In Search of Aluminum Hexathiohypodiphosphate
Aesar 99.9%) and a 10% excess of P (Alpha Aesar 98.9%) via a
conventional solid-state reaction. The mixture was vacuum-sealed in a
silica glass tube and heated up (50 K·h–1) to 1073 K, kept at that tem-
perature for 15 h, followed by cooling down to room temperature by
switching off the furnace. AlPS4 was obtained in a second reaction,
again carried out in a vacuum-sealed silica glass tube from the AlP
precursor and a 10% excess of S (Alfa Aesar 99.5%). Depending on
the reaction temperature and time, mixtures of two different crystal
morphologies were obtained. While a good yield was obtained after
1–2 d, well-shaped crystals, especially of ht-AlPS4 were only obtained
ulated one. For the oblique zone axes presented below, ad-
ditional reflections are visible that are not observed in the sim-
ulation (zero-order Laue zone, ZOLZ) but again very good
agreement is obtained when the first-order Laue zone (FOLZ)
reflections are included into the simulations. The appearance
of these reflections may be attributed to the sample mor-
phology, that is, thin, partially cleaved and curved lamellae
(see BF TEM image in Figure 3A). This effectively leads to a
rod-like smear-out of the reflections which then cut through
the Ewald sphere. The FOLZ reflections turned out to be very after long annealing times.
useful to corroborate our structure model elaborated above.
lt-AlPS4: Phase-pure tetragonal lt-AlPS4 was obtained when the reac-
While the strong reflections from the zero order Laue zone are
very similar for the alternative models in Cm or C2/m, the
reflections from the first order Laue zone are very distinct for
each model and again infer space group C2 to be the most
likely one. Based on these considerations, we propose this
model which can, however, only be considered as preliminary
tion was carried out at lower temperatures and with long annealing
times: the mixture of AlP and S was heated to 923 K (50 K·h–1), held
at that temperature for 30 d and then cooled down to room temperature
(50 K·h–1). Well-shaped colorless transparent platelets of tetragonal lt-
AlPS4 were formed at the cold end of the silica tube in the natural
gradient of the tube furnace. The crystals are sensitive against moisture
and qualitative given the low crystal quality. Nevertheless, the and have to be stored and handled under inert conditions.
identity of Al4(P2S6)3 along with the presence of hexathiohy-
ht-AlPS4: Phase-pure orthorhombic ht-AlPS4 was obtained when the
podiphosphate building units, and the structural relation to the
reaction was carried out at higher temperatures: the mixture of AlP
FePS3 structure type are confirmed.
and S was heated to 1023 K (50 K·h–1), held at that temperature for
30 d and then cooled down to room temperature (50 K·h–1). Long col-
orless transparent needle-shaped crystals were formed in the natural
gradient of the furnace. The needle-shaped crystallites were very frag-
Conclusions
ile and split easily into thinner fibers under mechanical stress (cf. Fig-
ure 1A, right). ht-AlPS4 is much more sensitive against moisture than
lt-AlPS4.
In this contribution we describe and revisit the synthesis and
structural characterization of three thiophosphates – two modi-
fications of aluminum tetrathioorthophosphate AlPS4, and alu-
minum hexathiohypodiphosphate Al4(P2S6)3, all of which have
a long-standing and partially interwoven history. In an attempt
to synthesize the elusive Al4(P2S6)3 following a procedure
originally described by Friedel,[1] we have obtained the high
temperature modification of AlPS4, which can easily be
quenched to room temperature and crystallizes in the ortho-
rhombic space group I222. The low-temperature modification
of AlPS4, which is the stable modification below 950 K and
was initially reported by Weiss and Schäfer,[6] crystallizes in
Preparation of Al4(P2S6)3: Stoichiometric amounts of Al (Alfa Aesar
99.9%), P (Alpha Aesar 98.9%), and S (Alfa Aesar 99.5%) were first
treated in a high-energy ball mill (Fritsch Premium Line 6) for 6 h at
500 rpm in an argon atmosphere. For the high-pressure synthesis, the
resulting black precursor powder was tightly precompacted in a Au
crucible (Ø 4 mm). While being heated to temperatures 1023 K for 10 h,
a pressure of 5 GPa was applied to the crucible in a Belt-type press.
Intergrown and easily cleavable platelets of Al4(P2S6)3 were obtained
as the only phase. In contrast to AlPS4, Al4(P2S6)3 is fairly stable
towards air and moisture, i.e. decomposition when exposed to air is
observed only after several days. The dissolution process in water takes
several hours. The chemical composition of the crystals as determined
by SEM-EDX was in accordance with the expectations within 1 at%.
¯
the tetragonal space group P42c forming transparent rectangu-
lar platelets. Finally, we find that the hexathiohypodiphosphate
Al4(P2S6)3 is accessible via high-pressure synthesis as platelet-
shaped colorless crystallites, which easily cleave into thinner
lamellae. Due to this fact we only obtained crystallites of low
quality. Nevertheless, a plausible structure model could be de-
rived from single-crystal X-ray diffraction, which is in line
with the TEM and SAED results. Al4(P2S6)3 crystallizes in the
monoclinic space group C2 in a superstructure of the FePS3
structure type with tripled a axis and Al3+ occupying 2/3 of
the Fe2+ sites in an ordered fashion.
X-ray Diffraction: For powder X-ray diffraction, the powders were
sealed in glass capillaries and the diffraction pattern was measured in
Debye-Scherrer geometry using a STOE StadiP diffractometer work-
ing with Ge-monochromated Mo-Kα radiation. Rietveld refinements
were performed with the TOPAS v.4.2 software (Bruker AXS).
For single-crystal X-ray diffraction, crystallites were picked under dry
petroleum and mounted in sealed in glass capillaries. The single-crystal
X-ray diffraction of ht-AlPS4 and Al4(P2S6)3 was performed with a
STOE IPDS II diffractometer working with graphite-monochromated
Mo-Kα radiation. For the integration of the reflection intensities and
the calculation of the reciprocal lattice planes, the STOE X-Area 1.56
software was used. For lt-AlPS4, the single-crystal X-ray diffraction
was carried out using a SMART-APEX CCD X-ray diffractometer
(Bruker AXS) working with graphite-monochromated Mo-Kα radia-
tion. For the integration of the reflection intensities, the SAINT soft-
Experimental Section
Preparation of AlPS4: All preparations and manipulations were car-
ried out in an argon atmosphere. All products were characterized by
powder and single-crystal XRD, and the chemical composition was
confirmed via SEM-EDX analysis.
The direct synthesis from the elements is possible but the crystals show ware (Bruker AXS) was used. The structures were solved with Direct
better quality when AlPS4 is produced from AlP and S as described in Methods and refined by least-squares fitting using the SHELXTL pro-
the literature.[4] Therefore, AlP was prepared from Al-shots (Alfa gram.[7]
Z. Anorg. Allg. Chem. 2014, 2663–2668
© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2667
Kuhn, Alexander
