Metal selenides bonding

More quantitatively, it appears to a first approximation that the unit cell contraction of a compound containing Mn2+, Co2+, Ni2+, or Fe2+, relative to the isomorphous Mg+2 compound, is a linear function of the Ax of the metal-ligand bond if we neglect selenides and tellurides. Inclusion of these more covalent compounds indicates a greater dependence on Ax. 

The fourth and final crystal structure type common in binary semiconductors is the rock salt structure, named after NaCl but occurring in many divalent metal oxides, sulfides, selenides, and tellurides. It consists of two atom types forming separate face-centered cubic lattices. The trend from WZ or ZB structures to the rock salt structure takes place as covalent bonds become increasingly ionic [24]. 

Two factors combine to lend a greater diversity in the stereochemistries exhibited by bivalent germanium, tin and lead compounds, the increased radius of Mn compared with that of Mw and the presence of a non-bonding pair of electrons. When the non-bonding pair of electrons occupies the isotropic valence level s orbital, as in, for example, the complex cations Pb[SC(NH2)2]6+ and Pb[antipyrine]6+, or when they are donated to conductance band levels, as in the binary tin and lead selenides or tellurides or the perovskite ternary phases CsMX3 (M = Sn, Pb X = Cl, Br, I), then the metal coordination is regular. However, in the majority of compounds an apparent vacancy in the coordination sphere of the metal is observed, which is usually ascribed to the presence of the non-bonding pair of electrons in a hybrid orbital and cited as evidence for a stereochemically active lone pair . 

Allylic metals, in propargylic alcohol alkylation, 11, 129 ir-Allylic palladium complexes, and carbocyclization, 11, 426 Allylic position, alkenes, dienes, polyenes, metallation, 9, 6 Allylic selenides, [2,3]sigmatropic rearrangement, 9, 481 Allylic substitution reactions for C-N bonds via amination... 

Rhenium Sulfides and Selenides.208 209 These catalysts are characterized by their outstanding resistance to poisoning and minimal tendency to cause the hydrogenolysis of carbon-sulfur bonds than the base metal sulfides. Rhenium heptasulfide is easily prepared from boiling 6M hydrochloric acid solutions of perrhenate with hydrogen sulfide. It has been noted that occasional exposure of the dried, powdered catalyst to the atmosphere is not deleterious. 

Treatment of potassium salts 19 and 20 with sodium borohydride, followed by deacetylation, produced the diselenides 23 and 24 which, on treatment with metallic potassium in methanol, underwent cleavage of the Se-Se bond with formation of potassium salts 25 and 26. Products 19 and 20 are excellent precursors in the synthesis of symmetrical and unsymmetrical sugar selenides 27-32, as reported by Wagner and Nuhn.25... 

---