Switching of binding site from nonpolar to polar ligands toward cationic benzonitrile revealed by infrared spectroscopy.

Abstract

Noncovalent interactions of aromatic molecules in their various charge states with their surrounding environment are of fundamental importance in chemistry and biology. Herein, we analyze the infrared photodissociation spectra of mass-selected cationic clusters of benzonitrile (BN, cyanobenzene, C6H5CN) with L = Ar, N2, and H2O (W), in the CH and OH stretch range (2950-3800 cm-1) with the aid of density functional theory calculations at the dispersion-corrected B3LYP-D3/aug-cc-pVTZ level to probe the interaction of this fundamental aromatic cation in its 2B1 ground electronic state with nonpolar, quadrupolar, and dipolar solvent molecules. While Ar and N2 prefer π-stacking to the aromatic ring of BN+ strongly supported by dispersion forces, W forms a bifurcated CH⋯O ionic hydrogen bond to two adjacent CH groups stabilized by electrostatic forces. Comparison of the BN+-L dimers with related aromatic clusters reveals the effect of ionization, protonation, and substitution of functional groups on the type and strengths of the competing ligand binding motifs.