Halides selenides

TMSlsSiH is an effective reducing agent for the removal of a variety of functional groups, including halides, selenides, xanthates, and isocyanides. 

Tin hydride 2 prepared from hydroxyl acid behaves like the conventional Bu3SnH in standard free-radical reactions, but the tin-containing by-products are easily removed by mild hydrolysis which converts them into base-soluble materials. The performance of these tin hydrides is evaluated for a range of radical reactions involving halides, selenides, Barton-McCombie deoxygenation, and enyne cyclizations.72... 

Radicals can be generated by homolysis of weak a-bonds. Homolysis is effected by photochemical, thermal or redox (electron transfer) methods. A common method to initiate a radical reaction is to warm a peroxide such as benzoyl peroxide or azobi-sisobutyronitrile (AIBN) 1 (4.2). The radical -C(CN)Me2 generated from AIBN is rather umeactive, but is capable of abstracting a hydrogen atom from weakly bonded molecules such as tributyltin hydride (4.3). The resulting tributyltin radical reacts readily with alkyl halides, selenides and other substrates to form a carbon-centred radical. 

Radical reductions. This silane is less reactive than Bu38nH, but is useful for reduction of substrates when the product is formed by slow hydrogen transfer. In the general procedure it is used in combination with AIBN (10-20%) in toluene or benzene at 75 -90°. It is effective for reduction of halides, selenides, thionoesters, and isocyanides. 

Nitrogen and sodium do not react at any temperature under ordinary circumstances, but are reported to form the nitride or azide under the influence of an electric discharge (14,35). Sodium siHcide, NaSi, has been synthesized from the elements (36,37). When heated together, sodium and phosphoms form sodium phosphide, but in the presence of air with ignition sodium phosphate is formed. Sulfur, selenium, and tellurium form the sulfide, selenide, and teUuride, respectively. In vapor phase, sodium forms haHdes with all halogens (14). At room temperature, chlorine and bromine react rapidly with thin films of sodium (38), whereas fluorine and sodium ignite. Molten sodium ignites in chlorine and bums to sodium chloride (see Sodium COMPOUNDS, SODIUM HALIDES). 

Compounds Octacarbonyidicobalt Dicaesium selenide non-metal halides... 

Gold telluride iodide, AuTczI, was the first example of a gold chalco-genide halide, and was found in 1969 (305). Systematic investigations confirmed the existence of at least six compounds four telluride halides and two selenide halides (see Table IV). No sulfide halides have been reported. 

When exposed to daylight, the sulfide and selenide halides HgsY2X2 are blackened within a few minutes. This black color reversibly disappears when the sample is heated to 90 to 120°C, or stored in the dark for several days 204, 375-377). The nature of this phototropic behavior has now been widely investigated by analytical, spectroscopic, structural, magnetic, EPR, and radiotracer investigations 205, 233, 375-377, 379, 380, 382). During irradiation of the compounds, electrons belonging to or I ions are excited to upper states. The result-... 

Very little is known about chalcogenide halides of Group IVB elements. Although the existence of sulfide chlorides (45, 274, 329, 365) and of a selenide chloride (329) of titanium was claimed in early publications, their true composition, and even their existence, remains doubtful. They have usually been obtained by the reaction of titanium chlorides with sulfur and selenium, respectively, or with hydrogen sulfide. The synthesis of a pure compound, TiSClj, was published in 1959 (113). It is an intermediate of the reaction of TiCU with HjS. 

Growth of single crystals. Crystals of the aluminum selenide halides (needles, maximum length 15 mm) were grown by vapor transport in sealed ampoules between two temperatures (380 and 320°C for Al-SeCl, and 350 and 300°C for AlSeBr and AlSel) over a period of two months. A large excess of the halogenide was used (266). 

AlSCl has an orthorhombic structure, with the lattice constants a - 8.09, b = 10.52, c = 3.86 A, andZ = 4. It is probably isotypic with SbSCl and BiSCl, crystallizing in a layer type of lattice (157) (see Section XII,C,5). The selenide halides are monoclinic, with the probable space-group P2,/m. The lattice constants are given in Table XVII. The constancy of the b parameters for all three compounds suggests the general presence of an Al-Se chain extending in that direction (266). 

Growth of single crystals. Single crystals of the selenide and tel-luride halides can be grown by recrystallization at 360-390°C, or sublimation at 420 (InSeCl) and 370°C (InTel), respectively (162). 

The sulfide halides TISX are prepared by heating a stoichiometric mixture of the thallium halogenide and sulfur in a sealed ampoule at 180°C for 30 h. The mixture is then slowly cooled to room temperature. The compounds TlSeX are obtained by reaction between thallium metal and selenide halide at 280°C during 40 h (22). On heating TlYCl to 500°C in vacuo, the compounds TI4YCI4 result (322). Dissolution of... 

Packings of spheres having occupied tetrahedral and octahedral interstices usually occur if atoms of two different elements are present, one of which prefers tetrahedral coordination, and the other octahedral coordination. This is a common feature among silicates (cf. Section 16.7). Another important structure type of this kind is the spinel type. Spinel is the mineral MgAl204, and generally spinels have the composition AM2X4. Most of them are oxides in addition, there exist sulfides, selenides, halides and pseudohalides. 

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