New gadolinium polyselenide GdSe1.89(6) in the PbFCl matlockite structure type

Optimal growth conditions for GdSe1.85 crystals are found by the thermodynamic simulation of the Gd–Se–I system. The obtained data are used to grow GdSe1.85 crystals by the vapor transport method using iodine as a transport agent. The grown crystals are identified by microprobe and powder XRD analyses. The structure is determined by the single crystal XRD analysis and the composition is refined. The crystal structure is in general typical of the structures of REM polychalcogenides, however, the unit cell represents the metric type unknown previously: a = 4.0562(2) A, b = 8.1065(5) A, c = 9.2489(5) A, α = 115.9990(10)°, β = 90.000(2)°, γ = 89.9750(10)°, V = 273.34(3) A3, Z = 4, dcalc = 7.659 g/cm3, space group Pb11. The experimental material for the single crystal XRD analysis is obtained on an automated Bruker X8 APEX diffractometer (MoK α radiation, graphite monochromator, CCD detector resolution 1024×1024 pixel, distance to the detector L = 50 mm, rotation about the φ axis 15 min) by the standard procedure, 2274 measured reflections, out of them 1523 independent (R(int) = 0.0352), R factor [I > 2σ(I)] = 0.0517, R factor (all measured) = 0.0694).