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)

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 MX 3 (M = Sb, Bi; X = Cl, Br) leads to the isolation of known compounds BiCl 5 (boxH) 2 ( 6 : 33%) and SbBr 5 (boxH) 2 ( 7 : 31%) and the novel material BiBr 5 (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 [(MX 5 ) 2– ] ∞ units classified as Type A in structure. In contrast, mixtures of box, conc. HCl and SbCl 3 yield, following recrystallization, to small quantities of Sb 2 OCl 6 (boxH) 2 ( 2 : 0.4%); a hitherto unknown complex containing the less common Sb 2 OCl 6 2− anion. Hypotheses as to the origin of 2 are presented including its formation by hydrolysis of known SbCl 4 (boxH). Hydroiodic acid solutions of box treated with SbI 3 leads to the isolation of the SbI 6 (boxH) 3 ∙(H 2 O) ( 9 : 42%) which displays a rare example of the isolated SbI 6 3− anion. The treatment BiI 3 under similar conditions leads to the precipitation of previously known Bi 2 I 9 (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 : BiI 6 (boxH) 3 ∙(H 2 O). 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. • Second known unequivocal example of a SbI 6 3− containing complex. • First solid-state characterisation of any members of the Sb/Bi halido benzoxazolium series. • Isolation of a rare example of a material with the Sb 2 OCl 6 2− anion.