The preparation of S7BrMF6 (M = As, Sb), and the preparation and crystal structure of (S7Br)4S4(AsF6)6 containing the bromo-cycloheptasulphur (1+) cation

Abstract

S7BrMF6 (M = As, Sb) were prepared essentially quantitatively by a variety of similar routes to those that led to S7IMF6; and in addition, by the reaction of bromine and S7IAsF6. (S7Br)4S4(AsF6)6 was prepared essentially quantitatively directly from sulphur, bromine, and arsenic pentafluoride in the appropriate ratios. Crystals of (S7Br)4S4(AsF6)6 are isostructural with (S7I)4S4(AsF6)6 space group P4/n, a = 19.19(3), c = 8.01(1) Å. The structure was refined from a low temperature set of data to a final R = 0.12. The salt contains a discrete planar S42+ and bromo-cycloheptasulphur (1+) cations, the latter having a similar geometry, sulphur–sulphur bond distances and an intra-cationic halogen–sulphur contact to that observed in S7I+.