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S,142+(AsF,-), has been prepared and its crystal structure determined in which the S,1,,+ cation was found to have a distorted right triangular prismatic structure, with one S, and two I, units joined by weak sulphuriodine bonds; the sulphur-sulphur bond distance is the shortest reported in an isolated compound, and is indicative of the presence of a 3p7r-3pw bond and a bond order greater than two.

Inorg. Chem. 1981, Acknowledgment. Thanks are expressed to Dr. B. E. Mann, University of Sheffield, for running some 31P N M R spectra. Registry No. I, 78355-34-7; 11, 78355-36-9; [(np3)Pd(P4)], 78 3 5 5-3 7-0; [ Pt (P3) (triphos)] BF4, 78 3 5 5-3 9-2; [ Pd2( P3) (np,) 2 ] B F4, 20, 3839-3845 3839 78355-41-6. Supplementary Material Available: Listings of structure factor amplitudes (22 pages). Ordering information is given on any current masthead page.S71AsF6 and S71SbF6 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) A, b = 9.187 (1) A, c = 12.400 (3) A, and ddCd = 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 R , = 0.046 and R2 = 0.061 for 1628 independent reflections with 11. 2a(I). S7IASF6 crystallizes in the triclinic space group Pi with a = 15.516 (1 1) A, b = 11.813 ( 8 ) A, c = 11.650 (8) A, a = 107.30 (4)", @ = 74.71 (S)', y = 104.62 ( S ) ' , and dald = 2.78 Mg m-3 for Z = 6. The structure was refined to a final agreement index R = 0.14. The s71+ cations in both salts and in (S71)4S4(A~F6)6 are essentially identical. S71+ 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 S 7 0 . The sulfur-iodine bond length is 2.342 (3) A and corresponds to a bond order of 1. The sulfur-sulfur distances within the ring vary from 1.906 ( 5 ) to 2.389 (4) A. There is one short intracationic iodine-sulfur contact of 3.394 (3) A. The geometry and bond length variations in S71+ are discussed and compared with those of related systems. Some experimental observations on & ( A s F~)~, 19 I x 2 16, are presented and the nature of these species is discussed. IntroductionGenerally any pair of main-group elements, excepting those of group 8A, form binary compounds or alloys. At one time sulfur and iodine were thought' to be one of the pairs of elements that were an exception to this generalization. Since then, evidence has been presented for sulfur iodides prepared at low temperatures, although they are unstable under ambient conditions. Solid S212 has been characterized at -90 "C by its infrared and electronic ~p e c t r a ,~.~ and infrared evidence has been presented4 for SI2 isolated in an argon matrix at 9 K. An attempted preparation of SI3+ (cf. Se13+) led instead5 to the relatively stable S71MF6 (M = As and Sb) salts, containing a binary sulfur-iodine cation, and a full account of this work is reported below. Subsequently, [(S71)21] (SbF6)3-2AsF3 and S214(AsF6)2,7 which also contain stable sulfur-iodine cations, were prepared and characterized.The ability of sulfur to catenate is well established; however,

Attempts to prepare S51MF6 ( M = As, Sb) led instead to crystalline (S71)4S4(A~F6)6 and [(S71),I](SbF6),.2AsF3. These compounds were prepared essentially quantitatively from sulfur, iodine, and the corresponding pentafluoride in appropriate ratios. Their structures were determined by single-crystal X-ray diffractometry. (S71)4S4(A~F6)6 is tetragonal, space group P4/n, with a = 19.585 (7) A, c = 8.321 (3) A, and Z = 2. Data were collected for 2066 reflections with 28 I 45O, and the structure was refined to R = 0.106 with use of 1307 reflections with I 2 3u(I). [(S,I),I](SbF6),.2AsF3 is triclinic, space group P i , with a = 9.240 (3) A, b = 13.321 (6) A, c = 8.247 ( 5 ) A, CY = 91.16 (4)O, fl = 94.22 (4)O, y = 111.04 (3)O, and 2 = 1. Data were collected for 2426 reflections with 28 I 45O of which 1775 had I > 3a(I). The structure was refined to R = 0.1 18. The structure of [(S71),I]3+ consists of two equivalent S71+ units that have geometries similar to those observed in S71MF6 ( M = As, Sb) and (S71),S4(AsF ) 6 . They are linked via an iodine atom, which is at a center of symmetry, by a linear S(4)-1(2)-S(4) (S-I = 2.674 (7) 1) arrangement. In addition, the bridging iodine atom has a very weak contact (1(2)-S(6), 3.777 (8) A) with each of the s71+ units. The square-planar geometry of S t + in (S7I),S,(AsF6), is similar to those in S4(AsF6)6.0.6S02 and (S7Br),S4(AsF6),.