Barbituric acid reacts with potassium tetrachloroplatinate(II) and potassium iodide giving crystals of the composition K2(Pt2I6) · 2C4H4N2O3, the structure of which has been determined by X-ray crystallography. The complex consists of a layer structure, where planes containing (Pt2I6)2− anions alternate at 3.45 Å with those containing the barbituric acid molecules and the K+ ions. The coordination around the potassium atoms consists of centro-symmetric dimers (O2I2 – K – O2I2 – K – O2I2) so that each K+ ion is within the bonding distance of eight sources of electron density, two oxygen and two iodine atoms bonding independently and two oxygen and two iodine atoms shared between potassium atoms.