Poly-pnictogen bonding: trapping halide ions by a tetradentate antimony(iii) Lewis acid

Abstract

A highly halide affine, tetradentate pnictogen-bonding host-system based on the syn-photodimer of 1,8-diethynylanthracene was synthesized by a selective tin-antimony exchange reaction. The host carries four CC–Sb(C₂F₅)₂ units and has been investigated regarding its ability to act as a Lewis acidic host component for the cooperative trapping of halide ions (F⁻, Cl⁻, Br⁻, I⁻). The chelating effect makes this host-system superior to its bidentate derivative in competition experiments. It represents a charge-reversed crown-4 and has the ability to dissolve otherwise poorly soluble salts like tetra-methyl-ammonium chloride. Its NMR-spectroscopic properties make it a potential probe for halide ions in solution. Insights into the structural properties of the halide adducts by X-ray diffraction and computational methods (DFT, QTAIM, IQA) reveal a complex interplay of attractive pnictogen bonding interactions and Coulomb repulsion.