Subject tellurides

Mercury-cadmium-telluride is the principal semiconductor now being used in advanced infrared systems, both for military and other surveillance applications. Its preparation and use in infrared detectors and arrays was the subject of Volume 18 of this treatise. New generations of detectors and arrays require sophisticated epitaxial growth, which in turn requires precise phase diagram data. 

When the allylic alcohol is the desired product of the kinetic resolution process, the accompanying epoxy alcohol also may be converted to the desired allylic alcohol by the two-step sequence shown in Scheme 6A. 1. The epoxy alcohol, after separation from the allyl alcohol, is mesylated and then subjected to reaction with sodium telluride, which effects the transformation of epoxy mesylate to the allylic alcohol with inversion at the asymmetric carbinol center [ 115e]. Preliminary results suggest that the rearrangement follows this pathway only when the epoxy alcohol is unsubstituted at the 3-position. 

Representative examples of these reactions are shown in Table 4. For more details, see recent reviews.8 10 Recently, more complex unsaturated systems were subjected to the tellurium-lithium exchange reaction.137,141 In Scheme 98, some examples of such a process are shown. In all cases, the (Z)-stereochemistry of the starting vinylic telluride was preserved.137... 

DiaUcyl as well as diaryl tellurides behave as monodentate ligands. Consistent with their soft character, their best explored group of complexes involves Pd(II) and Pt(II) centers. A variety of techniques have been applied to the characterization of their solid state and solution stractures. In such square-planar complexes, [MX2(TeR2)2] (M = Pd, Pt X = Cl, Br, I), cis - trans isomerization, intramolecular ligand exchange and tellurium inversion processes have all been observed by detailed far-infrared and variable-temperature NMR studies (see Refs. 14,15,17,3 5 for a more detailed review of the subject). 

Thermal and photoconductive detectors are used to measure radiation intensities, but all have relatively slow responses and are subject to drift. The lead sulfide or telluride photoconductive cell has a response time of about 0.5 ms, but sensitivity decreases sharply above 2900 cm" for the sulfide and above 1700 cm- for the telluride. Thermal detectors are employed at longer wavelengths. The simplest of these is the thermocouple, which has a relatively slow response (about 60 ms), and several are usually linked to form a thermopile. Bolometers... 

Phosphine oxides have fallen upon hard times, judging by the current literature, which this year has provided fewer publications on the subject than were reviewed in the first volume of this series A timely reminder that the subject is nevertheless alive comes from the thorough reviews of phosphine oxides, sulphides, selenides, and tellurides in the new edition of Kosolapolf s compilation. These chapters are likely to be of particular value to chemists requiring a quick guide to known structures and their preparation. 

The chief sources of tellurium at the present time are the slimes from the electrolytic tanks of the copper and lead refineries and the flue dusts from the smelters using certain ores, especially telluride gold ores. It is estimated 1 that the United States alone could produce annually as much as 125,000 pounds of tellurium without making any material additions to the present plants. The amount actually marketed has been small and subject to material variations. No reliable data are available as to the amount sold. 

On the one hand XPS studies of TmS confirmed the trivalent character of Tm, as can be seen in Fig. 14. On the other hand the results of TmSe and TmTe (51) showed for the first time in a photoemission experiment the coexistence of both 4/ configurations in the final state. The origin and magnitude of the 3 + signal in TmTe has subsequently become the subject of controversy (27), it being thought that Tm in TmTe should be essentially 2 +. Further systematic investigations of the solid state chemistry of this telluride are clearly needed. We therefore focus the discussion on metallic TmSe, which is known from bulk measurements (48) to have a valence ratio / = Tm3+/Tm2+ of about 4, i.e. 80% trivalent and 20% divalent. 

Catalytic carbopalladation is a ubiquitous process and alkynes are viable substrates. Alkenyl tellurides couple efficiently with alkynes with retention of the double bond geometry. Relatively large amounts of palladium catalyst are required.Oxidative dimerization of monoterpenes has been assumed to involve alkenylpalladium(ii) intermediates. Alkenylpalladium(ii) and di(alkenyl)palladium(iv) complexes have been put forward as intermediates in a similar reaction of halogenoterpenes. The subject has been reviewed concerning the formation of heterocycles by intramolecular cyclization of intermediate alkenylpalladium intermediates. ... 

A number of relevant review articles have appeared. Their subjects include the chemistry of antitumor platinum complexes, complexes of platinum metals with weak donor ligands, and transition metal complexes of sulfide, selenide, and telluride ligands (which includes much material on square-planar compounds). A review by Chanon and Tobe " on electron transfer catalysis relates to many reaction types, including ligand replacements at square planes. 

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