Computational Study of Copper(II) Complexation and Hydrolysis in Aqueous Solutions Using Mixed Cluster/Continuum Models

Abstract

We use density functional theory (B3LYP) and the COSMO continuum solvent model to characterize the structure and stability of the hydrated Cu(II) complexes [Cu(MeNH 2 2-x (x ) 1-3) as a function of metal coordination number (4-6) and cluster size (n ) 4-8, 18). The small clusters with n ) 4-8 are found to be the most stable in the nearly square-planar four-coordinate configuration,, which is three-coordinate. In the presence of the two full hydration shells (n ) 18), however, the five-coordinate square-pyramidal geometry is the most favorable for Cu (MeNH 2 ) 2+ (5, 6) and Cu(OH) + (5, 4, 6), and the four-coordinate geometry is the most stable for Cu(OH) 2 (4, 5) and Cu(OH) 3 -(4). (Other possible coordination numbers for these complexes in the aqueous phase are shown in parentheses.) A small energetic difference between these structures (0.23-2.65 kcal/mol) suggests that complexes with different coordination numbers may coexist in solution. Using two full hydration shells around the Cu 2+ ion (18 ligands) gives Gibbs free energies of aqueous reactions that are in excellent agreement with experiment. The mean unsigned error is 0.7 kcal/mol for the three consecutive hydrolysis steps of Cu 2+ and the complexation of Cu 2+ with methylamine. Conversely, calculations for the complexes with only one coordination shell (four equatorial ligands) lead to a mean unsigned error that is >6.0 kcal/mol. Thus, the explicit treatment of the first and the second shells is critical for the accurate prediction of structural and thermodynamic properties of Cu(II) species in aqueous solution.

The roles of mercapto, benzene, and methyl groups in the corrosion inhibition of imidazoles on copper: II. Inhibitor–copper bonding

“…A considerable improvement in the accuracy of the calculated ion solvation free energies is achieved by treating explicitly at least the first shell water molecules [90]. The free energies of complexation are therefore estimated using a mixed cluster/continuum model, following a method of Bryantsev et al [90,91]. We model the hydrated Cu 2+ using a first shell [Cu(H 2 O) 4 …”

“…(aq) mixed cluster/continuum model [91], where the label (aq) implies the implicit description of aqueous-phase by the continuum SMD model. We also used a larger [Cu(…”

“…10). Within the mixed cluster/continuum model, the complexation reaction of inhibitor molecule with hydrated Cu 2+ ion can be written as: The free energies of reaction (10) are calculated using a termodynamic cycle, as proposed by Bryantsev et al [91], which is shown in Fig. 11.…”

“…Thermodynamic cycle[91] used for the calculation of the Gibbs free energy of complexation of inihibitor molecule with the hydrated Cu 2+ ion. The superscripts 0 and 1 indicate the 1 atm and 1 M standard states, respectively (see footnote 12).…”

Origins of optical absorption characteristics of Cu2+ complexes in aqueous solutions

“…34 Accordingly, FPMD simulations of solvated Cu 2+ -ligand complexes were performed within the Quantum-ESPRESSO package 35 using density functional theory (DFT) in the plane-wave pseudopotential approximation. 34 Accordingly, FPMD simulations of solvated Cu 2+ -ligand complexes were performed within the Quantum-ESPRESSO package 35 using density functional theory (DFT) in the plane-wave pseudopotential approximation.…”