Structural and optical studies of silver sulfide nanoparticles from silver(I) dithiocarbamate complex: molecular structure of ethylphenyl dithiocarbamato silver(I)

Article abstract of DOI:10.1080/17415993.2020.1784895

We report the synthesis and crystal structure of ethylphenyl dithiocarbamato silver(I) complex. The compound crystallized as [Ag₄(EtphDTC)₄] in which four Ag(I) ions and four molecules of ethylphenyl dithiocarbamato ligands constitut

Full text of DOI:10.1080/17415993.2020.1784895

Journal of Sulfur Chemistry
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Structural and optical studies of silver sulfide
nanoparticles from silver(I) dithiocarbamate
complex: molecular structure of ethylphenyl
dithiocarbamato silver(I)
Peter A. Ajibade & Nandipha L. Botha
To cite this article: Peter A. Ajibade & Nandipha L. Botha (2020): Structural and optical
studies of silver sulfide nanoparticles from silver(I) dithiocarbamate complex: molecular
structure of ethylphenyl dithiocarbamato silver(I), Journal of Sulfur Chemistry, DOI:
10.1080/17415993.2020.1784895
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JOURNAL OF SULFUR CHEMISTRY
https://doi.org/10.1080/17415993.2020.1784895
Structural and optical studies of silver sulfide nanoparticles
from silver(I) dithiocarbamate complex: molecular structure
of ethylphenyl dithiocarbamato silver(I)
Peter A. Ajibade and Nandipha L. Botha
School of Chemistry and Physics, University of KwaZulu Natal, Pietermaritzburg, South Africa
ABSTRACT
ARTICLE HISTORY
Received 28 December 2019
Accepted 15 June 2020
We report the synthesis and crystal structure of ethylphenyl
dithiocarbamato silver(I) complex. The compound crystallized as
[Ag4(EtphDTC)4] in which four Ag(I) ions and four molecules of
ethylphenyl dithiocarbamato ligands constitute the metal cluster
in the asymmetric unit. Each ethylphenyl dithiocarbamato ligand
in the cluster is bonded to three Ag(I) ions through the sulfur
atoms with one sulfur covalently bonded while the other sulfur
atoms act as two electrons-three centres within the metal clus-
ter. Each Ag(I) ion is linked to three Ag(I) ions through Ag–Ag
metallic bond distance of 2.9115(3) Å and 3.0376(4) Å. The com-
plex was thermolyzed at 120, 180 and 220 °C as single source
precursor to prepare silver sulfide nanoparticles. Powder XRD pat-
terns confirmed the as-prepared silver sulfide nanoparticles as
acanthite Ag1.93S irrespective of the thermolysis temperature. TEM
images of the silver sulfide nanoparticles showed particle of 2.99 nm
for AgS1 nanoparticles obtained at 120 °C, 6.71 nm for AgS2
obtained at 180 °C and HRTEM image of AgS3 obtained at 220
°C showed average particle size of 32.90 nm. The results showed
that the particle sizes of the as-prepared silver sulfide nanoparticles
increases with thermolysis temperature. The as-prepared silver sul-
fide nanoparticles have spherical shapes irrespective of thermolysis
temperature.
KEYWORDS
Ag(I) dithiocarbamate;
crystal structure; silver
sulfide; nanoparticles;
structural studies
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
Supplemental data for this article can be accessed here. https://doi.org/10.1080/17415993.2020.1784895
© 2020 Informa UK Limited, trading as Taylor & Francis Group

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P. A. AJIBADE AND N. L. BOTHA
1. Introduction
Metal nanoparticles are of interest and can be prepared and functionalized to enhance their
applications especially in biotechnology and targeted drug delivery [1–4]. Metal sulfide
nanoparticles are versatile, broad and exciting class of inorganic compounds [5–7]. Interest
in Group 11 metal complexes are due to their properties and diverse structural chemistry
[8]. Silver sulfide is a semiconductor with unique properties such as enhanced optical non-
linearity and high photoluminescence that are useful in the design of new optoelectronic
devices [9]. Potential applications of nanostructure materials depend on their crystallinity,
porosity and hierarchical architecture [10] as well their morphologies [11–13] that can be
controlled by capping agents or subtle changes in reaction conditions [14]. Among tech-
niques used for the synthesis of silver sulfide nanoparticles, the thermolysis of silver(I)
dithiocarbamate complexes as single source precursors have proven to be suitable for the
synthesis of acanthite silver sulfide nanoparticles [15–18].
Mothes et al. reported the synthesis of silver(I) dithiocarbamate complexes with phos-
phine. Molecular structures of two of the complexes revealed that the dithiocarbamate

JOURNAL OF SULFUR CHEMISTRY
3
ligand coordinate Ag(I) as bidentate chelating ligands [17]. Gimeno et al. reported poly-
meric chains of silver(I) with bis(diethyldithiocarbamate)ferrocene in which the dithio-
carbamate moiety acts as bridging ligands between the ferrocene and Ag(I) [19]. Liu et
al. [20] reported the first elemental cluster with hexacapped trigonal bipyramidal geome-
try with undecanuclear silver(I) complex stabilized by nine dithiocarbamate ligands and
has an interstitial hydride whose position was confirmed by DFT calculation. Zhang et al.
[21] reported silver(I) thiolate complex in which the diethyldithiocarbamate ligands act as
µ4- or µ3-bridging ligands within the cluster while Ebihara et al. [22] reported the bimetal-
lic complexes of silver(I) with bis(dialkyldithiocarbamato)platinum(II) complexes with Pri
or Bun substituents on the dithiocarbamato ligands and Ag(I). Pt and Ag NMR confirmed
Pt-Ag bond interactions and their X-ray structures showed that the complexes consist of
two Ag atoms surrounded by three molecules of the starting Pt complex. In their study,
Koreeva et al. [23] reported the molecular structure of hexamethylene dithiocarbamate
cluster in which each of the dithiocarbamate acts as µ3-bridging ligand, asymmetrically
linking three silver atoms. Thermal studies of the metal clusters identified Ag2S as an
intermediate and Ag as the final products [23]. In this study, we report the synthesis and
crystal structure of ethylphenyl dithiocarbamato silver(I) and its use as a precursor to
prepare silver sulfide nanoparticles at 120, 180 and 220 °C to study the effects of thermol-
ysis temperature on the structural and optical properties of the as prepared silver sulfide
nanoparticles.
2. Results and discussion
2.1. Molecular structure of the silver(I)dithiocarbamate complex
The silver complex, [Ag4(EtphDTC)4] crystallizes in the tetragonal space group 141/a
in which four Ag(I) ions and four molecules of ethylphenyl dithiocarbamato ligand are
bonded in the asymmetric unit (Figure 1 and Figure S1). The molecular structure of the
complex is presented in Figure 1. Structure refinements and crystal data of [Ag4(etphdtc)4]
are presented in Table S1. Selected bond lengths (Å) and bond angles (°) for the compound
are presented in Table 1. The molecular structure revealed argentophilic tetrahedron Ag4
inner core with four silver ions in the silver clusters [24]. The silver inner core interacts
with the ligands in terms of the overall molecular structure and charge distributions [25].
In the molecular structure of the compound, each dithiocarbamato ligand is bonded to
three Ag(I) ions through the sulfur atoms as shown in Figure 1 and Figure S1.
One sulfur atom of each dithiocarbamate moiety coordinate one Ag(I) and the other
sulfur atom acts as bridging donor atom between two Ag(I) ions within the cluster. Thus,
each Ag atom in the Ag clusters bond to the ligands and each Ag(I) is linked to three Ag(I)
ions through Ag–Ag argentophilic interactions [26] to overcome the electrostatic repul-
sion among the Ag ions [25]. The transannular Ag—Ag distances 2.9115 (3) and 3.0376(4)
Å are like those found in other Ag cluster compounds with Ag4 inner core [25–27]. These
distances are comparable to the known short Ag . . . .Ag distances [25–30]. This clearly
confirmed the closed shell d10-d10 argentophilic interactions within the cluster unit. The
three bonds on each Ag–S forms a triangle and the Ag(I) is linked to the other three Ag(I)
through another triangle while the six-coordinate geometry around each Ag(I) can be
described as trigonal prismatic structure (Figure 1). The bond distances between Ag–S

4
P. A. AJIBADE AND N. L. BOTHA
Figure 1. Molecular structure of [Ag4(Etphdtc)4]. The thermal ellipsoids are shown at 50% probability
level.
Table 1. Selected bond length (Å) and bond angles (°) for
[Ag4(etphdtc)4] compounds.
Atom
Length/Å
Atom
Angle/°
Ag1–Ag11
Ag1–Ag12
Ag1–Ag13
Ag1–S13
Ag1–S2
Ag1–S22
S1–C9
S2– C9
C9–N1
N1–C1
N1–C8
C4–C3
C4–C5
C1–C2
C1–C6
C2–C3
C5–C6
2.9115 (3)
2.9115 (3)
3.0376 (4)
2.4490 (7)
2.4962 (7)
2.5732 (7)
1.700 (3)
1.758 (3)
1.341 (3)
1.449 (3)
1.483 (3)
1.369 (4)
1.395 (4)
1.385 (4)
1.386 (4)
1.393 (4)
1.386 (4)
Ag11–Ag1–Ag12
Ag12–Ag1–Ag13
Ag11–Ag1–Ag13
S13–Ag1–Ag11
S13–Ag1–Ag13
S13–Ag– Ag12
S13–Ag1–S22
S13 –Ag1– S2
S22–Ag1–Ag12
S22–Ag1–Ag11
S2–Ag1– Ag11
S2–Ag1–Ag13
S2–Ag1–Ag12
S22 –Ag1–Ag13
S2–Ag1–S22
62.888 (8)
58.557 (4)
58.557 (4)
146.166 (17)
88.065 (17)
96.465 (17)
109.12 (2)
128.18 (2)
53.717 (16)
81.088 (16)
56.197 (16)
79.815 (16)
117.896 (16)
111.228 (15)
122.295 (13)
107.39 (9)
C9–S1–Ag13
Ag1–S2–Ag11
70.087 (18)
Symmetry operation 13/4+y,5/4-x,9/4-z; 25/4-y,-3/4+x,9/4-z; 32-x,1/2-
y,+z.
varies from 2.44 to 2.57Å which is comparable with the Ag–S bond distance of 2.43 to
2.56Å reported for silver(I) diisopropyl monodithiocarbamate hexamer [27]. The three
bonded Ag(I) ions form angles that vary from 58.8-62.8° which is comparable with other
reported angles, 58.25-62.16° for silver atoms in poly-silver cluster [23,29]. In the packing
diagram of [Ag4(EtphDTC)4] as shown in Figure S2, there are six [Ag4(EtphDTC)4] units

JOURNAL OF SULFUR CHEMISTRY
5
within the crystal lattice in a pair of two and each one is linked to neighboring molecule
through intermolecular hydrogen bonds as shown in Figure S3.
2.2. Spectra studies of N-ethyl aniline DTC and the silver(I) complex
FTIR spectra of N-ethyl phenyl dithiocarbamate ligand and the ethylphenyl dithiocarbam-
ato silver(I) complex were compared and carefully assigned. The ligand showed the v(C–N)
stretching vibration at 1444 cm−1 [31] which shifted to 1438 cm−1 in the silver(I) com-
plex, due to the coordination of the ligand to the Ag(I) ions. The vibrations observed at
997 cm−1 and 1021 cm−1 in the spectrum of the ligand are ascribed to the symmetric and
asymmetric v(C–S) vibrations. This shifted to a single peak at 987 cm−1 in the spectrum
of the Ag(I) complex which indicate that ligand is acting as chelating ligands to the Ag(I)
as confirmed by the single crystal X-ray structure. The C–H from the ethyl group of the
ligand and C = C stretching vibrations from the ring were observed in both the ligand and
complex spectra around 2900 cm−1 and 1500 cm−1 respectively.
2.3. Powder X-ray diffraction patterns of AgS nanoparticles
Figure 2 shows the powder X-ray diffraction patterns of the silver sulfide nanoparticles syn-
thesized at three different temperatures. The XRD pattern peaks were indexed according
to the literature [32]. For AgS1 nanoparticles synthesized at 120°C, the angle 2θ = 36.75°,
40.62°, 50.37° and 53.85° are indexed to (013), (031), (014), and (−224) miller indices.
The peaks 2θ = 39.90, 42.67°, 46.81°, 50.62° and 75.65°, for AgS2 nanoparticles synthe-
sized at 180 °C corresponds to (031), (−202), (−214), (014) and (−227) miller indices
respectively. AgS3 nanoparticles synthesized at 220 °C 2θ angles are 33.43°, 36.44°, 40.01°,
42.74°, 73.91°, 47.43°, 50.62°, 55.79°, 57.13° and 62.25° corresponding to (−121), (022),
(031), (023), (112), (014), (−224), (−142), (042) and (015) planes respectively. The phase
of the particles was determined to be acanthite α-Ag2S for AgS1 and AgS2 while AgS3 is
cubic argentite β-Ag2S crystalline phase [33,34].
2.4. Morphological studies of silver sulfide nanoparticles
TEM/HRTEM images of the nanoparticles (Figure 3) showed monodispersed silver sul-
fide nanoparticles with spherically shaped particles irrespective of thermolysis temperature
with little or no trace of agglomeration. The TEM micrograph of AgS1 obtained at 120°C
showed spherically shaped silver sulfide nanoparticles with particle size in the range
2.43–7.40 nm and the particle size distribution of 2.99 0.08 nm (Figure 4). At 180 °C,
the particle sizes of AgS2 is in the range 5.60-16.87 nm and the particle size distributions
showed average particle size of 6.71 0.11 nm while at the highest thermolysis tempera-
ture of 220°C, the particle size of the as-prepared AgS3 silver sulfide ranged from 35.58 to
52.86 nm. The particles size distributions of AgS3 nanoparticles showed average particle
size of 32.90 0.48 nm. Variation of thermolysis temperatures have been shown to lead to
as-prepared nanoparticles dominated by growth route or a nucleation driven process that
produces nanoparticles in which the particle sizes depends on temperature. The results
of this study showed that the particle sizes of the as-prepared silver sulfide nanoparticles

6
P. A. AJIBADE AND N. L. BOTHA
Figure 2. p-XRD patterns of AgS1, AgS2 and AgS3 nanoparticles.
increases as thermolysis temperature increases as follows: 2.99 nm for AgS1 prepared at
120 °C, 6.71 nm for AgS2 at 180 °C and 32.90 nm for AgS3 at 220 °C.
The SEM micrograph (Figure S6) showed surface morphology of AgS1 nanoparticles
prepared at 120°C with almost smooth dark surface while AgS2 nanoparticles obtained at
180°C exhibited rocky like surface morphology. The surface of AgS3 synthesized at 220°C
is made up of fibers like morphology packed into layers. The observations confirm the
influence of reaction temperature on the surface morphologies of the as-prepared AgS

JOURNAL OF SULFUR CHEMISTRY
7
nanoparticles. The EDX spectra (Figure S6) showed the presence of silver and sulfur in
the nanoparticles. FTIR was used to confirm functional groups of the capping agents in
the nanoparticles. The FTIR spectra of the silver sulfide nanoparticles were compared with
the spectra of oleic acid and oleylamine. The spectra of pure oleic acid show the C–H and
C = H bending modes from 1600 to 1400 cm−1 of the alkyl chain and C = O stretching
Figure 3. TEM micrographs of AgS1, AgS2 and HRTEM micrograph of AgS3 nanoparticles.

8
P. A. AJIBADE AND N. L. BOTHA
Figure 3. Continued.
mode at 1700cm−1 from the carboxylic acid [35]. These vibrations were all observed also
in the spectra of the nanoparticles. Therefore, oleic acid has bonded to the nanoparticles
surface.
2.5. Absorption and emission spectra studies of AgS nanoparticles
The absorption spectra of the AgS nanoparticles are displayed in Figure 5 with their respec-
tive Tauc plots. The Tauc plot was used to estimate the band gap energy of the nanoparticles.
The estimated band gap energy for AgS1, AgS2 and AgS3 are 2.37, 2.86 and 3.74 eV
respectively, which are greater than 0.9 eV band gap energy of the bulk. The estimated
band gap energies showed considerable blue shift which is attributed to the smaller sized
nanoparticles [36].
Figure 6 shows the emission spectra of the AgS nanoparticles synthesized at 120, 180
and 220°C. The emission maxima were observed at 341, 311 and 379 nm for AgS1, AgS2
and AgS3 respectively. These have shifted in comparison to the absorption band edges. The
intense red shift could be attributed to the trap electron-hole recombination as a result of
the nanoparticle sizes [37].
3. Experimental
3.1. Materials and characterization techniques
All reagents were used as purchased without further purification. The FTIR spectra of the
ligand and the complex were recorded using Perkin Elmer FTIR spectrometer. Their elec-
tronic spectra in solution were recorded using the Cary 100 UV-Vis spectrophotometer

JOURNAL OF SULFUR CHEMISTRY
9
Figure 4. Size distribution histogram of AgS1, AgS2 and AgS3 nanoparticles.

10
P. A. AJIBADE AND N. L. BOTHA
Figure 5. Overlay UV-Vis spectra and Tauc plot of AgS1, AgS2 and AgS3 nanoparticles.
(Agilent technologies), water and DMSO were used to dissolve the ligand and complex
respectively. Powder X-ray diffraction patterns were obtained on Philips PW1830 X-ray
Diffractometer. TEM micrograph were collected using Joel 1400 Transmission Elec-
tron Microscope and (HRTEM) micrograph were obtained using JEOL HRTEM 2100.
SEM and EDS images were obtained from ZEISS EVO LS 15 Scanning Electron Micro-
scope. Perkin Elmer LS 45 fluorescence spectrometer was used for photoluminescence
studies.
3.2. Synthesis of the N-ethylphenyl dithiocarbamate sodium salt
The ligand was prepared based on our previous procedure [38]. N-ethylphenyl dithiocar-
bamate sodium salt ligand was synthesized by adding N-ethylaniline (0.005 mol, 6.3 mL)
into a solution of sodium hydroxide (0.005 mol, 2 g) at a temperature below 4 °C. This
was followed by dropwise addition of carbon disulfide (0.005 mol, 3 mL) and the mixture
was stirred for 5 h. The precipitate was filtered, washed several times with diethyl ether

JOURNAL OF SULFUR CHEMISTRY
11
Figure 6. Overlay photoluminescence spectra of AgS1, AgS2 and AgS3 nanoparticles.
and dried. Yield = 52%, Anal. Cal for C9H10NaNS2: C, 49.29; H, 4.60; N, 6.39; S, 29.24.
Found: C, 50.16; H, 4.48; N, 6.36; S, 29.33, Selected IR (Solid state, cm−1): V(C–N) =1444,
Vs(C–S) = 997, Va(C–S) = 1021. 1H NMR (400 MHz, D2O, ppm): 7.2 (d,2H); 7.4 (t, 1H);
7.5 (t, 2H). 4.4 (q, 2H); 1.2 (t, 3H). 13C NMR (400 MHz, D2O, ppm): 210 (CS); 149, 139,
127, 128 (C6H5); 52 (CH2N), 12 (CH3).
3.3. Synthesis of Ag(I) dithiocarbamate complex, [Ag4(EtphDTC)4]
Silver nitrate, (0.005 mol, 0.849 g) was dissolved in distilled water follow by the addition
of N-ethylphenyl dithiocarbamate sodium salt (0.005 mol, 1.096 g). Precipitate formed
immediately but the reaction was stirred at room temperature for 2 h. The yellow pre-
cipitate was filtered, washed with water and dried in the desiccator. Yield = 61%, Anal.
Cal for C36H40Ag4N4S8: C, 35.54; H, 3.31; N, 4.60; S, 21.08. Found: C, 35.47; H, 3.28; N,
4.36; S, 20.82, Selected IR (Solid state, cm−1): V(C–N) =1438, V(C–S) = 987. Colur:
Yellow.

12
P. A. AJIBADE AND N. L. BOTHA
3.4. Single crystal X-ray crystallography of [Ag4(EtphDTC)4]
Single yellow block-shaped crystals of [Ag4(EtphDTC)4] were obtained from dichlorome
thane solution by slow evaporation. A suitable crystal (0.31 × 0.17 × 0.12) mm3 was
selected and mounted on a mitigen holder in paratone oil on a Bruker APEX-II CCD
diffractometer at 100(2) K temperature. Using Olex2 [39], the structure was solved with
the ShelXS-2013 [40] structure solution program, using the direct solution method. The
model was refined with version 2016/6 of ShelXL [41] using Least Squares minimization.
3.5. Synthesis of the silver sulfide nanoparticles
0.4 g of the compound was dispersed in oleic acid. The mixture was added to hot oley-
lamine in a three-necked flask at 120°C under inert atmosphere and maintained at this
temperature for 1 h. The resultant mixture was cooled to 70 °C, followed by the addition
of excess cold ethanol to precipitate the nanoparticles which was separated through cen-
trifugation [42]. The experiment was repeated at 180 and 220 °C and the prepared silver
sulfide are labeled as AgS1, AgS2 and AgS3 for nanoparticles prepared at 120, 180 and 220
°C respectively.
4. Conclusion
The synthesis and crystal structure of ethylphenyl dithiocarbamato silver(I) complex was
synthesized and characterized. The Ag(I) complex crystallizes in the tetragonal space group
141/a in which argentophilic tetrahedron Ag4 inner core consists of four silver ions in the
silver clusters. Each Ag ions is linked to three Ag ions through Ag–Ag argentophilic inter-
actions and bond to the ligand to overcome the electrostatic repulsion, charge distribution,
energetics and stabilize the molecule. The complex was used as precursor and thermolyzed
at 120, 180 and 220°C to prepare silver sulfide nanoparticles. TEM/HRTEM images showed
spherically shaped silver sulfide nanoparticles irrespective of the thermolysis temperature
with particle size in the range 2.43–7.40 nm, 5.6–16.87 nm and 11.93–19.10 nm for silver
sulfide nanoparticles prepared at 120, 180 and 220°C respectively. This confirmed that sil-
ver complex precursor even though it crystallized as a metal cluster can be thermolyzed as
single source precursor to prepare silver sulfide nanoparticles. The results also confirmed
that as the thermolysis temperature increases, there is a slight increase in particle in the
size of the nanoparticles which indicate the particle sizes of the as-prepared silver sulfide
nanoparticles are temperature dependent.
Acknowledgements
The authors gratefully acknowledge the financial support of National Research foundation and Sasol,
South Africa.
Disclosure statement
No potential conflict of interest was reported by the author(s).

JOURNAL OF SULFUR CHEMISTRY
13
Funding
This work was supported by National Research Foundation and Sasol, South Africa.
Data availability statement
CCDC 1841556 contain the supplementary crystallographic data for the structure and
can be obtained free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK; fax:
(+44)-1223-336-033 or email: deposit@ccdc.cam.ac.uk.
ORCID
Peter A. Ajibade http://orcid.org/0000-0002-8581-2387
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