Single crystals of arsenicv ditelluroidide semihydrate, AsTe2I · 0.5 H2O(Fw = 466.033), were prepared hydrothermally. The crystal structure was determined from the intensities of 501 independent reflections, measured on a computer-controlled single-crystal diffractometer (Philips PW 1100), with MoKα radiation (λ = 0.71069 Å). The cell constants at 293 K, refined by least-squares, are a = b = 7.221(1) Å, c = 21.478(7) Å, Z = 6, space group R3. The density values are ϱmeas = 4.6 g · cm−3 and ϱcalc = 4.786 g · cm−3.
Solution of the structure was performed by Patterson methods combined with successive Fourier syntheses. The positional and anisotropic thermal parameters were refined by full-matrix least-squares calculations. All reflections were corrected for absorption (μ = 177.365 cm−1) and values for anomalous dispersion used to all non hydrogen atoms. Refinement converged to R = 0.051 and Rw = 0.050.
The As atoms are surrounded by six [Te, I] atoms, three with shorter and three with longer distances, forming strongly distorted octahedra. Each of the As(1) octahedra is linked with three As(2) octahedra by common edges [Te, I](1)–[Te, I](2), and vice versa, forming an infinite band perpendicular to the c axis. In each unit cell are three parallel bands, an arrangement analogous to AsI3. The water molecules are enclosed between successive bands. The bands are connected by hydrogen bonds.