Synthesis and characterization of the rare-earth vanadium oxyselenides Ln7VO4SE8 (Ln = Nd, Sm, Gd)

Article abstract of DOI:10.1006/jssc.2000.8884

The new compounds Ln₇VO₄Se₈ (Ln = Nd, Sm, Gd) were each prepared by heating V, Se, and the corresponding rare-earth sesquioxide at 1223 K in a sealed fused-silica tube. Single crystals have been grown through the use of an antimony flux. They have been characterized by single-crystal and powder X-ray diffraction measurements and by energy dispersive X-ray analysis. These isostructural compounds crystallize with two formula units in the orthorhombic space group Pbam in cells (at 153 K) of dimensions: Nd₇VO₄Se₈, a = 14.3419(9) A, b = 15.5528(10) A, c = 3.9948(3) A; Sm₇VO₄Se₈, a = 14.200(2) A, b = 15.451(2) A, c = 3.9511(6) A; Gd₇VO₄Se₈, a = 14.075(8) A, b = 15.424(6) A, c = 3.903(1) A. The new structure type comprises four crystallographically independent Ln atoms with three different coordination geometries and one V atom in an octahedral environment. Magnetic measurements reveal that Gd₇VO₄Se₈ is paramagnetic down to 5 K. (C) 2000 Academic Press.

Full text of DOI:10.1006/jssc.2000.8884

Journal of Solid State Chemistry 154, 564}568 (2000)
doi:10.1006/jssc.2000.8884, available online at http://www.idealibrary.com on
Synthesis and Characterization of the Rare-Earth Vanadium
Oxyselenides Ln7VO4Se8 (Ln ؍ Nd, Sm, Gd)
Olivier Tougait and James A. Ibersꢀ
Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113
Received May 3, 2000; in revised form June 20, 2000; accepted June 20, 2000; published online September 30, 2000
13, 14, or 15 (2). Their structures are built from (¸nO) and
The new compounds Ln7VO4Se8 (Ln ؍ Nd, Sm, Gd) were
each prepared by heating V, Se, and the corresponding rare-earth
sesquioxide at 1223 K in a sealed fused-silica tube. Single
crystals have been grown through the use of an antimony 6ux.
They have been characterized by single-crystal and powder
X-ray di4raction measurements and by energy dispersive X-ray
analysis. These isostructural compounds crystallize with two
formula units in the orthorhombic space group Pbam in cells (at
153 K) of dimensions: Nd7VO4Se8, a ؍ 14.3419(9) A, b ؍
15.5528(10) A, c ؍ 3.9948(3) A; Sm7VO4Se8, a ؍ 14.200(2) A,
b ؍ 15.451(2) A, c ؍ 3.9511(6) A; Gd7VO4Se8, a ؍ 14.075(8) A,
(M Q ) layers that stack successively along a crystallo-
V W
graphic axis with the cations speci"cally surrounded by one
type of anion. In the second category are most of the
quaternary ¸n/M/O/Q compounds, where the 3d-transition
metal M belongs to group 4, 5, or 6. In such compounds the
3d cation is usually in an octahedral hole whereas the 4f
element is usually in a trigonal prismatic hole and each may
ꢁ\
ꢁ\
be surrounded by a combination of O and Q anions.
Among the latter quaternary systems that contain
a group 5 transition metal are ¸n V O S (¸n"La, Ce, Pr,
ꢃ ꢄ ꢅ ꢆ
b؍ 15.424(6) A, c ؍ 3.903(1) A. The new structure type comprises Nd) (3, 4), ¸n Ta O Q (¸n"La, Ce, Pr, Nd) (5}7), and
ꢁ
ꢄ ꢇ ꢁ
four crystallographically independent Ln atoms with three
di4erent coordination geometries and one V atom in an
octahedral environment. Magnetic measurements reveal that
Gd7VO4Se8 is paramagnetic down to 5 K. ( 2000 Academic Press
Key Words: X-ray structure; neodymium; samarium; gadolin-
ium; oxychalcogenide; magnetism.
Sm NbO Se (8). We present here the synthesis and struc-
ꢄ
ꢂ ꢄ
tural analysis of a new series of quaternary rare-earth
vanadium oxyselenides, ¸n VO Se (¸n"Nd, Sm, Gd).
ꢅ
ꢂ ꢇ
We also examine the close resemblance of their crystal
structures to that of U ScS (9).
ꢄ
ꢆ
EXPERIMENTAL
Syntheses
INTRODUCTION
Syntheses were carried out in sealed fused-silica tubes.
Materials used included Nd, Alfa, 40 mesh 99.9%; Sm, Alfa,
The majority of oxychalcogenide compounds reported to
date contain a rare-earth element. Their crystal structures
can be classi"ed in two broad categories. In the "rst, the
40 mesh 99.9%; Gd, Alfa, 40 mesh 99.9%; Nd O , Aldrich,
ꢁ ꢄ
99.9%; Sm O , Aldrich, 99.9%; Gd O , Aldrich, 99.9%; Se,
ꢁ ꢄ
ꢁ ꢄ
ꢁ\
ꢁ\
and Q ions (Q"chalcogen"S, Se, or Te) are separ-
O
Alfa, 325 mesh, 99.99%; V, Alfa, 325 mesh, 99.99%; VCl ,
ꢄ
ated in distinct sheets; in the second, there is a three-dimen-
ꢁ\ ꢁ\
Aldrich, 99%; and Sb, Alfa, 325 mesh, 99.5%.
sional arrangement in which both O
and Q
anions
Single crystals of Sm VO Se were "rst obtained from
ꢅ
ꢂ ꢇ
pack in the same plane with the cations located in the
interstitial sites to minimize the electrostatic repulsion be-
tween neighboring ions. Examples of the "rst category are
the reaction of Sm, V, and Se in the ratio 3:1:6 together with
a small amount of VCl in an unprotected sealed fused-silica
ꢄ
tube. The reaction tube was heated at a rate of 10 K/h
legion. They include the ternary (¸nO) S phases
to 1223 K and held there for 96 h. It was then cooled to
973 K at 3 K/h and then the furnace was turned o!. The
sample was washed with a mixture of CH OH/ H O and
ꢁ ꢁ
¸n"rare-earth (1), in which there are (¸nO) layers formed
ꢁ
from corner-sharing of [¸nO ] tetrahedra that are well
ꢂ
ꢄ
ꢁ
ꢁ\
separated by sheets of S disul"de anions. Other striking
dried with acetone. A few dark red needle-like crystals of
what turned out to be Sm VO Se were found.
ꢁ
examples are the layered oxychalcogenides formed by
ꢅ
ꢂ ꢇ
a rare-earth and a second metal (M) belonging to group 11,
Attempted quantitative syntheses (c.a. 0.5 g) at 1223 K of
¸n VO Se (¸n"Nd, Sm, Gd) from stoichiometric
ꢅ
ꢂ ꢇ
amounts of ¸n, ¸n O , V, and Se (ratio 13:4:3:24, respective-
ꢁ ꢄ
ꢀTo whom correspondence should be addressed. E-mail: ibers@chem.
nwu.edu.
ly) yielded poorly crystalline samples contaminated with
564
0022-4596/00 $35.00
Copyright ( 2000 by Academic Press
All rights of reproduction in any form reserved.

¸n VO Se (¸n"Nd, Sm, Gd)
565
ꢅ
ꢂ ꢇ
¸n Se of the U S structure type (10) and with ¸n OSe of
ꢁ ꢄ
the Dy OS structure type (11), as determined from powder
X-ray diagrams.
TABLE 1
X-Ray Crystallographic Details
ꢁ
ꢄ
ꢁ
ꢁ
ꢁ
ꢁ
Nd VO Se
Sm VO Se
Improved yields of about 50% of crystalline ¸n VO Se
ꢅ
ꢂ
ꢇ
ꢅ
ꢂ ꢇ
ꢅ
ꢂ ꢇ
(¸n"Nd, Sm, Gd) were obtained from the reaction of a
Crystal symmetry
Space group
a (A)
b (A)
c (A)
< (Aꢄ)
¹ (K)
Z
Orthorhombic
mixture of 0.8 mmol of ¸n, 0.4 mmol of ¸n O , 0.4 mmol of
Pbam
ꢁ ꢄ
V, and 2.4 mmol of Se, together with 0.4 to 0.8 mmol Sb to
14.3419(9)
15.5528(10)
3.9948(3)
891.1(1)
153
14.200(2)
15.451(2)
3.9511(6)
866.9(2)
153
2
6.98
406.1
0.206/0.729
assist the crystallization. The reagents were loaded into
\ꢂ
fused-silica tubes, sealed under vacuum of 10 Torr, heated
to 1223 K over a 48 h period, maintained there for 96 h,
cooled to 923 K at 2.5 K/h, and then the furnace was turned
o!. The "nal products appeared as colored needle-like crys-
tals on the surface of unreacted materials on the walls of the
tube.
2
o
(g cm\ꢄ)
6.55
368.3
#!ꢀ
k (cm\ꢀ)
Min and max transmission
factors
0.060/0.468
Crystal color and habit
Crystal size (mm)
No. measured re#ections
Plum needle
0.304;0.026;0.022 0.390;0.012;0.008
Dark red needle
Energy-Dispersive X-Ray (EDX) Analysis
7736
0.0451
1248
0.0267
0.0618
5362
0.0309
1200
0.0306
0.0630
R
EDX analyses were carried out on three di!erent single
crystals from each preparation with the use of a 3500N
Hitachi SEM. The presence of O was detected, but reason-
able semi-quantitative analysis for this element could not
be obtained. EDX results on the other elements gave the
average atomic ratios: Nd(45(2)), V(5(1)), Se(50(2)); Sm(44(2)),
V(6(1)), Se(50(2)), Gd(44.5(20)), V(5(1)), Se(50.5(15)) which
can be compared with the calculated values for a composi-
tion ¸n VO Se , ¸n(43.7)V(6.3)Se(50) (¸n"Nd, Sm, Gd).
*ꢁꢂ
No. unique re#ections
R(F)!
Rw(Fꢁ)@
ꢃ
?R(F)"&""F "!"F ""/R"F ",
ꢃ
#
#
@Rw(Fꢁ)"[Rw(Fꢁ!Fꢁ)ꢁ/RwFꢂ]ꢀꢈꢁ, where w\ꢀ"pꢁ(Fꢁ)#(0.04Fꢁ)ꢁ
ꢃ
ꢃ
#
ꢃ
ꢃ
ꢃ
for Fꢁ50 and w\ꢀ"pꢁ(Fꢁ) for Fꢁ(0.
ꢃ
ꢃ
ꢃ
ꢅ
ꢂ ꢇ
are presented in Table 1. Atomic coordinates and equivalent
atomic displacement parameters, with their standard devi-
ations, are given in Tables 2 and 3. Selected bonds distances
Crystal Structure Analyses
X-ray di!raction data were collected on a Bruker Smart for both compounds are given in Table 4.
1000 CCD di!ractometer at 153 K with the use of mono-
From X-ray di!raction powder patterns, collected on a
chromatized MoKa radiation (j"0.71073 A). The di!rac- Rigaku di!ractometer equipped with monochromatized
ted intensities generated by a scan of 0.33 in u were recorded CuKa radiation, Gd VO Se was found to be isostructural
ꢀ
ꢅ
ꢂ ꢇ
ꢅ
on 1878 and 1271 frames covering more than a hemisphere with Nd VO Se and Sm VO Se . Accurate lattice con-
ꢅ
ꢂ
ꢇ
ꢂ ꢇ
of the Ewald sphere for Nd VO Se and Sm VO Se , stants of a"14.075(8) A, b"15.424(6) A, c"3.903(1) A
ꢅ
ꢂ
ꢇ
ꢅ
ꢂ ꢇ
respectively. The exposure times were 25 s/frame for
Sm VO Se and 15 s/frame for Nd VO Se . For both com-
ꢅ
ꢂ
ꢇ
ꢅ
ꢂ ꢇ
TABLE 2
pounds, cell re"nement and data reduction were carried out
with the use of the program SAINT#(12) and a face-
indexed absorption correction was made with the use of
the program XPREP (12). Then the program SADABS (12)
was employed to make incident beam and decay correc-
tions.
Atomic Coordinates and Equivalent Isotropic Displacement
Parameters for Nd7VO4Se8
Wycko!
position
Atom
x
y
z
;
) (Aꢁ)?
%ꢄ
The crystal structures were solved in the centrosymmetric Nd(1)
4h
4h
4g
2c
4h
4h
4g
4g
2a
4h
4g
0.00602(3)
0.21991(3)
0.21022(3)
0
0.35456(5)
0.38152(5)
0.07038(5)
0.34458(5)
0
0.18989(2)
0.33653(2)
0.11717(2)
0.5
0.02889(4)
0.46902(4)
0.32776(4)
0.26479(4)
0
0.5
0.5
0
0.0063(1)
0.0071(1)
0.0066(1)
0.0084(2)
0.0085(2)
0.0070(2)
0.0079(2)
0.0073(2)
0.0066(3)
0.008(1)
Nd(2)
space group Pbam of the orthorhombic system. The posi-
tions of ¸n, Se, and V were located by direct methods with
the program SHELXS of the SHELXTL-PC suite of pro-
Nd(3)
Nd(4)
Se(1)
Se(2)
0
0.5
0.5
0
0
0
grams (13) and the positions of the O atoms were located
from successive di!erence electron density syntheses. Se(3)
Se(4)
V(1)
O(1)
O(2)
Atomic positions were then standardized as recommended
(14). The structures were re"ned by full-matrix least-squares
techniques with the program SHELXL of the SHELXTL-
PC suite of programs (13). Final re"nements included ani-
0.1726(4)
0.0434(4)
0.1884(3)
0.1178(3)
0.5
0
0.007(1)
sotropic displacement parameters. Crystallographic details
?; is de"ned as one third of the trace of the orthogonalized ; tensor.
%ꢄ
GH

566
TOUGAIT AND IBERS
TABLE 3
the present compounds the four independent ¸n atoms per
asymmetric unit are found in three di!erent coordination
polyhedra: ¸n(1) and ¸n(3) are in bicapped trigonal prisms
(¸nO Se ) as shown in Fig. 1a; ¸n(2) is in a 7-octahedron
Atomic Coordinates and Equivalent Isotropic Displacement
Parameters for Sm7VO4Se8
ꢄ
ꢃ
Wycko!
position
(¸nOSe ) as shown in Fig. 1b; ¸n(4) is in an octahedron
ꢆ
Atom
x
y
z
;
(Aꢁ)
%ꢄ
(¸nSe ) as shown in Fig. 1c. Such octahedral ¸nSe moieties
ꢆ
ꢆ
have been found in the ternary selenides Ba¸n Se
Sm(1)
Sm(2)
Sm(3)
Sm(4)
Se(1)
Se(2)
Se(3)
Se(4)
V(1)
4h
4h
4g
2c
4h
4h
4g
4g
2a
4h
4g
0.00661(3)
0.21969(3)
0.21038(3)
0
0.19011(3)
0.33605(3)
0.11778(3)
0.5
0.5
0.5
0
0.0067(1)
0.0077(1)
0.0072(1)
0.0092(2)
0.0092(2)
0.0076(2)
0.0083(2)
0.0077(2)
0.0064(4)
0.008(1)
ꢁ
ꢂ
(¸n"Nd, Sm, Gd) crystallizing with the CaFe O structure
ꢁ ꢂ
type (16) and in A¸nSe compounds (A"alkali metal)
ꢁ
0
crystallizing with the a-NaFeO structure type (17). In the
ꢁ
0.35454(7)
0.38045(6)
0.06986(7)
0.34482(7)
0
0.02887(6)
0.46812(5)
0.32837(5)
0.26442(6)
0
0.5
0.5
0
0
0
present structure the coordination geometry of the unique
V atom per asymmetric unit is also octahedral, with four Se
atoms forming the pseudo equatorial plane and two
O atoms in trans positions.
The main building units of the structure are motifs de-
rived from trigonal prisms and octahedra. The heights of
these moieties correspond to the length of the c-parameter,
and thus interconnection in the [001] direction occurs by
O(1)
O(2)
0.1731(5)
0.0448(4)
0.1887(4)
0.1184(4)
0.5
0
0.006(1)
were obtained at 153 K from a single crystal with the use of the face sharing of trigonal prisms and Se}Se edge sharing
the Bruker di!ractometer.
of octahedra. A projection on the a}b plane of the three-
dimensional structure of Sm VO Se is displayed in Fig. 2.
ꢅ
ꢂ ꢇ
The structure can be viewed as a succession of alternating
slabs along the b-axis of single slabs of octahedra centered
Magnetic Measurements
Magnetic measurements were carried out with a SQUID by V(1) and Sm(4) and slabs of joined polyhedra centered by
magnetometer (MPMS5, Quantum Design). The sample, Sm(1), Sm(2), and Sm(3). Within the Sm layers, the three
7.8 mg of selected single crystals of Gd VO Se ground to di!erent polyhedra pack by edge sharing and face sharing.
ꢅ
ꢂ ꢇ
a "ne powder, was loaded in a gelatin capsule. Zero-"eld Along the b-direction, they are separated by single slabs
cooled measurements were performed with a 5 kG applied of octahedra. Within this second slab, the two di!erent
"eld in the temperature range 5}300 K. All data were cor- species, namely Sm(4)Se and VO Se , are bridged by
ꢆ
ꢁ ꢂ
rected for electron core diamagnetism (15).
Sm(1)O Se and Sm(3)O Se trigonal prisms, which also
ꢄ
ꢃ
ꢄ ꢃ
bring about by edge sharing the interconnection between
the adjacent slabs.
RESULTS AND DISCUSSION
The three-dimensional structure of ¸n VO Se
ꢅ
ꢂ ꢇ
The new compounds ¸n VO Se (¸n"Nd, Sm, Gd) are (¸n"Nd, Sm, Gd) results in the following coordination
ꢅ
ꢂ ꢇ
isostructural and crystallize in a new structure type. These geometries about O and Se. Atoms O(1) and O(2) are
phases are perhaps most readily obtained for the intermedi- tetrahedrally coordinated: O(1) is surrounded by four ¸n
ꢄ>
ate ¸n cations as attempts to prepare the Ce analogue atoms, whereas O(2) is surrounded by three ¸n atoms and
a!orded Ce V O Se , which is isostructural with the series one V atom; atoms Se(1), Se(3), and Se(4) are surrounded by
ꢃ ꢄ ꢅ ꢆ
ꢃ ꢄ ꢅ ꢆ
of oxysul"des ¸n V O S (¸n"La, Ce, Pr, Nd) (3, 4). In "ve ¸n atoms in a square pyramid; atom Se(2) adopts an
TABLE 4
Interatomic Distances (A) for Ln7VO4Se8 (Ln ؍ Nd, Sm)
¸n"Nd
¸n"Sm
¸n"Nd
¸n"Sm
¸n(1)
¸n(1)
¸n(1)
¸n(1)
¸n(1)
¸n(2)
¸n(2)
¸n(2)
¸n(2)
¸n(2)
O(2);2
O(1)
Se(2)
Se(3);2
Se(4);2
O(1)
Se(4);2
Se(3);2
Se(2)
2.352(2)
2.389(5)
2.329(3)
2.364(7)
3.031(1)
3.0452(8)
3.1104(9)
2.371(6)
2.8784(8)
2.9058(8)
3.062(1)
3.160(1)
¸n(3)
¸n(3)
¸n(3)
¸n(3)
¸n(3)
¸n(4)
¸n(4)
O(1);2
O(2)
Se(4)
Se(1);2
Se(2);2
Se(3);2
Se(1);4
2.347(3)
2.392(5)
2.320(3)
2.351(6)
2.963(1)
3.1592(9)
3.3036(8)
2.8314(9)
2.8928(8)
3.0491(8)
3.0724(6)
3.1380(6)
2.401(5)
2.9037(6)
2.9337(6)
3.1014(8)
3.1767(8)
2.9974(8)
3.1876(6)
3.3211(6)
2.8627(7)
2.9227(5)
V(1)
V(1)
O(2);2
Se(2);4
1.936(5)
2.6663(5)
1.937(6)
2.6510(7)
Se(1)

¸n VO Se (¸n"Nd, Sm, Gd)
567
ꢅ
ꢂ ꢇ
FIG. 2. View of the unit cell of Sm VO Se along the c axis.
ꢅ
ꢂ ꢇ
structure of U ScS comprises layers of octahedra centered
ꢄ
ꢆ
ꢄ>
by Sc cations and layers of trigonal prisms centered by ¸n
cations that stack successively along a crystallographic axis
of an orthorhombic unit-cell. The obvious di!erences be-
tween the U ScS and ¸n VO Se structures are in the
ꢄ
ꢆ
ꢅ
ꢂ ꢇ
substitution of two S or Se atoms by two O atoms and the
substitution of one 3d cation within the layer of octahedra
by a ¸n cation. It is useful in this regard to think of
¸n VO Se as ¸n [¸nV]Q . There are also structural dif-
ꢅ
ꢂ
ꢇ
ꢆ
ꢀꢁ
ferences in the packing mode within the ¸n slab. In the
U ScS type structure, the three di!erent polyhedra
ꢄ
ꢆ
centered by f elements lie in the same a}b plane and pack by
sharing triangular faces, whereas in the ¸n VO Se struc-
ꢅ
ꢂ ꢇ
FIG. 1. View of the environment of (a) ¸n(1), (b) ¸n(2), and (c) ¸n(4) in ture type, one polyhedron, namely ¸n(3)O Se , is shifted by
ꢄ
ꢃ
¸n VO Se . Displacement ellipsoids are drawn at the 60% probability
b/2, increasing the close-packing among the three
ꢅ
ꢂ ꢇ
level.
nonequivalent polyhedra. Consequently, the interatomic
irregular octahedral geometry constructed from four ¸n
atoms and two V atoms.
The charge balance is achieved in the phases ¸n VO Se
ꢅ
ꢂ ꢇ
(¸n"Nd, Sm, Gd) with the metals in their expected
trivalent oxidation states. The V}O(2) bonds (see Table 4)
'''
are 0.06 A shorter than an expected V }O contact of about
2.0 A (18, 19). On the other hand, the V}Se(4) bonds are
approximately 0.08 A longer than the average values re-
'''
ported for the V compounds TlV Se (20) and AgVP Se
ꢃ
ꢇ
ꢁ ꢆ
(21). Such di!erences may result from the oxyphilic nature
'''
of V .
The crystal structure of these new compounds is closely
related to that of U ScS (9), which is also commonly
ꢄ
ꢆ
adopted by rare-earth and trivalent cations, for example,
Sm InS (22), ¸n InSe (¸n"Pr, Sm, Gd) (23, 24), and
FIG. 3. s\ꢀ versus ¹ for Gd VO Se . The solid line is the Curie}
ꢅ
ꢂ ꢇ
ꢄ
ꢆ
ꢄ
ꢆ
Weiss "t.
¸n CrSe (¸n"Sm, Gd, Tb, Dy, Y) (24, 25). The crystal
ꢄ
ꢆ

568
TOUGAIT AND IBERS
distances between ¸n cations shrink signi"cantly; for
example, the shortest Sm}Sm contact decreases from
3.929(1) A in Sm CrSe to 3.678(1) A in Sm VO Se .
7. G. Guo, Y. Wang, J. Chen, H. Zhuang, J. Huang, and Q. Zhang, Acta
Crystallogr., Sect. C: Cryst. Struct. Commun. 51, 1964}1966 (1995).
8. A. Meerschaut, C. Boyer, A. Lafond, L. Cario, and J. Rouxel, J. Solid
State Chem. 137, 122}126 (1998).
9. N. Rodier and V. Tien, Acta Crystallogr., Sect. B: Struct. Crystallogr.
Cryst. Chem. 32, 2705}2707 (1976).
ꢄ
ꢆ
ꢅ
ꢂ ꢇ
Magnetic susceptibility measurements as a function of
temperature (Fig. 3) indicate that Gd VO Se is paramag-
ꢅ
ꢂ ꢇ
netic down to 5 K. The inverse susceptibility obeys the 10. J. Flahaut, in &&Handbook on the Physics and Chemistry of Rare
Earths'' (K. A. Gschneidner Jr. and L. R. Eyring, Eds.), Vol. 4, pp. 1}88,
North-Holland, New York, 1979.
\ꢀ
Curie}Weiss law s "(¹!h)/C. The "t of the data in the
temperature range 50}300 K results in a Curie constant
11. T. Schleid, Z. Anorg. Allg. Chem. 602, 39}47 (1991).
12. SMART Version 5.054 Data Collection and SAINT-Plus Version
6.02A Data Processing Software for the SMART System, Bruker
Analytical X-Ray Instruments, Inc., Madison, WI, 2000.
13. G. M. Sheldrick, SHELXTL DOS/Windows/NT Version 5.10, Bruker
Analytical X-Ray Instruments, Inc., Madison, WI, 1997.
14. L. M. Gelato and E. Parthe, J. Appl. Crystallogr. 20, 139}143 (1987).
15. L. N. Mulay and E. A. Boudreaux, Eds., &&Theory and Applications of
Molecular Diamagnetism,'' Wiley-Interscience, New York, 1976.
16. J. Dugue, D. Carre, and M. Guittard, Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem. 34, 3564}3568 (1978).
\ꢀ
C"52.3(2) emu K mol
\ꢀ
and a paramagnetic temper-
ature h"!14.3(7) K. The value of C agrees with that of
\ꢀ
\ꢀ
ꢄ>
58.0 emu K mol calculated from 7 C(Gd )#C(spin-
ꢄ>
only V ) (26).
ACKNOWLEDGMENTS
This research was supported by the U.S. National Science Foundation
under Grant DMR 97- 09351. This work made use of facilities supported
by the MRSEC program of the National Science Foundation (DMR96-
32472) at the Materials Research Center of Northwestern University.
17. W. Bronger, W. Bruggemann, M. von der Ahe, and D. Schmitz, J.
Alloys Compd. 200, 205}210 (1993).
18. W. R. Robinson, Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst.
Chem. 31, 1153}1160 (1975).
19. P. Bordet, C. Chaillout, M. Marezio, Q. Huang, A. Santoro, S.-W.
Cheong, H. Takagi, C. S. Oglesby, and B. Batlogg, J. Solid State Chem.
106, 253}270 (1993).
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