Synthesis and spectral studies on Cd(II) dithiocarbamate complexes and their use as precursors for CdS nanoparticles

Article abstract of DOI:10.1016/j.molstruc.2017.06.080

Bis(N-cyclopropyl-N-4-chlorobenzyldithiocarbamato-S,S′)cadmium(II) (1) and (2,2′-bipyridine) bis(N-cyclopropyl-N-4-chlorobenzyldithiocarbamato-S,S′)cadmium(II) (2) have been synthesized and characterized by FT-IR, ¹HNMR and ¹³C NMR analyses. For the complex 2, single crystal X-ray diffraction analysis and computational studies (optimized geometry, HOMO-LUMO and MEP) have been executed employing DFT/B3LYP method with LANL 2DZ basic set. The optimized bond lengths and bond angles agree well with the experimental results. The complexes 1 and 2 have been used as single source precursors for the synthesis of ethyleneglycol capped CdS1 and CdS2 nanoparticles, respectively. CdS1 and CdS2 nanoparticles have been synthesized by solvothermal method. PXRD, SEM, Elemental colour mapping, EDAX, TEM and UV–Vis spectroscopy have been used to characterize the as-prepared CdS nanoparticles. The X-ray diffraction pattern confirms both their hexagonal structures.

Full text of DOI:10.1016/j.molstruc.2017.06.080

Accepted Manuscript
Synthesis and spectral studies on Cd(II) dithiocarbamate complexes and their use
as precursors for CdS nanoparticles
Ethiraj Sathiyaraj, Krishnaraj Padmavathy, Chandran Udhaya kumar, Kannan
Gokula Krishnan, Chennan Ramalingan
PII:
S0022-2860(17)30861-X
10.1016/j.molstruc.2017.06.080
MOLSTR 23966
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Revised Date:
Accepted Date:
04 February 2017
14 June 2017
17 June 2017
Please cite this article as: Ethiraj Sathiyaraj, Krishnaraj Padmavathy, Chandran Udhaya kumar,
Kannan Gokula Krishnan, Chennan Ramalingan, Synthesis and spectral studies on Cd(II)
dithiocarbamate complexes and their use as precursors for CdS nanoparticles, Journal of
Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.06.080
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ACCEPTED MANUSCRIPT
Synthesis and spectral studies on Cd(II) dithiocarbamate complexes and their
use as precursors for CdS nanoparticles
Ethiraj Sathiyaraj, Krishnaraj Padmavathy, Chandran Udhaya kumar, Kannan Gokula Krishnan,
Chennan Ramalingan*
Department of Chemistry, Kalasalingam University, Krishnankoil-626 126, Tamilnadu, India
GRAPHICAL ABSTRACT

ACCEPTED MANUSCRIPT
Synthesis and spectral studies on Cd(II) dithiocarbamate complexes and their
use as precursors for CdS nanoparticles
Ethiraj Sathiyaraj, Krishnaraj Padmavathy, Chandran Udhaya kumar, Kannan Gokula Krishnan,
Chennan Ramalingan*
Department of Chemistry, Kalasalingam University, Krishnankoil-626 126, Tamilnadu, India
-------------------------------------------------------------------------------------------------------
*Address for correspondence
Dr C. Ramalingan
Associate Professor
Department of Chemistry
Kalasalingam University
Krishnnan koil- 626 126
Tamilnadu, INDIA
Tel: +91 8489736207
E-mail: ramalinganc@gmail.com; chemcram@yahoo.co.in
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Synthesis and spectral studies on Cd(II) dithiocarbamate complexes and their
use as precursors for CdS nanoparticles
Ethiraj Sathiyaraj, Krishnaraj Padmavathy, Chandran Udhaya kumar, Kannan Gokula Krishnan,
Chennan Ramalingan*
Department of Chemistry, Kalasalingam University, Krishnankoil-626 126, Tamilnadu, India
Abstract
Bis(N-cyclopropyl-N-4-chlorobenzyldithiocarbamato-S,S)cadmium(II) (1) and (2,2-bipyridine)
bis(N-cyclopropyl-N-4-chlorobenzyldithiocarbamato-S,S)cadmium(II)
(2)
have
been
1
13
synthesized and characterized by FT-IR, HNMR and C NMR analyses. For the complex 2,
single crystal X-ray diffraction analysis and computational studies (optimized geometry,
HOMO-LUMO and MEP) have been executed employing DFT/ B3LYP method with LANL
2DZ basic set. The optimized bond lengths and bond angles agree well with the experimental
results. The complexes 1 and 2 have been used as single source precursors for the synthesis of
ethyleneglycol capped CdS1 and CdS2 nanoparticles, respectively. CdS1 and CdS2 nanoparticles
have been synthesized by solvothermal method. PXRD, SEM, Elemental colour mapping,
EDAX, TEM and UV-Vis spectroscopy have been used to characterize the as-prepared CdS
nanoparticles. The X-ray diffraction pattern confirms both their hexagonal structures.
Keywords: Cadmium complex, dithiocarbamate, nanoparticles, X-ray diffraction, computational
study
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1. Introduction
Dithiocarbamate anions, [S2CNR1R2] are highly versatile ligands, forming metal
complexes with a diverse array of applications, including uses as pesticides [1], fungicides [2], as
precursors of metal sulfides nanoparticles [3, 4], as well as in analytical chemistry for the
separation and determination of metals [5]. Dithiocarbamates of cadmium have continued to
attract attention in recent years on account of their recent industrial application [6] and biological
profiles [7]. Dithiocarbamate complexes of divalent transition metals, in which the central atom
is partially coordinatively unsaturated, are able to reversibly link molecules of organic S-, N-, P-
donor bases. The resulting intermolecular heteroleptic complexes are generally called adducts
[2]. The dithioacid complexes of CdL2 (L= H2XCS2H or X2PS2H) type are coordinately
unsaturated; this leads to the formation of compounds of higher coordination number either by
the addition of one or two molecules of a Lewis base or by polymerization of CdL2 [8].
Previously, various research groups have reported the preparation and the crystal and molecular
structures of adducts of various dialkyldithiocarbamate cadmium(II) complexes with bidentate
N,N'-donor bases: 2,2'-bipyridine and 1,10-phenanthroline. All prepared adducts are
characterized by distorted octahedral geometries of [CdS4N2] chromophores. Besides, nitrogen
donor adducts of dithiocarbamate complexes are also widely used in the preparation of thin film
semiconductor [9] and electroluminescent [10] and solar cell technology [11]. In recent years,
the researchers use computational methods to characterize the organic compounds and metal
complexes because of their good efficiency and great precision with respect to the expected
number of molecular properties [12]. Also, theoretical studies were very supportive to evaluate
compound molecular properties economically and to clarify some experimental phenomena
insightfully [13, 14]. Metal dithiocarbamate complexes have proven to be successful as single
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source precursors for the preparation of EuS, PdS, PtS, PbS, Bi2S3, NiS, Ni3S2, CuS, ZnS, and
CdS nanoparticles [15]. The phase and morphology of the resultant materials are often
influenced by the precursors (as well as by the solvent and thermolysis temperature) [16].
Cadmium dithiocarbamate complexes have been used as a precursor for the synthesis of CdS
nanoparticles [17]. Recently many efforts have been undertaken to synthesize and study the
optical properties of CdS nanoparticles and quantum dots due to their wide range of applications
such as laser light emitting diodes, solar cells and optoelectronic devices based on nonlinear
properties [18-20]. In this work, we have used complexes 1 and 2 as single source precursors and
ethyleneglygol, a non-volatile diol, as a solvent for the preparation of CdS nanoparticles via
solvothermal method. This is a simple and versatile method for the synthesis of nanoparticles in
a single pot process. The reaction is very rapid and the nanoparticles are easily purified. The
purpose of adding capping agent is to prevent agglomeration and attaining the material in a
nanosize. Ethylene glycol is used probably to increases stability of CdS nanoparticles, decreasing
aggregation, and keeping nanoparticles away from one another, even it effects morphology and
size of nanoparticles. We herein report synthesis and spectral studies on complexes 1 and 2 for
the preparation of CdS-nanoparticles. Single-crystal X-ray structure analysis and computational
studies of one of the complex 2 are also discussed.
2. Experimental
2.1. Materials and methods - general
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Commercial reagents and solvents used without further purification and all experiments
were carried out in air atmosphere. FT-IR spectra were recorded in the 4000–400 cm-1 region as
KBr pellets on a thermo scientific SHIMADZU spectrophotometer. The NMR spectra were
recorded on Bruker 400 MHz spectrometer at room temperature in CDCl3, using TMS as internal
reference (400 MHz for 1H NMR and 100 MHz for 13C NMR). The wide-angle X-ray diffraction
(XRD) was recorded using BRUKER ECO D8 ADVANCE X-ray diffractometer with CuK
radiation (=1.54178Å). Scanning Electron Microscopy (SEM, ZEISS instrument) was used to
characterize the morphologies of the samples.
2.2. X-ray crystallography and computational studies
Single crystal X-ray diffraction data for 2 were recorded on a Bruker APEX2
diffractometer using graphite-monochromated MoKα radiation (λ=0.71073 Å) at an ambient
temperature. The structure was solved by direct method using SHELXS-97 [21] (Sheldrick 2008)
and refined on F2 by full matrix least squares technique using SHELXL-2014/7 [22]. Non-
hydrogen atoms were refined anisotropically and the hydrogen atoms were refined isotropically.
Diagram for complex 2 were prepared using ORTEP [23] and Mercury software. The CIF files
have been deposited at the Cambridge Crystallographic Data Centre with reference numbers
CCDC no. 1525706. All the theoretical calculations were performed with GAUSSIAN09
program package [24] with the aid of the Gauss View-05 visualization program [25].
2.3 Synthesis of cadmium(II) complexes
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2.3.1 Synthesis of complex 1, bis(N-cyclopropyl-N-4-chlorobenzyldithiocarbamato-
S,S)cadmium(II)
Cyclopropylamine (4.6 mmol, 0.5 mL) and 4-chlorobenzaldehyde (5.1 mmol, 0.4 mL)
were dissolved in methanol (30 mL). The solution was stirred well for 2 h. and the solvent was
then removed by using rotary evaporator. Yellow oily product was obtained. The product thus
obtained was dissolved in a mixture of methanol-dichloromethane (1:1; 20 mL) and then sodium
borohydride (13.8 mmol, 0.5 g) was added. The reaction mixture was stirred at 5 °C for 2 h.
followed by room temperature for 20 h. After evaporation of the solvent, a viscous liquid was
resulted. It was then washed with water and, dichloromethane was added in order to extract the
product. After evaporation of the organic layer, N-cyclopropyl-N-(4-chloro)benzylamine was
obtained as a pale yellow oil. Then, carbon disulfide (4.0 mmol) was added drop wise to a
ethanolic solution of N-cyclopropyl-N-(4-chlorobenzyl)amine (4.0 mmol) and the solution was
stirred for 30 min. under the ice cold condition to get the intermediate, N-cyclopropyl-N-4-
chlorobenzyldithiocarbamic acid as a yellow liquid.
Complex 1 was achieved by mixing an aqueous solution of cadmium acetate (2.0 mmol)
and an ethanolic solution of the intermediate N-cyclopropyl-N-4-chlorobenzyldithiocarbamic
acid. The addition of metal salt into the yellow dithiocarbamic acid solution resulted in the
immediate formation of pale yellow precipitate. After stirring for 30 min, the pale yellow
precipitate was filtered off, washed with cold water and dried to get pure title molecule 1. Yield
78%. IR (KBr, cm–1):  = 1433 (C–N); 984 (C–S). 1H NMR (400 MHz, CDCl3, ppm): = 5.15 (s,
4H, 4Cl–C6H4–CH2–N); 3.00-3.06 (m, 2H, N–CH (cPr)); 0.83-0.88 (m, 8H, CH2 (cPr)); 7.23-
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7.32 (m, 8H, aromatic protons). 13C NMR (100 MHz, CDCl3, ppm):  = 10.5 (CH2 (cPr)); 38.4
(CH (cPr)); 59.5 (C6H5–CH2–N); 128.7-134.5 (aromatic carbons); 210.1 (NCS2); Anal. Calcd. for
Chemical Formula: C24H30N2NiS4 (%):Elemental Analysis: C, 49.09; H, 5.15; N, 4.77; Found: C,
48.96; H, 5.03; N, 4.67.
2.3.2 Synthesis
of
complex
2,
(2,2-bipyridine)bis(N-cyclopropyl-N-4-
chlorobenzyldithiocarbamato-S,S)cadmium(II)
A hot solution of 2,2-bipyridine (2.0 mmol, 0.31 g) in ethanol was added to a hot solution
of (N-cyclopropyl-N-4-chlorobenzyldithiocarbamato-S,S)cadmium(II) (1.0 mmol, 0.494 g) in
chloroform. The resulting mixture was cooled and then it was diluted with petroleum ether (40-
60). The heteroleptic complex 2 was separated out as a yellow precipitate, which was filtered
and dried. Yield: 90%,. IR (KBr, cm–1):  =1445(C–N); 978 (C–S). 1H NMR (400 MHz, CDCl3,
ppm): = 5.18 (s, 4H, 4Cl–C6H4–CH2–N); 2.96-3.00 (m, 2H, N–CH (cPr)); 0.83-0.88 (m, 8H,
CH2 (cPr)); 7.17-9.09 (m, 16H, aromatic protons); 13C NMR (100 MHz, CDCl3, ppm):  =10.4
(CH2 (cPr)); 37.7 (CH (cPr)); 59.0 (4Cl–C6H4–CH2–N); 121.3-150.3 (aromatic carbons); 213.2
(NCS2). Anal. Calcd. for Chemical Formula: C32H30CdCl2N4S4 (%):Elemental Analysis: C, 49.14;
H, 3.87; N, 7.16; Found: C, 49.01; H, 3.63; N, 7.12.
2.4. Synthesis of ethylene glycol capped cadmium sulfides
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2.4.1 Synthesis of cadmium sulfide
The complex 1 (0.5 g) was dissolved in ethylene glycol (15 mL) in a RB flask and then
heated to 120 ºC and maintained at the same temperature for 5 min. After cooling, the obtained
yellow precipitate was filtered and washed with methanol to furnish pure cadmium sulfide
nanoparticles (CdS1). Similar procedure was adopted for the synthesis of CdS2 nanoparticles
from complex 2.
3. Results and discussion
3.1. Synthesis
The schematic representation for the synthesis of complexes 1 and 2 is furnished in
Scheme 1. Reaction between cyclopropylamine and 4-chlorobenzaldehyde at ambient
temperature gave its corresponding imine, which upon reduction with sodium borohydride, a
secondary amine, N-cyclopropyl-N-(4-chloro)benzylamine was produced. The secondary amine
thus obtained was then treated with carbon disulfide to furnish the intermediate N-cyclopropyl-
N-4-chlorobenzyldithiocarbamic acid. The cadmium complex 1, bis(N-cyclopropyl-N-4-
chlorobenzyldithiocarbamato-S,S)cadmium(II) was then synthesized by the reaction of aforesaid
N-cyclopropyl-N-4-chlorobenzyldithiocarbamic acid intermediate with cadmium acetate. The
cadmium complex 2, (2,2-bipyridine)bis(N-cyclopropyl-N-4-chlorobenzyldithiocarbamato-
S,S)cadmium(II) was eventually synthesized from the cadmium complex 1 by its reaction with
2,2-bipyridine.
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Scheme 1
3.2. IR spectral studies
Two significant expected bands in the FT-IR spectra of dithiocarbamate complexes 1 and
2 are due to the C–N and C–S modes [26]. In the present study, the IR spectra of 1 and 2 show
the thioureide (C–N) band at 1433 and 1445 cm-1, respectively, indicating its partial-double-bond
character. In complex 2, the shift in νC–N (thioureide) band appeared with a higher wave number
(1445 cm-1) compared with parent complex 1 (1433 cm-1) and this difference in wave numbers is
due to the change of coordination geometry from tetrahedral to octahedral [27, 28]. The C–S
band resulted around 980 cm-1 for complexes 1 and 2 without any splitting, supporting the
bidentate coordination of the dithiocarbamate moiety [29]. The characteristic bands due to 2,2'-
bipyridine was observed at 1589 cm-1 in complex 2 [30].
3.3. 1H NMR Spectral Studies
In the complexes 1 and 2, eight protons multiplets observed in the extreme upfield region
between 0.83 and 0.88 ppm are assigned to methylene protons of cyclopropyl moiety. Two
protons multiplets observed around 2.96-3.06 ppm are due to the methyne protons of cyclopropyl
unit and four protons singlets resulted at 5.15-5.18 ppm are corresponds to methylene protons of
benzyl moiety. The observed significant downfield shift of methlene protons of benzyl moiety
compared to the methylene protons of cyclopropyl moiety is apparently because of the electron
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with drawing nature of the aryl ring and the presence of nitrogen at the -position [31]. In
complexes 1-2, the aromatic protons observed as multiplets in the region 7.17-9.09 ppm.
3.4. 13C NMR Spectral Studies
The most important 13C NMR chemical shift value of the thioureide carbon (N13CS2) is
observed at 210.1 and 213.2 ppm for complexes 1 and 2, respectively. The N13CS2 carbon sites
of adduct (2,2'-bipyridine) complex (213.2 ppm) are additionally deshielded compared to the
parent complex (210.1 ppm). Additional coordination of nitrogenous bases to cadmium
dithiocarbamates yields a decrease of nitrogen-carbon partial double bond character and, as a
result, displacement of electron density from carbon to nitrogen of dithiocarbamate occurs
[32]. This explains the additional deshielding of carbon sites in the N13CS2 of adducts. In the
complexes 1 and 2, the signals for methylene carbons of benzyl group and methylene carbons of
cyclopropyl group appear around 59.0 and 10.0 ppm, respectively. The signal resulted at around
38.0 ppm for both the complexes is assigned to the methyne carbon of cyclopropyl group. In all
the cases, aromatic carbon signals appeared in the region 121.3-150.3 ppm.
3.5. X-ray crystallography
Figure 1
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ORTEP of complex 2 is shown in Fig. 1. Details of the crystal data, data collection and
refinement parameters for complex 2 are summarised in Table 1. Selected bond distances and
angles are presented in Table 2. The structure of complex 2 contains four discrete monomeric
units (Z=4) per unit cell. Cadmium ion is hexa-coordinated with four sulfur atoms from two
chelating dithiocarbamates and two nitrogen atoms from 2,2'-bipyridine rings. The 2,2-
bipyridine ligand is almost planar. Molecular parameters associated with 2,2-bipyridine are
normal.
Table 1
Table 2
The fact is that the dithiocarbamate ligand linked to cadmium and almost symmetric C–S
[C11-S1=1.702(6); C11-S2=1.721(5)] distances are shorter than the typical C–S single bond
distance 1.81 Å. Consequently, all the C–S bonds in the present structure are of partial double
bond character as observed in most of the dithiocarbamates [33-34]. The Cd–S [2.6567(9) and
2.6609(7) Å] bonds are also almost symmetric, showing that the negative charge on the
dithiocarbamate ligand is equally distributed all over the two donor atoms. Average C–N
distances of complex are 1.327(4) and 1.308(17) Å, which clearly indicates the contribution of
the thioureide form to the dithiocarbamate ligand. This contrast well with the adjacent typical
single bonded N–C distances. For complex 2, in addition to the van der Waals interactions, the
complex molecules are bonded to neighboring molecule through C1-H1…S3 and C10-H10…S2
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interactions, resulting in a polymeric chain structure (Fig. 2, Table 3). The intermolecular C-
H…π hydrogen bond interaction was resulting in a flying birds structure (Fig. 3).
Figure 2
Figure 3
Table 3
3.6. Theoretical studies
3.6.1. Optimized geometry
The optimized molecular structure of complex 2 was calculated using DFT/B3LYP
method with LANL2DZ basis set. The optimized structure is shown in Fig. 4 and the comparison
between selected bond lengths and bond angles are given in Table 4. The experimental N-C
bond length is 1.35(6) Å, while the computed length is 1.37 Å. This confirms the thioureide (C–
N) bond. The X-ray C=S bond length of CS2, C-S is 1.72 Å (computed is 1.779 Å). The result is
as expected for partial double bonds of CS2M. The important X-ray bond angles between the
planes S-C-S and N-C-S are 117.23(15)° (computed is 118.8°) and 121.23(19)° (computed is
120.4°) respectively. The experimental and computed data are in good agreement with each
other. There are observable intermolecular interactions in the complex 2 [Figs. 2 and 3]. It is
found that most of the optimized geometry parameters are slightly higher than the experimental
values. These deviations from the experimental and computed structural parameters are due to X-
ray measurement being in the solid state whereas computations are performed in the gaseous
phase [35]. In the solid state, the existence of a crystal field along with the intermolecular
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interactions connects the molecules together, which results in the small differences in bond
parameters between the calculated and experimental values.
Figure 4
Table 4
The frontier molecular orbitals play an important role in the electric and optical
properties, as well as in UV-Vis spectra and chemical reactions [36]. The pictorial diagram of
HOMO-LUMO energy gap for the conformers 2 are shown in Fig. 5. The HOMO–LUMO
orbital's for complex 2 were also calculated through DFT/ B3LYP method using LANL2DZ
basis set. As can be seen that for the complex 2, HOMO is concentrated over the CS2 moiety
while LUMO spreads over the 2,2'-bipyridine ring without involving [Cd(dtc)2]. The HOMO and
LUMO energies, the energy gap (∆E), the ionization potential (I), the electron affinity (A), the
absolute electronegativity (χ), the absolute hardness (η) and softness (S) [37] for the complex 2
have been calculated at B3LYP/LANL2DZ basis set (Fig 5) and the results are given in the
Table 5. The energy gap between the HOMO and LUMO are related to the hardness of a
molecule, η, which is defined as: η = (I-A)/2, where I and A are the ionization potential and the
electron affinity of the system, respectively. The hardness of complex 2 is then calculated as -
1.2299 eV.
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Figure 5
Table 5
Investigating the molecular electrostatic potential (MEP) generated in the space around a
molecule by the charge distribution is very helpful in understanding the sites for electrophilic
attacks and nucleophilic reactions for the study of biological recognition processes and hydrogen
bonding interactions [38]. The different values of the electrostatic potential at the surface are
represented by different colors; red represents regions of most electronegative electrostatic
potential, blue represents regions of the most positive electrostatic potential and green represents
region of zero potential. Potential increases in the order red<orange<yellow<green<blue [39].
The MEP map of complex 2 is given in Fig. 6, and it was based on the calculations performed in
the B3LYP/LANL2DZ. As can be seen in Fig. 6, there are several possible sites for nucleophilic
attack (bule). According to these calculated results, the MEP map shows that the negative
potential sites are on sulfur atoms and the positive potential sites are around the nitrogen atoms,
respectively.
Figure 6
3.7. Characterization of ethyleneglycol capped CdS nanoparticles
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The powder X-ray diffraction patterns of CdS1 and CdS2 are shown in Fig. 7. In the Fig.
7 (a and b), the observed peaks are widened, which indicate nano crystalline size of both the
systems. All diffraction peaks can be indexed to the hexagonal CdS (JCPDS: 00-041-1049) [40].
No impurity phase was detected for the CdS pattern. The mean crystallite sizes are estimated using
Debye-Scherrer formula as 6 and 4 nm for CdS1 and CdS2, respectively.
Figure 7
The morphologies of CdS1 and CdS2 are observed by SEM measurement. SEM images
of CdS1 and CdS2 are shown in Figs. 8 and 9, respectively. SEM image of CdS1 (Fig. 8) shows
that two types of morphologies are present; most of the particles are quasi-spherical while the
rest of them are shapeless. SEM image of CdS2 (Fig. 9) exhibits that all the particles are
shapeless. The HRTEM images of CdS2 are shown in Fig. 10. The CdS2 appear to be
agglomerated although the extent of agglomeration in cube shaped particles. Inter planar distance
for CdS2 an individual crystallite size was estimated around d=2.0645 which corresponding to
the (112) lattice plane of the hexagonal phase CdS (JCPDS: 00-041-1049).
Elemental colour mapping of CdS1 and CdS2 shows homogeneity of the particles, which
supports the uniform distribution of cadmium and sulfur. This also indicates the high purity of
the CdS nanoparticles. It is evident from the Figs 8 and 9 (b and c) that Cd and S are higher in
density. The formation of ethylene glycol capped cadmium sulfide was confirmed using the
EDAX analysis. EDAX spectra of CdS1 and CdS2 are shown in Fig. 11 (a and b). Energy
dispersive X-ray spectra of CdS1 and CdS2 reveal the presence of Cd and S. In both the cases
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strong signals are confirmed on the presence of Cd to S close to ratio 1:1, which corresponds to
the formation of CdS.
Figure 8
Figure 9
Figure 10
Figure 11
UV-Vis absorption spectra for as-prepared cadmium sulfide (CdS1 and CdS2)
nanoparticles from different precursors 1 and 2 are shown in Fig. 12. An absorption shoulder
peak was observed at 503 and 509 nm for CdS1 and CdS2, respectively. In the cases, the blue
shift of the absorption peak relative to bulk CdS (512 nm) [41] indicates that the cadmium
sulfide particles are quantum confined.
Figure 12
The DRS UV–vis absorption spectra for CdS1 and CdS2 are shown in Fig. 13. In
amorphous and crystalline material, the optical absorption coefficient (α) at the absorption edge
is expressed by the following relationship
α = β/hv(hv−Eg )n
where β is the energy independent constant dependent on the nature of optical
transition, Eg is the optical band gap of nanocrystallite and exponent n may have the values 1/2
or 2 depending on whether the transition is indirect or direct respectively. The UV–vis spectra
for CdS1 and CdS2 exhibit excitonic peak in the range of 400-450 nm. For n = 1/2, Eg in above
equation is direct allowed band gap. The average band gap were estimated from the linear
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portion of (αhν)2 Vs hν plots. The band gap is found to be 2.579 and 2.558 eV (Fig.14) which is
higher than the value of bulk CdS (eV) due to quantum confinement of CdS nanoparticles.
Figure 13
Figure 14
Fluorescence spectra of CdS1 and CdS2 nanoparticles were recorded at excitation
wavelength of 400 nm at room temperature and the resulting spectra are shown in Fig. 15. The
fluorescence peaks around 470 and 515 nm for as-prepared CdS1 and CdS2 was observed. They
are commonly attributed to the excitonic (or) band edge emission and surface trapped emission,
respectively.
Figure 15
4. Conclusions
New Cd(II) complexes 1 and 2 were prepared and characterized by IR and NMR
spectroscopy. A Complex 2 were characterized by single crystal X-ray diffraction analysis. All
the theoretical results show good correlations with experimental data. The lowering of HOMO
and LUMO energy gap gives significant information about the complex 2. Further, reported
herein is a simple solvothermal decomposition method for the synthesis of very high quality
cadmium sulfide (CdS1 and CdS2) using a new single source precursor in a single pot reaction
process. CdS (CdS1 and CdS2) were homogeneously dispersed surface of Cd and S by using
elemental colour mapping.
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Acknowledgement
Dr ES gratefully thanks Dr. S. Thirumaran, Department of Chemistry, Annamalai
University, India for some important clarifications.
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Scheme 1. Preparation of complexes 1and 2

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Fig. 1. ORTEP diagram of complex 2.

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Fig. 2. Polymeric chain through intermolecular C-H…S interactions.

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Fig. 3. Intermolecular flying birds C–H…π interactions (2.997 Å) in complex 2.

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Fig.4. Optimized structure of complex 2 computed at B3LYP-LANL2DZ.