The solvothermal technique was used for the synthesis of MHgSbSe~3 (M=K, Rb, Cs) and the crystal structures were determined by single crystal X-ray diffraction methods. CsHgSbSe~3(I) crystallizes in the orthorhombic, space group Cmcm with a=0.4444(1)nm, b=1.5514(6)nm, c=1. 1261(7)nm, V=0.7764(6)nm^3, Z=4, R=0.0605, ωR=0.1234. RbHgSbSe~3(II) crystallizes in monoclinic, space group P2~1/c with a=0.7758(2)nm, b=1.1234(2)nm, c=0.8849(2)nm, β=106.60(3)ⅲ, V=0.7391(3)nm^3, Z=4, R=0.0552, ωR=0.1198. KHgSbSe~3(III) crystallizes in the orthorhombic, space group Pnma with a=1.9482(4)nm, b=0.8523(2)nm, c=0.9830(2)nm, V=1.6322(6)nm^3, Z=8, R=0.077, ωR=0.118. The crystal structures of I and II consist of two dimensional layers of ~∞^2[HgSbSe~3]^- with M^+ (M=Rb, Cs) counter ions located between the layers, while that of III consists of a three dimensional network with big channels (about 0.9nm×1.2nm) along the b direction, with K atoms located in the center of the channels. Optical studies performed on the powder sample of these compounds, suggested that they are the semiconductors with a band gap of 1.65eV for I, and 1.75eV for II and 1.85eV for III.

Key words: SELENIDE, CRYSTAL STRUCTURE, SEMICONDUCTOR MATERIAL, ANTIMONY COMPOUNDS, MERCURY COMPOUNDS, POTASSIUM COMPOUNDS, RUBIDIUM COMPOUNDS, X-RAY DIFFRACTION ANALYSIS