Er2Au2Sn and other Ternary Rare Earth Metal Gold Stannides with

Er2Au2Sn and other Ternary Rare Earth Metal Gold Stannides with Ordered
Zr3A l2-Type Structure
Rainer Pöttgen
M ax-Planck-Institut für F estkörperforschung, H eisenbergstraße 1, D-70569 S tuttgart,
G erm any
Z. N aturforsch.
49b,
1309-1313 (1994); received M ay 20, 1994
R are E arth G old Tin, Interm etallic C om pounds, O rd ered Z r3A l2-Structure
The ternary stannides R E 2A u2Sn (R E = Y, Dy, H o, E r, Tm , Lu) w ere p rep ared by arcm elting of the elem en tal com ponents and su b seq u en t annealing at 800 °C. The stru ctu re of
E r2A u2Sn (single crystal. X-ray, P 4 2/m nm , Z = 4, a = 778.2(2) pm , c = 739.6(3) pm , V =
0.4479 nm 3 and R = 0.026) is described as the tern ary ord ered version of the Z r3A l2-type
structure, a su p erstru ctu re o f th e U 3Si2-type. It consists of tw o-dim ensionally infinite layers
(A u2Sn)„ which are sep arated by the erbium atom s. The structure is built up from slightly
distorted [SnE r8] square prism s and [A uE r6] trigonal prism s which are condensed in all three
directions. T hese fragm ents are derived from th e well know n A1B2 and CsCl-type structures.
Introduction
Uranium forms a silicide of composition U 3Si2
[1, 2]. Its tetragonal crystal structure (space group
P4/mbm) contains two different uranium positions
and one silicon site. Several years ago it was ob­
served, that these three different crystallographic
sites may also be occupied by three different
atoms, thus forming a ternary ordered version of
the U3Si2-type with the composition R 2T2X. N u­
merous investigations of such compounds resulted
in the syntheses of several borides [3], aluminides
[4-6], indides [7], silicides [8], and phosphides [9],
Only very recently the first ternary uranium tran­
sition metal stannides U 2T2Sn (T = Fe, Co, Ni, Ru,
Rh, Pd) and indides U 2T2In (T = Co, Ni, Rh, Pd,
Ir, Pt) have been reported [10-12].
Interestingly, the binary aluminide Z r3Al2 [13]
forms a crystal structure very similar to U 3Si2.
However, the difference in size between the zir­
conium and aluminium atoms results in small dis­
tortions and in a doubling of the c lattice constant
as compared to U 3Si2. Z r3Al2 may therefore be
considered as a superstructure of U 3Si2, crystalliz­
ing in the klassengleiche supergroup P 42/mnm. In
the present paper we report on the first rare-earth
stannides R E 2Au2Sn (R E = Y, Dy, Ho, Er, Tm,
Lu) with the ternary ordered Z r3Al2-type. Very re­
cently the same ordered structure has been re­
ported for U 2Pt2Sn [14] and U 2Ir2Sn [15] from in­
dependent investigations.
Sample Preparation and Lattice Constants
Starting materials for the preparation of the ter­
nary stannides were ingots of the rare-earth el­
ements (Johnson Matthey, >99.9%), gold wire
(Degussa, 99.9%) and tin granules (Merck,
99.9%). The samples were prepared by arc-melt­
ing of the elemental components of the ideal com­
positions in an argon (99.996%) atmosphere. The
argon was further purified by molecular sieves and
an oxisorb catalyst [16]. The melted buttons were
turned over and remelted several times to ensure
good homogeneity. The weight loss after several
meltings was always smaller than 0.5%. The pel­
lets were subsequently enclosed in evacuated silica
tubes and annealed at 800 °C for ten days. All
melted and annealed buttons had a light grey
color, but the materials are dark grey in powdered
form. Single crystals of E r2Au2Sn have metallic
lustre. They are stable in air over long periods of
time.
The tetragonal lattice constants (see Table I)
were obtained by least-squares fits of the Guinier
powder data. CuKö! radiation was used with 5N
silicon (a = 543.07 pm) as an internal standard.
The identification of the diffraction lines was fa­
cilitated by intensity calculations [17] using the
positional param eters of the refined structure.
* R eprint requests to R. Pöttgen.
0932-0776/94/1000-1309 $06.00
© 1994 Verlag der Zeitschrift für Naturforschung. A ll rights reserved.
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.
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.
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.
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.
R. Pöttgen • Er 2 Au2Sn
1310
Table I. L attice constants (pm ) of the tetragonal stannides with E r2A u2Sn-type structure.
C om pound
fl(pm)
c(pm )
c/a
V (nm 3)
Y 2A u2Sn
D y2A u2Sn
H o 2A u2Sn
E r2A u2Sn
Tm^AuoSn
L u2A u2Sn
781.4(1)
782.2(1)
779.7(1)
778.2(2)
776.0(3)
772.8(6)
753.5(1)
750.3(1)
745.5(1)
739.6(3)
738.0(4)
734.2(6)
0.964
0.959
0.956
0.950
0.951
0.950
0.4601
0.4591
0.4532
0.4479
0.4444
0.4385
Structure Determination
The structural similarity of the stannides with
the U 3Si2-type structure was already recognized
on the Guinier powder patterns, but several weak
reflections remained, and the whole pattern could
only be indexed, when doubling the c lattice con­
stant, indicating a superstructure. Further investi­
gations were then carried out on single-crystals in
order to determ ine the correct structure. Single­
crystals of E r2Au2Sn were isolated from an an­
nealed button by mechanical fragmentation. They
were examined with a Buerger precession camera
to establish their symmetry and suitability for
intensity data collection. The crystals had the high
Laue symmetry 4/mmm, and the systematic extinc­
tions (OkI observed only with k + l - 2n, hOO only
with h - 2n) led to the space groups P 42/mnm,
P4n2, and P 42nm. The structure refinements
eventually showed that the space group with the
highest symmetry compatible with these extinc­
tions P 42/mnm - D 44h was the correct one.
Intensity data were collected on an autom ated
four-circle diffractom eter (CAD 4) with graphite
m onochrom ated A gK a radiation and a scintil­
lation counter with pulse-height discrimination.
Further experimental details are summarized in
Table II.
The starting atomic param eters were deduced
from a Patterson interpretation [18] and the struc­
ture was then successfully refined using SHELXL93 [19], which minimizes a weighted square re­
sidual “w R 2” from all data using structure ampli­
tudes IF21 rather than structure factors F. The
standard residual “R l ” is calculated purely for
comparision. Measured intensities more than two
sigma below zero (one independent reflection)
were suppressed for refinement purposes. The final
residuals are listed in Table II. The final difference
Fourier synthesis revealed as highest peak an elec-
Table II. C rystal d ata and stru ctu re refin em en t for
E r2A u2Sn.
Empirical formula
Formula weight
Temperature
Wavelengths
Crystal system
Space group
Unit cell dimensions
Formula units per cell
Calculated density
Crystal size
Absorption coefficient
F(000)
0 range for data collection
Range in h k l
Total no. reflections
Independent reflections
Refinem ent m ethod
Data/restraints/parameters
G oodness-of-fit on F 2
Final R indices [I>2cr(I)]
R indices (all data)
Extinction coefficient
Largest diff. peak and hole
Er2Au2Sn
847.14
293(2) K
56.087 pm
4/mmm
P 42/mnm
see Table I
Z =4
12.563 Mg/m 3
4 0 x 5 0 x 6 0 ^m 3
578.1 cm “1
1376
3.70° to 34.99°
+ 12, ± 12, ±11
3729
569 (R mt = 0.0552)
Full-matrix least-squares on
F2
568/0/18
1.211
R 1=0.0257, wR 2 = 0.0558
R 1 = 0.0330, wR 2 = 0.0625
0.00020(7)
5186 and -2 7 0 4 e/nm 3
Table III. A tom ic co o rd in ates and anisotropic displace­
m en t p a ram eters (pm 2x l 0 _1) for E r2A u2Sn. U eq is d e ­
fined as one third of the trace of the o rthogonalized U,y
tensor. T he anisotropic displacem ent facto r exponent
takes the form : - 2 j i 2[(ha*)2\J n -\-----\-2 h k a * b * \J i2]Atom
P42/mnm
X
E rl
Er 2
Au
Sn
4f
4g
0.1836(1)
0.3427(1)
0.3724(1)
4d
0
Atom
u„ = U 22
u 33
u 23 =
E rl
Er 2
Au
Sn
12( 1)
12( 1)
7(1)
7(1)
12( 1)
23(1)
0
0
0 ( 1)
0
8j
7(1)
8 ( 1)
-
y
z
u eq
X
0
0
10( 1)
10( 1)
0.2784(1)
1/4
9(1)
13(1)
u13
u12
X
X
1/2
- 4 (1 )
5(1)
- 2 ( 1)
0
tron density of 5186 e/nm3, too close to the Au pos­
ition to be suitable for an additional atomic site. It
most likely resulted from an incomplete absorption
correction of the data. Atomic coordinates and an­
isotropic therm al param eters are given in Table III,
interatomic distances in Table IV*.
* F u rth e r d etails m ay be o b tain ed from th e Fachinform ationszentrum K arlsruhe, G esellschaft für w issen­
schaftlich-technische In form ation m bH . D-76344 Eggenstein-L eopoldshafen (G erm an y ) on quoting the
depository n u m b er CSD 58358. the nam e of the
a u th o r and th e jo u rn al citation.
1311
R. Pöttgen • Er 2 Au2Sn
Table IV. Interatom ic distances (pm ) in th e stru ctu re of
E r2A u2Sn. All distances sh o rter than 530 pm ( E r - A u ,
E r - S n ) , 410 pm (A u -A u , A u -S n ) and 365 pm ( E r - E r ,
S n -S n ) are listed. S tandard deviations are all equal or
less than 0.1 pm.
E r l:
2 Au 292.5
4 Au 295.7
4 Sn 339.4
E r 2:
2
4
1
4
Au
Au
Er 2
Sn
Au:
1
1
1
2
2
2
1
288.0
303.4
346.1
346.9
Sn:
Au
Er 2
E rl
E rl
Er 2
Sn
Au
280.8
288.0
292.5
295.7
303.4
307.1
327.9
4 Au 307.1
4 E r l 339.4
4 E r 2 346.9
0 1/2
u
O
Rh
•
Sn
#
U2 Rh 2 Sn
Discussion
Six ternary stannides R E 2Au2Sn (R E = Y, Dy,
Ho, Er, Tm, Lu) were synthesized and their crystal
structure was determined from single crystal dif­
fractom eter data for the erbium compound. The
structure of E r2Au2Sn represents a new type. It is
derived from the structure of binary Z r3Al2 [13]
by an ordered arrangement of the E r l , E r 2, Au
and Sn atoms on the Z r l, Zr2, Al and Z r3 po­
sitions of Z r3Al2, respectively. Ternary stannides
with the ordered U3Si2 type structure have been
reported recently: U 2T2Sn (T = Fe, Co, Ni, Ru,
Rh, Pd) [10-12]. Interestingly, Z r3A l2 (space
group P 42/mnm) is a superstructure of the binary
uranium silicide U3Si2 (space group P4/mbm)
[1, 2]. Small distortions, due to the difference in
size between zirconium and aluminium [13], result
in a doubling of the lattice constant c, when com­
pared to U 3Si2. Thus, Z r3Al2 crystallizes in the
klassengleiche supergroup P42/mnm of U 3Si2. The
crystallographic relationship between the struc­
tures of U 3Si2 [1, 2] and Z r3Al2 [13] and their terP4/m2i/b2/m
P4/m2i/b27m
P42/m2i/n2/m
P42/m2i/n2/m
k2
|U 2 R h 2 S n |
M -----
|Zf3Al2| ---- ► |Er2Au2Sn]
| U3Si21
Fig. 2. P rojections o f the crystal structures of U 2R h 2Sn
(o rd ered U 3Si2-type) and E r2A u2Sn (o rd ered Z r3A l2type) on th e x y plane. The z p aram eters of the atom s
are indicated. The A1B2- and CsCl-like fragm ents are
outlined. The tw o different erbium positions in the stru c­
tu re of E r2A u2Sn are indicated.
31, 32, 2c
1/2 , 0 , 0
r —►
'— ►
Sn
Rh
2a
4g
U2
Si
2a
4g
Zr1
Zr2
Zr3
Al
4f
4g
4d
8j
Er1
Er2
Sn
Au
4f
4g
4d
8j
Fig. 1. C rystal chemical relationship b etw een the stru c­
tures of U 3Si2, Z r3A l2, U 2R h 2Sn and E r2A u2Sn. The
space group, the group-subgroup relationship and occu­
pancy of the different W yckoff sites is indicated.
nary ordered variants U 2R h2Sn [10-12] and
E r2Au2Sn is shown in Fig. 1 in the manner for­
malized by Bärnighausen [20],
The crystal structures of E r2Au2Sn and the un­
distorted variant U 2Rh2Sn are shown in Fig. 2 as
projections on the xy planes. From this Figure it
can clearly be seen that both structures are built
1312
up from [SnU8] and [SnEr8] tetragonal prisms and
[RhU6] and [AuEr6] trigonal prisms, respectively.
However, both types of prisms are distorted in the
structure of Er2Au2Sn, while they are more or less
regular in the uranium compound. Always two of
the [AuEr6] prisms are face-shared forming an
AlB2-like fragment. The [SnEr8] fragments are de­
rived from the well known CsCl-type structure.
However, no binary compound of the composition
ErSn is known [3] and ErA u2 crystallizes in the
tetragonal MoSi2-type structure [21], not in the
AlB2-type. Such an AlB2-type arrangem ent was
up to now only observed for the binary gold intermetallics BaAu2 [22], NbAu2 [23,24], ThAu2
[25,26], and UAu2 [27-29],
In E r2Au2Sn the A1B2- and CsCl-like fragments
are condensed within the xy plane by common
square faces in such a way, that every CsCl-fragm ent is connected to four AlB2-fragments and vice
versa. These layers are stacked one upon the other
in c direction.
Alternatively, the structure of E r2Au2Sn may
also be described as consisting of slightly waved
two-dimensionally infinite layers (Au2Sn)„ within
the xy plane which are separated by the rareearth atoms. The main difference between the
undistorted structure of U 2R h2Sn and the dis­
torted one of E r2Au2Sn is the slight puckering of
the Au2Sn-nets. A similar behavior was observed
recently for the silicides ThAuSi [30] and LuAuSi
[31]. While ThAuSi crystallizes with an ordered
AlB2-type (LiBaSi-type) structure, LuAuSi shows
a slight puckering of the BN-like hexagonal
AuSi-nets, resulting in the doubling of the c lat­
tice constant.
In the structure of E r2Au2Sn there are two
different crystallographic erbium positions, while
there is only one uranium position in U 2R h2Sn.
The Er 1 atoms have a coordination num ber
(C.N.) of 10 (6 Au and 4 Sn). The average E r l Au and E r l - S n distances amount ato 294.6 and
339.4 pm, respectively. A similar near neighbor
environment is observed for the Er2 atoms with
average E r2 -A u and E r2 -S n distances of 298.3
and 346.9 pm, respectively. However, the E r 2
atoms have a further Er 2 atom at 346.1 pm in
their coordination shell, while the nearest E r l E r l contact is 370.9 pm with a negligible bond­
ing character. This difference in the coordination
shell of the erbium atoms is certainly due to
R. Pöttgen • Er2 Au2Sn
the distortions in the superstructure. The larger
coordination num ber of the Er 2 atoms is also
reflected by the somewhat larger average Er 2 Au and E r2 -S n distances.
The gold atoms in E r2Au2Sn are all within the
distorted trigonal [Er6] prisms forming the A1B2like fragment. Each gold atom has two other gold
neighbors, one Au atom within the Au2Sn net­
work at 280.8 pm and one other Au atom in the
next Au2Sn plane at 327.9 pm. The coordination
shell of the gold atoms is completed by six Er
atoms at an average A u -E r distance of 296.5 pm
and two Sn atoms, each at 307.1 pm. The differ­
ence between the two A u -A u distances is quite
large. The short A u -A u contact of 280.8 pm
within the A1B2 fragments may certainly be con­
sidered as strongly bonding. This distance is even
somewhat smaller than the interatomic distance of
288.4 pm in elemental gold [32]. Similar short A u Au distances have also be determined in KAu5
[33] (277.4 and 283.1 pm), NaAu2 [34] (276.2 pm),
and UAu2 [29] (274.6 pm). The A u -A u distances
of 327.9 pm between the Au2Sn layers are about
40 pm longer than the corresponding distances in
elemental gold and may therefore only be con­
sidered as due to very weak interactions. However,
in molecular compounds like [Au(/-C3H 70 ) 2PS2]2
[35], i-C3H 7N H 2A u O C C 6H 5 [36] or
A u(III)(D M G )2Au(I)C12 [37] such secondary
bonds (291.4 pm up to 327 pm) are sufficiently
strong to cause dimerization in solution and poly­
m erization in the solid state. Similar weak A u Au interactions were also observed in Au2P3 and
Au7P 10l [38],
The tin atoms are located in the distorted square
prisms of the erbium atoms. They have four Er
neighbours at 339.4 pm and four Er neighbours at
346.9 pm. The average S n -E r distance of 343.2
pm is only somewhat longer than the S n -E r bond
length of 328.7 pm in binary ErSn3 [39] with
Cu3Au-type structure. The coordination shell of
the tin atoms is completed by four gold atoms at
a distance of 307.1 pm. This is essentially the same
value as the E r-A u distances of 306.1 pm in ErAu
[40] with CsCl-type structure.
Acknowledgments
I am grateful to Prof. Dr. Arndt Simon for his
interest and steady support of this work. I thank
Dr. H. Borrmann for the collection of the four-
R. Pöttgen • Er2 Au2Sn
1313
circle diffractometer data, W. Röthenbach for the
Guinier powder patterns, and Dr. W. G erhartz
(Degussa AG) for a generous gift of gold metal. I
am also indebted to the Stiftung Stipendienfonds
des Verbandes der Chemischen Industrie for a
Liebig fellowship.
[1] W. H. Z achariasen, A cta C rystallogr. 1, 265 (1948).
[2] K. Rem schnig, T. Le Bihan, H. N oel, P. Rogl, J.
Solid State Chem. 97, 391 (1992).
[3] P. Villars, L. D. C alvert, P earso n 's H an d b o o k of
C rystallographic D ata for In term etallic Phases, Se­
cond E dition, A m erican Society for M etals, M aterials Park, O H 44073 (1991).
[4] A. O. Sampaio, E. Santa M arta, H. L. Lukas, G. P etzow, J. Less-Com m on Met. 14, 472 (1968).
[5] A. P. Prevarskiy, Yu. B. Kuz’m a, M. S. Z rad a, R u s­
sian M etallurgy 177 (1979).
[6] A. T. Tyvanchuk, T. I. Yanson, B. Ya. K otur, O. S.
Z arechnyuk, M. L. K h arakterova, R ussian M etal­
lurgy 190 (1988).
[7] Ya. M. K alychak, V. I. Z arem b a, V. M. B aranyak,
P. Yu. Zavalii, V. A. Bruskov, L. V. Sysa, O. V.
D m ytrakh, Inorg. M ater. 26, 94 (1990).
[8] G. Steinberg, H.-U. Schuster, Z. N aturforsch. 34b,
1237 (1979).
[9] Ya. F. Lom nitskaya, Yu. B. K uz’m a, Inorg. M ater.
19, 1191 (1983).
[10] F. M iram bet, P. G ravereau, B. C hevalier, L. Trut, J.
E to u rn eau , J. A lloys C om pounds 191, L I (1993).
[11] M. N. Peron, Y. K ergadallan, J. R eb izan t, D. M eyer,
J. M. W inand, S. Z w irner, L. H avela, H. N akotte,
J. C. Spirlet, G. M. Kalvius, E. C olineau, J. L. O ddou, C. Jeandey, J. P. Sanchez, J. A lloys C om pounds
201, 203 (1993).
[12] F. M iram bet, B. Chevalier, L. Fournes, P. G rav ereau ,
J. E to u rn eau , J. A lloys C om pounds 203, 29 (1994).
[13] C. G. Wilson, F. J. Spooner, A cta Crystallogr. 13,
358 (1960).
[14] P. G ravereau, F. M iram bet, B. C hevalier, F. Weill, L.
Fournes, D. Laffargue, J. E to u rn e a u , 24lfemes Journees des A ctinides, A bstract PB.12, O bergurgl (A u ­
stria) (1994).
[15] L. C. J. Pereira, J. M. W inand, F. W astin, J. R ebizant,
J. C. Spirlet, 24lfemes Journees des A ctinides, A b ­
stract PB.9, O bergurgl (A ustria) (1994).
[16] H. L. Krauss, H. Stach, Z. A norg. Allg. C hem . 366,
34 (1969).
[17] K. Yvon, W. Jeitschko, E. P arth e, J. A ppl. C rys­
tallogr. 10, 73 (1977).
[18] G. M. Sheldrick, SH ELX -86, P rogram for the S olu­
tion of Crystal Structures, U niversity of G öttingen,
G erm any (1986).
[19 G. M. Sheldrick, SH ELX L-93, Program for the
C rystal S tructure R efinem ent, U niversity of
G ö ttin g en , G erm any (1993).
[20 H. B ärnighausen, C om m un. M ath. Chem . 9, 139
(1980).
[21 A. E. D w ight, J. W. Downey, R. A. C o n n er (Jr.),
A cta C rystallogr. 22, 745 (1967).
[22 G. B ruzzone, A tti A cad. Naz. Lincei 48, 235 (1970).
[23 K. S chubert, T. R. A n an th aram an , H. O. K. A ta,
H. G. M eissner, M. Pötzschke, W. R osstdeutscher,
E. Stolz, N aturw issenschaften 47, 512 (1960).
[24 A. E. D wight, M etallurgical Society C onferences,
Proceedings 10, 383 (1961).
[25 A. B row n, A cta Crystallogr. 14, 860 (1961).
[26 A. P alenzona, S. Cirafici, J. L ess-Com m on M et. 124,
245 (1986).
[27 A. D om m ann, F. H ulliger, J. Less-Com m on M et.
141, 261 (1988).
[28 A. P alenzona, S. Cirafici, J. L ess-Com m on M et. 143,
167 (1988).
[29 R. P ö ttg en , D. K aczorow ski, R.-D. H offm ann, V. H.
Tran, to be published.
[30 J. H. A lbering, R. Pöttgen, W. Jeitschko, R.-D.
H offm ann, B. C hevalier, J. E to u rn eau , J. Alloys
C o m pounds 206, 133 (1994).
[31 M. L. Fornasini, A. Iandelli, M. Pani, J. A lloys C om ­
po unds 187, 243 (1992).
[32 J. D o n o h u e, The S tructures of the E lem ents, Wiley,
N ew Y ork (1974).
[33 U. Z achw ieja, J. Alloys C om pounds 196,187 (1993).
[34 U. Z achw ieja, J. Alloys C om pounds 196, 171 (1993).
[35 S. L. L aw ton, W. J. R o hrbaugh, G. T. K okotailo, In ­
org. C hem . 11, 2227 (1972).
[36 P. W. R. C orfield, H. M. M. Shearer, A cta C rys­
tallogr. 23, 156 (1967).
[37 R. E. R undle, J. A m . Chem . Soc. 76, 3101 (1954).
[38 W. Jeitschko, M. H. M öller, A cta C rystallogr. B35,
573 (1979).
[39 K. M iller, H. T. H all, Inorg. Chem . 11, 1188 (1972).
[40 O. D. Me M asters, K. A. G schneidner (Jr.), G. B ruz­
zone, A. Palenzona, J. Less-C om m on M et. 25, 135
(1971).