Cationic species, chalcogen

Figure 3.2. Film formation using a dimensional reduction approach involves three steps 1) breaking up the insoluble extended inorganic framework (a) into more soluble-isolated anionic species, which are separated by some small and volatile cationic species (b). 2) Solution-processing thin films of the precursor (b). 3) Heating the precursor films such that the cationic species and corresponding chalcogen anions are dissociated, leaving behind the targeted inorganic semiconductor (c).

Chalcogenides, 5 94-96 berkelium, 28 49, 53-54 lattice energies of, 1 192, 193 ligands, 45 16 Chalcogen(II) compounds binary halides, 35 274—280 complexes with Lewis bases, 35 293-295 halo-chalcogenates(ll), 35 280-288 mixed-valence compounds, 35 288-293 cationic species, 35 291-293... 

Se2Br5+, as the first reported example of a novel dinuclear cationic halogen-chalcogen species, was prepared as the deep-purple crystalline hexafluoroarsenate. The cation consists of two trigonal pyramidal SeBrs units connected via a linear Se-Br-Se bridge. The formally positive Br+ links two SeBr2 molecules with formal oxidation number - -2 for Se. 

Scheme 8.15 compels attention to the following features of the resulting species Complexation of the cation-radical with parent neutral counterparts enhances mobility of an unpaired electron. Introduction of selenium (heavier and bulkier atom) increases the overlap among donor planes due to the better chalcogen-chalcogen intermolecular contacts. The presence of the paramagnetic nitroxyl moiety is decisive for magnetism of the product. 

Binary Anions and Cations. The heavy pnictogens in combination with chalcogens form a large variety of anions.Although many of these binary species form oligomers or polymers with layered or framework structures, there are a number of examples of discrete anions with cyclic structures that are formed with large counterions such as tetralkylammonium or tetraarylphosphonium... 

Mixed group 15 group 16 polycations are rare and tend to form clusters. For example, the arsenic-chalcogen cations [As3E4]" (E = S, Se) have polycyclic structures similar to those of the well-known isovalent species P4S3 and the bismuth-tellurium cation [Bi4Te4]" " adopts a slightly distorted cubic... 

Tellurium forms the most extensive series of homoatomic chalcogen cations. The list of structurally characterised tellurium polycations includes Te4, 6, Te6, Teg and Teg and also the polymeric species (Te4 ) ,... 

The tetranuclear sulfur and selenium derivatives [E(AuPPh3)4]2+ show a square pyramidal geometry with the chalcogen atom in the apical position [241]. These cations dimerize in the solid state through Au-E interactions (Figure 1.40). Further auration of sulfur and selenium to give the penta- and hexa-nudear species has been achieved and trigonal bipyramidal and octahedral structures have been proposed [242]. 

Depending on the desired species to be analyzed, a variety of primary ion beams may be used such as Cs" ", Oj, O, Ar" ", and Ga" ". Whereas a cationic primary beam such as Cs+ is used to ionize electronegative elements e.g., O, C, N, chalcogens. 

Some preliminary results on the electrochemical behaviour of elemental sulphur (and selenium) in AlCla-NaCl melts have been reported. The results for both elements were difficult to interpret, due in part to the low solubility of both elements in the melt and the modification of the electrode surfaces by the products of electrode reactions. In basic melts it was suggested that an cation is formed, in agreement with spectral studies. In acidic melts the results were more complex, and no exact conclusions could be drawn as to the nature of the species. A spectrophotometric study of the reactions of sulphur, selenium, and tellurium with aqueous solutions of NaOH at 150 °C (S, Se) and 300 °C (Te) has been carried out. From the experimental data the formation of the chain-like structure of polychalcogenide compounds was presumed. The spectra confirmed previous results concerning the mechanism of interaction of elemental chalcogens with aqueous NaOH solutions. 

---