Molecular recognition of a fluoride anion receptor: the importance of C-H (N-H)center dot center dot center dot F- and "electropositive field space"center dot center dot center dot F- interactions

Abstract

Host molecules effectively prefer to recognize F- ion rather than H2O through the upper rim, utilizing strong C-H (N-H)center dot center dot center dot 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 center dot center dot center dot F- and C(N)-H-a center dot center dot center dot O interactions much enhanced. The calculated vibrational frequencies and NMR chemical shifts are consistent with experimental trends.