The new orthorhombic meta-oxoborates RE(BO2)3 (≡REB3O6) (RE = Dy-Lu) have been synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C. They are isotypic to the known ambient pressure phase Tb(BO2)3, space group Pnma. In contrast to Dy(BO2)3, which was also obtained in small amounts under high-temperature conditions, the preparation of the higher orthorhombic homologues RE(BO2)3 (RE = Ho-Lu) was only possible using high-pressure. The meta-oxoborates RE(BO2)3 (RE = Dy-Er) were synthesized as pure products, whereas the orthorhombic phases with RE = Tm-Lu were only obtained as byproducts. With the exception of Yb(BO2)3 it was possible to establish single crystal data for all compounds. The results of temperature-resolved in-situ powder-diffraction measurements, DTA, IR-spectroscopic investigations, and magnetic properties are also presented.
Inhaltsübersicht. Das Terbium-meta-Oxoborat Tb(BO 2 ) 3 (ϵ TbB 3 O 6 ) entsteht einkristallin bei der Reaktion von Terbium, Tb 4 O 7 und TbCl 3 mit einem Überschuß von B 2 O 3 in gasdicht verschlossenen Platinampullen nach drei Wochen bei 950°C. Die Verbindung ist luft-und wasserstabil und fällt in langen, dünnen, farblosen Nadeln an, die aufgrund ihres ausgeprägt faserigen Habitus zur Wachstumsverzwillingung neigen. Die Kristallstruktur von Tb(BO 2 ) 3 (orthorhombisch, Pnma; a ϭ 1598,97(9), b ϭ 741,39(4), c ϭ 1229,58 (7) pm; Z ϭ 16) enthält parallel (100) verlaufende, stark Abstract. The terbium meta-oxoborate Tb(BO 2 ) 3 (ϵ TbB 3 O 6 ) is obtained as single crystals by the reaction of terbium, Tb 4 O 7 and TbCl 3 with an excess of B 2 O 3 in gastight sealed platinum ampoules at 950°C after three weeks. The compound appears to be air-and water-resistant and crystallizes as long, thin, colourless needles which tend to growth-twinning due to their marked fibrous habit. The crystal structure of Tb(BO 2 ) 3 (orthorhombic, Pnma; a ϭ 1598.97(9), b ϭ 741.39(4), c ϭ 1229.58 (7) pm; Z ϭ 16) contains strongly corrugated oxoborate layers 2 ϱ {(BO 2 ) Ϫ } built of vertex-Einleitung Während man bei den sogenannten ortho-Oxoboraten der dreiwertigen Lanthanide (M ϭ La Ϫ Lu) mit der Zusammensetzung MBO 3 (M[BO 3 ]; β-, λ-, ν-, π-und H-Typ [1Ϫ9] oder M 3 [B 3 O 9 ]; µ-und χ-Typ [1, 6, 10Ϫ12]) eine überraschend große Strukturvielfalt vorfindet, ist bei den meta-Oxoboraten MB 3 O 6 (ϵ M(BO 2 ) 3 ) bislang nur ein einziger Kristallstrukturtyp für die leichten, aber voluminösen M 3ϩ -Vertreter (M ϭ La Ϫ Gd) [13Ϫ16] bekannt. Für die ortho-Oxoborate variiert die Koordinationszahl des M 3ϩ -Kations je nach Ionenradius zwischen sechs und neun [4], die Oxoborat-Gruppen liegen entweder als isolierte, trigonal-planare [BO 3 ] 3Ϫ -Anionen oder als diskrete, ringförmige Kondensate cyclo-[B 3 O 9 ] 9Ϫ dreier [BO 4 ] 5Ϫ -Tetraeder mit gemeinsamen Sauerstoffecken vor. Nur im χ-Typ trifft man ein Kettenfragment catena-[B 3 O 9 ] 9Ϫ an, in dem eine tetra-
About Lanthanide Oxotantalates with the Formula MTaO4 (M = La – Nd, Sm – Lu)Besides being a by‐product of solid state syntheses in tantalum ampoules the lanthanide(III) oxotantalates of the formula MTaO4 can be easily prepared by sintering lanthanide sesquioxide M2O3 and tantalum(V) oxide Ta2O5 with sodium chloride as flux. Under these conditions two structure types emerge depending upon the M3+ cationic radius. For M = La – Pr the MTaO4‐type tantalates crystallize in the space group P21/c with lattice constants of a = 762(±1), b = 553(±4), c = 777(±4) pm, β = 101(±1)° and four formula units per unit cell. With M = Nd, Sm – Lu, the monoclinic cell dimensions (space group P2/c) shrink to the lattice constants like a = 516(±9), b = 551(±9), c = 534(±9) pm, β = 96.5(±0.3)° and there are only two formula units present. Both structures show a coordination sphere of eight oxygen atoms for the lanthanide trications shaped as distorted square antiprism for the structure with the larger lanthanides (in the following referred to as A‐type) and as trigonal dodecahedron for the structure with the smaller ones (called as B‐type in the following). The coordination environment about the Ta5+ cations can be described as a slightly distorted octahedron (CN = 6) for the A‐type structure of MTaO4 and a heavily distorted one (CN = 6) for the B‐type. The difference between the two types results from the interconnection of these [TaO6]7− octahedra. Whereas they are connected via four vertices to form corrugated layers according to $^{2}_{\infty}\rm[TaO^{v}_{4/2}O^{t}_{2/2}]^{3-}$ parallel the bc‐plane in the A‐type, the octahedra of the B‐type MTaO4 structure share edges to built up zig‐zag chains $^{1}_{\infty}\rm[TaO^{e}_{4/2}O^{t}_{2/2}]^{3-}$ along the c axis.
-009Pr(BO 2 ) 3 and PrCl(BO 2 ) 2 : Two Praseodymium meta-Borates in Comparison.-Single crystals of PrCl(BO 2 ) 2 (I) are obtained from the reaction of Pr 6 O 11 and PrCl 3 with excess B 2 O 3 (evacuated quartz tube, 850 • C, 7 d). The addition of NaCl as fluxing agent results in the formation of single crystals of Pr(BO 2 ) 3 (II) as the main product. (I) crystallizes in the triclinic space group P1 with Z = 2 and contains zigzag chains of corner-sharing BO 3 triangles. Pr 3+ is coordinated by three Cl − and seven O 2− anions forming a tetracapped trigonal prism. In the structure of compound (II) (monoclinic, space group C2/c, Z = 4) the boron atoms are present in both trigonal planar and tetrahedral oxygen coordination. The two types of polyhedra form chains via common corners. The coordination sphere of the Pr atoms is a bicapped square antiprism formed by ten O atoms.
Single crystals of La 4 B 14 O 27 could be synthesized by the reaction of La 2 O 3 , LaCl 3 and B 2 O 3 with an access of CsCl as fluxing agent in gastightly sealed platinum ampoules within twenty days at 710°C and appear as colourless, transparent and waterresistant platelets. The new lanthanum oxoborate La 4 B 14 O 27 (monoclinic, C2/c; a ϭ 1120.84(9), b ϭ 641.98(6), c ϭ 2537.2(2) pm, β ϭ 100.125(8)°; Z ϭ 4) is built of a three-dimensional boron-oxygen framework containing seven crystallographically different boron atoms. Four of these B 3ϩ cations are surrounded by four O 2Ϫ anions tetrahedrally, whereas the other three have only three oxygen neighbours with nearly plane triangular coordination figures. Three of the [BO 4 ] 5Ϫ tetrahedra form [B 3 O 9 ] 9Ϫ rings by cyclic vertex-con-Einleitung In den Systemen M 2 O 3 ϪB 2 O 3 (M ϭ Sc, Y, La; Ce Ϫ Lu) sind Verbindungen mit sechs verschiedenen Formeltypen von Selten-Erd-Metall(III)-Oxoboraten bekannt. Ortho-Oxoborate mit der Summenformel MBO 3 (meist gemäß M[BO 3 ]) [1], meta-Oxoborate MB 3 O 6 (ϵ M(BO 2 ) 3 ) [1], weiterhin Hochdruck-Oxoborate der Zusammensetzungen M 4 B 6 O 15 [2, 3], M 2 B 4 O 9 [3Ϫ7], M 4 B 10 O 21 [8] und M 3 B 5 O 12 [9] sowie Oxid-Oxoborate, die einen Überschuss von nicht an das Bor gebundenen Oxid-Anionen aufweisen, nämlich M 3 BO 6 (ϵ M 3 O 3 [BO 3 ]) [10, 11] und M 26 B 8 O 51 (ϵ M 26 O 27 [BO 3 ] 8 ) [12]. In den Kristallstrukturen liegen seltener isolierte, häufiger verknüpfte [BO 3 ] 3Ϫ -Dreiecke und/ oder [BO 4 ] 5Ϫ -Tetraeder vor. Bis zu den Hochdruck-Untersuchungen von Huppertz et al. galt die Eckenverknüpfung dieser beiden fundamentalen Baueinheiten [13Ϫ15] als Ausschließlichkeitsprinzip, nunmehr kennt man jedoch auch kantenverknüpfte [BO 4 ] 5Ϫ -Tetraeder aus den Kristallstrukturen von M 4 B 6 O 15 (M ϭ Dy, Er) [2, 3] und Ͱ-M 2 B 4 O 9 (M ϭ EuϪDy [6], Sm, Ho [7]). 49 densation, which are further linked via [BO 3 ] 3Ϫ units to infinite layers. Two of these layers connect via one [B 2 O 7 ] 8Ϫ unit of two corner-shared [BO 4 ] 5Ϫ tetrahedra to double layers, which themselves build up a three-dimensional framework together with chains consisting of two [BO 4 ] 5Ϫ tetrahedra and one [BO 3 ] 3Ϫ triangle. One of the two crystallographically independent La 3ϩ cations (La1) is surrounded by ten O 2Ϫ anions and resides within the oxoborate double layers. (La2) 3ϩ shows a (8ϩ2)-fold coordination of O 2Ϫ anions and occupies channels along the [110] direction.
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