Antimony(III) tris(monothioacetate) has been prepared from thioacetic acid and antimony(III) oxide as a water-stable compound, in contrast to the extreme instability to water of the analogous triacetate. X-Ray structure determinations, however, show similar molecular structures for the two compounds. Crystals of antimony triacetate are monoclinic, space group P2₁, Z= 2, with a= 7.463(5), b= 9.346(5), c= 7.740(5)Å, and β= 116.20(5)°, whereas those of antimony tris(monothioacetate) are monoclinic, space group P2₁/c, Z= 4, with a= 8.884(5), b= 16.819(5), c= 8.964(5)Å, and β= 117.26(5)°. Primary bonding in the former is to three oxygen atoms (mean Sb–O, 2.06 Å) but to three sulphur atoms (mean Sb–S, 2.47 Å) in the latter. Vibrational spectra suggest the presence of secondary bonding in both compounds, which has been confirmed by the observation of three weak intramolecular interactions (Sb–O, 2.596–2.775 Å in the acetate and 2.745–2.918 Å in the thioacetate). One of the ligands, in addition to behaving as a chelate, bridges between molecules (Sb–O, 2.600 and 3.043 Å for the acetate and thioacetate respectively) leading to polymeric chains in the solid. The overall co-ordination polyhedron, which includes the stereochemically active lone pair, is best described in terms of a distorted dodecahedron.