Some sulphur-nitrogen ring transformations using tetrasulphur tetranitride and trichlorotrithiatriazene as precursors

As part of a general study of 1, 2, 3, 5-dithiadiazolium cations, a series of 4-phenyl-1, 2, 3, 5-dithiadiazolium salts were produced by anion exchange reactions, both in the solid phase and in solution. The reduction of the 4-phenyl -1, 2, 3, 5- dithiadiazoliurn cation gave the previously unreported, 4-phenyl- 1, 2-dithia-3, 5-diazole, the crystal structure of which indicates that the dithiadiazole exists as an eclipsed dimmer. By analogy with the solid phase exchange reactions which occur between 4-phenyl-1, 2, 3, 5-dithiadiazolium chloride and Group I metal halides, the metathetical reactions between s (_3) N (_2) Cl and metal halides were investigated. The product isolated from the reaction of s (_3) N(_2) Cl with CsI was identified as tetrasulphur tetranitride. The reductions of S (_4) N (_3) C1, S (_3) N (_2) C1 (_2) and (NSC1) (_3) were studied using a variety of reducing agents. The majority of the reduction reactions gave tetrasulphur tetranitride but the reduction of trichlorotrithiatriazene by iron using sulphur dioxide as a solvent provided a convenient synthesis of the cyclocyclopentathiapentazenium cation (S (_5) N (_5) +). The reduction of chlorothiodithiazyl chloride by iron using sulphur dioxide as a solvent produced the previously unreported salt (s (_10) N (_8) (^2) +) (FeC1 (_4) -) (_2). The synthesis of the cations S (_x) N (^+) (x>l) was approached from two angles, that of reacting sulphur polycations (s (_8) (^2+) (AsF (_6) (^-)) (_2)) with nitrogen containing species (MN (_3) and S (_4) N (_4) and that of reacting the thionitrosyl cation (NS (^+)) with sulphur. The reactions of s (_8) (^2) (^+) (AsF (_6) (^-)) (_2) with azides and tetrasulphur tetranitride led to the formation of the S (_2) N(^+) cation and with excess tetrasulphur tetranitride to the production of S (_10) N (_8) (^2) (^+) (AsF (_6) (^-)) (_2) Some preliminary investigative reactions of selenium (Se (_4) (^2) (^+) (AsF (_6) (^-)) (_2) and Se (_8) (^2) (^+) (AsF (_6) (^-)) (_2)) and tellurium (Te (_4) (^2) (^+) (AsF (_6) (^-)) (_2)) polycations with both azides and tetrasulphur tetranitride were carried out and a selenium analogue of "S (_3) N (_2) (^+)” isolated. In an attempt to prepare thiazyl fluoride (as a precursor to thionitrosyl salts) by a simple single stage process, chlorine monofluoride was reacted with S (_4) N (_4) and (NSCL) (_3) are discussed. NSF was synthesised by a metathersis reaction between thiazyl chloride and cesium fluoride. A facile route to the thionitrosyl cation via the oxidation of (NSCL) (_3) and S (_4) N (_4) using Group V Lewis acids (AsF (_5), SbF (_5)) at 100-150 C failed. However a convenient route to thionitrosyl hexachloroantimonate (v) has been found in the vapour phase reaction of thiazyl chloride with antimony pentachloride

Evidence for magnetoplasmon character of the cyclotron resonance response of a two-dimensional electron gas

Experimental results on the absolute magneto-transmission of a series of high density, high mobility GaAs quantum wells are compared with the predictions of a recent magnetoplasmon theory for values of the filling factor above 2. We show that the magnetoplasmon picture can explain the non-linear features observed in the magnetic field evolution of the cyclotron resonance energies and of the absorption oscillator strength. This provides experimental evidence that inter Landau level excitations probed by infrared spectroscopy need to be considered as many body excitations in terms of magnetoplasmons: this is especially true when interpreting the oscillator strengths of the cyclotron transitions

Experimental evidence of delocalized states in random dimer superlattices

We study the electronic properties of GaAs-AlGaAs superlattices with intentional correlated disorder by means of photoluminescence and vertical dc resistance. The results are compared to those obtained in ordered and uncorrelated disordered superlattices. We report the first experimental evidence that spatial correlations inhibit localization of states in disordered low-dimensional systems, as our previous theoretical calculations suggested, in contrast to the earlier belief that all eigenstates are localized.Comment: 4 pages, 5 figures. Physical Review Letters (in press

Frohlich mass in GaAs-based structures

The Frohlich interaction is one of the main electron-phonon intrinsic interactions in polar materials originating from the coupling of one itinerant electron with the macroscopic electric field generated by any longitudinal optical (LO) phonon. Infra-red magneto-absorption measurements of doped GaAs quantum wells structures have been carried out in order to test the concept of Frohlich interaction and polaron mass in such systems. These new experimental results lead to question the validity of this concept in a real system.Comment: 4 pages, 3 figure