Anion-binding properties of π-electron deficient cavity in tetraoxacalix[2]arene[2]triazine by a computational study

Abstract

Host-guest inclusion complex formation of tetraoxacalix[2]arene[2]triazine (1) with anions X(CH3COO−, ClO4−, BrO4−, IO4−, SO42−, SO32−, CO32−, SiO32−) was studied by DFT calculations at M062X/6-311+G** level, together with their equilibrium geometries, binding energies and electronic structures. MESP, NCI-RDG and AIM topography analysis were performed to explore underlying interactions. The inclusion complexes in 1:1 ratio were stabilized through a cooperative effect of non-covalent interactions, including anion-π, σ-interactions, hydrogen bonds and van der Waals interactions. The recognition process of anions within 1 was spontaneous both thermodynamically and dynamically. The structure of molecule 1 changed slightly after encapsulation, reflected in IR and NMR spectra. After complexation, the red shifts of CH stretching and triazine rings bending in IR were attributed by hydrogen bonds and anion-π interactions. Anions encased in the host cavity exhibited magnetic shielding; those bifurcate hydrogen bonds could cause chemical shifts signals in 1H NMR spectra.