Synthesis and Crystal Structure of Hg3S2I2 and Hg3Se2I2, New Members of the Hg3E2X2 Family

The reactions of HgS and HgSe with HgI2 yield Hg3S2I2 and Hg3Se2I2, respectively. Orange crystals of Hg3S2I2 and light red crystals of Hg3Se2I2 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, wR(F2)=0.0751 for Hg3S2I2 and R=0.0518, wR(F2)=0.0993 for Hg3Se2I2 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 Hg3S2I2 and a= 976.60(9) pm, b=1938.1(3) pm, c=963.32(9) pm for Hg3Se2I2. The structures contain one-dimensional polycationic folded bands (Hg3E2)2+ (E=S, Se) with intercalated I- ions. Alternatively, the polycationic part can be described as trigonal Hg3E pyramids which are interconnected in the way that they form one-dimensional channels. Discrete iodide ions separate these cationic channels.