Abstract The reactions of HgS and HgSe with HgI 2 yield Hg 3S 2I 2 and Hg 3Se 2I 2, respectively. Orange crystals of Hg 3S 2I 2 and light red crystals of Hg 3Se 2I 2 are formed in evacuated glass ampoules at 260°C in yields of 50% as the only crystalline compounds. The crystal structures have been solved and refined to R=0.0449, w R( F 2)=0.0751 for Hg 3S 2I 2 and R=0.0518, w R( F 2)=0.0993 for Hg 3Se 2I 2 on the basis of single-crystal X-ray diffraction data. Both compounds are isotypic and crystallize in the orthorhombic space group Imma with Z=8. The lattice constants are a=979.92(8) pm, b=1870.3(3) pm, c=946.22(7) pm for Hg 3S 2I 2 and a= 976.60(9) pm, b=1938.1(3) pm, c=963.32(9) pm for Hg 3Se 2I 2. The structures contain one-dimensional polycationic folded bands (Hg 3 E 2) 2+ ( E=S, Se) with intercalated I − ions. Alternatively, the polycationic part can be described as trigonal Hg 3 E pyramids which are interconnected in the way that they form one-dimensional channels. Discrete iodide ions separate these cationic channels.