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The Quaternary Arsenide Oxides Ce Au As O and Pr Au As O

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The Quaternary Arsenide Oxides Ce Au As O and Pr Au As O Z. Naturforsch. 2016; 71(12)b: 1245–1252 Timo Bartsch, Rolf-Dieter Hoffmann and Rainer Pöttgen* The quaternary arsenide oxides Ce9Au5–xAs8O6 and Pr9Au5–xAs8O6 DOI 10.1515/znb-2016-0160 and Ag+ and this is possible with uranium and especially Received July 19, 2016; accepted July 26, 2016 thorium. Electronic structure calculations [14] show sub- stantial covalent bonding within the [Th O ] and [Cu Pn ] Abstract: The quaternary gold arsenide oxides 2 2 2 2 layers which are held together by ionic interactions. The Ce Au As O and Pr Au As O were synthesized from 9 5−x 8 6 9 5−x 8 6 charge transfers range from 1.94 to 2.08 e−, much smaller the rare earth elements (RE), rare earth oxides, arsenic than expected from a formal charge splitting (Th O )4+ and gold powder at maximum annealing temperatures 2 2 (Cu Pn )4−. of 1173 K. The structures were refined from single crys- 2 2 Polycrystalline and single crystalline UCuPO samples tal X-ray diffractometer data: Pnnm, a = 1321.64(6) pm, show a high Néel temperature of T = 220 K [8–10]. The b = 4073.0(3), c = 423.96(2), wR2 = 0.0842, 3106 F2 values, N spin alignment (AF I type; + − + −) was determined from 160 variables for Ce Au As O and Pnnm, a = 1315.01(4), 9 4.91(4) 8 6 neutron diffraction data. Isotypic NpCuPO [10] was b = 4052.87(8), c = 420.68(1) pm, wR2 = 0.0865, 5313 F2 obtained by reaction of neptunium metal, CuO and phos- values, 160 variables for Pr Au As O . They represent 9 4.75(1) 8 6 phorus. Resistivity measurements indicate long-range a new structure type and show a further extension of magnetic ordering around 90 K which has been confirmed pnictide oxide crystal chemistry. A complex polyanionic by DFT calculations. gold arsenide network [Au As ]15− (with some disorder in 5 8 Besides the ZrCuSiAs-type phases, U Cu P O (formerly the gold substructure) is charge compensated with poly- 2 2 3 reported as a ternary phosphide U Cu P [15–18] with a cationic strands of condensed edge-sharing O@RE and 4 4 7 4/4 half-occupied phosphorus site) and U Cu As O [19] have O@RE tetrahedra ([RE O ] 12+) as well as RE3+ cations in 2 2 3 4/3 4 3 2 been reported. These structures contain similar layers cavities. of condensed OU4/4 and CuPn4/4 tetrahedra. U2Cu2P3O Keywords: arsenide oxides; crystal structure. orders antiferromagnetically at TN = 146 K [16]. Resistiv- ity measurements on single crystals (grown with iodine as transport agent) show distinctly anisotropic transport 1 Introduction behavior [17]. The rare earth-based phosphide oxides RE3Cu4P4O2 (RE = La–Nd, Sm) [20–23] and arsenide oxides RE Cu As O The crystal chemistry of pnictide (Pn) oxides [1–5] is domi- 3 4 4 2 (RE = La–Pr) [24] also exhibit layers of condensed CuPn nated by compounds with the ZrCuSiAs-type structure. 4/4 tetrahedra, however, they are related by a mirror plane, More than 150 phases with this structure type have been leading to the formation of P and As dumbbells with reported. The most prominent examples are the super- 2 2 single bond character. Incorporation of purely ionic LaOCl conductors LaFeAsO F (x = 0.05–0.12; T = 26 K) [6] and 1−x x C slabs into La Cu P O and La Cu As O was observed for SmFeAsO F (x = 0.1; T = 55 K) [7]. Besides the intensive 3 4 4 2 3 4 4 2 1−x x C La Cu P O Cl (≡ La Cu P O ⋅2LaOCl) [23] and isotypic studies on the iron based phases, such pnictide oxides have 5 4 4 4 2 3 4 4 2 La Cu As O Cl (≡ La Cu As O ⋅2LaOCl) [25], nicely extend- also been reported with manganese, cobalt, zinc or ruthe- 5 4 4 4 2 3 4 4 2 ing the structural chemistry of these pnictide oxides. nium [2]. Comparatively few representatives are known The gold-based pnictide oxides show different with the coinage metals, i.e. UCuPO [8–10], ThCuPO [11], crystal chemistry. Nd Au As O and Sm Au As O [26] ThAgPO [12, 13] and ThCuAsO [11]. For an electron-precise 10 3 8 10 10 3 8 10 are remarkable compounds with Au(I) in almost square- description one needs a tetravalent cation besides Cu+ planar coordination by arsenic dumbbells. These poly- anionic layers are stacked and charge-compensated by polycationic layers of condensed edge-sharing ORE4/4 *Corresponding author: Rainer Pöttgen, Institut für Anorganische tetrahedra. Almost trigonal-planar coordination of Au(I) und Analytische Chemie, Universität Münster, Corrensstrasse 30, by two P3− and one P 4− dumbbell (end-on) occurs in the 48149 Münster, Germany, e-mail: [email protected] 2 = Timo Bartsch and Rolf-Dieter Hoffmann: Institut für Anorganische phosphide oxides RE2AuP2O (RE La–Nd) [27, 28]. Both und Analytische Chemie, Universität Münster, Corrensstrasse 30, the polyanionic and the polycationic substructures are 48149 Münster, Germany one-dimensional and arranged in the motif of a hexagonal 1246 T. Bartsch et al.: The quaternary arsenide oxides Ce9Au5−xAs8O6 and Pr9Au5−xAs8O6 rod packing, an entirely new motif in pnictide oxide struc- was obtained almost phase pure (see Fig. 1). The cerium tural chemistry. compound on the contrary could not be synthesized In continuation of our phase analytical studies of the without rare earth oxide and arsenide impurities. quaternary systems RE-Au-Pn-O we obtained well-shaped Suitable crystals for structure determination were single crystals of Ce9Au5−xAs8O6 and Pr9Au5−xAs8O6 from prepared via salt flux synthesis [29]. Polycrystalline NaCl/KCl salt flux synthesis. The structural chemistry of RE9Au5−xAs8O6 (200–300 mg) and an equimolar NaCl/KCl these arsenide oxides is reported herein. mixture (~1 g) were sealed in evacuated silica ampoules, heated up to 1223 K (72 h, 100 K h−1), slowly cooled down to 773 K (2 K h−1) and finally to room temperature by shutting off the furnace. Slat-shaped single crystals 2 Experimental (especially for the praseodymium compound, see Fig. 2) with metallic luster could be isolated from the reaction 2.1 Synthesis mixture after dissolving the NaCl/KCl flux with deminer- alised water. Starting materials for the syntheses were cerium (Sigma- Aldrich, >99.9%), praseodymium (Sigma-Aldrich, >99.9%), cerium(IV) oxide (ChemPur, >99.99%), praseodymium 2.2 X-ray image plate data and data (III,IV) oxide (ChemPur, >99.9%), gold (Agosi, >99.9%) collections and arsenic granules (Ventron). Filings of cerium and pra- seodymium were prepared under dried paraffin oil (sodium The polycrystalline RE9Au5−xAs8O6 samples were charac- wire), washed with cyclohexane and stored under argon terized by Guinier powder patterns: Enraf Nonius FR 552 prior to synthesis. Argon was purified with titanium sponge camera, image plate system Fuji film, BAS-1800, CuKα1 (870 K), silica gel and molecular sieves. Gold powder was radiation and α-quartz (a = 491.30, c = 540.46 pm) as an obtained by dissolving gold pieces in aqua regia and sub- internal standard. The orthorhombic lattice parameters 3 sequent precipitation using (NH4)2Fe(SO4)2 · xH2O (VWR, (a = 1321.7(3), b = 4073.5(6), c = 423.9(1) pm, V = 2.2823 nm >99%). Arsenic was resublimed, stored under argon and for the Ce9Au5−xAs8O6 and a = 1316.1(2), b = 4051.4(6), 3 pulverized prior synthesis. c = 421.1(1) pm, V = 2.2453 nm for the Pr9Au5−xAs8O6 Black, polycrystalline samples were prepared via sample) were deduced from least-squares refinements. mixing filings of the rare earth elements (RE), their Correct indexing was facilitated by intensity calculations oxides, gold powder and powder of arsenic in the molar with LazyPulverix [30]. 63 6 ratios 6:3:5:8 (Ce9Au5As8O6) and /11: /11:5:8 (Pr9Au5As8O6). Well-shaped single crystals of both compounds Amounts of 0.5 g were cold-pressed to pellets, sealed in were glued to thin quartz fibers using bees wax and first evacuated silica ampoules and heated in a resistance tested by Laue photographs on a Buerger camera (white furnace; first up to 873 K (24 h annealing) and finally molybdenum radiation, image plate technique, Fuji- at 1173 K (72 h annealing). Heating rates were 100 K h−1, film, BAS-1800). Intensity data were collected at ambient cooling was done by shutting off the furnace. Except for temperature by use of a Stoe StadiVari diffractometer a small impurity of elemental gold and with regard to the equipped with a Mo micro focus source and a Pilatus limit of detection via XRD, the praseodymium compound detection system. Due to a Gaussian-shaped profile of the Fig. 1: Experimental (blue) and calculated (red) Guinier powder pattern (CuKα1 radiation) of Pr9Au4−xAs8O6. T. Bartsch et al.: The quaternary arsenide oxides Ce9Au5−xAs8O6 and Pr9Au5−xAs8O6 1247 3 Results and discussion 3.1 Structure refinements Analyses of the four data sets revealed primitive orthorhombic lattices and the systematic extinctions were compatible with the centrosymmetric space group Pnnm. The starting atomic parameters were deduced with the Superflip algorithm [31] and the structures were refined 2 with Jana2006 (full-matrix least-squares on Fo ) [32] with anisotropic displacement parameters for the RE, Au and As atoms and isotropic ones for the oxygen atoms. Except for the partially occupied Au3 and Au4 sites, all posi- tions were fully occupied within two standard deviations. The partial occupancies were refined as least-squares variables in the final cycles.
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