13
Ζ. Kristallogr. NCS 215 (2000) © by Oldenbourg Wissenschaftsverlag, München
Redetermination of the crystal structure of copper dibromide, CuBr2 O. Oeckler* and A. S i m o n Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart, Germany Received September 6, 1999, CSD-No. 409450
Diffractometer settings were optimized for minimum absorption. For the refinement lattice parameters from Guinier powder data were used [1]. They agree with those determined from the single crystal but have higher precision.
Discussion The crystal structure of СиВгг can be viewed as a very much distorted Cdl2 type structure. Chains of edge-sharing CuBr4 squares are connected to form layers by longer Си—Br contacts, so that the Си atoms have a 4+2 coordination. The accuracy of a previous structure determination [2] could be considerably enhanced. From our data, we can conclude that there is no need to describe the structure in the acentric space group C2 as fixed in the ICSD database. With four short distances of 2.4143(3) Ä and two longer distances of 3.1478(4) A the Jahn-Teller distortion of the Си coordination polyhedron is comparable to that in CuO {dcu—о = 1.951 Ä and 2.784 Ä) [3].
Abstract Br 2 Cu, monoclinic, C12/ml (No. 12), a = 7.2096(5) Ä, b = 3.4742(2) Ä, с = 7.0475(6) Ä, β = 119.610(5)°, V = 1 5 3 . 5 Ä 3 , Z = 2, Rsl(F)
= 0.049, wR(F2)
Table 1. Data collection and handling.
= 0.124, Τ = 293 К .
Source of material A dark brown solution of СиВгг was prepared by reacting concentrated aqueous HBr with a slightly substoichiometric amount of CuO. Thin black platelets (dark brown in transmission) of СиВгг of several cm in size formed upon slow evaporation at 328 К within 6 weeks. The crystals are extremely soft, so that cutting or even touching makes them unsuitable for structure determinations. The top of a lath shaped crystal had to be used for the data collection.
Crystal: Wavelength: μ: Diffractometer, scan mode: 29max: N(hkl)mtasured, N(hkl)u„ique: Criterion for /0ь5, N(hkl)gt: N(param)K fined: Programs:
dark-brown lamina, size 0.08 χ 0.6 χ 0.8 mm Ag Ka radiation (0.56086 A) 174.76 cm"' Enraf-Nonius CAD4, ω 59.86° 871,495 U s > 2 σ(/obsj, 474 12 SHELXS-97 [4], SHELXL-97 [5], ATOMS [6]
Table 2. Atomic coordinates and displacement parameters (in Ä 2 ). Atom
Site
χ
у
г
и II
t/22
t/33
и 12
U13
t/23
Си Br
2a 4i
0 0.22883(8)
0 1/2
0 0.23887(8)
0.0196(4) 0.0192(3)
0.0109(4) 0.0128(3)
0.0230(4) 0.0197(3)
0 0
0.0037(3) 0.0047(2)
0 0
References 1. Simon, Α.: Eine Methode zur Untersuchung extrem luftempfindlicher Substanzen mit der Guinier-Methode. J. Appl. Crystallogr. 3 (1970) 11. 2. Helmholz, L.: The Crystal Structure of Anhydrous Cupric Bromide. J. Am. Chem. Soc. 69 (1947) 886. 3. Garcia-Martinez, O.; Rojas, R. M.; Vila, E.; Martin de Vidales, J. L.: Microstructural characterization of nanocrystals of ZnO and CuO obtained from basic salts. Solid State Ionics 63-65 (1993) 442.
4. Sheldrick, G. M.: SHELXS-97. Program for solving crystal structures. University of Göttingen, Germany 1997. 5. Sheldrick, G. M.: SHELXL-97. Program for refining crystal structures, University of Göttingen, Germany 1997. 6. Dowty, E.: Atoms 5.0, A Complete Program for Displaying Atomic Structures. By Shape software, 521 Hidden Valley Road, Kingsport, TN 37663, USA 1999.
* Correspondence author (e-mail:
[email protected])
Unauthenticated Download Date | 9/24/15 11:15 PM
