The H•/H^– Redox Couple and Absolute Hydration Energy of H^–

Abstract

A supermolecule-continuum approach with water clusters up to n = 16 H2O molecules has been used to predict the absolute hydration free energies at 298 K (ΔG hyd) of both hydrogen (H•) and hydride (H–) to be 4.6 ± 1 and −78 ± 3 kcal/mol, respectively. These values are combined with a high accuracy prediction of the gas-phase electron affinity (ΔG gas,298K = −16.9 kcal/mol) to determine the aqueous electron affinity of H• of 99.5 ± 3 kcal/mol, which yields a reduction potential for H• vs SHE of −0.03 ± 0.15 V. This value is in agreement within 0.2 V with most estimates obtained using a wide variety of approaches. These results can be used to improve the absolute hydricity scale in water which provides additional insights into how a putative hydride interacts with solvent but do not change the ability to predict the relative reactivity of two species using relative hydricity scales.

Absolute Hydration Free Energy of Small Anions and the Aqueous pKa of Simple Acids

“…In our prior work, we showed that the free energy of solvation of some simple ions could be calculated using optimized gas phase clusters of water molecules with the ion and then correcting the energetics using an implicit solvent model as described below. In addition, by calculating the energy of a neutral atom or molecule and that of the anion, it was possible to make reliable predictions of redox potentials. , …”

“…In addition, by calculating the energy of a neutral atom or molecule and that of the anion, it was possible to make reliable predictions of redox potentials. 38,39 All geometry optimizations and frequency calculations of the neutrals and anions in water clusters at the density functional theory and MP2 levels were performed using the Gaussian 16 40 software package. Starting geometries for OH − (H 2 O) 4 and F − (H 2 O) 4 are taken from prior work 7,32 and retain their original labels.…”

Ambiguities in solvation free energies from cluster-continuum quasichemical theory: lithium cation in protic and aprotic solvents

“…Despite important findings were obtained with the hybrid approach of solvation, [56][57][58]64,[67][68][69][70][71][72][73] the results were shown to be considerably affected by the choice of: a) initial state of the solvent (separate molecules or clusters); 60,61,66 b) dielectric continuum model; 61,66 c) electronic structure theory method. 62 In this work using the cluster/continuum framework, we systematically assess the influence of factors a) -c) on resulting solvation free energies of lithium cation in a number of protic (water, methanol) and aprotic (acetonitrile, DMSO, dimethylacetamide, dimethoxyethane, dimethylformamide, gamma-butyrolactone, pyridine, sulfolane) solvents.…”

Chemical Shift of Solvated Hydride Ion: Comparative Study with Solvated Fluoride Ion

“…Even in the case of very low abundances of ions and weak peak intensities, computational studies can provide information on the physicochemical background as well as on the possibility of detection. There have been several theoretical studies concerning the solvation of hydride ion, but all of them deal with the hydrated cluster consisting of a hydride ion and water molecules. − This is because the clusters such as H – -(H 2 O) n ( n = 1, 2, 5, and 11) have been experimentally observed in the gas phase . The theoretical studies have focused on what kind of cluster structure is stable, and comparisons with experimentally obtained binding energies have been performed.…”