A R T I C L E S
Hyett et al.
for the oxysulfides was required to avoid the formation of elemental
copper by the reduction of Cu+ ions in the chalcogenide layers which
occurred if too much NaH was used or if the reaction temperature was
higher than 180 °C. However, the reduced selenide was made in a single
data were used for analysis of the magnetic structures; form factors
for magnetic scattering were taken from the International Tables for
Crystallography.26
Electron Diffraction Measurements. Measurements were carried
reaction step: 4 g of Sr
0.0226 g) of NaH at 180 °C for 5 days and washed as described above.
When the reductions were attempted using a 5% H /95% N mixture
at 200 °C, decomposition occurred with the formation of large amounts
of elemental copper. Attempts to fluorinate the reduced materials were
also unsuccessful as the reduced product was extremely reactive toward
4
Mn
3
O
7.5Cu
2
Se
2
was reacted with 0.2 mol equiv
out on a Phillips CM20 transmission electron microscope with a LaB
filament.
6
(
2
2
Magnetic Susceptibility Measurements. Measurements were car-
ried out using Quantum Design MPMS-5 or MPMS-XL SQUID
magnetometers on approximately 50 mg of the same materials as were
measured using neutron diffraction. Samples were contained in gelatin
capsules, which in the case of the air-sensitive reduced materials were
sealed with superglue immediately on removal from the glove box.
The magnetic moments of the samples were measured as a function of
temperature on warming in fields of 10 mT and 100 mT after cooling
in zero field (zero-field cooled: ZFC) and then in the measuring field
(field-cooled: FC). Magnetization isotherms were measured in the range
(5 T with cooling in a 5 T field.
Electrical Resistivity Measurements. Measurements were made on
sintered pieces of as-made oxysulfide samples between 100 and 300
K using a homemade DC four-probe instrument. These measurements
revealed the as-made materials to be semiconducting (Figure S1),
suggesting they should be classified as Mott-Hubbard-type insulators.
No measurements were made on reduced or fluorinated materials as
these could not be sintered without decomposition.
XeF
between XeF
containing substantial amounts of SrF
2
(reaction occurred spontaneously and vigorously on contact
and the reduced powder), and inhomogeneous products
were obtained.
2
2
Chemical Analysis. EDX analysis using a JEOL JSM-840A
scanning electron microscope equipped with an Oxford Instruments
ISIS300 energy dispersive X-ray analysis system was carried out on
crystals of the oxysulfide to determine the approximate elemental
content. Attempts to measure the Mn oxidation state using iodometric
2
+
-
titration were hampered by the formation of Cu which oxidizes I .
Oxidative thermogravimetric analysis (TGA) carried out in air using a
Rheometric Scientific STA 1500 instrument was hampered by the air-
sensitivity of the reduced materials.
Powder X-ray Diffraction (PXRD). Measurements were made on
Panalytical X’pert Pro and Siemens D5000 diffractometers using Cu
1
KR radiation with the sample mounted on a glass slide. The
air-sensitive reduced materials were contained within a homemade
Results and Discussion
sealed sample holder.
Compositions and Crystal Structures. Crystal Structure
Single-Crystal X-ray Diffraction (SXRD). Intensity data for a black
and Mn-Deficiency in Sr Mn3-γO7.5-ꢀCu S . The crystal
4
2 2
3
platelet single crystal (0.06 × 0.03 × 0.01 mm ) of Sr
4
Mn2.94(1)-
structures of Sr4Mn3O7.5Cu2S2 and Sr4Mn3O7.5Cu2Se2 have been
Cu
2
O S
7.42(5) 2
were collected on a Nonius Kappa CCD diffractometer
8
reported, derived from powder X-ray diffraction data. Exami-
using graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) at
room temperature. The frames were recorded using ∆ω ) 1.20° rotation
scans with an X-ray exposure time of 100 s per frame. Reflection
indexing, Lorentz-polarization correction, peak integration, and back-
ground determination were performed using the program DENZO20 of
nation of the single-crystal diffraction data for crystals of Sr4-
Mn3O7.5Cu2S2 did not show any systematic absences other than
those corresponding to a body-centered tetragonal lattice sug-
gesting space groups I4, I 4h , I4/m, I422, I4mm, I4/mmm, or I 4h m2.
The lattice parameters of 3.9046(1) and 34.468(1) Å together
with the Sr/Mn/Cu/S ratio of 2:1.5:1:1.1 (with estimated standard
deviations of 10% on these values) obtained from EDX
measurements suggested that the material was isostructural with
the Kappa CCD software package. An absorption correction, using a
2
1
Gaussian integration method based on the crystal shape, was applied
to the reflection intensities. Structure solution using Direct Methods
22
was performed using SIR97, and all structure refinements were carried
2
3
8
out using the SHELXL97 structural refinement program.
the reported Sr Mn Cu O S . Structure solution in I4/mmm
4
3
2
7.5 2
Powder Neutron Diffraction (PND). Two to four gram samples
contained in 8-mm diameter vanadium cans (sealed in the glove box
with indium gaskets in the case of the reduced materials) were measured
at temperatures between 2 and 298 K on the diffractometer POLARIS
at the ISIS Facility, Rutherford Appleton Laboratory, UK and on the
instrument D2B at the Institute Laue-Langevin (ILL), Grenoble. On
POLARIS diffraction patterns were measured by the time-of-flight
method in the d-spacing range 0.5 < d < 8 Å using detector banks at
mean scattering angles 2θ of 35°, 90°, and 145°; typically, measurement
was carried out such that the product of the sample mass, measuring
time, and proton current at the production target was approximately
by Direct Methods confirmed this. Initial refinement was
performed using isotropic atomic displacement parameters
2
2
(ADP) and led to R-factors R1(F ) ) 0.0603 and wR2(F ) )
0
.1217. The isotropic ADP of O2 located in the central MnO2
layer at (1/2 0 0) was a factor of 8 larger than those of the
other oxygen atoms. Consequently the fractional site occupancy
of the O2 site was refined, converging to 0.71(1), consistent
8
with the earlier report. Refinement of the occupancy factors
of the other sites showed that the Mn2 site, also located in the
central MnO2 layer, was also slightly deficient. Refinement with
anisotropic ADPs for all atoms produced a very large U22 (0.17
1
000 µA h g. All measurements used for structural comparisons were
made on POLARIS. On D2B neutrons with wavelengths of 1.59 or
.39 Å were selected using a 28-crystal Ge(335) monochromator and
2
Å ) for O2 (1/2 0 0), and a marginally superior refinement
2
against SXRD data was achieved with this atom located on a
were detected over the 2θ range 0-160° in steps of 0.05° for 5 s per
point. Low-temperature data were collected down to 5 K with the
samples in a closed-cycle helium refrigerator. Rietveld refinements were
split site (1/2 (y 0) with y ) 0.070(8) and modeled as a pair of
2
fairly isotropic and overlapping ellipsoids (U22 of 0.08(3) Å )
with their centers displaced by 0.3 Å from the ideal position. A
similar model has been required in the closely related materials
2
4
25
carried out using the GSAS suite via the EXPGUI interface. D2B
2
7,28
29
Sr4Mn3O7.56Cl2,
Sr4Co3O7.5Cl2, and Pb4Fe3O8X (X ) Cl,
(
20) Otwinowski, Z.; Minor, W. DENZO-SMN. In Macromolecular Crystal-
lography, Part A; Carter, C. W., Jr., Sweets, R. M., Eds.; Methods of
Enzymology, Vol. 276; Academic Press: New York, 1997.
(24) Larson, A. C.; Von Dreele, R. B. General Structure Analysis System (GSAS);
Los Alamos National Laboratory Report LAUR 86-748; Los Alamos
ccp/ccp14/ftp-mirror/gsas/public/gsas/manual/GSASManual.pdf.
(25) Toby, B. H. J. Appl. Crystallogr. 2001, 34, 210.
(26) Wilson, A. J. C., Ed. International Tables for Crystallography; Kluwer
Academic Publishers: Dordrecht, The Netherlands, 1995; Vol. C.
(
21) Busing, W. R.; Levy, H. A. Acta Crystallogr. 1957, 10, 180.
22) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115.
(
(23) Sheldrick, G. M. SHELX97: Programs for Crystal Structure Analysis
(Release 97-2); University of G o¨ ttingen: Germany, 1997.
11194 J. AM. CHEM. SOC.
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VOL. 129, NO. 36, 2007