Crystal structure of dicerium antimonide, Ce2Sb

Ce2Sb, tetragonal, 14/mmm (No. 139), a = 4.538(1) Â, c = 17.861(3) Â, V= 367.8 Â, Z = 4, R#(F) = 0.031, wRKf(F) = 0.076, T= 293 K. Source of material Ce2Sb was synthesized from the elements in a sealed tantalum ampoule at 1675 Κ for 4 hours. Single crystals were obtained from slowly cooled samples (cooling rate: 25 K/h). Discussion Ce2Sb belong to the i/12 structure type of La2Sb as shown by Borsese et al. [1] from powder diffraction data. The strong bonded heteroatomic 3D framework ^[Sb(Ce 1)4/4^2)5/5] is formed by condensed SbCeç mono-capped square antiprism Table 2. Atomic coordinates and displacement parameters (in Â). (d(Sb—Cel) = 3.344( 1 ) À (4x); d(Sb—Ce2) = 3.276( 1 ) À ( 1 x), 3.293(1) À (4x). The nearest neighbours of the Ce2 atoms are five Sb atoms arranged at the corners of a square pyramid, forming NaCl type fragments. The short Ce l—Cel distances of about 3.209 Â in the non-capped square of the SbCeg polyhedra indicate additional Ce—Ce interaction in the 4 4 nets of Cel (see figure). Obviously this leads to the large c!a ratio (3.936 » 3.414 = V2+2) compared with that of e.g. Eu4Sb20 [2] (K2N1F4 structure type). Consequently, the final difference Fourier synthesis gave no evidence for an interstitial atom in the quasi-octahedral Cee cavities (see also [3]). Table 1. Data collection and handling. Crystal: dark, metallic lustre. size 0.1 xO.l χ 0.2 mm Wavelength: Mo Ka radiation (0.71073 λ ) μ· 313.41 cm" Diffractometer, scan mode: STADI4, Stoe, 20/cu 20m»: 74.92° N<Admeasured, WAW)iinique: 578,334 Criterion for /obs. Nfhkljg.: /obs > 2 a(Iobs), 302 N(param)„fxno¡: 11 Programs: SHELXL-97 [4], ATOMS [5] References 1. Borsese, Α.; Bolzone, G.; Mazzone, D.; Ferro R.: Heats of formation of Ce-Sb Alloys. J. Less Comm. Met. 79 (1981) 57-63. 2. Schaal, H.; Nuss, J.; Hönle, W.; Grin, Yu.; von Schnering, H. G.: Crystal structure of tetraeuropium diantimonide oxide, Eu4Sb20. Z. Kristallogr. NCS 213 (1998) 15. 3. Wang, Y.; Calvert, L. D.; Taylor, J. B.: Is there an oxygen atom in LaîSb? Acta Crystallogr. B36 (1980) 220-221. 4. Sheldrick, G. M.: SHELXL-97. Program for crystal structure refinement. University of Göttingen, Germany 1997. 5. Dowty, E.: ATOMS (V 5.1). Shape Software, Kingsport, USA 1999. Atom Site X y ζ Un U22 t/33 t/12 1/13 t/23 Ce(l) 4c 0 1/2 0 0.0127(3) 0.0214(4) 0.0115(3) 0 0 0 Ce(2) 4e 0 0 0.17903(4) 0.0103(2) t/11 0.0104(3) 0 0 0 Sb 4e 0 0 0.36247(4) 0.0101(2) Un 0.0107(3) 0 0 0 * Correspondence author (e-mail: j.nuss@fkf.mpg.de)