Croatica Chemica Acta, Vol. 66 No. 3-4, 1993.
Izvorni znanstveni članak
On the Nature of Hypervalent S-O Bonds in Sulfuranes
Alajos Kálmán
; Central Research Institute for Chemistry, Hungarian Academy of Sciences, Budapest, P. O. Box 17, H-1525, Hungary
Sažetak
Sulfuranes with pseudo-trigonal-bipyramidal geometry are hallmarked by two apical hypervalent S-0 bonds. According to Musher’s classification, the quasi-linear arrangement of the atoms involved can be interpreted approximately in terms of an s-p basis, assuming four-electron-three-center bonds. However, substantial differences between the electronegativities of the apical groups give rise to rather unsymmetric three-center bonds. In spirosulfuranes, the unsymmetric polarization of the O-S-O bonds is terminated at around an interatomic distance of 2.26 Å, balanced by an S-0 single bond with a length of 1.63 Å. These asymmetric O-S-O bonds are formed in sulfonium salts with spirosulfurane geometry. Further asymmetry of the O-S • • • O grouping can be generated only for two-electron-three-center bonds formed by S(H) atoms.
After a few guidelines on the basic forms of sulfuranes, starting with SF4, a short review of the analogous azasulfuranes and their sulfonium salts is presented, demonstrating how the N lone pair participates in the formation of S(IV)-N multiple bonds which, in turn, terminate the hypervalent bonds. These three centers possess only three electrons and form a transitional state with long S---0 single-bond/no-bond resonance interactions (2.13-2.80 Å) between four-electron-three-center (he. hypervalent) bonds and two-electron-three-center bonds. The unsymmetric sulfuranes (or sulfonium cations) are best described by six-electron-five-center bond models. S-O bonds retaining a bond number of at least n = 1/4 can still be regarded as hypervalent. Further polarization (n < 0.2) of these bonds balanced by covalent bonds (n > 0.8) results in three-electron-three-center systems with no hypervalent character.
Ključne riječi
Hrčak ID:
137053
URI
Datum izdavanja:
1.3.1994.
Posjeta: 675 *