Molecular recognition of a fluoride anion receptor: the importance of C–H (N–H)⋯F− and “electropositive field space”⋯F− interactions

Abstract

Host molecules effectively prefer to recognize F⁻ ion rather than H₂O through the upper rim, utilizing strong C–H (N–H)⋯F⁻ interactions. The electropositive field space (“electropositive field space”) at the lower rim of the host molecules can also act as a good binding site for small anions such as F⁻. The electron withdrawing substituent at the para-position (X) makes the C(N)–H_a⋯F⁻ and C(N)–H_a⋯O interactions much enhanced. The calculated vibrational frequencies and NMR chemical shifts are consistent with experimental trends.