2,4,5-Trimethylimidazolium Scaffold for Anion Recognition Receptors Acting Through Charge-Assisted Aliphatic and Aromatic C–H Interactions

A series of two-armed
2,4,5-trimethylimidazolium-based oxoanion
receptors, which incorporate two end-capped photoactive anthracene
rings, being the central core an aromatic or heteroaromatic ring,
has been designed. In the presence of HP2O73–, H2PO4–,
and SO42– anions, 1H- and 31P NMR spectroscopical data clearly indicate the simultaneous
occurrence of several charge-assisted aliphatic and aromatic C–H
noncovalent interactions, i.e., significant downfield shifts were
observed for the imidazolium C(2)–CH3 protons, the
methylene N–CH2 protons, and the inner aromatic
proton or the outer heteroaromatic protons. Density functional theory
calculations confirm the occurrence of these noncovalent interaction
and suggest that the interaction between the anions and the receptors
is mainly electrostatic in nature.