i. e., a value that agrees closely with the ratio of the observed shifts given in (6). [8l R. Hoffmann, J. Chem. Phys. 39, 1397 (1963): R. Hoffmann and W N . Lipscomb, ibid. 36, 2179, 3489 (1962); 37, 2872 (1972). - -34 16 -63 49 45 3 -104 0 0 164 147 237 -5 234 164 12 262 386 From this result the general conclusion can be drawn that Koopmans’ theorem is not always a valid approximation, even in the form (3), i.e. as a basis for perturbation calculations. It must fail in particular when, for example, for symmetry reasons, the orbital Jr, that is vacated by the electron e- in process (2) is localized only in one part of the molecule M (cf. (8)).According to the assumptions under which Koopmans’ theorem was derived [same SCF orbitals JIJ for M and M+(JIJ)] first a positive charge increase described by JI: will be produced, which is necessarily localized [cf. M+(Jr,)]. The subsequent relaxation process spreads the positive charge into the region of Q -e- Relax. + .v; the system where $:=O [cf. M,’(JIJ)]. The resultant charge equalization stabilizes the radical cation (Pading’s electroneutrality rule). If M is substituted in a region where JIj=O, then clearly one must take into account the changes SAQn and &AQo caused by electron relaxation since they give rise to first-order perturbations. Similar considerations apply also to orbitals whose “localization” is not due to symmetry, such as those of “lone pairs”. On the other hand, the usual procedures within the framework of Koopmans’ theorem may be expected to give reasonable results when Jr, extends more or less uniformly over the whole molecule M. Received. February 23, 1973 [Z 807 IE] German version: Angew. Chem. H5, 414 (1973) [I] 1 Koopmans, Physica I , 104 (1934).  W C . Richards, Int. J. Mass Spectrom. Ion Phys. 2, 149 (1969).  D. R. Lloyd and N. Lynaugh in D . E . Shirley: Electron Spectroscopy. North Holland, Amsterdam 1972, p. 445.  A. N 4 u r d . Chem. Commun. 1969, 1022, 1427.  M:M. Rohmer and A VeiUard, J. C. S. Chem. Comm. 1973, 250.  E . Hrilbronnrr, V. Hornung, F. H . Pinkrrton, and S . F . Thames, Helv. Chim. Acta 55, 289 (1972): M. Klrssinger, Angew. Chem. 84. 544 (1972): Angew. Chem. internat. Edit. 1 1 , 525 (1972): R. Susrmann and R . Schtrberr, Tetrahedron Lett. 1972, 2739: P. A. Clark, Theor. Chim. Acta 2X. 75 (1972).  E Hrilhronnrr, R Gleirrr, H . Hop% V Hornuny, and A . drMeijrre, Helv. Chim. Acta 54. 783 (1971). 31 - 42 48 - 26 -4 74 -131 -9 188 9 229 376  M J. S . Dewar and E. Haselback, 3. Amer. Chem. Soc. 92, 590 (1970); N . Bodor, M . J. S . Dewar, A . Hargrt, and E . Haselhach. ihid. 92, 3854 (1970); M . J. S . Dewar, E. Haselbach, and S . D . Worlry, Proc. Roy. SOC.London A 315,431 (1970). [lo] C. Fridh, L. Asbrink, and E. Lindholm, Chem. Physics Lett. 15, 282 (k972); L. Asbrmk, C. Fridh, and E . Lmdholm, ihid. 15, 567 (1972): J . Amer. Chem. Soc. 94, 5501 (1972). [ I l l J. A. Pople, D. L. Beueridgr, and P . A . Dobosh, J. Chem. Phys. 47, 2026 (1967).  Un’published results. Crystal and Molecular Structure of Cyclooctasulfur Oxide, SSO[~] By Ruff Steudel, Peter Luger, Hans Bradaczek, and Michael Rebsch“] S,O is formed on condensation of SOClz with “crude sulfane” (H,S,; n = 3,4,5.. .) by the dilution technique; it crystallizes from CS2 in yellow needled2].We have carried out a single-crystal X-ray structure analysis of such crystals at 10°C. The crystals belong-to space group Pca2, with a= 13.197, b=7.973,c=8.096A,d,,i,=2.11,de,,=2.13gcm~3. 1008 reflections with 8 between 3” and 27” were measured on an automatic Siemens single-crystal diffractometer. 128 reflections whose intensity was less than twice the statistical error were regarded as unobserved. As the substance decomposed gradually the intensity measurements were effected with three different crystals. Scaling was achieved by a reference reflection. We determined the phases by the tangent formula[31; the structure was refined by the method of least squares with anisotropic temperature factors for all atoms. After convergence of all the parameters the final R value amounted to 5.0%. Figure I shows the result. Table 1 contains the intramolecular nuclear distances and angles. The molecule of S,O belongs to the point group C,. The S atoms form a crownshaped ring in which each set of four atoms lies approximately in one plane. The two planes are almost parallel. The 0 atom is in an axial position to the ring. The S-0 internuclear distance of 1.483 corresponds to the value of 1.49 A calculated from the valence force constantr21. [*] Prof. Dr. R. Steudel and Dr. M. Rebsch lnstitut fur Anorganische und Analytische Chemie der Technischen Universitat I Berlin 12, Strasse des 17. Juni 135 (Germany) Prof. Dr. H. Bradaczek and Dr. P Luger lnstitut fur Kristallographie der Freien Universitat I Berlin 33, Takustrasse 6 (Germany) 423 Table I . Bond lengths and angles in the S,O molecule. Standard deviations in parentheses. lnternuclear distances s10 S'SZ S W s3s4 s4ss [A] 1.483 (0.009) 2.204 (0.004) 2.000 (0.005) 2.064 (0.004) 2.044 (0.005) S5Sb S"S7 S'SX SXS' Valence angles [ ] OS'S' OSiSH S2S'Sn S1S'S3 S2S'S4 106.0 (0.4) 106.3 (0.4) 101.8 (0.2) 102.3 (0.2) 108.4 (0.2) 2.047 2.071 2.006 2.200 (0.005) (0.005) (0.005) (0.004) 3.066 (0.009) 3.096 (0.010) 2.976 (0.010) 2.977 (0.009) s70 s30 s20 seo Dihedral angles ["I S'S4S' S4S5Sh S5ShS7 ShS7S8 SiSHS' 105.9 (0.2) 106.7 (0.3) 107.9 (0.2) 107.4 (0.2) 101.6 (0.2) S'S'SJ/S2SJS' S'S'S'/S3S4Ss S'S4SS/S4SSSh S4SSSh/SSShS7 94.8 102.3 107.1 98.8 S'Ss"S'/S"S'Sn SbS'SH/S'SnSs' S'SnSr/SXSiS2 S8SiSz/SiS'S' 93.1 101.7 1 1 1.5 102.2  R. Srrudel and M. Rebsch, Angew. Chem. 84, 344 (1972): Angew. Chem. internat. Edit. I / , 302 (1972).  J . K u r l r and H . Huuprmunn. Acta Crystallogr. Y. 635 11956).  J . Donohrrr in 5. M r y r r . Elemental Sulfur. Wiley-Interscience, New York 1965, p. 13.  F . Xrinstru: Structural Aspects of the Allotropy of Sulfur and the other Divalent Elements. Waltman, Delft 1967. p. 23. m Fig. I . Structure of the molecule of SeO The intramolecular S-S distances show more pronounced variations than in the S, ring of rhombic a-sulfur where they vary between 2.042 and 2.050A14'. Very striking are the two unusually large S-S distances involving the thionyl group (S'S' and S'S8: 2.20A); these S-S bonds are to be regarded as partial bonds and their ready cleavage probably accounts for the ease of decomposition of S 8 0 at room temperature. SO, and polymeric sulfur are produced in this decomposition'']; elimination of SOz can occur without diffusion or rotation of the S,O molecule in the crystal since the packing is such that the SO groups of molecules stacked next to and above each other form a planar zig-zag chain: The unit cell contains two such chains parallel to the c-axis. Within each chain the intermolecular S-0 distance amounts to 2.935A (van der Waals bond length: 3.2A): the OSO and SOS angles amount to 175 and 131O, respectively. Such intermolecular interaction of the S,O molecules was supposed previously on the basis of the IR spectrum[']. The smallest intermolecular S-S distance of 3.388 A accords with findings for rhombic (van der Waals distance: 3.6 In the S,O ring the dihedral angles, much discussed in connection with the stability of sulfur rings, vary within relatively large limits. The mean value 101.4". however, is only slightly greater than that (99")found for rhombic cycIo~ctasulfur~~~. A). Tetrasulfur Tetranitride-A Insertion Reagent [**I New By Herbert W Roesky and Michael Diet/[*] Cleavage of silicon-nitrogen or tin-nitrogen bonds by halides R X has proved to be a versatile synthetic procedure[" 'I, but insertion reactions with S4N, have not hitherto been reported. We have now treated SIN (and also SnN) compounds of type ( with tetrasulfur tetranitride (2) in the molar ratio 2: 1, and obtained products containing an S,N, skeleton (J), e. 61.: 2 (CH,),SiNR, ( 1) + S4N4 + (2) 2 (CH3),Si-N=S=N-S-NR2 /3u), R = CH, : b.p. 2 9 OC/O.Ol t o r r (3b), R = C,H,: b.p. 3 7 OC/O.Ol t o r r The reaction appears to involve nucleophilic attack by the amino nitrogen on a sulfur atom of the S4N, ring, leading to electrophilic cleavage of the metal-nitrogen bond[,]. N-S-N R,N: I II 2s: (CH,),Si,:N-S-N I :", S i ( C H3) I I :S@?:NR~ /I 0 In this connection particular interest attaches to the reaction of S,N,CI, ( 4 ) with SIN compounds. For example, if ( 4 ) is allowed to react with ( I a ) in the molar ratio 1 : 2, then S4N4 (2) is formed as intermediate. Received. March 5, 1973 [Z XI2 I€] German version: Angew Chem. 85. 452 (1973) [ I ] Part 20 of Sulfur-Oxygen Compounds. This work was supported by the Fonds der Chemischen lndustrie and the Senator fur Wirtschaft des Landes Berlin. Part 19. R . Sfrirdrl. P. Lugrr, and H. Brudoczck. Angew. Chem. 85. 307 (1973): Angew. Chem. internat. Edit. I2, 316 f 1973). 424 [*] Prof. Dr H. W. Roesky and DiplLChem. M. Diet1 Anorganisch-chemisches lnstitut I der L'niversitit 6 Frankfurt, Robert-Mayer-Strasse 7--9 (Germany) [**I This work was supported by the Fonds der Chemrschen lndustrie and the Deutsche Forschungsgemeinschaft.