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Zur Kenntnis ternärer Oxoarsenate(III) dreiwertiger Lanthanoide: Synthese und Charakterisierung von LnAsO3- und Ln 2As4O9-Vertretern mit Ln = La und Ce sowie Ln = Pr, Nd, Sm–Gd
Zeitschrift für Naturforschung B ( IF 0.8 ) Pub Date : 2023-10-09 , DOI: 10.1515/znb-2023-0069 Ralf J. C. Locke 1 , Florian Ledderboge 1 , Thomas Schleid 1
Zeitschrift für Naturforschung B ( IF 0.8 ) Pub Date : 2023-10-09 , DOI: 10.1515/znb-2023-0069 Ralf J. C. Locke 1 , Florian Ledderboge 1 , Thomas Schleid 1
Affiliation
The title compounds have been prepared from the elemental lanthanoids and arsenic sesquioxide in 1:1 and 2:3 molar ratios in the presence of a cesium-halide flux at temperatures near 1000 °C generating elemental arsenic as the by-product. With the preparation of B -type La[AsO3 ] crystallizing in the monoclinic space group P 21 /c with the lattice parameters a = 904.03(8), b = 789.96(7), c = 837.49(7) pm and β = 103.354(3)°, both A - and B -type Ln [AsO3 ] representatives are now available for lanthanum and cerium. The crystal structure consists of two crystallographically distinct Ln 3+ cations with eight- or ninefold coordination by O2− anions. The Ln 3+ cations are arranged in layers of (Ln 1)3+ and corrugated bilayers of (Ln 2)3+ cations in the (100) plane. The two different As3+ cations appear in [AsO3 ]3− units, which differ mainly in their environment of Ln 3+ cations. The successful synthesis of the compounds Ln 2 As4 O9 (Ln = Pr, Nd, Eu and Gd) reported here on the one hand closes the structural gap between cerium and neodymium, and on the other hand also extends the spectrum of ternary oxoarsenates(III) of lanthanoids to gadolinium, with the neodymium compound for the first time at standard temperature. The crystals of the Ln 2 As4 O9 compounds are triclinic (space group: P 1 ‾ $P\bar{1}$ ) with lattice parameters nicely reflecting the lanthanoid contraction from a = 690.61(5), b = 768.95(6), c = 959.72(8) pm, α = 96.927(3), β = 103.812(3), γ = 104.441(3)° for Pr2 As4 O9 to a = 676.12(5), b = 751.58(6), c = 951.57(8) pm, α = 96.462(3), β = 103.678(3), γ = 104.409(3)° for Gd2 As4 O9 with two crystallographically independent lanthanoid(III) positions. The oxidic environments on these sites show the shape of square antiprisms with significant distortions, but (Ln 2)3+ has a ninth oxygen contact in a capped antiprism. The linkage of the polyhedra creates layers in the ab plane, which are separated by the complex anions of arsenic. The oxoarsenate(III) units [AsO3 ]3− are linked by sharing oxygen corners to form both dinuclear [As2 O5 ]4− and cyclic tetranuclear [As4 O8 ]4− complex anions, which is why the compounds can also be represented with their structured molecular formula Ln 4 [As2 O5 ]2 [As4 O8 ]. The free electron pairs of the arsenic(III) cations point into channels, which are built up in the crystal structure along [010].
更新日期：2023-10-09
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