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Title: Photoelectron Spectroscopy and Theoretical Studies of Anion-pi Interactions: Binding Strength and Anion Specificity

Abstract

Proposed in theory and confirmed to exist, anion–π interactions have been recognized as new and important non-covalent binding forces. Despite extensive theoretical studies, numerous crystal structural identifications, and a plethora of solution phase investigations, intrinsic anion–π interaction strengths that are free from complications of condensed phases’ environments, have not been directly measured in the gas phase. Herein we present a joint photoelectron spectroscopic and theoretical study on this subject, in which tetraoxacalix[2]arene[2]triazine 1, an electron-deficient and cavity self-tunable macrocyclic was used as a charge-neutral molecular host to probe its interactions with a series of anions with distinctly different shapes and charge states (spherical halides Cl⁻, Br⁻, I⁻, linear thiocyanate SCN⁻, trigonal planar nitrate NO₃⁻, pyramidic iodate IO₃⁻, and tetrahedral sulfate SO₄²⁻). The binding energies of the resultant gaseous 1:1 complexes (1•Cl⁻,1•Br⁻, 1•I⁻, 1•SCN⁻, 1•NO₃⁻, 1•IO₃⁻ and 1•SO₄²⁻) were directly measured experimentally, exhibiting substantial non-covalent interactions with pronounced anion specific effects. The binding strengths of Cl⁻, NO₃⁻, IO₃⁻ with 1 are found to be strongest among all singly charged anions, amounting to ca. 30 kcal/mol, but only about 40% of that between 1 and SO₄²⁻. Quantum chemical calculations reveal that all anions reside in the center of the cavity of 1more » with anion–π binding motif in the complexes’ optimized structures, where 1 is seen to be able to self-regulate its cavity structure to accommodate anions of different geometries and three-dimensional shapes. Electron density surface and natural bond orbital charge distribution analysis further support anion–π binding formation. The calculated binding energies of the anions and 1 nicely reproduce the experimentally estimated electron binding energy increase. This work illustrates that size-selective photoelectron spectroscopy combined with theoretical calculations represent a powerful technique to probe intrinsic anion–π interactions and has potential to provide quantitative guest-host molecular binding strengths and unravel fundamental insights in specific anion recognitions.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1184979
Report Number(s):
PNNL-SA-105824
Journal ID: ISSN 3131-3141; 48584; 48136; KC0301020
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Chemistry Chemical Physics. PCCP; Journal Volume: 17; Journal Issue: 5
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Photoelectron spectroscopy; anion‒interactions; anion stabilization; non-covalent binding; anion recognition; specific anion effects; Environmental Molecular Sciences Laboratory

Citation Formats

Zhang, Jian, Zhou, Bin, Sun, Zhenrong, and Wang, Xue B. Photoelectron Spectroscopy and Theoretical Studies of Anion-pi Interactions: Binding Strength and Anion Specificity. United States: N. p., 2015. Web. doi:10.1039/C4CP04687K.
Zhang, Jian, Zhou, Bin, Sun, Zhenrong, & Wang, Xue B. Photoelectron Spectroscopy and Theoretical Studies of Anion-pi Interactions: Binding Strength and Anion Specificity. United States. doi:10.1039/C4CP04687K.
Zhang, Jian, Zhou, Bin, Sun, Zhenrong, and Wang, Xue B. Thu . "Photoelectron Spectroscopy and Theoretical Studies of Anion-pi Interactions: Binding Strength and Anion Specificity". United States. doi:10.1039/C4CP04687K.
@article{osti_1184979,
title = {Photoelectron Spectroscopy and Theoretical Studies of Anion-pi Interactions: Binding Strength and Anion Specificity},
author = {Zhang, Jian and Zhou, Bin and Sun, Zhenrong and Wang, Xue B.},
abstractNote = {Proposed in theory and confirmed to exist, anion–π interactions have been recognized as new and important non-covalent binding forces. Despite extensive theoretical studies, numerous crystal structural identifications, and a plethora of solution phase investigations, intrinsic anion–π interaction strengths that are free from complications of condensed phases’ environments, have not been directly measured in the gas phase. Herein we present a joint photoelectron spectroscopic and theoretical study on this subject, in which tetraoxacalix[2]arene[2]triazine 1, an electron-deficient and cavity self-tunable macrocyclic was used as a charge-neutral molecular host to probe its interactions with a series of anions with distinctly different shapes and charge states (spherical halides Cl⁻, Br⁻, I⁻, linear thiocyanate SCN⁻, trigonal planar nitrate NO₃⁻, pyramidic iodate IO₃⁻, and tetrahedral sulfate SO₄²⁻). The binding energies of the resultant gaseous 1:1 complexes (1•Cl⁻,1•Br⁻, 1•I⁻, 1•SCN⁻, 1•NO₃⁻, 1•IO₃⁻ and 1•SO₄²⁻) were directly measured experimentally, exhibiting substantial non-covalent interactions with pronounced anion specific effects. The binding strengths of Cl⁻, NO₃⁻, IO₃⁻ with 1 are found to be strongest among all singly charged anions, amounting to ca. 30 kcal/mol, but only about 40% of that between 1 and SO₄²⁻. Quantum chemical calculations reveal that all anions reside in the center of the cavity of 1 with anion–π binding motif in the complexes’ optimized structures, where 1 is seen to be able to self-regulate its cavity structure to accommodate anions of different geometries and three-dimensional shapes. Electron density surface and natural bond orbital charge distribution analysis further support anion–π binding formation. The calculated binding energies of the anions and 1 nicely reproduce the experimentally estimated electron binding energy increase. This work illustrates that size-selective photoelectron spectroscopy combined with theoretical calculations represent a powerful technique to probe intrinsic anion–π interactions and has potential to provide quantitative guest-host molecular binding strengths and unravel fundamental insights in specific anion recognitions.},
doi = {10.1039/C4CP04687K},
journal = {Physical Chemistry Chemical Physics. PCCP},
number = 5,
volume = 17,
place = {United States},
year = {Thu Jan 01 00:00:00 EST 2015},
month = {Thu Jan 01 00:00:00 EST 2015}
}