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Die monoklinen Seltenerdmetall(III)-Chlorid-Oxidoarsenate(III) mit der Zusammensetzung SE₅Cl₃[AsO₃]₄ (SE=La–Nd, Sm)

Goerigk, Felix C., Schander, Svetlana, Hamida, Makram Ben, Kang, Dong-Hee, Ledderboge, Florian, Wickleder, Mathias S., Schleid, Thomas
Zeitschrift für Naturforschung 2019 v.74 no.6 pp. 497-506
anions, arsenic, arsenic oxide, cations, ceric oxide, crystal structure, glass, oxygen, prisms, silica
The rare earth metal(III) chloride oxidoarsenates(III) with the composition RE₅Cl₃[AsO₃]₄ (RE = La–Nd, Sm) could be synthesized via solid-state methods through the reaction of arsenic sesquioxide (As₂O₃) with the corresponding rare earth metal compounds (La₂O₃, CeO₂ + metallic Ce, Pr₆O₁₁, Nd₂O₃ or metallic Sm) using several chloride-containing fluxing agents in evacuated silica glass ampoules. The compounds build up non-isotypic crystal structures in the monoclinic space groups C2/c for RE = La–Pr, and P2/c for RE = Nd and Sm. All rare earth metal(III) cations exhibit coordination numbers of eight. While (RE1)³⁺ and (RE2)³⁺ are only surrounded by oxygen atoms in the form of distorted square antiprisms or prisms, (RE3)³⁺ is coordinated square antiprismatically by four oxygen atoms and four chloride anions. Although the coordination polyhedra in both structures differ only marginally, their connection patterns show more pronounced differences. This regards especially the (RE)³⁺ cations and results from different site symmetries of the (Cl1)⁻ anions. All As³⁺ lone-pair cations are coordinated by three oxygen atoms to form ψ¹-tetrahedral [AsO₃]³⁻ complex anions with their non-binding (lone) electron pairs pointing into empty channels along [010].