et al.

(1)

N otizen 1363

T h e Space G roup o f M gA l2S e4 and M gIn2S e4

K laus-Jürgen Range*

Institut für A n organ isch e C hem ie,

U n iversität R egen sb urg, U n iversitätsstrasse 31, D -9 3 0 5 3 R egen sb u rg, G erm any

Z. N aturforsch. 51b, 1 3 6 3 -1 3 6 4 (1996);

receiv ed June 7, 1996

M agnesium D ialu m in iu m T etraselen id e, M agnesium D iin d iu m T etraselen id e, Sp ace G roup, C rystal Structure

T he correct sp ace group o f M g A l2S e4 and M gIn 2S e4 is m ost probably R 3 m and not R 3 m as p reviou sly reported.

T he crystal structures of M gA l2Se4 and M g In 2Se4 were d eterm in ed 20 years ago by D ot- zel, S chäfer and Schön from Precession and Weis- sen b erg data [1], These authors selected the a cen tric space group R3m for both com pounds by analogy w ith the structure of the (III)a-polytypic m odification of Z n In 2S4 [2],

R ecently we could show th at the analogous c o m p o u n d M nIn2Se4 [3] is basically isostructural w ith M gIn2Se4. All attem pts, how ever, to refine th e stru ctu re of M n In 2Se4 in the acentric space g ro u p R3m failed com pletely. D uring the refin e

m en t p o o r convergence, strong correlations and ir

reg u lar beh av io u r of even the isotropic therm al p a ra m e te rs w ere observed. These are typical sym ptom s w hen a centrosym m etric stru ctu re is re fined in a non-centrosym m etric space group. It fi

nally ap p e a re d th at space group R 3 m is indeed th e co rrect one for M nIn2Se4 [3],

A n inspection of the d ata given by Schäfer

et al.

[1] show s th a t the sam e might be true for M g In 2Se4 and M gA l2Se4 as well. If for M gA l2Se4 0.167 is su b tracted from all z co ordinates of the p u blished stru ctu re (an allowed tran sfo rm atio n b ecause of the floating origin in R 3m ), a new set of co o rd in ates is o b tained, in which the two alu

m inium atom s A l(l), A l(2) as well as the selenium ato m s S e (l), Se(2) and Se(3), Se(4) respectively, are re lated by a c e n ter of sym m etry at the origin

* R ep rin t req u ests to Prof. Dr. K.-J. Range.

Table I. A to m ic co o rd in a tes for M g A l2S e4 in sp ace group R 3 m as given by D o tz e l et al. [1] and after a shift o f the origin.

A to m ic co o rd in a tes as given A to m ic coord in ates by D o tz e l et al. [1] after shifting the origin by

A to m X y z

(0,0,

X

-0 .1 6 7 )

y z

M g 0 0 0 .1 6 7 (3 ) 0 0 0

A l ( l ) 0 0 0 .9 3 3 (3 ) 0 0 0.766

A l(2 ) 0 0 0 .4 0 4 (3 ) 0 0 0.237 = -0 .7 6 3 S e ( l ) 0 0 0 .0 4 4 (1 ) 0 0 -0 .1 2 3

S e (2 ) 0 0 0 .2 9 1 (1 ) 0 0 0.124

S e (3 ) 0 0 0 .4 6 5 (1 ) 0 0 0.298

S e (4 ) 0 0 0 .8 6 9 (1 ) 0 0 0.702 = -0 .2 9 8

(0,0,0), occupied by the m agnesium atom s (Ta

ble I). T he sam e relatio n holds for M gIn2Se4.

U n fortunately, the original X -ray d ata are not available for a re-refin em en t of the structures of M gA l2Se4 and M gIn2Se4. T here is little doubt, how ever, th at the centrosym m etric space group R 3 m is indeed the correct one for these two com pounds. N o co o rd in ate has to be changed by m ore th an one stan d ard d eviation in o rd er to conform w ith the space group R 3 m .

Table II shows the revised crystallographic data for M gA l2Se4 and M gIn2Se4 as well as a com pari

son with th e d ata for M n In 2Se4 [3] and (III)a- Z n In 2S4 [4]. A s can bee seen from these data, the stru ctu ral type p re se n te d here can accom odate cations w ith various site p references for te tra h e dral or o ctah ed ral co o rdination. E xam ples for com pounds M M ’2X 4 w ith a “n o rm a l” cation distri

b u tio n (M octM ’2tetX 4,

e.g.,

M gA l2Se4) or with an

“ in v erse” cation d istrib u tio n (M ’octM tetM 'tetX 4,

e.g.,

Z n In 2S4) as well as com pounds with a statisti

cal cation d istrib u tio n

(e.g.,

M gIn2Se4 and M n In 2Se4) can be found.

It should be em p hasized th at the centric space group R 3 m was found to be the correct one also for the p ro to ty p e com p o u n d (III)a-Z n In 2S4 [4], For this co m p o u n d th e stru ctu ral changes in tro d uced by the space g ro u p change are ra th e r seri

ous: in co n trast to th e original description [2] th ere is a statistical d istrib u tio n of In and Z n over the te tra h e d ral positions. T he essential crystallochem i- cal featu res of the stru ctu res of M gA l2Se4 and M gIn2Se4, how ever, rem ain u n altered by the space group change, so th a t th e description given in [1]

is still valid.

This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution-NoDerivs 3.0 Germany License.

On 01.01.2015 it is planned to change the License Conditions (the removal of the Creative Commons License condition “no derivative works”). This is to allow reuse in the area of future scientific usage.

Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschung in Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht:

Creative Commons Namensnennung-Keine Bearbeitung 3.0 Deutschland Lizenz.

Zum 01.01.2015 ist eine Anpassung der Lizenzbedingungen (Entfall der Creative Commons Lizenzbedingung „Keine Bearbeitung“) beabsichtigt, um eine Nachnutzung auch im Rahmen zukünftiger wissenschaftlicher Nutzungsformen zu ermöglichen.

(2)

1364 N otizen Table II. Revised crystallographic data for MgAl2Se4 and MgIn2Se4 and comparison with MgIn2Se4 and (III)a-ZnIn2S4.

MgAl2Se4 MgIn2Se4 MnIn2Se4 [3] (III)a-ZnIn2S4 [4]

Space group R3m R3m R3m R3m

Unit cell parameters

«[A ] 3.88(1) 4.07(1) 4.051(1) 3.8674(3)

c[A ] 38.34(5) 39.50(5) 39.464(2) 37.007(5)

c/a

9.881 9.705 9.742 9.569

V [A?] 499.86 566.65 560.86 479.35

Z

Atomic coordinates

3 3 3 3

Moct in 3 a: (0, 0, 0)

Moc, Mg 0.5 Mg + 0.5 In 0.56 Mn + 0.44 In In

Mtet in 6c: ± (0, 0,

z)

Mtet Al 0.25 Mg + 0.75 In 0.22 Mn + 0.78 In 0.5 Zn + 0.5 In

z

0.236 0.234 0.23404(3) 0.22956(3)

X (l) in 6c: ± (0, 0,

z)

X (l) Se Se Se S

z

^0.123 ^0.127 ^0.12764(3) ^0.12593(4)

X(2) in 6c: ±(0, 0,

z)

X(2) Se Se Se S

z

0.298 0.298 0.29807(3) 0.29622(7)

[1] P. Dotzel, H. Schäfer. G. Schön, Z. Anorg. Allg. [3] K.-J. Range, U. Klement, G. Döll, E. Bucher, J. R.

Chem. 426, 260 (1976). Baumann, Z. Naturforsch. 46b. 1122 (1991).

[2] F. Lappe, A. Niggli. R. Nitsche, J. G. White. Z. Kris- [4] N. Berand, K.-J. Range. J. Alloys Comp. 205. 295

tallogr. 117, 146 (1962). (1994).