Penta- and Hexacoordination of Silicon with Heavier Chalcogens S, Se, Te

3 Penta- and Hexacoordination of Silicon with Heavier Chalcogens (S, Se, Te) 

To our best knowledge, there is no crystallographic evidence for telluroether silicon coordination compounds to date. 

Thiocarbonyl compounds as ligands in the Si coordination sphere are encountered with thiocarboxylate (184, 185), thiocarbamate (186), and thiourea (187, 188) derivatives [346-348]. Whereas in the first case (184, 185) only capped tetrahedral 

Si coordination spheres have been reported (with weak S Si interactiOTis indicated by interatomic separations of 3.05-3.48 A), thiocarbamate was shown to form a noticeably shorter Si—S bond in 186 (2.70 A) and the animi of the thiourea derivative methimazole was shown to be capable of forming a trisilane (187) with two adjacent octahedral Si coordination spheres, one of which comprises four Si—S bonds (with separations ranging between 2.35 and 2.48 A). Notably, this trisilane with a central Si(Si2S4) skeleton is one out of only few crystallographically characterized hexacoordinated Si compounds which are devoid of first and second row elements in the octahedral Si coordination sphere of one of their Si atoms (further examples can be found with P and Cl in the coordination sphere, vide infra). The kind of tetrahedral capping by rather long Si S separations of about 3.17-3.50 A is encotmtered with various methimazolyl-substituted silanes such as 188 [349]. 

In further studies this strategy of including thiolate donor moieties in chelating ligands (see compounds 41, 124-127, 130, and 193-199) proved successful to 

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