Homoatomic Rings

NMR spectroscopy ( Se, /= 1/2, 7%) is a powerful technique for identifying cyclic selenium molecules, especially the heteroatomic ring systems that contain sulfur or tellurium in addition to selenium, for which several isomers are possible for most compositions (Section 12.1.2). Solutions of monoclinic selenium in CS2 have been shown by high-performance liquid chromatography to form an equilibrium mixture of cyclo-Seg, cyclo-Sey and cyclo-Se6. The Se NMR spectra of such solutions show two singlets that are attributable to cyclo-Seg and cyclo-Se with relative intensities that correspond to a molar ratio of ca 6 No resonance is observed for cyclo-Sey presumably as a result of the fluxional behaviour (pseudorotation) of the seven-membered ring (Section 12.1.2). 

Although cyclo-Tcg has not been isolated, this tellurium homocycle has been tentatively identified by the observation of a Te NMR resonance in the 820-870 ppm region for (a) the product of the decomposition of thermally unstable tellurium halides 702X2 (X = C1, Br), (b) the cyclocondensation product of the reaction of two equivalents of Te2Cl2 with Cp 2Ti(p-Te2)2TiCp 2 (Cp = MeC5H4) and (c) a molten S-Se-Te mixture at 145 

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K. F. Tebbc, in Homoatomic Rings, Chains and Macromolecules of Main-Group Elements (Ed. A. L. Rheingold), Elsevier, Amsterdam, 1977, pp. 551-606. 

Pitt, G. G. In Homoatomic Rings. Chains and Macromolecules of the Main Group Elements. Rheingold, A. L., ed. Elsevier New York, 1977 and references cited therein. 

West, B.O. in "Homoatomic Rings, Chains and Macromolecules of Main-Group Elements", Rheingold, A.L., Ed. Elsevier Amsterdam, 1977 Chapter 18. 

Table 3 Reported homoatomic rings in alkali/alkaline earth metal containing solid state compounds of group 14 elements...

An increased value results in the formation of isolated rings of group 15 elements in solid state structures. Besides these rings, of course two-dimensionally extended layers and one-dimensionally extended chains are observed, according to the 8-N rule for these values. In Table 7, solid state compounds are hsted in which homoatomic rings are present in the crystal structure. 

There are three kinds of rings of different nuclearity known for homoatomic group 15 anions (Fig. 7). For arsenic, three-, five-, and six-atom rings are described in solid state compounds, and for phosphorus only the six-atom ring is reported, whereas for antimony and bismuth no homoatomic rings are known in neat solid state materials of alkali and alkaline earth metals. 

Table 7 Homoatomic rings of group 15 elements in solid state structures...

HOMOATOMIC RINGS UNSATURATED SYSTEMS 10.2.1 Three-membered Rings... 

Politzer P (1977) In Rheingold AL (ed) Homoatomic rings, chains, and macromolecules of main-group elements, Elsevier, Amsterdam, p 95... 

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