TY - JOUR
T1 - Theoretical study of formation of ion pairs in (NH3·HCl)(H2O)6 and (NH3·HF)(H2O)6
AU - DeKock, Roger L.
AU - Brandsen, Benjamin M.
AU - Strikwerda, John R.
N1 - Funding Information:
We gratefully acknowledge the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. We thank Laura A. Schipper and Stephanie C. Dykhouse for the preliminary work that they performed on this project. Computer hardware was provided by a Major Research Instrumentation Grant from the National Science Foundation, Award No. OCI-0722819.
PY - 2011/12
Y1 - 2011/12
N2 - We have performed theoretical studies on sixteen molecular cubes for both (NH3·HCl)(H2O)6 and (NH3·HF)(H2O)6. We use an empirical gauge, based upon the N-H and H-X bond lengths, to categorize the degree to which the cubes are neutral adduct or ion pair in character. On this basis, we describe all sixteen cubes of the former as highly ionized, but only five of the latter as greater than 85% ionic in character. Addition of one or two bridging water molecules to form (NH3·HF)(H2O)7 or (NH3·HF)(H2O)8 raises the percent ionic character to greater than 85% for these systems. The relative energy of the cubes can be categorized based on simple chemical principles. The computed vibrational frequency corresponding to the proton stretch in the N-H-F framework shows the highest degree of redshifting for systems near 50% ion-pair character. Molecular cubes close to neutral adduct or to ion-pair character show less redshifting of this vibrational motion.
AB - We have performed theoretical studies on sixteen molecular cubes for both (NH3·HCl)(H2O)6 and (NH3·HF)(H2O)6. We use an empirical gauge, based upon the N-H and H-X bond lengths, to categorize the degree to which the cubes are neutral adduct or ion pair in character. On this basis, we describe all sixteen cubes of the former as highly ionized, but only five of the latter as greater than 85% ionic in character. Addition of one or two bridging water molecules to form (NH3·HF)(H2O)7 or (NH3·HF)(H2O)8 raises the percent ionic character to greater than 85% for these systems. The relative energy of the cubes can be categorized based on simple chemical principles. The computed vibrational frequency corresponding to the proton stretch in the N-H-F framework shows the highest degree of redshifting for systems near 50% ion-pair character. Molecular cubes close to neutral adduct or to ion-pair character show less redshifting of this vibrational motion.
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U2 - 10.1007/s00214-011-1032-7
DO - 10.1007/s00214-011-1032-7
M3 - Article
AN - SCOPUS:81855197051
VL - 130
SP - 871
EP - 881
JO - Theoretical Chemistry Accounts
JF - Theoretical Chemistry Accounts
SN - 1432-881X
IS - 4-6
ER -