Synthesis, spectral, structural, Hirshfeld surface and DFT studies on bis(N-(4-fluorobenzyl)-N-(2-phenylethyl)dithiocarbamato-S,S′)zinc(II) and its use for the preparation of ZnS and ZnO nanoparticles

Article abstract of DOI:10.1080/17415993.2017.1327592

Two new complexes, bis(N-(2-phenylethyl)-N-(4-fluorobenzyl)dithiocarbamato-S,S′)zinc(II) (1) and bis(N-(2-phenylethyl)-N-(4-chlorobenzyl)dithiocarbamato-S,S′)zinc(II) (2), have been synthesized and characterized by various physicochemical techniques. Structure of 1 has been determined by single crystal X-ray diffraction. Complex 1 is a dimer. Zinc atom is four coordinated with a distorted tetrahedral environment. Geometry optimization, geometrical parameters, molecular electrostatic potential (MEPs) and frontier molecular orbital analysis of dimeric and monomeric structures of 1 have been carried out by DFT methods and compared with the experimental X-ray diffraction data. The noncovalent interactions in the complex 1 have been analyzed using Hirshfeld surface analysis. 1 and 2 have been used as single source precursors for the preparation of zinc sulfide and zinc oxide nanoparticles. As-prepared zinc sulfides and zinc oxides have been characterized by powder X-ray diffraction (PXRD), scanning electron microscope (SEM), UV–vis absorption, photoluminence and energy dispersive X-ray spectroscopy (EDS). X-ray diffraction study reveals that zinc sulfides and zinc oxides are composed of rhombohedral and hexagonal phases, respectively. Photocatalytic activities of zinc sulfides and zinc oxides were evaluated by degradation of rhodamine B in aqueous solution under UV light irradiation. The results demonstrated the capability of zinc sulfides and zinc oxides as photocatalyst under UV irradiation to degrade the dye.

Full text of DOI:10.1080/17415993.2017.1327592

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Synthesis, spectral, structural, Hirshfeld surface
and DFT studies on bis(N-(4-fluorobenzyl)-N-
(2-phenylethyl)dithiocarbamato-S,S′)zinc(II)
and its use for the preparation of ZnS and ZnO
nanoparticles
Ethiraj Sathiyaraj, Sundaramoorthy Tamilvanan, Subbiah Thirumaran &
Samuele Ciattini
To cite this article: Ethiraj Sathiyaraj, Sundaramoorthy Tamilvanan, Subbiah Thirumaran &
Samuele Ciattini (2017): Synthesis, spectral, structural, Hirshfeld surface and DFT studies on bis(N-
(4-fluorobenzyl)-N-(2-phenylethyl)dithiocarbamato-S,S′)zinc(II) and its use for the preparation of
ZnS and ZnO nanoparticles, Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2017.1327592
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Date: 01 July 2017, At: 11:26

JOURNAL OF SULFUR CHEMISTRY, 2017
https://doi.org/10.1080/17415993.2017.1327592
Synthesis, spectral, structural, Hirshfeld surface and DFT
studies on bis(N-(4-fluorobenzyl)-N-(2-
phenylethyl)dithiocarbamato-S,Sꢀ)zinc(II) and its use for the
preparation of ZnS and ZnO nanoparticles
Ethiraj Sathiyaraja†, Sundaramoorthy Tamilvananb†, Subbiah Thirumaranb and
Samuele Ciattinic
aDepartment of Chemistry, Kalasalingam University, Virudhunagar, India; bDepartment of Chemistry,
Annamalai University, Chidambaram, India; cCentro di Cristallografia Strutturale, Polo Scientifio di Sesto
Fiorentino, Firenze, Italy
ABSTRACT
ARTICLE HISTORY
Received 22 July 2016
Accepted 2 May 2017
Two new complexes, bis(N-(2-phenylethyl)-N-(4-fluorobenzyl)dithio-
carbamato-S,Sꢀ)zinc(II) (1) and bis(N-(2-phenylethyl)-N-(4-chloro
benzyl)dithiocarbamato-S,Sꢀ)zinc(II) (2), have been synthesized and
characterized by various physicochemical techniques. Structure of
1 has been determined by single crystal X-ray diffraction. Complex
1 is a dimer. Zinc atom is four coordinated with a distorted tetra-
hedral environment. Geometry optimization, geometrical parame-
ters, molecular electrostatic potential (MEPs) and frontier molecular
orbital analysis of dimeric and monomeric structures of 1 have been
carried out by DFT methods and compared with the experimental
X-ray diffraction data. The noncovalent interactions in the complex
1 have been analyzed using Hirshfeld surface analysis. 1 and 2 have
been used as single source precursors for the preparation of zinc sul-
fide and zinc oxide nanoparticles. As-prepared zinc sulfides and zinc
oxides have been characterized by powder X-ray diffraction (PXRD),
scanning electron microscope (SEM), UV–vis absorption, photolumi-
nence and energy dispersive X-ray spectroscopy (EDS). X-ray diffrac-
tion study reveals that zinc sulfides and zinc oxides are composed
of rhombohedral and hexagonal phases, respectively. Photocatalytic
activities of zinc sulfides and zinc oxides were evaluated by degrada-
tion of rhodamine B in aqueous solution under UV light irradiation.
The results demonstrated the capability of zinc sulfides and zinc
oxides as photocatalyst under UV irradiation to degrade the dye.
KEYWORDS
Zinc(II) dithiocarbamates;
zinc sulfide; zinc oxide;
nanoparticles; DFT studies
CONTACT Subbiah Thirumaran
sthirumaran@yahoo.com
Department of Chemistry, Annamalai University,
Annamalainagar, Chidambaram, Tamil Nadu 608 002, India
†Equally contributed.
Supplemental data for this article can be accessed at doi:10.1080/17415993.2017.1327592
© 2017 Informa UK Limited, trading as Taylor & Francis Group

2
E. SATHIYARAJ ET AL.
1. Introduction
Dithiocarbamates have considerable industrial and technological significance and have a
variety of uses such as a pivotal role in biological activities [1], in the medical area [2–5],
chronic alcoholism [6], vulcanization of rubber [7], catalysis [8,9] high-pressure lubricat-
ing agents [10], organic synthesis [11], analytical chemistry [12], and zinc dimethyldithio-
carbamate is a carbamate fungicide [13,14] used in agriculture to control fungal infections.
The nitrogen bound organic moiety is functionalized in various ways or moieties to mod-
ify the physico-chemical properties of the ensuing metal complex [15] and generate a
great variety of molecular architectures, afforded by C–H···π, C–H···π (chelate, CS2M),
S···H and C–H···X (X = O, N, halides) and π···π interactions. Most of the zinc dithio-
carbamate complexes are dimeric in the solid state [16,17]. Freezing point depression
and vapor pressure measurements of bis(N,N-dimethyldithiocarbamato-S,Sꢀ)zinc(II) and
bis(N,N-diethyldithiocarbamato-S,Sꢀ)zinc(II) indicated that the dimeric structure of these
two species is not retained in solution and hence solvated monomers are formed upon
dissolution [18–20]. The gas-phase structure of Zn(S2CNMe2) has been determined by
electron diffraction. This study showed that the molecule has a monomeric nature in
the gas phase [21]. Several complexes have been fully optimized using the density func-
tional theory (DFT)-based B3LYP method with 6-31G** for all atoms except metal atoms
and LANL2DZ for metal atoms [22]. This DFT method has been tested before by several
authors in similar zinc bis(dithiocarbamate) complexes [23,24] and other metal dithiocar-
bamate complexes [25] showing good results in a reasonable amount of time. Therefore,
full optimization and molecular electrostatic potential calculation of monomeric and
dimeric structures of 1 were performed using the same combination of method and
basis set. Zinc(II) dithiocarbamate complexes have been used as single-source precur-
sor for the preparation of zinc sulfide and zinc oxide [26]. The size, shape, and phase
of zinc sulfide and zinc oxide depend on the N-bound organic moiety of the dithio-
carbamate ligand. In this study, we report synthesis and spectral studies on complexes
(bis(N-(2-phenylethyl)-N-(4-fluorobenzyl)dithiocarbamato-S,Sꢀ)zinc(II)(1) and bis(N-
(2-phenylethyl)-N-(4-chlorobenzyl) dithiocarbamato-S,Sꢀ)zinc(II) (2)) and X-ray struc-
ture and DFT calculations of monomeric and dimeric structures of 1. In addition, prepa-
ration, characterization, and photocatalytic activities of zinc sulfides and zinc oxides are
presented.

JOURNAL OF SULFUR CHEMISTRY
3
2. Results and discussion
2.1. Infrared spectral studies
The Infrared spectra of 1 and 2 clearly showed that two single sharp intensity bands
appeared at around 1490 and 1015 cm−1 due to νC−N and νC–S stretching vibrations. The
observed N–CS2 stretchings for both complexes are intermediates of C=N double-bond
and C–N single-bond stretchings, due to the mesomeric drift of the electron cloud of the
dithiocarbamate motif towards the metal ion and confirmed the partial double-bond char-
acter of the C–N bond [27]. The νC–S stretching vibrations are observed without splitting in
complexes 1 and 2, suggesting the bidendate coordination of dithiocarbamate moiety [28].
2.2. NMR spectral studies
2.2.1. 1H NMR spectral studies
In the 1H nuclear magnetic resonance (NMR) spectra of complexes of 1 and 2, the methy-
lene protons of 2-phenylethyl group resonate as two triplets around 3.05 and 3.90 ppm. The
protons of methylene bound to nitrogen appear at a relatively low field (∼3.90 ppm). A sin-
glet observed around 5.00 ppm is assigned to the methylene protons of a substituted benzyl
group. The signals due to the methylene protons adjacent to nitrogen atom are deshielded
on complexation. The other proton signals are not affected in all three complexes because
of the relative distance from the thioureide π-system [29]. The signals are observed in the
region of 6.78–7.40 ppm due to the aromatic protons of dithiocarbamate ligands.
2.2.2. 13C NMR spectral studies
In both the complexes, three signals in the aliphatic region are associated with the methy-
lene carbons of benzyl and phenylethyl groups of dithiocarbamate complexes. The signal
for methylene carbon of benzyl group appears at around 57.6 ppm. The remaining two sig-
nals in the aliphatic region are due to the methylene carbons of the phenylethyl group of
dithiocarbamate complexes. All the complexes show a single downfield resonance charac-
teristic of the CS2 unit of the N-(2-phenylethyl)-N-(4-substitutedbenzyl)dithiocarbamate
ligands at 205 ppm. The 13C NMR spectrum of complex 1 shows two signals at 161.4 and
163.9 ppm due to the ipso carbon.
2.3. Single-crystal X-ray structural analysis
Single crystals of complex 1 were grown by slow evaporation of a solution of the crude
products in dichloromethane: acetonitrile. Selected bond distances and angles are listed
in Table 1. The Oak Ridge Thermal-Ellipsoid Plot Program diagram of complex 1 is
shown in Figure 1. The crystal structure of complex 1 is built up of centrosymmetric
dimeric entities. One dithiocarbamate is chelating with Zn–S distances of 2.3448(7) Å
for S1 and 2.435(7) Å for S2. Another dithiocarbamate coordinates the zinc atom in a
bridging bidentate manner, forming two distinctly unequal bonds [Zn-S3 = 2.3245 and
Zn···S4 = 2.9697 (5) Å]. Atom S4i interacts across the inversion center with an adjacent
Zn atom forming Zn-S4i bond [2.3437 Å; symmetry code: i = 1 − x, 1 − y, 1 − z ]. If the
long Zn···S4 interaction is taken into account the coordination geometry of Zn is inter-
mediate between the tetragonal pyramid and the trigonal bipyramidal. The angles are

4
E. SATHIYARAJ ET AL.
Table 1. Selected bond distances (Å) and bond angles (°) for complex 1.
1
Zn1-S1
Zn1-S2
Zn1-S3
Zn1-S4i
S1-C1
2.3448(7)
2.4365(7)
2.3245(7)
2.3437(5)
1.735(2)
1.714(2)
1.333(3)
1.466(3)
1.464(3)
1.751(2)
1.724(2)
1.322(3)
1.473(3)
1.477(3)
1.364(2)
1.363(2)
S3-Zn1-S4
S3-Zn1-S1
S4-Zn1-S1
S3-Zn1-S2
S4-Zn1-S2
S1-Zn1-S2
C17-N2-C25
C17-N2-C18
C25-N2-C18
C1-N1-C9
C1-N1-C2
C9-N1-C2
N2-C17-S3
N2-C17-S4
S3-C17-S4
N1-C1-S2
N1-C1-S1
S2-C1-S1
106.70(2)
134.33(2)
114.32(2)
102.86(2)
116.70(2)
76.277(18)
121.89(18)
123.68(17)
114.42(17)
121.40(17)
122.43(17)
116.10(17)
120.41(15)
121.64(16)
117.88(12)
122.09(15)
120.04(14)
117.86(12)
S2-C1
N1-C1
N1-C2
N1-C9
S4-C17
S3-C17
N2-C17
N2-C25
N2-C18
C6-F2
C22-F1
Note: Symmetry code i : 1 − x, 1 − y, 1 − z.
Figure 1. Oak Ridge Thermal-Ellipsoid Plot Program diagram of complex 1.

JOURNAL OF SULFUR CHEMISTRY
5
somewhat distorted from the ideal tetrahedral geometry with bite angle 76.28(2)° and the
remaining angles in the range 102.86(2)–134.33(2)°. The ZnS2C four-membered ring is
almost planar. This dimeric structure features one 8-membered [–S–C–S–Zn–]2 ring with
a Zn1···Zn1i separation of 3.7850(4) Å. The eight-membered ring forms a stable chair con-
formation. The carbon-sulfur bonds have an average length of 1.7310 Å which is shorter
than the typical C–S single-bond length (1.82 Å) due to partial π-conjugation over the
N–C–S group. The N1–C1 and N2–C17 bond distances [1.333(3) and 1.322(3) Å, respec-
tively] are shorter than the other N–C bond distances, and are indicative of considerable
double-bond character.
Recently, Tiekink and Zukerman-Schpector [30] have reported C–H···π (chelate
ring) interactions play an important role in stabilizing crystal structures of metal
bis(1,1-dithiolates). C–H···π(chelate) interactions lead to the formation of 1D, 2D,
and 3D supramolecular assemblies. The dimeric structure is further stabilized by the
C–H···π(chelate = ZnS2C ring) interactions (Figure S1). In this structure, the fluorine
atom of substituted benzyl plays a prominent role in the overall crystal packing via C–H···F
hydrogen bonding (Table S1, Figure S2). The dinuclear molecules link through two
C–H···F interactions [C10–H10B···F = 2.781 Å and C2–H2A···F1 = 2.687 Å] providing
a linear chain motif. The polymeric structure is further stabilized by the intermolecular
C–H···π and C–H···S interactions (Figure S3). Four intramolecular C–H···S interactions
are also observed (Figure S4).
2.4. Hirshfeld surface analysis
Hirshfeld surface analysis offers a facile way of obtaining information on trends in crystal
packing and provide a convenient means of quantifying the interactions within the crystal
structures. The Hirshfeld surfaces for the crystal structure of 1 have been mapped over
d
norm, shape index and curvedness (Figure S5). The dominant intermolecular interactions
are shown as bright red areas on the dnorm surface areas. On the Hirshfeld surface of 1
mapped with the dnorm function, 17 red areas are visible. The two large red areas (Figure
S6) correspond to C–H···S and C–H···F interactions. Examination of the decomposed fin-
gerprint plots indicates that H···H (42.7%), C···H (23.2%), S···H (14.7%) and F···H (12.4%)
interactions constitute most of the Hirshfeld surface. The introduction of fluoro on the
paraposition of the phenyl group enhances the weak interactions (F···H (12.4%)) which
lead to the formation of the linear chain motif. The functionalization of N-bound organic
moiety of dithiocarbamate can be utilized to generate various intermolecular interactions.
2.5. DFT studies on 1
2.5.1. Optimized geometry
The geometries of monomeric and dimeric structures of bis(N-(2-phenylethyl)-N-(4-
fluorobenzyl)dithiocarbamato-S,Sꢀ)zinc(II) were optimized in the gas phase employing the
DFT-based B3LYP method with 6-31G∗∗ for H,C,N,F and S atoms and LANL2DZ for the
Zn atom. The optimized geometries of the monomer and dimer of complex 1 are shown
in Figure S7. Selected structural parameters by theoretical and X-ray calculations for com-
plex 1 are shown in Table S2. The coordination geometry of the zinc atom in the optimized

6
E. SATHIYARAJ ET AL.
structure of monomer 1 is distorted tetrahedral, while dimer 1 optimized close to the start-
ing model, i.e. the coordination geometry around the zinc atom in the dimer is intermediate
between the tetragonal pyramid and trigonal bipyramid. Comparison of the experimen-
tal bond parameters with the calculated values for the monomer and dimer shows that
the calculated bond lengths are longer than those obtained from experimental XRD. The
experimental and calculated bond angles for the dimeric structure are almost equal except
S4-Zn-S2. This may be because all the calculated data are for the isolated monomeric and
dimeric molecules whereas the experimental data are for the dimeric molecules in solid
state. In solid state, the packing effects and various interactions affect the bond parame-
ters. A large difference is observed between the bond angles of XRD and those calculated
for monomeric structures. This is due to the absence of bridging bond in the monomeric
structure.
2.5.2. Frontier molecular orbital analysis (FMOs)
The frontier molecular orbitals highest occupied molecular orbital (HOMO) and low-
est unoccupied molecular orbital (LUMOs) play an important role in chemical reactivity.
The HOMO and LUMOs plots are shown in Figure 2. The red and green colors of the
molecular orbital plot represent the positive and negative phases. The plots reveal that
the HOMO is primarily composed of all S atoms in both the cases. The LUMO spread
over metal atoms and NCS2 groups of bridging dithiocarbamate ligands in the dimer and
NCS2 group of both ligands in the monomer. The HOMO and LUMO are used to deter-
mine several chemical reactivity parameters as a measure of relative stability and reactivity
Figure 2. Frontier molecular orbital diagram of complex 1 (a) monomer and (b) dimer.

JOURNAL OF SULFUR CHEMISTRY
7
Table 2. Calculated values for the energies of frontier molecular orbital’s for complex 1.
Frontier
Molecular
Orbital’s (eV)
Energy
Chemical
Chemical
MEP
Complex
No 1
Gap (ꢀE) Total Energy Dipolemoment Hardness Potential (µ) Electrophilicity Energy
(eV)
(E0) (a.u.)
(Debye)
(η) (eV)
(eV)
(ω) (eV)
(kJ/mol)
Monomer LUMO = −1.4021 5.0205
HOMO = −6.4226
−1652.5796
3.5985
2.5103
−3.9124
3.0489
−1583.7 to
+1583.7
Dimer
LUMO = −1.7234 4.3636
−3305.1728
0.0001
2.1818
−3.9053
3.4951
−1586.9 to
HOMO = −6.0871
+1586.9
[31]. The parameters of complex 1 include total energy (E0), dipolemoment (D), chem-
ical hardness (η), electronic chemical potentials (μ), and electrophilicity (ω). Calculated
values for the energies of frontier molecular orbitals for complex 1 are given in Table 2.
The calculated EHOMO energy, ELUMO energy, Ionization potential (I), Electron affinity (A),
Energy gap (ꢀE), Chemical hardness (η), chemical potential, and global electrophilicity for
monomeric and dimeric structures of 1 are given in Table 2. The HOMO-LUMO energy
gap values for the dimer and monomer are 4.3645 eV and 5.0205 eV, respectively. This indi-
cates that the dimer is more reactive than the monomer in a gaseous state. The smaller the
chemical potential value, the more stable is the complex. The monomer has the lowest
chemical potential value (µ); it is expected to be more stable than the dimer. The DFT
study on complex 1, bis(N-furfuryl-N-(4-methoxybenzyl)dithiocarbamato-S,Sꢀ)zinc(II)]
and bis(N-furfuryl-N-(4-chlorobenzyl)dithiocarbamato-S,Sꢀ)zinc(II)] [24] shows that the
zinc bis(dithiocarbamate) complexes exist as a monomer in the gas phase. This is further
supported by the structural studies on [Zn(S2CNMe2)2]. Single-crystal XRD and gas-phase
electron diffraction studies on [Zn(S2CNMe2)2] reveal that the complex exists as a dimer
in the solid state and a monomer in the gas phase, respectively [21].
2.5.3. Molecular electrostatic potential (MEP)
The MEP plot is used to understand the reactive behavior of a molecule, in that the neg-
ative regions can be regarded as nucleophilic centers, whereas the positive regions are
electrophilic sites [32,33]. To predict reactive sites of electrophilic and nucleophilic attacks
for the dimeric and monomer of 1, MEP at the B3LYP-level optimized geometry was cal-
culated for the dimer and monomer. MEP plots and contour maps are shown in Figure 3.
The different values of the electrostatic potential at the MEP surface and represented by
different colors red, green, and blue represent the regions of most negative, zero electro-
static potential, and most positive, respectively. In both the cases, the negative electrostatic
potentials are mainly localized on fluorine atoms and sulfur atoms which are possible sites
for electrophilic attack. The positive regions are localized on nitrogen atoms in both the
structures, indicating possible sites for nucleophilic attack.
2.6. Characterization of zinc sulfides (ZnS1 and ZNS2)
The PXRD patterns of ZnS1 and ZnS2 are shown in Figure 4(a, b). The diffraction peaks at
27.3°, 28.5°, 30.7°, 40.4°, 47.5°, 52.3°, and 56.4° are assigned to the (1 0 10), (0 1 20), (1 0 31),
(0 0 84), (1 1 0), (1 0 91), and (2 0 20) planes of rhombohedral ZnS (JCPDS: 01-089-2166).
The elemental analysis of the products is performed by EDS and presented in Figure
S8. The EDS spectrum confirms the presence of zinc and sulfur in the product obtained
by solvothermal decomposition of 1 and 2. The atomic ratio of sulfur is slightly higher

8
E. SATHIYARAJ ET AL.
Figure 3. Electrostatic potential surface of complex 1 (a) monomer and (b) dimer.
Figure 4. PXRD patterns of as-prepared (a) ZnS1, (b) ZnS2, (c) ZnO1, and (d) ZnO2.

JOURNAL OF SULFUR CHEMISTRY
9
Figure 5. SEM images of as-prepared (a) ZnS1, (b) ZnS2, (c) ZnO1, and (d) ZnO2.
than zinc [1.12(S): 1 (Zn) and 1. 16 (S): 1 (Zn) for ZnS1 and ZnS2, respectively], which
indicates that there are some vacancies of Zn2+ or some sulfur dangling bonds are present
in the sample. The morphology of zinc sulfide nanoparticles is investigated by scanning
electron microscopy. Figure 5(a) reveals that the morphology of ZnS1 appears as cotton
due to the combined appearance of fibrous particles. An SEM image of ZnS2 shows that
zinc sulfide particles are fibrous and spherical (Figure 5(b)). The length of the fibers in
ZnS1 is more than those of fibers in ZnS2.
The absorption spectra of ZnS1 and ZnS2 are displayed in Figure S9. Absorption max-
ima appeared at 274 and 277 nm for ZnS1 and ZnS2. A blue shift was observed in relation
to bulk ZnS (345 nm, 3.59 eV) [24]. This shows the existence of a strong quantum con-
finement effect. Room temperature photoluminence spectra of ZnS1 and ZnS2 are shown
in Figure S10. The photoluminescence spectra of ZnS1 and ZnS2 exhibit a strong band
at 440 nm and 465 nm, respectively, due to excitonic recombination corresponding to the
near-band-edge emission.
Infrared spectra of ZnS1 and ZnS2 were recorded to find the presence of a capping
agent (triethylenetetramine). Infrared spectra of ZnS1 and ZnS2 are displayed in Figure
S11. IR spectra of both zinc sulfides exhibit three bands in the region 2850–2965 cm−1
due to aliphatic νC–H. A broad band around 3440 cm−1 is assigned to the N–H stretching
vibration. These data confirm the presence of capping agent triethylenetetramine in ZnS1
and ZnS2.

10
E. SATHIYARAJ ET AL.
2.7. Characterization of zinc oxides (ZnO1 and ZnO2)
Zinc oxide nanoparticles prepared from complexes 1 and 2 are represented as ZnO1 and
ZnO2, respectively. The PXRD patterns of ZnO1 and ZnO2 are shown in Figure 4(c, d).
In both the cases, the peaks observed in the XRD patterns of 2θ values of 31.8°, 34.5°,
36.3°, 47.6°, 56.7°, 62.9°, 66.8°, 68.5°, and 69.1° match with (1 0 0), (0 0 2), (1 0 1), (1 0 2),
(1 1 0), (1 0 3), (2 0 0) (1 1 2), and (2 0 1) crystalline planes of hexagonal wurtzite ZnO
in the reference pattern of JCPDS No-36-1451. The diffraction peaks in both the cases are
sharp and intense, revealing the highly crystalline character of ZnO1 and ZnO2. The mor-
phology of both the samples was studied by scanning electron microscopy. SEM images of
ZnO1 and ZnO2 are shown in Figure 5(c) and (d). Figure 5(c) reveals that the morphology
of ZnO1 obtained from complex 1 appears as cotton due to the combined appearance of
fibrous particles. SEM image of ZnO2 (Figure 5(d)) shows that uniform size nanospheres
agglomerated to produce shapeless flakes. The elemental analysis of the products is per-
formed by energy-dispersive X-ray spectroscopy and the spectra are presented in Figure
S12. The spectra of both samples containing characteristic peaks of zinc and oxygen con-
firm the obtained products (ZnO1 and ZnO2) are zinc oxide. The absence of peaks due
to sulfur indicates that the thermal decomposition of complexes 1 and 2 did not yield zinc
sulfide. The EDS lines of oxygen occur close to the detection limit of EDS, for which reason
the analysis does not provide information on oxygen stoichiometry.
UV–vis absorption spectra of ZnO1 and ZnO2 are shown in Figure S13. Absorption
maxima appeared at 226 and 272 nm for ZnO1 and ZnO2, respectively. In both cases, a
blue shift was observed in relation to bulk ZnO (388 nm). This reveals the existence of a
strong quantum confinement effect [34]. Room temperature photoluminescence spectra
of ZnO1 and ZnO2 are shown in Figure S14. The photoluminescence spectra of ZnO1
and ZnO2 exhibit a broad emission band at 445 and 452 nm, respectively, due to excitonic
recombination corresponding to the near-band-edge emission.
2.8. Photocatalytic response of ZnS and ZnO nanoparticles
Photocatalytic degradation of rhodamine-B was observed at λ
= 554 nm. Degradation
max
of the dyes in the absence of semiconductor (ZnS or ZnO) is negligible. Absorption spectra
of exposed samples at various time intervals were recorded to get the response of photo-
catalytic activities of as-prepared ZnS and ZnO nanoparticles. Figure 6 shows absorption
changes when the dye aqueous solutions were degraded by the ZnS1, ZnS2, ZnO1 and
ZnO2 nanoparticles. The percentage of decolorization efficiency of the samples has been
calculated as
ꢀ
ꢁ
ꢀ
ꢁ
A0 − A
C0 − C
Efficiency (%) = 100 ×
= 100 ×
,
A0
C0
where A0, A, C0, and C are initial absorbance, absorbance after radiation at various time
intervals, initial concentration of solutions, and concentration of dyes after irradiation
at various time intervals, respectively. It was observed that the as-prepared ZnS1, ZnS2,
ZnO1, and ZnO2 nanoparticles degraded 94%, 96%, 95%, and 97% of rhodamine-B in
180 min. This study indicated that the photocatalytic activity of ZnO nanoparticles is
slightly greater than that of ZnS nanoparticles.

JOURNAL OF SULFUR CHEMISTRY
11
Figure 6. Time-dependent UV–Vis absorption spectra for decolorization of Rhodamine-B using (a)
ZnS1, (b) ZnS2, (c) ZnO1, and (d) ZnO2 under ultraviolet light.
3. Conclusions
Complexes 1 and 2 have been prepared and characterized. Complex 1 crystallizes as
a dimer linked by intermolecular Zn–S bonds. The intermolecular C–H···F hydrogen-
bonding interactions lead to the supramolecular frameworks. Quantification of the inter-
molecular interactions present in complex 1 was realized by the Hirshfeld surface analysis
and 2D finger plots. This study indicates that the variety of molecular architectures can
be obtained by functionalization of the N-bound organic moiety. The X-ray crystallo-
graphic results of complex 1 are compared to those obtained by the DFT method. The
frontier molecular orbital analysis showed that the monomer is more stable than the
dimer in the gaseous state. Complexes 1 and 2 were effective as single-molecule pre-
cursors for the preparation ZnS and ZnO nanoparticles. This study also reveals that the
funtionalization of N-bound organic moiety affects the shape of zinc sulfide and zinc
oxide nanoparticles. The as-prepared ZnS and ZnO nanoparticles have the advantage
of high-UV photocatalytic activity for decomposing organic pollutants (dyes) in mild
conditions.

12
E. SATHIYARAJ ET AL.
4. Experimental
4.1. Materials and methods
All reagents and solvents were used without further purification and all experiments were
carried out in atmospheric air. Melting points were determined by electro-thermal melting
point apparatus and are uncorrected. Microanalyses for carbon, hydrogen, and nitrogen
in the synthesized complexes were done on an Elementar model Vario MICRO V2.2.0.
Infrared spectra were recorded in the region of 4000–400 cm−1 as KBr pellets on a SHI-
MADZU FT-IR spectrophotometer. The 1H NMR and 13C NMR spectra were recorded on
a Bruker 400 MHz spectrometer at room temperature in CDCl3 as a solvent, using Tetram-
ethylsilane as an internal standard. UV–Vis and fluorescence spectra were recorded on a
SHIMADZU UV-1650-PC and Perkin-Elmer L555 spectrofluorimeter, respectively. The
PXRD and EDS were recorded using inel EQUINX 1000 and SUPRA 55VP CARL, respec-
tively. Scanning electron microscopy (SEM, FEI quanta 200 scanning electron microscope
instrument) was used to characterize the morphologies of the samples. DFT studies were
performed with the GAUSSIAN-03 program package with the aid of the Gauss view
program. Molecular geometries were optimized with DFT using the B3LYP calculation
method and LANL2DZ basis set.
4.2. Synthesis of zinc(II) complexes
4.2.1. Preparation of N-(2-phenylethyl)-N-(4-fluorobenzyl)amine and
N-(2-phenylethyl)-N-(4-chlorobenzyl)amine
2-phenylethylamine (4.6 mmol) and substituted benzaldehydes (4-F and 4-Cl) (5.1 mmol)
were dissolved in methanol (30 mL) and the solution was stirred for 2 h at room
temperature. The solvent was removed by evaporation. The resulting colorless oil was
dissolved in methanol–dichloromethane solvent mixture (1:1, 20 mL) and sodiumborohy-
dride (13.8 mmol) was added slowly at 5°C and stirred for 2 h before removal in an ice bath.
The reaction mixture was stirred at room temperature for 20 h. After evaporation of the sol-
vent, the resulting viscous liquid was washed with water and dichloromethane was added
in order to extract the product. Evaporation of the organic layer gave secondary amine
N-(2-phenylethyl)-N-(4-fluorobenzyl)amine and N-(2-phenylethyl)-N-(4-chlorobenzyl)
amine [35].
4.2.2. Preparation of complex 1
N-(2-phenylethyl)-N-(4-fluorobenzyl)amine (4.0 mmol) in ethanol was mixed with car-
bon disulfide (4.0 mmol) under ice cold condition. To the resultant yellow dithiocar-
bamic acid solution, aqueous solution of ZnSO4·7H2O (2.0 mmol) was added with
constant stirring. The solid which precipitated was washed several times with cold
water and then dried. Yield: 70%, m.p: 140–142°C. IR (KBr, cm–1): ν = 1484 (νC–N);
1016 (νC–S).1H NMR (400 MHz, CDCl3, ppm): δ = 3.06 (b, 4H, (C6H5–CH2–CH2–N));
3.94 (t, 4H, (C6H5–CH2–CH2–N); 4.94 (s, 4H,4F–C6H4–CH2–N); 7.04–7.31 (aro-
matic protons). 13CNMR (100 MHz, CDCl3, ppm): δ = 33.0 (C6H5–CH2–CH2–N);
55.2 (C6H5–CH2–CH2–N); 57.8 (4F–C6H4–CH2–N); ipso carbon; 161.4, 163.9 (Ar-4F);
115.8–137.9 (other aromatic carbons); 205.1 (NCS2). Anal. Calcd. for Chemical Formula:

JOURNAL OF SULFUR CHEMISTRY
13
C32H30F2N2S4Zn (%): Elemental Analysis: C, 57.00; H, 4.48; N, 4.15; Found: C, 56.67; H,
4.44; N, 4.13.
4.2.3. Preparation of complex 2
The same procedure used as earlier described for the synthesis of complex 1 was
adopted; however, N-(2-phenylethyl)-N-(4-chlorobenzyl)amine was used instead of N-
(2-phenylethyl)-N-(4-fluorobenzyl)amine. Yield: 82%, m.p: 135–137°C. IR (KBr, cm–1):
ν = 1495 (νC–N); 1017 (νC–S); 1H NMR (400 MHz, CDCl3, ppm): δ = 3.11(t, 4H,
(C6H5–CH2–CH2–N)); 3.99 (t, 4H, (C6H5–CH2–CH2–N)); 4.97 (s, 4H,4Cl–C6H4–
CH2–N); 7.24–7.40 (aromatic protons); 13CNMR (100 MHz, CDCl3, ppm): δ = 33.0
(C6H5–CH2–CH2–N); 55.4 (C6H5–CH2–CH2–N); 57.8 (4Cl–C6H4–CH2–N); ipso car-
bon: 134.2 (Ar–Cl); 126.9–137.8 (aromatic carbons); 205.5 (NCS2); Anal. Calcd. for chem-
ical formula: C32H30Cl2N2S4Zn (%): Elemental analysis: C, 54.35; H, 4.28; N, 3.96; Found:
C, 54.29; H, 4.29; N, 3.93.
4.3. XRD analysis
Single-crystal XRD data for complex 1 were performed on an Xcalibur, sapphire3 area
detector diffractometer using graphite-monochromated MoKα radiation (λ = 0.71073 Å)
at an ambient temperature. The structure was solved and refined by direct method
using SHELXL-2014/7 (Sheldrick, 2014) [36]. All the non-hydrogen atoms were refined
anisotropically and hydrogen atoms were refined isotropically. The model for the refine-
ment of hydrogen atoms is constrained. Details of the data collection, crystal data, and
structure refinement parameters for complex 1 are given in Table 3. Crystallographic
data for the structure reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication number of CCDC No –
1495185.
4.4. Hirshfeld surface
Hirshfeld surface and 2D fingerprint calculations were performed using the Crystal
Explorer package ver3.1 [37]. Crystal structures were imported from CIF files. Hirshfeld
surfaces were generated for complex 1 using a high surface resolution and mapped with
the dnorm of shape index functions. 2D fingerprint plots were prepared with the use of the
same software.
4.5. Theoretical studies
To compare the structural parameters and the properties of monomeric and dimeric struc-
tures of 1, DFT calculations were carried out for both structures of 1. DFT studies were
performed with the GAUSSIAN-03 program package with the aid of the Gauss View
visualization program. Molecular geometrics were optimized with DFT using the B3LYP
calculation method and LANL2DZ basic set.

14
E. SATHIYARAJ ET AL.
Table 3. Crystal data, data collection, and refinement parameters for complex 1.
Empirical formula
FW
C32 H30 F2 N2 S4 Zn
674.19
Crystal dimensions (mm)
Crystal system
Space group
a/Å
0.60 × 0.50 × 0.40
triclinic
¯
P i
10.3700(10)
b/Å
11.4930(10)
c/Å
13.5850(10
α/°
94.4320(10)
β/°
107.3680(10)
γ /°
94.6430(10)
1531.4(2)
V/Å3
Z
2
Dc/g cm–3
1.462
1.112
μ/cm–1
F(000)
696
λ/Å
MoKα(0.71073)
θ Range/°
4.4440–27.9820
Index ranges
−13 ≤ h ≤ 14, −15 ≤ k ≤ 14, −18 ≤ l ≤ 17
Reflections collected
Observed reflections [I > 2σ(I)]
Weighting scheme
Number of parameters refined
R[F2 > 2σ(F2)], wR(F2)
GOOF
33326
7416
Calc.w = 1/[s2(F02) + (0.0274P)2 + 0.8319P] where P = (F02 + 2Fc2)/3
490
0.0356, 0.0761
1.021
4.6. Preparation of zinc sulfides and zinc oxides
4.6.1. Preparation of ZnS nanoparticles (ZnS1 and ZnS2)
Zinc sulfide nanoparticles obtained from complexes 1 and 2 are represented by ZnS1 and
ZnS2.
4.6.1.1. Preparation of ZnS1. 1 g of complex 1 was dissolved in 30 mL of triethylenete-
tramine in a flask and then heated to 120°C and maintained at this temperature for 20 min.
The dirty white precipitate obtained was filtered off and washed with methanol.
4.6.1.2. Preparation of ZnS2. A method similar to that described for the preparation of
ZnS1 was adopted; however, complex 2 was used instead of 1.
4.6.2. Preparation of ZnO nanoparticles (ZnO1 and ZnO2)
Zinc oxide nanoparticles obtained from complexes 1 and 2 are represented by ZnO1 and
ZnO2.
4.6.2.1. Preparation of ZnO1. 1.5 g of complex 1 was placed in a muffle-furnace at 500°C
for 30 min in the presence of air.
4.6.2.2. Preparation of ZnO2. A method similar to that described for the preparation of
ZnO1 was adopted, however; complex 2 was used instead of 1.

JOURNAL OF SULFUR CHEMISTRY
15
4.7. Photocatalytic experiments
A HEBER Multi Lamp Photo Reactor was used for photo catalytic experiment. The photo-
catalytic performance of the as-prepared zinc sulfide and zinc oxide was evaluated through
the photocatalytic degradation of rhodamine-B. Double-distilled water was used to pre-
pare all solutions. In a typical photocatalytic experiment, 0.1 g of as-prepared ZnS/ZnO
nanoparticles was added to 250 ml of aqueous solution of rhodamine-B in the concentra-
tion of 0.01 M. The suspensions were magnetically stirred under darkness for 1 h to reach
the adsorption–desorption equilibrium. The suspension was irradiated by UV light from a
mercury vapor lamp in a photocatalytic instrument with a water cooling device. At certain
time intervals, 3 ml of suspension was centrifuged to remove the photocatalyst and ana-
lyzed by a UV–visible spectrophotometer at a wavelength of 554 nm. The measurements
were carried out up to 180 min [38].
Disclosure statement
No potential conflict of interest was reported by the authors.
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