Homonuclear tris-dithiocarbamato ruthenium(III) complexes as single-molecule precursors for the synthesis of ruthenium(III) sulfide nanoparticles

Article abstract of DOI:10.1080/17415993.2016.1262373

Tris(N-phenyldithiocarbamato) ruthenium(III) complexes, [Ru(L¹)₃] (1); tris(N-(4-methylphenyl)dithiocarbamato)) ruthenium(III), [Ru(L²)₃] (2); and tris(N-(4-methoxyphenyl)dithiocarbamato)) ruthenium(III), [Ru(L³)₃] (3) were synthesized and characterized by elemental analysis, thermogravimetric analysis, FTIR, UV–VIS and NMR spectroscopy. TGA analyses show major degradation of all complexes in the range 120–350°C, leading to the formation of residual weight corresponding to ruthenium (III) sulfides. The ¹H-NMR spectra of the ligands and complexes are in agreement with the proposed structures. FTIR studies confirmed that the ligands coordinate the Ru³⁺ ion in a bidentate chelating mode. The complexes were thermolysed at 180°C to prepare hexadecylamine-capped Ru₂S₃ nanoparticles. Powder X-ray diffraction patterns revealed the formation of hexagonal-phase Ru₂S₃ nanoparticles with average crystallite sizes ranging from 8.3 to 9.5 nm. TEM images showed the crystalline clusters with shapes ranging from square to hexagonal, while SEM images elucidated that the particles were agglomerated. Energy-dispersive X-ray spectra confirmed the presents of Ru₂S₃ nanoparticles.

Full text of DOI:10.1080/17415993.2016.1262373

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Homonuclear tris-dithiocarbamato ruthenium(III)
complexes as single-molecule precursors for the
synthesis of ruthenium(III) sulfide nanoparticles
Johannes Z. Mbese & Peter A. Ajibade
To cite this article: Johannes Z. Mbese & Peter A. Ajibade (2017) Homonuclear tris-
dithiocarbamato ruthenium(III) complexes as single-molecule precursors for the synthesis
of ruthenium(III) sulfide nanoparticles, Journal of Sulfur Chemistry, 38:2, 173-187, DOI:
10.1080/17415993.2016.1262373
To link to this article: http://dx.doi.org/10.1080/17415993.2016.1262373
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Date: 25 February 2017, At: 12:17

JOURNAL OF SULFUR CHEMISTRY, 2017
VOL. 38, NO. 2, 173–187
http://dx.doi.org/10.1080/17415993.2016.1262373
Homonuclear tris-dithiocarbamato ruthenium(III) complexes
as single-molecule precursors for the synthesis of
ruthenium(III) sulfide nanoparticles
Johannes Z. Mbese and Peter A. Ajibade
Department of Chemistry, University of Fort Hare, Alice, South Africa
ABSTRACT
ARTICLE HISTORY
Received 16 July 2016
Accepted 12 November 2016
1
Tris(N-phenyldithiocarbamato) ruthenium(III) complexes, [Ru(L )3]
2
(
(
[
1);tris(N-(4-methylphenyl)dithiocarbamato))ruthenium(III),[Ru(L )3]
2); and tris(N-(4-methoxyphenyl)dithiocarbamato)) ruthenium(III),
Ru(L )3] (3) were synthesized and characterized by elemental analy-
KEYWORDS
Dithiocarbamate;
ruthnium(III); single source
precursor; ruthenium(III)
sulfides; structural properties
3
sis, thermogravimetric analysis, FTIR, UV–VIS and NMR spectroscopy.
TGA analyses show major degradation of all complexes in the range
1
20–350°C, leading to the formation of residual weight correspond-
1
ing to ruthenium (III) sulfides. The H-NMR spectra of the ligands and
complexes are in agreement with the proposed structures. FTIR stud-
3
+
ies confirmed that the ligands coordinate the Ru ion in a biden-
tate chelating mode. The complexes were thermolysed at 180°C
to prepare hexadecylamine-capped Ru2S3 nanoparticles. Powder
X-ray diffraction patterns revealed the formation of hexagonal-phase
Ru2S3 nanoparticles with average crystallite sizes ranging from 8.3
to 9.5 nm. TEM images showed the crystalline clusters with shapes
ranging from square to hexagonal, while SEM images elucidated that
the particles were agglomerated. Energy-dispersive X-ray spectra
confirmed the presents of Ru2S3 nanoparticles.
CONTACT Peter A. Ajibade
pajibade@ufh.ac.za
Department of Chemistry, University of Fort Hare, Private Bag
X1314, Alice 5700, Eastern Cape, South Africa
Supplemental data for this article can be accessed here. doi:10.1080/17415993.2016.1262373
2016 Informa UK Limited, trading as Taylor & Francis Group
©

174
J. Z. MBESE AND P. A. AJIBADE
1. Introduction
Chemical synthesis of inorganic nanomaterials has proved to be more effective and ver-
satile than physical methods and have been employed widely to synthesize a variety
of nanomaterials, including zero-dimensional nanocrystals, one-dimensional nanowires
and nanotubes, as well as two-dimensional nanofilms and nanowalls [1–3]. There is
much progress in the synthetic fabrication of transition metal sulfides nanocrystals with
controlled shape, size, and surface functionality [4,5]. The inorganic nanomaterials syn-
thesized from molecular precursor complexes often show catalytic properties in reac-
tions involving hydrogenation (HN) of olefins, hydroformylations, and hydrogenolysis
of alkanes [6]. Ruthenium sulfide nanoparticles in particular have tremendous potential,
due to their important industrial applications as catalysts for hydrodenitrogenation,
hydrodesulfurization, and aromatic HN in the presence of sulfur impurities [7,8].
Ruthenium sulfide belongs to the family of transition metal chalcogenides that crystal-
lize in the pyrite-like structure with a direct band gap of ≥2.2 eV [9,10]. The pyrite-like
structures that are widely studied belong to the active phase during HDS, with the coor-
dinatively unsaturated sites at sulfur vacancies acting as the specific catalytic sites [11].
Numerous studies have been carried out on the synthesis of metal sulfide nanoparticles
[
[
12–14] and specifically metal complexes of dithiocarbamate as single source precursors;
15–18] however, to the best of our knowledge, there is no literature on the use of tris-
dithiocarbamato ruthenium(III) complexes as single-molecule precursor for the synthesis
of ruthenium(III) sulfide nanoparticles. The +2, +3, and +4 are the most common oxi-
dation states of ruthenium compounds, and therefore one would anticipate the transition
of the atomic ratio of [Ru:S] from 1:1 (in RuS) to 1:1.5 (in Ru S ) to 1:2 (in RuS ) upon
2
3
2
thermolysis of tris-dithiocarbamato ruthenium(III) complexes [19,20]. Herein, we report
synthesis, as well as structural and optical properties of ruthenium (III) sulfide (Ru S )
2
3
from dithiocarbamato ruthenium (III) precursor complexes. The optical properties of the
resulting nanocrystals were studied with optical absorption and photoluminescence (PL)
spectroscopy. The structural properties were examined using powder X-ray diffraction
(
PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM),
and energy-dispersive X-ray spectroscopy (EDS).
2. Experimental
2.1. Physical measurements
The optical measurements of samples were measured using Perkin Elmer Lambda 25
UV−VIS spectrophotometer at room temperature. The PL of the nanoparticles was
measured using the Perkin Elmer LS 45 fluorimeter. PXRD analysis was recorded on
the Bruker-D8 advance operating at a voltage of 40 kV and a current of 30 mA with
Cu Kα radiation. The FTIR was done as KBr discs on a Perkin Elmer Paragon 2000
−
1
FTIR spectrophotometer in the range 4000–370 cm . A Perkin Elmer TGA 7 fitted
with a thermal analysis controller (TAC7/DX) and differential scanning calorimeter was
used to study thermal stability of metal complexes under nitrogen condition. The TEM
morphologies were obtained using a ZEISS Libra 120 electron microscope operated at
1
20 kV. The SEM images were obtained on a Jeol, JSM-6390 LV apparatus, using an
accelerating voltage between kV at different magnifications. Energy-dispersive spectra

JOURNAL OF SULFUR CHEMISTRY
175
were processed using EDS attached to a Jeol, JSM-6390 LV SEM with Noran system six
software.
2.2. Synthesis of ligands
2
.2.1. Synthesis of ammonium N-phenyldithiocarbamate, L1
This compound was prepared by a modified literature method [21]. In a typical exper-
iment, 30 mL of concentrated ammonia solution was added slowly to 9.13 mL (0.1 mol)
aniline in an ice cold mixture at 0–5 °C. To this mixture, 6.04 mL (0.1 mol) of carbon disul-
fide was added drop-wise with constant stirring in an ice bath and refluxed for a further
2
h at room temperature. The resulting yellowish solid obtained was filtered by suction and
rinsed three times with cold ethanol. The product obtained is air and thermally unstable
and was stored in the refrigerator.
−
1
1
Yield: 6.9 g (57%). Selected IR (KBr), v (cm ) L : 1488 (C–N str.), 2930 (C–H), 950
(
C=S), 3,429 (N–H str.), 1603σ (N–H).
2
.2.2. Synthesis of ammonium N-(4-methy1phenyl) dithiocarbamate, L2
A modified literature method [22] was used to prepare this compound. In a typical
synthesis process, 10.21 mL (0.1 mol) of p-toluidine in a 250 mL Erlenmeyer flask with
magnetic stirrer placed in an ice cold bath at 0–5°C, 30 mL of concentrated ammonia
solution and 6.04 mL (0.1 mol) of carbon disulfide was added drop-wise in a period of
2
0–30 min with vigorous stirring. After the addition was complete, the reaction mixture
was further refluxed for 3 h at room temperature. The brownish product was filtered with
suction and the residue was washed with three 20-mL portions of cold absolute ethanol
and dried under vacuum over CaCl , yielding the ammonium N-(4-methy1phenyl)
2
dithiocarbamate.
Yield: 8.6 g (71%). Selected IR (KBr), v (cm−1) L : 1492 (C–N str.), 2979 (C–H str.
2
asym.–CH ), 1040 (C=S), 3430 (N–H str.), 1606σ(N–H).
3
2
.2.3. Synthesis of ammonium N-(4-methoxyphenyl) dithiocarbamate, L3
This ligand was prepared using a modified literature method [23]. In a 250 mL Erlen-
meyer flask with a magnetic stirrer placed in an ice cold bath at 0–5 °C, p-anisidine 12.32 g
(
0.1 mol) was treated with 6.04 mL (0.1 mol) CS To this mixture, 30 mL of concentrated
2.
ammonia solution was added. After the addition was complete, the reaction mixture was
further refluxed for 3 h at room temperature. The brownish product was filtered with
suction and the residue was washed with three 20 mL portions of cold ether and dried
under vacuum over CaCl , yielding the ammonium N-(4-methoxyphenyl) dithiocarba-
2
−
1
3
mate. Yield: 9.0 g (74%). Selected IR (KBr), v (cm ) L : 1490 (C–N), 1264 (Ar–O–CH
str.), 2930 (C–H), 956 (C=S), 3429 (N–H str), 1603σ(N–H).
3
2
.3. Synthesis of Ru(III) dithiocarbamate complexes
1
2
.3.1. Synthesis of tris(N-phenyldithiocarbamato) ruthenium(III), [Ru(L ) ]
3
The three complexes were prepared by a modification of the method reported in litera-
ture [24]. An ethanol solution (10 mL) of ammonium N-phenyldithiocarbamate (0.9348 g,
5
mmol) was added to an ethanol solution (10 mL) of RuCl ·3H O (0.4445 g, 1.7 mmol),
3
2

176
J. Z. MBESE AND P. A. AJIBADE
under constant stirring. To this mixture, deionized water (5 mL) was added to enhance
precipitation. A dark brown precipitate formed immediately, and the solution was allowed
to stir for about 45 min to ensure complete reaction. The dark brown powder was col-
lected by vacuum filtration, washed three times with deionized water, and allowed to dry
−
1
under vacuum over CaCl . Yield: 0.9475 g (92%), m.p. 160°C. Selected IR (KBr), v (cm
)
2
1
[
Ru(L ) ]: 1460 (C–N str.), 2940 (C–H), 1030 (C–S), 3429 (N–H str.), 501 Ru–S. Anal.
3
Calc. (%) for C H N S Ru (605.85): C, 41.63; H, 2.99; N, 6.94; S, 31.76. Found: C, 41.55;
2
1
18 3 6
1
H, 2.97; N, 6.96; S, 31.78. HNMR (600 MHz, DMSO-d ): δ 3.44 (s, 1H, N–H), 7.92–7.66
6
(
d, 2H, J = 7.8 Hz, –C H ), 6.99–6.54 (m, 3H, J = 7.7 Hz, –C H ) ppm.
6
5
6
5
2
.3.2. Synthesis of tris (N-(4-methy1phenyl)dithiocarbamato) ruthenium(III),
2
[
Ru(L ) ]
3
An ethanol solution (10 mL) of ammonium N-(4-methy1phenyl) dithiocarbamate
(
1
1.0016 g, 5 mmol) was added to an ethanol solution (10 mL) of RuCl ·3H O (0.4445 g,
3
2
.7 mmol) under constant stirring. To this mixture, deionized water (5 mL) was added to
enhance precipitation. A dark brown precipitate formed immediately, and the solution was
allowed to stir for about 45 min to ensure complete reaction. The dark brown powder was
collected by vacuum filtration, washed three times with deionized water, and allowed to
dry under vacuum over CaCl . Yield: 0.9681 g (94%), m.p. 185 °C. Selected IR (KBr), v
2
−1
2
(
cm ) [Ru(L ) ]: 1473 (C–N str.), 2945 (C–H), 1010 (C–S), 3429 (N–H str.), 490 Ru–S.
3
Anal. Calc. (%) for C H N S Ru (619.93): C, 46.50; H, 3.90; N, 6.77, S, 31.04. Found:
C, 46.52; H, 3.91; N, 6.76; S, 31.03. HNMR (600 MHz, DMSO-d ): δ 3.32 (s, 1H, N–H),
2
4
24 3 6
1
6
7
.34–7.28 (d, 2H, J = 2.2 Hz, –C H ), 6.92–6.86 (m, 2H, J = 2.2 Hz, –C H ), 3.31 (bs, 3H,
6
5
6
5
C–CH ) ppm.
3
2
.3.3. Synthesis of tris (N-(4-methoxyphenyl)dithiocarbamato) ruthenium(III),
3
[
Ru(L ) ]
3
An ethanol solution (10 mL) of ammonium N-(4-methoxyphenyl) dithiocarbamate
(
1
1.0816 g, 5 mmol) was added to an ethanol solution (10 mL) of RuCl ·3H O (0.4445 g,
3
2
.7 mmol) under constant stirring. To this mixture, deionized water (5 mL) was added to
enhance precipitation. A dark brown precipitate formed immediately, and the solution was
allowed to stir for about 45 min to ensure complete reaction. The dark brown powder was
collected by vacuum filtration, washed three times with deionized water, and allowed to
dry under vacuum over CaCl . Yield: 0.9990 g (97%), m.p. 200°C. Selected IR (KBr), v
2
−1
3
(
cm ) [Ru(L ) ]: 1468 (C–N str.), 3035 (C–H), 1010 (C–S), 3410 (N–H str.), 480 Ru–S.
3
Anal. Calc. (%) for C H N O S Ru (667.93): C, 43.15; H, 3.90; N, 6.29; S, 28.80. Found:
C, 43.13; H, 3.92; N, 6.28; S, 28.83. HNMR (600 MHz, DMSO-d ): δ 3.32 (s, 1H, N–H),
2
4
24
3
3 6
1
6
7
.33–7.28 (d, 2H, J = 2.4 Hz, –C H ), 6.92–6.86 (m, 2H, J = 2.4 Hz, –C H ), 3.74 (s, 3H,
6
5
6
5
OCH ) ppm.
3
2
.4. Synthesis of hexadecylamine (HDA)-capped Ru S nanoparticles
2 3
The as-synthesized complexes were used as precursors for the preparation of Ru S
2
3
1
nanoparticles following the literature [25]. In a typical experiment, 0.3 g of [Ru(L ) ]
3
n
complex was dissolved in 5 mL of tri octylphosphine and then injected into 4 g of
hot HDA at a temperature of 180°C. A decrease in temperature of about 20–30°C

JOURNAL OF SULFUR CHEMISTRY
177
was observed and the solution was then allowed to reach a temperature of 180°C and
then heated for a further 60 min. The solution was cooled to about 70°C, and large
amounts of methanol were added to remove excess HDA. The as-synthesized flocculent
precipitate was separated by centrifugation and was re-dispersed in toluene. The sol-
vent was removed by evaporation under reduced pressure to give HDA-capped Ru2S3
nanoparticles.
3. Results and discussion
3.1. Synthesis
The ligands and corresponding complexes were isolated in solid form and found read-
ily soluble in methanol, ethanol, DMF chloroform, and DMSO. Attempts to isolate
diffraction-quality crystals suitable for X-ray crystallography failed. The yield obtained
1
for ligands: ammonium N-phenyldithiocarbamate, (L ); ammonium N-(4-methylphenyl)
2
3
dithiocarbamate (L ); and ammonium N-(4-methoxyphenyl) dithiocarbamate (L ) were
5
7%, 71%, and 74%, respectively. RuCl ·3H O was dissolved in ethanol and added to an
3
2
aqueous solution of the dithiocarbamate ligand in a 1:3 metal-to-ligand ratio. All the tris-
dithiocarbamato ruthenium(III) complexes were brownish in color and obtained in good
yields (92–97%).
3.2. Electronic absorption studies of complexes
1
2
3
The absorption spectra of all the complexes ([Ru(L ) ], [Ru(L ) ], [Ru(L ) ]) recorded
3
3
3
−5
in DMSO (1 × 10 M) at 298 K showed similar behavior. The small spectral changes
shown by a decrease in absorbance values could be ascribed to reduced solubility of the
complexes, and their nature. In the electronic spectra of the three complexes, bands are
assigned to electronic transitions located in the d orbitals of the ruthenium center and
π → π* and n → π* of the dithiocarbamato moieties. The broad bands around 635 nm
could be assigned to the d
→ d
2
−
2
, d
2
, and d → d transitions and are in
xz,yz,xy
x −
y
z
xy
yz
agreement with the octahedral environment around the metal ion [26,27]. The weak shoul-
ders around 271 nm are attributed to n → π* transition in sulfur atoms, whereas bands at
2
83 nm can be ascribed to intramolecular intraligand charge transfer π → π* transitions
located in the S–C–S and N–C–S chromophores of the bidentate dithiocarbamate ligands,
respectively [28–30].
3.3. FTIR studies of complexes
The diagnostic peaks of the dithiocarbamate ligands and their corresponding metal com-
plexes were carefully compared and assigned. The v(C–H) frequencies were observed
−
1
at 2930 and 2852 cm . Infrared spectra of the complexes showed that the thioureide
−
1
ν(C–N) band is in the regions 1450–1500 cm as observed in the ligands. Other v(C–N)
vibrations,(1359 and 1261 cm ) were somewhat lower in the complexes. Both complexes
showed single strong bands in the 950–11050 cm region due to v(C–S), supporting that
−
1
−
1
the dithiocarbamate ligands are bidentately coordinated to the ruthenium ions [21,25].
−
1
The v(S–N) vibration is observed around 855 cm in the complexes as well as the ligands,
but the thioureide ν(C–N) bands are blue shifted, indicating the bidentate nature of the

1
1
3
1
3
Table 1. H NMR spectral data for ligands L –L and complexes C –C . Coupling constants in italics.
1H NMR
2/6
3/5
2 /6
ꢀ
ꢀ
ꢀ ꢀ
3 /5
N–H
C–H
C–CH3
3.31 bs
C–OCH3
1
L
7.92–7.66 d J = 7.8
7.34–7.28 d J = 2.2
7.33–7.28 m J = 2.4
6.99–6.54 m J = 7.7
6.92–6.86 m J = 2.2
6.92–6.86 m J = 2.4
3.44 s
3.32 s
3.31 s
3.65 s
3.99 s
3.31 s
4.98 s
2
L
3
L
3.74 s
1
C
7.70–7.47 dd J = 8.1
7.50–7.13 m J = 8.0
7.33–7.28 m J = 2.0
7.38–7.05 m J = 7.9
6.99–6.29 m J = 2.2
6.92–6.87 m J = 2.0
3.87 s
2
C
2.32 bd J = 2.0
3
C
2.08 d J = 2.2
Notes: The spectra were obtained in DMSO-d6, chemical shifts in ppm, and coupling constants (J) in Hz. Numbering pattern as shown in Scheme 1. Abbreviations used: s, singlet; d, doublet; dd,
double doublet; bs, broad singlet; bd, broad doublet.

JOURNAL OF SULFUR CHEMISTRY
179
dithiocarbamate moiety. The bands in the far IR region in the spectra of the complexes are
attributed to the frequencies of metal–sulfur bond, and the v(Ru–S) stretching vibrations
−
1
were observed around 522 cm region [31].
3
.4. NMR study
1
The summary of H-NMR signals and coupling constants are given in Table 1. The
1
1
H-NMR spectrum of ammonium N-phenyldithiocarbamate ligand, (L ) display a broad
singlet peak of one proton at 3.44 ppm, (1H, s) ascribed to (N–H) proton. The doublet
peaks appearing from 7.92–7.66 (d, 2H, J = 7.8 Hz, H /H of –C H ) ppm and the mul-
3
5
6
5
tiplet from 6.99–6.54 (m, 3H, J = 7.7 Hz, H -H of –C H ) ppm were due to the phenyl
2
6
6
5
2
ring protons [32]. L show a sharp singlet peak of one proton at 3.32 (s, 1H, N–H) ppm. An
2
1
up-field of 0.12 ppm was observed in L when compared to L . The doublet peaks appear-
ing from 7.34–7.28 (d, 2H, J = 2.2 Hz, H /H of –C H ) ppm and a multiplet in the region
3
5
6
5
6
.92–6.86 (m, 2H, J = 2.2 Hz, H /H of –C H ) ppm were due to the phenyl ring protons.
2
6
6
5
A broad singlet peak at 3.31 (bs, 3H, C–CH ) ppm is assigned to methyl group of tolui-
3
3
dine. L display a doublet from 7.33–7.28 (d, 2H, J = 2.4 Hz, H /H of –C H ) ppm and a
3
5
6
5
multiplet at 6.92–6.86 (m, 2H, J = 2.4 Hz, H /H of –C H ) ppm due to the aromatic ring
2
6
6
5
protons.
A singlet peak at 3.74 (s, 3H, OCH ) ppm assigned to methyl group of anisidine. The
3
2
3
doublet and triplet peaks in L and L appeared in the same region, suggesting that the
ꢀ
R = CH or OCH does affect the proton environment of the phenyl ring. The single peak
3
3
appearing in all spectra at δ = 2.50 ppm is due to dimethylsulfoxide (DMSO-d ), the sol-
6
1
2
3
vent used. The signals of complexes ([Ru(L ) ], [Ru(L ) ], and [Ru(L ) ]) were assigned
3
3
3
and compared to those of their respective ligands. The N–H and phenyl rings protons
were found more or less at the same position as the ligands. The major notable change
ꢀ
was observed in the peaks associated with the R substituents of the complexes that shifted
up-field, indicating the presence of ruthenium in the complexes.
3.5. TGA
The TGA was employed on the tris-dithiocarbamato ruthenium(III) complexes to elu-
cidate the temperature at which decomposition takes place and also to determine the
suitability of these compounds as single source molecular precursors for the synthesis
of metal sulfides nanoparticles. According to the thermogram in Figure 1, the results
revealed that all complexes are stable initially up to about 120°C, after which the three
decomposition processes occurred and completed at about 580°C.
The first stage of decomposition in all complexes may be possibly assigned to the loss
of solvents, including water used during synthesis. The second stage of decomposition was
assigned to the loss of dithiocarbamate ligands moieties –(S CNR ), which was biden-
2
2
tately attached to ruthenium ion, due to the steric hindrances arising from 3:1 ratio of
ligand to the metal center. The third stage in all complexes are decompositions around
5
80.01–733.45°C that yielded ruthenium sulfide. Scheme 1 outlines the possible decompo-
sition stages of the tris-dithiocarbamato ruthenium(III) complexes up until the ruthenium
sulfide is formed.

180
J. Z. MBESE AND P. A. AJIBADE
105
[
[
[
Ru(L1)3]
Ru(L2)3]
Ru(L3)3]
9
8
7
6
5
4
3
2
1
5
5
5
5
5
5
5
5
5
5
3
0
130
230
330
430
530
630
730
Sample Temperature (oC)
Figure 1. Thermogravimetric pattern of tris-dithiocarbamato ruthenium(III) complexes.
Scheme 1. The possible decomposition stages of tris-dithiocarbamato ruthenium(III) complexes.
All the complexes showed no volatility after this stage, and the total weight loss (%)
as shown in Table 2 decreases from 80.22% to 70.71% as we vary the substituents in the
ꢀ
para-position (R ) of the ligand L.
These overall weight loss results are to some extent in agreement with the calculated val-
ues from chemical analysis and also their proposed molecular formula was confirmed. Sim-
ilar results on the decomposition of some ruthenium, copper, and iron dithiocarbamates
complexes have been reported [33].
Table 2. Thermogravimetric studies of tris-dithiocarbamato ruthenium(III) complexes.
Temperature
range in °C
Possible
assignment
(%) Total weight
loss
Complex
(%) Weight loss
1
[
[
[
Ru(L )3] = C21H18N3S6Ru
90.60–123.20
Loss of solvents
Decomposition of L
Formation of RuS
12.23
47.31
20.68
80.22
75.47
70.71
1
30.32–350.43
580.01–690.40
2
Ru(L )3] = C24H24N3S6Ru
89.80–119.50
Loss of solvents
Decomposition of L
Formation of RuS
11.22
42.86
21.39
1
28.79–335.34
610.01–700.38
3
Ru(L )3] = C24H24N3O3S6Ru
93.10–120.40
Loss of solvents
Decomposition of L
Formation of RuS
9.30
34.43
26.98
1
34.77–340.56
590.41–733.45

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181
Figure 2. Absorption and emission spectra of HDA-capped Ru2S3 nanoparticles. (a) Ru2S31 from
1
2
3
[
Ru(L )3], (b) Ru2S32 from [Ru(L )3], and (c) Ru2S33 from [Ru(L3) ].
4
. Optical and structural studies of the nanoparticles
.1. Optical studies of the nanoparticles
The tris-dithiocarbamato ruthenium(III) complexes were used as precursors for the
synthesis of HDA-capped Ru S nanoparticles and absorption and emission spectra of
4
2
3
nanoparticles were studied using UV–VIS and PL spectroscopy, as shown in Figure 2.
The spectra showed strong cut off where the absorbance is minimum at a = 285, b = 287,
and c = 289 nm for Ru S 1, Ru S 2, and Ru S 3 nanoparticles, respectively. The cut off
2
3
2 3
2 3
∗
wavelength was then used to determine the energy band gap E of the Ru S nanopar-
g
2 3
ticles. The particle size was estimated using Brus equation [34], and were found to be
(
a = 4.82 nm, 4.36 eV), (b = 4.79 nm, 4.33 eV), and (c = 4.75 nm, 4.30 eV). The absorp-
tion spectra exhibited a blue shift with respect to that of the bulk materials due to quantum
confinement effects as a result of their small crystallite sizes [35]. The emission spectra were
recorded by keeping excitation wavelength fixed at 394 nm. The PL spectra showed narrow
emission curves with the emission maximum at a = 290, b = 291, and c = 292 nm. Ru S
2
3
gave emission maxima that are red shifted to the absorption band edges [36].
4
.2. TEM studies of the nanoparticles
The TEM image of Ru S 1 nanoparticles (Figure 3(a)) shows an exceptionally narrow size
2
3
distribution of ruthenium sulfide nanoparticles capped in HDA, with an average size rang-
ing from 8 to 20 nm. The nanoparticles are spherical in shape. The TEM image of Ru S 2
2
3
nanoparticles (Figure 3(b)) indicates that the crystalline clusters has shapes ranging from
square to hexagonal. The average particle size is around 80 nm, and the particles have lower
standard deviation compared to those obtained for Ru S 1 nanoparticles (Figure 3(a)),
2
3
whereas Ru S 3 nanoparticles (Figure 3(c)) showed particles ranging from hexagonal to
2
3
spherical shape with an average diameter of 10 nm.

182
J. Z. MBESE AND P. A. AJIBADE
1
Figure 3. TEM images of HDA-capped Ru2S3 nanoparticles. (A) Ru2S3 from [Ru(L )3], (B) Ru2S3 from
2
3
[
Ru(L )3], and (C) Ru2S3 from [Ru(L )3].

JOURNAL OF SULFUR CHEMISTRY
183
1
Figure 4. SEM images and EDS of HDA-capped Ru2S3 nanoparticles. (A) Ru2S3 from [Ru(L )3], (B) Ru2S3
2
3
from [Ru(L )3], and (C) Ru2S3 from [Ru(L )3].

184
J. Z. MBESE AND P. A. AJIBADE
Figure 5. XRD of HDA-capped Ru2S3 nanoparticles.
4
.3. SEM images and EDS spectra of the nanoparticles
Scanning electron microscope (SEM) was used to further establish the morphology of the
nanoparticles. Figure 4 shows the SEM images and Energy-dispersive Spectroscopy (EDS)
of as-synthesized ruthenium sulfide nanopartilces. Figure 4(a–c) elucidates that the parti-
cles were agglomerated and probably the samples were not completely dry during the time
of analysis. However, the application of EDS analysis confirmed the presence of ruthenium
sulfide.
4
.4. XRD studies of the nanoparticles
Figure 5 shows the XRD patterns of the ruthenium sulfide nanoparticles prepared at 180°C.
All the diffraction patterns can be indexed to the polycrystalline ruthenium sulfide by com-
parison with the data from JCPDS file number 19-1107. However, the XRD patterns of
the as-prepared nanoparticles are noticeably thickened due to the very small size of these
particles and the strong, and narrow diffraction peaks indicated good crystallinity of the
nanoparticles. The XRD patterns exhibit narrow peaks at 26.79, 29.72, 44.02, 48.58, and
5
2.20, which are assignable to the (111), (220), (311) and (400) Miller indices, respectively,
suggesting small crystallite sizes of hexagonal phase. The calculated average crystallite sizes
from these peaks using Scherer’s formula were found to be 8.3 nm for Ru S 1, 9.2 nm for
2
3
Ru S 2, and 9.5 nm for Ru S 3, respectively.
2
3
2 3
5. Conclusion
Tris-dithiocarbamato ruthenium(III) complexes were successfully synthesized and char-
acterized using elemental analysis and spectroscopic techniques. FT-IR spectra studies
confirmed that the dithiocarbamate ligands are bidentately bonded to ruthenium metal ion

JOURNAL OF SULFUR CHEMISTRY
185
through sulfur atoms. The NMR spectra confirmed the proposed structures of six coordi-
nate octahedral geometry for the ruthenium(III) complexes in which the ruthenium ion is
bonded to three molecules of the dithiocarbamate ligands. The TGA analysis showed that
the complexes decomposed to form ruthenium sulfides as the final product, indicating
that the compounds will be good as single source molecular precursors for ruthenium sul-
fide nanoparticles. XRD patterns revealed that the as-synthesized Ru S nanoparticles are
2
3
in the hexagonal crystalline phase. TEM images showed the polydispersity and polycrys-
talline nature of the as-synthesized nanoparticles. EDS spectra revealed that the prepared
nanoparticles are mainly composed of Ru and S, thereby confirming the formation of Ru2S3
nanoparticles. The particle sizes obtained in optical studies, XRD, and TEM were found to
be in good agreement.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
The authors gratefully acknowledge financial support from SASOL University Research Grant and
Govan Mbeki Research and Development Centre, University of Fort Hare, South Africa.
ORCID
Peter A. Ajibade http://orcid.org/0000-0002-8581-2387
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