DFT/PCM investigation of the Mn(II) chemical speciation in aqueous solution

Abstract

Chemical speciation of Mn(II) in aqueous solution has been investigated by means of density functional methods. Different geometries and electronic states of all species arising from the Mn(II) hydrolysis have been calculated. The Gibbs free energy of the hydrolysis reaction and the respective equilibrium constants have been estimated and compared with the available experimental data. Polarizable continuum model (PCM-UAHF/6-31ϩG(d)) was used to estimate the solvation energy. The ionization potential of the predominant species are linearly dependent on the number of hydroxyls in their structure. The Mn(II)/Mn(III) oxidation potential estimate is in good agreement with the experimental value, about 0.2 V smaller. The estimated hydrolysis reaction energies are in good agreement with the experimental values with an error of about 3 kcal mol Ϫ1 (PBE/TZVP). The unique exception is the [Mn(OH) 3 ] Ϫ hydrolysis constant which is not in good agreement with the experimental value. This is attributed to inaccuracy of the presently available experimental value and the PCM solvation free energy estimate. The results shown in this work reinforce the importance of the chemical speciation in order to understand at a molecular level the mechanism of processes involving transition metal ions.

Dynamical Discrete/Continuum Linear Response Shells Theory of Solvation: Convergence Test for NH4+ and OH− Ions in Water Solution Using DFT and DFTB Methods

“…These hybrid methodologies were used to study the solvation of species like OH -, 36 Be 2+ , 35 K + , 38 and others 4,6,33,37,39 in different solvents. Hybrid models combined with gas-phase calculations have been used to calculate pK a 33,34,[40][41][42][43][44][45] and redox 42,43,45 potential, obtaining good agreement with the experimental data for both organic and inorganic species. Although hybrid methods produce good results, many questions about the influence of the explicit solvent molecules are still open and were recently pointed out by Zhao et al 46 How many solvent molecules must be used to describe the specific interaction?…”

As(III) immobilization on gibbsite: Investigation of the complexation mechanism by combining EXAFS analyses and DFT calculations

“…Indeed, it has been the subject of many studies (Abreu et al, 2006(Abreu et al, ,2008Guimarães et al, 2007b;Noronha et al, 2007;Rodrigues et al, 2011). However, in the case of the arsenous acid, at the pH range used at the experiments, the predominant species is fully protonated H 3 AsO 3 , (pKa $9).…”

DFT study of vanadyl (IV) complexes with low molecular mass ligands: Picolinate, oxalate, malonate, and maltolate

“…The Gibbs free reaction energy of the complex formation is usually calculated using the thermodynamic cycle in which the reactants are the neutral protonated ligand and the metal cation normally in the form of aqua complexes27–29. The gas phase free energy is accurately estimated using DFT methods.…”

“…On the other side, the estimate of the free energy calculations depends strongly of the model used to estimate the solvation free energy of the reactants and products. The theoretical estimate of the Gibbs free reaction energy of the complex formation in aqueous solution using the thermodynamic cycle together with continuum model has been shown to be possible with an error bar about 5–8 kcal mol −1 22–25, 27–29, 32.…”