Preparation and crystal structures of diphenylantimony(III) thiocyanate and bis(2,6-dimethylphenyl)antimony(III) thiocyanate

Abstract

Diphenylantimony(III) and bis(2,6-dimethylphenyl)antimony(III) thiocyanates have been prepared by metathesis reactions between the appropriate diarylantimony(III) halide and potassium thiocyanate in acetonitrile solution. The second compound was also obtained by thermal decomposition of tris(2,6-dimethylphenyl)antimony(V) dithiocyanate. Crystal structure determinations showed that in SbPh₂(NCS) the thiocyanate group bridges between antimony centres to give an infinite polymer, while the 2,6-dimethyl-substituted analogue is an N-bonded monomer. The diphenylantimony structure is probably unique in that the asymmetric unit consists of three formula units and, although each thiocyanate group is bridging, two are primarily N-bonded while the third is primarily S-bonded. Angles at the bridging nitrogens are large (150.4–174.9°) while those at sulfur are close to 90°(85.7–98.6°). These in conjunction with the presence of thiocyanate groups in the axial positions of pseudo-trigonal-bipyramidal arrangements about antimony lead to a curious ‘triangular spiral’ structure for the polymeric chains.