Crystal Growth & Design
Article
Single-Crystal X-ray Diffraction. Black single crystals of ζ-TeI4
were selected and mounted on the tip of a glass fiber for an intensity
measurement using a single-crystal X-ray diffractometer (STOE IPDS
2-T, Darmstadt, Germany), equipped with (graphite) monochromatic
Mo Kα radiation (λ = 0.71073 Å) at room temperature. Raw data
intensities were corrected for Lorentz factors and polarization by the
IPDS software. Absorption effects were corrected by the X-Red/X-
Shape program of the STOE software. Crystal structure solutions
were obtained by direct methods (SHELXS), followed by full-matrix
least-squares structure refinements with SHELXL-2017.13 Details of
Electron Microscopy. Scanning electron microscopy (SEM) was
performed on a Hitachi SU8030 scanning electron microscope at a
maximum acceleration voltage of 30 kV and a free working distance of
15.0 mm. EDX investigations were performed with an acceleration
voltage of 30 kV.
The results of DFT calculations reveal the structure of δ-TeI4
to represent the thermodynamic ground state, and all other
polymorphs of TeI4 are truly metastable and require kinetic
control for synthesis.
The formation of ζ-TeI4 is enabled by the presence of an
impurity derived from W, Mo, or Sn phases which did not turn
out to be a significant constituent in the structure. δ-TeI4 can
be transformed into ζ-TeI4 in the presence of small amounts of
one of the aforementioned external phases via gas-phase
reactions at approximately 200 °C. The temperature depend-
ence of partial pressures of relevant gas-phase species such as
20
TeI4, TeI2, and I2 and the influence of a secondary phase do
not provide a uniform picture of the crystallization of TeI4 to
understand the formation of ζ-TeI4.
ICP-OES. After dissolution of TeI4 in 2 wt % of NaOH/H2O2 the
W:Te:I ratio was determined by ICP-OES (iCAP 7400 Thermo
Scientific).
Electron Microprobe Analysis. Electron microprobe analysis
was performed on a JEOL 8900 Superprobe spectrometer using an
acceleration voltage of 20 kV, a probe current of 10−9 A, and a beam
diameter of 10−6 m. The samples were coated with carbon prior to the
measurements.
Density Functional Theory. DFT calculations were carried out
using the Abinit software package with the projector-augmented wave
(PAW) method.14,15 Convergence studies (to 1% in pressure) were
used to choose a 3 × 2 × 2 Monkhorst−Pack grid16 of k points, an 18
Ha coarse grid, and 108 fine-grid plane-wave basis set energy cutoffs.
PAW data sets were used as received from the Abinit library.14,17,18
Example input files are available as part of the Supporting
EXPERIMENTAL SECTION
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Synthesis. Manipulations of starting materials, such as charging
the fused silica ampules with starting materials, were performed in an
argon-filled glovebox (MBraun, Labmaster 130, O2 <1 ppm, H2O <1
ppm).
WTe2. WTe2 was prepared from the elements W (ABCR GmbH,
99.95%) and Te (Evochem, 99.999%) and iodine (sublimed, 99.99
%), vacuum-sealed into a silica tube in stoichiometric proportions and
heated at 800 °C for 24 h.
ζ-TeI4 (bulk). A mixture of 100 mg WTe2 (0.23 mmol) and 300 mg
of I2 (2.4 mmol), fused into an evacuated silica tube, was heated in a
̈
Simon-Muller furnace at a rate of 2.0 K/min to 520 °C and kept at
this temperature for 48 h (we note that the amount of iodine was
erroneously given as 0.683 mmol instead of 6.83 mmol in ref 2).
Afterward, the ampule was cooled to room temperature at a rate of 0.5
K/min. ζ-TeI4 was obtained at the cooler part of the ampule as a
black crystalline powder, in addition to crystals of (TeI3)2[W6I14].10
δ-TeI4. This form was synthesized from stoichiometric proportions
of Te powder and I2 under conditions identical with those described
for ζ-TeI4.
ζ-TeI4 (Single Crystals). Single crystals of ζ-TeI4 were synthesized
by heating 100 mg of WTe2 (0.23 mmol) and 300 mg of I2 (2.4
mmol) at a rate of 2.0 K/min up to 360 °C in an evacuated silica tube.
The ampule was kept at this temperature for 8 h and then cooled to
room temperature at a rate of 2.0 K/min. The single crystals
(approximate size 0.2 mm) were found in the middle part of the
ampule.
Alternative Synthesis Routes for ζ-TeI4. With W(CO)6. ζ-TeI4
was obtained by reacting 50.00 mg of tellurium (0.4 mmol) and
198.91 mg of iodine (1.6 mmol) with an addition of 6.89 mg of
W(CO)6 (0.02 mmol) fused into an evacuated silica tube. The
ampule with the mixture was heated at a rate of 2.0 K/min to 620 °C,
kept at this temperature for 48 h, and then cooled to room
temperature at a rate of 0.5 K/min. ζ-TeI4 was obtained as a black
powder at the cooler part of the ampule. Similar results were obtained
in the presence of Sn or Mo.
With WTe2. ζ-TeI4 was obtained by reacting 50.00 mg of tellurium
(0.39 mmol) and 198.91 mg of I2 (0.78 mmol) with an addition of
8.60 mg WTe2 (0.02 mmol) fused into an evacuated silica tube. The
ampule with the mixture was heated at a rate of 2.0 K/min to 620 °C,
kept at this temperature for 48 h, and then cooled to room
temperature at a rate of 0.5 K/min. TeI4 was obtained as a black
powder at the cooler part of the ampule.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
Comparison of the results of single-crystal refinements
for WI4 and ζ-TeI4, comparison of the atomic
coordinates of WI4 with those of ζ-TeI4, results of the
electron microprobe measurements, one layer of the
crystal structure of ζ-TeI4 highlighting the octahedral
voids (some are highlighted as polyhedra) in the
structure of Te4□4I16 (PDF)
Accession Codes
CCDC 1940965 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Author
Hans-Ju
̈
rgen Meyer − Section for Solid State and Theoretical
Inorganic Chemistry, Institute of Inorganic Chemistry, Eberhard
Powder X-ray Diffraction Studies. All reaction products were
investigated by powder X-ray diffraction (PXRD) using a StadiP
diffractometer (Stoe, Darmstadt) with Ge-monochromated Cu Kα1
radiation and a Mythen1 Detector. A black crystalline powder of ζ-
TeI4 was selected and indexed as triclinic, isotypic with WI4, and the
lattice parameters were refined using the LeBail fit of the Fullprof
Suite7 with the lattice parameters of WI4 as starting values. The
refined lattice parameters in comparison with the literature values are
given in Table 1.
̈
̈
̈
Karls Universitat Tubingen, D-72076 Tubingen, Germany;
Authors
Philipp Schneiderhan − Section for Solid State and Theoretical
Inorganic Chemistry, Institute of Inorganic Chemistry, Eberhard
̈
̈
̈
Karls Universitat Tubingen, D-72076 Tubingen, Germany
D
Cryst. Growth Des. XXXX, XXX, XXX−XXX
Schneiderhan, Philipp
