Oxidation dichalcogenides

As an indication of the types of infonnation gleaned from all-electron methods, we focus on one recent approach, the FLAPW method. It has been used to detennine the band stmcture and optical properties over a wide energy range for a variety of crystal stmctures and chemical compositions ranging from elementary metals [ ] to complex oxides [M], layered dichalcogenides [, and nanoporous semiconductors The k p fonnulation has also enabled calculation of the complex band stmcture of the A1 (100) surface... 

The reactions of carbon dichalcogenides other than C02 with Ni° have also been studied quite intensively.2460,2461 Inter alia, Ni polymeric complexes with metallic properties have been prepared using CS2 as the starting material.2462 Some further impetus was given by the observation that CS2 can mimic the binding of CO to the CODH enzyme active site, although CS2 itself does not undergo oxidation/reduction and does not appear to bind to center C (the site of CO oxidation and C02 reduction).2463... 

The ability to manipulate the anodic corrosion problem using high concentrations of redox active electrolyte also makes possible the sustained oxidation of Br" at illuminated metal dichalcogenide-based cells, Figure 1.(15) The use of high concentrations of electrolyte has proven valuable in situations involving other photoanode materials, notably n-type Si.(36,37)... 

Scheme IV. Representation of the Is /T mediated oxidation of S02 at illuminated metal dichalcogenide photoanodes (top) and interface energetics with and without If/I in 6 M H2SOh/l M SOt for MoS2 (bottom) (31). In the absence of the mediator system the photovoltage for the S02 oxidation is expected to be negligible. The adsorption of the Is /T is unaffected by the S02 so the negative shift of the fiat band potential can be exploited to give a photovoltage for the desired process with the h /T system simultaneously providing an acceleration of the S02 oxidation.

Surprisingly the layered oxides with the same structures as the layered dichalcogenides were not studied in that time period. The thought was presumably that oxides toward the right of the periodic table would be of little interest, and it was not considered that lithium could be readily removed... 

Chalcogenolato complexes of mercury can be prepared by a variety of methods. Early preparations involve the reactions of thiols with mercury cyanide,1 the reaction of mercury salts with alkali chalcogenolates, electrochemical methods,2 and the oxidative addition of dichalcogenides to metallic mercury.3 The last method is very convenient for the preparation of complexes with sterically undemanding ligands, but becomes less facile as the... 

The tendency of intermediate heterocyclic ditellurides to eliminate one of the tellurium atoms thus contracting the size of the ring is illustrated by the course of the oxidative cyclization of the dilithio dichalcogenides 78 (84JHC413). Whereas in the case of the diselenolate 78 (M = Se) the expected heterocyclic diselenide 79a is formed, albeit in low yield, the analogous reaction with the ditellurolate 78 (M = Te) results in an extrusion of elemental tellurium affording dibenzotellurophene 79b. 

Alkali metal intercalation in dichalcogenides is also achieved by direct reaction of the elements at around 1070 K e.g. AxMCh2 whereM=V, Nb or Ta) in sealed tubes. Alkali metal intercalation compounds with dichalcogenides form hydrated phases, A HjOJy MCh2, just like some of the layered oxides e.g. 

Tris(thiolato) complexes are made from MC13 and NaSR. While Al and Ga are insufficiently reactive, metallic In is oxidized by dichalcogenides E2R2 to give [In(ER)3] . The compound In(SePh)3 has a chain structure with octahedral indium, [In -SePh),]..39... 

Equally important are steric influences in the product. For example, diaryl dichalcogenides ArE—EAr (E = S, Se, Te) have long been known to react with metallic mercury to give stable oxidative addition products Hg(EAr>2 ... 

The disproportionation reactions with graphite of oxidants that are also strong Tewis acids parallel the intercalation of molecular species into the layered dichalcogenides, which are reductants and Tewis bases (see Section 3.2.1). 

The ammonia molecules occupy trigonal prismatic sites between the dichalcogen layers and NMR measurements show that they are oriented with the threefold axis parallel to the dichalcogenide layers, indicating only weak Lone Pair interactions with the layers. Careful study of the reaction stoichiometry, prompted by this observation, led to the conclusion that ammonia oxidation was involved and that the overall mechanism of reaction conld be summarized by equation (11). The reaction product has x in the range 0.1 -0.3 and contains ammonium ions solvated by nentral ammonia molecules. 

---