The synthesis, characterisation and structure of compounds with formula Pt(ligand) 4 I 6 is described, in which the ligands are 1-methylimidazole, 2-methylimidazole and 1,2-dimethylimidazole (DMIz). Upon treatment of acidic solutions containing the Pt(ligand) 2+ 4 cations, with a large excess of aqueous KI, invariably precipitates of the above formula result. Infrared and NMR spectra of the compounds in organic solvents agree with the presence of Pt(ligand) 2+ 4 cations, whereas polyiodide anions are suggested from far-IR spectra (solid state) and visible spectra (CH 3 CN solution). To understand the poor solubility in aqueous solution (other Pt(ligand) 2+ 4 compounds, with Cl, Br, I, ClO 4 anions, are very soluble) the structure of one of these mutually similar compounds was solved with the aid of single-crystal X-ray diffraction. Pt(DMIz) 4 I 6 crystallizes in the monoclinic space group P2 1 /c with two formula units in a unit cell of dimensions a = 9.376(3), b = 19.849(6) and c = 10.387(3) Å , β = 113.25(3)°. The structure has been determined by the heavy-atom method, using both Pt and I in the starting model, and refined by least-squares techniques to R = 0.035 and R w = 0.040 for 3615 reflections. It consists of discrete Pt(1,2-DMIz) 2+ 4 and I − 3 ions. The Pt(II) is square planar coordinated by the four 1,2-DMIz ligands, with PtN distances of 2.009(8) and 2.014(5) Å and a NPtN angle of 88.6(3)°. Two of the four DMIz ligands occur in two unequally-occupied disordered positions (72% and 28%), which do not influence the crystal packing. The II distances in the I − 3 ion are 2.856(1) and 3.005(1) Å , whereas the III angle is 177.71(3)°. There are no unusual, short intermolecular contacts between the cations and the anions, and between the anions and I atoms from other anions.