Crystal structure and stereoisomerism of tris (O-ethylxanthato) antimony (III) in its lattice hemiadduct with 4, 4′-bipyridyl

The preparation and crystal structure determination of the adduct [Sb(S2COEt)3], 0.5C₁₀H₈N2 is reported. Crystals are triclinic, P1, a 6.064(3), b 10.825(6), c 17.723(7) Å, α 104.77(4), β 96.78(3), γ 97.14(4)°, Z 2. The compound is a lattice adduct, the bipyridyl molecule being located about a crystallographic centre of symmetry. The complex molecule geometry is unlike that of the compound [Sb(S₂COEt)₃]; in the latter the molecule has crystallographic symmetry 3, the three equivalent ligands being unsymmetrically coordinated, while in the present molecule the chirality is lost, the molecule conforming to approximate pseudo-m symmetry: two ligands are similar [Sb-S, 2.615(2), 2.892(2); 2.612(2), 2.878(2) Å] and the other, located in the pseudo-mirror plane, is different [Sb-S, 2.477(2), 3.091(2) Å], Electron-pair repulsion theory shows that the bond angles, the relative bond lengths, and the coexistence of different stereoisomers of this molecule, can be ascribed to the stereochemically active lone pair of electrons being close to the antimony atom.