Pale yellow, needle‐shaped single crystals of Sm2[SeO3]3 were obtained by heating stoichiometric mixtures of Sm2O3 and SeO2 (molar ratio: 1:3) along with substantial amounts of CsCl as fluxing agent in evacuated sealed silica tubes at 830 °C for one week. According to X‐ray single‐crystal diffraction data, Sm2[SeO3]3 crystallizes triclinic (space group: $P{\bar 1}$ ) with two formula units per unit cell of the dimensions a = 698.62(7), b = 789.71(8), c = 910.34(9) pm, α = 96.693(5), β = 104.639(5), γ = 115.867(5)°. Its crystal structure contains two crystallographically distinct Sm3+ cations in eight‐ and ninefold coordination with oxygen atoms arranged as distorted uncapped or capped square antiprisms (d(Sm3+−O2−) = 232−271 pm). These [(Sm1)O8] and [(Sm2)O9] polyhedra share opposite edges and faces to form zigzag chains along [100] with discrete pyramidal [SeO3]2− anions bridging units. Further linkage by [SeO3]2− anions in [010] direction leads to a three‐dimensional network, which exhibits almost rectangular channels along [111]. These tunnels offer width enough to incorporate the free non‐bonding electron pairs („lone pairs”︁) at the Se4+ cations, since all nine different Ψ1‐tetrahedral [SeO3]2− groups (d(Se4+−O2−) = 165−173 pm, ∢(O–Se–O) = 94 – 108°) exhibit a pronounced stereochemical „lone‐pair”︁ activity. For not being isotypic with neither triclinic Er2[SeO3]3 (CN(Er3+) = 7 and 8) nor the remainder rare‐earth metal(III) oxoselenates(IV) of the composition M2[SeO3]3 (≡ M2Se3O9; M = Sc, Y, La, Ce – Lu), Sm2[SeO3]3 claims a unique crystal structure among them.
Inhaltsu È bersicht. Hellgru È ne Einkristalle von Pr 4 (SeO 3 ) 2 -(SeO 4 )F 6 wurden bei der Zersetzung von Pr 2 (SeO 4 ) 3 in Gegenwart von LiF in einer Goldampulle erhalten. Die Verbindung kristallisiert monoklin (C2/c, Z = 4, a = 2230,5(3), b = 710,54(9), c = 835,6(1) pm, b = 98,05(2)°, R all = 0,0341) und entha È lt zwei kristallographisch unterschiedliche Pr 3+ -Ionen. Pr(1) 3+ ist von sechs Fluoridionen und zwei chelatisierend angreifenden SeO 3 2± -Gruppen umgeben (CN = 10), Pr(2) 3+ wird von vier Fluoridionen, drei einza È hnig koordinierenden SeO 3 2± und zwei SeO 4 2± -Gruppen umgeben. Da eines der Selenationen chelatisierend angreift, hat auch Pr(2) 3+ die CN 10. Die Selenitgruppen sind ihrerseits von fu È nf, die Selenatgruppen von vier Pr 3+ -Ionen umgeben, wa Èhrend die F ± -Ionen an drei bzw. vier Pr 3+ -Ionen gebunden sind. Die Verknu È pfung der Koordinationspolyeder fu È hrt zu Hohlra È umen in der Kristallstruktur, die der Aufnahme der freien Elektronenpaare der Selenitionen dienen. Hellgelbe Einkristalle von NaSm(SeO 3 )(SeO 4 ) bilden sich bei der Umsetzung von Sm 2 (SeO 4 ) 3 und NaCl, ebenfalls in einer Goldampulle. Die monokline Verbindung (P2 1 /c, Z = 4, a = 1066,9(2), b = 691,66(8), c = 825,88(9) pm, b = 91,00(2)°, R all = 0,0530) entha È lt zehnfach von Sauerstoffatomen koordinierte Sm 3+ -Ionen. Die Sauerstoffatome geho È ren zu fu È nf SeO 3 2± -Gruppen, von denen zwei chelatisierend angreifen und zwei SeO 4 2± -Ionen, von denen eines chelatisierend koordiniert. Die Natriumionen sind von fu È nf SeO 4 2± -Ionen und einer SeO 3 2± -Gruppe umgeben. Eines der Selenationen fungiert als chelatisierender Ligand, so daû fu È r Na + eine Koordinationzahl von sieben resultiert. Jede Selenitgruppe ist ihrerseits von sechs (5´Sm 3+ und 1´Na + ), jedes Selenation von sieben Kationen (5´Na + und 2´Sm 3+ ) umgeben.Abstract. Light green single crystals of Pr 4 (SeO 3 ) 2 (SeO 4 )F 6 have been obtained from the decomposition of Pr 2 (SeO 4 ) 3 in the presence of LiF in a gold ampoule. The monoclinic compound (C2/c, Z = 4, a = 2230.5(3), b = 710.54(9), c = 835.6(1) pm, b = 98.05(2)°, R all = 0.0341) contains two crystallographically different Pr 3+ ions. Pr(1) 3+ is attached by six fluoride ions and two chelating SeO 3 2± groups (CN = 10), Pr(2) 3+ is surrounded by four fluoride ions, three monodentate SeO 3 2± and two SeO 4 2± groups. One of the latter acts as a chelating ligand, so the CN of Pr(2) 3+ is 10. The selenite ions are themselves coordinated by five and the selenate ions by four Pr 3+ ions. The coordination number of the F ± ions is three and four, respectively. The linkage of the coordination polyhedra leads to cavities in the crystal structure which incorporate the lone pairs of the selenite ions. The reaction of Sm 2 (SeO 4 ) 3 and NaCl in gold ampoules yielded light yellow single crystals of NaSm(SeO 3 )(SeO 4 ). The monoclinic compound (P2 1 /c, Z = 4, a = 1066.9(2), b = 691.66(8), c = 825.88(9) pm, b = 91.00(2)°, R all = 0.0530) contains tenfold oxygen coordinated Sm 3+ ions. The ...
Single crystals of Er2(SeO4)3 ・ 8H2O were obtained by dissolving Er2O3 in selenic acid. The selenate crystallizes in the monoclinic space group C2/c (Z = 4, a = 1372.8(2), b = 687.51(7), c = 1860.2(3) pm, β = 101.85(2)◦, Rall = 0.0518) and contains the Er3+ ions in eightfold coordination of oxygen atoms that belong to two crystallographically different SeO42− ions and to four H2O molecules. According to DTA/TG measurements and temperature dependent powder diffraction data, Er2(SeO4)3 ・8H2O decomposes in several steps yielding finally Er2O3. Er2(SeO4)3 and Er2(SeO3)3 could be identified as intermediates, and for Er2(SeO4)3 a phase transition was detected.
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