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Local Vibrational Mode Analysis of π–Hole Interactions between Aryl Donors and Small Molecule Acceptors

1
Department of Chemistry, Southern Methodist University, 3215 Daniel Avenue, Dallas, TX 75275, USA
2
Institute of Modern Physics, Northwest University, Xi’an 710127, China
*
Author to whom correspondence should be addressed.
Crystals 2020, 10(7), 556; https://doi.org/10.3390/cryst10070556
Received: 6 June 2020 / Accepted: 24 June 2020 / Published: 30 June 2020
(This article belongs to the Special Issue σ- and π-Hole Interactions)
11 aryl–lone pair and three aryl–anion π –hole interactions are investigated, along with the argon–benzene dimer and water dimer as reference compounds, utilizing the local vibrational mode theory, originally introduced by Konkoli and Cremer, to quantify the strength of the π –hole interaction in terms of a new local vibrational mode stretching force constant between the two engaged monomers, which can be conveniently used to compare different π –hole systems. Several factors have emerged which influence strength of the π –hole interactions, including aryl substituent effects, the chemical nature of atoms composing the aryl rings/ π –hole acceptors, and secondary bonding interactions between donors/acceptors. Substituent effects indirectly affect the π –hole interaction strength, where electronegative aryl-substituents moderately increase π –hole interaction strength. N-aryl members significantly increase π –hole interaction strength, and anion acceptors bind more strongly with the π –hole compared to charge neutral acceptors (lone–pair donors). Secondary bonding interactions between the acceptor and the atoms in the aryl ring can increase π –hole interaction strength, while hydrogen bonding between the π –hole acceptor/donor can significantly increase or decrease strength of the π –hole interaction depending on the directionality of hydrogen bond donation. Work is in progress expanding this research on aryl π –hole interactions to a large number of systems, including halides, CO, and OCH3 as acceptors, in order to derive a general design protocol for new members of this interesting class of compounds. View Full-Text
Keywords: π–hole interaction; substituent effects; vibrational spectroscopy; local vibrational mode theory; direct measure for π–hole interaction strength; noncovalent interaction; hydrogen bonding π–hole interaction; substituent effects; vibrational spectroscopy; local vibrational mode theory; direct measure for π–hole interaction strength; noncovalent interaction; hydrogen bonding
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Yannacone, S.; Freindorf, M.; Tao, Y.; Zou, W.; Kraka, E. Local Vibrational Mode Analysis of π–Hole Interactions between Aryl Donors and Small Molecule Acceptors. Crystals 2020, 10, 556.

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