micro-hydration number n H 2 O is usually equal to the number of solvent molecules in the first coordination shell. 25,26 However, ionic species like H x PO 4 3Àx are characterised by multiple and very flexible first hydration shells, 27 and the hydrated phosphate clusters H x PO 4 3Àx (H 2 O) n should probably include a relatively large number of explicit water molecules to achieve a converged value of the solvation free energy. This would consequently introduce the problem of determining the low energy conformers of the hydrated clusters, thus increasing the cost and complexity of the computation.…”

Section: Introductionmentioning

confidence: 99%

Accuracy of the microsolvation–continuum approach in computing the pKa and the free energies of formation of phosphate species in aqueous solution

Tang

Tommaso

Leeuw

2010

Phys. Chem. Chem. Phys.

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First principles density functional theory (Perdew-Burke-Ernzerhof) calculations have been used to compute the hydration properties, aqueous-phase acid dissociation constants (pK(a)) and Gibbs free energies of formation of small polyphosphates in aqueous solution. The effect of the hydrated environment has been simulated through a hybrid microsolvation-continuum approach, where the phosphate species are simulated as microsolvated solutes, while the remainder of the bulk solvent is treated as a dielectric continuum using the COSMO solvation model. The solvation free energies of orthophosphates and pyrophosphates have been computed applying monomer and cluster thermodynamic cycles, and using the geometries optimised in the gas-phase as well as in the COSMO environment. The results indicate that the simple polarisable continuum or microsolvation-continuum models are unable to compute accurate free energies of solvation for charged species like phosphates. The calculation of the pK(a) shows that the computed values of acid dissociation constants are critically dependent on the number of water molecules n(H(2)O) included in the hydrated phosphate clusters. The optimal number n(H(2)O) is determined from the minimum value of the "incremental" water binding free energy associated with the process of adding a water molecule to a micro-solvated phosphate species. Analysis of the effect of n(H(2)O) on the free energies of orthophosphate condensation reactions shows that can vary by tenths of kcal mol(-1), depending on the particular choice of n(H(2)O) for the monomeric and dimeric species. We discuss a methodology for the determination of n(H(2)O); for the orthophosphates the "incremental" binding energy approach is used to determine n(H(2)O), whereas for the polyphosphates the number of explicit water molecules is simply equal to the effective charge of these anions. The application of this method to compute the free energy of formation of pyro- and tri-phosphates gives generally good agreement with the available experimental data.

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“…47 The structure and energetics of zinc chlorides in aqueous solutions have been studied by ab initio molecular orbital methods. 48 Structural and dynamical properties of Zn 2+ in aqueous solution were investigated, based on an ab initio quantum mechanical/ molecular mechanical (QM/MM) molecular dynamics (MD) simulation at the double HF quantum mechanical level, including the first and second hydration spheres into the QM region but only for small hydrated Zn(H 2 O)n 2+ clusters with n = 1-4, and 6. 49 Hydration and water exchange mechanism of Zn 2+ have been studied at the B3LYP level of theory with a variety of different basis sets for complexes of the type [Zn(H 2 O) n ] 2+ only for n = 1-6.…”

Section: Introductionmentioning

confidence: 99%

Micro-solvation of the Zn2+ ion—a case study

Ali

et al. 2009

Phys. Chem. Chem. Phys.

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The structures and thermodynamic parameters of hydrated zinc ion clusters incorporating a single zinc ion and up to eighteen water molecules have been determined with a quantum mechanical hybrid density functional, namely B3LYP using cc-PVDZ basis functions for H and O and a split valence 6-31G (d, p) basis function for Zn. The geometries for all the zinc ion water clusters are optimized with several initial guess structures and without imposing any initial symmetry restriction. Zinc metal ion is found to be preferably four coordinated for smaller sizes of hydrated cluster but attains an octahedral coordination for larger sizes (n >or= 11) of hydrated cluster. Structures with seven or more than seven water molecules attached directly to the central zinc ion are not found. The calculated gas phase coordination number in the first solvation sphere of a large hydrated zinc metal ion is found to be six and the same is also confirmed in the force field based classical molecular dynamics simulation study for an aqueous zinc ion and thus confirms the experimental findings. The equilibrium zinc-oxygen distance of 2.09328 A at the present B3LYP level of study is in excellent agreement with the X-ray diffraction result of 2.093 +/- 0.002 A for a hexahydrated zinc cluster.

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Speciation in Aqueous Zinc Chloride. An ab Initio Hybrid Microsolvation/Continuum Approach

Cited by 32 publications

References 40 publications

An ab initio investigation of zinc chloro complexes

An ab initio investigation of zinc chloro complexes

Accuracy of the microsolvation–continuum approach in computing the pKa and the free energies of formation of phosphate species in aqueous solution

Micro-solvation of the Zn2+ ion—a case study

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