Joseph Wontcheu

Tb2Se2O7: Terbium(III) Oxide Oxoselenate(IV) according to Tb2O[SeO3]2 with a “Lone—Pair” Channel Structure

The colourless title compound Tb2Se2O7 (≡ Tb2O [SeO3]2, terbium(III) oxide oxoselenate(IV)) was obtained by reacting a mixture of Tb4O7, Tb and SeO2 in a 3:2:14-molar ratio at 850 °C for seven days in an evacuated silica vessel as needle-shaped single crystals. It crystallizes tetragonally (space group: P42/ncm, a = 1064.57(8), c = 521.56(4) pm, c/a = 0.490, Z = 4) and exhibits Tb3+ cations in square-antiprismatic coordination of eight oxygen atoms each. Six of the latter belong to six different isolated ψ1-tetrahedral [SeO3]2— anions whereas the remaining two are not bonded to selenium at all. Their coordination sphere actually consists of four Tb3+ cations arranged as tetrahedron. These [OTb4]10+ tetrahedra form infinite one-dimensional {[OTb4/2]4+} chains along [001] by sharing trans-oriented edges which are packed such that a central strand is quadratically surrounded in (001) projection by four chains at a distance of √2 and another square of four more of them a factor of √2 (≡ the value of a) further apart and rotated by 45°. Charge balance and three-dimensional interconnection of this particular rod-packing occurs via discrete trigonal [SeO3]2— pyramids so that the whole structure gets strongly influenced by the stereochemical lone-pair activity of these groups. Remarkably enough, the 4¯ symmetry of the {[OTb4/2]4+} chains is perfectly repeated by the “lone-pair” channels of the non-binding electrons at the Se4+ cations. Tb2Se2O7: Terbium(III)-Oxid-Oxoselenat(IV) gemas Tb2O[SeO3]2 mit einer Kanalstruktur aus nicht-bindenden Elektronenpaaren Die farblose Titelverbindung Tb2Se2O7 (≡ Tb2O-[SeO3]2, Terbium(III)-Oxid-Oxoselenat(IV)) wurde durch die Umsetzung eines Gemenges Tb4O7, Tb und SeO2 im molaren Verhaltnis 3:2:14 in evakuierten Quarzglasampullen innerhalb von sieben Tagen bei 850 °C in Form von nadelformigen Einkristallen erhalten. Sie kristallisiert tetragonal (Raumgruppe: P42/ncm; a = 1064, 57(8), c = 521, 56(4) pm, c/a = 0, 490; Z = 4) und enthalt Tb3+-Kationen in quadratisch-antiprismatischer Koordination von acht Sauerstoffatomen. Sechs davon gehoren zu sechs unterschiedlichen, isolierten, ψ1-tetraedrischen [SeO3]2—-Anionen, wahrend die restlichen beiden nicht an Selen gebunden sind. Deren Koordinationssphare besteht vielmehr aus vier Tb3+-Kationen in tetraedrischer Anordnung. Diese [OTb4]10+-Tetraeder bilden durch Verknupfung uber trans-standige Kanten eindimensional unendliche Ketten {[OTb4/2]4+} parallel [001], die so gepackt sind, das ein Zentralstrang in (001)-Projektion im Abstand √2 quadratisch von vier nahen und von noch vier um den Faktor √2 (≡ a) weiter entfernten Ketten, deren projiziertes Quadrat um 45° gedreht ist, umgeben wird. Der Ladungsausgleich und die dreidimensionale Vernetzung dieser speziellen Stabpackung erfolgt durch diskrete, trigonale [SeO3]2—-Pyramiden, so das die Gesamtstruktur stark von der stereochemischen Aktivitat der nicht-bindenden Elektronenpaare dieser Baugruppen beeinflust ist. Bemerkenswerterweise wiederholt sich die 4¯-Symmetrie der {[OTb4/2]4+}-Ketten auch in den Kanalen, die durch die nicht-bindenden Elektronenpaare („lone pairs”) der Se4+-Kationen gebildet werden.

CsTmCl2[SeO3]: a quinary phase in the system CsCl/TmOCl/SeO2

CsTmCl 2 [SeO 3 ] was prepared by reaction of a stoichiometric mixture of Tm 2 O 3 , TmCl 3 , SeO 2 and CsCl in an evacuated torch-sealed silica tube at 830°C for 7 days as colourless single crystals (monoclinic, P2 1 /n; a = 658.92(5), b = 689.26(6). c =1752.5(1) pm, β = 99.093(7)°, Z = 4; κ-CCD, R all = 0.035, GooF = 1.090). The structure is characterized by layers parallel to (001) consisting of parallel zigzag strands 1 ∞{[TmO e 4/2 O t 1/1 Cl t 2/1 ] 5- }(≡ 1 ∞{(TmO 3 Cl 2 ] 5- }) with both chloride anions occupying apical positions in the pentagonal bipyramid [TmO 5 Cl 2 ] (d(Tm-O)=225-240pm, a(Tm-Cl)=261 pm, 2 ×). Four of the five equatorial oxygen atoms are utilized to share trans-edges, whereas one remains terminal and is syndiotactically ordered along the chain direction [010]. Within the layers these different chains are held together by Se 4+ cations via both an edge and a vertex of a trigonal [SeO 3 ] 2 pyramid. The Cs + coordination sphere can be described as a (2+1)-capped trigonal prism (d(Cs-Cl) = 336-385 pm, 6 x ) with all three oxygen atoms (d(Cs-O) = 320, 383 and 407 pm) being the triangular face of a single [SeO 3 ] 2- anion. The crystal structure is strongly influenced by the stereochemical lone-pair effect at the Se 4+ cations reflected by the formation discrete of ψ 1 -tetrahedral [SeO 3 E] 2- groups (E = non-binding electron pair) with Se-O distances of 166, 170 and 171 pm.

Ho2O[SiO4] und Ho2S[SiO4]: Zwei Chalkogenid-Derivate von Holmium(III)-ortho- Oxosilicat

Ho2O[SiO4] kristallisiert monoklin mit der Raumgruppe P21/c (a = 904, 15(9), b = 688, 93(7), c = 667, 62(7) pm, β = 106, 384(8)°, Z = 4) im A-Typ der Selten-Erd(III)-Oxid-Oxosilicate. Es entsteht in Form gelber, plattchenformiger Einkristalle als Nebenprodukt eines Versuchs zur Darstellung von Ho3Cl[SiO4]2 nach Umsetzung von Ho2O3 und SiO2 im Verhaltnis 4 : 6 mit einem Uberschus an HoCl3 als Flusmittel durch siebentagiges Tempern bei 1000 °C in evakuierten Kieselglasampullen. Die beiden kristallographisch unterschiedlichen Ho3+-Kationen weisen Koordinationszahlen von 8+1 und 7 auf, mit 2+1-fach uberkappten trigonalen Prismen bzw. Oktaedern, deren eine Ecke sich durch zwei statt einem koordinierenden Teilchen zur Kante umformt, als Koordinationsfiguren. Das nicht an Silicium gebundene O2—-Anion ist tetraedrisch von vier Ho3+-Kationen umgeben und bildet mit diesen durch Kanten- und Eckenverknupfung eine Schicht gemas {[(O5)(Ho1)1/1(Ho2)3/3]4+} parallel (100) aus, in deren rautenformigen Maschen die isolierten Oxosilicat-Tetraeder [SiO4]4— zu liegen kommen. Ho2S[SiO4] kristallisiert orthorhombisch mit der Raumgruppe Pbcm (a = 605, 87(5), b = 690, 41(6), c = 1064, 95(9) pm, Z = 4). Auch dieses stellt ein Nebenprodukt dar, das bei der Synthese von Ho2OS2 durch Reaktion eines Gemenges von Ho2O3, Ho und S mit der Wand der als Behalter verwendeten evakuierten Kieselglasampulle in einem Uberschus an CsCl als Flusmittel bei 800 °C einkristallin entsteht. Die Struktur der gelben, plattchenformigen, luft- und wasserbestandigen Einkristalle unterscheidet ebenfalls zwei Ho3+-Kationen mit doppelt uberkappten trigonalen Prismen bzw. Trigondodekaedern als Koordinationspolyedern fur CN = 8. Die S2—-Anionen sind annahernd quadratisch planar von vier Ho3+-Kationen umgeben, befinden sich jedoch vollstandig auserhalb dieser Ebene. Die [SHo4]10+-Quadrate bilden durch Eckenverknupfung eine stark gewellte Schicht gemas {[(S)(Ho1)2/2(Ho2)2/2]4+} senkrecht zu [100]. Die isolierten Oxosilicat-Tetraeder [SiO4]4— kommen hier im Gegensatz zum Oxid-Oxosilicat nicht innerhalb der ebenfalls rautenformigen Maschen dieser Schichten zu liegen, sondern in Blickrichtung [100] sowohl ober- als auch unterhalb der (Ho2)3+-Kationen. Ho2O[SiO4] and Ho2S[SiO4]: Two Chalcogenide Derivatives of Holmium(III) ortho-Oxosilicate Ho2O[SiO4] crystallizes monoclinically with the space group P21/c (a = 904.15(9), b = 688.93(7), c = 667.62(7) pm, β = 106.384(8)°, Z = 4) in the A-type structure of rare-earth(III) oxide oxosilicates. Yellow platelet-shaped single crystals were obtained as by-product during an experiment to synthesize Ho3Cl[SiO4]2 by reacting Ho2O3 and SiO2 in the ratio 4 : 6 with an excess of HoCl3 as flux at 1000 °C for seven days in evacuated silica ampoules. Both crystallographically different Ho3+ cations show coordination numbers of 8+1 and 7 with coordination figures of 2+1-fold capped trigonal prisms and octahedra, in which one of the vertices changes to an edge by two instead of one coordinating atoms, respectively. The O2— anion not linked to silicon is surrounded tetrahedrally by four Ho3+ cations which built a layer parallel (100) by vertex- and edge-sharing of the [OHo4]10+ units according to {[(O5)(Ho1)1/1(Ho2)3/3]4+}. Within rhombic meshes of these layers the isolated oxosilicate tetrahedra [SiO4]4— come to lie. Ho2S[SiO4] crystallizes orthorhombically in the space group Pbcm (a = 605.87(5), b = 690.41(6), c = 1064.95(9) pm, Z = 4). It also emerged as a single-crystalline by-product obtained during the synthesis of Ho2OS2 by reaction of a mixture of Ho2O3, Ho and S with the wall of the evacuated silica tube used as container with an excess of CsCl as flux at 800 °C. The structure of the yellow platelet-shaped, air and water resistant crystals also distinguishes two Ho3+ cations with bicapped trigonal prisms and trigondodecahedra as coordination polyhedra for CN = 8. The S2— anions are almost square planar surrounded by four Ho3+ cations, but situated completely outside this plane. The [SHo4]10+ squares form strongly corrugated layers perpendicular to [100] by corner-sharing according to {[(S)(Ho1)2/2(Ho2)2/2]4+}. Contrary to the oxide oxosilicates the isolated oxosilicate tetrahedra [SiO4]4— do not lie within the rhombic meshes of these layers, but above and below the (Ho2)3+ cations while viewing along [100].

Die Lanthanoid(III)-Oxid-Oxoselenate(IV) Ln2O[SeO3]2 (Ln=Sm–Tm)

Abstract Single crystals of compounds with the composition Ln2O[SeO3]2 (Ln=Sm–Tm) were synthesized by solid-state reactions of the lanthanoid sesquioxides (Ln2O3) with the corresponding tribromides (LnBr3) and selenium dioxide (SeO2) in a molar ratio of 2:1:2 in evacuated torch-sealed silica ampoules. For the terbium case, Tb4O7 and SeO2 have been reacted with elemental Tb in a molar ratio of 3:14:2. These lanthanoid(III) oxide oxoselenates(IV) all crystallize tetragonally with the space group P42/ncm and decreasing lattice parameters from the lighter to the heavier Ln3+ cations (from a=1077.03(8) pm and c=526.38(4) pm for Ln=Sm to a=1049.60(8) pm and c=516.04(4) pm for Ln=Tm) according to the lanthanide contraction. They show a three-dimensional network of condensed [LnO8]13− polyhedra with a channel structure, where all ψ1-tetrahedral [SeO3]2− units are coordinating with their O2− anions to square antiprisms [LnO8]13− and pointing with their non-bonding electron pairs into the empty channels, which propagate along [001]. As another characteristic feature of the crystal structure, [OLn4]10+ tetrahedra containing the non-selenium-bonded O2− anions are trans-edge-connected to form {[OLn4/2e]4+}∞1

Sc2Se3O9: Scandium(III) Oxoselenate(IV) According to Sc2[SeO3]3 with a Hexagonal "Lone‐Pair" Channel Structure

{}_\infty ^{\rm{1}}{\rm{\{ [O}}Ln_{4/2}^{\rm{e}}{{\rm{]}}^{{\rm{4}} + }}{\rm{\} }}

Tb3O2Cl[SeO3]2 and Tb5O4Cl3[SeO3]2: Oxide Chloride Oxoselenates(IV) of Trivalent Terbium with “Lone‐Pair” Channel or Layer Structures

chains, which run parallel to the lone-pair channels in [001] direction and build up a tetragonal rod-packing.