| Summary: | 11 aryl–lone pair and three aryl–anion <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>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 <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>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 <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole systems. Several factors have emerged which influence strength of the <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole interactions, including aryl substituent effects, the chemical nature of atoms composing the aryl rings/<inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole acceptors, and secondary bonding interactions between donors/acceptors. Substituent effects indirectly affect the <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole interaction strength, where electronegative aryl-substituents moderately increase <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole interaction strength. N-aryl members significantly increase <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole interaction strength, and anion acceptors bind more strongly with the <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole compared to charge neutral acceptors (lone–pair donors). Secondary bonding interactions between the acceptor and the atoms in the aryl ring can increase <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole interaction strength, while hydrogen bonding between the <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole acceptor/donor can significantly increase or decrease strength of the <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole interaction depending on the directionality of hydrogen bond donation. Work is in progress expanding this research on aryl <inline-formula> <math display="inline"> <semantics> <mi>π</mi> </semantics> </math>–</inline-formula>hole interactions to a large number of systems, including halides, CO, and OCH<sub>3</sub><sup>-</sup> as acceptors, in order to derive a general design protocol for new members of this interesting class of compounds.
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