Selenides, structure

Planar four-membered rings are again found in the dimeric species 64 and 65 . In the former, the geometry at tin(II) is pyramidal with As—Sn distances of 2.77 A and ring angles of 102.22 at arsenic and 77.78° at tin. Refinement of the arsenic selenide structure 65... 

Lead fluoride, 193 Lead halides, 197 bivalent structure, 193 Lead iodide, 194 Lead oxide structure, 202 Lead phosphates, 222 Lead selenide structure, 202 Lead sulfate, 222 Lead sulfide structure, 202 Lead tclluride structure, 202 Lewisite, 256 Lipophilicity... 

Tin iodide, 194 Tin oxides structure, 192,202 Tin phosphates, 222 Tin selenide structure, 202 Tin sulfate, 222 Tin sulfide structure, 202 Tin telluride structure, 202 Titanium, 323-358 coordination numbers, 327 discovery, 324 isotopes, 325,326 oxidation states, 327 preparation, 324 properties, 325... 

The upper limit is evidently due to the fret that above 20 at.% of arsenic the structure of the glass is completely determined by the arsenic selenide structure. It should be noted that the composition dependences of the electrical conductivity at room temperature, the microhardness, and the density of the glasses of this system are similar (Figs. 2 and 3). The minimum of the conductivity, microhardness, and density correspond to alloys containing 8-10 at.% of... 

Several triarylphosphine oxides and related compounds have been reported. The tri-o-tolylphosphine, phosphine oxide, and phosphine selenide structures have been determined in order to study the rotational isomerism of the P-C(aryl) bonds. The geometry at the phosphorus is normal, with P-C... 

The structure of the isomeric benzo-l,2,3-thiadiazole 11.30 is unknown, but the 1 1 adduct with AsFs (11.31) has been structurally characterized. The AsFs molecule is coordinated to the carbon-bonded nitrogen atom. Cycloocteno-l,2,3-selenadiazole is an effective source of selenium for the production of semi-conductors such as cadmium selenide." ... 

Selenides and tellurides are, again, broadly similar to the sulfides in structure and properties. 

Chalcogenides of Cd are similar to those of Zn and display the same duality in their structures. The sulfide and selenide are more stable in the hexagonal form whereas the telluride is more stable in the cubic form. CdS is the most important compound of cadmium and, by addition of CdSe, ZnS, HgS, etc., it yields thermally stable pigments of brilliant colours from pale yellow to deep red, while colloidal dispersions are used to colour transparent glasses. 

The Transition to the Sphalerite Structure.—The oxide, sulfide and selenide of beryllium have neither the sodium chloride nor the cesium chloride structure, but instead the sphalerite or the wurzite structure. The Coulomb energy for the sphalerite arrangement is... 

It is also shown that theoretically a binary compound should have the sphalerite or wurzite structure instead of the sodium chloride structure if the radius ratio is less than 0.33. The oxide, sulfide, selenide and telluride of beryllium conform to this requirement, and are to be considered as ionic crystals. It is found, however, that such tetrahedral crystals are particularly apt to show deformation, and it is suggested that this is a tendency of the anion to share an electron pair with each cation. 

The acyl selenide 19 affords the decarbonylated )S-lactam in good yield. A N-hydroxypyridine-2-thione ester 20 is used in the key step to construct the chiral cis-cyclopropane structure in compounds designed as antidopaminergic agents. The observed high cis selectivity is due to the hydrogen abstraction from the sterically demanding (TMSlsSiH, which occurs from the less-hindered side of the intermediate cyclopropyl radical. 

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-... 

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). 

The phase transiton from a paraelectric to a ferroelectric state, most characteristic for the SbSI type compounds, has been extensively studied for SbSI, because of its importance with respect to the physical properties of this compound (e.g., J53, 173-177, 184, 257). The first-order transition is accompanied by a small shift of the atomic parameters and loss of the center of symmetry, and is most probably of a displacement nature. The true structure of Sb4S5Cl2 106), Bi4S5Cl2 194), and SbTel 108,403) is still unknown. In contrast to the sulfides and selenides of bismuth, BiTeBr 108) and BiTel (JOS, 390) exhibit a layer structure similar to that of the Cdl2 structure, if the difference between Te, Br, and I (see Fig. 36) is ignored. 

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