Crystal structures have been determined for M(S₂PPh₂)₃(M = Sb or Bi). The antimony compound crystallises in the triclinic space group P with a= 11.321(5), b= 9.413(4), c= 17.933(6)Å, α= 100.41(2), β= 97.60(2), γ= 95.80(2)°, and Z= 2; the structure has been solved by Patterson and Fourier methods and refined to R 0.033 for 5 837 observed reflections. The structure consists of isolated molecules in which the central antimony is surrounded by six sulphur atoms at the corners of a distorted pentagonal pyramid. The distance to the apical atom (2.456 Å) is the shortest; the basal Sb–S distances divide into sets of two short (mean 2.595 Å) and three longer (2.923–3.187 Å) bonds in keeping with anisobidentate co-ordination by the dithiophosphinate groups. The bismuth analogue, Bi(S₂PPh₂)₃, is also triclinic (P), with a= 11.909(5), b= 24.174(6), c= 15.652(5)Å, α= 107.80(2), β= 92.89(2), γ= 93.11(2)°, and Z= 4; there are two independent molecules in the asymmetric unit. The structure has been solved and refined to R 0.063 for 8 779 observed reflections. Co-ordination about each independent bismuth atom is similar to that in the antimony analogue with short axial distances (2.629 Å) and two short (mean 2.715 Å) and three longer basal Bi–S distances (mean 2.980 Å). However, the molecules dimerise through intermolecular Bi ⋯ S contacts of 3.173 and 3.301 Å which are trans to the apical atoms and complete pentagonal bipyramidal co-ordination about each bismuth atom. In this case, lone-pair activity at bismuth is considered unlikely and, because of the strong structural similarities between the bismuth and antimony compounds, the antimony lone pair is also not considered to be stereochemically active.