Steffen F. Meier

Ho2Te4O11 und Ho2Te5O13: Zwei tellurdioxidreiche Oxotellurate(IV) des dreiwertigen Holmiums

Ho2Te4O11 (monoklin, C2/c; a = 1240,73(8), b = 511,21(3), c = 1605,84(9) pm, β = 106,142(7)°; Z = 4) und Ho2Te5O13 (triklin, P1; a = 695,67(5), b = 862,64(6), c = 1057,52(7) pm, α = 89,057(6), β = 86,825(6), γ = 75,056(6)°; Z = 2) entstehen durch Umsetzung von Holmiumsesquioxid mit Tellurdioxid in geeigneten molaren Verhaltnissen (Ho2O3 : TeO2 = 1 : 4 bzw. 1 : 5) innerhalb von acht Tagen in evakuierten Quarzglasampullen bei 800 °C. Der Einsatz von Caesiumchlorid (CsCl) als Flusmittel in etwa funffach molarem Uberschus sorgt fur schnelle und quantitative Reaktionen zu einkristallinen Zielprodukten. In der Kristallstruktur von Ho2Te4O11 erfolgt die Verknupfung von [HoO8]-Polyedern uber Sauerstoffkanten, wodurch sich ein Netz {[Ho2O10]14–} parallel zur (001)-Ebene ausbildet. Der Kristallstruktur von Ho2Te5O13 liegen dagegen nur noch von sauerstoffverknupften [(Ho1)O8]- und [(Ho2)O7]-Polyedern aufgebaute Bander {[(Ho1)2(Ho2)2O20]28–} zugrunde, die langs [100] verlaufen. Gemeinsam ist beiden Strukturen allerdings die stereochemische Aktivitat der nicht-bindenden Elektronenpaare („lone pairs”) samtlicher Te4+-Kationen (Te1 und Te2 in Ho2Te4O11; Te1–Te5 in Ho2Te5O13), die ψ1-polyedrische Koordinationsfiguren mit 3 + 1, 4 bzw. 3 + 2 Sauerstoffatomen um die Zentralteilchen bewirkt. Ho2Te4O11 and Ho2Te5O13: Two Telluriumdioxide-rich Oxotellurates(IV) of Trivalent Holmium Ho2Te4O11 (monoclinic, C2/c; a = 1240.73(8), b = 511.21(3), c = 1605.84(9) pm, β = 106.142(7)°; Z = 4) and Ho2Te5O13 (triclinic, P1; a = 695.67(5), b = 862.64(6), c = 1057.52(7) pm, α = 89.057(6), β = 86.825(6), γ = 75.056(6)°; Z = 2) are obtained by the reaction of holmium sesquioxide with tellurium dioxide in appropriate molar ratios (Ho2O3 : TeO2 = 1 : 4 and 1 : 5, respectively) in evacuated silica tubes within eight days at 800 °C. The application of cesium chloride (CsCl) as flux in about five times molar excess secures fast and complete reactions to the single-crystalline products aimed at. In the crystal structure of Ho2Te4O11 [HoO8] polyhedra are connected via oxygen edges thereby building up a network {[Ho2O10]14–} (001). On the other hand, the crystal structure of Ho2Te5O13 exhibits oxygen-linked [(Ho1)O8] and [(Ho2)O7] polyhedra, which form ribbons {[(Ho1)2(Ho2)2O20]28–} running along [100]. Common to both structures, however, is the stereochemical activity of the non-bonding electron pairs (“lone pairs”) of all the of the Te4+ cations (Te1 and Te2 in Ho2Te4O11, Te1–Te5 in Ho2Te5O13) causing ψ1-polyhedral figures of coordination with 3 + 1, 4 and 3 + 2 oxygen atoms, respectively, around the central atoms.

Synthese und Kristallstruktur des Holmium(III)-chlorid-oxotellurats(IV) HoClTeO3

Synthesis and Crystal Structure of the Holmium(III) Chloride Oxotellurate(IV) HoClTeO3 Orange coloured, rod—shaped single crystals of the holmium( III) chloride oxotellurate(IV) HoClTeO3 (orthorhombic, Pnma; a = 730.25(5), b = 696.54(5), c = 905.18(7) pm; Z = 4) are obtained during attempts to synthesize holmium(III) oxochlorotellurates(IV) by reaction of holmium oxychloride (HoOCl) and tellurium dioxide (TeO2; 1:1—2molar ratio, 800 °C, 40 d) in evacuated silica tubes. The crystal structure contains sevenfold coordinated Ho 3+ cations surrounded by five oxide and two chloride anions forming a pentagonal bipyramid. Interconnection of the [Ho(O1)(O2)4Cl2] polyhedra occurs via two edges made of four equatorial oxygen atoms (O2) under formation of {[Ho(O1)(O2)4/2Cl2/1]5-} chains running parallel [010]. These arrange as hexagonal closest packing of rods and are linked to each other by Cl- anions to a three—dimensional {[Ho(O1)1/1(O2)4/2Cl2/2]4-} network. All Te4+ cations are embedded therein and exhibit ψ1—tetrahedral coordination figures as discrete anionic [Te(O1)(O2)2]2- pyramids due to the stereochemical activity of the non—binding electron pairs („lone pairs”). They stabilize the {[HoO3Cl]4-} network via covalent bonds to one axial (O1) and two equatorial oxygen atoms (O2) of each [HoO5Cl2] polyhedron.

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].

ζ-Y2[Si2O7]: Ein neuer Strukturtyp in der Yttrialit-Reihe / ζ -Y2[Si2O7]: A New Structure Type within the Yttrialite Series

Abstract During attempts of preparing yttrium oxotellurates(IV) using Y2O3 and TeO2 in YCl3 fluxes, the occasional reaction of these educts with the walls of the evacuated silica ampoules led to colourless, lath-shaped single crystals of Y2[Si2O7] in the new ζ -type structure as a minor by-product which was investigated by X-ray diffraction. The title compound crystallizes monoclinically in the space group P21/m (a = 503.59(5), b = 806.47(8), c = 732.65(7) pm, β = 108.633(6)°) with two formula units per unit cell. The crystallographically unique Y3+ cation is coordinated by seven oxygen atoms (d(Y-O = 221 - 248 pm) arranged in the shape of a slightly distorted monocapped octahedron. The isolated oxodisilicate units [Si2O7]6− consist of two Si4+ cations and seven O2− anions of which five are crystallographically independent. These pyroanions (d(Si-O) = 161 - 168 pm, ∢ (O-Si-O) = 91 - 117°, ∢ (Si-O-Si) = 156°) exhibit an almost perfectly eclipsed conformation built of a horseshoeshaped backbone with the two silicon and three of the oxygen atoms situated on the mirror planes of the unit cell. The remaining four oxide anions complete this [Si2O7]6− entity of two vertex-sharing [SiO4]4− tetrahedra as terminal ligands for silicon. Assembled in planar layers parallel to (−1 0 1), the [Si2O7]6− anions are packed with their wide basal faces of the tetrahedra pointing towards the small waist of the adjacent units and vice versa. The yttrium cations reside between these layers in order to interconnect them three-dimensionally.

Oxotellurate(IV) der lanthanide: I. Die isotype reihe M2Te4O11 (M = La - Nd, Sm - Yb)

Abstract The present work is the first comprehensive account of the knowledge acquired from single crystals of the isotopic series M2Te4O11 (M = La - Nd, Sm - Yb). In the crystal structure, the M3+ cation is coordinated by eight oxygen atoms in the shape of a distorted square antiprism. Out of these polyhedra a mesh-like [M2O16]14− layer parallel to the (001) plane is built via three common edges. The [Te4O11]6− double layers in turn build two tellurium-oxygen chains crosswise to each other. The construction of the tellurium-oxygen partial structure is, however, only possible taking the secondary Te-O contacts into consideration. In most oxotellurates(IV), three oxygen atoms are covalently bound to the Te atoms (d(Te-O) ≈ 180−200 pm; ψ1 tetrahedron). Another oxygen atom is found in the near vicinity at a distance of 230 to 280 pm. The significance of such secondary interactions for the stability of the crystal structures was recognized recently in theoretical as well as experimental investigations. All oxygen atoms with distances smaller than 280 pm are counted to the secondary coordination sphere. This limit may seem somewhat arbitrary but it accounts very well for the Te-O partial structure. The coordination sphere for the tellurium center is a ψ1 trigonal bipyramid including the stereochemically active electron pair (“lone pair”). A description of the crystal structure is also possible without this partial structure, however in the [TeO3+1]4− polyhedra above and below the meshes of [M2O10]14− layers are linked via Te2-O6-Te2 contacts only.

Oxotellurate(IV) der Lanthanide: II. Die isotype Reihe M2Te5O13 (M = Dy – Lu) / Oxotellurates(IV) of Lanthanides: II. The Isotypic Series M2Te5O13 (M = Dy – Lu)

For the shortly discovered formula type M2Te5O13 (triclinic, P1̄), the establishment of an isostructural series in the last third of the lanthanide family (M = Dy - Lu) was possible. The excessive formula unit TeO2 additional to the well-known composition M2Te4O11 (monoclinic, C2/c) leads to the slicing of the [M2O10]14− layers which are typical for the tellurium-oxide poorer compounds. By coupling together the bicapped trigonal prismatic (M1, CN = 8) and the pentagonal bipyramidal (M2, CN = 7) lanthanide-oxygen polyhedra via edges, [M4O20]28− bands are formed stretching along the a axis and piling up to a primitive rod-packing. The linkage of these bands occurs parallel to the (010) plane via Te3 as well as via Te4 parallel to (100). Besides the usual 3+1 coordination, two of the five crystallographically independent tellurium sites are coordinated regularly fourfold (d(Te−O) ≈ 186−213 pm) and even 3+2-fold by oxygen atoms. The tellurium-oxygen polyhedra form corrugated layers running parallel to (101) which follow so close to each other that the tellurium-oxygen partial structure appears to be almost three-dimensional at a passing glance. As in M2Te4O11-type representatives, the non-bonding electron pair (lone pair) of each Te4+ cation shows stereochemical activity which always appears to flock together in large tellurium neighboured positions.