Rare-earth-rich tellurides: Gd4NiTe2 and Er 5M2Te2 (M=Co, Ni)

Article abstract of DOI:10.1016/j.jssc.2004.07.019

Three new rare earth metal-rich compounds, Gd₄NiTe₂, and Er₅M₂Te₂ (M=Ni, Co), were synthesized in direct reactions using R, R₃M, and R₂Te₃ (R=Gd, Er; M=Co, Ni) and single-crystal structures were determined. Gd ₄NiTe₂ is orthorhombic and crystallizes in space group Pnma with four formula units per cell. Lattice parameters at 110(2) K are a=15.548(9), b=4.113(2), c=11.7521(15)A. Er₅Ni ₂Te₂ and Er₅Co₂Te₂ are isostructural and crystallize in the orthorhombic space group Cmcm with two formula units per cell. Lattice parameters at 110(2) K are a=3.934(1), b=14.811(4), c=14.709(4)A, and a=3.898(1), b=14.920(3), c=14.889(3)A, respectively. Metal-metal bonding correlations were analyzed using the empirical Pauling bond order concept. Slightly-off [010] projection of the Gd₄NiTe₂ structure, featuring Gd₆Ni ₂ chains that exemplify an increasingly common structural motif in reduced ternary tellurides of the rare-earth metals.

Full text of DOI:10.1016/j.jssc.2004.07.019

ARTICLE IN PRESS
Journal of Solid State Chemistry 177 (2004) 3896–3902
www.elsevier.com/locate/jssc
Rare-earth-rich tellurides: Gd NiTe and Er M Te (M=Co, Ni)
4
2
5
2
2
Ã
Carmela Magliocchi, Fanqin Meng, Timothy Hughbanks
Department of Chemistry, Texas A&M University, TAMU 3255, P.O. Box 30012, College Station, TX 77842-3012, USA
Received 16 April 2004; received in revised form 8 July 2004; accepted 12 July 2004
Available online 18 September 2004
Abstract
Three new rare earth metal-rich compounds, Gd
M, and R Te (R=Gd, Er; M=Co, Ni) and single-crystal structures were determined. Gd
in space group Pnma with four formula units per cell. Lattice parameters at 110(2) K are a ¼ 15:548ð9Þ; b ¼ 4:113ð2Þ; c ¼
4
NiTe
2
, and Er
5
M
2
Te
2
(M=Ni, Co), were synthesized in direct reactions using R,
R
3
2
3
4
NiTe is orthorhombic and crystallizes
2
(
1
1:7521ð15Þ A: Er
5 2 2 5 2 2
Ni Te and Er Co Te are isostructural and crystallize in the orthorhombic space group Cmcm with two formula
(
units per cell. Lattice parameters at 110(2) K are a ¼ 3:934ð1Þ; b ¼ 14:811ð4Þ; c ¼ 14:709ð4Þ A; and a ¼ 3:898ð1Þ; b ¼ 14:920ð3Þ;
(
c ¼ 14:889ð3Þ A; respectively. Metal–metal bonding correlations were analyzed using the empirical Pauling bond order concept.
r 2004 Elsevier Inc. All rights reserved.
Keywords: Crystal structure; Rare-earth telluride; Intermetallic Bonding; Chalcogenide
1
. Introduction
rich of the ternary rare-earth-metal chalcogenides. The
principal structural feature in this class of compounds is
the centered tricapped trigonal prism (TTP). These are
condensed into infinite chains in a manner are similar to
those found in Gd MnI [9], Y MI (M=Ru, Ir) [10],
Synthetic exploration of metal-rich chalcogenides
guided by Brewer’s Lewis-acid–base concept of polar
intermetallic bonding has focused on the early transition
metals, namely, Zr, Hf, Nb and Ta [1]. Brewer’s
viewpoint, in which electron donation from late-transi-
tion elements to early transition elements is seen as
especially important, has been extended to ternary
compounds of the electron-poor rare-earth metal
systems and has led to the expectation and realization
of many new compounds with novel compositions,
structures, and properties. These include Sc Ni Te [2],
3
3
3
3
Sc Ni Te [2], Y Ni Te and (M=Fe, Co, Ni) [11]. This
2
5
2
2
5
2
paper presents the synthesis and structural features of
new compounds, Er M Te (M=Co, Ni), isotypic with
5
2
2
Y Ni Te , and Gd NiTe , a structure-type in a new class
5
2
2
4
2
of metal-rich telluride compounds. Evident structural
relationships between the title compounds and other
intermetallic compounds are discussed with respect to
the condensation of the metal–metal bonded frame-
work.
5
2
2
Dy MTe (M=Fe, Co, Ni) [3], R CoTe (R=Y, La) [3],
2
6
2
6
Sc MTe (M=Mn, Fe, Co, Ni) [4], which were
6
2
synthesized and characterized. Our group has reported
the synthesis of Zr MTe (M=Mn, Fe, Co, Ni, Ru, Pt)
6
2
2
. Experimental
and Zr Fe Q2+x,(Q=Se, S) [5], Gd MTe (M=Ni,
2
6
1ꢀx
Co) and Er RuTe [6], Hf FeTe and Hf FeTe
6
6
2
5
3
8
6
2.1. Techniques and materials
(
M=Mn, Fe) [7], and Er Ni Te [8].
7 2 2
New compounds Gd NiTe and Er M Te (M=Co,
2
Ni) discussed in this paper are among the most metal-
4
2
5
2
All materials were manipulated in a nitrogen atmo-
sphere glovebox or vacuum line. Gd and Er foils
99.99 at%, Ames Laboratory), and Co, Ni (both
99.998%, Alfa Aesar), and Te (99.997%, Aldrich)
Ã
(
Corresponding author. Fax: +1-979-847-8860.
E-mail address: trh@mail.chem.tamu.edu (T. Hughbanks).
0022-4596/$ - see front matter r 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2004.07.019

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C. Magliocchi et al. / Journal of Solid State Chemistry 177 (2004) 3896–3902
3897
powders (at%, metals basis) were used as purchased.
Ames Laboratory carbon and oxygen analysis for the
Gd and Er metals were o0.0002 and o0.0003 at%,
respectively. R Te compounds were made in stoichio-
metric reactions of the constituent elements in evacuated
silica tubes at 750–850 1C, as described in the literature
coexisted as a minor phase. Er Co Te was synthesized
5 2 2
analogously. Reactions run at 850 1C for a month
yielded the title compounds with poor crystallinity.
Guinier powder patterns of the lower-temperature
products appear to be ‘‘clean’’, but the presence of
other phases might not be detectable by due to their
poor crystallinity.
2
3
[
12]. R M (M=Co, Ni) compounds were synthesized by
3
arc melting cold-pressed pellets (crushed foils or chips)
of R and M in 3:1 ratio. Nb tubes were used as the
reaction containers to make the ternary compounds—
stoichiometric proportions of reactants were loaded
in Nb tubes that were welded under an argon atmo-
sphere (150–250 torr). The Nb tubes were then sealed in
an evacuated silica jacket and heated in an electric
furnace.
2.3. X-ray crystallography
Single-crystal X-ray diffraction data were collected at
110(2) K using a Siemens (Bruker) diffractometer
equipped with SMART CCD and a graphite mono-
chromator using MoKa radiation (l ¼ 0:71073 A) with
(
a LT-2 low-temperature apparatus. Data were measured
using omega scans of 0.31 per frame for 40 s, such
that a hemisphere was collected. The first 50 frames were
used as check reflections at the end of the data
collection. Cell parameters were retrieved using SMART
software [13] and data reduction was performed using
SAINT, which corrects for Lorentz polarization and
decay [14]. SADABS was used to make absorption
corrections [15]. The structures were then solved by
direct methods using the SHELXS program and refined
with the full-matrix least-squares program SHELXL
and the remaining atomic positions were located from
the electron density difference maps using the
SHELXTL package [16]. All atoms were refined
anisotropically.
2
.2. Syntheses
Gd NiTe was first discovered in an attempt to
4
2
synthesize
Gd MTe structure [6]. Stoichiometric proportions of
a Ni containing compound with the
6
2
Gd, Gd Ni, and Gd Te in the presence of few
3
3
2
milligrams of GdBr (added in an attempt to promote
3
vapor phase transport) were loaded into a niobium tube
and welded. In some instances, molybdenum foils were
used to minimize tellurium attack on the Nb tube; for
the same reason, reaction temperatures were ramped to
5
50 1C over 2 days, maintained there for 2 more days,
then steadily raised to 1000 1C over 4 days. After 8 days
at 1000 1C, the reaction was cooled to 500 1C over 4 days
and then cooled to room temperature. The powder
diffraction pattern revealed a mixture of Gd NiTe as
The reaction loaded to make Gd NiTe produced a
6
good yield of reflective, dark, rod-like, single crystals,
but which proved to be Gd NiTe . A suitable crystal
2
4
2
4
2
3
the major phase (yield: 80–90%); GdTe was the minor
phase. Single-crystal diffraction (see below) determined
the identity of Gd NiTe , and further reactions with the
with dimensions 0.003 ꢂ 0.01 ꢂ 0.17 mm was coated
s
with Apiezon -T stopcock grease, subsequently
mounted on the tip of a glass fiber, and immediately
inserted into the low-temperature nitrogen stream of the
diffractometer for data collection. A total of 4689
reflections (4.341o2yo551, 7h, 7k, 7l) were collected
and 1046 were unique. Initially, the refinement yielded
systematically oblate displacement parameters for all
atoms, illustrating an inadequate absorption correction.
Therefore we performed an empirical absorption correc-
tion on the raw data using the empirical DIFABS
program, which applies an empirical absorption correc-
tion based on direction cosines by fitting the observed
data to calculated intensities. The data was then refined
in SHELXL-97 and the displacement parameters
were approximately spherical. A total of 44 vari-
ables were used in the refinements and data converged
to R1 ¼ 0:0568; wR2 ¼ 0:1327 (all data).
4
2
4
:1:2 stoichiometry were attempted. These yielded
mostly the binary phase GdTe. Nb was not detected in
EDS analyses of products, but tubes were not scraped
after reaction either—in some cases the Nb tubes
showed some embrittlement indicative of attack. Much
better yields of Gd NiTe were achieved by loading
reactions with excess Gd. In all these cases, the
temperature profile was not varied, and no GdBr was
included.
4
2
3
Er Ni Te was first discovered as single crystals in a
5
2
2
reaction intended to make Er Ni Te . Subsequent
7
2
2
reactions were loaded to make Er Ni Te by combining
2
5
2
Er Ni, NiTe , and Er in a 1:1:2 mole ratio. As usual, Nb
3
2
tubes were used as reaction containers that in turn were
sealed in evacuated silica jackets. Since all the starting
materials have low volatility, the reaction temperature
was ramped directly up to 1000 1C over 24 h and
maintained there for three weeks. The reaction was
cooled radiatively afterwards. The Guinier powder
diffraction pattern of the product indicated the desired
ternary compound was made in ꢁ85% yield and ErTe
A black rod-shaped single crystal of Er Ni Te with
5
2
2
3
dimensions of 0.18 ꢂ 0.04 ꢂ 0.01 mm was picked from
the reaction product, protected with a thin layer of
Apiezon-T grease and mounted on the tip of a glass
fiber. Data collection and structural refinements were
carried out following the same procedure as for the

ARTICLE IN PRESS
C. Magliocchi et al. / Journal of Solid State Chemistry 177 (2004) 3896–3902
3898
Table 1
Crystallographic data for metal-rich ternary tellurides
Table 3
3
˚
Positions and equivalent isotropic displacement parameters (A ꢂ 10 )
a
for Er
5
M
2
Te
2
(M=Ni, Co)
Chem. formula
Gd NiTe
4
2
Er
5
Ni
2
Te
2
5 2 2
Er Co Te
M
Ni
Co
fw, g/mol
Space group
3771.64
Pnma
1208.92
Cmcm
1209.36
Cmcm
3.8976(8)
14.920(3)
14.889(3)
865.8(3)
2
b
b
Atom
y
z
U
eq
y
Z
U
eq
˚
a (A)
15.548(9)
4.113(2)
11.752(7)
751.6(7)
4
3.9338(11)
14.811(4)
14.709(4)
857.0(4)
2
˚
b (A)
Er1
Er2
Er3
Te1
M1
M2
0.0388(1)
0.2580(1)
0.6070(1)
0.3844(1)
0.4137(4)
0.6232(1) 13(1) 0.0365(1) 0.6233(1) 7(1)
0.3726(1) 13(1) 0.2567(1) 0.3713(1) 7(1)
˚
c (A)
3
V (A )
˚
1/4 13(1) 0.6069(1) 1/4
0.5388(1) 13(1) 0.3825(1) 0.5374(1) 7(1)
7(1)
Z
T (K)
110(2)
0.71073
8.333
110(2)
0.71073
4.685
110(2)
0.71073
4.639
1/4
16(1) 0.4118(3) 1/4
16(1) 0.8195(3) 1/4
7(1)
7(1)
˚
0.8130 (4) 1/4
l (MoKa)(A)
3
r
calcd(g/cm )
a
ꢀ
1
x=0 for all atoms.
m (mm
R
)
44.755
0.0568
0.1327
29.628
0.0661
0.1574
29.069
0.0979
0.1202
b
a
ij
Ueq equals one-third of the trace of the orthogonalized U tensor.
1
2,b(I42s(I))
wR
a
R
1
=S| |F
o c o
|—|F | |/S|F |.
2 2
b
2
2 2 0.5
3. Results and discussion
wR =[S[w(F –F ) ]/S[w(F ) ]] .
2
o c o
3.1. Syntheses
Table 2
Synthetic routes to these compounds are similar to
those used to make Gd NiTe [6]. The use of the binary
rare earth late transition metal compounds Gd M
3
3
˚
Positions and isotropic displacement parameters (A ꢂ 10 ) for
6
2
4 2
Gd NiTe
a
(M=Co, Ni) apparently facilitates incorporation of
the ternary element, M, in the product; elemental
starting materials results in formation of GdTe as the
major phase. One advantage conferred by use of the
Atom
x
y
z
U
eq
Gd1
Gd2
Gd3
Gd4
Te1
Te2
Ni1
0.1327(1)
0.0417(1)
0.2747(1)
0.1034(1)
0.0734(1)
0.2800(1)
0.0473(2)
1/4
1/4
1/4
3/4
1/4
3/4
3/4
0.4173(1)
0.7016(1)
0.1314(1)
0.9656(1)
0.1564(1)
0.3426(2)
0.5282(3)
7(1)
7(1)
7(1)
7(1)
7(1)
8(1)
9(1)
binary Gd M compounds (vs. elemental starting materi-
3
als) is their brittleness, which allows them to be crushed
into small particles that provide a larger surface area for
reaction. In addition, since the reactions were run at
a
small scales (less than 500 mg in total), use of Gd Ni as
3
Ueq is defined as one-third of the trace of the orthogonalized Uij
tensor.
the nickel source reduces its relative weighing error. In
contrast, rare earth metals are available as malleable
chips or shavings, and therefore have a lower surface
area. If metals do yield the desired products, they have
an advantage over powders, since the latter are highly
susceptible to reaction with oxygen and hydrogen. Arc
melting of reactants for Gd NiTe was not necessary for
Gd NiTe crystal.
2
A
total of 2626 reflections
4
(
51o2yp56.51) were collected, of which 607 were
int
unique (R ¼ 0:1799). A total of 32 variables were
4
2
used in the refinements and data converged to R1 ¼
a complete reaction.
0
single-crystal structure of Er Co Te was also deter-
:0661; wR2 ¼ 0:1574 (all data). Similarly, the X-ray
3.2. Structure and bonding
5
2
2
mined.
(
A
hemisphere of data was collected
51o2yp56.51). Of 6626 reflections collected, 1215 were
int
Gd NiTe adopts a new structure type, shown in Fig.
4 2
unique (R ¼ 0:1703). A total of 32 variables were used
1 in a view down its b-axis; important Gd–Te bond
distances are listed in Table 4, intermetallic distances are
in the refinements and data converged to R ¼ 0:0979;
1
1
4
wR2 ¼ 0:1202 (all data). Crystallographic data for
in Table 5. All atoms lie on mirror planes at y ¼
3
4
Gd NiTe , Er Ni Te , and Er Co Te are summarized
2
and : This view of the structure highlights the
4
2
5
2
2
5
2
in Table 1. The atomic positions and isotropic displace-
ment factors are given in Tables 2 and 3.
Routine X-ray powder diffraction data were collected
Ni-centered chains in a polyhedral representation.
The shortest distance between separate Gd Ni chains,
6
2
(
dðGd12Gd2Þ ¼ 4:020ð3Þ A (marked in Fig. 1), is pre-
sumably a weak interaction. Fig. 2 illustrates structural
details within the Gd Ni tricapped trigonal prisms
(
using CuKa (l ¼ 1:5406 A) radiation on a Philips X-ray
1
Generator with a mounted Guinier Camera with
germanium monochromator or using the GADDS
6
3
that form the inner cluster core of the Gd Ni chain.
6
2
(General Area Detector Diffraction System) V4.1.08
by Bruker AXS.
The triangular faces are isosceles, with one long
˚
(4.113(2) A=b) and two short (3.679(2) A) Gd–Gd
˚

ARTICLE IN PRESS
C. Magliocchi et al. / Journal of Solid State Chemistry 177 (2004) 3896–3902
3899
Table 5
Intermetallic distances, bond orders and valence electron counts for
Gd NiTe
4
2
Atom
Bond
Bond
distance
Pauling
bond order
VEC
4.057
a
Gd1( ꢂ 2)
Gd1( ꢂ 2)
Gd1( ꢂ 2)
Gd1( ꢂ 2)
Gd1( ꢂ 2)
Gd1( ꢂ 2)
Gd1( ꢂ 2)
Gd2( ꢂ 2)
Gd2( ꢂ 2)
Gd2( ꢂ 2)
Gd2( ꢂ 2)
Gd2( ꢂ 2)
Gd2( ꢂ 2)
Gd2( ꢂ 2)
Gd3( ꢂ 2)
Gd3( ꢂ 2)
Gd3( ꢂ 2)
Gd3( ꢂ 2)
Gd3( ꢂ 2)
Gd3( ꢂ 2)
Gd4( ꢂ 2)
Gd4( ꢂ 2)
Gd4( ꢂ 2)
Gd4( ꢂ 2)
Ni1( ꢂ 2)
Ni1( ꢂ 2)
Ni1( ꢂ 2)
Ni1( ꢂ 2)
Ni1( ꢂ 2)
Ni1( ꢂ 2)
ꢀGd1( ꢂ 2)
ꢀGd2( ꢂ 2)
ꢀGd2( ꢂ 1)
ꢀGd3( ꢂ 2)
ꢀGd3( ꢂ 1)
ꢀNi1( ꢂ 2)
ꢀNi1( ꢂ 1)
–Gd2( ꢂ 2)
ꢀGd1( ꢂ 2)
ꢀGd1( ꢂ 1)
ꢀGd3( ꢂ 2)
ꢀGd4( ꢂ 2)
ꢀNi1( ꢂ 2)
ꢀNi1( ꢂ 1)
ꢀGd3( ꢂ 2)
ꢀGd1( ꢂ 2)
ꢀGd1( ꢂ 1)
ꢀGd2( ꢂ 2)
ꢀGd4( ꢂ 2)
ꢀNi1( ꢂ 1)
ꢀGd4( ꢂ 2)
ꢀGd4( ꢂ 2)
ꢀGd2( ꢂ 2)
ꢀGd3( ꢂ 2)
ꢀNi1( ꢂ 2)
ꢀGd1( ꢂ 2)
ꢀGd1( ꢂ 1)
ꢀGd2( ꢂ 2)
ꢀGd2( ꢂ 1)
ꢀGd3( ꢂ 1)
4.113(2)
3.679(2)
3.628(2)
3.555(2)
4.020(3)
2.773(3)
2.871(4)
4.113(2)
3.679(2)
3.628(2)
3.614(2)
3.843(2)
2.897(3)
3.035(4)
4.113(2)
3.555(2)
4.020(3)
3.614(2)
3.888(2)
3.022(4)
4.113(2)
3.902(3)
3.843(2)
3.888(2)
2.614(5)
2.773(3)
2.871(4)
2.897(3)
3.035(4)
3.022(4)
0.035
0.188
0.228
0.302
0.051
1.016
0.697
0.035
0.188
0.228
0.241
0.100
0.631
0.372
0.035
0.302
0.051
0.241
0.084
0.391
0.035
0.079
0.100
0.084
0.313
1.016
0.697
0.631
0.372
0.391
2.990
1.766
0.596
5.380
Fig. 1. Slightly off [010] projection of the Gd
Gd Ni polyhedra are highlighted. All atoms lie on the mirror planes
at y ¼ or :
4 2
NiTe structure. The
6
2
1
4
3
4
Table 4
Gd–Te distances (A) in Gd
a
˚
(Gd–Gd)=3.243 A, D
˚
˚
(Ni–Ni)=2.311 A;
D
1
1
(Gd–Ni)=2.777 A, D
–D )/0.6
1
˚
4
NiTe
2
Pauling bond order n: log10 n=(D
1
n
a
Distances
Gd1–Te1
3.201(3)
3.202(2)
3.196(2)
3.228(2)
3.143(3)
Gd3–Te2 ( ꢂ 2)
Gd3–Te2
3.225(2)
3.499(3)
3.079(2)
3.100(2)
3.099(2)
Pauling bond order sums are tabulated in Table 5.
These have been computed with tellurium regarded as
Gd1–Te2 ( ꢂ 2)
Gd2–Te1 ( ꢂ 2)
Gd2–Te2
Gd4–Te1 ( ꢂ 2)
Gd4–Te1
2
ꢀ
Te , and so computed valence electron count (VEC)
figures reflect only electrons devoted to Gd–Gd and
Gd–Ni bonding. Single bond radii are obtained for Gd
and Ni by use the Pauling bond order formula,
elemental structural data [17] and respective valences
of 3 and 6. A comparison of VECs among Gd atoms is
consistent with our depiction of the structure: virtually
all the metal–metal bonding occurs within condensed
Gd3–Te1
Gd4–Te2 ( ꢂ 2)
a
˚
All atoms also have two like neighbors at 7b, 4.113(2) A. Distance
˚
limits are 4.10 A.
distances. Relatively short distances (d(Gd1–Gd2)=
3
˚
.614(2) A, d(Gd1–Gd3)=3.555(2) A) separate the cap-
˚
Gd Ni chains. The ‘isolated’ Gd4 atoms may be
3
III
formally regarded as a Gd ions; if we sum all the
ping Gd atoms from Gd atoms making up the prism. A
view of a portion of the one-dimensional condensed-
cluster chain (tellurium atoms omitted) is shown in
Fig. 2. The metal framework can be viewed as cluster
condensation of the Ni-centered gadolinium tetrakaide-
cahedra along the rectangular faces of the trigonal prism
so that the Ni atoms in adjacent trigonal prisms act as
two of the caps to the trigonal prisms. Also recognizable
is a chain of face-sharing trigonal prisms of gadolinium
threaded by a zigzag chain of Ni atoms.
VECs for all the other Gd and the Ni atoms, we obtain
ꢀ
ꢀ
28.39e per Gd Ni unit (or 29.58e if the Gd4
6
2
contribution is considered to be donated to the chain).
If the formula is written to reflect formal electron
3
+
2+
2
counting assignments, Gd NiTe ꢂ 2=(Gd ) (Gd Ni
)
(Te ) , then there are 36 electrons per Gd Ni unit
4
2
2
6
2
ꢀ
4
6
2
available for bonding in the chain if all the surplus
valence electrons are assigned to metal–metal bond-
ing. However, it should be noted that the Pauling Ni

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3900
6 2 4 2
Fig. 2. Two views of the Gd Ni chain imbedded in Gd NiTe , with
˚
numbering scheme and selected bond distances (A) marked.
single-bond radius was originally calculated by assigning
only 6 electrons to nickel (cf. p. 397, Ref. [18]). If we are
consistent with this assignment, then we should perhaps
expect to find only 28 electrons for the summed VEC—
ꢀ
remarkably close to 28.39e . This assignment is, of
course, in closer correspondence with the individual Ni
ꢀ
atom VEC of 5.38e .
While the internal consistency of bond sums is a
source of some interest, one should not attach too much
physical significance to the individual atom VECs. Even
if the ‘missing’ 4 Ni electrons are added to the computed
VEC (an omission which Pauling associated with the
rather contracted nature of the Ni 3d orbitals), the Ni
Fig. 3. (a) Near [100] projection of the Er
the environment of one Te atom. (b) An Er
5
M Te
2
2
structure showing
5
M layer (ab-plane slice)
2
highlighting links via Er1 atoms and zig-zag M-atom chains.
‘
charge’ would still be positive. We view this as unlikely
efficient packing around Te atoms that occupy voids
with an eight-coordinate environment between the
metal–metal bonded layers. Te–Er distances range from
since the nickel atoms are bound only to more
electropositive gadolinium. Similarly, if the VECs for
the Gd atoms are literally equated with electron
densities, Gd1 is quite anionic (ꢀ1.06), Gd2 is virtually
neutral, and Gd3 would be +1.23. Clearly, a physical
partitioning of the Gd–Ni bonds would reflect the highly
polar nature of those bonds—as is seen in band
structure calculations we have presented for similar
compounds in the past [7,19–21].
˚
3.079 to 3.314 A. As seen in many other metal-rich
telluride compounds, the shortest Te–Te distance is
equal to the short crystallographic axis and is close to
the van der Waal’s diameter of Te. Important metal–
metal distances are listed in Table 6.
Isolated R M chains like those found in Gd NiTe
2
6
2
4
are also found in a series of iodide compounds with the
composition R MI ; these include Gd MnI [9], Y MI
3
A near-[100] projection of the Er M Te (M=Co, Ni)
5
2
2
3
3
3
3
3
structure is shown in Fig. 3a. Er M chains homologous
6
(M ¼ Ru; Ir), [10] and other members with R ¼ La; Pr,
Gd, Er, and Y with M ¼ Ru and Ir. In these compounds
however, there are no rare-earth atoms beyond those in
the intermetallic chains. It is not clear whether telluride
phases isostructural to the iodides might be synthesized,
but in more rare-earth-rich tellurides condensation of
the chains into layers (e.g., Y Ni Te ) [11] and double
2
to the Gd Ni chain already discussed interconnect by
6
2
sharing the capping Er1 atoms to form layers that
propagate in the ab plane (Fig. 3b). These Er–Er/Er–M
bonded layers (normal to vertical on the page) are
separated by Te atoms. A view down on one Er M
5
2
layer in Fig. 3b clearly shows the condensation of the
Er M chains at the Er1 position and a/2 shift in the
5
2
2
chains (e.g., Sc Ni Te ) [2] occurs.
5 2 2
6
2
zigzag M chains on moving between adjacent chains.
The overall 3D framework is formed when layers stack
Illustrations comparing the extended metal chain
structures and are presented in Fig. 4. Within these
compounds, there is considerable structural flexibility
that distinguishes the other phases from the monoclinic
R MI . Gd NiTe is the first chalcogenide compound to
˚
up the c-axis with displacements of 3.170(4) A (M ¼ Ni)
˚
and 3.190(4) A (M ¼ Co) along the b direction between
adjacent layers. This displacement (ꢁ0.214b) results in
3
3
4
2

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3901
Table 6
Important metal–metal distances (A) for Er
Table 7
Comparison of M–M and bond lengths and Pauling bond orders for
Gd NiTe , Sc Ni Te , and Er Ni Te
˚
M
5 2
Te
2
(M=Co, Ni)
M=Ni
4
2
5
2
2
5
2
2
Bonds
M=Co
a
˚
d(Ni–Ni)/d(R–Ni) (A) Bond order
Compound Bonds
Er3–Er2 ( ꢂ 5)
Er1–Er3 ( ꢂ 5)
Er2–Er2 ( ꢂ 1)
Er3–Er3 ( ꢂ 1)
Er1–Er3 ( ꢂ 4)
Er1–Er1 ( ꢂ 1)
M2–Er1 ( ꢂ 1)
M2–Er2 ( ꢂ 3)
M2–Er3 ( ꢂ 5)
M1–Er3 ( ꢂ 1)
M1–Er2 ( ꢂ 3)
M1–Er1 ( ꢂ 5)
M1–M2 ( ꢂ 4)
3.472(1)
3.455(1)
3.614(2)
3.8976(8)
3.650(1)
3.774(2)
2.911(5)
2.936(4)
2.820(2)
3.172(5)
2.818(2)
2.859(4)
2.386(4)
3.482(2)
3.466(2)
3.606(3)
3.934(1)
3.596(2)
3.732(3)
3.051(7)
2.790(2)
2.881(5)
2.864(7)
2.926(5)
2.801(2)
2.468(6)
Gd NiTe
4
2
Ni1–Ni1( ꢂ 2)
2.614(5)
0.313
1.016
0.697
0.631
0.372
0.391
0.547
0.293
0.800
0.565
0.603
0.475
0.767
0.265
0.970
0.727
0.930
0.386
0.868
0.372
0.829
0.977
0.389
1.031
Ni1–Gd1( ꢂ 2) 2.773(3)
Ni1–Gd1( ꢂ 1) 2.871(4)
Ni1–Gd2( ꢂ 2) 2.897(3)
Ni1–Gd2( ꢂ 1) 3.035(4)
Ni1–Gd3( ꢂ 1) 3.022(4)
Er
5
Ni
2
Te
2
Ni1–Ni2( ꢂ 4)
Ni1–Er1( ꢂ 1)
Ni1–Er2( ꢂ 3)
Ni1–Er3( ꢂ 3)
Ni2–Er1( ꢂ 1)
Ni2–Er2( ꢂ 3)
Ni2–Er3( ꢂ 3)
Ni1–Ni2( ꢂ 2)
Ni1–Sc1( ꢂ 2)
Ni1–Sc2( ꢂ 1)
Ni1–Sc4( ꢂ 2)
Ni1–Sc4( ꢂ 1)
Ni1–Sc5( ꢂ 1)
Ni2–Sc1( ꢂ 1)
Ni2–Sc3( ꢂ 1)
Ni2–Sc4( ꢂ 2)
Ni2–Sc4( ꢂ 1)
Ni2–Sc5( ꢂ 2)
2.468(6)
3.051(7)
2.790(2)
2.881(5)
2.864(7)
2.926(5)
2.801(2)
2.657(2)
2.624(2)
2.699(4)
2.635(3)
2.864(4)
2.653(4)
2.874(4)
2.665(4)
2.622(3)
2.862(4)
2.608(2)
5 2 2
Sc Ni Te
a
˚
(Ni–Ni)=2.311 A,
˚
(Ni–Gd)=2.777 A,
˚
(Sc–Ni)=2.616 A,
D
1
D
1
D
1
˚
D (Er–Ni)=2.732 A.
1
for the scandium compound than for the two lantha-
nide-containing compounds. The origins of these
differences are not readily apparent; explanations may
become clearer as synthetic exploration yield more data
from which trends can be extracted.
Fig. 4. Structural relationship between (a) Gd
R ¼ Er; Y; M ¼ Fe; Ni, Co), and (c) Sc Ni
alternative condensation modes of the of the single 1-D chain in
Gd NiTe
4
NiTe
2
, (b) R
5 2 2
M Te
(
5
2 2
Te illustrating the
4
2
.
4. Conclusions
incorporate the R M double chain. The Mn-centered
6
The new compounds, Gd NiTe and Er M Te
2
2
4
2
5
2
double chain units found in Gd MnI are much less
3
(M ¼ Ni; Co), were synthesized by high-temperature
solid-state reactions and crystallize in the orthorhombic
Pnma and Cmcm space groups, respectively. Gd NiTe
3
symmetrical than the Gd Ni chain in Gd NiTe . In
4
6
2
2
Sc Ni Te (Fig. 4d), condensation occurs at just the
5
2
2
4
2
2
rare-earth-atom positions that are not shared in
Er M Te (Fig. 4c). Double chains of Ni-centered units
is the first chalcogenide to exhibit infinite Gd Ni
6
double-chains, a motif long known for lanthanide-
iodides with the R MI structure-type. The Er M Te
2
5
2
2
that share trans edges and are further condensed side-
by-side occur in Sc Ni Te ; vertex condensation to form
3
3
5
2
compounds are isostructural to the lighter rare earth
homolog, Y Ni Te . The prevalence of tricapped
5
2
2
layers in the R M Te (R ¼ Y; Er; M ¼ Fe; Co, Ni)
5
2
2
5
2
2
structure.
Comparison of Gd NiTe and the structurally related
trigonal prisms throughout these compounds’ structures
demonstrate their electronic and structural flexibility.
These compounds further extend the number of
chalcogenide examples wherein early late transition
metal bonding in to electron poorer rare-earth metals
is of prime importance. With increasing late transition
metal contents, there is a progression of TTP units to
link together to form single chains, then double chains,
then layers and 3-D networks. This is illustrated by the
4
2
Ni-containing compounds Sc Ni Te and Er Ni Te
2
5
2
2
5
2
reveals some interesting contrasts in these Ni-centered
chains (Table 7). Ni–Ni distances and some VECs are
˚
given in Table 6. The Ni–Ni distance (2.468(6) A) in
Er Ni Te is markedly shorter than the corresponding
2
5
2
˚
distances in Gd NiTe (2.614(6) A) and Sc Ni Te
2
4
2
5
2
˚
2.657(2) A). The nickel VECs are considerably larger
(

ARTICLE IN PRESS
C. Magliocchi et al. / Journal of Solid State Chemistry 177 (2004) 3896–3902
3902
structural comparison between R M Te (R ¼ Y; Er;
[8] F. Meng, T. Hughbanks, Inorg. Chem. 40 (2001) 2482–2483.
9] M. Ebihara, J.D. Martin, J.D. Corbett, Inorg. Chem. 33 (1994)
079–2084.
5
2
2
[
M ¼ Co; Ni) and Sc Ni Te . Synthetic efforts in this
5
2
2
2
area continue and discovery leads to new materials
whose compositions and structure show ever more
versatility.
[
[
10] M.W. Payne, P.K. Dorhout, S.-J. Kim, T.R. Hughbanks, J.D.
Corbett, Inorg. Chem. 31 (1992) 1389.
11] P.A. Maggard, J.D. Corbett, J. Am. Chem. Soc. 122 (2000)
1
0740–10741.
[
[
12] K.A.J. Gschneider, J. Mater. Eng. Performance 7 (1998) 656–660.
13] SMART, Software for the CCD Detector System, Bruker
Analytical X-ray System: Madison, WI, 1995.
Acknowledgments
[14] SAINTPLUS, Software for the CCD Detector System, Madison,
WI, 1999.
We thank the Robert A. Welch Foundation for its
support through Grant A-1132 and the Texas Advanced
Research Program through Grant # 010366-0188-200.
[15] G.M. Sheldrick, SADABS: Program for Absorption Corrections,
Institute fur Anorganishe Chemie der Universitat Gottingen,
Gottingen, Germany, 1999.
¨
¨
¨
¨
[16] G.M. Sheldrick, SHELXTL-PLUS an Integrated System for
Solving Refining and Displaying Crystal Structures from Diffrac-
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