Selenium binary structures

Hydrides of variable composition are not only formed with pure metals as solvents. A large number of the binary metal hydrides are non-stoichiometric compounds. Non-stoichiometric compounds are in general common for d,f and some p block metals in combination with soft anions such as sulfur, selenium and hydrogen, and also for somewhat harder anions like oxygen. Hard anions such as the halides, sulfates and nitrides form few non-stoichiometric compounds. Two factors are important the crystal structures must allow changes in composition, and the transition metal must have accessible oxidation states. These factors are partly related. FeO,... 

Fergusson et al. were the first to report the existence of binary compounds with a general formula Se Sg in these melts. They carried out an extensive investigation by X-ray powder diffraction and by absorption spectroscopy in the infrared, visible, and ultraviolet regions over the whole composition range of molten mixtures of sulfur and selenium cooled down to 20 °C. They also examined phases obtained by recrystallization of the cooled melts from carbon disulfide. All phases were isomorphic with one of the allotropes of Sg and SCg indicating that the structures also consist of cyclic eight-membered molecules ... 

Earlier X-ray powder diffraction studies by de Haan and Visser provided similar results. These authors investigated the impact of the selenium content on the structure type of the crystals and deduced the existence of eight-memteed ring molecules but were unable to decide whether the crystals consisted of binary compounds of sulfur and selenium or simply of Seg and Sg. 

Binary phosphorus-sulfur and -selenium compounds have polycyclic structures.The most common examples are P4E3 and P4E10 (E = S, Se). The... 

There are single examples of sulfur and selenium xanthates with the remaining structures to be described in this section featuring tellurium as the central element. There are a significant number of binary xanthates and, in common with these, their organotellurium xanthates feature extensive supra-molecular association, usually, but not exclusively, via Te- S secondary bond interactions. A rare example of mixed-ligand 1,1-dithiolate structure is available where the odd dithiolate ligand is a dithiocarbamate. 

Two characteristic structural and bonding features of the chlorine and bromine compounds of selenium(IV), in which the role of the inert pair determines much of stereochemistry and reactive properties of the entire class of compounds, are already evident in the simple binary halides. 

In the series of the binary halides of selenium and tellurium, the crystal structure determinations of tellurium tetrafluoride (100) and of tellurium tetrachloride on twinned crystals (65, 66) were the key to understanding the various and partly contradictory spectroscopic and other macroscopic properties (e.g., 66,161,168,169,219,220, 412), as well as the synthetic potential of the compounds. In contrast to the monomeric molecular i//-tbp gas phase structures with C2v symmetry (417), the solid state structures of both are polynuclear. As the prototype of the chlorides and bromides of selenium and tellurium, crystalline tellurium(IV) chloride has a cubane-like tetrameric structure with approximate Td symmetry (Fig. 1). Within the distorted TeCla+a octa-hedra the bonds to the triply bridging chlorine ligands are much longer than to the terminal chlorines. The bonding system can be described either covalently as Te4Cli6 molecules, or, in an ionic approximation, as [(TeCl Cn4] with a certain degree of stereochemical activity of the lone pairs toward the center of the voluminous cubane center (65, 66). 

A novel class of chalcogen(II) halogen compounds was established recently by the preparation of the first simple binary mononuclear and oligomeric haloanions of divalent selenium and tellurium. The chemistry of these compounds is especially variable for selenium, and a number of highly interesting mono-, di-, tri, tetra- and pentanuclear anionic species with composition X Ym have been synthesized and characterized by structure analyses and spectroscopic studies up... 

Use the group structure of the periodic table to predict the empirical formulas for the binary compounds that hydrogen forms with the elements antimony, bromine, tin, and selenium. 

U, Np, and Pu selenide and oxide-selenide molecular and cluster cations were synthesized by LA of dilute mixtures of An oxides in a selenium matrix (Gibson, 1999d) binary ions, AnSe +, and ternary cluster ions, An OmSe +, were observed, with the compositions of the mixed 0/Se clusters suggesting the aggregation of AnOm with Se , the presence of Se ions in analogy with 0 , or the presence of structures involving O—Se bonding. 

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