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Title: Theoretical Characterization of Oxoanion, XOmn-, Solvation

Abstract

We propose an empirically-derived cavity definition scheme that permits the prediction of accurate solvation energies of oxoanions using a COSMO dielectric continuum model of solvation. Assuming a cavity made up of interlocked atomic spheres, the radii are given by simple, empirically-derived, expressions involving effective atomic charges of the solute atoms that fit the solute molecular electrostatic potential (from DFT calculations), and a bond length-dependent factor to account for atomic size and hybridization. We illustrate the new scheme for the case of oxoanions. The expression for the atomic radii of the terminal oxygen atoms is based on a training set that included only O-, O2-, and O2. The expression for the radius of the central atom is based on a limited training set made of O3-, NO2-, HCO2-, NO3-, ClO2-, O3, NO2, CO2, ClO2, and SO2. The scheme is applied to several oxoanions outside the training sets, such as CO2-, CO3-, CO32-, NO32-, SO2-, ClO3-, and ClO4-. The predicted solvation energies and half-reaction potentials are in close agreement with experiment. The new cavity scheme shows substantial qualitative differences from other previously proposed schemes. For example in contrast to the widely used UAHF scheme that assigns small radii to the central atomsmore » of these oxoanions, our new scheme assigns large radii. This difference is put on a firm theoretical basis in the case of nitrate NO3- through an analysis of the molecular electrostatic potential of the nitrate ion and an analysis of its interaction with a `solvent? water molecule. In spite of a large positive partial charge assigned to nitrogen in nitrate ion, the water `solvent? molecule remains acting as an H-bond donor in the region of the central N-atom as a result of the electrostatic potential of the anion, although the water-nitrate interaction in that region is weaker than near the terminal O atoms. From these results we surmise that the solvent molecules remain further away from the nitrogen atom, a finding consistent with the large `best? radius for nitrogen assigned by the new scheme. The same qualitative argument holds true for all the oxoanions considered here. Thus the new scheme reflects important ab initio characteristics of solute-solvent `specific? interactions.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
892241
Report Number(s):
PNNL-SA-37591
KP1302000; TRN: US200622%%799
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry A, 107:5778-5788
Additional Journal Information:
Journal Name: Journal of Physical Chemistry A, 107:5778-5788
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ATOMIC RADII; ATOMS; DIELECTRIC MATERIALS; ELECTROSTATICS; FORECASTING; HYBRIDIZATION; NITRATES; NITROGEN; OXYGEN; SOLUTES; SOLVATION; SOLVENTS; TRAINING; UNIVERSE; WATER

Citation Formats

Camaioni, Donald M, Dupuis, Michel, and Bentley, John. Theoretical Characterization of Oxoanion, XOmn-, Solvation. United States: N. p., 2003. Web. doi:10.1021/jp0343537.
Camaioni, Donald M, Dupuis, Michel, & Bentley, John. Theoretical Characterization of Oxoanion, XOmn-, Solvation. United States. https://doi.org/10.1021/jp0343537
Camaioni, Donald M, Dupuis, Michel, and Bentley, John. 2003. "Theoretical Characterization of Oxoanion, XOmn-, Solvation". United States. https://doi.org/10.1021/jp0343537.
@article{osti_892241,
title = {Theoretical Characterization of Oxoanion, XOmn-, Solvation},
author = {Camaioni, Donald M and Dupuis, Michel and Bentley, John},
abstractNote = {We propose an empirically-derived cavity definition scheme that permits the prediction of accurate solvation energies of oxoanions using a COSMO dielectric continuum model of solvation. Assuming a cavity made up of interlocked atomic spheres, the radii are given by simple, empirically-derived, expressions involving effective atomic charges of the solute atoms that fit the solute molecular electrostatic potential (from DFT calculations), and a bond length-dependent factor to account for atomic size and hybridization. We illustrate the new scheme for the case of oxoanions. The expression for the atomic radii of the terminal oxygen atoms is based on a training set that included only O-, O2-, and O2. The expression for the radius of the central atom is based on a limited training set made of O3-, NO2-, HCO2-, NO3-, ClO2-, O3, NO2, CO2, ClO2, and SO2. The scheme is applied to several oxoanions outside the training sets, such as CO2-, CO3-, CO32-, NO32-, SO2-, ClO3-, and ClO4-. The predicted solvation energies and half-reaction potentials are in close agreement with experiment. The new cavity scheme shows substantial qualitative differences from other previously proposed schemes. For example in contrast to the widely used UAHF scheme that assigns small radii to the central atoms of these oxoanions, our new scheme assigns large radii. This difference is put on a firm theoretical basis in the case of nitrate NO3- through an analysis of the molecular electrostatic potential of the nitrate ion and an analysis of its interaction with a `solvent? water molecule. In spite of a large positive partial charge assigned to nitrogen in nitrate ion, the water `solvent? molecule remains acting as an H-bond donor in the region of the central N-atom as a result of the electrostatic potential of the anion, although the water-nitrate interaction in that region is weaker than near the terminal O atoms. From these results we surmise that the solvent molecules remain further away from the nitrogen atom, a finding consistent with the large `best? radius for nitrogen assigned by the new scheme. The same qualitative argument holds true for all the oxoanions considered here. Thus the new scheme reflects important ab initio characteristics of solute-solvent `specific? interactions.},
doi = {10.1021/jp0343537},
url = {https://www.osti.gov/biblio/892241}, journal = {Journal of Physical Chemistry A, 107:5778-5788},
number = ,
volume = ,
place = {United States},
year = {2003},
month = {7}
}