La5Zn2Sn

Igor Oshchapovsky; Volodymyr Pavlyuk; Grygoriy Dmytriv; Igor Chumak; Helmut Ehrenberg

doi:10.1107/S1600536811042413

. 2011 Oct 22;67(Pt 11):i65. doi: 10.1107/S1600536811042413

La₅Zn₂Sn

Igor Oshchapovsky ^a,^*, Volodymyr Pavlyuk ^a,^‡, Grygoriy Dmytriv ^a, Igor Chumak ^b, Helmut Ehrenberg ^c

PMCID: PMC3246910 PMID: 22219730

Abstract

A single crystal of pentalanthanum dizinc stannide, La₅Zn₂Sn, was obtained from the elements in a resistance furnace. It belongs to the Mo₅SiB₂ structure type, which is a ternary ordered variant of the Cr₅B₃ structure type. The space is filled by bicapped tetragonal antiprisms from lanthanum atoms around tin atoms sharing their vertices. Zinc atoms fill voids between these bicapped tetragonal antiprisms. All four atoms in the asymmetric unit reside on special positions with the following site symmetries: La1 (..m); La2 (4/m..); Zn (m.2m); Sn (422).

Related literature

For general background to {Tb,La}–Zn–{Sn,Pb} ternary systems, see: Manfrinetti & Pani, (2005 ▶); Oshchapovsky et al. (2010 ▶, 2011 ▶); Pavlyuk et al. (2009 ▶). For related structures, see: Bertaut (1953 ▶). For isotypic structures, see: Aronsson (1958 ▶).

Experimental

Crystal data

La₅Zn₂Sn
M _r = 944.04
Tetragonal,
a = 8.3277 (12) Å
c = 14.334 (3) Å
V = 994.1 (3) Å³
Z = 4
Mo Kα radiation
μ = 28.10 mm⁻¹
T = 293 K
0.04 × 0.04 × 0.01 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2004 ▶) T _min = 0.340, T _max = 0.765
9291 measured reflections
419 independent reflections
346 reflections with I > 2σ(I)
R _int = 0.091

Refinement

R[F ² > 2σ(F ²)] = 0.027
wR(F ²) = 0.056
S = 1.14
419 reflections
14 parameters
Δρ_max = 1.60 e Å⁻³
Δρ_min = −1.59 e Å⁻³

Data collection: APEX2 (Bruker, 2004 ▶); cell refinement: SAINT (Bruker, 2004 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶) and JANA2006 (Petricek et al., 2006 ▶); molecular graphics: DIAMOND (Brandenburg, 2006 ▶) and VESTA (Momma & Izumi, 2008 ▶); software used to prepare material for publication: publCIF (Westrip, 2010 ▶).

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536811042413/ru2016sup1.cif

e-67-00i65-sup1.cif^{(19.7KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811042413/ru2016Isup2.hkl

e-67-00i65-Isup2.hkl^{(21.8KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

Financial support from the Ministry of Education and Science, Youth and Sport of Ukraine (N 0111U001089) is gratefully acknowledged.

supplementary crystallographic information

Comment

Ternary compounds formed by rare-earth, transition metal and d-metal often have interesting physical and chemical properties e. g. strong ferromagnetism, hydrogen storage capabilities and so on. The systematic investigation of the components interaction in the {Tb, La}-Zn-{Sn,Pb} ternary systems can lead to development of functional materials (for crystal structures of ternary compounds see: TbZnSn –Manfrinetti & Pani, (2005), Pavlyuk et al., (2009), TbZnSn₂ - Pavlyuk et al., (2009), Tb₁₃ZnSn₁₃-Oshchapovsky et al., (2010) and LaZn_12.37-Oshchapovsky et al., (2011)).

The title compound crystallizes in Mo₅SiB₂ (Aronsson, 1958) structure type which is an ordered superstructure of Cr₅B₃ type (Bertaut, 1953). Unit cell projection together with coordination polyhedra are given in Fig.1. Coordination polyhedra of the La1 atoms are 16- vertex polyhedra. Sn atoms are surrounded by ten neighbours forming bicapped tetragonal antiprism. La2 atoms are enclosed into trigon - tetrahexahedron with CN=14. And coordination polyhedra of the Zn atoms are bicapped trigonal prisms with CN=9. Coordination polyhedra of Sn atoms share their vertices forming three dimensional framework. The voids in this framework are filled by zinc atoms. (See graphical abstract).

The way of bond formation in this compound was assumed using only X-ray diffraction data. Further structure refinement was carried out by means of Jana2006 software package using anharmonic ADP for La1 and Zn atoms. Anharmonic displacement parameters for other atoms were not refined because in case of their refinement their standard deviations were larger than obtained values. As the result we gained lower absolute values of peak and hole in the difference Fourier map (1.02 and -1.17 e Å^-3 respectively). The resulting isosurface drawn at the level 0.308 e/Å³ and sections of difference Fourier map are given in Fig. 2. These maps and sections are noisy but some trends in location of positive and negative regions can be noticed. Positive residual electron density is mostly situated around zinc atoms and near layers made of tin atoms. Negative residual density is mostly located between lanthanum atoms which means that lanthanum atoms donate their electrons to zinc and tin atoms. Similar behaviour of lanthanum atoms can be observed in the LaZn_12.37 compound using electronic structure calculations (See Oshchapovsky et al., (2011)). As a conclusion this compound besides dominate metallic bonding has a weak ionic interaction between lanthanum and zinc and tin atoms.

Experimental

Small good quality single-crystal of title compound was isolated from alloy with composition La₇ZnSn₂ during systematic investigation of lanthanum-rich region of La—Zn—Sn ternary system. The samples with high lanthanum contents were prepared by melting of pieces of pure metals in evacuated quartz ampoule with subsequent annealing at 600 ⁰C for 30 days. Further phase analysis showed the existence of title compound in sample with composition La₇ZnSn₂ as well as in the other lanthanum-rich ternary alloys. However they were non equilibrium.