The crystal structures of M2[PtCl2(SnCl3)2][M = PMePh3(1) and PPh3(CH2Ph)(2)] have been determined from three-dimensional X-ray data collected by counter methods. Compound (1) crystallises in space group P21/n with a= 11.815(2), b= 14.172(3), c= 13.848(2)Å, β= 96.56(1)°, and Z= 2. Compound (2) crystallises in space group P, with a= 12.722(3), b= 11.518(2), c= 10.674(2)Å, α= 110.73(1), β= 79.86(2), γ= 114.39(1)°, and Z= 1. Both structures were refined by least-squares methods: refinement was halted at R= 0.13 for (1); for (2) refinement was concluded at R= 0.033 for 3 344 reflections with I/σ(I) 3.0. Both crystals contain cis-[PtCl2(SnCl3)2]2– ions, disordered in such a way as to be pseudo-centrosymmetric. This disordering involves a half-occupied PtCl2 unit appearing on either side of the centre. Simultaneously, one chlorine from each SnCl3 unit changes sides while the other two chlorines appear in average positions with very small displacements between their positions. The Pt–Sn distance (average 2.3556 Å) is significantly shorter than that found in [Pt(SnCl3)5]3–(average 2.5530 Å) consistent with the much larger J(195Pt–119Sn) coupling constants in (1) and (2)(27 640 vs. 16 030 Hz). The Pt–Cl distance (average 2.296 Å), although not accurately determined, is relatively short. The l95Pt and 119Sn n.m.r data, the far-i.r. spectral data, and X-ray data, when compared to those of [Pt(SnCl3)5]3–, suggest a greater amount of Pt–Sn π bonding in the four-co-ordinate than in the five-co-ordinate complex.