B6Ho2Ni3, orthorhombic, Cmmm (No. 65), a = 7.6865(9) Å, b = 8.6679(9) Å, c = 3.4742(4) Å, V = 231.5 Å3, Z = 2, Rgt(F) = 0.021, wRref(F2) = 0.048, T= 300 K

Geupel, S.

Graw, G.

Paufler, P.

Zahn, G.

English

Repositorium für Naturwissenschaften und Technik  (TIB Hannover)

Z. Kristallogr. NCS 215 (2000) All-M% 477 © by Oldenbourg Wissenschaftsverlag, München Refinement of the crystal structure of diholmium trinickel hexaboride, Ho2Ni3B6 S. Geupel*11, G. Zahn1, P. Paufler1 and G. Graw11 1 Technische Universität Dresden, Institut für Kristallographie und Festkörperphysik, D-01062 Dresden, Germany " Institut für Festkörper- und Werkstofforschung Dresden, Postfach 270016, D-01171 Dresden, Germany Received May 8, 2000, CSD-No. 409497 Experimental details Accurate lattice parameters of H02NÌ3B6 were measured at temperatures between 300 K and 100 K using a STOE STADI4 four-circle diffractometer equipped with a CRYOSTREAM cooling system (Oxford Cryosystems). Abstract B6Ho2Ni3, orthorhombic, Cmmm (No. 65), a = 7.6865(9) A , b = 8.6679(9) A , c = 3.4742(4) A , V= 231.5 A 3 , Z= 2, Rgt(F) = 0.021, wRlef(F2) = 0.048, T= 300 K. Source of material A coarse-grained sample with nominal composition Ho2Ni3B6 was prepared from holmium pieces, nickel powder and boron powder. A stoichiometric mixture of the high-purity elements was pressed to pellets, which have been arc melted under argon atmosphere on a water-cooled copper heart. Melting of the buttons has been repeated three times in order to improve the sample homogeneity. A special annealing treatment (duration 75 h, temperature up to 1733 K) was performed within a resistance furnace under argon atmosphere. The composition of the annealed sample was determined with electron probe microanalysis applying the WDX mode. A single grain was extracted from the polycrystalline aggregate for single-crystal diffractometry. Discussion The title compound, which is isotypic with LU2N13B6 [1], was first characterized with X-ray powder diffraction [2], but no structure refinement has been performed. The crystal structure of Ho2Ni3B6 (Cmmm - pjhga) is closely related to that of TI1M0B4 (Cmmm - pjihg), with 1/3 of Ni atoms replaced by B-B dumb-bells [3]. The structure consists of two equidistant planar layers which are alternately stacked along the c axis. Within the Ho-Nil network, each Nil atom is coordinated by 2 Ho atoms at 2.865 A and 2 Ho atoms at 2.958 A, leading to a distorted square-planar arrangement. Both symmetry-independent B at-oms are located inside trigonal prisms formed by 4 Ho atoms and 2 Ni 1 atoms. Within the Ni2-B 1-B2 network, each B2 atom is co-ordinated by 2 B1 atoms at 1.74 A and 1 B2 atom at 1.75 A, whereas the Ni2 atom is surrounded by 4 B1 atoms at 2.22 A. The two layers are connected by the Ni2 atom with a square-planar co-ordination by Ni 1 atoms. The Ni 1—Ni2 distances of 2.452 A are slightly shorter than those found in metallic nickel (2.50 A), indi-cating a strong metal-metal bonding. The analysis of the U\\ shows a preferred displacement in the a-b plane for the metal at-oms, but in the c direction for the boron atoms. The refinement of site occupancies results in the composition Hoi.90,-1 (NisBf,. Atomic coordinates correspond to the standardized form accord-ing to STRUCTURE TIDY [4], shifting the origin by [0 0 1/2], The coefficients of linear thermal expansion at temperatures between 300 K and 100 K are a a = 8.5 x 10"6 K"1, cxb = 6.7 x 10"6 K"1, and etc = 1.4 x 10"5 K"1. Table 1. Data collection and handling. Crystal: Wavelength: H: Diffractometer, scan mode: 28max : N(hkl)measured, N(hkl)umq\ie-Criterion for /0bs, N(hkl)g<: N(param)re fined: Programs: * Correspondence author (e-mail: sandra.geupel@uni-bayreuth.de) 1 current address: Universität Bayreuth, Lehrstuhl für Kristallographie, D-95440 Bayreuth, Germany metallic lustre, block, size 0.02 x 0.04 x 0.08 mm Mo Ka radiation (0.71073 Â) 455.78 cm"1 STOE STADI4, co/6 62.78° 815,246 Us > 2 a(Us), 222 24 STRUCTURE TIDY [4], SHELX-97 [5], SCHAKAL92 [6] 4 7 8 Holmium nickel bonde ( 2 : 3 : 6 ) Table 2. Atomic coordinates and displacement parameters (in Â2). Atom Site Occ. x y z Un i/22 t/33 Un Un t/23 Ho 4j 0.951(5) 0 0.27673(5) 1/2 0.0069(2) 0.0055(3) 0.0033(2) 0 0 0 Ni(l) 4 h 0.2251(2) 0 1/2 0.0076(6) 0.0064(5) 0.0039(6) 0 0 0 Ni(2) 2a 0 0 0 0.0073(8) 0.0085(8) 0.0046(8) 0 0 0 B ( l ) 8p 0.2345(9) 0.1497(9) 0 0.006(3) 0.008(3) 0.014(3) 0.001(3) 0 0 B(2) 4 g 0.386(1) 0 0 0.008(4) 0.010(4) 0.015(5) 0 0 0 Acknowledgment. Support by the Deutsche Forschungsgemeinschaft is grate-fully acknowledged. References 1. Dub, O. M.; Kuz'ma, Yu. B.; Mazus, M. D.; Chaban, N. F.; Malinovskii, T. I.: Crystal structure of the boride Lu2Ni3B6. Doklady Akademii Nauk Ukr. SSR, Ser. B: Geol. Khim. Biol. Nauki 2 (1987) 35-37. 2. Gubich, I. B.; Chaban, N. F.; Kuz'ma, Yu. B.: New borides with the Lu2Ni3Bô structure. Izvestiya Akademii Nauk SSSR, Neorganicheskie Materialy 25 (1989) 1317-1320. 3. Rogl, P.; Nowotny, H.: Ternare Komplexboride mit ThMoB4-Typ. Monatsh. Chemie 105 (1974) 1082-1098. 4. Gelato, L. M.; Parthi, E.: STRUCTURE TIDY - a computer program to standardize crystal structure data. J. Appl.Crystallogr.20(1987) 139-143. 5. Sheldrick, G. M.: SHELX-97, program for the solution and refinement of crystal structures. University of Gottingen, Germany 1997. 6. Keller, E.: SCHAKAL92, computer program for the graphic representa-tion of molecular and crystallographic models. University of Freiburg, Germany 1992. 

Refinement of the crystal structure of diholmium trinickel hexaboride, Ho2Ni3B6

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Refinement of the crystal structure of diholmium trinickel hexaboride, Ho2Ni3B6

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