Chelating ligands antimony

Bridging and chelating ligands. An example for a bidentate chelate ligand is an antimony sulphur diimid which coordinates to group 6 transition metals to form complexes of the type [Bu Sb(N=S=N)]2M(CO)4 (M = Cr, Mo, W) (45). 

Antimony-sulphur compounds are quite widespread and stable, probably a consequence of soft acid-soft base interaction, and the solid state structures are characterized by the formation of a number of weaker Sb... S secondary bonds. In phenylantimony bis(monothioacetate), the ligands are bonded primarily via sulphur (Sb—S 2.451, 2.471 A), but, as Sb(III) is coordinatively unsaturated, there is substantial secondary interaction with the oxygen atom of the thioacetate (mean Sb...02.81 A) giving a bis chelate structure with antimony in distorted square-pyramidal coordination . The apical position is occupied by the phenyl group and the two sulphur atoms are eis to each other (S—Sb—S 84.8°) in the basal plane. Weak dimers are present in the solid state as a result of Sb... S bonding to the sulphur forming the longer Sb—S bond. 

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