Bis-(N-ethylphenyldithiocarbamato)palladium(II) as molecular precursor for palladium sulfide nanoparticles

Article abstract of DOI:10.1016/j.molstruc.2021.130777

Bis(N-ethylphenyldithiocarbamato)palladium(II) was synthesized and characterized by elemental analysis, spectroscopic techniques and single crystal X-ray crystallography. The molecular structure confirmed the N-ethylphenyldithiocarbamato anions coordinate

Full text of DOI:10.1016/j.molstruc.2021.130777

Journal of Molecular Structure 1243 (2021) 130777
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Bis-(N-ethylphenyldithiocarbamato)palladium(II) as molecular
precursor for palladium sulfide nanoparticles
Athandwe M. Paca, Peter A. Ajibade∗
School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Bis(N-ethylphenyldithiocarbamato)palladium(II) was synthesized and characterized by elemental analy-
sis, spectroscopic techniques and single crystal X-ray crystallography. The molecular structure confirmed
the N-ethylphenyldithiocarbamato anions coordinated bidentately to the Pd(II) ion through the sulfur
atoms and resulted in the formation of a square planar geometry. The complex was used as a single-
molecule precursor and thermolyzed at three different temperature to investigate the influence of the
thermolysis temperature on the optical and morphological properties of the as-prepared palladium sul-
fide nanoparticles. The pXRD proved that variation of the thermolysis temperature resulted in palladium
sulfide nanoparticles with different diffraction patterns. TEM images showed that nanoparticles with par-
ticle sizes of 2.01–2.50 nm, 4.00–4.86 nm and 2.53–4.12 nm were obtained at 160, 200 and 240 °C,
respectively. This revealed that increase in temperature resulted in larger nanoparticles but as tempera-
ture gets higher the particle size distribution becomes non-uniform. SEM micrographs revealed that the
nanoparticles have a rough surface with different surface morphologies. The optical band gap (Eg) range
between 4.90–5.02 eV and was slightly increased when the temperature was increased.
Received 5 March 2021
Revised 12 May 2021
Accepted 22 May 2021
Available online 28 May 2021
Keywords:
Metal sulfide
Thermal decomposition
Octadecylamine
Single-source molecule
Palladium(II) dithiocarbamate
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
nanoparticles to prevent aggregation, protects the particles from
its surroundings and affords electronic equilibrium to the sur-
Metal sulfide are important class of compounds that are being
studied due to the existence of different crystalline structures [1].
They are major group of minerals with various structural phases
with general formula MxSy [2,3]. They have unique electrical, mag-
netic and optical properties that make them useful in solar cells
[4], fuel cells [5], gas sensors [1] and laser devices [6]. Different
fabrication methods have been used to synthesized metal sulfide
nanoparticles [7], these include chemical vapour deposition [8,9],
hydrothermal [10,11], solvothermal [12,13] and thermal decompo-
sition of single source precursors [14–16]. Thermal decomposition
of single-source precursors (SSP) method has been explored for
the fabrication of metal sulfide nanoparticles especially from metal
dithiocarbamate complexes in appropriate capping agents [17].
The formation of nanoparticles through the thermal decom-
position method is influenced by the reaction conditions such as
the temperature, capping agents, thermolysis time, and the single
source precursor complexes. Research have shown that thermol-
ysis temperature influences the physical attributes of nanoparti-
cles such as shape, size, particle size distribution and crystallinity
[18,19]. Capping agents acts as protective surface atoms on the
face of the nanoparticles [20–24]. The capping agent bonds cova-
lently to surface metal atoms like a Lewis base and passivate the
nanoparticles [25,26]. Metal dithiocarbamate complexes are well-
known single-source precursors for the preparation of metal sul-
fide nanoparticle due to their facile synthesis and the ability to
modify their volatility and decomposition attributes based on the
amine substituents [27]. This synthetic method eliminates impuri-
ties as the metal is already coordinated to the sulfide atoms.
Palladium sulfide exist in various crystalline phases. Ehsan
et al. [28] prepared vysotskite structured PdS thin film with a
direct band gap of 1.56 eV from a palladium(II) dithiocarbamate
complex. Ajibade and Nqombolo [29] thermolyzed palladium(II)
imidazolyldithiocarbamate complex in hexadecylamine at 220 °C
to obtained PdS nanoparticles. The nanoparticles showed crys-
talline sizes ranging between 10.65 and 16.25 nm with an op-
tical band gap of 3.90 eV. The particle size of the nanoparti-
cles is influenced by the reaction parameters such as the dura-
tion of the reaction, thermolysis temperature and nature of the
precursor [25]. Variation of these reaction conditions influences
the crystalline phase and particle size of the nanoparticles. In this
work, bis(N-ethylphenyldithiocabamato)palladium(II) was synthe-
sized and characterized by elemental analysis, spectroscopic tech-
niques and single crystal X-ray crystallography. The compound was
∗
Corresponding author.
E-mail address: ajibadep@ukzn.ac.za (P.A. Ajibade).
https://doi.org/10.1016/j.molstruc.2021.130777
0022-2860/© 2021 Elsevier B.V. All rights reserved.

A.M. Paca and P.A. Ajibade
Journal of Molecular Structure 1243 (2021) 130777
Table 1
thermolyzed at three different temperatures to prepare palladium
sulfide nanoparticles and investigate the effect of decomposition
temperature on the optical and morphological properties of the as-
prepared PdS nanoparticles.
Summary
of
crystal
data
and
structure
refinement
for
bis(N-
ethylphenyldithicarbamato)palladium(II).
Identification code
Compound
Empirical formula
Formula weight (g/mol)
Temperature (K)
Wavelength
C18H20N2PdS2
499
2. Experimental
100(2)
1.54178
Monoclinic
P21/n
2.1. Reagents and solvents
Crystal system
Space group
˚
All chemicals and solvents were of analytical grades purchased
from Merck chemical and were used as obtained without fur-
ther purification. Chemicals and solvents used: N-ethylaniline,
aqueous ammonia, carbon disulphide, diethyl ether, palladium
nitrate dihydrate (Pd(NO3)2·2H2O), chloroform, dimethyl sulfox-
ide (DMSO), trioctylphosphine (TOP), octadecylamine (ODA) and
methanol. The 1H and 13C NMR spectra were recorded on Bruker
Biospin 600 MHz spectrometer. Samples were prepared in deuter-
ated water (D2O) and deuterated chloroform (CDCl3). Residual sig-
nals of D2O (δ = 4.79 ppm for 1H NMR) and CDCl3 (δ = 7.26 ppm
for 1H NMR and δ = 77.16 ppm for 13C NMR) were used as
the internal reference. Chemical shifts were reported in parts per
million (ppm). The spectra were processed using Bruker TopSpin
4.0.3 NMR prediction software. The FTIR spectra were recorded
by an Agilent Technologies Cary 630 FTIR spectrometer (4000 –
650 cm−1). Electronic spectra measured by a Perkin Elmer Lambda
25 spectrometer from 200 to 700 nm at room temperature. Pow-
der X-ray diffraction (pXRD) patterns were recorded by a Bruker
D8 advanced diffractometer using Cu Kα radiation. Samples were
mounted on a flat steel and scanned from 5 to 70°. Transmis-
sion electron microscopy (TEM) images were obtained from JEOL
−1400 electron microscope while high resolution transmission
electron microscopy (HRTEM) images were obtained from JEOL
HRTEM-2100. The nanoparticles were dispersed in distilled wa-
ter and dropped on carbon coated copper grid and evaporated
at room temperature. Scanning electron microscopy (SEM) images
were obtained by a ZEISS EVO LS 15 electron microscope. Elec-
tron dispersive X-ray spectroscopy (EDX) spectra were obtained by
ZEISS EVO LS 15 electron microscope. The nanoparticles were fixed
on aluminium studs by a double-sided carbon tape and coated
with gold. The ligand ammonium N-ethylphenyldithiocarbamate
was prepared as reported previously [30]
Unit cell dimensions (A)
˚
a (A)
7.3467(4)
90
α (°)
˚
b (A)
6.9378(3)
95.466(3)
19.7917(8)
90
β (°)
˚
c (A)
γ (°)
3
˚
Volume (A )
1004.19(8)
4
Z
Calculated density (Mg/m3)
Absorption coefficient (mm−1
F(000)
1.650
)
11.364
505
Crystal size (mm3)
0.370 × 0.060 × 0.050
Theta range for data collection (°)
Limiting indices
4.488 to 69.259
−8<=h<=8, −8<=k<=8, −23<=l<=23
1781 / 1781 [R(int) = ?]
96.8 %
Reflections collected / unique
Completeness to theta = 25.242 (%)
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
Refinement method
0.7530 and 0.3783
Full-matrix least-squares on F2
1781 / 0 / 117
Data / restraints / parameters
Goodness-of-fit on F2
1.179
Final R indices [I>2sigma(I)]
R indices (all data)
Largest diff. peak and hole (e.A3)
R1 = 0.0358, wR2 = 0.0833
R1 = 0.0392, wR2 = 0.0851
0.650 and −0.667
dimethyl sulfoxide (DMSO) at room temperature. A crystal with
dimensions 0.370 × 0.060 × 0.050 mm3 was isolated under oil
and fixed on a MITIGEN crystal mounter. The data was gathered
by a Bruker APEX-II CCD diffractometer fitted with an Oxford
Cryostems low temperature instrument, running at T = 100(2) K.
The structure was resolved by the She1XS-2013 software and
refined using She1XL 2016/6 version [31,32].
2.4. Synthesis of palladium sulfide nanoparticles
2.2. Synthesis of bis(N-ethylphenyldithiocarbamato)palladium(II)
Bis(N-ethylphenyldithicarbamato)palladium(II) (0.1 g) dispersed
in trioctylphosphine (TOP) (2 mL) was injected into 2 g of octyldec-
ulamine (ODA) stabilized at 160, 200 and 240 °C under nitrogen
flow and the reaction was maintained for 1 h. After, the reaction
was cooled down to about 65 °C and cold methanol was added.
The nanoparticles were separated by centrifugation, washed sev-
eral times with cold methanol and dried. The prepared nanoparti-
cles were labelled PdS1, PdS2 and PdS3 for nanoparticles prepared
at 160, 200 and 240 °C, respectively.
The Pd(II) precursor complex was prepared as pre-
sented in Scheme 1. In
a typical synthesis, ammonium N-
ethylphenyldithiocarbamate ligand (0.40 g, 1.88 mmol) dissolved
in distilled water (50 mL) was added to an aqueous solution
of Pd(NO3)2·2H2O (0.25 g, 0.94 mmol) with constant stirring. A
dusty orange precipitate formed immediately, and the reaction
was continued for 2 h. After which chloroform was added, two
phases (aqueous and organic) formed. The two phases were sep-
arated using a separating funnel. The aqueous phase was further
extracted with chloroform. The extracts were combined with the
organic phase and left to dry in open air. Yield: 27.05 %, Selected
3. Results and discussion
3.1. Molecular structure of
FTIR, v(cm−1): N–C (1469), C–S (1276), C S (989). 1H NMR (CDCl3,
=
bis(N-ethylphenyldithicarbamato)palladium(II)
ppm): 7.44–7.48(t, 2H), 7.40–7.242 (t, 1H), 7.21–7.24 (d, 2H), 4.04–
4.12 (d, 2H), 1.23–1.28 (t, 3H). 13C NMR (D2O, ppm): 127.63–139.95
(C6H5), 48.06 (-CH2-), 12.68 (-CH3), 213.42 (C-S). Anal. Calc. for
C18 H20N2PdS2: C, 49.71; H, 4.63; N, 6.44. Found: C, 49.33; H, 4.24;
N, 6.37.
Single crystals of bis(N-ethylphenyldithicarbamato)palladium(II)
suitable for X-ray crystallography were obtained by slow evapo-
ration of DMSO solution of the compound. The molecular struc-
ture of the complex is presented in Fig. 1 and the unit cell
packing diagram in Fig. S1. Crystallographic and refinement in-
formation are given in Table 1. Selected bond lengths and an-
gles are provided in Table 2. The crystal structure of bis(N-
ethylphenyldithicarbamato)palladium(II) is made up of two N-
ethylphenyldithiocarbamato anions bonded to a Pd(II) metal cen-
2.3. X-ray data collection
A single crystal of bis(N-ethylphenyldithicarbamato)palladium(II)
was obtained by slow evaporation of the compound solution in
2

A.M. Paca and P.A. Ajibade
Journal of Molecular Structure 1243 (2021) 130777
Scheme 1. Synthesis of N-ethylphenyldithiocarbamate ligand and bis(N-ethylphenyldithiocarbamato)palladium(II).
tre. The complex resides on a monoclinic P21/n site with four
molecules occupying the unit cell (Z = 4). The Pd(II) ion is coordi-
nated to four sulfur atoms from the two dithiocarbamate anions to
form a square planar geometry similar to other related compounds
in literature [33–36]. In the Pd(II) complex, Pd—S bond lengths
tion in comparison to the previous reported related compounds
with an average value of 75.28° for the cited complexes found
in literature [36,40–42]. The C–S bond lengths of 1.725(5) and
˚
1.719(5) A are intermediate between double and single bond sug-
gesting the resonance phenomenon in the CS2 moiety and compa-
rable to 109 related structures retrieved from CSD database [43–
˚
of 2.3173 and 2.3350 A and comparable to 55 related compounds
˚
found from the Cambridge Structural Database (CSD) records [37–
46]. The N(1)–C(1) bond distance of 1.317(6) A is very close to the
˚
39]. The S—Pd—S bond angle of 75.64(4)° show a slight devia-
mean value of 1.332 A recorded for 53 related compounds in the
Fig. 6.. FTIR spectra of ODA and the PdS nanoparticles prepared from different temperatures.
3

A.M. Paca and P.A. Ajibade
Journal of Molecular Structure 1243 (2021) 130777
Fig. 1.. Molecular structure of bis(N-ethylphenyldithicarbamato)palladium(II) showing 50 % probability displacement ellipsoid and atom labelling. The hydrogen atoms are
excluded for clearness.
Table 2
. In the FTIR spectrum of N-ethylphenyldithiocarbamate ligand, the
v(N–C) stretching frequency was observed at 1585 cm−1, v(C–S)
˚
Bond
lengths
(A)
and
angles
(°)
for
bis(N-
ethylphenyldithicarbamato)palladium(II).
at 1234 cm−1 and v(C S) at 988 cm−1. In the complex the v(C–
=
N) band shifted to 1588 cm−1. The CS2 groups also shifted to
higher frequencies. The presence of a single sharp v(C–S) band in
the spectrum of the complex implies that the ethylphenyldithio-
carbamato anions coordinated bidentately to the Pd(II) center [50].
The electronic spectrum of the ligand in water showed two
broad absorption bands with high intensity. The first band at
˚
Bond length (A)
Bond angles (°)
Pd(1) - S(1)#1
Pd(1) - S(1)
Pd(1) - S(2)#1
Pd(1) - S(2)
S(1) - C(1)
2.3173(12)
2.3173(12)
2.3350(11)
2.3349(11)
1.725(5)
S(1)#1-Pd(1)-S(1)
S(1)#1-Pd(1)-S(2)#1
S(1)-Pd(1)-S(2)#1
S(1)#1-Pd(1)-S(2)
S(1)-Pd(1)-S(2)
S(2)#1-Pd(1)-S(2)
C(1)-S(1)-Pd(1)
C(1)-S(2)-Pd(1)
N(1)-C(1)-S(1)
180.0
75.64(4)
104.36(4)
104.36(4)
75.64(4)
180.000
86.40(17)
85.96(15)
123.6(4)
124.5(4)
111.9(3)
121.7(4)
121.8(4)
S(2) - C(1)
1.719(5)
260 nm associated with the π → π∗ transitions of the N–C
S
=
N(1) - C(1)
N(1) - C(4)
N(1) - C(2)
1.317(6)
1.443(6)
of the dithiocarbamate moiety [51]. The second absorption band
1.483(6)
at 280 nm was ascribed to the π → π∗ transitions of the S–
N(1)-C(1)-S(2)
=
C
S moiety [52]. Another band with very low intensity was
S(1)-C(1)-S(2)
observed at about 453 nm, attributed to the n → π∗ transi-
tion located on the sulfur atom. The electronic absorption spec-
trum of bis(N-ethylphenyldithiocarbamato)palladium(II) complex
showed one strong broad band with an absorption maximum of
311 nm. This band was associated with the metal-to-ligand charge
transfer (M→LCT) transitions due to the coordination of the ligand
to the Pd(II). Since Pd(II) ion is a d8 configuration and all the elec-
trons are paired, therefore no D-d bands were visible.
C(1)-N(1)-C(4)
C(1)-N(1)-C(2)
CSD database [47,48]. This bond implies a partial double bond be-
haviour because of higher electron density anticipated upon coor-
dination, and delocalization of electron density in the dithiocar-
bamate moiety, as confirmed by FTIR and 13C NMR spectra. The
molecular structure of the compound is like the reported bis(N-
butylphenyldithicarbamato)palladium(II) [48].
The 1H NMR of N-ethylphenyldithiocarbamate ligand showed a
doublet at 7.27–7.29 ppm, a triplet at 7.42–7.43 ppm and a triplet
at 7.44–7.45 ppm of the phenyl ring. The quartet observed at 4.41
– 4.36 ppm was assigned to the hydrogen atoms of the ethyl group
and triplet at 1.28 – 1.24 ppm assign to methyl group. The 13C NMR
showed signals at 126.89–140.64 ppm attributed to the (C6H5) of
the phenyl group. The -CH2- carbon signal appeared at 53.21 ppm
and -CH3 signal was observed at 11.70 ppm. The signal due to the
C–S bond was observed at 210.85 ppm. Similar bonds were ob-
served when the ligand was coordinated to the Pd(II) ion to form
bis(N-ethylphenyldithicarbamato)palladium(II), except that a shift
to an upfield environment was observed for the protons of the
complex and the carbons shifted to a downfield environment. The
3.2. Spectroscopic studies
Dithiocarbamate ligands can be distinguished by the presence
of the NCS2 dithiocarbamate moiety. A strong absorption band in
the region 1450 – 1590 cm−1, is due to the v(C–N) (thioureide)
=
stretching vibrations of the N–C S system, the stretching vibra-
tions in the region 1150 – 1280 cm−1 is attributed to v(C–S) and
a single sharp vibrational band in the region 950 – 1050 cm−1
,
=
is ascribed to the v(C S) stretching vibration which denotes the
symmetrical bidentate coordination of the ligand through the sul-
fur atoms of the dithiocarbamate anions to the Pd(II) centre [40,49]
4

A.M. Paca and P.A. Ajibade
Journal of Molecular Structure 1243 (2021) 130777
Fig. 2.. Absorption spectra of PdS1, PdS2 and PdS3 (a), Tauc plot of PdS1 (b) and PdS2 and PdS3 (c) and emission spectra of PdS1, PdS2 and PdS3 (d) nanoparticles.
observed shift confirmed the successful coordination of the two
ligands to the metal ion.
the PdS nanoparticles appeared at lower wavelength (blue-shifted)
due to the quantum confinement influence of the nanoparticles
particle size in comparison to bulk PdS [54]. Tauc plots were used
to determine the optical band gap of the PdS nanoparticles where
(αhv)2 against hv was plotted. The optical band gap was obtained
by extrapolating the linear region of the plot to (αhv)2 = 0 as
shown in Fig. 2(b,c). The optical band gaps were found to be 4.90,
4.98 and 5.02 eV for PdS1, PdS2 and PdS3, respectively. Increase in
temperature resulted in slight increase in the band gap values. The
obtained optical band gap values were higher than the reported
values found in literature [55]. The increased band gap suggested
that the as-prepared PdS nanoparticles have small particle sizes,
and more atoms occupied the surface of the particles. The emis-
sion spectra are shown in Fig. 2(d). Broad emission maxima were
3.3. Optical studies of PdS nanoparticles
The optical properties of the as-prepared PdS nanoparticles
were studied by means of UV–Vis and photoluminescence spec-
troscopy. UV–Vis spectroscopy was used to observe the absorption
of the PdS nanoparticles in DMSO, which correlates with the elec-
tron excitation from the valence band to conduction band [53]. The
absorption spectra of the nanoparticles are illustrated in Fig. 2(a).
PdS1 showed no noticeable excitonic maximum. The spectra dis-
played band edges at 295, 258 and 264 nm for nanoparticles la-
belled PdS1, PdS2 and PdS3, respectively. The optical absorption for
5

A.M. Paca and P.A. Ajibade
Journal of Molecular Structure 1243 (2021) 130777
Fig. 3.. pXRD spectra of PdS nanoparticles prepared at different temperatures.
observed at 389, 390 and 388 nm for PdS1, PdS2 and PdS3, respec-
tively. These are red shifted with respect to their absorption band
edges. It was evident that variation of thermolysis temperature did
not show any noticeable effect on the emission spectra of the PdS
nanoparticles as the values obtained are almost equal.
3.4. Structural properties of PdS nanoparticles
3.4.1. Powder X-ray diffraction (pXRD) of PdS nanoparticles
Palladium sulfide exist in several crystalline phases such as PdS,
Pd3S, Pd4S, Pd16 S7 and PdS2 [28,56]. The pXRD patterns of the as-
6

A.M. Paca and P.A. Ajibade
Journal of Molecular Structure 1243 (2021) 130777
Fig. 4.. HRTEM images of (a) PdS1, (b) PdS2 and (c) PdS3 nanoparticles.
prepared PdS nanoparticles shown in Fig. 3 showed peaks at 22.94,
24.71, 42,60 and 47.00° which can be indexed to (100), (111), (102),
(013) and (200) planes of a tetrahedral-Pd4S crystalline phase. PdS2
nanoparticles showed diffraction patterns at 24.27, 27.27, 30.97,
41.86, 46.86 and 53.91° and can be indexed to (111), (002), (201),
(212), (200) and (132) lattice planes of a tetragonal-PdS phase
[57,58]. The diffraction patterns of PdS3 nanoparticles were ob-
served at 2θ values of 23.18, 24.74, 42.67, 42.67 and 46.89° which
correspond to (100), (211), (002), (013) and (200) lattice planes of a
Pd4S crystalline phase [59]. The peaks denoted with (∗) are due to
the octadecylamine capping agent [60]. The obtained phases sug-
gested that the decomposition temperature has an impact on the
crystalline phases of the as prepared PdS nanoparticles.
3.4.2. TEM images of the as-prepared PdS nanoparticles
HRTEM images of the nanoparticles are shown in Fig. 4 and the
TEM images are shown in Fig. S7. The PdS nanoparticles prepared
at 160 °C is spherical in shape with particle size in the range 2.01–
2.50 nm. The PdS nanoparticles prepared at 200 °C were clustered
together and spherical in shape with particle sizes ranging be-
7

A.M. Paca and P.A. Ajibade
Journal of Molecular Structure 1243 (2021) 130777
Fig. 5.. SEM images and EDS spectra of (a) PdS1, (b) PdS2 and (c) PdS3.
tween 4.00and4.86 nm. The PdS prepared at 240 °C were unevenly
distributed with particle sizes ranging between 2.53and4.12 nm.
The results show that the nanoparticles increased in size when
the temperature was raised from 160 to 200 °C, but at a higher
temperature, uniform particles were obtained. When the tempera-
ture was raised to 240 °C, a mixture of small and large particles
was obtained. It is evident that better nanoparticles are obtained
at 200 °C.
SEM images and EDS spectra of PdS1, PdS2 and PdS3 nanoparti-
cles are shown in Fig. 5. The nanoparticles were imaged at 20 μm.
PdS1 nanoparticles prepared at 160 °C (Fig. 5(a)) showed flake-
like surface morphology with no uniform pattern. PdS2 nanopar-
ticles (Fig. 5(b)) also showed flake-like surface morphology but
were more pronounced than PdS1 nanoparticles. PdS3 nanoparti-
cles shown in Fig. 5(c) exhibited rough sweet thorn-like surface
morphology. The smooth dark surfaces were due to the carbon
tape used to fix the nanoparticles on the studs. The modifica-
tions noted on the surface morphologies of the as-prepared PdS
nanoparticles implies that the decomposition temperature influ-
ence the formation of the nanoparticles resulting in the nanopar-
ticles with different morphologies. The EDS spectra showed the
Pd and S atoms, confirming the successful fabrication of the PdS
nanoparticles. The C and O atoms were from the capping agent and
the double-sided carbon tape. And the Au atom was from the gold
that was used to coat the nanoparticles for imaging [61].
3.5. FTIR studies of the PdS nanoparticles
FTIR spectra of octadecylamine (ODA) and the ODA capped PdS
nanoparticles are shown in Fig. 6. The PdS nanoparticles spectra
were compared with that of pure ODA spectrum. The spectra have
few distinctions confirming the interaction of the PdS nanoparti-
cles with the capping agent. Of note is the three absorption bands
at 3326, 3248 and 3166 cm−1 observed in the spectrum of ODA
ascribed to v(N–H) stretching vibrations [62,63]. These bands were
not evident in the spectra of the PdS nanoparticles, suggesting that
the capping of the nanoparticles occurred through the -NH2 group
of ODA capping agent. The variation of the stretching vibrations in-
tensities from the PdS nanoparticles spectra signifies that nanopar-
ticles prepared at different temperatures interact differently with
the capping agent. The nanoparticles prepared at 160 and 200 °C
exhibited low intensity and those at 240 °C showed high intensity.
The high intensity observed in the PdS3 spectrum might be due
to the random size distribution of the nanoparticles compared to
that of PdS1 and PdS2 which showed uniform size distribution as
shown in the TEM images (Fig. 4).
8

A.M. Paca and P.A. Ajibade
Journal of Molecular Structure 1243 (2021) 130777
4. Conclusion
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In this study, bis-(N-ethylphenyldithiocarbamato)palladium(II)
was synthesized and characterized using elemental analysis,
spectroscopic techniques and single crystal X-ray crystallogra-
phy. The compound crystallized in
a monoclinic space group
P21/n in which the Pd(II) ion coordinate two molecules of N-
ethylphenyldithiocarbamato anions to form a distorted square pla-
nar geometry. The complex was thermolyzed in octadecylamine
(ODA) at 160, 200 and 240 °C to prepared ODA capped PdS
nanoparticles and investigate the influence of thermolysis tem-
perature on the morphological and optical properties of the PdS
nanoparticles. Tetrahedral-Pd4S crystalline phases were obtained
for nanoparticles prepared at 160 and 240 °C, whereas tetragonal-
PdS phase was obtained for PdS nanoparticles prepared at 200 °C.
pXRD patterns of the as-prepared nanoparticles proved that differ-
ent crystalline phases were obtained by varying the temperature.
The surface morphology of the as-prepared nanoparticles was in-
vestigated by TEM/HRTEM and SEM/ EDS. The TEM/HRTEM analy-
sis revealed PdS1 nanoparticles are spherically shaped with some
particles agglomerated to larger particles with particle sizes rang-
ing between 2.01 and 2.50 nm. PdS2 nanoparticles were monodis-
persed spherically shaped with sizes of 4.00–4.86 nm. The PdS3
were randomly distributed with particle sizes of 2.53–4.12 nm.
SEM micrographs of PdS1, PdS2 and PdS3 nanoparticles revealed
that the thermolysis temperature plays a role on the surface mor-
phology of the nanoparticles. Absorption and emission studies in-
dicates that thermolysis temperature influence the energy band
gap of the as-prepared PdS nanoparticles but does not have any
significant effect on the emission properties of the PdS nanoparti-
cles. A red shift was observed in the emission spectra in compari-
son to the absorption spectra. FTIR spectra study showed that PdS
nanoparticles were stabilized with the ODA capping agent through
the nitrogen atoms of the capping agent.
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Declaration of Competing Interest
[19] P.A. Ajibade, J.Z. Mbese, B. Omondi, Group 12 dithiocarbamate complexes: syn-
thesis, characterization and X-ray crystal structures of Zn(II) and Hg(II) com-
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capping agent in nanocatalysis: recent advances and perspectives, Catalysts 6
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The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
CRediT authorship contribution statement
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Athandwe M. Paca: Data curtion, Formal analysis, Writing –
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Acknowledgments
The authors acknowledge the award of research grant by Na-
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Supplementary materials
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mage, Z. Arifin, M. Mazhar, Vysotskite structured photoactive palladium sul-
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4083–4091.
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.130777.
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