Pr5F[SiO4]2[SeO3]3: Another Complex Fluoride Oxosilicate Oxoselenate(IV)

• Published in: Zeitschrift für anorganische und allgemeine Chemie (1950) Vol. 638; no. 5; pp. 779 - 784
• Main Authors: Lipp, Christian, Burns, Peter C., Schleid, Thomas
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.04.2012; WILEY‐VCH Verlag
• Subjects: Fluoride derivatives; Oxosilicates; Praseodymium oxoselenates(IV); X-ray diffraction
• ISSN: 0044-2313; 1521-3749
• DOI: 10.1002/zaac.201100493

During attempts to synthesize lanthanoid(III) fluoride oxoselenates(IV) with the simple composition MF[SeO3], not only Pr3F[SeO3]4, but also Pr5F[SiO4]2[SeO3]3 appeared as pale green crystalline by‐products in the case of praseodymium. Pr5F[SiO4]2[SeO3]3 crystallizes triclinically in space group P$\bar{1}$ (no. 2) with a = 701.14(5), b = 982.68(7), c = 1286.79(9) pm, α = 70.552(3), β = 76.904(3), γ = 69.417(3)° and Z = 2. The five crystallographically different Pr3+ cations on the general positions 2i show coordination numbers of eight and nine. [(Pr1)O8]13– and [(Pr2)O8]13– polyhedra are connected to$\bar{1}${[(Pr1, 2)2O12]18–} chains along the [100] direction. [(Pr3)O7F]12–, [(Pr4)O8F]14– and [(Pr4)O8F]14– polyhedra generate [F(Pr3, 4, 5)3O19]30– units about their central F– anion in triangular Pr3+ coordination. These units form $\bar{1}${[F(Pr3, 4, 5)3O16]24–} strands, again running parallel to [100]. Their alternating connection with the $\bar{1}${[(Pr1, 2)2O12]18–} chains results in $\bar{1}${[Pr5O20F]26–} sheets parallel to the (001) plane. Like in the already known related compound Er3F[SiO4][SeO3]2, a three‐dimensional network $\bar{1}${[Pr5O17F]20–} is achieved without the contribution of both the tetravalent silicon and selenium components. However, two Si4+ and three Se4+ cations forming tetrahedral [SiO4]4– and ψ1‐tetrahedral [SeO3]2– units with all O2– anions guarantee the charge balance. The formation of Pr5F[SiO4]2[SeO3]3 was observed when praseodymium sesquioxide (Pr2O3: in‐situ produced from Pr and Pr6O11 in a molar ratio of 3/11:4/11),praseodymium trifluoride (PrF3) and selenium dioxide (SeO2) in 1:1:3 molar ratios were reacted with CsBr as fluxing agent for five days at 750 °C in evacuated fused silica (SiO2) ampoules.