Design, Synthesis, and Structural Characterization of a Bisantimony(III) Compound for Anion Binding and the Density Functional Theory Evaluation of Halide Binding through Antimony Secondary Bonding Interactions

Abstract

Density functional theory calculations were used to design an anion receptor that utilizes antimony(III) secondary bonding interactions. Calculations were performed on promising motifs found in the chemical literature where two antimony sites were found in close proximity to a halide anion. The study was extended to a structurally related class of 1,3,2-benzodioxastibole derivatives to elucidate their potential for binding halide ions. Multiple geometric conformations were evaluated and various ratios of halide anions were considered. According to the computation results, this class of anion receptors shows strong affinities toward charge-dense halides. These 1,3,2-benzodioxastibole derivatives were prepared to evaluate their synthetic accessibility. Structural characterization of one species revealed the ability to bind up to three electron donors through secondary bonding interactions. This gates the future experimental study of these antimony systems for anion binding and recognition.

Sigma-Hole Interactions in Anion Recognition

“…Under identical conditions of 10 mol % catalyst loading in THF at room temperature, azo-bispyridinium catalyst 66 showed the least activity, giving a 14% substrate conversion after 6 hr. Comparative monodentate XB catalysts containing iodoimidazolium (67) and iodobenzimidazolium (70) showed greater activities, giving 25% and 49% substrate conversions, respectively. Because of their more effective halide coordination, even more facile reactions were observed with bidentate catalysts 68a, 68b, and 69, which showed no appreciable differences in catalytic activity induced by either the iodoimidazolium or iodotriazolium motifs, reflecting their comparable anion affinities.…”

“…69 In a 2016 survey of the CSD, Cozzolino and co-workers identified a bidentate PnB anion-binding motif containing two Sb(III) centers bridged by either an oxygen or sulfur atom with the general formula X 2 Sb-E-SbX 2 (E = O or S; X = F, Cl, or Br). 70 70 Copyright 2016 American Chemical Society.…”

“…Building on these findings, a PnB host molecule (43) was then computationally designed with the same X 2 Sb-E-SbX 2 structure but having the terminal halides replaced by catecholates and their halide (F À , Cl À , Br À , and I À ) binding behavior modeled by DFT calculations. 70 The presence of carbon-based peripheral groups allows the possibility of tuning the electronics of the Sb(III) centers by functionalization of the catechol aromatic rings, whereas the restricted five-membered catecholate complex provides a more exposed area on the Sb atom for anion access. In the gas phase, energy-minimized halide complexes with host-guest binding stoichiometries of 1:1, 2:1, and 1:2 were observed (Figure 20C), and terminal halide coordination appeared to be energetically more favored than the bridging mode for the 1:1 and 1:2 complexes.…”

“…(C) Cozzolino's bis-Sb(III)-catecholate complex 43 and its DFT energy-minimized structures with halide anions; PnB interactions are shown as dashed lines. DFT structures are reproduced with permission from Qiu et al70 Copyright 2016 American Chemical Society.…”

On the Importance of σ–Hole Interactions in Crystal Structures

“…In this context, Gabbaï et al have successfully used bis-stilbonium to build a preorganized host [97] including two strong σ-hole donors that establish several PnB interactions with electron-rich guests. Additionally, Cozzolino et al have also synthesized anion receptors based on bidentate anion-binding motifs containing two Sb(III) centers bridged by either oxygen or sulfur atoms as PnB donors [98].…”