Synthese und Kristallstruktur von Terbium(III)‐meta‐Oxoborat Tb(BO₂)₃ (≡ TbB₃O₆)

Abstract

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-

High-Pressure Syntheses, Crystal Structures, And Thermal Behaviour Of β-Re(Bo2)3 (Re = Nd, Sm, Gd)

“…They are built up of chains of triangular [BO 3 ] 3− and tetrahedral [BO 4 ] 5− units, representing the longest known phases. In 2003, Nikelski and Schleid solved the structure of the second polymorph β -RE(BO 2 ) 3 (RE = Tb), built up exclusively of [BO 4 ] 5− tetrahedra, forming corrugated layers [10]. This second modification was also observed with RE = Dy under ambient-pressure conditions.…”

“…1 shows a view of the crystal structure of β -RE(BO 2 ) 3 , which is composed of strongly corrugated layers of corner sharing [BO 4 ] 5− tetrahedra. A detailed description of this structure type can be found in the references [10] and [11]. The characteristic aspects of the new compounds are briefly reported in the following.…”

Ce2B8O15: High-pressure synthesis and crystal structure determination of a rare-earth polyborate exhibiting a new “Fundamental Building Block”

“…The varying B-O bond lengths result in moderately distorted BO 4 tetrahedra in the crystal structure of Ce 2 B 8 O 15 . The elongated bond length of threefold coordinated oxygen to boron atoms have already been observed in few minerals, synthetic oxoborates, but especially in high-pressure phases like b-MB 4 O 7 (M ¼ Mn, Fe, Co, Ni, Cu, Zn) [25][26][27], the metaborates b-, g-, and d-RE(BO 2 ) 3 [7][8][9][28][29][30], and the high pressure modification of B 2 O 3 [31]. The corresponding average B-O distances in these compounds range around 153 pm [32].…”

Crystal structure of dysprosium meta-oxoborate, β-Dy(BO2)3, via normal-pressure synthesis

“…Two highpressure high-temperature modifications were recently synthesized: the orthorhombic g-M(BO2)3-type (M = La -Nd, Pca21) [2] and the monoclinic d-La(BO2)3-type compounds (P21/c) [3]. For the first time, an example of the fourth known phase of metaoxoborates, b-Tb(BO2)3 was obtained under normal-pressure high-temperature conditions [4], whereas single crystals of b-M(BO2)3 with M = Dy -Lu [5] …”