Structure of dysprosium polysulfide DyS1.83 (Dy6S11) according to X-ray diffraction analysis

The crystal structure of a single crystal of dysprosium polysulfide DyS1.83 = Dy6S11 is determined. The unit cell parameters are similar to those esta blished for DyS1.76 = DyS1.76, but the composition is different. The unit c ell is monoclinic, space group P2(1)/m, a = 11.009(2), b = 11.531(2), c = 1 1.023(1) Angstrom, beta = 91.152(8)degrees, V = 1398.1(4) Angstrom(3); for Z = 4 this gives the composition Dy6S11, regarding the experimental values of the partial statistic of the S atoms and d(calc) = 6.303 g/cm(3) (Enraf- Nonius CAD-4 automatic diffractometer, lambda MoKalpha, R-aniso = 0.0349 fo r 6381 unique I-hkl > 2 sigma(I) of 9804 measured ones). An empirical absor ption correction was applied based on transmission curves and habit data. T he polysulfide is a PbFCl type structure; the monoclinic unit cell paramete rs are related to a(0) and c(0) of the tetragonal cell of PbFCl as [101] co ngruent to 4a(0), [010] congruent to 3a(0), [10(1) over bar] congruent to 2 c(0). The crystal is a twin with the ratio of components k(2) = 1 - k(1) = 0.243(2) and a transition matrix 001/<0(1)over bar>0/100. The composition D yS1.83+/-0.02 agrees with the chemical analysis data and the experimental v alue d(exp) = 6.30+/-0.08 g/cm(3). The phase individuality of the polysulfi de is confirmed by the form of the P-T projection of the P-T-X diagram of t he Dy-S system.