Important Phase Control of Indium Sulfide Nanomaterials by Choice of Indium(III) Xanthate Precursor and Thermolysis Temperature

Article abstract of DOI:10.1002/ejic.201900007

Four In(III) xanthate complexes, [In(S₂COR)₃] where R = Me, Et, iPr and sBu, respectively, were synthesized, characterized and subsequently used as single source molecular precursors via a solventless thermolysis route to obtain indium sulfide materials. By choice of precursor and reaction temperature crystalline powders of tetragonal In₂S₃, cubic In₂S₃ and cubic In_2.77S₄ were acquired. The phase identification and purity were conducted through examination of the experimental powder X-ray diffraction patterns relative to the simulated patterns for single X-ray crystal diffraction.

Full text of DOI:10.1002/ejic.201900007

A Journal of
Accepted Article
Title: Important phase control of indium sulfide nanomaterials by choice
of indium (III) xanthate precursor and thermolysis temperature
Authors: Siphamandla Cecil Masikane, Paul McNaughter, David Lewis,
Inigo Vitorica-yrezabal, Bryan Doyle, Emanuela Carleschi,
Paul O’Brien, and Neerish Revaprasadu
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201900007
Link to VoR: http://dx.doi.org/10.1002/ejic.201900007

European Journal of Inorganic Chemistry
10.1002/ejic.201900007
FULL PAPER
Important phase control of indium sulfide nanomaterials by
choice of indium (III) xanthate precursor and thermolysis
temperature
[
a]
[b]
[b,c]
[b]
Siphamandla C. Masikane, Paul D. McNaughter, David J. Lewis, Inigo Vitorica-Yrezabal, Bryan
P. Doyle, Emanuela Carleschi, Paul O’Brien, and Neerish Revaprasadu*[a]
[
d]
[d]
[b,c]
Dedicated to the late Prof. Paul O’Brien FRS who untimely passed away during preparation of this paper.
Abstract: Four In(III) xanthate complexes, [In(S
2
COR)
3
] where R =
species.13 The In
α- In , β- In
trigonal crystallographic systems, respectively. The γ-In
has similar 2D structural features to InS. Polymorphism in In
2
S
3
phase exists in three polymorphic forms, i.e.
and γ- In which exhibit cubic, tetragonal and
phase
i
s
Me, Et, Pr and Bu, respectively, were synthesized, characterized and
subsequently used as single source molecular precursors via a
solventless thermolysis route to obtain indium sulfide materials. By
choice of precursor and reaction temperature crystalline powders of
2
S
3
S
2 3
2 3
S
2 3
S
2 3
S
is attributed to vacancies within the structure as a result of
tetragonal In
2
S
3
, cubic In
2
S
3
and cubic In2.77
S
4
were acquired. The
structural defects.14 The β-In
room temperature.15
2
S
3
and γ-In
2
S
3
phases are stable at
phase identification and purity were conducted through examination
of the experimental powder X-ray diffraction patterns relative to the
simulated patterns for single X-ray crystal diffraction.
Fabrication methods to afford β-In S thin films and
2 3
nanoparticles can employ either multiple-source or single-source
molecular precursors (SSPs). Since control over phase is a
common challenge to both routes, the former is usually chosen
due to compatibility with various synthetic approaches such as
chemical bath deposition4,6,16–18 and spray pyrolysis.19–23 However,
Introduction
a variety of In(III) complexes as SSPs for the preparation of β-
The indium-sulfur (In-S) binary metal chalcogenide system is of
interest in the optoelectronics1,2 and catalysis research fields
due to attractive properties such as the variety of crystallographic
phases and band gap of ~2 eV. The notable recent advances
on the specialised applications of indium sulfide include
fabrication of photoanodes for photoelectrochemical water
In
2
S
3
and related nanostructures have been explored.
3,4
Dithiocarbamates, among other classes of SSPs, have largely
contributed towards the literature coverage on indium sulfide
materials mainly due to the flexibility in designing and derivatizing
the ligands using vast possibilities of moieties. Crystallographic
phase and morphology control of indium sulfide synthesized from
the corresponding dithiocarbamate SSPs has been achieved by
careful selection of the ligand (i.e. the nature of the organic
backbone affects the physicochemical properties and thus
decomposition pattern of the SSP) and fabrication method (i.e.
manipulation of reaction parameters assists in lowering energy
5,6
7
8
9
splitting, nanohybrid paper electrodes for Na-ion batteries, as
well as a thorough investigation of charge transport behaviour of
indium sulfide under high pressures.10 These applications have in
common the necessity to utilize indium sulfide in its pure phases.
The most easily accessed and found phases are InS, In
3
S
4
, In
6
S
7
2
and In
2
S
3
. Indium sulfide semiconductors are classified as non-
barriers for nucleation and particle growth processes). For
toxic and have potential as an alternative to the toxic cadmium
sulfide buffer in cadmium gallium indium selenide/sulfide solar
cells.11 More recently in the search for 2D materials beyond
graphene, the InS phase has gained considerable interest,12
particularly in the form of a two atom-thin layered material or two-
dimensional (2D) nanomaterial. However, synthetic chemical
routes rarely produces crystalline InS, and any heating usually
24
sheets,25,26
example, β-In
2
S
3
urchin-like microspheres, β-In S
2 3
27
and InS quantum dots have been prepared from the In(III)-
trisdiethyldithiocarbamate SSP, [In(S
2 2 3
CNEt ) ], through the
hydrothermal, amine-mediated solvent thermolysis, and the
TOPO-mediated
respectively.
solvent
Furthermore,
thermolysis
the organo-In
synthetic
routes,
derivatives,
[
RIn(S
2
CNEt
2
)] where R = dimethyl, diethyl and neopentyl,
and β-In films deposited by the low-
2 3
induces a phase change to the thermodynamically stable In S
produced InS, In
6
S
7
2 3
S
pressure metal organic chemical vapour deposition (LP-MOCVD)
method; different phases are attributed to the nature of ligand and
deposition temperature.28 In another instance, the mixed
[
a]
Department of Chemistry, University of Zululand,
Kwa-Dlangezwa, 3886, South Africa.
E-mail: RevaprasaduN@unizulu.ac.za
School of Chemistry, The University of Manchester,
Oxford Road, Manchester, M13 9PL, UK
School of Materials, The University of Manchester,
Oxford Road, Manchester, M13 9PL, UK.
Department of Physics, University of Johannesburg,
PO Box 524, Auckland Park, 2006, Johannesburg, South Africa
alkydithiocarbamates of the formula [In(S
2 3
CNMeR) ], where R =
thin films by LP-MOCVD.29
[
[
[
b]
c]
d]
n-Butyl and n-Hexyl, produced α-In
2 3
S
An example of organo-In complexed with
a
mixed
n
alkydithiocarbamate ligand, [Et
2 2
In(S CNMe Bu)], gave β-In
2
S
3
13,30
thin films using the standard MOCVD method.
Alkyl
thiolates,3
1–33
thiobenzoates,
34
thiocarbazates,
35
thiobiurets,
36
thiophosphinates37 and thiocarboxylates38,39 are also examples of
x y
SSPs which have been exploited in the fabrication of In S
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Inorganic Chemistry
10.1002/ejic.201900007
FULL PAPER
nanoparticles and thin films displaying different phases and
diverse morphological features.
microelemental and thermogravimetric analyses, the contrary
procedure to the single crystal X-ray analysis. A plausible
explanation for the difference observed between the
Xanthate metal complexes are a class of dithiolates with
breakdown temperatures typically lower than that of metal
dithiocarbamates. Metal xanthate complexes have been explored
to produce thin films and nanoparticles of a variety of metal
chalcogenides at low temperatures ideal for large scale industrial
processes where energy use is a major factor.40–46 By choice of
ligand McNaughter et al.43,44 demonstrated size control of PbS
within melts and when mixed in polystyrene. Variation of xanthate
49
decomposition profiles by Dutta et al. and ours is a slower
-
1
-1
heating rate (5 °C.min ) versus faster heating rate (10 °C.min )
used, respectively. The phenomenon of an inflection point
levelling off into a plateau at slower heating rate is explained in a
55
TGA-themed review by Coats and Redfern.
Thus, this
demonstrates the importance of adjusting the heating rate
especially when an intricate system like indium sulfide is a subject
of study. Our TGA profiles exhibited two plateaus which,
interestingly, become less resolved in the order of complex alkyl
x y
ligand length was also explored in Cu S demonstrating a similar
effect on particle size.42 Various ternary phases have also been
accessed using metal xanthate complexes.47 In contrast, very few
indium xanthate complexes have been prepared and used as
s
i
chain length of Bu<Pr<Et<Me and with
a decrease in
decomposition temperature. The data provided in Table 2 clearly
indicates that TGA might not be a reliable tool to identify/match
the weight percentage of the residue with those of known indium
sulfide compounds. Dutta et al.49 deduced that all the residues
molecular precursors to afford indium sulfide and related
nanocomposites.4
8–50
However, interest has mainly been on thin
films.51,52
In this work, we have prepared a series of In(III) xanthate
complexes, [In(S COR)
] where R = Me, Et, iPr and sBu,
respectively, and evaluated them as potential precursors for In S
y
materials through a solventless pyrolysis method at different
decomposition temperatures.
2 3
match to the anticipated In S . They however did not account for
2
3
the discrepancies in obtained and calculated weight percentages.
Thus, our approach rather explores the appropriate identification
of the materials obtained at selected regions of the TGA curves.
Evaluation of the DTA in Figure S1 and Table 3 also provides
additional information pertaining to the decomposition pathway of
x
the precursors. Single curves observed for [In(S
2 3
COEt) ] (1) and
Results and Discussion
[In(S COMe) ] (2) precursors are typical of a simultaneous
2
3
melting with decomposition. A similar observation was made
during the traditional melting point determination experiments; no
melting and instead a change in colour signifying decomposition
was observed. The simultaneous melting and decomposition was
Amongst the complexes used in this work (Figure 1), two have X-
53
ray crystal structures known in literature, [In(S
2
COEt)
].54 We have obtained the latter as a cyclohexane
2 3
In(S COPr)
3
]
and
i
[
also observed at a larger scale when the powder of [In(S
2
COEt)3]
solvate, where an asymmetric unit cell consists of a pair of
complex and solvent compounds as opposed to a pair of isomeric
complexes reported by Jain and co-workers. Regardless of this,
both structures have Z = 4 in to chiral pairs (i.e. Δ and Λ forms).
(1) was decomposed in a furnace with the fully decomposed
product retaining a similar shape to the parent crystalline powder,
i
Figure S2. The lower temperature peak from the [In(S
2
COPr)
3
] (3)
s
s
and [In(S CO Bu) ] (4) DTA profiles are assumed to be melting
2 3
In [In(S CO Bu) ] as synthesized from racemic sec-butyl xanthate
2
3
curves of the corresponding experimental melting point
temperatures. The samples from the two complexes exhibited a
slight yellow colour during the experimental melting point
determinations, suggesting a melting point temperature in close
vicinity of the decomposition temperature. It was further observed
ligand, a disordered structure formed. It is formed of a random
crystal packing, formed by the racemic ligand. This was
corroborated by a complex synthesized from enantiomerically
pure S-(+)-sec-butyl xanthate (Figure 2). All three ligands retained
the parent stereochemistry and the structure did not show signs
that when fully decomposed [In(S
2 3 2 3
COMe) ] (2) and [In(S COEt) ]
of distortions. Furthermore, the asymmetric unit contains a pair of
i
(1) afford orange to brown-coloured residue which is powdery,
isomers, similarly to the [In(S
2 3
COPr) ] structure by Jain and co-
i
s
whereas [In(S
coloured crystalline flakes, Figure 4.
The melt reaction conditions were optimised using
[In(S COEt) ] (1) due to the distinct steps in the decomposition
2 3 2 3
COPr) ] (3) and [In(S CO Bu) ] (4) afford red-
workers. The crystallographic data for the new structures is
provided in Table 1.
TGA of the complexes has been reported, the profiles were
however not provided.49 Furthermore, their physico-chemical
2
3
profile, Figure 3. Exploration of the phases produced was based
on the temperatures of the two final plateaus and the temperature
of the final decomposition step midpoint. The heated samples
showed three prominent colour transitions (orange, brown and
dark grey) with increasing decomposition temperature. The
properties were not disseminated in-depth. This experimental
data become crucial as both TGA and melt method exhibit similar
procedural protocols, as opposed to the solvothermal route
chosen by the authors which follows a different decomposition
pathway. Regardless of this, the authors report a single-step
decomposition profile for all precursors. To the contrary, our
profiles in Figure 3 show 4-step, 2-step, 3-step and 4-step
powder XRD pattern of the solid formed from [In(S
2 3
COEt) ] (1) at
200 °C displayed highly broadened and overlapped peaks which
is typical of sub 5 nm nanocrystal formation unlike the well-defined
patterns observed at higher decomposition temperatures, Figure
5. The powders obtained at 300, 350, 400 and 600 °C exhibit
2 3
decomposition curves for [In(S COR) ] where R = Me (2), Et (1),
i
s
Pr (3) and Bu (4), respectively. The anticipated inflection point
i
for [In(S
2
COPr)
3
] (3) corresponding to the loss of cyclohexane
diffraction patterns typical of In
crystallinity and crystallite sizes increase with an increase in
2 3
S phases; as expected, the
solvent of crystallisation was not observed since the mother liquor
was removed completely to obtain a dry sample prior to
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European Journal of Inorganic Chemistry
10.1002/ejic.201900007
FULL PAPER
annealing temperature as shown in Figure 5 and Table 4. The
understood by examining the intensity of the peaks on individual
patterns, in relation to precursor type and reaction temperature.
observed diffraction patterns from [In(S
2 3
COEt) ] (1) heated at 350
and 400 °C were matched and indexed to tetragonal (β) In
2
S
3
2 3 2 3
In both β-In S and α-In S -matched patterns (Figure S5 and
Figure S6, respectively) there is clear evidence of an inverse
proportion trend between peak intensities and reaction
56
(
PDF no. 00-025-0390). However, the absence of the (112)
reflection peak when heating [In(S COEt) ] (1) at 300 °C and
00 °C are in line with cubic (α) In (PDF no. 03-065-0459)
calculated from the single crystal data collected by Adenis et al.
This cubic-tetragonal phase transformation has been observed by
Dutta et al.49 albeit as a function of fabrication method (i.e. α-In
and β-In obtained by solvothermal and solventless thermolysis
2
3
6
2
S
3
4
temperature. The cubic In2.77S series displayed interesting
5
7
temperature-dependant behaviour. The inverse proportion trend
is observed in most of the reflection peaks, however, a significant
discrepancy is observed in the (311) and (440) reflection peaks
which appear interlinked (Figure S7). The intensities of the two
peaks are nearly equal at 300 °C reaction temperature. An
increase to 350 °C results in a significant drop in the intensity of
the (311) peak relative to the (440) peak, while vice versa is
observed at 400 °C. This observation is generally explained as
preferred growth orientation strongly dependant on reaction
parameters.
2
S
3
2 3
S
routes, respectively). Another encounter of the phenomenon is
reported by Bessergenev et al.51 where the polymorphism is
i
observed in thin films deposited from the vapours of [In(S
2
COPr)
3
]
at different temperatures; deposition is however conducted at
reduced pressure. α-In sometimes is expressed as cubic β-
due to their structural relationship inferred by the ordering
2 3
S
58
2 3
In S ,
of the vacant indium tetrahedral sites, the phenomenon is
explained by van Landuyt et al.59 Pistor et al. further outlines the
confusion perpetuated by the contradictory literature on the α–β–
Complimentary to the p-XRD data, measurements of the
lattice fringes from the high-resolution transmission electron
60
microscope images were conducted as means of
a
γ polymorphism of In
phases which is known to follow either the α–β–γ or β–α–γ order
with increase in temperature. According to the literature analysis
of Pistor et al.60 α-In
when it is sulfur-deficient, thus resulting in the α–β–γ order. When
the phase is stoichiometric, it becomes a high temperature system
and the β–α–γ order is obeyed. Both our 300°C and 600°C
2
S
3
, centred mostly on thermal stability of the
supplementary phase detection technique (Figure 8). This
improved imaging technology enabled us to extract detailed and
high quality information from the nanoparticles, compared to the
corresponding data obtained through technological limitations
2 3
S can exist as a low temperature phase
reported by Dutta et al.46 [In(S
[In(S COEt) ] (1) at 300 °C and [In(S
COMe)
] (2) annealed at 350 °C,
2
3
s
2
3
2
CO Bu)
3
] (4) at 350 °C were
chosen as representative samples of the three phases obtained,
i.e. β-In , α-In , respectively. As expected, values
samples, indexed to α-In
2
S
3
, showed sulfur-deficient In
S
2 3
2
S
3
2 3 4
S and In2.77S
confirmed by the energy dispersive x-ray diffraction (EDX)
spectroscopy analysis, Figure S8.
of the lattice fringes were successfully matched to d-spacing
values corroborating miller indices of multiple reflection planes
from the simulated standard diffraction patterns. The improved
imaging technology has enabled us to extract detailed information
on the nanoparticles, compared to acquire quality of the
morphology of the nanoparticles,
XPS was employed to gain insights into the electronic
structure of the different samples. For consistency purposes, the
representative samples used for HR-TEM imaging were used.
The survey spectrum provided in Figure 9 revealed only In, S, C
and O elements being present in the representative samples of
Figure 6. The detection of the C and O elements is generally
ascribed to adventitious hydrocarbons and oxygen or carbon
dioxide being adsorbed on the surface of the samples.
i
s
2 3
[In(S COR) ], where R = Me (2), Pr (3) and Bu (4), were
decomposed at 300, 350 and 400 °C. The indium sulfide phases
obtained from all precursors are summarized in Figure 6. The
[
In(S
physical characteristics (texture and colour) as the [In(S
1). However, the material obtained at 300 °C is composed of very
2
COMe)
3
] (2) precursor yields a material exhibiting the same
2
COEt)
3
]
(
small-sized nanoparticles, causing a high degree of broadening
in the p-XRD pattern, regardless that the precursor had a lower
decomposition temperature than [In(S
patterns from [In(S COMe) ] (2) heated at 350 °C and 400 °C, as
well as those from [In(S
matched to β-In [PDF no. 00-025-0390 and pattern simulated
2 3
COEt) ] (1). The p-XRD
2
3
i
2
3
COPr) ] (3) at all temperatures were also
2 3
S
from ICSD 183879 (data in Table S3)], see Figure 6a. However,
High-resolution XPS spectra of the In 3d core level shown
in Figure 10 contain a line shape composed of two main peaks
located at 445.2 eV and 452.7 eV binding energy, corresponding
to In 3d5/2 and In 3d3/2 spin-orbit peaks, separated by a spin-
s
decomposition of the [In(S
2
CO Bu)
3
] (4) precursor yielded a
material matching to cubic In2.77
Table S5), Figure 6c.
S from ICSD 41680 (data in
4
To support the phase identification by matching peak
positions, the peak intensities were compared to the powder
diffraction patterns generated from previously reported single
crystal structures in Figure 7. A linear plot of observed pattern
intensity vs intensity from a previously reported powder pattern
orbit splitting of 7.5 eV. The line shape of the peaks for samples
s
2 3
[In(S COMe) ] (2) and [In(S
2
CO Bu)
3
] (4) is clearly asymmetric,
indicating that each peak is composed of two sub-components.
The de-convolution of the In 3d core level spectra for these two
samples yielded two spin orbit doublets, labelled as “comp1” and
“comp2” in Figure 10. On the contrary, the line shape of this core
x y
indicates a strong match with the reference In S phase. Phase
identification across all three phases displays a linear trend. To
the contrary, the phase purity comparable to the single crystal
materials does not display a perfect linear trend. This can be
ascribed to contributing factors such as background noise on the
2 3
level for sample [In(S COEt) ] (1) is symmetric. The spectrum was
therefore fitted with a single spin-orbit doublet. The binding
energies of the In 3d5/2 peak for comp1 and comp2 are reported
in Table 5, together with their percentage area calculated with
respect to the overall area of the In 3d signal after background
subtraction.
patterns as
a function of crystallinity, as observed from
inconsistencies in the magnitude of errors. The error was better
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European Journal of Inorganic Chemistry
10.1002/ejic.201900007
FULL PAPER
Two spin-orbit doublets labeled as “comp1” and “comp2” in Conclusions
Figure 11 were also necessary to fit the S 2p spectra for samples
s
[
In(S
2
COMe)
3
] (2) and [In(S
2
CO Bu)
3
] (4), similarly to their In 3d
The melting of crystalline powders of [In(S
Pr and Bu) resulted in crystalline In S
x y
2
COR)
materials. By the choice
of complex and temperature different phases of pure In were
obtained: tetragonal (β) In , cubic (α) In and cubic In2.77
3
], (R = Me, Et,
i
s
core level counterparts. The binding energies of the S 2p3/2 peak
for comp1 and comp2 are reported in Table 6, together with their
percentage area calculated with respect to the overall area of the
S 2p signal after background subtraction. S 2p3/2 and 2p1/2 spin-
orbit peaks are separated by a spin-orbit splitting of 1.2 eV. A
single spin-orbit doublet was enough to fit the S 2p spectrum for
x y
S
2
S
3
2
S
3
S
4.
The ease of access to these phases through this simple, cost-
efficient and scalable method. The phases were determined by
powder X-ray diffraction and the energy dispersive X-ray
sample [In(S
Fu et al.58 synthesized the cubic and tetragonal polymorphs
and observed their XPS spectra to be identical. This
suggests that the differences in their spinel structures arising from
the ordering of the ⅓ vacancies in the indium tetragonal sites have
minor or negligible effect on the binding energies of the core levels.
2
COEt)
3
] (1).
x y
spectroscopy confirmed the melts being of the In S class. The
surface morphology of the melts, observed through the scanning
electron microscopy imaging technique, shows the formation of
nanoparticles and aggregates influenced by the nature of the alkyl
backbone in the xanthate complexes.
2 3
of In S
2 3 2 3
Interestingly, our polymorphic samples [In(S COEt) ] (1) (α-In S )
and [In(S COMe) ] (2) (β-In ) did not conform to the similar
observation, as will be elucidated in the following paragraphs. The
binding energies of the In 3d and S 2p core peaks for the
2
3
2 3
S
Experimental Section
Chemicals: Indium(III) chloride (98%, Aldrich), potassium ethyl
xanthogenate (96%, Aldrich), 1-propanol (anhydrous 99.7%, Aldrich),
methanol (≥99.9%, Aldrich), 2-butanol (anhydrous, 99.5%), potassium
hydroxide, sodium hydride (dry 95%, Sigma-Aldrich), carbon disulfide (low
benzene ≥99.9%, Sigma-Aldrich), diethylether (≥99.8%, Sigma-Aldrich),
chloroform (≥99.5%, Sigma-Aldrich), and magnesium sulfate (anhydrous,
[
2 3
In(S COEt) ] (1) sample agree with the values recorded by Fu et
58
3+
2-
al. , indicating In and S oxidation states for In
2 3
S material. The
tetragonal counterpart [In(S COMe) ] (2), on the other hand,
2
3
identifies the major component (comp1) of the spin-orbit doublets
exhibiting similar In 3d and S 2p core binding energies to the
≥
99.5%, Sigma-Aldrich) were used as received.
[
In(S
2
COEt)
3
] (1) sample. Thus, also suggesting In3 and S2-
+
s
oxidation states for this In
2
S
3
material. [In(S
2
CO Bu)
3
] (4) sample
COMe)
] (2) and
Characterisation of In(III) xanthate complexes: NMR spectra were
recorded using a Bruker Ascend spectrometer operating at 400 MHz;
analytes were prepared in CDCl solution. Thermogravimetric analysis
3
exhibits an identical electronic behavior to that of [In(S
2
3
]
(
2). The minor component (comp2) for both [In(S
2
COMe)
3
s
[In(S
2
CO Bu)
3
] (4) samples display In 3d and S 2p core binding
(TGA) and elemental analysis (EA) were collected by the University of
Manchester Microanalytical Laboratory. TGA was conducted on a Mettler
energies which are ca. 1 eV more than those of the major
component. The identification of the compound responsible for
e
Toledo TGA/DSC1 star system in the range of 30-600 °C, at a heating
−
1
rate of 10 °C.min . EA was performed on a Thermo Scientific Flash 2000
Elemental Analyser.
comp2 excludes possibilities on the presence of In
2 3
O or InS,
which have the In 3d5/2 binding energies of 445.2 eV61 and 444.8
eV, respectively, compared to 445.1 eV61 for In
13
2 3
S . Therefore,
x y
Characterisation of In S nanoparticles: Grazing incidence X-ray
the minor components may result from contaminated In
x y
S
diffraction (XRD) patterns for the melt products were acquired with a
Bruker D8 Advance diffractometer using a Cu Kα source (λ = 1.5418 Å) at
room temperature. The standard diffraction patterns were simulated online
using the single-crystal diffraction data from http://www2.fiz-
karlshuhe.de/icsd_web.htlm, using Cu Kα source (λ = 1.54184 Å) and 2θ
range of 10°-80° parameters. Low intensity peaks we omitted from the
plots for clarity purposes. Surface morphology and elemental composition
of the nanomaterials were determined using an FEI Quanta 200 SEM
equipped with an EDAX Genesis spectrometer. Transmission electron
microscopy (TEM) and high resolution TEM (HR-TEM) images were
obtained from nanoparticles prepared by sonication in ethanol, using a
JEOL 2100 HRTEM at accelerating voltage of 200kv, equipped with a
camera and software from Gatan. ImageJ software was used to calculate
lattice fringes through the profile plot technique. X-ray photoemission
(XPS) measurements were performed at room temperature using a
SPECS PHOIBOS 150 hemispherical electron energy analyser. The
photon source used was a SPECS XR 50 M monochromatised X-ray
source (Al Kα, h = 1486.71 eV). The overall energy resolution was set to
2 3-3x
phases such as the In S O3x species, as reported by Barreau et
al.62 where asymmetric line shapes in their XPS spectra were
s
2 3
detected, similarly to our [In(S COMe) ] (2) and [In(S
2
CO Bu)
3
] (4)
samples. The source of the oxygen contaminant can be traced to
the chemical component of the complexes, although it is expelled
as a volatile compound, COS, during the Chugaev elimination
pathway. Furthermore, the indium-rich composition for both
s
[
In(S
existence of the In
The similarities of the XPS spectrum of [In(S
with those of [In(S COMe) ] (2) and [In(S COEt)
attributed to the spinel-like nature of the polymorphs for
In(S COMe) ] (2) and [In(S COEt) ] (1). The spinel-like structures
are assigned the formula [In
2
COMe)
3
] (2) and [In(S
2
CO Bu)
3
] (4) may suggest the
2
3-3x
S O3x species.
s
2
CO Bu)
3
] (4)
2
3
2
3
] (1) can be
[
2
3
2
3
2
]Oh[In
⅔
V
⅓
]
Td
S
4
, where V, Oh and Td
1
are vacant, octahedral and tetrahedral sites, respectively. Thus,
s
the In2.77
S
4
phase of [In(S
2
CO Bu)
3
] (4) identified through p-XRD
0
.7 eV for survey spectra and 0.5 eV for all other spectra shown in this
technique suggests partial occupancy of the V sites by indium
atoms. Therefore, exhibiting similar electronic properties to the
work. A low energy flood gun was used in order to counteract the charging
of the sample surface (electron energy = 2 eV, electron flux = 20 µA)
2 3 2 3
[In(S COMe) ] (2) and [In(S COEt) ] (1) spinel samples.
Single crystal X-ray diffraction studies: Crystals suitable for the single-
crystal X-ray diffraction (XRD) studies were grown by the slow evaporation
methods in cyclohexane or dichloromethane solutions. The measurements
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European Journal of Inorganic Chemistry
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were conducted on a Bruker Prospector diffractometer equipped with a Cu
Kα source (λ = 1.5418 Å) and an Agilent diffractometer equipped with a
Mo Kα source (λ = 0.71073 Å), at various temperatures.
the UK Royal Society/Department for International Development
(RS-DFID) program for financial support.
Keywords: xanthates • X-ray diffration • thermolysis • indium
sulfide • nanoparticles
Preparation of ligands: The xanthate ligands were prepared as
potassium salts following standard literature methods which involve the
2
reaction between the corresponding alcohol with CS , in the presence of
KOH in an ice bath.39 The S-(+)-sec-butyl xanthate ligand was prepared
as a sodium salt from S-(+)-sec-butanol, following a modified NaH-
mediated route reported in literature.40
[1]
[2]
N. Barreau, Sol. Energy, 2009, 83, 363–371.
S. Lugo-Loredo, Y. Peña-Méndez, M. Calixto-Rodriguez, S. Messina-
Fernández, A. Alvarez-Gallegos, A. Vázquez-Dimas and T. Hernández-
García, Thin Solid Films, 2014, 550, 110–113.
[
[
[
[
[
3]
4]
5]
6]
7]
S. Cingarapu, M. A. Ikenberry, D. B. Hamal, C. M. Sorensen, K. Hohn
and K. J. Klabunde, Langmuir, 2012, 28, 3569–3575.
2 3
Preparation of tris-ethyl xanthato indium(III), [In(S COEt) ] (1):
Indium(III) chloride (1.00 g, 4.52 mmol) was dissolved in dry
tetrahydrofuran (100 mL). A solution of potassium diethylxanthogenate
R. Sumi, A. R. Warrier and C. Vijayan, J. Phys. Appl. Phys., 2014, 47,
105103.
(2.18 g, 13.6 mmol) in tetrahydrofuran was added to indium chloride
A. Y. Zavrazhnov, A. V. Naumov, P. V. Anorov, E. G. Goncharov, V. I.
Sidei and V. S. Pervov, Inorg. Mater., 2006, 42, 1294–1298.
solution forming a colourless precipitate. The white precipitate was
collected by filtration and the indium ethyl xanthate was extracted by
dissolving in chloroform. Residual water was removed by an organic work
up prior to slow evaporation of chloroform in open air resulting in colourless
A. V. Kosyakov, A. Y. Zavrazhnov and A. V. Naumov, Inorg. Mater., 2010,
46, 343–345.
P. D. Matthews, P. D. McNaughter, D. J. Lewis and P. O’Brien, Chem.
Sci., 2017, 8, 4177–4187.
crystals; Yield: 1.30 g, 60%. Anal. Calc. % (Obtained) for C
9
H
15
S
6
O
3
In: C,
1
2
2.60 (22.95); H, 3.16 (2.94); S, 40.21 (39.84); In, 24.00 (23.64). H NMR
-, t). 1 C( H) δ: 229.82, 76.13, 14.01.
3
1
[8]
D. Chen, Z. Liu, ACS Sustainable Chem. Eng. 2018, 6, 12328.
J. Choi, Y. Myung, S.-K. Kim, Appl. Surf. Sci. 2019, 467-468, 1040.
δ: 4.51 (CH
CH -, q), 1.49 (CH CH
3 2 3 2
[
[
9]
10] Y. Li, Y. Gao, N. Xiao, P. Ning, L. Yu, J. Zhang, P. Niu, Y. Ma, C. Gao,
AIP Adv. 2018, 8, 115202.
2 3
Preparation of tris-methylxanthato indium(III), [In(S COMe) ] (2): The
synthesis of (2) followed the same procedure as for (1) except potassium
methylxanthogenate (1.99 g, 13.6 mmol) was used in place of potassium
diethylxanthogenate. Pale yellow crystals were obtained; Yield: 906 mg,
[
[
11] M. I. Hossain, P. Chelvanathan, M. Zaman, M. Karim, M. Alghoul and N.
Amin, Chalcogenide Lett., 2011, 8, 315–324.
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497.
4
6%. Anal. Calc. % (Obtained) for C
6
H
9
S
6
O
3
In: C, 16.52 (16.83); H, 2.08
(
2.00); S, 44.09 (43.97); In, 26.31 (26.33). 1H NMR δ: 4.19 (CH
3
-, s).
1
3
1
[13] A. N. MacInnes, M. B. Power, A. F. Hepp and A. R. Barron, J. Organomet.
C( H) δ: 231.47, 65.83.
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[
[
[
14] Y. Sharma and P. Srivastava, Mater. Chem. Phys., 2012, 135, 385–394.
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AIP Conf. Proc., 2013, 1536, 455–456.
i
Preparation of tris-isopropylxanthato indium(III), [In(S
2
3
CO Pr) ] (3):
The synthesis of (3) followed the same procedure as for (1) except
potassium isopropylxanthogenate (2.37 g, 13.6 mmol) was used in place
of potassium ethyl xanthogenate. Colourless crystals were obtained using
cyclohexane for recrystallisation; Yield: 1.69 g, 72%. Anal. Calc. %
[
[
[
[
[
[
[
[
17] R. Sumi, A. R. Warrier and C. Vijayan, AIP Conf. Proc., 2014, 1576, 141–
1
43.
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161–1169.
(
(
(
21 6 3
Obtained) for C12H S O In: C, 27.69 (28.01); H, 4.07 (4.01); S, 36.96
36.99); In, 22.06 (21.96). 1H NMR δ: 5.16 ((CH
CH-, sep), 1.48
3
)
2
1
CH-, d). 13C( H) δ: 229.04, 86.16, 21.79.
1
3
(CH )
2
19] A. V. Sergeeva, A. V. Naumov, V. N. Semenov and Y. V. Sokolov, Inorg.
Mater., 2007, 43, 1046–1049.
s
Preparation of tris-2-butylxanthato indium(III), [In(S
2
CO Bu)
3
] (4): The
20] K. Otto, A. Katerski, A. Mere, O. Volobujeva and M. Krunks, Thin Solid
Films, 2011, 519, 3055–3060.
synthesis of (4) followed the same procedure as for (1) except potassium
-butylxanthogenate (4.77 g, 17.5 mmol) was used in place of potassium
ethyl xanthogentate. Colourless oily product was obtained; Yield: 3.75 g,
9%. Anal. Calc. % (Obtained) for C15 In: C, 32.02 (32.21); H, 4.84
4.76); S, 34.20 (34.05); In, 20.41 (20.23). 1H NMR δ: 4.97
2
21] F. Rahman, J. Podder and M. Ichimura, Surf. Rev. Lett., 2013, 20,
1350014.
7
27 6 3
H S O
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J. Semicond., 2014, 35, 063002.
(
(
(
CH
3
CH
2
(CH-)CH
3
, sextet), 1.94, 1.79 (CH
3
CH(CH-)CH
3
, each m), 1.44
, t). 13C( H) δ: 229.08,
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1
CH
3
CH
2
(CH-)CH
3
, d), 1.00 (CH CH (CH-)CH
3
2
3
2
015, 6, 487–490.
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07, 482–486.
9
0.79, 28.77, 18.86, 9.59.
4
In
x
S
y
nanoparticles: In a typical experiment, under Schlenk conditions 0.4
atmosphere
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Pradhan, Chem. Mater., 2012, 24, 1779–1785.
mmol of the complex was placed in a ceramic boat under N
2
at 50 °C. The furnace was then heated at 10 °C min-1 and held at the target
temperature (200 - 600 °C) for an hour. The reaction was stopped by
quickly air cooling the reaction vesicle to room temperature.
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3812–3817.
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The authors express their gratitude to the National Research
Foundation (NRF), South Africa (NRF Grant Number 64820) and
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European Journal of Inorganic Chemistry
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Figure 1. Structures of (a) tris-methylxanthato indium(III), (b) tris-isopropylxanthato indium(III) and tris-secbutylxanthato indium(III) [CCDC numbers 1875344, 1875347
and 1875345 respectively]. Hydrogens omitted for clarity. Black = C, yellow = S, red = O, purple = In.
s
Figure 2. The asymmetric unit cell of the (+)- Bu crystal structure (CCDC number 1875346).
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European Journal of Inorganic Chemistry
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A
B
C
D
E
100
Me (2)
Et (1)
90
80
70
60
50
40
30
i
Pr (3)
4
0
0
s
Bu (4)
3
100
200
300
400
500
600
200
300
400
500
600
Temperature (C)
-
1
Figure 3. The TGA profiles of the In(III) xanthate precursors from 30 °C to 600 °C at a heating rate of 10 °C.min . The vertical lines represent the chosen temperatures
for the melt reactions.
2 3
Figure 4. The physical features of the pyrolysis products showing orange-brown powdery texture from [In(S COEt) ] (1), while red crystalline texture from
s
[
2 3
In(S CO Bu) ] (4), decomposed at 350°C.
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European Journal of Inorganic Chemistry
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(a)
6
00 C
*
*
4
00 C
350 C
3
2
00 C
00 C
1
0
20
30
40
q (degree)
50
60
2
2
4
(b)
2
2
1
1
1
1
1
2
0
8
6
4
2
0
8
6
3
00
350
400
450
500
550
600
Temperature (C)
2 3 2 3 2
Figure 5. The (a) p-XRD patterns for In S obtained from [In(S COEt) ] (1) precursor heated for 1 h at the stated temperatures under an N atmosphere, and the
corresponding (b) crystallite sizes.
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European Journal of Inorganic Chemistry
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(a)
(b)
(c)
1
00
100
75
100
75
7
5
2
5
0
5
0
50
50
25
25
0
0
100
100
100
7
5
2
5
0
5
0
75
50
25
0
75
50
25
0
1
0
15 20 25 30 35 40 45 50 55 60
q (degree)
10 15 20 25 30 35 40 45 50 55 60
10 15 20 25 30 35 40 45 50 55 60
2
2q (degree)
2q (degree)
i
Figure 6. Average patterns (a) [In(S
b) [In(S COEt) ] (1) {300 & 600 °C} matching to α-In
patterns are provided in Figure 5a and Figure S4.
2
COMe)
3
] (2) {350 & 400 °C} + [In(S
2
COEt)
3
] (1) {350 & 400 °C} + [In(S
2
COPr)
3
] (3) {all °C} matching to β-In
2 3
S (ICSD 183879),
s
(
2
3
2
S
3
(ICSD 202353) and (c) [In(S
2
CO Bu)
3
] (4) {all °C} matching to cubic In2.77S
4
(ICSD 41680). Sources of averaged
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European Journal of Inorganic Chemistry
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6
5
4
3
2
1
0
0
0
0
0
0
(
a)
100
(b)
80
60
40
20
0
10
20
30
q (degree)
Tetragonal In S3 standard pattern
40
50
60
0
20
40
60
80
100
2
Relative Intensity (%)
Tetragonal In2S3 standard pattern
(d)
2
6
0
(
c)
100
5
4
3
2
1
0
0
0
0
0
8
6
4
0
0
0
20
0
1
0
20
30
q (degree)
Cubic In S3 standard pattern
40
50
60
0
20
40
60
80
100
2
Relative Intensity (%)
Cubic In2S3 standard pattern
(f)
2
60
50
40
30
20
10
(e)
100
80
60
40
20
0
10
20
30
q (degree)
Cubic In2.77S4 standard pattern
40
50
60
0
20
40
Relative Intensity (%)
Cubic In2.77S4 standard pattern
60
80
100
2
Figure 7. Correlation of peak positions for (a) tetragonal In
f), respectively.
2 3 2 3 4
S , (c) cubic In S and (e) cubic In2.77S matched melt products, with their relative intensities (b), (d) and
(
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European Journal of Inorganic Chemistry
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s
Figure 8. TEM images of (a) [In(S
2
COMe)
3
] (2) annealed at 350 °C, (b) [In(S
2
COEt)
3
] (1) at 300 °C and (c) [In(S
2
CO Bu)
3
] (4) at 350 °C with the corresponding (d)-(f)
HR-TEM images.
Figure 9. XPS survey scans for the representative samples of Figure 6. All relevant XPS and Auger peaks have been identified and labeled accordingly.
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European Journal of Inorganic Chemistry
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Figure 10. In 3d XPS spectra for the investigated samples. Black circles represent the raw data; thick lines are the overall fit to the data; dashed lines represent the
background (given by a combination of a Shirley-type background with a linear slope). Spectra were normalized to the maximum height of the 3d5/2 peak for better
comparison.
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Figure 11. S 2p XPS spectra for the investigated samples. Black dots represent the raw data; thick lines are the overall fit to the data; dashed lines represent the
background (given by a combination of a Shirley-type background with a linear slope). Spectra were normalized to the maximum height of the 2p3/2 peak for better
comparison.
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i
s
s
Table 1. Crystal structure and structure refinement for [In(S
2
COR)
3
] where R = Me (2), Pr (3), Bu (4) and (+)- Bu, respectively.
iPr ( sBu (
s
Parameter
Me (
2
)
3
)
4
)
(+)- Bu
Empirical formula
C
6
H
9
InO
3
S
6
C
12
H
21InO
3
S
6
, C
6
H
12
C
15
H
26InO
3
S
6
15 3 6
C H27InO S
Formula weight
436.31
293
604.62
150
561.54
293
562.55
150
Temperature/K
Wavelength/Å
1.54184
1.54184
1.54184
0.71073
Crystal system
Monoclinic
P21/n
Monoclinic
P21/n
Orthorhombic
Pna21
Orthorhombic
P212121
10.8724(3)
11.2857(3)
38.3026(13)
90
Space group
a/Å
9.6364(1)
14.6235(1)
11.0022(1)
90
14.3780(1)
10.9636(1)
17.9856(2)
90
11.7522(5)
19.7056(4)
10.3925(2)
90
b/Å
c/Å
α/°
β/°
109.133(1)
90
105.160(1)
90
90
90
γ/°
Volume/Å3
90
90
1464.76(2)
4
2736.49(5)
4
2406.74(12)
4
4699.8(2)
8
Z
Density calculated/Mg m-3
Absorption coefficient/mm-1
F(000)
1.979
1.468
1.550
1.590
20.830
856.0
11.310
1240.0
5689
12.814
1140.0
4748
1.551
2288.0
12125
Reflections collected
Final R indices [I > 2sigma(I)]
3041
R
1
= 0.0240, wR
0.0668
2
R
1
= 0.0302, wR
2
=
R
1
= 0.0662, wR
0.2310
2
=
R
1
= 0.0599, wR
0.0958
2
=
=
0.0741
Table 2. The residue weight percentages from TGA of the precursors and the corresponding percentages of the indium
sulfide phases.
Isotherm
C
Compound
In
Precursors
Et (1)
A
B
D
E
InS
In
2
S
3
3
S
4
In
6
S
7
5 4
In S
-
38.54
35.82
31.05
29.31
37.42
35.04
30.90
28.99
36.63
35.04
30.99
28.82
-
33.66
30.70
28.22
26.11
37.34
34.05
31.30
28.96
36.11
32.94
30.27
28.01
34.89
31.82
29.25
27.06
32.19
29.36
26.99
24.97
Me (2)
35.99
35.19
iPr (3)
sBu (4)
-
-
-
-
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European Journal of Inorganic Chemistry
10.1002/ejic.201900007
FULL PAPER
Table 3. Decomposition temperatures from DTA curves and experimental melting points. Data recorded in degrees Celsius.
st
nd
rd
1
turning
point
144.8
133.0
127.2
122.7
2
turning
point
-
3
turning
point
-
-
145.5
-
Experimental melting
Precursors
Et (1)
Decomposition onset
Decomposition offset
point
-
-
127-129
117-118
126.2
119.7
120.8
111.7
166.7
140.3
176.3
165.2
Me (2)
iPr (3)
-
139.5
140.8
s
Bu (4)
Table 4. Data from p-XRD of solids from [In(S
2
COEt)
3
] (1) precursor.
3
00°C (cubic In
2
3
S )
350°C (tetragonal In
2
S
3
)
400°C (tetragonal In
2
S
3
)
2 3
600°C (cubic In S )
Reflection
peak
Crystallite
size
Crystallite
size
Crystallite
size
Crystallite
size
d
hkl
FWHM
(°)
d
hkl
FWHM
(°)
d
hkl
FWHM
(°)
d
hkl
FWHM
(°)
2θ (°)
(Å)
(nm)
(Å)
(nm)
(Å)
(nm)
(Å)
(nm)
3
4
4
3
3
7
2.7053
2.0795
1.9083
0.8913
1.1274
1.1301
9.2980
7.5862
7.6835
8.1893
0.9615
2.7064
2.0798
1.9095
0.6688
0.7214
0.7339
12.3909
11.8555
11.8301
12.0255
0.3167
2.7055
2.0797
1.9099
0.4295
0.4529
0.4385
19.2952
18.8840
19.7988
19.3260
0.4582
2.7013
2.0770
1.9071
0.3561
0.3620
0.3842
23.2756
23.6308
22.6034
23.1699
0.5218
Average
Error
Table 5. Fitting parameters for In 3d core level.
comp1
comp2
comp1
comp2
Sample
Me (2)
sBu (4)
Et (1)
(BE 3d5/2) (eV)
(BE 3d5/2) (eV)
(% area)
(% area)
445.18
445.16
445.19
446.08
446.12
N/A
81
19
29
0
71
100
Table 6. Fitting parameters for S 2p core level.
comp1
comp2
comp1
comp2
Sample
Me (2)
sBu (4)
Et (1)
(BE 2p3/2) (eV)
(BE 2p1/2) (eV)
(% area)
(% area)
161,84
161,85
161,85
162,87
162,92
N/A
90
72
10
28
0
100
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201900007
FULL PAPER
FULL PAPER
Indium xanthate complexes have
been synthesized and their crystal
structures elucidated. Solventless
thermolysis of the complexes provide
an easy and effective route to indium
sulfide nanoparticles of high purity
and quality. Choice of alkyl chain
backbone of the xanthate ligand and
thermolysis temperature determine
the crystallographic phase.
Key Topic*
Siphamandla C. Masikane, Paul D.
McNaughter, David J. Lewis, Inigo
Vitorica-Yrezabal, Bryan P. Doyle,
Emanuela Carleschi, Paul O’Brien and
Neerish Revaprasadu*
Page No. – Page No.
Important phase control of indium
sulfide nanomaterials by choice of
indium (III) xanthate precursor and
thermolysis temperature
Indium sulfide nanoparticles
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