Preparations and X-ray crystal structures of iodo-cyclo-heptasulfur hexafluoroantimonate(V) and hexafluoroarsenate(V), S7ISbF6 and S7IAsF6

Article abstract of DOI:10.1021/ic50225a048

S₇IAsF₆ and S₇ISbF₆ were prepared essentially quantitatively by a variety of routes. Attempts to prepare S₈I⁺ salts were unsuccessful. S₇ISbF₆ crystallizes in the orthorhombic space group P2₁2₁2₁ with a = 11.786 (2) ?, b = 9.187 (1) ?, c = 12.400 (3) ?, and d_calcd = 2.90 Mg m^-3 for Z = 4. The structure has been determined by multiple-solution direct methods and refined by least squares to final agreement indices R₁ = 0.046 and R₂ = 0.061 for 1628 independent reflections with I ≥ 2σ(I). S₇IAsF₆ crystallizes in the triclinic space group P1 with a = 15.516 (11) ?, b = 11.813 (8) ?, c = 11.650 (8) ?, α = 107.30 (4)°, β = 74.71 (5)°, γ= 104.62 (5)°, and d_calcd = 2.78 Mg m^-3 for Z = 6. The structure was refined to a final agreement index R = 0.14. The S₇I⁺ cations in both salts and in (S₇I)₄S₄(AsF₆)₆ are essentially identical. S₇I⁺ contains a seven-membered sulfur ring with a slightly twisted chair conformation, similar to that of S₇, with an exocyclic iodine, and has a geometry similar to that of S₇O. The sulfur-iodine bond length is 2.342 (3) ? and corresponds to a bond order of 1. The sulfur-sulfur distances within the ring vary from 1.906 (5) to 2.389 (4) ?. There is one short intracationic iodine-sulfur contact of 3.394 (3) ?. The geometry and bond length variations in S₇I⁺ are discussed and compared with those of related systems. Some experimental observations on S_x(AsF₆)₂, 19 ≥ x ≥ 16, are presented and the nature of these species is discussed.