The preparation of SeI3SbF6 and TeI3SbF6; the X-ray crystal structures of SBr3AsF6, SeI3AsF6, SeI3SbF6, and TeI3SbF6; some considerations of the energetics of the formation of SBr3AsF6 and SeI3AsF6

The crystal structures of the compounds SBr3AsF6 (1), SeI3AsF6 (2), SeI3SbF6 (3), and TeI3SbF6 (4) are reported and the quantitative preparation of the hitherto unknown 3 and 4 from SbF5 and the respective elements in SO2 are given. Crystal data are as follows: 1, monoclinic, space group P21/c, with a = 8.015(1) Å, b = 9.342(1) Å, c = 12.126(2), β = 97.81(1)°, and Z = 4; 2, monoclinic, space group P21/c, with a = 8.380(2) Å, b = 10.237(1) Å, c = 12.524(1) Å, β = 99.36(1)°, and Z = 4; 3, monoclinic, space group P21/c, with a = 8.548(2) Å, b = 10.297(6) Å, c = 12.877(8) Å, β = 98.70(3)°, and Z = 4; 4, monoclinic, space group P21/c, with a = 8.463(1) Å, b = 10.676(2) Å, c = 13.121(4) Å, β = 100.05(1), and Z = 4. Compounds 1, 2, 3, and 4 are isostructural and were refined to a final R values of 0.040, 0.051, 0.047, and 0.037, respectively. The structures of these salts consist of essentially discrete MX3+ cations and M′F6− anions (M = S, Se, Te; X = Br, I; M′ = As, Sb) with some cation–anion interactions. TheSeI3+ bond distances and angles were essentially identical in both AsF6− and SbF6− salts (average Se—I distance and I—Se—I angle for AsF6− salt; 2.508(2) Å, 102.4(1)° and for SbF6− salt; 2.512(1) Å, 102.3(1)°). Similarly the average Te—I bond distance and I—Te—I angle for TeI3SbF6 were 2.666(1) Å and 99.8(1)° which are essentially identical to those in the previously reported TeI3AsF6. The average S—Br distance and Br—S—Br angle were 2.142(6) Å and 103.4(2)° in SBr3AsF6. Estimates of the S—I bond distance and I—S—I bond angle in the as yet unknown SI3M′F6 are made from the extrapolation of MX3+ data. The bond distances observed in the simple MX3+ cations (M = S, Se, Te; X = Cl, Br, I) with anions of very low basicity are within 0.02 Å of the corresponding distances calculated by the Schomaker–Stevenson equation. The observed and estimated bond distances in SBr3+, SI3+, and SeI3+ are significantly longer than the corresponding S—Br, S—I, and Se—I distances in S7I+, S7Br+, and Se6I22+. This observation is used to support the thesis that the long intra-cationic halogen–chalcogen contacts in polychalcogen–halogen cations are weakly bonding, and responsible for the cluster-like nature of these cations. The heats of formation of 1 and 2 from their respective elements and AsF5 were estimated.