Two new binary lanthanide polytellurides: Syntheses and crystal structures of CeTe1.90 and SmTe1.80

Article abstract of DOI:10.1016/j.jssc.2006.07.010

Single crystals of the new binaries CeTe_1.90 and SmTe_1.80 have been obtained. CeTe_1.90 was synthesized at 1023 K from the reaction of Ce, TeO₂, and Te with the use of a CsCl flux. It crystallizes in the tetragonal space group P4₂/n with 20 formula units in a cell of dimensions at 153 K of a = 10.0261 (5), c = 18.1336 (12) A, V = 1822.84 (18) A³. It is isostructural with the LnSe_1.9 polyselenides (Ln=La, Ce, Pr) and with SmS_1.90. SmTe_1.80 was synthesized at 1223 K from the reaction of Sm and Te in a KBr flux. SmTe_1.80 crystallizes in a new structural type in the tetragonal space group P4/n with 20 formula units in a cell of dimensions at 153 K of a = 9.7026 (4), c = 18.0072 (14) A, V = 1695.21 (14) A³. Both of these layered structures, which may be derived from the ZrSiS structure type, consist of double layers of [LnTe] polyhedra separated by planar Te nets that contain vacancies. In these nets the shortest Te-Te distances are 2.9194(5), 3.1204(5), and 3.3324(6) A in CeTe_1.90 and 2.878(1), 2.9932(3), and 3.2114(7) A in SmTe_1.80. Neither a simple delineation of the Te-Te bonding nor an assignment of individual formal oxidation states is possible in either of these compounds if one takes strict account of the Te-Te distances.

Full text of DOI:10.1016/j.jssc.2006.07.010

ARTICLE IN PRESS
Journal of Solid State Chemistry 179 (2006) 3456–3460
www.elsevier.com/locate/jssc
Two new binary lanthanide polytellurides: Syntheses and crystal
structures of CeTe1.90 and SmTe1.80
Ã
Ismail Ijjaali, James A. Ibers
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3113, USA
Received 27 March 2006; received in revised form 7 July 2006; accepted 11 July 2006
Available online 16 July 2006
Abstract
Single crystals of the new binaries CeTe1.90 and SmTe1.80 have been obtained. CeTe1.90 was synthesized at 1023 K from the reaction of
Ce, TeO , and Te with the use of a CsCl flux. It crystallizes in the tetragonal space group P4 /n with 20 formula units in a cell of
2
2
˚
˚
3
dimensions at 153 K of a ¼ 10:0261ð5Þ, c ¼ 18:1336ð12Þ A, V ¼ 1822:84ð18Þ A . It is isostructural with the LnSe1.9 polyselenides
Ln ¼ La, Ce, Pr) and with SmS1.90. SmTe1.80 was synthesized at 1223 K from the reaction of Sm and Te in a KBr flux. SmTe1.80
crystallizes in a new structural type in the tetragonal space group P4/n with 20 formula units in a cell of dimensions at 153 K of
(
˚
˚
3
a ¼ 9:7026ð4Þ, c ¼ 18:0072ð14Þ A, V ¼ 1695:21ð14Þ A . Both of these layered structures, which may be derived from the ZrSiS structure
type, consist of double layers of [LnTe] polyhedra separated by planar Te nets that contain vacancies. In these nets the shortest Te–Te
˚
and 2.878(1), 2.9932(3), and 3.2114(7) A in SmTe1.80. Neither a simple
˚
distances are 2.9194(5), 3.1204(5), and 3.3324(6) A in CeTe
1
.90
delineation of the Te–Te bonding nor an assignment of individual formal oxidation states is possible in either of these compounds if one
takes strict account of the Te–Te distances.
r 2006 Elsevier Inc. All rights reserved.
Keywords: Binary lanthanide polytelluride; Synthesis; Crystal structure; Hypostoichiometry
1
. Introduction
tical calculations have attempted to rationalize the distor-
tions of these nets and the resultant superstructures
[20–22].
The binary lanthanide polychalcogenides LnQ and their
2
LnQ2 derivatives (Ln ¼ lanthanide, Q ¼ S, Se, Te) have
Among the X-ray single-crystal studies of Ce/Te and
Sm/Te phases that have been carried out are those for
ꢀx
been extensively studied, especially for Q ¼ S [1], because
of their interesting physical properties and rich structural
chemistry. Physical properties include thermodynamic,
magnetic, optical, transport, thermoelectric, and charge
density wave behavior [2–14]. The structural features of
many of these compounds have been reviewed [1,15]. These
layered phases, which may be derived from the ZrSiS
structure type and also may be considered as super-
CeTe [13,23], SmTe [6], SmTe
2
[11], and Sm Te [6].
2 5
3
1.84
The present paper describes the syntheses and the crystal
structures of the two new binary polytellurides CeTe1.90
and SmTe1.80
.
2. Experimental
structures of the anti-Cu Sb structure type, consist of
2
2.1. Syntheses
double layers of [LnQ] polyhedra separated by planar Q
nets [15–19]. The hypostoichiometry common in these
compounds arises entirely from vacancies in these planar
nets. In some structures these vacancies are ordered
2.1.1. CeTe1.90
Black block-shaped single crystals of CeTe1.90 were
obtained in the reaction of Ce (20 mmol, Alfa, 99.9%),
TeO (1 mmol), and Te (27 mmol, Aldrich, 99.8%). TeO
[
16,17,19] whereas in others they are not [11,13]. Theore-
2
2
was synthesized by dissolving Te metal in aqua regia at
53 K, followed by the slow addition of NH OH. The
resultant precipitate of TeO was filtered and washed with
2
Ã
3
Corresponding author. Fax: +1 847 491 2976.
E-mail address: ibers@chem.northwestern.edu (J.A. Ibers).
4
0022-4596/$ - see front matter r 2006 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2006.07.010

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3457
deionized water. Its purity was established by means of an
X-ray powder diffraction pattern. A CsCl (Strem, 99.9%)
flux in approximately five times molar excess was used to
promote the growth of single crystals. The starting
materials were mixed together in a fused-silica tube that
was then evacuated to approximately 10 Torr and sealed.
The tube was heated to 1023 K over 48 h, kept at 1023 K
for 5 days, cooled at 1.5 K/h to 873 K, and then the furnace
was turned off. The reaction mixture was washed free of
chloride salts with water and then dried with acetone. The
yield of CeTe1.90 was about 5%.
provided the unit cell reported here and it gave no evidence
for supercells or for twinning. For each compound data
reduction and the final cell refinement were carried out
with the use of the program SAINT [24] and face-indexed
absorption corrections were carried out numerically
with the program XPREP [27]. Then the program
SADABS [27] was employed to make incident beam and
decay corrections.
Each structure was solved with the direct methods
program SHELXS and refined with the full-matrix least-
squares program SHELXL of the SHELXTL suite of
programs [27]. The refinement of the Ce structure in the
ꢀ
5
2
.1.2. SmTe1.80
Sm (1 mmol, Alfa, 99.9%), Te (2 mmol, Aldrich, 99.8%),
centrosymmetric space group P4 /n was straightforward
2
and resulted in satisfactory anisotropic displacement
parameters for all atoms. The resultant values of R and
Rw are 0.032 and 0.085, respectively. Each atomic site is
fully occupied; the final composition from the X-ray
structure determination is CeTe1.90. This space group and
the resultant structure are known for the LnSe1.9 poly-
and KBr (4 mmol, Alfa, 99%) were mixed together and
loaded into a fused-silica tube in an argon-filled dry box.
The tube was then evacuated to approximately 10 Torr,
sealed, and placed in a furnace. The tube was heated to
1
2
reaction mixture was washed free of bromide salts with
water and then dried with acetone. Black block-shaped
crystals of SmTe1.80 suitable for X-ray structure analysis
were produced in about 5% yield.
ꢀ
5
223 K over 72 h, kept at 1223 K for 4 days, cooled at
.5 K/h to 973 K, and then the furnace was turned off. The
selenides (Ln ¼ La, Ce, Pr) [16,17], SmS
[19], and
does not
crystallize in space group P4 /n but rather in space group
1
.90
SmTe
[11]. As opposed to CeTe , SmTe
.84 1.90 1.80
1
2
P4/n. (There are 45 out of 51 exceptions to the systematic
absences for 0 0 ‘ reflections required in the former space
group.) Solution and refinement of the SmTe1.80 structure
were straightforward in the latter space group. The
resultant equivalent isotropic displacement parameter for
atom Te(3) was excessively large. Anisotropic refinement,
including the occupancy of atom Te(3), refined satisfacto-
Semiquantitative analyses performed with a Hitachi
500N SEM confirmed the presence of Ce or Sm and Te
3
in the approximate ratio of 1:2, in reasonable agreement
with the X-ray structure determinations from which the
stated formulas were derived. The SEM studies provided
no evidence for the presence of other heavier elements or of
O in either compound. Both compounds are modestly
stable in air.
rily to values of R and R of 0.025 and 0.064, respectively,
w
and to a value for the occupancy of atom Te(3) of 0.497(1).
The occupancy was fixed at 0.5 in the final refinement. The
resultant composition is SmTe1.80. Despite the excellent
refinement, concern over the disorder of atom Te(3) led us
to attempt to re-solve the structure in several lower
symmetry space groups, including Pmmn, P2/n, P2/c, and
2
.2. Crystallography
For each compound a single crystal was placed in the
¯
P1. These attempts were unsuccessful. Subsequently,
cold stream of a Bruker SMART-1000 CCD diffractometer
24]. The crystal was kept at 153 K throughout the data
collection. X-ray diffraction data were collected with the
[
Table 1
Crystal data and structure refinement for CeTe1.90 and SmTe1.80
˚
use of monochromatized MoKa radiation (l ¼ 0:71073 A).
The diffracted intensities generated by a scan of 0.31 in o
were recorded on sets of 606 frames at f angles of 01, 901,
CeTe1.90
SmTe1.80
1
801, and 2701 with the use of the program SMART [24].
Formula weight
Space group
˚
a (A)
382.56
/n
380.03
P4/n
P4
2
The exposure time was 15 s per frame. The resultant frames
were free of obvious diffuse scattering. Because both super
cells and twinning are known to occur in some of the rare-
earth hypochalcogenides [19,25] additional exposures of
10.0261(5)
18.1336(12)
1822.84(18)
20
9.7026(4)
18.0072(10)
1695.21(14)
20
˚
c (A)
3
Volume (A )
˚
Z
3
0 s/frame were employed in the collection of three groups
T (K)
153
153
˚
l (MoKa) (A)
0.71073
6.970
271.05
0.71073
7.445
321.94
of frames. For each compound reflections in diverse
regions of reciprocal space on both the 30- and 15-s frames
were centered with the use of the program SMART [24]. A
low threshold value of 5.0 for I/s(I) was employed. Because
possible superlattice reflections might have very low
intensities [25] the stronger reflections were deleted to
ensure that a large number of weak reflections remained.
The program CELL_NOW [26] was used to obtain possible
unit cells and twinning conditions. In each instance, it
3
(g/cm )
r
c
ꢀ
1
m (cm
Transmission factors
)
0.072–0.205
21946/2322
0.032
0.030–0.164
20458/2152
0.025
Total reflections/unique reflections
a
R(F) (F 42s(F ))
2
o
2
o
2
o
b
R
w
(F
)
(all data)
0.085
0.064
a
R(F) ¼ SjjF j–jF
o
c
jj/S9F j.
o
2 2
) /SwF
b
2
2
o
4 1/2
ꢀ1
2
2
o
2 2
R
w
(F
o
) ¼ [Sw(F
—F
c
o
]
,
w
¼ s (F
)+(0.025 ꢁ F
o
)
for
2
ꢀ1
2
2
o
2
o
F 40; w ¼ s (F ) for F p0.
o

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3458
Table 2
Selected bond lengths (A) for CeTe1.90 and SmTe1.80
separated by essentially planar Q nets. In the LnQ2
ꢀx
hypostoichiometric derivative structures these nets possess
˚
vacancies, ordered or random. The LnQ2 derivatives
ꢀx
CeTe1.90
SmTe1.80
crystallize in a number of subgroups of P4/nmm, mainly in
the tetragonal and orthorhombic systems, depending on
the nature of these vacancies and the concomitant
distortions of the nets. CeTe1.90, a new binary in the Ce/
a
Ce(1)–Te(5)
Ce(1)–Te(6)
Ce(1)–Te(3)
Ce(1)–Te(2)
Ce(1)–Te(1)
Ce(1)–Te(2)
Ce(1)–Te(3)
Ce(1)–Te(1)
Ce(1)–Te(4)
Ce(2)–Te(3)
Ce(2)–Te(2)
Ce(2)–Te(3)
Ce(2)–Te(4)
Ce(2)–Te(2)
Ce(2)–Te(1)
Ce(2)–Te(5)
Ce(2)–Te(4)
Ce(3)–Te(3)
Ce(3)–Te(5)
Ce(3)–Te(1)
Ce(3)–Te(2)
Ce(3)–Te(4)
Te(1)–Te(4)
Te(1)–Te(4)
Te(1)–Te(6)
3.2597(4)
3.3046(4)
3.3106(5)
3.3130(6)
3.3136(5)
3.3170(5)
3.3282(5)
3.3866(5)
3.4183(5)
3.2368(5)
3.2418(4)
3.2504(4)
3.2623(5)
3.2687(4)
3.2712(5)
3.2932(4)
3.3266(5)
3.2702(4) ꢁ 2
3.2935(7)
3.3034(5) ꢁ 2
3.3294(4) ꢁ 2
3.3955(5) ꢁ 2
2.9194(5)
3.1204(5)
3.3324(5)
Sm(1)–Te(3)
Sm(1)–Te(4)
Sm(1)–Te(1)
Sm(1)–Te(4)
Sm(1)–Te(4)
Sm(1)–Te(7)
Sm(1)–Te(4)
Sm(1)–Te(5)
Sm(1)–Te(3)
Sm(2)–Te(1)
Sm(2)–Te(6)
Sm(2)–Te(5)
Sm(2)–Te(2)
Sm(2)–Te(2)
Sm(2)–Te(2)
Sm(2)–Te(1)
Sm(3)–Te(7)
Sm(3)–Te(4)
Sm(3)–Te(1)
Sm(4)–Te(2)
Sm(4)–Te(3)
Sm(4)–Te(6)
Te(1)–Te(5)
Te(3)–Te(3)
Te(1)–Te(3)
3.1142(6)
3.1378(4)
3.1633(4)
3.1967(4)
3.2071(4)
3.2345(3)
3.2363(5)
3.3036(4)
3.4044(6)
3.1578(4)
3.1799(3)
3.1997(4)
3.2062(4) ꢁ 2
3.2390(4)
3.2629(5)
3.3169(4)
3.2546(7)
3.2625(4) ꢁ 4
3.2754(5) ꢁ 4
3.1338(3) ꢁ 4
3.1415(7) ꢁ 4
3.1583(7)
2.9932(3)
2.878(1)
Te system, crystallizes in space group P4 /n and is
2
isostructural with the LnSe1.9 polyselenides (Ln ¼ La, Ce,
Pr) [16,17]. Its structure is illustrated in Fig. 1. SmTe , a
1
.80
new binary in the Sm/Te system, crystallizes in space group
P4/n and possesses a different defect Te net.
In the CeTe1.90 structure the three independent Ce atoms
are coordinated by 9, 8, and 9 Te atoms, respectively. The
˚
Ce–Te distances range from 3.2368(5) to 3.4183 (5) A. The
corresponding range in the structure of CeTe is 3.28 to
2
˚
.33 A [30] but see [13]. In the SmTe
3
independent Sm atoms are coordinated by 9, 8, 9, and 9 Te
structure the four
.80
1
3.2114(7)
a
The occupancy of atom Te(3) is 0.5.
careful examination of the structure solution in space
group P4/n led to a rationalization for this disorder, as will
be discussed below.
In both structures the program Structure Tidy [28] was
used to standardize the positional parameters. Selected
crystallographic data are listed in Table 1 and in
Supplementary information. Selected bond distances for
CeTe1.90 and SmTe1.80 are reported in Table 2.
3
. Results and discussion
3
.1. Syntheses
Ce, TeO , and Te were reacted at 1023 K in an effort to
2
produce a cerium oxytelluride. Instead, the reaction
afforded a 5% yield of high quality crystals of CeTe1.90
.
Sm and Te together with a KBr flux were reacted at 1223 K
in a successful effort to synthesize a samarium telluride.
High-quality crystals of SmTe1.80 were obtained in about a
5% yield. No effort was made to increase the yields of
either compound.
3
.2. Crystal structures
The structures of the LnQ compounds as well as their
2
chalcogen-deficient LnQ2 derivatives have been discussed
ꢀx
in detail (see, for example, [15]). These structures, which
may be derived from the ZrSiS structure type (space group
P4/nmm) [29], consist of double layers of [LnQ] polyhedra
Fig. 1. View along [010] of the unit cell of CeTe1.90
.

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3459
˚
atoms, respectively. The Sm–Te distances range from
˚
.1142(6) to 3.4044(6) A; these may be compared with
of alternating bonds of length 2.9194(5) and 3.1204(5) A.
the net is ordered, at least in the model chosen here. If the
3
distances of 3.196(1)–3.336(1) A in SmTe [6].
2
ꢀ
˚
net consisted of interacting Te pairs, then atom Te(4)
would be split into two half-atoms separated by about
3
2
mꢀ
Visualization of specific [Qn] anions in binary lantha-
˚
0.4 A. Although attempts to refine such a model were
nide polychalcogenides and concomitant assignment of
formal oxidation states are common. Such formulations
often tend to emphasize geometries and to discount
variations in Q–Q distances. We prefer to take a more
conservative approach by emphasizing the Te–Te distances
in descriptions of the nets in the present structures. The
unsuccessful, the Bragg X-ray experiment affords only
electron density smeared by noise from various sources. Its
interpretation will always be somewhat subjective and
model dependent.
Fig. 3 displays the Te net in SmTe1.80 with bonds drawn
for the three shortest Te?Te interactions of 2.878(1),
˚
2.9932(3), and 3.2114(7) A (Table 2). The next shortest
˚
shortest Te–Te distance in elemental Te is 2.8345(8) A and
˚
the next shortest interaction is 3.4912(8) A [31]. The
˚
importance of second-nearest-neighbor Te?Te interac-
tions has been noted [22]. Accordingly, we have chosen to
draw bonds for such interactions. Thus, in Fig. 2 the Te net
in CeTe1.90 is displayed with bonds drawn for the three
Te ꢂ ꢂ ꢂ Te interaction is 3.444 A. In this net atom Te(5) has
site symmetry 2. All atoms in this net are ordered except at
the Te(3) site. The fourfold axes parallel to the c-axis and
perpendicular to the nets generate sites of four half-
occupied Te(3) atoms, as illustrated in Fig. 3. Because
adjacent Te(3) atoms are separated by the physically
shortest Te ꢂ ꢂ ꢂ Te interactions, namely those of 2.9194(5),
˚
.1204(5), and 3.3324(5) A (Table 2). The next shortest
3
˚
˚
Te ꢂ ꢂ ꢂ Te interaction in the net is 3.595 A. Atom Te(6) lies
impossible distance of 2.0351(8) A only the diagonal bonds
¯
on a site of symmetry 4. The net is essentially planar; for
example, the mean deviation from the least-squares plane
˚
through the 8-atom Te4/Te1 net is 0.009 A. Despite the
asymmetric nature of the 8-atom net, consisting as it does
˚
of length 2.878(1) A can be present among these half-
occupied Te(3) atoms The resultant structure comprises
two sets of Te chains. Only one of the sets can be present in
a given net. The two sets occur in equal numbers
throughout the structure, presumably in a random fashion
because diffuse scattering was minimal and no evidence of
a super cell was found. Of course, in the unit cell these two
sets are superimposed; hence the half-occupancy of the
Te(3) atom. The chains are nearly planar; for example, the
Te3–Te3–Te1–Te5–Te1–Te3 segment has a mean deviation
˚
from the least-squares plane of 0.071 A.
Fig. 3. The Te net near z ¼ 0:25 in SmTe1.80. The view is down [001]. The
crystallographically independent atoms Te(1), Te(3), and Te(5) are drawn
with different arbitrary radii to facilitate their identification in the net.
Bonds are drawn for the three shortest Te–Te interactions, namely
˚
Te(3)–Te(3) (2.878(1) A (solid line) across the diagonal of the disordered
˚
half atoms), Te(1)–Te(5) (2.9932(3) A) (dashed line), and Te(1)–Te(3)
Fig. 2. The Te net near z ¼ 0:25 in CeTe1.90. The view is down [001]. The
crystallographically independent atoms Te(1), Te(4), and Te(6) are drawn
with different arbitrary radii to facilitate their identification in the net.
Bonds are drawn for the three shortest Te–Te interactions, namely
˚
˚
Te(1)–Te(4) (2.9194(5) A (solid line) and 3.1204 (5) A (dashed line)) and
˚
(3.2114(7) A (dotted line)). The two sets of chains, equally distributed
˚
Te(1)–Te(6) (3.3324 A (dotted line)). Atom Te(6) sits on a site of
¯
symmetry 4.
throughout the structure, are superimposed in the unit cell. Atom Te(5)
sits on a site of site symmetry 2.

ARTICLE IN PRESS
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3460
In the SmTe1.80 structure described here, all atoms
[2] I.G. Vasilyeva, E.I. Balyaeva, J. Solid State Chem. 142 (1999)
2
3] J.S. Swinnea, H. Steinfink, L.R. Danielson, J. Appl. Crystallogr. 20
61–265.
refined anisotropically and only the Te(3) atom position is
not fully occupied. Contrast this structure with that
reported for SmTe1.84 [11]. SmTe1.84 was described in
[
[
(
1987) 102–104.
4] Y.S. Shin, C.W. Han, B.H. Min, H.J. Lee, C.H. Choi, Y.S. Kim, D.L.
Kim, Y.S. Kwon, Physica B 291 (2000) 225–227.
˚
space group P4 /n in a cell a ¼ 9:709ð1Þ, c ¼ 18:008ð7Þ A at
2
2
93 K that is strikingly similar to the one described here
˚
[5] B. Foran, S. Lee, M.C. Aronson, Chem. Mater. 5 (1993) 974–978.
[6] E. DiMasi, B. Foran, M.C. Aronson, S. Lee, Chem. Mater. 6 (1994)
(
a ¼ 9:7026ð4Þ, c ¼ 18:0072ð10Þ A at 153 K). In the asym-
1
7] K. Stowe, Z. Kristallogr. 216 (2001) 215–224.
867–1874.
¨
metric unit three Sm atoms and nine Te atoms were found.
Of the nine Te atoms, six were not fully occupied but had
occupancies that varied from 0.85 to 0.14 and three of these
could not be refined anisotropically. The composition
SmTe1.84 was derived from the X-ray refinement. There is
no way of knowing if SmTe1.80 described here and SmTe1.84
[
[
8] Y.S. Kwon, T.S. Park, K.R. Lee, J.M. Kim, Y. Haga, T. Suzuki,
J. Magn. Magn. Mater. 140–144 (1995) 1173–1174.
[9] M.H. Jung, Y.S. Kwon, T. Kinoshita, S. Kimura, Physica B 230–232
1997) 151–154.
(
[
[
10] M.H. Jung, Y.S. Kwon, T. Suzuki, Physica B 240 (1997) 83–87.
11] S.-M. Park, S.-J. Park, S.-J. Kim, J. Solid State Chem. 140 (1998)
[
11] are the same phase. Note, however, that in the Sm/S
300–306.
12] J.A. Aitken, J.A. Cowen, M.G. Kanatzidis, Chem. Mater. 10 (1998)
3928–3935.
system three discrete phases of nearly the same stoichio-
metry, namely SmS1.863, Sm1.893, and Sm1.900, have been
identified by thermodynamic means [2]. How these phases
differ structurally is not known.
[
[
[
[
13] K. Sto
14] S. Lee, B.J. Foran, J. Am. Chem. Soc. 118 (1996) 9139–9147.
15] P. Bottcher, T. Doert, H. Arnold, R. Tamazyan, Z. Kristallogr. 215
2000) 246–253.
16] P. Plambeck-Fischer, W. Abriel, W. Urland, J. Solid State Chem. 78
1989) 164–169.
¨
we, J. Alloys Compds. 307 (2000) 101–110.
¨
(
Supplementary material
[
(
[
[
17] M. Grupe, W. Urland, J. Less-Common Met. 170 (1991) 271–275.
18] R. Tamazyan, H. Arnold, V.N. Molchanov, G.M. Kuzmicheva, I.G.
Vasileva, Z. Kristallogr. 215 (2000) 272–277.
The crystallographic files in cif format for CeTe1.90 and
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