title: New quaternary arsenide oxides with square planar coordination of gold(I) - structure, (197)Au Mössbauer spectroscopic, XANES and XPS characterization of Nd10Au3As8O10 and Sm10Au3As8O10.
abstract: The quaternary gold(I) arsenide oxides Nd10Au3As8O10 and Sm10Au3As8O10 were synthesized in sealed quartz ampoules from the rare earth (RE) elements, their appropriate sesquioxides, arsenic, arsenic(III) oxide and finely dispersed gold at maximum annealing temperatures of 1223 K. Both structures were refined from X-ray single crystal diffractometer data at room temperature and at 90 K. Nd10Au3As8O10 and Sm10Au3As8O10 crystallize with a new structure type that derives from the BaAl4 structure through distortions and formation of ordered vacancies. The structures consist of stacked polycationic [RE10O10](10+) layers with oxygen in tetrahedral rare earth coordination and polyanionic [Au(I)3(As2)4](10-) layers with gold in square planar or rectangular planar coordination of four arsenic dumbbells (255 pm As1-As2). In contrast to the well known ionic rare earth oxide layers, the gold arsenide layers rather show covalent bonding and account for the metallic nature of these two new arsenide oxides. This is confirmed by electronic structure calculations and resistivity measurements. The oxidation state of gold was investigated by (197)Au Mössbauer, X-ray absorption near edge structure (XANES) and photoelectron (XPS) spectroscopy. Due to missing comparative gold arsenide compounds, the monovalent gold phosphide oxides RE2AuP2O were measured for comparison. The XANES measurements additionally comprise monovalent gold arsenides REAuAs2. The XPS study contains BaAuAs as reference compound instead. Combination of all data clearly indicates Au(I), which was not observed in square planar coordination up to now. Temperature dependent magnetic susceptibility data show Curie-Weiss paramagnetism for Nd10Au3As8O10 and no magnetic ordering down to 2.5 K. Sm10Au3As8O10 shows the typical Van Vleck type paramagnetism for samarium compounds along with a transition to an antiferromagnetically ordered state at TN = 8.6 K.
authors.affiliation: Institut für Anorganische und Analytische Chemie, Universität Münster, Corrensstrasse 30, D-48149 Münster, Germany. pottgen@uni-muenster.de.
authors.forename: Timo
authors.initials: T
authors.lastname: Bartsch
authors.forename: Oliver
authors.initials: O
authors.lastname: Niehaus
authors.forename: Dirk
authors.initials: D
authors.lastname: Johrendt
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Makoto
authors.initials: M
authors.lastname: Seto
authors.forename: Paula M
authors.initials: PM
authors.lastname: Abdala
authors.forename: Manfred
authors.initials: M
authors.lastname: Bartsch
authors.forename: Helmut
authors.initials: H
authors.lastname: Zacharias
authors.forename: Rolf-Dieter
authors.initials: RD
authors.lastname: Hoffmann
authors.forename: Birgit
authors.initials: B
authors.lastname: Gerke
authors.forename: Ute Ch
authors.initials: UCh
authors.lastname: Rodewald
authors.forename: Rainer
authors.initials: R
authors.lastname: Pöttgen