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 HP2O7(3-), H2PO4(-), and SO4(2-) anions, (1)H- and (31)P 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.