Absolute Single-Ion Solvation Free Energy Scale in Methanol Determined by the Lithium Cluster-Continuum Approach

Abstract

Absolute solvation free energy of the lithium cation in methanol was calculated by the cluster-continuum quasichemical theory of solvation. Clusters with up to five methanol molecules were investigated using X3LYP, MP2, and MP4 methods with DZVP, 6-311+G(2df,2p), TZVPP+diff, and QZVPP+diff basis sets and including the cluster solvation through the PCM and SMD continuum models. Our calculations have determined a value of -118.1 kcal mol(-1) for the solvation free energy of the lithium, in close agreement with a value of -116.6 kcal mol(-1) consistent with the TATB assumption. Using data of solvation and transfer free energy of a pair of ions, electrode potentials and pKa, we have obtained the solvation free energy of 25 ions in methanol. Our analysis leads to a value of -253.6 kcal mol(-1) for the solvation free energy of the proton, which can be compared with the value of -263.5 kcal mol(-1) obtained by Kelly et al. using the cluster pair approximation. Considering that this difference is due to the methanol surface potential, we have estimated that it corresponds to -0.429 V.

Proton solvation in protic and aprotic solvents

“…Proton solvation energies in different solvents were also determined by comparing computed and measured pK A values using a combination of quantum chemical and electrostatic energy computations. With these methods proton solvation energies were obtained for DMSO, [40][41][42][43] for MeOH, [43][44][45] and MeCN. [43] In an earlier theoretical study we computed pK A values for a diverse selection of 26 relatively rigid small molecules combining quantum chemistry with electrostatics.…”

The Protoelectric Potential Map (PPM): An Absolute Two‐Dimensional Chemical Potential Scale for a Global Understanding of Chemistry

“…[k] Values in parenthesis according to Fifen et al 88. [l] Values in parenthesis according to Pliego et al 89. [m] At a (H + )=1 mol L −1 →p${K{{\prime \hfill \atop {\rm e}\hfill}}}$ =pe abs . …”

Protonated Hexaazamacrocycles as Selective K+ Receptors

“…Table 2 compares the absolute 298 K free energy (ΔG solv ) values of Na + and K + in water and methanol, calculated using cluster continuum quasichemical theory of solvation [38,39]. The listed values indicate that the Na + desolvation free energy is 73 (methanol) or 84 kJ mol −1 (water) larger than that of K + .…”