Synthesis and structural characterisation of trivalent halidoantimonates and bismuthates of 2-methyl-2-benzoxazole (box): Reactivity and solid-state structural diversity within the [MX(6 – n)] [boxH](3 – n) series (M = Sb or Bi; X = Cl, Br, I; n = 0 or 1)

Abstract

The structural characterisation (X-ray diffraction) of a series of anionic antimony (III) and bismuth (III) halide complexes containing protonated 2-methyl-1,3-benzoxazole (boxH) countercations are reported. Treatment of aqueous strong acid (HCl or HBr) or strong acid/additional solvent mixtures of box with MX3 (M = Sb, Bi; X = Cl, Br) leads to the isolation of known compounds BiCl5(boxH)2 (6: 33%) and SbBr5(boxH)2 (7: 31%) and the novel material BiBr5(boxH)2 (8: 57%). In the solid state, 6–8 all display an anionic portion consisting of edge sharing infinite zig-zag chains of the metallic [(MX5)2–]∞ units classified as Type A in structure. In contrast, mixtures of box, conc. HCl and SbCl3 yield, following recrystallization, to small quantities of Sb2OCl6(boxH)2 (2: 0.4%); a hitherto unknown complex containing the less common Sb2OCl62− anion. Hypotheses as to the origin of 2 are presented including its formation by hydrolysis of known SbCl4(boxH). Hydroiodic acid solutions of box treated with SbI3 leads to the isolation of the SbI6(boxH)3·(H2O) (9: 42%) which displays a rare example of the isolated SbI63− anion. The treatment BiI3 under similar conditions leads to the precipitation of previously known Bi2I9(boxH)3 (10: 54%) as a major product. Further evaporation of the reaction mixture from which 10 was obtained yields a second minor product, 11 (3%), identified as the Bi analogue of 9: BiI6(boxH)3·(H2O). The species described herein are further discussed in terms of their general coordination properties and relevance to related complexes under current scrutiny for their solid-state materials properties.