Computational Prediction of All Lanthanide Aqua Ion Acidity Constants

Abstract

The protonation state of lanthanide-ligand complexes, or lanthanide-containing porous materials, with many Brønsted acid sites can change due to proton loss/gain reactions with water or other heteroatomcontaining compounds. Consequently, variations in the protonation state of lanthanide-containing species affect their molecular structure and desired properties. Lanthanide(III) aqua ions undergo hydrolysis and form hydroxides; they are the best characterized lanthanide-containing species with multiple Brønsted acid sites. We employed constrained ab initio molecular dynamics simulations and electronic structure calculations to determine all acidity constants of the lanthanide(III) aqua ions solely from computation. The first, second, and third acidity constants of lanthanide(III) aqua ions were predicted, on average, within 1.2, 2.5, and 4.7 absolute pK a units from experiment, respectively. A table includes our predicted pK a values alongside most experimentally measured pK a values known to date. The approach presented is particularly suitable to determine the Brønsted acidity of lanthanide-containing systems with multiple acidic sites, including those whose measured acidity constants cannot be linked to specific acid sites.

The solution structures and relative stability constants of lanthanide–EDTA complexes predicted from computation

“…The energies of each species in eqn ( 1) and ( 2) were calculated with all-electron single-point energy calculations, as performed in our previous work, where we calculated the acidity constants of Ln aqua ions. 12 All energy calculations were done with the M06 functional, a relativistic second order Douglas-Kroll-Hess (DKH2) Hamiltonian, 13,14 segmented all-electron relativistically contracted (SARC) basis set 15 for the Ln atoms, and the minimally augmented 16 ma-def2-TZVPP basis set 17,18 for ligand and water atoms. Studies demonstrate that the M06 functional is a reliable choice for the calculations of thermodynamic properties in broad variety of chemical systems, 19 including the Ln-containing molecules and Ln complexes.…”

Norm-Conserving 4f-in-Core Pseudopotentials and Basis Sets Optimized for Trivalent Lanthanides (Ln = Ce–Lu)

“…Two methods are employed for the prediction of the p K a value with explicit solvents. One method is through thermodynamic integration (TI) of vertical energy gaps between deprotonated and protonated species, , and the other one is calculated from AIMD with enhanced samplings, which gives the free energy of the hydrolysis reaction. − We use here the second method in this work. The hydrolysis reaction is a nonredox reaction which could be dealt with by 4f-in-core PPs.…”

“…This procedure is similar to the calculations using LnPP1 by Cantu and coworkers. 118 6, the pKa values computed by LnPP2 are generally in good agreement with those computed by LnPP1 considering that the pKa value is very sensitive with the free energy results. Not surprisingly, the difference of the pKa value of Gd calculated by LnPP1 and LnPP2 is larger, with an error of 1.6, consistent with the situation in the binding energy calculation using LnBS2-DZVP, as shown in Figure 4.…”

Water Defect Stabilizes the Bi3+ Lone-Pair Electronic State Leading to an Unusual Aqueous Hydration Structure

“…The first hydrolysis constant, logβ 1 , typically shows a linear dependence on the ratio of charge to M–O distance, z / d . Although their average M–O distances are approximately the same, their logβ 1 values are vastly different, with −7.53 for Dy 3+ and −0.92 for Bi 3+ . , This is another indicator of the anomalous behavior of aqueous Bi 3+ ions.…”

“…19 Although their average M−O distances are approximately the same, their logβ 1 values are vastly different, with −7.53 for Dy 3+ and −0.92 for Bi 3+ . 20,21 This is another indicator of the anomalous behavior of aqueous Bi 3+ ions.…”