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H-bond acceptor parameters for anions
Pike, Sarah J. Hutchinson, J.J. Hunter, C.A.
Pike, Sarah J.
Hutchinson, J.J.
Hunter, C.A.
Publication Date
2017-05
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© 2017 American Chemical Society. This is an open access article published under a Creative Commons Attribution (CC-BY)
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provided the author and source are cited.
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2017
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Abstract
UV/vis absorption titrations have been used to investigate the formation of H-bonded complexes between anionic H-bond acceptors (HBAs) and neutral H-bond donors (HBDs) in organic solvents. Complexes formed by three different HBDs with 15 different anions were studied in chloroform and in acetonitrile. The data were used to determine self-consistent HBA parameters (β) for chloride, bromide, iodide, phosphate diester, acetate, benzoate, perrhenate, nitrate, triflimide, perchlorate, hexafluorophosphate, hydrogen sulfate, methyl sulfonate, triflate, and perfluorobutyl sulfonate. The results demonstrate the transferability of H-bond parameters for anions between different solvents and different HBD partners, allowing reliable prediction of anion recognition properties in other scenarios. Carboxylates are the strongest HBAs studied, with β parameters (≈ 15) that are significantly higher than those of neutral organic HBAs, and the non-coordinating anion hexafluorophosphate is the weakest acceptor, with a β parameter comparable to that of pyridine. The effects of ion pairing with the counter-cation were found to be negligible, provided small polar cations were avoided in the less polar solvent (chloroform). There is no correlation between the H-bonding properties of the anions and the pKa values of the conjugate acids.
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Citation
Pike SJ, Hutchinson JJ and Hunter CA (2017) H-bond acceptor parameters for anions. Journal of the American Chemical Society. 139(19): 6700-6706.
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