Vier Oxidselenide des Praseodyms: Pr10OSe14, Pr2OSe2, Pr2O2Se und Pr4O4Se3 |
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Authors: | Frank A Weber Thomas Schleid |
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Abstract: | Four Oxyselenides of Praseodymium: Pr10OSe14, Pr2OSe2, Pr2O2Se, and Pr4O4Se3 By reacting elemental praseodymium with selenium and selenium dioxide (SeO2) as oxygen source in suitable stoichiometric ratios, it is possible to prepare the single‐phase praseodymium(III) oxyselenides Pr10OSe14, Pr2OSe2, Pr2O2Se, and Pr4O4Se3 each within seven days at 750 °C in torch‐sealed evacuated silica tubes. The addition of equimolar amounts of CsCl as flux guarantees quick and complete reactions to single‐crystalline, water‐ and air‐resistant products. Pr10OSe14 (tetragonal, I41/acd; a = 1568.74(8), c = 2073.4(1) pm; Z = 8) crystallizes as dark‐red polyhedra. Pr2OSe2 (monoclinic, P21/c; a = 882.05(6), b = 732.89(5), c = 732.94(5) pm, β = 100.288(7)°; Z = 4) and Pr2O2Se (trigonal, P3m1; a = 401.12(3), c = 705.51(5) pm; Z = 1) accumulate as yellowish green platelets with rectangular and hexagonal cross‐sections, respectively. Pr4O4Se3 (orthorhombic, Amm2; a = 849.92(6), b = 402.78(3), c = 1292.57(9) pm; Z = 2) forms lath‐shaped, pleochroitic crystals with a strong tendency for twinning, which appear green along 001], but red along 100] and 010]. All the crystal structures of these oxyselenides are dominated by OPr4] tetrahedra, whose condensation rate strongly increases with growing oxygen content. Se2– anions, in the case of Pr4O4Se3 (≡ {(Pr3+)4(O2–)4(Se2–)Se2]2–}) as well as Se2]2– dumb‐bells, take care of charge balance and threedimensional cross‐linkage. In the oxygen‐poor Pr10OSe14 the OPr4]10+ tetrahedra occur isolated and are embedded in the complex anionic matrix framework {(Pr6Se14)10–}. The oxygen‐rich links in this row show according to {OPr3/3Pr1/1]}Se2 (≡ Pr2OSe2), {(OPr4/4]2)}Se (≡ Pr2O2Se), and {(OPr4/4]4)}Se2]Se (≡ Pr4O4Se3) OPr4] tetrahedra which are connected to more or less dense layers via corners and respectively one, three and four common edges. |
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Keywords: | Praseodymium Oxyselenides Crystal structures |
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