Syntheses, structures, and theoretical studies of new ternary antimonides β-RECoSb3 (RE = La-Nd, Sm)

Article abstract of DOI:10.1002/ejic.200800836

Five new intermetallic ternary cobalt antimonides β-RECoSb₃ have been prepared by solid state reactions and characterized by single-crystal X-ray diffraction. The title compounds crystallize in β-RENiSb ₃-type structure, Pbcm (No.57)

Full text of DOI:10.1002/ejic.200800836

FULL PAPER
DOI: 10.1002/ejic.200800836
Syntheses, Structures, and Theoretical Studies of New Ternary Antimonides
β-RECoSb3 (RE = La–Nd, Sm)
Wei-Zhao Cai,[a,b] Li-Ming Wu,[a] Long-Hua Li,[a,b] and Ling Chen*[a,c]
Keywords: Transition metals / Rare earth metal compounds / Cobalt / Antimon / Electronic structure / Calculations /
Tight-bonding linear muffin-tin orbital method
Five new intermetallic ternary cobalt antimonides β-RE-
band structure of β-LaCoSb3 has been calculated with the
CoSb3 have been prepared by solid state reactions and char- aid of the tight-bonding linear muffin-tin orbital (TB-LMTO)
acterized by single-crystal X-ray diffraction. The title com- method and the results suggest that the three types of
pounds crystallize in β-RENiSb3-type structure, Pbcm
(No.57), 8, with a 12.985(4)–12.5530(13) Å,
6.1603(18)–6.1043(4) Å, c = 12.166(4)–12.0267(12) Å for RE =
La, Ce, Pr, Nd, and Sm. Their structures feature the anionic
Sb square nets and CoSb6 octahedron layers that are sepa-
rated by RE3+ cations along the a axis. The structural rela- tical to the corresponding Ni members.
RETSb3 are metallic in both b and c directions and the elec-
trical conductivities along the a direction are relatively weak.
The magnetic calculations indicated that the rare-earth
atoms would be the only source for the magnetic properties.
Therefore, β-type Co analogues should be magnetically iden-
Z
=
=
b =
tionship among parent-type (RECrSb3), α-type (RENiSb3),
and β-type (RECoSb3) has been presented. The electronic
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
The RENiSb3 exhibits interesting α- and β-type polymor-
phism. The α-RENiSb3 (RE = Ce, Pr, Nd, Sm) differs from
RECrSb3 (named “parent type” hereafter) by a tripled c
parameter, but similar TSb6 layer and Sb net. The electrical
conductivity perpendicular to the stacking direction is met-
allic. Unlike the parent structure type, the transition metal
in the α-type has no significant contributions on the mag-
netic properties, and this series of compounds only show
effective moments of free RE3+ ions.[17,18]
The β-RENiSb3 (RE = La, Ce) differs from the parent
type by a doubled c parameter. And β-type compounds are
also metallic perpendicular to the stacking direction; the
Ce member shows ferromagnetic ordering of Ce3+ free ion
only.[19] The disordered analogs of RENi(Sn,Sb)3 (RE = Pr,
Nd, Sm, Gd, and Tb) confirm that the RE3+ ions are the
sole source of the magnetic properties.[20] However, the
transition metal Ni has no contribution to the magnetic
property in both α- and β-type RENiSb3.[17–19] The replace-
ment of Ni by Co would provide a new opportunity to look
for structural and magnetic correlations.
Introduction
Rare-earth transition-metal antimonides have been
studied continuously because of their structural diversity,
unique bonding interactions, and various interesting physi-
cal properties.[1–3] The main structural motif of the layered
RETSb3 family (RE = La–Nd, Sm, Gd–Dy, Yb; T = V, Cr,
and Pd) are the condensed TSb6 octahedron layers and the
square Sb nets that are separated by the RE3+ cations along
the stacking direction.[4–13] Such anisotropic structure leads
to the anisotropic electrical conductivity of LaCrSb3, and
the ferromagnetic behavior corresponds to the existence of
an intermediate between Cr3+ and Cr4+ [7]
For other
.
RECrSb3 members (RE = Ce–Nd, Sm), the transition metal
Cr influences the magnetic behaviors by coupling with RE
at about 10 K.[8,14–16] However, the V analogs (RE = La–
Nd, Sm) show no 3d moment, and rare-earth cations are
the sole magnetic source.[4,6,14]
The known RE/Co/Sb compounds are RE5CoSb2 (RE =
Gd, Tb, Dy, Ho, Er),[21] RECo1–xSb2 (RE = La–Nd, Sm,
Gd),[22–24] and α-type RECoSb3 (RE = Ce, Pr).[25,26]
In this paper, we present the syntheses and structures of
a new series of β-type RECoSb3 (RE = La–Nd, Sm). The
structural relationship among parent type, α-, and β-type
RETSb3 has been presented, and the electronic band struc-
ture calculations with the aid of the TB-LMTO method
have been reported for the first time; also the electrical con-
ductivity and the magnetic properties are investigated.
[a] State Key Laboratory of Structural Chemistry, Fujian Institute
of Research on the Structure of Matter, Chinese Academy of
Sciences, Fuzhou,
Fujian 350002, People’s Republic of China
Fax: +86-591-83704947
E-mail: chenl@fjirsm.ac.cn
[b] Graduate School of the Chinese Academy of Sciences,
Beijing 100039, People’s Republic of China
[c] State Key Laboratory for Physical Chemistry of Solid Surfaces,
Xiamen University,
Xiamen 361005, People’s Republic of China
230
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Syntheses, Structures, and Theoretical Studies of New Antimonides
Results and Discussion
Structure
β-RECoSb3 (RE = La–Nd, Sm) is the isostructural form
of the β-RENiSb3-type compound.[19] The anionic moiety
of the structure consists of two independent parts: slightly
distorted Sb square nets and CoSb6 octahedron layers. Both
are stacked along the a axis and separated by RE3+ cations
as shown in Figure 1.
Figure 2. The connection motifs of the TSb6 octahedra along the
c axis of RETSb3. (a): T = Cr, (b): T = Co, and (c): T = Ni. A, B,
C represent the stacking sequences of the essentially close-packed
Sb atoms.
the three types, for example 13.283 Å for parent-type
LaCrSb3[5] and 12.985 Å for β-type LaCoSb3, and 12.634 Å
for α-type CeNiSb3.[17] The β-type RECoSb3 has shown
lanthanide contraction as indicated by Figure 3, in which
the lattice parameters as well as the cell volumes decrease
Figure 1. View down the b axis of β-LaCoSb3 with the unit cell monotonically with the increase of the atomic number of
outlined. The coordination around the La1 and La2 atom is
the lanthanide.
marked by dashed lines. For clarity, the Co–Co bonds are omitted.
To date, three structure types of antimonides with a com-
mon formula RETSb3 (T = transition metal), namely par-
ent-type RECrSb3,[5] α-type RENiSb3,[17,18] and β-type RE-
NiSb3[19] have been reported. Each structure has similar an-
ionic building units, Sb square nets and TSb6 octahedron
layers, with RE3+ cations inserted between them. The major
difference is their c parameters that are determined by the
different building units along the c axis. As shown in Fig-
ure 2, in the parent-type RECrSb3, the repeat unit is a
monooctahedron [CrSb6] that extends along c through face-
sharing. In the β-type, for example LaCoSb3, the building
unit is a dimer of the edge-shared octahedra, [Co2Sb10].
While in the α-type, for example LaNiSb3, the building unit
is a trimer of the edge-shared octahedra, [Ni3Sb14]. The di-
mer or trimer along c leads to the approximately doubled or
tripled c-parameter for β- or α-RETSb3, respectively. This
Figure 3. Plots of the lattice parameters [Å] and cell volumes [Å3]
relationship can also be understood by the stacking se-
for β-RECoSb3 (RE = La–Nd, Sm).
quences of the close-packed layers of Sb atoms along the c
direction as shown in Figure 2. Such stacking sequences are
AB in parent-LaCrSb3, ABCB in β-LaCoSb3, and AB- the β-type structure. Taking LaCoSb3 as an example, the
ACBC in α-LaNiSb3. Co–Sb bond lengths within the CoSb6 octahedron range
The five β-RECoSb3 compounds reported here belong to
On the other hand, the connection motifs and repeat unit from 2.5918(13) Å to 2.6661(12) Å with an average
along the b axis are similar for the three types; therefore the (2.629 Å) similar to 2.588 Å in binary CoSb (NiAs-type),[27]
b parameters are nearly the same, ranging from 6.160 Å for but slightly longer than that in CoSb3 (2.527 Å).[28] The dis-
the β-type to 6.203 Å for the α-type and to 6.212 Å for the tortion of the TSb6 octahedra is more obvious than that in
parent type.[5,17] Meanwhile, the a-parameter is determined parent-type LaCrSb3,[5] but comparable to that in CoSb3.[28]
by the thickness of the TSb6 octahedron layer, Sb square In addition, the Co–Co distances roughly decrease with a
net, and the size of the interstitial RE3+ cations. Therefore, decrease in the size of RE3+ cations, 2.756(2) Å for La-,
no significant change in a parameters is expected among 2.735(2) Å for Ce-, 2.729(2) Å for Pr-, 2.739(2) Å for Nd-,
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231

W.-Z. Cai, L.-M. Wu, L.-H. Li, L. Chen
FULL PAPER
and 2.718(2) Å for the Sm-member. Such distances are shown in Figure 5. The Sb nets in the parent type are an
slightly longer than 2.588 Å in binary CoSb.[27] The Sb–Sb ideal square net with Sb–Sb: 3.049(5)–3.108(5) Å; angle Sb–
bonds in the Co/Sb layer, such as Sb1–Sb1 [3.1598(9) Å], Sb–Sb: 90°,[5] and distorted in both α-type [3.0620(3)–
Sb1–Sb4 [3.1426(14) Å], and Sb1–Sb5 [3.3410(1) Å], are 3.1035(2) Å;
longer than that in the Sb square net, for example Sb3–Sb3 [3.0084(7)–3.0702(8) Å; 88.236(19)–91.749(20)°].[19] Such
[3.0128(12)–3.0806(9) Å]. distortion is caused by the different connection motifs of
84.953(6)–94.944(6)°][17]
and
β-type
There are two crystallographically independent La sites, the TSb6 octahedra along the c direction as described
La1 (Wyckoff site 4c) and La2 (4d) in β-LaCoSb3. As de- above. On the other hand, different RE3+ cations barely in-
picted in Figure 4 (a), the La1 atom adopts a square anti- fluence the geometry, for example, in the series of β-RE-
prismatic coordination, which is frequently found in the CoSb3, from La to Sm, the shorter Sb3–Sb3 bond lengths
rare-earth antimonides such as RECo1–xSb2 (RE = La, Ce, change 1%, the longer Sb3–Sb3 bond lengths only change
Pr, Nd, Sm, and Gd)[22–24] or RETSb2 (T = Ag, Ga, Mn, 0.9%, and the angular deviation is also negligible.
Zn, Cd).[29–33] One square base is constructed by two Sb2
atoms and two Sb4 atoms from the Co/Sb layer, and the
other is defined by four Sb3 atoms from the Sb net. The
La2 atom has similar square antiprismatic geometry with
an extra La2–Sb5 contact with the Co/Sb layer (Figure 4,
b). Compared with the β-RENiSb3 analogues, RE–Sb dis-
tances are not affected significantly by the different transi-
tion-metal ions, for example, 3.2573(9)–3.3940(9) Å for β-
LaCoSb3 and 3.2503(5)–3.3942(9) Å for β-LaNiSb3.[19] The
square Sb nets are composed of Sb3 atoms with bond
lengths of 3.0128(12)–3.0806(9) Å, and angle Sb–Sb–Sb:
87.434(5)–92.533(6)° as shown in Figure 5. Compared with
Figure 5. The Sb square nets in β-LaCoSb3 in the bc-plane with
angles and distances [Å] marked.
the Ni-analogue, different transition metal, Co vs. Ni,
slightly changes the bonds and angles. The Sb3 nets are
The structural comparison between β-RECoSb3 and β-
RENiSb3 suggests that the different transition metal does
not alter the crystallographic structure predominantly. The
electronic structures have therefore been studied to give
some insight into the physical properties.
Electronic Structure
The electronic structure for β-LaCoSb3 was calculated
with the TB-LMTO method. The band structure along the
special symmetry lines Γ-X, Γ-Y, and Γ-Z is shown in
Figure 6. Along Γ-Y, bands crossing the Fermi level are
quite dispersed with contributions largely from the orbitals
of either the Sb square net or Co/Sb layer extending along
the b axis (Figure 7, parts a, b, d). The bands crossing the
Figure 4. (a) La1 centered square antiprism. (b) La2 centered
monocapped square antiprism. The La–Sb, and Sb3–Sb3 bond
lengths less than 3.40 Å are indicated.
Figure 6. Band dispersion curves for β-LaCoSb3 along ΓX, ΓY,
and ΓZ. The Fermi level (εf = 0) is set at zero.
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Syntheses, Structures, and Theoretical Studies of New Antimonides
Figure 7. Spin-polarized densities of states (DOS) for β-LaCoSb3. (a) Partial DOS of Co ions; (b) partial DOS of La cations; (c, d)
partial DOS of Sb atoms from Co/Sb layer and Sb3 atoms of Sb square net, respectively. The Fermi level is marked by a dashed line at
0 eV.
Fermi level along Γ-Z mainly correspond to the contri- shorter, so the integrated –COHP value of 0.909 eV/cell is
butions of the layers of Co/Sb and Sb square net along the larger than that of the La1 sphere. As shown in parts c and
c axis. These features suggest that β-LaCoSb3 should be d of Figure 7, the partial DOS of Sb atoms in the Co/Sb
metallic in both b and c directions. Meanwhile, the three layer are more delocalized than that of the square net, for
types of RETSb3 have similar electronic structures; there- example Sb 5p (–7 to 0 eV) vs. Sb3 5p (–4.5 to 0 eV), which
fore, their electronic properties should be comparable. This illuminates that Sb atoms in the Co/Sb layer show abundant
statement has been supported by the experimental measure- bonding interactions compared with that in the square net.
ments on β-LaNiSb3 that displays metallic electrical con- In the region from –5 eV up to the Fermi level, a significant
ductivity from 1.8 K to 300 K along the b direction.[19] And mixture of Co 3d and Sb 5p states implies the strong coval-
the parent-type LaCrSb3 also exhibits metallic electrical ent character of Co–Sb bonds. As indicated by the COHP
conductivity from 20 K to 300 K along the c direction.[7] curves plotted in Figure 8 (b), the Co–Sb bonds (2.596–
As shown in Figure 6, the bands are flat along Γ-X and no 2.666 Å) within the CoSb6 octahedra are almost optimized
band crosses the Fermi level, which is consistent with the giving an integrated –COHP value from 1.985 to 2.221 eV/
existence of the intervening layers of La3+ ions that are cell. The Sb3–Sb3 bonds (3.0128–3.0806 Å) are covalent
weakly bonded to both the Sb net and Co/Sb layers. There- bonds with the integrated –COHP value of 0.893–1.100 eV/
fore, RETSb3 should show poor conductivity along the a cell. Any Sb–Sb distance beyond 3.3410 Å is not considered
axis. Such a prediction is worthy of further experimental since the Sb1–Sb5 (3.3410 Å) only has an –ICOHP about
measurement.
12% of the strongest Sb3–Sb3 bond.
The spin-polarized calculations of the partial densities of
states (DOS) of La, Co, and Sb atoms and the crystal or-
bital Hamilton population (COHP) curves for β-LaCoSb3
are shown in Figure 7 and Figure 8. The Fermi level crosses
partially filled bands in the DOS curve, which also indicates
the metallic behavior. Most of the La states (5d and 6s) are
unoccupied and locate above the Fermi level, as expected
for an electropositive element. The hybridization of La 5d
and Sb 5p states from –3 to 0 eV (Figure 7 b, c, d) implies
some bonding character between La and Sb. For instance,
La1–Sb bonds range from 3.2587(9) to 3.3940(9) Å, with
the integrated –COHP value varying from 1.017 to
0.837 eV/cell. Any La1–Sb bond longer than 3.50 Å is re-
garded as relatively weak because the integrated –COHP
value is only about half of the normal La1–Sb bonds. Simi-
larly, the distances of La2–Sb bonds between 3.2573(9) and
Figure 8. Crystal orbital Hamilton population curves for the Co–
Co, Co–Sb, and Sb3–Sb3 in β-LaCoSb3. The Fermi level is set at
3.3622(13) Å, with an average of 3.3098 Å are slightly εf = 0 eV.
Eur. J. Inorg. Chem. 2009, 230–237
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W.-Z. Cai, L.-M. Wu, L.-H. Li, L. Chen
FULL PAPER
The complex Sb substructure of β-LaCoSb3 adds diffi- The structure features the alternating layers of condensed
culty to charge formulation. A simple charge formulation CoSb6 octahedra and square Sb nets, with interventional
would be La3+[CoSb3]3–. The bond orders (vij) for the Sb RE3+ cations. Electronic structure calculations on β-La-
atoms can be calculated by vij = exp[(2.80 – dij)/0.37], where CoSb3 show anisotropic metallic conductivities in both b
dij is the bond length in Å.[35] The formal charges are thus and c directions that agree well with previous measure-
calculated to be –1.9 for Sb1, –2.5 for Sb2, –1.0 for Sb3, ments. The conductivity in the a direction should be weak
–2.6 for Sb4, and –2.5 for Sb5, giving an overall negative because of the intervention of RE3+ cations via weak bond
charge of –5.75 per formula unit in β-LaCoSb3. The calcu- interactions. The calculations also indicate no spin-polar-
lated charge of Sb3 agrees well with that deduced from the ization occurred around the Fermi level, which means that
Zintl–Klemm concept, i.e., four-bonded Sb3 atoms (Fig- LaTSb3 (T = Co, Ni) should be diamagnetic.[19] And for
ure 5) in square nets is assigned to –1.[2,34] This simple cal- other RE members, the magnetic rare-earth atoms are the
culation reveals the apparent charge of Co as +2.75.
only source for the magnetic properties. Therefore, the two
As shown in Figure 7 (a), the spin-up states (Ȇ) are series of β-type compounds, RECoSb3 and RENiSb3,
almost the same as the spin-down states (ȇ) around should be identical in magnetism.
the Fermi level (the calculated magnetic moment is
0.000013 µB), indicating that β-LaCoSb3 is not a spin-pola-
rized compound. This also agrees with the diamagnetic be-
Experimental Section
havior of Co atoms in many intermetallic compounds such
as Ce3Co4Sn13,[36] RE5Co4Si14 (RE = Ho, Er, Tm, Yb),[37]
Synthesis: The handling of all materials was carried out inside a
N2-filled glove box with controlled oxygen and moisture levels be-
low 0.1 ppm. The rare-earth metals, La, Pr, Nd, and Sm (99.5% or
higher, Huhhot Jinrui Rare Earth Co. Ltd), Ce foil (99.9%, Alfa
Aesar), Co power (99.94%, Shanghai Guoyao group), Sb shot
RE6Co1.67Si3 (RE = Ce, Nd, Gd, Tb, Dy).[38] Our calcula-
tions allow us to make the statement that for the β-RETSb3
series the rare-earth atoms are the only magnetic source.
Such a statement has been substantiated by the iso-
(99.999%, Alfa Aesar), and Sn shot (99.99%, Alfa Aesar) were
structural β-CeNiSb3 that shows an experimental effective
magnetic moment close to the value for free Ce3+ cations.[19]
On the basis of these calculations and observations, the
magnetism of β-RECoSb3 should be identical to the corre-
sponding Ni members. And the La members, β-LaCoSb3
and β-LaNiSb3, should be diamagnetic.
used as received. Single crystals of β-RECoSb3 (RE = La–Nd, Sm)
were prepared with Sn flux. The stoichiometric elemental mixture
of RE/Co/Sb (1:1:3 in molar ratio) and 0.3 g Sn was placed in an
evacuated fused-silica tube, then flame-sealed under vacuum at
10–3 Pa. The sealed tubes were placed into a temperature-controlled
tube furnace, heated at 640 °C for 1 d and 1050 °C for 3 d, and then
cooled to room temperature over 8 d. The Sn flux was removed by
hydrochloric acid, and the plate-like crystals were obtained after
being washed with distilled water. These crystals were stable in air
over a period of weeks.
Conclusions
In summary, we have synthesized five new ternary β-type
The power samples were prepared with RE:Co:Sb (RE = La, Ce,
RECoSb3 compounds with RE = La, Ce, Pr, Nd, and Sm. Pr, Nd, and Sm) in 1:1:3.15 molar ratio (the excess of Sb was to
Table 1. Crystal data and structural refinements for β-RECoSb3 (RE = La–Nd, Sm).
Chemical formula
LaCoSb3
CeCoSb3
PrCoSb3
NdCoSb3
SmCoSb3
Formula weight
Space group
a [Å]
563.09
564.30
565.09
568.42
574.57
Pbcm (No.57)
12.985(4)
6.1603(18)
12.166 (4)
973.19(50)
8
Pbcm (No.57)
12.829(8)
6.136(4)
12.109(7)
953.14(10)
8
Pbcm (No.57)
12.748(6)
6.131(3)
12.086(5)
944.65(75)
8
Pbcm (No.57)
12.651(5)
6.116(2)
12.073(4)
934.13(57)
8
Pbcm (No.57)
12.5530(13)
6.1043(4)
12.0267(12)
921.57(15)
8
b [Å]
c [Å]
V [Å3]
Z
Crystal size [mm]
Temperature [K]
ρcal [g/cm3]
Radiation, λ [Å]
θ range [°]
Index ranges
0.15/0.10/0.05
293(2)
7.686
Mo-Kα, 0.71073
3.14–27.48
–16 Յ h Յ 16
–7 Յ k Յ 6
–14 Յ l Յ 15
28.171
0.07/0.04/0.02
293(2)
7.865
Mo-Kα, 0.71073
3.18–27.42
–16 Յ h Յ 12
–7 Յ k Յ 7
–15 Յ l Յ 15
29.351
0.15/0.09/0.05
293(2)
7.947
Mo-Kα, 0.71073
3.20–27.47
–16 Յ h Յ 16
–7 Յ k Յ 7
–13 Յ l Յ 15
30.293
0.15/0.09/0.04
293(2)
8.084
Mo-Kα, 0.71073
3.22–27.47
–14 Յ h Յ 16
–7 Յ k Յ 7
–15 Յ l Յ 15
31.319
0.10/0.09/0.08
293(2)
8.282
Mo-Kα, 0.71073
3.25–27.47
–16 Յ h Յ 7
–7 Յ k Յ 7
–15 Յ l Յ 15
33.221
µ [mm–1]
Rint
0.0572
0.0375
0.0427
0.0643
0.0672
R1/ wR2 [I Ͼ 2σ(I)][a]
R1/wR2 (all data)
∆ρmax [e·Å–3]
∆ρmin [e·Å–3]
0.0316/0.0771
0.0355/0.0785
2.929
0.0232/0.0522
0.0275/0.0541
1.265
–1.121
1.092
0.0256/0.0619
0.0279/0.0633
1.827
–1.951
1.158
0.0457/0.1198
0.0463/0.1206
4.004
–5.434
1.184
0.0326/0.0740
0.0385/0.0778
2.576
–2.349
1.094
–3.329
2
Goodness of fit on Fo 1.094
[a] R1 = ∑||Fo| – |Fc||/∑|Fo| for Fo Ͼ2σ(Fo ); wR2 = ∑[w (Fo – Fc2)]/∑[w(Fo2)2]1/2,where w = 1/[σ2Fo + (AP)2 + BP], and P = (Fo + 2Fc2)/3.
2
2
2
2
2
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Syntheses, Structures, and Theoretical Studies of New Antimonides
compensate for evaporative losses). The heating profile for each
sample is 650 °C for 1 d and 950 °C for 8 d and then cooling to
300 °C at 5 °C/h before switching off the furnace. The X-ray dif-
fraction analyses show the existence of the minor byproducts of
CoSb3 and CoSb2. With the purpose to obtain singular β-RE-
CoSb3, the product was reground several times and pressed into a
pellet, sealed in a silica tube, then heated at 900 °C for 8 d, and
subsequently cooled to room temperature. Unfortunately, the by-
products, binary CoSb3 and CoSb2 (less than 10%), were irremov-
able by such treatment. The arc-melting technique yields β-RE-
CoSb3 as the major product together with minor CoSb3 and CoSb2
byproducts.
RECo1–xSb2 (HfCuSi2-type) with RE = Gd–Er and Y were pro-
duced.[39] When RE = Tm, binary TmSb was the main product.
In the diagram study of the RE/Co/Sb (RE = Ce, Pr) system, two
α-type compounds have been identified by XRD patterns, and their
annealed temperatures are 400 °C and 600 °C, respectively.[25,26]
Therefore, β-RECoSb3 is thought to be a high-temperature stable
phase.
Elemental Analysis: Microprobe elemental analysis was performed
on some single crystals of RECoSb3, including the single crystals
used for X-ray diffraction analyses. Spectra were collected on a
field emission scanning electron microscope (FESEM, JSM6700F)
equipped with an energy dispersive X-ray spectroscope (EDX, Ox-
ford INCA). The results indicated the presence of all three RE, Co,
Similar reactions were carried out for other rare-earth metals with
RE = Gd–Tm and Y for proposed RECoSb3 analogs. However,
Table 2. Atomic positions, site symmetry, and Ueq values for β-RECoSb3 (RE = La–Nd, Sm).
Atom
Wyckoff site
x
y
z
Ueq [Å2][a]
LaCoSb3
La1
La2
Co1
Sb1
Sb2
Sb3
Sb4
Sb5
4c
4d
8e
4c
4d
8e
4c
4d
0.70093(5)
0.30412(5)
0.09764(8)
0.97285(5)
0.79080(5)
0.50200(3)
0.21487(6)
0.94380(5)
1/4
0
3/4
0.86327(7)
0
3/4
0.87632(3)
0
3/4
0.00514(18)
0.00490(18)
0.00630(2)
0.00630(2)
0.00590(2)
0.00622(18)
0.00580(2)
0.00640(2)
0.27003(11)
0.03739(17)
1/4
0.26224(12)
0.51089(8)
1/4
0.88966(12)
CeCoSb3
Ce1
Ce2
Co1
Sb1
Sb2
Sb3
Sb4
Sb5
4c
4d
8e
4c
4d
8e
4c
4d
0.70037(4)
0.30463(4)
0.10094(7)
0.97276(5)
0.78711(4)
0.50195(3)
0.21779(5)
0.94424(4)
1/4
0
3/4
0.86292(6)
0
3/4
0.87627(3)
0
3/4
0.00566(13)
0.00561(13)
0.00853(19)
0.00790(15)
0.00624(14)
0.00675(12)
0.00628(14)
0.00780(15)
0.26810(7)
0.03510(13)
1/4
0.25898(8)
0.50995(6)
1/4
0.88655(9)
PrCoSb3
Pr1
Pr2
Co1
Sb1
Sb2
Sb3
Sb4
Sb5
4c
4d
8e
4c
4d
8e
4c
4d
0.70016(4)
0.30507(4)
0.10118(7)
0.97269(5)
0.78561(5)
0.50209(3)
0.21956(5)
0.94333(4)
1/4
0
3/4
0.86290(6)
0
3/4
0.87628(3)
0
3/4
0.00526(15)
0.00529(14)
0.00680(2)
0.00678(16)
0.00568(16)
0.00616(15)
0.00575(16)
0.00701(16)
0.26982(8)
0.03578(14)
1/4
0.25959(9)
0.51054(6)
1/4
0.88860(9)
NdCoSb3
Nd1
Nd2
Co1
Sb1
Sb2
Sb3
Sb4
Sb5
4c
4d
8e
4c
4d
8e
4c
4d
0.70015(6)
0.30479(6)
0.10065(9)
0.97244(7)
0.78390(7)
0.50246(4)
0.22162(8)
0.94260(6)
1/4
0
3/4
0.86343(9)
0
3/4
0.87615(4)
0
3/4
0.00640(3)
0.00620(3)
0.00850(3)
0.00760(3)
0.00660(3)
0.00710(3)
0.00690(3)
0.00740(3)
0.27282(11)
0.0376(2)
1/4
0.26240(12)
0.51204(10)
1/4
0.89053(12)
SmCoSb3
Sm1
Sm2
Co1
Sb1
Sb2
Sb3
Sb4
Sb5
4c
4d
8e
4c
4d
8e
4c
4d
0.69968(6)
0.30568(6)
0.10342(11)
0.97241(8)
0.78138(8)
0.50244(5)
0.22393(8)
0.94300(7)
1/4
0
3/4
0.86301(9)
0
3/4
0.87615(4)
0
3/4
0.00685(18)
0.00681(18)
0.01070(3)
0.00890(2)
0.00720(2)
0.00769(19)
0.00730(2)
0.00900(2)
0.27138(9)
0.03549(18)
1/4
0.25914(11)
0.51076(8)
1/4
0.88831(12)
[a] Ueq is defined as one-third of the trace of the orthogonalized Uij tensor.
Eur. J. Inorg. Chem. 2009, 230–237
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
235

W.-Z. Cai, L.-M. Wu, L.-H. Li, L. Chen
FULL PAPER
Table 3. Selected interatomic distances [Å] in β-RECoSb3 (RE = La–Nd, Sm).
LaCoSb3
CeCoSb3
PrCoSb3
NdCoSb3
SmCoSb3
RE1–Sb1
3.5308(14)
3.2587(9)
3.3729(10)
3.3940(9)
3.2685(9)
3.3379(13)
3.2732(12)
3.3622(13)
3.3414(10)
3.3539(10)
3.2573(9)
3.3026(13)
2.756(2)
2.5960(12)
2.6661(12)
2.6212(13)
2.6076(12)
2.5918(13)
2.6265(14)
3.1598(9)
3.1426(14)
3.3410(1)
3.0356(12)
3.0128(12)
3.0738(13)
3.0806(9)
3.4950(2)
3.2258(18)
3.3392(14)
3.3568(14)
3.2425(18)
3.2774(16)
3.2337(19)
3.3381(19)
3.3087(14)
3.3172(14)
3.2277(18)
3.2740(2)
2.735(2)
2.5902(13)
2.6829(13)
2.6081(13)
2.5963(13)
2.5965(14)
2.6183(15)
3.1464(19)
3.1430(2)
3.3166(17)
3.0472(15)
2.9994(19)
3.0580(2)
3.0682(19)
3.4743(18)
3.2125(13)
3.3226(12)
3.3412(11)
3.2317(14)
3.2676(14)
3.2175(15)
3.3349(15)
3.2887(12)
3.3015(11)
3.2146(13)
3.2494(16)
2.7291(19)
2.5889(11)
2.6747(11)
2.6100(12)
2.5977(11)
2.5934(13)
2.6197(13)
3.1435(14)
3.1472(17)
3.3164(13)
3.0358(13)
2.9940(15)
3.0526(15)
3.0658(14)
3.4447(17)
3.1997(10)
3.3052(11)
3.3256(11)
3.2141(10)
3.2581(15)
3.1975(13)
3.3173(14)
3.2732(11)
3.2879(11)
3.1994(10)
3.2115(16)
2.739(2)
2.5820(14)
2.6528(14)
2.6155(15)
2.5979(14)
2.5849(15)
2.6144(15)
3.1365(10)
3.1525(18)
3.3172(10)
3.0338(14)
2.9947(14)
3.0460(14)
3.0586(10)
3.4237(12)
3.1773(5)
3.2846(8)
3.2988(8)
3.1992(4)
3.2198(14)
3.1717(9)
3.3124(9)
3.2462(8)
3.2610(8)
3.1797(5)
3.2023(12)
2.718(2)
2.5802(12)
2.6708(13)
2.6047(13)
2.5919(13)
2.5903(15)
2.6125(13)
3.1297(5)
3.1574(14)
3.2985(5)
3.0398(12)
2.9825(10)
3.0344(10)
3.0528(2)
RE1–Sb2 (ϫ2)
RE1–Sb3 (ϫ2)
RE1–Sb3 (ϫ2)
RE1–Sb4 (ϫ2)
RE2–Co1
RE2–Sb2
RE2–Sb2
RE2–Sb3 (ϫ2)
RE2–Sb3 (ϫ2)
RE2–Sb4 (ϫ2)
RE2–Sb5
Co1–Co1
Co1–Sb1 (ϫ2)
Co1–Sb1(ϫ2)
Co1–Sb2(ϫ2)
Co1–Sb4
Co1–Sb5
Co1–Sb5
Sb1–Sb1 (ϫ2)
Sb1–Sb4
Sb1–Sb5 (ϫ2)
Sb2–Sb5
Sb3–Sb3
Sb3–Sb3
Sb3–Sb3 (ϫ2)
and Sb elements in molar ratios (19–21% RE, 19–20% Co, 58–
62% Sb) and no Sn element was detected, which is in good agree-
by the tetrahedron method[46] using a 2ϫ2ϫ4 k-mesh within the
Brillouin zone. The Fermi level (εf = 0 eV) was selected as the en-
ment with the stoichiometry refined from the single-crystal X-ray ergy reference.
structure determinations.
Structure Determination: The single-crystal X-ray diffraction data
Acknowledgments
were collected with
a Rigaku Mercury CCD diffractometer
equipped with a graphite-monochromated Mo-Kα radiation source
(λ = 0.71073 Å) at 293 K. The absorption corrections were done
by the Multi-scan method.[40] The space group was determined to
be Pbcm (No. 57) based on systematic absences, E-value statistics,
and subsequent successful refinements of the crystal structure. The
structures were solved without events by direct methods and re-
fined by full-matrix least-squares fitting on F2 by SHELXL-97.[41]
All of the atoms were refined with anisotropic thermal parameters.
Crystallographic data and structural refinements are summarized
in Table 1. Atomic coordinates and anisotropic displacement pa-
rameters are provided in Table 2. Table 3 gives the interatomic dis-
tances for β-RECoSb3 (RE = La–Nd, Sm) for comparison.
The research was supported by the National Natural Science Foun-
dation of China under Projects (20521101, 20773130, 20733003),
“Key Project from Fujian Institute of Research on the Structure of
Matter” (SZD08002), and the “Key Project from Chinese Academy
of Sciences” (KJCX2-YW-H01).
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Received: August 21, 2008
Published Online: December 9, 2008
Eur. J. Inorg. Chem. 2009, 230–237
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
237