Effects of Anion Size, Shape, and Solvation in Binding of Nitrate to Octamethyl Calix[4]Pyrrole

08 August 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

We present cryogenic ion vibrational spectroscopy of complexes of the anion receptor octamethyl calix[4]pyrrole (omC4P) with nitrate in vacuo. We compare the resulting vibrational spectrum with that in deuterated acetonitrile solution, and we interpret the results using density functional theory. Nitrate binds to omC4P through H-bonds between the four NH groups of the receptor and a single NO group of the nitrate ion. The shape of the ion breaks the C4v symmetry of the receptor, and this symmetry lowering is encoded in the pattern of the NH stretching modes of omC4P. We compare the spectrum of nitrate-omC4P with that of chloride-omC4P to discuss effects of ion size, shape, and solvent interaction on the ion binding behavior.

Keywords

anion receptors
molecular recognition
cryogenic infrared vibrational spectroscopy

Supplementary materials

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Description
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Supporting Information 1
Description
Methods; calculated lowest energy structure and NH stretching frequencies for neutral omC4P; mode patters of NH stretching vibrational modes; FTIR spectra of NO3−omC4P solutions in d3-acetonitrile and d6-acetone; atomic coordinates for neutral omC4P and for NO3−omC4P.
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Supporting Information 2
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Animations of NO vibrations in isomer A and isomer B.
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