Metal selenium—oxygen bonds

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... 

Oxygen, sulfur or selenium insert in the germanium aUcali-metal bond (equation 78 and equation 79 ). 

Metallaheterocycles with the metal atom capable of supporting a carbon-metal double bond, and with oxygen, nitrogen, sulfur, or selenium as the second heteroatom are the only structures capable of full conjugation. These compounds show furan-like aromaticity with the heteroatom /i-electrons participating. No examples of this type of ring system were uncovered, undoubtedly due to the stability of the metalla-carbon double bonds required for their formation. 

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