Die monoklinen Seltenerdmetall(III)-Chlorid-Oxidoarsenate(III) mit der Zusammensetzung SE ₅Cl₃[AsO₃]₄ (SE=La–Nd, Sm)

Abstract

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].

Composition and Crystal Structure of SmSb2O4Cl Revisited – and the Analogy of Sm1.5Sb1.5O4Br

“…More than twenty-five years later, with Lu 5 F 3 [AsO 3 ] 4 [4] the first analogous fluoride oxidoarsenate(III) was found to crystallize isotypically. Chloride-containing derivatives with the same formula, but completely different monoclinic crystal structures emerged a little earlier for the examples of Nd 5 Cl 3 [AsO 3 ] 4 [5] and Ce 5 Cl 3 [AsO 3 ] 4 , [6] as well as La 5 Cl 3 [AsO 3 ] 4 , Pr 5 Cl 3 [AsO 3 ] 4 and Sm 5 Cl 3 [AsO 3 ] 4 , [7] although they all display discrete ψ 1tetrahedra [AsO 3 ] 3-.…”

The Triclinic Lanthanoid(III) Halide Oxidoarsenates(III) Sm3Cl2[As2O5][AsO3] and Tm3Br2[As2O5][AsO3]

“…In comparison to hitherto described crystal structures of lanthanoid(III) halide oxidoarsenates(III), outstanding similarities can be observed. The monoclinic oxidoarsenates(III) with the composition Ln 5 Cl 3 [AsO 3 ] 4 ( Ln = La – Nd and Sm) exhibit an alternating stacking of the present oxide and halide layers in the crystal structure with different crystallographic positions for the Ln 3+ cations . In the crystal structures of the Ln 5 Cl 3 [AsO 3 ] 4 representatives, Ln 1 and Ln 2 are only coordinated by oxygen atoms with a coordination number of eight, whereas Ln 3 exhibits a (4+4)‐fold coordination of four oxygen atoms and four chloride anions.…”

“…The monoclinic oxidoarsenates(III) with the composition Ln 5 Cl 3 [AsO 3 ] 4 (Ln = La -Nd and Sm) exhibit an alternating stacking of the present oxide and halide layers in the crystal structure with different crystallographic positions for the Ln 3+ cations. [13] In the crystal structures of the Crystals of the thulium compound were further examined with electron-beam microprobe methods (see Experimental Section). To investigate the crystal growth and the possible incorporation of silica from the ampoule material or components of the fluxing agent, wavelength dispersive analyses of the crystal surface were performed.…”

“…The first members for the lighter lanthanoids of the series Ln 5 Cl 3 [AsO 3 ] 4 with Ln = La – Nd and Sm have been reported in 2006 and recently discussed again with regard to their syntheses and crystal structures. Moreover, the fluoride‐containing quaternary compounds Ln 5 F 3 [AsO 3 ] 4 with RE = Y, Yb and Lu are known as representatives for the heavier rare‐earth metals crystallizing with a non‐isotypic tetragonal structure in contrast to the monoclinic chloride congeners . With additional oxide anions, the series Ln 3 O X [AsO 3 ] 2 with Ln = La – Pr and Eu – Dy for X = Cl and Ln = La, Ce, Nd, Sm, Gd and Tb for X = Br as well as Ln 5 O 4 Cl[AsO 3 ] 2 with Ln = Nd and Pr can be observed .…”

“…Moreover, the fluoride-containing quaternary compounds Ln 5 F 3 [AsO 3 ] 4 with RE = Y, Yb and Lu are known as representatives for the heavier rare-earth metals crystallizing with a non-isotypic tetragonal structure in contrast to the monoclinic chloride congeners. [13][14][15][16] With additional oxide anions, the series Ln 3 OX[AsO 3 ] 2 with Ln = La -Pr and Eu -Dy for X = Cl and Ln = La, Ce, Nd, Sm, Gd and Tb for X = Br as well as Ln 5 O 4 Cl[AsO 3 ] 2 with Ln = Nd and Pr can be observed. [16][17][18][19][20][21][22]…”