Of chalcogens

Polymer and chain formation is another property of chalcogen-nitrogen compounds that distinguishes them from their oxygen analogues. In addition to the unique, superconducting poly(sulfur nitride) (SN) (1.24) (Section 14.2), a variety of poly(thiazyl) chains such as RS5N4R (1.25) (Section 14.3) have been characterized. Interest in these chains stems from their possible use as models for the behaviour of (SN) and as components in molecular materials, e.g., as molecular wires. 

The accessibility of the +4 and +6 oxidation states for sulfur and, to a lesser extent, selenium gives rise to both acyclic and cyclic molecules that have no parallels in N-O chemistry. Thus there is an extensive chemistry of chalcogen diimides RN=E=NR (E = S, Se, Te) (Section 10.4). In the case of Te these unsaturated molecules form dimeric structures reflecting the increasing reluctance for the heavier chalcogens to form multiple bonds to nitrogen. The acyclic molecule N=Sp3,... 

This chapter will provide an overview, illustrated with recent examples, of some applications of the most commonly used physical methods for the characterization of chalcogen-nitrogen compounds. 

The structures of chalcogen-nitrogen compounds are frequently unpredictable. For example, the reactions of heterocyclic systems often result in substantial reorganization of their structural frameworks, e.g. ring expansion or contraction. The formation of acyclic products from ring systems (or vice versa) is also observed. 

Specific structural information for various classes of chalcogen-nitrogen compounds will be discussed in the appropriate chapters. 

The " N nucleus (/ = 1, 99%) has a moderately large magnetic moment and hyperfine splittings from this nucleus are a distinctive feature of the EPR spectra of chalcogen-nitrogen radicals. A-Arylthio-2,4,6-triphenylanilino radicals (3.16) are exceptionally persistent and oxygen-insensitive m solution. They exhibit a characteristic 1 1 1... 

Electrochemical methods may also be used in the synthesis of chalcogen-nitrogen compounds. For example, the electrochemical reduction of salts of the [SsNs]" cation (Section 5.3.9) in SO2 or CH2CI2 at low temperatures produces microcrystals of the superconducting polymer (SN). ... 

The reaction of Me3SiNSNSiMc3 with TeCU is an especially fruitful source of chalcogen-nitrogen halides that contain both sulfur and tellurium. The initial product of this reaction is the bicyclic compound 8.17, which is obtained when the reaction is carried out in a 1 2 molar... 

The acyclic imidoselenium(II) dihalides ClSe[N( Bu)Se]nCl (8.23, n =1 8.24, n = 2) are obtained from the reaction SeCla with tert-butylamine in a 2 3 molar ratio in THF. There are no sulfur or tellurium analogues of this class of chalcogen-nitrogen halide. 

A common interpretation of the interaction of chalcogens with nucleophiles considers donation of electron density from a lone pair on the donor atom into the o- (E-X) orbital (Figure 15.1). As the degree of covalency increases, a hypervalent three-centre four-electron bond is formed. Real systems fall somewhere between secondary interactions and hypervalent (three centre - four electron) bonds. The two extremes can be distinguished by the correlation of X-E and E D distances.In the hypervalent case both bond distances decrease simultaneously, whereas in the secondary bond the distances are anticorrelated. This concept has been applied in a study of selenoquinones 15.17 (R = Ph, Me) with short Se 0 contacts,for... 

A bis(chelate) structure was found for the closely related germylene [MeC(NPr )2]2Ge, which was also made from GeCl2(dioxane) and 2 equivalents of the lithium amidinate (colorless crystals, 81%). The same synthetic approach was used to make bis(amidinato) metal dichlorides of silicon and germanium in high yields (83-95%). Rapid oxidative addition of chalcogen atom sources (styrene sulfide and elemental Se) to the germylene derivatives resulted in a series... 

Sheldrick WS (2007) Polychalcogenides. In DevrUanova FA (ed.), Handbook of chalcogen chemistry New perspectives in sulfur, selenium and tellurium, Royal society of Chemistry Cambridge, UK... 

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