Oxygen—selenium bonds

Selenium-oxygen bonds. The Se chemical shifts of some inorganic selenium-oxygen compounds are listed in the Tables 2 and 3. It is apparent that Se (Vl)-species are much more shielded (5 = 944-1076 Table 2) than the Se (IV)-species (5 = 1263-1559 Table 3). This holds as well for SeO3, the anhydride of selenic acid (H2SeO4), the halogen derivatives and its alkyl esters and amides. 

The platinum metal chalcogenides in general are easier to prepare than the corresponding oxides. Whereas special conditions of temperature and pressure are required to prepare many of the oxides, the platinum metals react most readily with S, Se, and Te. A number of additional differences concerning the chemistry of the chalcogenides and the oxides are summarized as follows The metal—sulfur (selenium, tellurium) bond has considerably more covalent character than the metal-oxygen bond and, therefore, there are important differences in the structure types of the compounds formed. Whereas there may be considerable similarity between oxides and fluorides, the structural chemistry of the sulfides tends to be more closely related to that of the chlorides. The latter compounds... 

Diaryl ditellurium compounds, when heated in pyridine, ethanol, or acetic acid with selenium dioxide, produced the corresponding bis[aryltelluro] selenium and derivatives of these compounds with oxygen bonded to tellurium and selenium4. 

Selenium-Oxygen Compounds.—Knudsen effusion measurements have been performed on powdered selenium dioxide at temperatures between 374 and 427 K, and the vapour pressure over this range has been determined.295 The enthalpy of formation of Se02(g) was computed to be AHT(298.i5) — -26.20 kcal mol-1 this leads to a value for an average bond energy of 99.80 kcal moF1, which is comparable with the spectroscopic dissociation energy. A vibrational analysis of the 3130 A absorption system of selenium dioxide has been carried out.296... 

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