Lanthanum dimagnesium

inorganic papers

Acta Cryst.(2005). E61, i155–i157 doi:10.1107/S1600536805021343 Belgacemet al. _LaMg

2

i155

Acta Crystallographica Section E

Structure Reports Online

ISSN 1600-5368

Lanthanum dimagnesium

Besma Belgacem,aSamia Yahyaoui,aP. Yu. Demchenko,b O. I. Bodak,bMichal Dusekcand Rached Ben Hassena*

a_{De´partement de Chimie, Unite´ de Chimie des}

Mate´riaux, Faculte´ des Sciences de Sfax BP 802, Sfax 3018, Tunisia,b_{Department of Inorganic}

Chemistry, Ivan Franko National University of Lviv, Kyryla i Mefodiya Str. 6, 79005 Lviv, Ukraine, andc_{Institute of Physics, Na Slovance}

2, Praha 8, Czech Republic

Correspondence e-mail: [email protected]

Key indicators

Single-crystal X-ray study

T= 295 K

Mean(La–Mg) = 0.0008 A˚

Rfactor = 0.008

wRfactor = 0.024

Data-to-parameter ratio = 12.5

For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e.

#2005 International Union of Crystallography

Printed in Great Britain – all rights reserved

Single crystals of the LaMg2 cubic Laves phase were

synthesized by arc melting. The binary LaMg2 compound

has been shown to adopt the MgCu2-type structure. The

coordination sphere of the rare earth metal, adopting a site symmetry of 1, consists only of 12 Mg atoms. The site symmetry of the alkaline earth metal is 3m, giving rise to superimposed distorted MgLa6and MgMg6octahedra.

Comment

Binary intermetallics with the general formulaRM2(whereR

is a rare earth and M an alkaline earth metal) have been studied extensively in the past because of their interesting magnetic properties (Leisure et al., 2003). These compounds can adopt a wide variety of crystal structures with different geometrical arrangements for the rare earth atoms and with, therefore, different R—R and R—M interatomic distances (Klaus, 2000). A new family with the general formula LaM2

crystallizes in different structure types (cubic and tetragonal; Liang et al., 2003). AB2-type intermetallic compounds have

been of interest because of their possible use in high-temperature structural applications (Leisureet al., 2003).

The C15 Laves phase compounds have received special

attention for their elastic and magnetic properties and ability to absorb hydrogen (Leisure et al., 2003). Moreover, many investigations have been carried out on MH electrode alloys

Received 24 May 2005 Accepted 5 July 2005 Online 9 July 2005

Figure 1

with higher energy density, such as AB2-type Laves phase

alloys (Liaoet al.,2004).

The La–Mg system was critically assessed by means of the calculation of phase diagram (CALPHAD) technique. The solution phases were modeled with the Redlich–Kister equa-tion (Cuiping & Zhenmin, 2004). The intermetallic compounds LaMg, LaMg2and La2Mg17were treated as

stoi-chiometric, while LaMg3 and LaMg12, which have a

homo-geneity range, were treated as (La,Mg)Mg3 and

(La,Mg)-(La,Mg)12, respectively (Cuiping & Zhenmin, 2004). Only

X-ray powder diffraction analysis has previously been undertaken for LaMg2(Kostet al.,1987) and no single-crystal

structural investigation has been carried out.

In the present work, we are interested in the synthesis and determination of the structural arrangement of LaMg2 by

X-ray single-crystal diffraction. The single crystals obtained are not very sensitive to air and moisture.

The structural arrangement of LaMg2at room temperature

seems to be the same as that of the Laves phase structure type of MgCu2. If we consider the arrangement of Mg atoms one

can see that they are disposed at the corners of tetrahedra and that these tetrahedra are linked into a three-dimensional framework by sharing each Mg atom with an adjacent tetra-hedron (Fig. 1); the disposition of the Mg atoms is therefore geometrically the same as that of O atoms in -cristobalite (Evans 1964). The cavities in this framework of Mg atoms are occupied by the larger La atoms, arranged in the same way as the C atoms in diamond.

The structure of the title compound contains different coordination polyhedra around the La and Mg atoms. The coordination sphere of lanthanum (site symmetry 1; Fig. 2) consists only of 12 Mg atoms with equal La–Mg distances (Table 1). The polyhedron around lanthanum can be described with four regular triangular faces and four hexagonal faces.

Magnesium (site symmetry 3m) is bonded to six lanthanum and six other magnesium neighbors (Fig. 3), with La—Mg and Mg—Mg distances of 3.6524 (8) and 3.1148 (7) A˚ , respectively, giving rise to distorted MgLa6 and MgMg6 octahedra. The

LaMg12 polyhedra are connected together by sharing

trian-gular faces.

Experimental

During the preparation of alkali/rare earth metal alloys, difficulties arise from the relatively low boiling points of the alkali metals compared with the high melting temperatures of the rare earth metals (Rangeet al.,1989). Essentially, a conventional melting process based on powder metallurgy cannot produce magnesium-based inter-metallics with a specific chemical composition, because magnesium evaporates easily as a result of its high vapor pressure. Thus, a repeated melting process with an additional supply of magnesium is needed to prepare an intermetallic (Liquan et al., 2004). Single crystals were extracted from alloys obtained by arc melting of the initial components (purity better than 99.9%) in an electric arc furnace in an argon atmosphere. A preliminary crystal investigation was performed using Laue and rotation methods (RKV-86 and RGNS-2 chambers, MoKradiation).

Crystal data

LaMg2

Mr= 187.53

Cubic,Fd3m a= 8.810 (2) A˚

V= 683.8 (3) A˚3 Z= 8

Dx= 3.642 Mg m

3

MoKradiation

Cell parameters from 25 reflections

= 2.2–27

= 12.55 mm1

T= 295 K

Elongated tablet, colorless

0.360.10.07 mm

Data collection

Oxford Diffraction Xcalibur point-detector diffractometer

!/2scans

Absorption correction: Gaussian (JANA2000; Petriceket al., 2000)

Tmin= 0.323,Tmax= 0.550

648 measured reflections 50 independent reflections 46 reflections withI> 3(I)

Rint= 0.031

max= 26.6

h=11!11

k=11!11

l= 0!11

3 standard reflections every 100 reflections intensity decay: 1.1%

inorganic papers

i156

2 Acta Cryst.(2005). E61, i155–i157

Figure 2

Coordination sphere of the La atom in the LaMg2structure.

Figure 3

Refinement

Refinement onF2

R[F2_{> 2(F}2_{)] = 0.008} wR(F2) = 0.025

S= 1.14

50 reflections

4 parameters

w= 1/[2_{(I) + 0.0004I}2_]

(/)max= 0.002

max= 0.11 e A˚

3

min=0.09 e A˚

3

Table 1

Selected geometric parameters (A˚ ,_).

La1—Mg1i 3.6524 (8) Mg1—Mg1ii 3.1148 (7)

Mg1i

—La1—Mg1iii

117.036

Mg1i—La1—Mg1iv 95.216

Mg1i

—La1—Mg1 50.479

Mg1i

—La1—Mg1v

144.903 La1vi

—Mg1—La1vii

117.036 La1vi

—Mg1—La1viii

180

La1vi

—Mg1—La1 62.964

La1vi—Mg1—Mg1ii 115.239

La1vi

—Mg1—Mg1 64.761

Mg1ii

—Mg1—Mg1 180

Mg1ii

—Mg1—Mg1v

120 Mg1ii

—Mg1—Mg1 60

Symmetry codes: (i)xþ1;y;z; (ii)yþ1

2;þxþ14;þz14; (iii)þxþ12;y;þzþ12; (iv)

yþ1;þxþ1 4;þzþ

1 4; (v)xþ

1 4;yþ

5

4;z; (vi) x1;y;z; (vii)þx 1 2;y;þz

1 2;

(viii)xþ1;yþ1;z.

Data collection: KM4B8(Galdecki et al., 1996); cell refinement:

KM4B8; data reduction: JANA2000 (Petricek et al., 2000); program(s) used to solve structure:JANA2000; program(s) used to refine structure: JANA2000; molecular graphics: DIAMOND

(Brandenburg, 1999); software used to prepare material for publi-cation:JANA2000.

This work was supported by the Grant Agency of the Czech Republic, grant 202/03/0430.

References

Brandenburg, K. (1999). DIAMOND. Version 2.1c. Crystal Impact GbR,

Bonn, Germany.

Cuiping, G. & Zhenmin, D. (2004).J. Alloys Compd,385, 109–113.

Evans, R. C. (1964).An Introduction to Crystal Chemistry, 2nd ed., pp. 312–

313. Cambridge University Press.

Galdecki, Z., Kowalski, A., Kucharczyk, D. & Uszynski, I. (1996).KM4B8.

Kuma Diffraction Ltd, Wrocław, Poland.

Klaus, S. (2000).J. Solid State Chem.149, 155–166.

Kost, M. E., Kuznetsov, N. T. & Shilov, A. L. (1987).Dokl. Akad. Nauk SSSR,

292, 632–634.

Liao, B., Lei, Y., Chen, L., Pan, H. & Wang, Q. (2004).J. Alloys Compd,376, 186–195.

Liang, J., Xianfeng, M., Jinkui, T., Xuewei, Y., Zhao, W. & Zhao, M. (2003).

Intermetallics,11, 875–878.

Liquan, L., Saita, I., Saito, K. & Akiyama, T. (2004).J. Alloys Compd,372, 218–223.

Leisure, R., Foster, K., Hightower, J. & Agosta, D. (2003).J. Alloys Compd,

356, 283–289.

Petricek, V., Dusek, M. & Palatinus, L. (2000).JANA2000. Institute of Physics, Prague, Czech Republic.

Range, K. J., Klement, U. & Rau, F. (1989).Acta Cryst.C45, 1069–1070.

inorganic papers

Acta Cryst.(2005). E61, i155–i157 Belgacemet al. _LaMg

supporting information

sup-1 Acta Cryst. (2005). E61, i155–i157

supporting information

Acta Cryst. (2005). E61, i155–i157 [https://doi.org/10.1107/S1600536805021343]

Lanthanum dimagnesium

Besma Belgacem, Samia Yahyaoui, P. Yu. Demchenko, O. I. Bodak, Michal Dusek and Rached

Ben Hassen

Lanthanum Dimagnesium

Crystal data

LaMg2

Mr = 187.53

Cubic, Fd3m

Hall symbol: -F 4vw 2vw 3

a = 8.810 (2) Å

V = 683.8 (3) Å3

Z = 8

F(000) = 648

Dx = 3.642 Mg m−3

Mo Kα radiation, λ = 0.71069 Å Cell parameters from 25 reflections

θ = 2.2–27°

µ = 12.55 mm−1

T = 295 K

Elongated tablet, colorless 0.36 × 0.1 × 0.07 mm

Data collection

Oxford Diffraction point-detector diffractometer

Radiation source: fine-focus sealed tube Graphite monochromator

ω/2θ scans

Absorption correction: gaussian (JANA2000; Petricek et al., 2000)

Tmin = 0.323, Tmax = 0.550 648 measured reflections

50 independent reflections 46 reflections with I > 3σ(I)

Rint = 0.031

θmax = 26.6°, θmin = 4.0°

h = −11→11

k = −11→11

l = 0→11

3 standard reflections every 100 reflections intensity decay: 1.1%

Refinement

Refinement on F2

R[F > 3σ(F)] = 0.008

wR(F) = 0.025

S = 1.14 50 reflections 4 parameters

Primary atom site location: Patterson

Secondary atom site location: difference Fourier map

Weighting scheme based on measured s.u.'s w = 1/(σ2_{(I) + 0.0004I}2₎

(Δ/σ)max = 0.002 Δρmax = 0.11 e Å−3 Δρmin = −0.09 e Å−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

supporting information

sup-2 Acta Cryst. (2005). E61, i155–i157

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2₎

x y z Uiso*/Ueq

La1 0.625 0.625 0.125 0.0195 (2) Mg1 0 0.5 0 0.0145 (2)

Atomic displacement parameters (Å2₎

U11 _U22 _U33 _U12 _U13 _U23

La1 0.0195 (2) 0.0195 (2) 0.0195 (2) 0 0 0

Mg1 0.0145 (3) 0.0145 (3) 0.0145 (3) −0.0012 (5) −0.0012 (5) −0.0012 (5)

Geometric parameters (Å, º)

La1—Mg1i _{3.6524 (8) La1—Mg1}x _{3.6524 (8)} La1—Mg1ii _{3.6524 (8) La1—Mg1}xi _{3.6524 (8)} La1—Mg1iii _{3.6524 (8) La1—Mg1}xii _{3.6524 (8)} La1—Mg1iv _{3.6524 (8) Mg1—Mg1}xiii _{3.1148 (7)} La1—Mg1v _{3.6524 (8) Mg1—Mg1}xiv _{3.1148 (7)} La1—Mg1vi _{3.6524 (8) Mg1—Mg1}vii _{3.1148 (7)} La1—Mg1vii _{3.6524 (8) Mg1—Mg1}xv _{3.1148 (7)} La1—Mg1viii _{3.6524 (8) Mg1—Mg1}xvi _{3.1148 (7)} La1—Mg1ix _{3.6524 (8) Mg1—Mg1}xii _{3.1148 (7)}

supporting information

sup-3 Acta Cryst. (2005). E61, i155–i157

supporting information

sup-4 Acta Cryst. (2005). E61, i155–i157

Mg1vii_—La1—Mg1viii _{117.036 La1}xxi_—Mg1—Mg1xii _64.761 Mg1vii_—La1—Mg1ix _{117.036 La1}xxii_—Mg1—La1xvii _62.964 Mg1vii_—La1—Mg1x _{95.216 La1}xxii_—Mg1—La1xviii _62.964 Mg1vii_—La1—Mg1xi _{95.216 La1}xxii_—Mg1—La1xix ₁₈₀ Mg1vii_—La1—Mg1xii _{50.479 La1}xxii_—Mg1—La1xx _117.036 Mg1viii_—La1—Mg1i _{95.216 La1}xxii_—Mg1—La1xxi _117.036 Mg1viii_—La1—Mg1ii _{50.479 La1}xxii_—Mg1—Mg1xiii _115.239 Mg1viii_—La1—Mg1iii _{95.216 La1}xxii_—Mg1—Mg1xiv _64.761 Mg1viii_—La1—Mg1iv _{95.216 La1}xxii_—Mg1—Mg1vii _64.761 Mg1viii_—La1—Mg1v _{144.903 La1}xxii_—Mg1—Mg1xv _115.239 Mg1viii_—La1—Mg1vi _{50.479 La1}xxii_—Mg1—Mg1xvi _64.761 Mg1viii_—La1—Mg1vii _{117.036 La1}xxii_—Mg1—Mg1xii _115.239 Mg1viii_—La1—Mg1ix _{117.036 Mg1}xiii_—Mg1—Mg1xiv ₁₈₀ Mg1viii_—La1—Mg1x _{50.479 Mg1}xiii_—Mg1—Mg1vii ₁₂₀ Mg1viii_—La1—Mg1xi _{144.903 Mg1}xiii_—Mg1—Mg1xv ₆₀ Mg1viii_—La1—Mg1xii _{95.216 Mg1}xiii_—Mg1—Mg1xvi ₆₀ Mg1ix_—La1—Mg1i _{50.479 Mg1}xiii_—Mg1—Mg1xii ₁₂₀ Mg1ix_—La1—Mg1ii _{95.216 Mg1}xiv_—Mg1—Mg1xiii ₁₈₀ Mg1ix_—La1—Mg1iii _{144.903 Mg1}xiv_—Mg1—Mg1vii ₆₀ Mg1ix_—La1—Mg1iv _{50.479 Mg1}xiv_—Mg1—Mg1xv ₁₂₀ Mg1ix_—La1—Mg1v _{95.216 Mg1}xiv_—Mg1—Mg1xvi ₁₂₀ Mg1ix_—La1—Mg1vi _{95.216 Mg1}xiv_—Mg1—Mg1xii ₆₀ Mg1ix_—La1—Mg1vii _{117.036 Mg1}vii_—Mg1—Mg1xiii ₁₂₀ Mg1ix_—La1—Mg1viii _{117.036 Mg1}vii_—Mg1—Mg1xiv ₆₀ Mg1ix_—La1—Mg1x _{144.903 Mg1}vii_—Mg1—Mg1xv ₁₈₀ Mg1ix_—La1—Mg1xi _{50.479 Mg1}vii_—Mg1—Mg1xvi ₁₂₀ Mg1ix_—La1—Mg1xii _{95.216 Mg1}vii_—Mg1—Mg1xii ₆₀ Mg1x_—La1—Mg1i _{95.216 Mg1}xv_—Mg1—Mg1xiii ₆₀ Mg1x_—La1—Mg1ii _{95.216 Mg1}xv_—Mg1—Mg1xiv ₁₂₀ Mg1x_—La1—Mg1iii _{50.479 Mg1}xv_—Mg1—Mg1vii ₁₈₀ Mg1x_—La1—Mg1iv _{144.903 Mg1}xv_—Mg1—Mg1xvi ₆₀ Mg1x_—La1—Mg1v _{95.216 Mg1}xv_—Mg1—Mg1xii ₁₂₀ Mg1x_—La1—Mg1vi _{50.479 Mg1}xvi_—Mg1—Mg1xiii ₆₀ Mg1x_—La1—Mg1vii _{95.216 Mg1}xvi_—Mg1—Mg1xiv ₁₂₀ Mg1x_—La1—Mg1viii _{50.479 Mg1}xvi_—Mg1—Mg1vii ₁₂₀ Mg1x_—La1—Mg1ix _{144.903 Mg1}xvi_—Mg1—Mg1xv ₆₀ Mg1x_—La1—Mg1xi _{117.036 Mg1}xvi_—Mg1—Mg1xii ₁₈₀ Mg1x_—La1—Mg1xii _{117.036 Mg1}xii_—Mg1—Mg1xiii ₁₂₀ Mg1xi_—La1—Mg1i _{50.479 Mg1}xii_—Mg1—Mg1xiv ₆₀ Mg1xi_—La1—Mg1ii _{144.903 Mg1}xii_—Mg1—Mg1vii ₆₀ Mg1xi_—La1—Mg1iii _{95.216 Mg1}xii_—Mg1—Mg1xv ₁₂₀ Mg1xi_—La1—Mg1iv _{95.216 Mg1}xii_—Mg1—Mg1xvi ₁₈₀

Symmetry codes: (i) x+1, y, z; (ii) x+1/2, y, z+1/2; (iii) x+1/2, y+1/2, z; (iv) −y+1, x+1/4, z+1/4; (v) −y+1, x+3/4, z−1/4; (vi) −y+3/2, x+3/4, z+1/4; (vii) −x+1/4, −y+5/4, z; (viii) −x+3/4, −y+5/4, z+1/2; (ix) −x+3/4, −y+3/4, z; (x) y+1/4, −x+1, z+1/4; (xi) y+1/4, −x+1/2, z−1/4; (xii) y−1/4, −x+1/2, z+1/4; (xiii) −y+1/2, x+1/4, z−1/4; (xiv) −y+1/2, x+3/4, z+1/4; (xv) −x−1/4, −y+3/4, z; (xvi) y−3/4, −x+1/2, z−1/4; (xvii) x−1, y, z; (xviii) x−1/2, y, z−1/2; (xix) x−1/2,