Crystal structure of Tl3AsSe3

The structure of Tl₃AsSe₃, which has been solved by the single-crystal x-ray method, is rhombohedral, with space group R3m and cell parameters $\text{a}\text{= 9.870(2)}\text{A}\text{?}\text{, c}\text{= 7.094(3)}\text{A}\text{?}\text{, z}\text{= 3}$. A full-matrix least-squares refinement gives weighted R = 0.058. The Se atoms form equilateral triangles around Tl at 3.178Å and around As at 2.207Å. The structure may be described in terms of units formed from three TlSe₃ triangles by corner-sharing. These units share corners to produce a helical arrangement along the c axis. The triangles of AsSe₃ are isolated from each other.