Complex selenium

The MS2N2 complexes and their selenium analogues are readily protonated at the nitrogen attached to the metal (Eq. 7.5). Competitive studies show that the selenium complex is a stronger base than its sulfur analogue. 

Complexes of the sulfenamido anion [RSNR ] with several transition metals [Zr(IV), Ti(IV), Mo(VI), W(Vf), Ni(If), and U(IV)] are known.They are prepared by the reaction of the lithium derivative of the sulfenamido anion with a metal halide complex. A selenium complex W(N Bu)2( BuNSePh)2 has been obtained in a similar... 

Mn2(/x-SAuPPh3)(CO)6(/i-dppm)].291 The selenium complex [Pd2Au2Se2 (SeH)2(PPh3)4] (517)1035 has also been obtained. 

A number of zinc selenium complexes have now been characterized, with particular interest in the formation of zinc selenide semiconductors and quantum dots. In many cases analogous structures to those observed with thiol or thiolates are recorded. 77Se NMR is frequently used in characterization, and comparison with the sulfur equivalent is relevant. Zinc selenium compounds are of particular interest as precursors for metal/selenide materials and their relevance as models for selenocysteine-containing metalloproteins. 

Selenium Selenium complexed with 4-nitro-o-phenylenediamine, extracted into toluene Gas chromatography — [555]... 

VII. Olefinic Oxygen, Sulphut and Selenium Complexes of Transition Metals... 

Schiff base complex, 32 13 -selenium complex FejScj complexes, 32 348 Fc4Se3 complexes, 32 349-350 Fc4Se4 complexes, 32 348-349 -selenium-nitrosyl complexes, 32 348-350 selenocyanates, 17 295, 296 sequestration in apoferritin, 36 463-464 silicates, Mbssbauer effect of, 6 474-479 -silicon compounds, 3 250 silyl complexes anionic tetracarbonyl, 25 37 binuclear carbonyls, 25 3, 5, 16, 33, 44-45, 116... 

Although selenium derivatives of gold occur less frequently than sulfur ones, the presence of Au- Se intermolecular weak interactions has also been reported in a number of selenium complexes. For example, the cations of the tetranuclear complex [Se(AuPPh3)4](CF3S03)2 [40] are paired across symmetry centers to form loose dimers via an [Au- -Se]2 unit (Figure 5.21), which resembles the supramolecular motif usually found in sulfur compounds of gold. The intermolecular Au---Se... 

The comparison of the Mo-Mo distances in the sulfur and selenium complexes shows that the selenium analogues have longer (ca. 0.04 A) distances. This can be explained by the larger intracluster matrix effect of selenium. This contrasts with the shorter average Mo-Mo distances for the selenium compounds in the solid-state Chevrel phases (52). 

A wide range of ligands of the type RXCH2C02H where R = alkyl, alkenyl or aryl and X = S, Se or Te have been reacted with silver ions and thermodynamic data for some representative examples are given in Table 49.358,359 The silver-selenium complexes were found to be more stable than their silver-sulfur analogues as a result of both larger favourable enthalpy and smaller unfavourable entropy changes. 

Figure 2 The yellow modification of the dimercury(I) selenium complex Hg2(Ph2Se)4(Q04)2...

Ruthenium ammine-phosphine and -selenium complexes are discussed in Sections 45.5.4.6 and 45.8 respectively. 

Whereas all (eight) possible sulfur and (eight) selenium complexes have been prepared and unequivocally characterized [217], some of the tellurium-rich compounds could not be isolated due to the ready formation of either Fc-TeTe-Fc or fc(Te3). 

Reactions of organosulfur and -selenium complexes with acetylenes (usually activated) either result in formal insertion of the acetylene into an S—C, Se—C, M—C, M—S, or M—Se bond or resemble a cycloaddition reaction to elements of the original complex. These descriptions do not, of course, have any mechanistic implications. 

Selenium enters the food chain mainly as selenomethionine from plants that take the element up from the soil but do not appear to use it. The soil content of selenium is highly variable and can be low in volcanic soils when soluble salts are leached out by ground water. Soils in parts of China and New Zealand are particularly low in selenium. Acid soils, where insoluble selenium complexes can be formed with iron and aluminum, occur in some parts of Europe, resulting in low available soil selenium. The geographical source of plant and animal foodstuffs determines the level of dietary intake. In the United States and Canada, wheat and other cereal products are a good source of selenium average intakes in North America range from 80 to 220 fig Se per day, whereas in the UK dietary intake is about 30 to 60 Llg/day. Intakes in China are as low as 11 lg/day and in New Zealand 28 fig/day. ... 

The colour reaction is carried out in 0.1 M HCl, and the time necessary for colour development in the aqueous pseudo-solution is 50 min. In the extractive spectrophotometric method [36], the time for reaction at pH 2-3 (in the presence of formic acid) is 30 min, after which the solution is neutralized to pH 6-7, and the piazselenol is extracted into toluene. The colour reaction may be accelerated by heating the solution. Within the pH range 5-10, the distribution coefficient of piazselenol between toluene and water is high, and one portion of toluene extracts practically all the selenium complex into the organic phase. The free reagent (DAB) is also extracted. Related solvents such as benzene and xylene may be substituted for toluene. 

Gronbaek H, Thorlacius-Ussing O. 1990. Selenium complexes in the anterior pituitary of rats exposed to L-selenomethionine. Virchows Arch B Cell Pathol 59(5) 291-296. 

Similar electronic effects are observed for the cyclic ligands, 2a and 2b. The sulfur complex, / ii(C vS3)2j, is oxidized quasi-reversibly at +0.72 V vs SCE (Figure la) while the selenium complex, Au(C3,Sc5)2, undergoes an irreversible oxidation at +0.34 V (Figure lb)13. Assignment of the 0/1 couple as a ligand-based oxidation was made on... 

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