Structural features of group V A xanthates. The crystal and molecular structures of tris( O-isopropylxanthatoarsenic(III), antimony(III) and -bismuth(II)

Abstract

The crystal structures of the title compounds, M(S 2CO iC 3H 7) 3, M = As(III), ( 1); Sb(III), ( 2); and Bi(III), ( 3) have been determined by three dimensional X-ray diffraction techniques and refined by a least square method. Crystals of ( 1) and ( 2) are isomorphous and both crystallize in the rhombohedral space group R 3 , with unit cell parameters for ( 1) a hex = 11.559(2), c hex = 28.131(3) Å and for ( 2) a hex = 11.696(2) and c hex = 28.135(2) Å, Z = 6. The central metal atom in both ( 1) and ( 2) is coordinated by three asymmetrically chelating xanthate ligands [AsS 2.305(2) and 2.978(2) Å and SbS 2.508(1) and 3.006(1) Å] which form a distorted octahedral environment consistent with the presence of a stereochemically active lone pair of electrons. Crystals of ( 3) are orthorhombic, space group Pnma, Z = 4 with dimensions a = 11.003(3), b = 20.833(4) and c = 9.428(2) Å. The environment of the bismuth atom in ( 3) is seven coordinate and is comprised of six sulphur atoms, derived from three asymmetrically coordinating xanthate ligands, and a bridging sulphur atom from a neighbouring molecule which results in the formation a polymeric array. For ( 1) final R and R W 0.050 and 0.047 respectively for 936 reflections [ I ⩾ 3σ( I); (2) R 0.040, R w 0.040 for 1455 reflections I ⩾ 2σ( I)]; and ( 3) R 0.052, R w 0.039 for 1796 reflections [ I ⩾ 2σ( I).