Organoantimony-sulfur compounds

This type of self-assembly is rather common, because antimony and sulfur form a soft acid-base pair. The Sb-S covalent bond is expected to be ca. 2.4 A (from the sum of the covalent radii) and the van der Waals interatomic distance has been estimated as ca. 4.0 A several self-assembled compoimds with interatomic Sb- - -S distances from 3.0 to slightly less than 4.0 A will be discussed in this section. 

A first example is 2-phenyl-1,3-dithiastibolane, in which the five-membered rings are assembled into helical chains, 168, by secondary Sb- - -S bonding (3.34 A) [427]. The structure is similar to that of 2-chloro-l,3-dithiastibolane, a compound without an Sb-C bond [428]. 

Double bridged self-assembly occurs in l-chloro-4,5-dimethyl-4,5-didehydro-2-thiastibolane, 169, and l-bromo-4,5-diphenyl-4,5-didehydro-2-thiastibolane, 170, to form dimeric molecules in the solid state. In benzene solution the dimers dissociate into monomers [429]. 

Self-assembly also occurs in trithiastibocanes. Thus, 2-phenyl-l,3,6,2-trithiastibocane molecules are associated via Sb- -S secondary bonds (3.594 and 3.868 A) into linear tetramers, 171, whereas the oxo analog, 5-phenyl-l,4,6,5-oxadithiastibocane is similarly self-assembled into double chains, 172 (Sb- -S 3.558 and 3.862 A) [430], The compounds also contain intramolecular, transannular Sb - - S and Sb - -O secondary bonds, respectively. 

The extent of association can vary with the nature of the organic groups attached to the metal, probably because of electronic influences which modify the Lewis acid-base properties of the metal. Thus, /7-nitrophenyl trithiastibocane molecules assemble into dimers only, 173 [431]. 

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