Synthesis and crystal structure of bis(morpholino dithiocarbamato) Cd(II) complex and its use as precursor for CdS quantum dots using different capping agents

Article abstract of DOI:10.1080/17415993.2019.1637876

Cadmium(II) morpholine dithiocarbamate complex [Cd(morphdtc)₂] was synthesized and characterized by single crystal X-ray crystallography. The molecular structure of the complex showed Cd(II) ion in a distorted 4 + 2 octahedral geometry, in which the two morpholine dithiocarbamates act as bidentate chelating and the central Cd ion bond the sulfur atoms of adjacent morpholine acting as bridging ligands to form centrosymmetric five coordinate dimeric molecules. The Cd(II) complex was thermolysed at 180°C to prepare CdS nanoparticles using three different capping agents. The pXRD patterns revealed a mixture of hexagonal and cubic crystalline phases of CdS nanocrystals. TEM images revealed semi-spherical and spherical nanoparticles, with the size range of 4.50–5.70 nm for OLM-CdS, 3.33–5.96 nm for HDA-CdS, and 3.00–5.83 nm for ODA-CdS. The particle size distribution of the CdS nanocrystallite is within the range 1.06 nm (SD ± 0.73) for OLM-CdS, 0.68 nm, (SD ±0.73) for HDA-CdS and 1.18 nm, (SD ± 0.60) for ODA-CdS. The lattice fringes showed that the particles are almost in the same environment with the interplanar of 0.32 nm for OLM-CdS, 0.34 nm for HDA-CdS, and 0.32 nm ODA-CdS. The band gaps energy were confirmed to be 1.59 eV for OLM-CdS, 1.65 eV for HDA-CdS, and 1.62 eV for ODA-CdS nanoparticles, respectively.

Full text of DOI:10.1080/17415993.2019.1637876

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: https://www.tandfonline.com/loi/gsrp20
Synthesis and crystal structure of bis(morpholino
dithiocarbamato) Cd(II) complex and its use as
precursor for CdS quantum dots using different
capping agents
Lebogang L. R. Mphahlele & Peter A. Ajibade
To cite this article: Lebogang L. R. Mphahlele & Peter A. Ajibade (2019): Synthesis and
crystal structure of bis(morpholino dithiocarbamato) Cd(II) complex and its use as precursor
for CdS quantum dots using different capping agents, Journal of Sulfur Chemistry, DOI:
10.1080/17415993.2019.1637876
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JOURNAL OF SULFUR CHEMISTRY
https://doi.org/10.1080/17415993.2019.1637876
Synthesis and crystal structure of bis(morpholino
dithiocarbamato) Cd(II) complex and its use as precursor for
CdS quantum dots using different capping agents
Lebogang L. R. Mphahlele and Peter A. Ajibade
School of Chemistry and Physics, University of KwaZulu-Natal, Scottsville, Pietermaritzburg, South Africa
ABSTRACT
ARTICLE HISTORY
Cadmium(II)morpholinedithiocarbamatecomplex[Cd(morphdtc)2]
was synthesized and characterized by single crystal X-ray crystal-
lography. The molecular structure of the complex showed Cd(II)
ion in a distorted 4 + 2 octahedral geometry, in which the two
morpholine dithiocarbamates act as bidentate chelating and the
central Cd ion bond the sulfur atoms of adjacent morpholine
acting as bridging ligands to form centrosymmetric five coordi-
nate dimeric molecules. The Cd(II) complex was thermolysed at
Received 24 April 2019
Accepted 20 June 2019
KEYWORDS
Dithiocarbamates; Cd(II);
crystal structure; CdS;
quantum dots
1
80°C to prepare CdS nanoparticles using three different cap-
ping agents. The pXRD patterns revealed a mixture of hexago-
nal and cubic crystalline phases of CdS nanocrystals. TEM images
revealed semi-spherical and spherical nanoparticles, with the size
range of 4.50–5.70 nm for OLM-CdS, 3.33–5.96 nm for HDA-CdS,
and 3.00–5.83 nm for ODA-CdS. The particle size distribution of
the CdS nanocrystallite is within the range 1.06 nm (SD ± 0.73) for
OLM-CdS, 0.68 nm, (SD ± 0.73) for HDA-CdS and 1.18 nm, (SD ± 0.60)
for ODA-CdS. The lattice fringes showed that the particles are
almost in the same environment with the interplanar of 0.32 nm for
OLM-CdS, 0.34 nm for HDA-CdS, and 0.32 nm ODA-CdS. The band
gaps energy were confirmed to be 1.59 eV for OLM-CdS, 1.65 eV
for HDA-CdS, and 1.62 eV for ODA-CdS nanoparticles, respectively.
CONTACT Peter A. Ajibade
ajibadep@ukzn.ac.za
School of Chemistry and Physics, University of
KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa
This article makes reference to supplementary material available on the publisher’s website at https://doi.org/10.1080/
7415993.2019.1637876.
1
©
2019 Informa UK Limited, trading as Taylor & Francis Group

2
L. L. R. MPHAHLELE AND P. A. AJIBADE
1. Introduction
−
2
−
Dithiocarbamates (R NCS or RNHCS2 ) are half amides which belong to a class of
2
monoanionic compounds known as 1,1-dithiolate that includes the dithiophosphates,
dithiophosphinates, dithiocarbamates, etc. [1,2]. Dithiocarbamates are versatile ligands
and bind metal ions as monodentate or bidentate chelating ligands [3,4], and have attracted
interest due to their rich and varied coordination geometries [5,6]. Dithiocarbamates
stabilizes transition metals with varied oxidation states and can stabilize the metal cen-
ter in an extraordinarily high apparent formal oxidation states [7,8], due to vacant dπ
orbitals on the sulfur atom of the dithiocarbamates moiety. They can also form mul-
tiple π-bonds and additional π-electrons which can flow from nitrogen to sulfur via
a planar delocalized π-orbital system, making dithiocarbamates strong electron donors
[
7]. Cadmium(II) dithiocarbamate complexes continued to draw attention, due to poten-
tial industrial applications [9]. Dithiocarbamates complexes constitute one of the most
promising species to provide the single-source precursor for the preparation of metal

JOURNAL OF SULFUR CHEMISTRY
3
sulfidessulfides [7,10]. Single-source molecular precursor (SSP) technique has been shown
to be versatile and a practical efficient route for the preparation of crystalline semicon-
ductor (quantum dots) [11–13], which has also proven to be an effective route for better
quality, crystalline monodispersed quantum dots (QDs) of semiconducting metal chalco-
genide [14,15]. The use of capping agents in the preparation of quantum dots offers size
stabilization and reduce reaction time [16–20]. Even though this type of technique gives
a way for better control of quantum dots synthesis, quantum dots are stabilized from
aggregation by addition of the capping agents as well, where the growth is hindered,
resulting in high-quality form and also modify its structure, morphology and enhances
their optical properties [21]. Trindade and O’ Brien studied the use of cadmium dithio-
and diselenocarbamate complexes as precursors for the synthesis of tri-n-octylphosphine
oxide/ tri-n-octylphosphine (TOPO/TOP)-capped CdS semiconductor nanoparticles [11]
Ajibade et al. reported the use of Cd(II) complex of N-alkyl-N-phenyl dithiocarbamate
for the synthesis hexadecylamine (HDA)-capped CdS semiconductor nanoparticles which
showed rods, tripods, and tetrapods [16]. Pawar et al. themolysed nanoparticles using
oleylamine/ tri-n-octylphosphine (OLM/TOP) as a capping agent and Cd(II) thiosemi-
carbazone which resulted in particles that are less than 10 nm in size [22]. In this study, we
present the synthesis and crystal structure of Cd(II) morpholine dithiocarbamate complex
and its use as a precursor to prepare CdS nanoparticles using oleylamine (OLM), hex-
adecylamine (HDA), and octadecylamine (ODA). The optical and structural properties
of the CdS nanoparticles were studied using Ultraviolet–Visible (UV–Vis), Photolu-
minescence (PL), powder X-ray diffraction (pXRD) high-resolution transmission elec-
tron microscopy (HRTEM), transmission electron microscopy (TEM), scanning electron
microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Fourier Transform
Infrared Spectroscopy (FTIR).
2. Experimental
2
.1. Material and physical characterization
All reagents and chemicals were of analytical grade and used without further purifica-
tion. Methanol, acetone, dimethyl sulfoxide, diethyl ether, morpholine, sodium hydrox-
ide, carbon disulfide, cadmium nitrate tetrahydrate, oleic acid (OA), octadecylamine
(
ODA), hexadecylamine (HDA), oleylamine (OLM). FTIR spectra were recorded on a
−
1
Carry 630 FTIR spectrometer using the range of 500–45,000 cm . Bruker ultra-shield
00 NMR spectrometer was used to determine the number of protons and carbons in
4
each compound at 400.1 MHz for 1H and 100.6 MHz for 13C nuclei. Elemental anal-
ysis was carried out using Thermo scientific Flash 2000. UV–vis spectra for the com-
pounds were obtained from PerkinElmer Lambda UV–VIS Spectrometer. P-XRD was
obtained Philips PW1830 X-Ray Diffraction Spectrometer X-ray Diffractometer (XRD).
JEOL HRTEM 2100 was used for imaging and pattern diffraction of the nanoparticles.
TEM images were captured using Joel 1400 Transmission Electron Microscope. SEM
and EDS images were obtained from ZEISS EVO LS 15 Scanning Electron Microscope.
Photoluminescence measurements were obtained from Perkin Elmer LS 45 fluorescence
spectrometer. The compounds were prepared as shown in Scheme 1.

4
L. L. R. MPHAHLELE AND P. A. AJIBADE
Scheme 1. Synthesis of morpholine dithiocarbamate ligand and Cd(II) dithiocarbamate complex.
2.2. Synthesis of dithiocarbamate (DTC) ligand and its Cd(II) complex
2.2.1. Synthesis of the sodium salt of morpholine dithiocarbamate ligand
The sodium salt of morpholine DTC ligand and Cd(II) DTC complex were synthesized
following a known procedure [23–26]. Sodium hydroxide (2.0 g, 0.05 mol) was dissolved
in 2 mL of distilled water and allowed to attain an ice temperature. This was followed by the
addition of morpholine (4.356 mL, 0.05 mol) and stirred for 5 min, after which cold carbon
disulfide (3.021 mL, 0.05 mol) was added dropwise for over 5 min. The mixture was stirred
for 4 h while keeping the temperature between 0°C and 4°C. The product was then fil-
tered and washed with diethyl ether and dried under vacuum [24,27]. Yield: 8.441 g (91%),
−
1
1
M.P: 202.3°C. FTIR (KBr, cm ): 1413 (νC–N), 1115 (νC=S), 939 (νC–S). H NMR (400
MHZ, D2O-d6): δ (ppm) = CH-protons 3.83–3.86 (t, 4H), CH-protons 4.45–4.47 (t, 4H)
1
3
ppm. C NMR (400 MHz, D2O-d6) δ (ppm): C -51.25 (C–H), C -65.98 (C–H), C -209.22
a
b
c
(
C–N). Anal. Calc. for [C H NOS –]: C, 29.83; H, 4.01; N, 6.96; S, 31.85. Found: C, 29.25;
5 8 2
H, 5.723; N, 6.94; S, 26.63.
2.2.2. Synthesis of cadmium(II)morpholine dithiocarbamate complex
Cadmium(II) morpholine dithiocarbamate complex was prepared by adding an aqueous
solution of the sodium salt of morpholine dithiocarbamate (3.705 g, 0.02 mol) to an aque-
ous solution of Cd(NO ) ·4H O (2.364 g, 0.01 mol), and stirred for 5 h. The precipitate was
3
2
2
formed, filtered and washed several times with distilled water and diethyl ether then dried
−
1
under vacuum [28]. Yield 5.179 g (88%), M.P: 326.6°C. FTIR (KBr, cm ): 1426 (νC-N),
1
9
80 (νC-S). H NMR (400 MHZ, DMSO-d6): δ (ppm) = CH– protons 3.64–3.66 (t, 8H),
1
3
CH– protons 4.07–4.09 (t, 8H) ppm. C NMR (400 MHz, DMSO-d6) δ (ppm): C -52.55
a
(
C–H), C -66.10 (C–H), C -205.65 (C–N). Anal. Calc. for [C10H16CdN2O2S4]: C, 27.49;
b
c
H, 3.69; N, 6.41; S, 29.35. Found: C, 27.36; H, 3.56; N, 6.32; S, 25.54.
2.2.3. X-ray crystallography
Single orange block-shaped crystals of bis(morpholino dithiocarbamato) Cd(II) complex
[
0
C H CdN O S ] were recrystallized from DCM by slow evaporation. A suitable crystal
.35 × 0.18 × 0.11 mm was selected and mounted on a MITIGEN holder in paratone oil
10 16 2 2 4
on a Bruker SMART APEX2 area detector diffractometer. The crystal was kept at a steady

JOURNAL OF SULFUR CHEMISTRY
5
T = 100(2) K during data collection. The structure was solved to be P21/n space group
with the ShelXS-2013 [29] structure solution program using the solution method and by
using Olex2 [30] as the graphical interface. The model was refined with version 2016/6 of
ShelXL [30,31] using Least Squares minimization.
2.2.4. Preparation of CdS nanoparticles
Cadmium sulfide nanoparticles were prepared using the bis(morpholino dithiocarbam-
ato) Cd(II) complex as a single-source precursor. 250 mg of the complex was dispersed in
oleic acid (6 mL) as a surfactant, which was then injected into three-necked flask charged
with hot octadecylamine (ODA), or hexadecylamine (HDA), or oleylamine (OLM) (3.00 g)
as capping agents. The resulting mixture was refluxed for 1 h under the inert atmosphere
with 400 rp, the temperature was maintained at 180°C. The product was cooled to 70°C,
and about 25 mL of methanol was used to wash off excess capping agent. The resulting pre-
cipitate was separated by centrifugation at 2000 rpm for 30 min and the supernatant was
discarded. The washing process was repeated thrice [22].
3. Results and discussion
3
.1. Molecular structure of the Cd(II) morpholine dithiocarbamate complex
The crystallographic and measurement data depicted in Table 1 and Figure 1 shows the
ellipsoid representations of the complex, respectively. Selected bond length and angles are
presented in Table 2. The structure indicates that the cadmium(II) complex at 100(2)k has
a monoclinic (P21/n) space group Z = 2. The planarity of the MS CNC is the important
2
2
aspect in metal dithiocarbamate complex. The complex contains Cd center with coordi-
nation sphere in which the binuclear Cd complex resides on a crystallographic inversion
center and each Cd atoms is coordinated to six sulfurs atoms as a result of the Cd-S sec-
ondary bond to give the geometry around the Cd(II) ions distorted octahedral geometry
[
32]. The molecular structure is an unusual linear coordinated polymer of the Cd(II) where
one morpholine ligand chelates one cadmium atom and simultaneously bridges the second
centro symmetrically related cadmium atom, which has just been reported for a Cd(II)
complex. This results in a chair conformation of the morpholine moiety.
The single crystal X-ray structure of [C H CdN O S ] showed that the Cd(II) ion
1
0
16
2
2 4
is in a distorted 4 + 2 octahedral environment. The distortion of the regular octahedron
geometry is mainly due to the small bite angles of the two morpholinyl dithiocarbamate lig-
ands [32], whose S1–Cd1–S2 gives [69.467(18)] and S11–Cd1–S21 with a chelate angle of
[
69.468(18)], respectively. These angles deviate prominently from the normal 90° expected
for a regular octahedral. The deviation produces bond angles that are different from the
expected. Other Cd–S bond angles such as S21–Cd1–S1 [110.532(18)] and S2–Cd1–S11
[
110.533(18)] are less than 120° which indicates that the atoms in equatorial positions.
The bridging S1 atom forms the longest of the Cd–S bond lengths in the structure at
2
2
.6213(6) Å, for the bridging bond. The Cd–S2 bond is shorter with the bond length of
.6130(6) Å due to the double bond [33]. The C–N is the shortest bond length of 1.325(3) Å
compared to the C–N bond on the ring with bond length of 1.472(3) Å due to the delocal-
ization of the electrons in the dithiocarbamate moiety caused by the ligands bonding the
2
+
Cd ion.

6
L. L. R. MPHAHLELE AND P. A. AJIBADE
Table 1. Summarized data of [C10H16CdN2O2S4] crys-
tal structure.
Formula
C10H16CdN2O2S4
Dcalc. (g cm 3)
−
2.033
2.112
−
1
μ (mm
)
Formula weight
Colour
436.89
orange
block
Shape
Size (mm )
3
0.35 × 0.18 × 0.11
100(2)
monoclinic
P21/n
T (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
4.2194(3)
11.4233(8)
14.8265(11)
90
α (°)
β (°)
92.955(3)
90
713.68(9)
2
γ (°)
3
V (Å )
Z
Z
ꢀ
0.5
Wavelength (Å)
Radiation type
0.71073
MoKα
ꢀ
ꢀ
min (°)
max (°)
2.252
28.436
1796
1796
1619
0.0467
88
0
Measured Refl.
Independent Refl.
Reflections with I > 2(I)
Rint
Parameters
Restraints
Largest peak
Deepest hole
GooF
0.563
−1.151
1.047
wR2 (all data)
wR2
R1 (all data)
R1
0.0623
0.0592
0.0314
0.0253
3
.2. FTIR spectral studies
FTIR spectrum of the free ligand and the metal complex were compared and assigned.
Normally, FTIR spectra of dithiocarbamates compounds have three main characteristic
stretching vibrations. The thioureide ν(C–N) stretching vibrations of the ligand appeared
at the fingerprint region, the mode of this vibration in relation to CN stretching frequency
band conformed to the fact that the bond assumes a double bond character. This band was
−
1
−1
observed at 1413 cm in the ligand and shifted to 1426 cm in the Cd(II) due to elec-
tron delocalization on the metal ion, which gives the complex higher frequency compared
to that of the ligand [34]. The change in geometry has affected the extent of interaction
between the DTC and the cadmium ion which resulted in the reduction of ν(C–N) stretch-
ing vibrations. The ν(C–S) which is primarily a strong band of the ligands appeared at
−
1
the region of 880–915 cm as two bands for both asymmetric and symmetric vibrations
due to the bidentate form of the ligand, and the stretching vibration band for the complex
−
1
appeared at 980 cm as a single pronounced band. A single band in this region indicates
complete symmetrical coordination of the DTC moiety to the metal center [35].

JOURNAL OF SULFUR CHEMISTRY
7
Figure 1. The molecular structure of bis(morpholino dithiocarbamato) Cd(II) complex
C10H16CdN2O2S4].
[
Table 2. Selected bond length (Å) and bond angle (°) of [C10H16CdN2O2S4].
Bond length (Å)
Bond angle (°)
Cd1–S1
Cd1–S11
Cd1–S21
Cd1–S2
S1–C1
S2–C1
N1–C1
N1–C2
2.6213(6)
2.6213(6)
2.6130(6)
2.6130(6)
1.745(2)
1.724(2)
1.325(3)
1.474(3)
S11–Cd1–S1
S2–Cd1–S11
S2–Cd1–S1
S21–Cd1–S11
S21–Cd1–S1
S21–Cd1–S2
C1–S1–Cd1
C1–S2–Cd1
C1–N1–C2
180.00(2)
110.533(18)
69.467(18)
69.468(18)
110.532(18)
180.00(2)
85.01(8)
85.67(8)
122.8(2)
C1–N1–C5
123.2(2)
C5–N1–C2
113.14(19)
3.3. Nuclear magnetic resonance (NMR) spectral studies
1
The H NMR spectrum of morpholine dithiocarbamate ligand revealed a peak at 3.88 ppm
that is due to N–CH . The second peak appeared at 4.45 ppm, which is for O–CH . The
2
2
1
3
last peak is at 4.8 ppm, which is a deuterated water peak. C NMR shows NCS peak at
2
09.22 ppm, the second peak appeared at 65.98 ppm for O–CH and the last peak appeared
2
1
at 51.25 ppm for N–CH . In the H NMR spectrum of the complex, N–CH appeared as
2
2
a triplet around 3.66 ppm and O–CH as a triplet around 4.03 ppm, respectively. The two
2
peaks are due to solvent, the peak at 2.52 ppm is for the solvent used for the analysis which
is DMSO d6 and the other peak at 3.26 ppm which is for the solvent used in the preparation
of the complex and the solvent used analysis. 13C NMR revealed C–S peak at 204.65 ppm,

8
L. L. R. MPHAHLELE AND P. A. AJIBADE
N–CH peak at 52.55 ppm and O–CH peak at 66.10 ppm [35].The peaks are down shifted
2
2
as a result of the coordination to the metal center.
3
.4. Structural studies of the CdS nanoparticles
3.4.1. Powder X-ray diffraction (pXRD) studies of CdS quantum dots
Structural identification of CdS nanoparticles was carried out using powder X-ray diffrac-
tion. The pXRD patterns of OLM, HDA, and ODA capped CdS nanoparticles are presented
in Figure 2. The observed peaks are widened, which indicate that the crystallite sizes of the
CdS nanoparticles are small. The diffraction patterns of the OLM-capped CdS nanoparticle
corresponded to (100), (002), (101), (102), (110), (103), (112), and (203) planes which cor-
respond to 23°, 26°, 27°, 33°, 51°, 56°, 60°, and 61°, which can be indexed to the hexagonal
phase of CdS nanoparticles in the crystal system, which exactly matched with the reference
code: [00-001-0780] [36]. The peaks of the HDA-capped CdS nanoparticle corresponded
to (100), (002), (101), (102), (110), (103), (112), and (203) planes which corresponds to 23°,
2
6°, 28°, 33°, 43°, 47°, 51°, and 60°, which resembles the hexagonal structure. The XRD
patterns of ODA- capped nanoparticles indicates that the (002) of the hexagonal peak is
missing, thus the nanoparticles are mixture of both cubic and hexagonal structure. The
pXRD peaks intensity is known to decrease and the width increases with decreasing crys-
talline size and there are no peaks corresponding to impurities in any of the as-prepared
CdS nanoparticles [37].
3.4.2. Morphological studies (TEM) of as-prepared CdS quantum dots
TEM images, lattice fringes, and selected-area electron diffraction (SAED) patterns of
OLM, HDA, and ODA-capped CdS nanoparticles are presented in Figure 3 and their par-
ticle size distributions are presented in Figure 4. The TEM image of OLM-capped CdS
(Figure 3(a)) nanoparticles shows a mixture of semi-spherical and spherical particles in
shapes, with uniform size distributions which range from 4.50 to 5.70 nm [38]. The lat-
tice fringes are shown in Figure 3(b) revealed that the nanoparticles are polycrystalline,
which are randomly distributed (0.90 nm) as shown in Figure 4(a) with an interplanar
distance of 0.32 nm. The SAED pattern presented in Figure 3(c) denotes that the nanopar-
ticles are polynanocrystalline in nature due to small spots making up a ring, each spot
arising from Bragg reflection from an individual crystallite. CdS nanoparticles obtained
from HDA-capped CdS shown in Figure 3(d) displayed close to monodispersed nanopar-
ticles which have more particles compared to those prepared using OLM. The particles
are spherical and their size ranges from 3.33 to 5.96 nm. The small size is ascribed to the
quantum confinement effect, the lattice fringes in Figure 3(e) revealed that the particles
are nanopolycrystalline, with a random distribution (5.250 nm) as shown in Figure 4(b)
and its interplanar distance is (0.34 nm). SAED shown in Figure 3(f) displayed the diffrac-
tion pattern of nanocrystalline particles which forms a ring pattern without bright spots.
There is a lot of speckle contrast blurring the contrast of the image since it has an amor-
phous layer at the top and bottom from the excess capping agent leading to diminishes
contrast of the lattice fringes. Nanoparticles, which are displayed in Figure 3(g) containing
ODA capped CdS showed little agglomeration and mixture of semi-spherical and spherical
nanoparticles, it has fewer particles compared to the one of HDA capped CdS and more
particles compared to the one of OLM) indicted its dom distribution (4.967 nm) as shown

JOURNAL OF SULFUR CHEMISTRY
9
Figure 2. XRD diffraction pattern of CdS nanoparticles with different capping agent.
in Figure 3(c) nanocrystalline particles with the interplanar distance of (0.32 nm). SAED
in Figure 3(i) displayed well-diffracted pattern, which is due to small spots that form rings
ascribed to the Bragg reflections from the individual crystallite. All the capping agent result
in quantum dots with the particle size less than 10 nm.

10
L. L. R. MPHAHLELE AND P. A. AJIBADE
Figure 3. TEM images, lattice fringes and SAED of OLM, HDA and ODA capped CdS nanoparticles.
3
.4.3. SEM and EDS studies of the CdS nanoparticles
The Scanning Electron Microscopy (SEM) images and Energy Dispersive Spectroscopy
EDS) were employed to study morphology and elemental composition of the as-prepared
(

JOURNAL OF SULFUR CHEMISTRY
11
(a)
(b)
(c)
Figure 4. Size distribution of as-prepared CdS nanoparticles.
CdS nanoparticles revealed that the morphology of OLM capped nanoparticles appeared
to be lumpy although it shows a smooth surface of the particles that does not have any
form of arrangement. SEM micrograph of HDA capped nanoparticles shows concrete mix-
ture like surface with different part of the particles whereas in ODA capped nanoparticles
showed stone-like morphology that are composed of triangular and semi-spherical shapes,
which have rough surface compared to those of OLM capped CdS. The EDS spectra of the
CdS nanoparticles confirmed the elemental composition of the CdS nanocrystals as well as

12
L. L. R. MPHAHLELE AND P. A. AJIBADE
OLM
HDA
ODA
1
10
00
1
9
0
0
0
0
0
0
0
8
7
6
5
4
3
-
1
wavenumber(cm )
Figure 5. FTIR spectra of (OLM, HDA, and ODA) capped as-prepared CdS nanoparticles.
those of the capping agents. There are an aluminum traces which displayed on the spectrum
due to the sputter-coater [39].
3.4.4. FTIR spectra studies of the CdS nanoparticles
FTIR spectra of OLM, HDA and ODA cadmium sulfide nanoparticles (Figure 5). The FTIR
−
1
spectra were obtained in the region between 4000 and 500 cm . All the spectrum shown
similar fatures which are ascribed to the capping agents as well as the surfactant [13]. The
−1
prominent band observed at 3336 cm of the nanoparticles are ascribed to v(N–H) from
the capping agents (OLM, HDA, and ODA). This shows that the CdS quantum dots are
capped via interaction of the –NH group of the capping agents adsorbed on the sur-
2
−
1
faces of the nanoparticles. The absorption band observed at 2920–2853 cm are due to
v(C–H) which arise because of the (oleic acid) surfactant used. The other important bands
−1
at 1456–1533 cm are attributed to v(C=O) from the carboxylic group of oleic acid (OA).
The vibrational frequencies of the surfactants are in the same region with the ones of the
capping agents, thus the surfactant can serve both its purpose and that of the capping
agents. The significant changes observed in the fingerprint region of the nanoparticles
spectra ascribed to interaction of surfactant and capping agents used. Hence the existences
of the above-mentioned bands identify the presence of CdS [40].
3
.5. Optical studies of CdS nanoparticles
3.5.1. Absorption and photoluminescence spectra studies of (OLM, HDA, and ODA)
capped CdS nanoparticle
Optical studies of the CdS nanoparticles were investigated by means of UV–Vis and pho-
toluminescence spectroscopy. The absorption spectra of the CdS nanoparticles presented
in Figure 6(a) displayed maximum peaks at about 250 nm with the absorbance of 0.823,
0
.562, and 0.551 a.u for HAD-CdS, OLM-CdS, and ODA-CdS, respectively. The absorp-
tion band edges were used to determine the band gaps energy of the CdS nanoparticles
41]. The sharp excitonic absorption peaks indicate narrow size distribution of the parti-
[
cles in the nanoparticles [42] The optical band gap of the cadmium sulfide nanoparticles
was determined using the Tauc plot shown in Figure 6(b), which were found to be 1.59 eV

JOURNAL OF SULFUR CHEMISTRY
13
Figure 6. Absorption (a), tauc plot (b) and emission (c) spectra of cadmium sulfide nanoparticles at
80°C.
1
for OLM-CdS, 1.65 eV for HDA-CdS, and 1.62 eV for ODA-CdS, respectively. These were
found to be blue-shifted compared to the bulk CdS [43]. The blue shift occurs due to strong
quantum confinement caused by a decrease in the CdS nanoparticles of nanocrystallite size.
The emission spectra Figure 6(c) displayed maxima at 421, 351, and 334 nm for ODA-CdS,
HDA-CdS, and OLM-CdS, respectively. The emission maxima for ODA capped CdS was
found to be higher compared to those which are obtained from HDA and OLM capped

14
L. L. R. MPHAHLELE AND P. A. AJIBADE
nanoparticles, which shows that the capping agent plays a significant role in the decompo-
sition of the compound and the formation of the nanoparticles. The emission maxima were
found to be red-shifted in comparison to the optical absorption band edges. Sizes and the
increase in band gaps with the decrease in particle sizes are due to quantum confinement
effects in the nanoparticles [44].
4. Conclusion
Bis(morpholino dithiocarbamato) Cd(II) complex was synthesized and characterized by
single crystal X-ray crystallography, FTIR, NMR spectroscopy, and elemental analysis.
The molecular structure of the compound is monoclinic with a space group of P21/n in
which the compound dimerized to form a chair conformation. The bond angles of the
compound denote that the molecule is 4 + 2 octahedral environment consisting of two
chelating morpholine dithiocarbamate and two sulfur atoms from bridging morpholine
ligands of the adjacent Cd complex. Cd(II) dithiocarbamate complex was used as single-
source precursors for CdS at 180°C using three different capping agent (OLM, HDA, and
ODA). The pXRD patterns show a mixture of hexagonal and cubic crystalline phases
of the CdS nanocrystals. TEM images show semi-spherical particles with the size range
of (4.50–5.70 nm) for OLM-CdS, (3.33–5.96 nm) for HDA-CdS and (3.00–5.83 nm) for
ODA-CdS. The lattice fringes denoted that the particles are almost in the same environ-
ment with the interplanar spacing of (0.32 nm) for OLM-CdS, (0.34 nm) for HDA-CdS
and (0.32 nm) for ODA-CdS. The absorption studies of the as-prepared CdS nanoparticles
showed that the edges are blue-shifted whiles the emission studies indicate that they are
red-shifted due to the nanosize of the particle, the bad gaps were confirmed to be 1.59 eV
for OLM-CdS, 1.65 eV for HDA-CdS, and 1.62 eV for ODA-CdS.
Supplementary materials
CCDC 1877637 contains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data or from The Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (e-mail: deposit@ccdc.cam.ac.uk).
Disclosure statement
The authors declare no conflicts of interest.
ORCID
Peter A. Ajibade http://orcid.org/0000-0002-8581-2387
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