On the rare earth metal bismuthide oxides RE2BiO2 (RE = Nd, Tb, Dy, Ho)

Article abstract of DOI:10.1002/zaac.201100529

A series of new RE₂BiO₂ compounds (RE = Nd, Tb, Dy, Ho) has been synthesized from elemental bismuth, REBi, and RE₂O ₃ in all-solid state reactions in sealed tantalum ampoules at 1770 K. The dark grey metallic compounds adopt the anti-ThCr₂Si₂ type of structure (I4/mmm, tI10), according to X-ray single crystal structure analysis. As a main structural feature, there are PbO analogous slabs, [REO]⁺, and 4⁴ nets of Bi^2- anions, alternately stacked along the c-axis. Copyright

Full text of DOI:10.1002/zaac.201100529

SHORT COMMUNICATION
DOI: 10.1002/zaac.201100529
On the Rare Earth Metal Bismuthide Oxides RE2BiO2 (RE = Nd, Tb, Dy, Ho)
Jürgen Nuss[a] and Martin Jansen*[a]
Keywords: Rare earths; Bismuthide oxides; Solid-state reactions; Solid-state structures; X-ray diffraction
Abstract. A series of new RE2BiO2 compounds (RE = Nd, Tb, Dy, ture (I4/mmm, tI10), according to X-ray single crystal structure analy-
Ho) has been synthesized from elemental bismuth, REBi, and RE2O3 sis. As a main structural feature, there are PbO analogous slabs,
in all-solid state reactions in sealed tantalum ampoules at 1770 K. The [REO]+, and 44 nets of Bi2– anions, alternately stacked along the c-
dark grey metallic compounds adopt the anti-ThCr2Si2 type of struc-
axis.
Herein we report on the synthesis and single crystal struc-
Introduction
ture refinements of new RE2BiO2 representatives, with RE rep-
resenting the trivalent rare earth metals neodymium, terbium,
dysprosium, and holmium.
Rare earth metal pnictide oxides have attracted interest as
potential thermoelectrics, in recent times.[1–3] On one hand,
they contain some of the heaviest elements in the periodic table
which reduces thermal lattice vibrations, on the other the com-
bination with oxide may also minimize thermal conductivity,
since the efficiency of phonon propagation is perturbed by
structural complexity.[1,4]
Results and Discussion
Starting from elemental bismuth, the bismuthides (REBi)
and oxides (RE2O3), Nd2BiO2, Tb2BiO2, Dy2BiO2 and
Ho2BiO2 have been synthesized by all-solid state reactions.
When exposed to humid air, the dark grey metallic compounds
slowly corrode, and may start smoldering after mechanical
treatment.
The title compounds crystallize in the tetragonal space group
I4/mmm (no. 139) adopting a structure analogous to anti-
ThCr2Si2 (Table 1, Table 2). The rare earth metal cations,
which are occupying the Si positions, are surrounded by four
oxygen and four bismuth atoms in the shape of square anti-
prisms (Figure 1). The oxygen atoms (Cr positions) are tetra-
hedrally coordinated by four rare earth metals forming PbO
analogous slabs, and finally, the bismuth atoms are arranged
in 44 nets, along (001), separating the REO slabs, whereby
each bismuth atom is surrounded by eight RE atoms in the
function of a slightly elongated cube.
The distances between neighboring bismuth atoms range
from 385.83(3) to 399.11(3) pm (Table 3), which correspond
to the a-axis of the respective compound, are too long for as-
suming a chemical bond. However, the bismuth atoms in each
refined structure show significant anisotropy of thermal mo-
tion, which is expressed by the ratio of the maximum and mini-
mum displacement parameters U11/U33 ≈ 2.2–4.3. This is indi-
cating some local disorder, which gives freedom to assume real
Bi–Bi distances shorter by approx. 28 pm (= 2√U11, cf.
Table 2). This value is independently confirmed by applying a
split model for the Bi position (8i site instead of 2a). In ele-
mental bismuth, the Bi–Bi distances are 307 pm, and within
1D Bi– zigzag chains[9] or Bi24– dumbbells[10] the distances are
322 and 329 pm, respectively, the latter are usually addressed
as single bonds. In the 2D Bi– square sheets, present in EuBi2,
The rare earth metal pnictide oxides, Ce2SbO2 and Ce2BiO2,
were already reported by Benz in 1971,[5] the charge balance
as adjusted by the presence of Ce3+ and Ce4+, together with
the formation of Pn3– (Pn = Sb, Bi), was assumed to stabilize
these compounds. Recent studies, including additional
praseodymium representatives, have clearly shown that in all
of these examples the rare earth metal is in the trivalent state,
exclusively. This finding was evidenced by magnetic suscep-
tibility measurements.[6] The electron count according to
[RE3+]2[Pn2–][O2–]2, in analogy to isoelectronic RE2TeO2,[7]
seems to be valid for all of them. While semiconducting be-
havior is observed for the antimonides, due to Sb–Sb bond
formation, the bismuthides display metallic conductivity. The
latter appear to formally contain unusual Bi2– anions, without
any effective chemical bond between them.[2] Consequently,
there is no need for the presence of Ce4+ or Pr4+, and it should
be possible to extend this class of materials including other
rare earth metals.
The validity of this assumption was already affirmed by
powder diffraction studies on RE2BiO2 representatives with RE
= Nd, Sm, Gd, Ho, Er, and Y.[2] However, for understanding
the properties of this class of materials, more accurate structure
data are desirable. In particular, the localization of the oxygen
atoms in such heavy-element structures, using powder meth-
ods, can be a rather difficult task.[8]
* Prof. Dr. M. Jansen
Fax: +49-711-689-1502
E-Mail: M.Jansen@fkf.mpg.de
[a] Max-Planck-Institut für Festkörperforschung
Heisenbergstr. 1
70569 Stuttgart, Germany
Z. Anorg. Allg. Chem. 2012, 638, (3-4), 611–613
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
611

J. Nuss, M. Jansen
SHORT COMMUNICATION
Table 1. Crystal data, data collection, and refinement details at 298 K.
Compound
Nd2BiO2
Tb2BiO2
Dy2BiO2
Ho2BiO2
Formula weight
529.46
558.82
565.98
570.84
Space group (no.), Z
Lattice constants /pm
I4/mmm (139), 2
a = 399.11(3)
c = 1366.3(3)
c/a = 3.423
217.63(5)
I4/mmm (139), 2
389.62(6)
1331.7(3)
3.418
202.16(6)
9.180
I4/mmm (139), 2
387.61(3)
1323.3(2)
3.414
198.82(4)
9.454
I4/mmm (139), 2
385.83(2)
1321.8(1)
3.426
196.77(2)
9.635
V /Å3
ρxray /g·cm–3
8.080
Crystal size
0.08ϫ 0.06ϫ 0.04
0.07ϫ 0.07ϫ 0.04
0.12ϫ 0.06ϫ 0.03
0.15ϫ 0.10ϫ 0.05
Diffractometer
X-ray radiation, λ /pm
Absorption correction
2θ range /°
SMART APEX II, Bruker AXS
71.073
multi-scan, SADABS[15]
5.96 Յ 2θ Յ 73.78
–6 Յ h Յ 6,
–6 Յ k Յ 6,
–22 Յ l Յ 22
2785
201, 0.051
9
0.185, 0.080
0.022
6.12 Յ 2θ Յ 68.76
6.16 Յ 2θ Յ 73.74
–6 Յ h Յ 6,
–6 Յ k Յ 6,
–22 Յ l Յ 22
2432
6.16 Յ 2θ Յ 73.88
–6 Յ h Յ 6,
–6 Յ k Յ 6,
–22 Յ l Յ 22
2385
184, 0.028
9
0.102, 0.028
0.016
Index range
–6 Յ h Յ 6,
–6 Յ k Յ 6,
–20 Յ l Յ 20
1583
Reflection collected
Data, Rint
No. of parameters
Transmision: tmax, tmin
R1[F2 Ͼ 2σ (F2)]
wR(F2)
161, 0.033
9
185, 0.054
9
0.147, 0.074
0.019
0.195, 0.037
0.036
0.048
0.050
0.107
0.041
Extinction coefficient
0.0043(5)
CSD-423917
0.020(1)
CSD-423916
0.010(1)
CSD-423915
0.0019(3)
CSD-423914
Deposition no.[17]
Table 2. Atomic coordinates and displacement parameters Uij /pm2 at
298 K (U11 = U22, U12 = U13 = U23 = 0).
Atom
Site
x
y
z
U11
U33
Ueq
Nd2BiO2
Bi
Nd
O
2a
4e
4d
0
0
0
0
0
½
0
203(2) 87(3)
66(2) 96(3)
56(16) 149(26) 87(11)
164(2)
76(2)
0.33596(3)
¼
Tb2BiO2
Bi
Tb
O
2a
4e
4d
0
0
0
0
0
½
0
188(3) 61(3)
57(2) 63(3)
80(15) 59(22)
146(2)
59(2)
73(11)
0.33422(3)
¼
Dy2BiO2
Bi
Dy
O
2a
4e
4d
0
0
0
0
0
½
0
195(4) 45(4)
145(3)
64(3)
0.33412(2)
¼
67(3)
57(4)
63(12) 107(23) 77(9)
Ho2BiO2
Bi
Ho
O
2a
4e
4d
0
0
0
0
0
½
0
196(2) 88(2)
71(2) 94(2)
58(10) 134(21) 83(8)
160(2)
79(2)
0.33374(2)
¼
Figure 1. Perspective representation of the crystal structure of
RE2BiO2 compounds (RE = Nd, Tb, Dy, Ho), showing the coordination
of the anions (left) and cations (right) in polyhedral representation.
The central part is drawn in ball-and-stick mode emphasizing the con-
nectivity. The unit cell is drawn in dotted lines.
the Bi–Bi distances of 334 pm are considered to be “hyperval-
ent“ Bi–Bi bonds.[9] In comparison, the Bi–Bi contacts of 360–
370 pm encountered in RE2BiO2 compounds appear still too
long. Thus at best non-covalently bonded Bi2– anions can be
assumed, which would be in agreement with the metallic con-
ductivity observed.[2,6] It was suggested,[6] and later confirmed
by band structure calculations,[2] that the partially filled 6p
band of Bi2– is responsible for this behavior.
Table 3. Interatomic distances /pm at 298 K (RE = Nd, Tb, Dy, Ho).
Atomic contact Nd2BiO2 Tb2BiO2 Dy2BiO2 Ho2BiO2 mult.
In structural details the bismuthides are clearly distinct from
the respective antimonides Ce2SbO2 and Pr2SbO2, where a ra-
tio of U11/U33 Ͼ 15 is observed, indicating pronounced Sb–
Sb bonding interactions, which allows for the description of
covalently bonded Sb24– dimers, in agreement with their semi-
conducting behavior.[6]
RE
–Bi
–O
–RE
–RE
–RE
–Bi
360.38(4) 353.04(5) 351.16(3) 350.32(3)
231.55(3) 224.79(3) 223.50(2) 222.42(2)
367.17(7) 355.28(6) 353.10(5) 351.34(4)
360.38(4) 353.05(5) 351.16(3) 350.33(3)
231.55(3) 224.79(3) 223.50(2) 222.41(2)
399.11(3) 389.62(6) 387.61(3) 385.83(2)
4
4
4
8
4
4
Bi
O
Bi
612
www.zaac.wiley-vch.de
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2012, 611–613

On the Rare Earth Metal Bismuthide Oxides RE2BiO2
Conclusions
Acknowledgments
Nd2BiO2, Tb2BiO2, Dy2BiO2, and Ho2BiO2 have been syn-
thesized by solid state reaction from elemental bismuth, REBi,
and RE2O3, and characterized by single crystal diffraction.
Their existence clearly demonstrates that there is no need for
the rare earth metal to adopt the tetravalent oxidation state,
and consequently bismuth must be present as Bi2– anions. The
particular bonding situation, as revealed for bismuth, clearly
deserves further attention.
The authors gratefully acknowledge the help of Mrs S. Prill-Diemer
for carrying out the synthesis.
References
[1] P. Wang, S. Forbes, T. Kolodiazhnyi, K. Kosuda, Y. Mozhariv-
skyj, J. Am. Chem. Soc. 2010, 132, 8795–8803.
[2] H. Mizoguchi, H. Hosono, J. Am. Chem. Soc. 2011, 133, 2394–
2397.
The title compounds complete the series of rare earth metal
pnictide oxides: RE4Pn2O,[8] RE9Pn5O5,[11–13] RE2PnO2,[2,5,6]
RE8Pn3O8,[1] and RE3PnO3.[1]
[3] P. Wang, S. Forbes, V. Svitlyk, A. Aushana, Y. Mozharivskyj,
Eur. J. Inorg. Chem. 2011, 3887–3895.
[4] G. A. Slack, in: CRC Handbook of Thermoelectrics (Ed.: D. M.
Rowe), CRC Press, Boca Raton, USA 1995.
[5] R. Benz, Acta Crystallogr., Sect. A 1971, 27, 853–854.
[6] J. Nuss, M. Jansen, J. Alloys Compd. 2009, 480, 57–59.
[7] F. A. Weber, T. Schleid, Z. Anorg. Allg. Chem. 1999, 625, 1833–
1838.
[8] J. Nuss, U. Wedig, M. Jansen, Z. Anorg. Allg. Chem. 2011, 637,
1975–1981.
[9] Z.-M. Sun, J.-G. Mao, J. Solid State Chem. 2004, 177, 3752–
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[10] G. Derrien, M. Tillard-Charbonnel, A. Manteghetti, L. Moncond-
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[11] J. Nuss, H. G. von Schnering, Y. Grin, Z. Anorg. Allg. Chem.
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[12] J. Nuss, M. Jansen, Acta Crystallogr., Sect. B 2007, 63, 843–849.
[13] J. Nuss, M. Jansen, Z. Kristallogr. New Cryst. Struct. 2009, 224,
11–12.
Experimental Section
Syntheses
The RE2BiO2 (RE = Nd, Tb, Dy, Ho) compounds have been synthe-
sized in approx. 1 g batches from REBi, elemental bismuth, and
RE2O3, respectively (ChemPur, Karlsruhe, Germany 99.9%). The bi-
nary rare earth bismuthides were prepared from the elements in tanta-
lum ampoules. The reactions were done in dynamic vacuums, when
heating the ampoules at 1270 K for 48 h to remove potential impurities
of hydrogen. Stoichiometric amounts of the starting materials were
mixed and sealed in tantalum ampoules. The following temperature
profile was applied: 298 Ǟ 1770 K (100 K·h–1, subsequent annealing
for 72 h); 1770 Ǟ 1470 K (25 K·h–1, subsequent annealing for 72 h);
1470 Ǟ 298 K (50 K·h–1).
[14] Bruker Suite, Version 2008/3, Bruker AXS Inc., Madison, USA
2008.
[15] G. M. Sheldrick, SADABS, Bruker AXS area detector scaling and
absorption, Version 2008/1, University of Göttingen, Germany
2008.
[16] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[17] Further details may be obtained from Fachinformationszentrum
Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (Fax:
+49-7247-808-666; E-Mail: crysdata(at)fiz-karlsruhe.de, http://
www.fiz-karlsruhe.de/request for deposited data.html) on quoting
the CSD numbers (CSD-423914–423917).
Structure Determinations
The diffraction data were collected at 298 K with a SMART-APEX-II
CCD X-ray diffractometer (Bruker AXS, Karlsruhe, Germany) with
graphite-monochromated Mo-Kα radiation (λ = 71.073 pm). The re-
flection intensities were integrated with the SAINT subprogram in the
Bruker Suite software package,[14] a multi-scan absorption correction
was applied using SADABS.[15] The structures were solved by direct
methods and refined by full-matrix least-squares fitting with the
SHELXTL software package.[16] Experimental details are given in
Table 1 and Table 2. Further details may be obtained from Fach-
informationszentrum Karlsruhe.[17]
Received: December 8, 2011
Published Online: January 9, 2012
Z. Anorg. Allg. Chem. 2012, 611–613
© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
613