Synthesis, spectral and X-ray structural studies on Hg(II) dithiocarbamate complexes: A new precursor for HgS nanoparticles

Article abstract of DOI:10.1016/j.poly.2015.04.020

Bis(N-furfuryl-N-(2-phenylethyl)dithiocarbamato-S,S′)mercury(II) (1), bis((furan-2-yl)methyl(2-(thiophen-2-yl)ethyl)dithiocarbamato-S,S′)mercury(II) (2), bis(N-benzyl-N-(2-(thiophen-2-yl)ethyl)dithiocarbamato-S,S′)mercury(II) (3) and bis(N-furfuryl-N-prop

Full text of DOI:10.1016/j.poly.2015.04.020

Polyhedron 96 (2015) 16–24
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, spectral and X-ray structural studies on Hg(II)
dithiocarbamate complexes: A new precursor for HgS nanoparticles
b
Sajad Hussain Dar a, S. Thirumaran a, , S. Selvanayagam
⇑
a Department of Chemistry, Annamalai University, Annamalainagar 608 002, India
b Department of Physics, Kalasalingam University, Krishnankoil 626 126, India
a r t i c l e i n f o
a b s t r a c t
Bis(N-furfuryl-N-(2-phenylethyl)dithiocarbamato-S,S0)mercury(II) (1), bis((furan-2-yl)methyl(2-(thio-
phen-2-yl)ethyl)dithiocarbamato-S,S0)mercury(II) (2), bis(N-benzyl-N-(2-(thiophen-2-yl)ethyl)dithiocar-
bamato-S,S0)mercury(II) (3) and bis(N-furfuryl-N-propyldithiocarbamato-S,S0)mercury(II) (4) have been
prepared and characterized by IR and NMR spectroscopy. Compounds 1 and 2 have also been character-
ized by the X-ray diffraction technique. In complexes 1 and 2, the metal centres are five and four coor-
dinated, respectively. The coordination geometry of 1 is intermediate between a square pyramidal and
Article history:
Received 1 January 2015
Accepted 8 April 2015
Available online 28 April 2015
Keywords:
Mercury(II) dithiocarbamates
Single source precursor
Mercury sulfide nanoparticles
Hydrogen bond
trigonal bipyramidal coordination polyhedron, with s5 = 0.53. Hg(II) is in a distorted [HgS4] tetrahedral
environment in compound 2. This difference in geometry between complexes 1 and 2 is probably due
to the effect of the N-bound organic moiety of the dithiocarbamate ligand and the crystal packing. The
crystal structures show the presence of C–Hꢀ ꢀ ꢀS interactions. Complex 2 has been dissolved in ethylene-
diamine and refluxed for 15 min and 1 h to yield ethylenediamine capped mercury sulfide and mercury
sulfide without a capping agent (en), respectively. The resulting nanoparticles have been characterized by
powder X-ray diffraction (PXRD), SEM, EDAX, IR, UV–Vis and fluorescence spectroscopy. The powder X-
Crystal structure
ray diffraction data confirm the particles to be very crystalline with the
both samples.
a phase (cinnabar) present in
Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction
to the group II–IV chalcogenides and they are a useful material
with wide applications in many fields, such as ultrasonic transduc-
ers, image sensors, electrostatic image materials, photoelectric
conversion devices, catalysts and infrared detectors, because of
their narrow band gap [14–16]. Hg(II)dithiocarbamates have been
used as single source precursors to produce nanocrystalline HgS
[17–19]. The phase and morphology of the metal sulfide nanopar-
ticles are influenced by the precursor (as well as by the solvent and
thermolysis temperature) [18–20].
Due to the interesting structural variations of Hg(II) dithiocar-
bamate complexes and the applications of HgS nanoparticles,
herein we present the synthesis and spectral studies on complexes
1–4 and the structures of 1 and 2. In addition, preparation of mer-
cury sulfide nanoparticles with and without a capping agent
(ethylenediamine) from 2 and their characterization are also
reported.
Dithiocarbamates (R2NCSꢁ2 ) are a versatile class of monoanionic
1,1-dithio ligand which form stable complexes with transition and
non-transition metal ions and show a variety of coordination
modes [1,2]. Metal dithiocarbamate complexes have been exten-
sively studied in different fields, including industrial applications
such as vulcanization additives and stabilizers for PVC, as well as
pharmacological activities like anticancer, anti-inflammatory, anti-
fungal, antimalarial, antiulcer and antioxidant activities [3–12].
Five distinct structural motifs have been reported for mercury
i.e., two monomeric motifs (tetrahedral and square planar), two
dimeric motifs (in one motif there is a centrosymmetric relation-
ship, implying the bridging dithiocarbamate ligands are on either
side of the central Hg2S2 trapezoidal plane, whereas in the other
motif there is a 2-fold symmetry so that the bridging ligands are
on the same side of the central plane) and [Hg(S2CNH2)2] adopts
a 2-dimensional motif [13]. Mercury sulfide nanoparticles belong
2. Experimental
All reagents and solvents were commercially available high-
grade materials (Merck/Sd fine/Himedia) and were used as
received. Elemental analysis was performed using a Perkin Elmer
⇑
Corresponding author at: Department of Chemistry, Annamalai University,
Annamalainagar 608 002, Tamil Nadu, India. Tel.: +91 9842897597.
E-mail address: sthirumaran@yahoo.com (S. Thirumaran).
http://dx.doi.org/10.1016/j.poly.2015.04.020
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

S.H. Dar et al. / Polyhedron 96 (2015) 16–24
17
2400 series II CHN analyzer. IR spectra were recorded on a Thermo
NICOLET AVATAR 330 FT-IR spectrophotometer (range 400–
4000 cmꢁ1) as KBr pellets. The NMR spectra were recorded on
either a BRUKER 400 MHz or BRUKER 500 MHz NMR spectrometer
at room temperature in CDCl3, using TMS as an internal reference.
The powder X-ray diffraction (XRD) patterns of the samples were
recorded at room temperature using a SEIFERT JHOD DYE FLEX
2.2.2. Preparation of 1
N-furfuryl-N-(2-phenylethyl)amine (6 mmol, 1.2 mL) in ethanol
was mixed with carbon disulfide (6 mmol, 0.4 mL) under ice cold
condition. To the resultant yellow dithiocarbamic acid solution,
an aqueous solution of HgCl2 (3 mmol, 0.814 g) was added with
constant stirring. The solid which precipitated was washed several
times with cold water and then dried. Single crystals suitable for X-
ray structural analysis were obtained by slow evaporation of an
2002 diffractometer with Cu Ka radiation (1.54178 Å). The surface
morphology and EDAX studies were performed using a JEOL 6360
microscope operating at 15.0 kV. A Perkin Elmer Lambda 35
UV–Vis spectrophotometer was used for recording UV–Vis absorp-
tion spectra of the HgS nanoparticles. Fluorescence spectra were
recorded using a Perkin Elmer LS 55 spectrofluorimeter.
acetonitrile solution of 1. Yield: 74%. IR (KBr, cmꢁ1): 1480 (
1013 (
C–S); 3107 (mC–H (furyl)); 3068 (mC–H (phenyl)). 1H NMR
mC–N);
m
(500 MHz, CDCl3, ppm) d: 3.06 (4H, t, J = 8HZ, CH2–C6H5), 4.01
(4H, t, J = 8HZ N–CH2–CH2–C6H5), 4.96 (4H, s, N–CH2(furfuryl)),
6.40–7.32 (aromatic protons); 13C NMR (125 MHz, CDCl3, ppm) d:
2.1. X-ray crystallography
Diffraction data for 1 and 2 were recorded on an Xcalibur
Sapphire3 diffractometer using graphite-monochromated Mo K
a
radiation (k = 0.71073 Å) at an ambient temperature (100 K). The
structures were solved by SIR92 [21] and refined by full-matrix
least-square methods in SHELXL-97 [22]. All the non-hydrogen atoms
were refined anisotropically and the hydrogen atoms were refined
isotropically. Details of the crystal data and structure refinement
parameters for 1 and 2 are summarized in Table 1.
2.2. Preparation of the complexes
2.2.1. Preparation of the amines
N-furfuryl-N-(2-phenylethyl)amine,
(furan-2-yl)methyl(2-
(thiophen-2-yl)ethyl)amine, benzyl(2-(thiophen-2-yl)ethyl)amine
and N-furfuryl-N-propylamine were prepared by general methods
reported earlier [23] (Scheme 1 and Fig. 1). The aldehyde was con-
densed with the primary amine to form the imine. Sodium borohy-
dride reduction of the imine in methanol–dichloromethane yielded
the secondary amine.
Complex 1; R= Phenylethyl, R'=Furfuryl
Complex 2; R= Thiopheneethyl, R' =Furfuryl
Complex 3; R= Thiopheneethyl, R' =Benzyl
Complex 4; R= Propyl, R' =Furfuryl
Scheme 1. Preparation of complexes.
Table 1
Crystal data, data collection and refinement parameters for 1 and 2.
1
2
Empirical formula
Formula weight
Crystal dimensions
Crystal system
Space group
a (Å)
C
56H56Hg2N4O4S8
C48H48Hg2N4O4S12
1530.81
1506.70
0.30 ꢂ 0.25 ꢂ 0.20
0.25 ꢂ 0.20 ꢂ 0.15
triclinic
triclinic
ꢀ
ꢀ
P1
P1
10.0521(3)
12.1659(4)
13.4372(5)
89.583(2)
73.585(2)
68.128(2)
1453.94(8)
1
10.0468(3)
10.2979(3)
14.2050(4)
74.032(2)
87.815(2)
83.924(2)
1404.96(7)
1
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg mꢁ3
)
1.721
5.608
740
1.809
5.949
748
Absorption coefficient (mmꢁ1
F(000)
)
k (Å)
Mo Ka
(0.71073)
Mo Ka (0.71073)
h Range (°)
1.59–29.43
1.49–30.59
Index ranges
ꢁ13 6 h 6 13, ꢁ16 6 k 6 16, ꢁ18 6 k = 18
ꢁ14 6 h 6 14, ꢁ14 6 k 6 14, ꢁ20 6 k = 19
Reflections collected
Independent reflections
Weighting scheme
27805
34110
7927 [Rint = 0.0277]
8598 [Rint = 0.0265]
Calc. w = 1/(
r
2(F2o) + (0.0411P)2) where P = (Fo2 + 2F2c)/3
Calc. w = 1/(r
2(Fo2) + (0.0443P)2 + 0.0000P) where P = (Fo2 + 2F2c)/3
Number of parameters refined
334
316
Final R indices [I > 2
R indices (all data)
Goodness-of-fit (GOF)
r
(I)]
R1 = 2.6%, wR2 = 6.0%
R1 = 4.7%, wR2 = 8.0%
1.099
R1 = 3.9%, wR2 = 11.6%
R1 = 6.1%, wR2 = 13.23%
1.021

18
S.H. Dar et al. / Polyhedron 96 (2015) 16–24
Yield: 75%. IR (KBr, cmꢁ1): 1480 (
mC–N); 1017 (mC–S); 3112 (mC–H
(aromatic)). 1H NMR (500 MHz, CDCl3, ppm) d: 3.28 (4H, t,
J = 8HZ, N–CH2–CH2–C4H3S), 4.08 (4H, t, J = 8HZ, N–CH2–
CH2–C4H3S), 4.98 (4H, s, N–CH2 (furfuryl)), 6.40–7.45 (aromatic
protons); 13C NMR (125 MHz, CDCl3, ppm) d: 27.0 (N–CH2–
CH2–C4H3S), 53.7 (N–CH2–CH2–C4H3S), 57.7 (N–CH2 (furfuryl)),
110.6–148.1 (aromatic carbons), 205.9 (NCS2). Anal. Calc. for
C24H24HgN2O2S6: C, 37.63; H, 3.14; N, 3.66. Found: C, 37.49; H,
3.06; N, 3.58%.
2.2.4. Preparation of 3
A method similar to that described for the synthesis of 1 was
adopted; however benzyl(2-(thiophen-2-yl)ethyl)amine was used
instead of N-furfuryl-N-(2-phenylethyl)amine. Yield: 78%. IR (KBr,
cmꢁ1): 1489 (
(
m
C–N); 1019 (
mC–S); 3107 (mC–H (thiophene)); 3068
mC–H (phenyl)). 1H NMR (500 MHz, CDCl3, ppm) d: 3.33 (4H, t,
J = 7.5HZ, N–CH2–CH2–C4H3S), 3.97 (4H, t, J = 7.5HZ, N–CH2–CH2–
C4H3S), 4.98 (4H, s, N–CH2 (benzyl)), 6.88–7.41 (aromatic protons);
13C NMR (125 MHz, CDCl3, ppm) d: 27.1 (N–CH2–CH2–C4H3S), 57.3
(N–CH2–CH2–C4H3S), 61.4 (N–CH2–C6H5), 124.3–139.9 (aromatic
carbons), 205.7 (NCS2). Anal. Calc. for C28H28HgN2O2S6: C, 42.81;
H, 3.59; N, 3.57. Found: C, 42.67; H, 3.51; N, 3.49%.
2.2.5. Preparation of 4
A method similar to that described for the synthesis of 1 was
adopted; however N-furfuryl-N-propylamine was used instead of
N-furfuryl-N-(2-phenylethyl)amine. Yield: 69%. IR (KBr, cmꢁ1):
1462 (mC–N); 1016 (m
C–S); 3101 (mC–H (furyl)). 1H NMR (500 MHz,
CDCl3, ppm) d: 0.92 (6H, t, J = 7.5HZ, N–CH2–CH2–CH3), 1.77–1.80
(4H, m, N–CH2–CH2–CH3), 3.77 (4H, t, J = 7.5HZ, N–CH2–CH2–
CH3), 5.15 (4H, s, N–CH2 (furfuryl)), 6.39–7.42 (aromatic protons);
13C NMR (125 MHz, CDCl3, ppm) d: 11.2 (N–CH2–CH2–CH3), 20.1
(N–CH2–CH2–CH3), 53.2 (N–CH2–CH2–CH3), 58.7 (N–CH2 (fur-
furyl)), 110.6–148.0 (furyl ring carbons), 203.6 (NCS2). Anal. Calc.
for C18H24HgS4N2O2: C, 34.36; H, 3.84; N, 4.45. Found: C, 33.98;
H, 3.77; N, 4.39%.
2.3. Preparation of mercury sulfide
2.3.1. Preparation of ethylenediamine capped mercury sulfide (HgS1)
0.5 g of 2 was dissolved in 15 mL of ethylenediamine in a flask
and then refluxed for 15 min. The red precipitate obtained was fil-
tered and washed with methanol.
2.3.2. Preparation of mercury sulfide (HgS2)
0.5 g of 2 was dissolved in 15 mL of ethylenediamine in a flask
and then refluxed for 1 h. The black precipitate obtained was fil-
tered and washed with methanol.
3. Results and discussion
Fig. 1. Structure of complexes (a) 1 (b) 2 (c) 3 (d) 4.
3.1. Spectroscopic characterization
The IR spectra of complexes 1–4 exhibit a characteristic band in
the region 1462–1489 cmꢁ1 corresponding to the (N–CS2) stretch-
ing vibration. The values indicate that the carbon–nitrogen bond
32.8 (N–CH2–CH2–C6H5), 53.7 (N–CH2–CH2–C6H5), 58.1 (N–CH2
(furfuryl)), 110.7–148.1 (aromatic carbons), 204.8 (NCS2). Anal.
Calc. for C28H28S4N2O2Hg: C, 44.60; H, 3.72; N, 3.72. Found: C,
44.38; H, 3.58; N, 3.64%.
order (N–CS2) is intermediate between
a
single (1250–
1350 cmꢁ1) and double bond (1640–1690 cmꢁ1) [24,25]. The IR
spectra of metal dithiocarbamate complexes show that the pres-
ence of only one band in the region 940–1060 cmꢁ1 can be attrib-
uted to the completely symmetrical bonding of the
dithiocarbamate ligand, acting in a bidentate mode, as reported
by Bonati and Ugo [26]. In the complexes 1–4, the presence of only
one band around 1015 cmꢁ1, suggests a bidentate coordination of
the dithiocarbamate moiety. The phenyl ring C–H and
2.2.3. Preparation of 2
A method similar to that described for the synthesis of 1 was
adopted; however (furan-2-yl)methyl(2-(thiophen-2-yl)ethyl)amine
was used instead of N-furfuryl-N-(2-phenylethyl)amine. Single
crystals suitable for X-ray structural analysis were obtained by
slow evaporation of
a chloroform–acetonitrile (1:1) solution.

S.H. Dar et al. / Polyhedron 96 (2015) 16–24
19
furyl/thiophenyl ring C–H vibrations appear around 3060 and
3110 cmꢁ1, respectively.
two Hg atoms, forming a tricyclic fragment [Hg2S4C2]. As for most
of the known similar dithiocarbamate complexes, its geometry can
be approximated by the chair conformation [2]. The geometry of
this coordination polyhedron [HgS5] is intermediate between
tetragonal pyramid and trigonal bipyramid. The structure adopted
In the 1H NMR spectra of complexes 1–3, together with signals
in the aromatic region, there are three signals in the aliphatic
region. A singlet around 5.00 ppm is assigned to the methylene
protons of the furfuryl/benzyl groups and two triplets around 3.3
and 4.0 ppm are assigned to the ethylene group; that are shifted
to lower field, being nitrogen bound. For complex 4, a singlet
observed at 5.15 ppm and a triplet observed at 3.77 ppm are
assigned to the methylene protons of the furfuryl group and
NCH2 (propyl) protons, respectively. The methylene protons adja-
cent to nitrogen atom are observed in the downfield region com-
pared to other methylene protons due to the release of electron
density from the nitrogen of the NR2 group to the sulfur via the
by this complex is characterized by using the
coordination suggested by Addision et al. [27]. From the
s
-descriptor for five
value
s
(0.53), the coordination geometry is described as being 53% along
the pathway of distortion from tetragonal pyramid to trigonal
bipyramid. The crystal structure is stabilized by weak intramolec-
ular C–Hꢀ ꢀ ꢀS and C–Hꢀ ꢀ ꢀO hydrogen bonds. (Fig. 3, Table S1). One
hydrogen atom from each methylene group adjacent to the nitro-
gen atoms show weak intramolecular hydrogen bonding with the
sulfur atoms and each sulfur atom reveals two C–Hꢀ ꢀ ꢀS hydrogen
bonds. This indicates that the hydrogen atoms of the methylene
group adjacent to the nitrogen atoms are acidic; i.e., it may be
assumed that these hydrogen atoms are made more acidic in terms
of the identities of their adjacent atoms [28].
thioureide p-system.
The 13C NMR spectra of all the complexes exhibit one signal in
the downfield region, 203.6–205.9 ppm, which is due to the NCS2
carbon. In addition, the signals for the carbons of methylene
attached directly to the N atom appear at about 50–60 ppm.
These complexes also show the expected signals due to the carbons
of the aryl groups in the region 110–148 ppm.
3.3. Structural analysis of 2
The ORTEP diagram of 2 is shown in Fig. 4. Selected bond
lengths and angles are given in Tables 2 and 3, respectively.
[Hg2(ftpedtc)4] crystallized in the space group P1 with Z = 1. Each
3.2. Structural analysis of 1
ꢀ
The ORTEP diagram of 1 is shown in Fig. 2. Selected bond
lengths and angles are given in Tables 2 and 3, respectively. The
unit cell consists of half a molecule in the asymmetric unit and
the remaining part is generated with the symmetry (1 ꢁ x ꢁ 1,
ꢁy + 2, ꢁz + 2). A binuclear molecule is formed as adjacent mercury
atoms are connected by two bridging dithiocarbamate ligands, and
the remaining two dithiocarbamate ligands in the binuclear mole-
cule are terminal ligands. The terminal dithiocarbamate ligands are
coordinated to the mercury atom in a bidentate manner (Hg1–
S1 = 2.725 Å and Hg1–S4 = 2.4463 Å). The ligands with the mixed
(chelating and bridging) structural function are involved in the
dimerization of 1 via coordination to two Hg atoms. The bridging
S atoms are bound to the adjacent mercury atom more strongly
(Hg1–S1 = 2.725 Å and Hg1–S4 = 2.711 Å) than in their own che-
late ring [HgS2C] (Hg1–S8 = 3.109 Å and Hg2–S1 = 3.101 Å). The
ligands with the mixed structural function are coordinated by
mercury atom in the binuclear molecule is coordinated to two sul-
fur atoms of a chelating dithiocarbamate ligand to form a four-
membered ring defined by [HgS2C]. The other two dithiocarbamate
ligands bridge the two mercury atoms, which results in the forma-
tion of an eight membered [–Hg–S–C–S–]2 ring. The HgS bonds are
asymmetric. The coordination geometry about the Hg atom is dis-
torted tetrahedral, with the S1–Hg1–S2 bond angle substantially
compressed. The distorted tetrahedral arrangement of four sulfur
atoms around the mercury atom is supported by the dihedral
angle, 0.91(14)° [between Hg1–S3–C13–S4 and Hg2–S7–C37–S8],
of the two chelate planes (Hg–S–C–S). The crystal packing is
further stabilized by C–Hꢀ ꢀ ꢀS interactions. Two C–Hꢀ ꢀ ꢀS
(C–H18Bꢀ ꢀ ꢀS2 and C–H18Biꢀ ꢀ ꢀS2i; symmetry I = x ꢁ 1, y, z) inter-
molecular hydrogen bonds run in opposite directions, which lead
to the formation of a polymeric chain structure (Fig. 5). In this case
also the hydrogen atom of the methylene adjacent to the nitrogen
Fig. 2. ORTEP diagram of 1.

20
S.H. Dar et al. / Polyhedron 96 (2015) 16–24
Fig. 3. Molecular structure of 1 with intramolecular hydrogen bonds as dashed lines. For the sake of clarity, H atoms not involved in hydrogen bonds have been omitted.
Fig. 4. ORTEP diagram of 2.
atoms forms intramolecular hydrogen bonds with S atoms (Fig. 6).
This indicates that these hydrogen atoms are acidic in nature.
Details of the hydrogen bonding interactions are given in Table S2.
In both the complexes, the N–CS2 bond distances [1.33(2) and
1.32(2) for complexes 1 and 2, respectively] are significantly
shorter than the N–CH2 bonds. Moreover, the C2N–CS2 moieties
are almost planar: the C–N–C–S torsion angle values are close to
0° or 180°. Both of these features reflect the partial double bond
character of the N–CS2 bond. The average C–S bond lengths are
intermediate values between the C–S single bond and C@S double
bond distances, and are of partial double bond character [1,2].
Single crystal X-ray structural analysis of 1 and 2 show that
both complexes adopt a centrosymmetric dimeric structure. In
complex 1, the Hg atom is chelated by one dithiocarbamate anion
and the other dithiocarbamate anion uses one of its sulfur atoms to
bind to two Hg atoms through two bonds. The coordination geom-
etry around each Hg atom is intermediate between tetragonal
pyramid and trigonal bipyramid [HgS5]. In complex 2, however,
the Hg atom is chelated by one dithiocarbamate anion and the
other dithiocarbamate uses the two S atoms to bind to two differ-
ent Hg atoms. The geometry of the coordination polyhedron is dis-
torted tetrahedral (Fig. 1). The Hg–S bond lengths show that there
are two shorter Hg–S interaction (Table 2) for each mercury atom
which define the wide angle at mercury. To a first approximation,
these shorter Hg–S interactions satisfy the valency of mercury. The
other interactions mainly depend on the size and electronic effects
of the N-bound organic moiety of the dithiocarbamate ligands and
also crystal packing effect [13].
4. Characterization of HgS
4.1. Powder X-ray diffraction studies on HgS
To study the crystalline structures of the products, XRD
measurements were carried out at room temperature.

S.H. Dar et al. / Polyhedron 96 (2015) 16–24
21
Fig. 5. Perspective view of 2 showing intermolecular C–Hꢀ ꢀ ꢀS hydrogen bonds as dashed lines, which runs in opposite directions. For the sake of clarity, H atoms not involved
in hydrogen bonds have been omitted.
Fig. 6. Molecular structure of 2 with intramolecular hydrogen bonds as dashed lines. For the sake of clarity, H atoms not involved in hydrogen bonds have been omitted.
Table 2
with the standard data from the JCPDS card No. 6-0256. The sharp
peaks indicate that the products are well crystalline. The mean
Selected bond lengths (Å) of 1 and 2.
crystallite size can be determined from the half-width of the
diffraction peaks using the Debye–Scherrer formula [29]
1
2
Hg(1)–S(1)
Hg(1)–S(2)
Hg(1)–S(3)
Hg(1)–S(4)
Hg(1i)–S(1)
S(1)–C(1)
2.7247(8)
2.4100(9)
2.4629(9)
2.7109(9)
2.7250 (9)
1.722(3)
1.729(3)
1.733(3)
1.705(3)
1.318(4)
1.327(4)
Hg(1)–S(1)
Hg(1)–S(2)
Hg(1)–S(3)
Hg(1)–S(4)
Hg(1i)–S(1)
S(1)–C(1)
2.4165(13)
2.6894(12)
2.4884(11)
2.6856(13)
2.7250 (9)
1.726(5)
1.729(3)
1.733(3)
1.705(3)
1.318(4)
a
k
D ¼
b cos h
where D is the mean particle size,
a
is the geometric factor (equal to
0.94), k is the X-ray wavelength (1.5406 Å), b is the full-width at
half-maximum of the diffraction peak on the 2h scale and h is the
angle of diffraction peak. The calculated mean crystallite sizes are
33 and 29 nm for HgS1 and HgS2, respectively.
S(2)–C(1)
S(2)–C(1)
S(3)–C(15)
S(4)–C(15)
N(1)–C(1)
N(2)–C(15)
S(3)–C(15)
S(4)–C(15)
N(1)–C(1)
N(2)–C(15)
1.327(4)
4.2. Scanning electron microscopy (SEM) studies
Ethylenediamine capped mercury sulfide and mercury sulfide
without a capping agent, prepared by refluxing an ethylenedi-
amine solution of [Hg(ftpedtc)2] for 15 min and 1 h, are repre-
sented as HgS1 and HgS2, respectively. The powder X-ray
diffraction patterns of HgS1 and HgS2 are shown in
Fig. 7(a) and (b), respectively. All the diffraction peaks can be
indexed to hexagonal HgS (cinnabar), and are in good agreement
The morphologies of HgS1 and HgS2 are observed by SEM mea-
surements. The SEM images of HgS1 and HgS2 are shown in Fig. 8.
The SEM images of HgS1 (Fig. 8(a)) show that two types of mor-
phology are present; most of the particles are shapeless, while
the remainder are cubic. The surfaces of all the particles are
smooth. All the shapeless particles consist of relatively big aggre-
gates of thin layers, the particle size ranges from several hundred

22
S.H. Dar et al. / Polyhedron 96 (2015) 16–24
Fig. 7. Powder X-ray diffraction of (a) HgS1 and (b) HgS2.
nanometers to a few micrometers. The SEM images of HgS2
(Fig. 8(b)) show that all the particles are shapeless and the surfaces
are not smooth. The average size of the particles in HgS1 is larger
than in HgS2. In both cases, the average size of the particles is lar-
ger than that estimated by the Scherrer formula from the PXRD
pattern. Thus we considered that the particles are composed of
smaller crystallites.
Fig. 8. SEM images of (a) HgS1 and (b) HgS2.
4.3. Energy dispersive X-ray (EDAX) analysis
The formation of mercury sulfide was confirmed using EDAX
analysis. The EDAX spectra of HgS1 and HgS2 are shown in
Fig. 9(a) and (b), respectively. Energy dispersive X-ray spectra of
HgS1 and HgS2 reveal the presence of Hg and S. In both cases,
strong signals are observed for Hg and S. This indicates that the
synthesized products are HgS. The elemental analytical data of
HgS1 show that the atomic ratio of S:Hg is 1.14:1. The atomic ratio
of sulfur is slightly higher than mercury, which indicates that there
is a vacancy of Hg2+ or some sulfur dangling bonds are present in
Table 3
Selected bond angles (°) for 1 and 2.
1
2
S(2)–Hg(1)–S(3)
S(2)–Hg(1)–S(4)
S(4)–Hg(1)–S(3)
S(2)–Hg(1)–S(1)
S(4)–Hg(1)–S(1)
S(3)–Hg(1)–S(1)
N(1)–C(1)–S(1)
N(1)–C(1)–S(2)
S(8)–C(1)–S(2)
N(2)–C(15)–S(4)
N(2)–C(15)–S(3)
S(3)–C(15)–S(4)
150.42(3)
118.18(3)
69.78(3)
100.42(3)
106.08(3)
104.37(3)
121.1(2)
118.9(2)
120.08(17)
121.0(2)
S(3)–Hg(1)–S(1)
S(1)–Hg(1)–S(4)
S(3)–Hg(1)–S(4)
S(1)–Hg(1)–S(2)
S(3)–Hg(1)–S(2)
S(4)–Hg(1)–S(2)
N(1)–C(1)–S(1)
N(1)–C(1)–S(2)
S(1)–C(1)–S(2)
N(2)–C(24)–S(4)
N(2)–C(24)–S(3)
S(4)–C(24)–S(3)
147.84(5)
116.09(4)
69.96(4)
106.44(5)
101.99(4)
104.05(4)
118.2(3)
120.9(3)
120.8(3)
120.7(4)
119.5(4)
119.8(3)
119.8(3)
119.25(19)
Fig. 9. EDAX of (a) HgS1 and (b) HgS2.

S.H. Dar et al. / Polyhedron 96 (2015) 16–24
23
the sample. In the case of HgS2, the atomic ratio of S:Hg is 0.93:1.
This indicates the presence of excess Hg2+ in the HgS2 sample.
4.4. Optical properties
UV–Vis absorption spectroscopy is used to study the optical
properties of quantum-sized particles. Generally, the wavelength
at the maximum exciton absorption (kmax) decreases with a
decreasing size of the nanoparticles, as a consequence of quantum
confinements of the photogenerated electron–hole carriers [30].
The UV–Vis absorption spectra of HgS1 and HgS2 are shown in
Fig. 10(a) and (b), respectively. The absorption spectrum of HgS1
shows an absorption peak at 313 nm. An absorption peak at
317 nm with a tailing of the absorption band was observed for
HgS2. The tailing of the absorption features from HgS2 may be
due to the fact that the particle sizes range from significantly small
to larger and there is a growth of particles in the form of layers. In
both the cases, the clear appearance of a blue shift of the absorp-
tion peak relative to bulk HgS (620 nm) [31] indicates that the
HgS1 and HgS2 particles are quantum confined.
The fluorescence spectra of HgS1 and HgS2 are shown in
Fig. 11(a) and (b), respectively. The spectra of both HgS1 and
HgS2 exhibit two emission peaks on excitation at 460 nm. One is
a sharp emission peak around 530 nm and the other is a broad
red emission peak around 600 nm. The emission peak around
530 nm is attributed to the core state radioactive decay from CB
to VB and the emission peak blue shifts due to quantum confined
effect (bulk HgS: 588 nm) [32]. The additional broad red emission
in the fluorescence spectra at around 600 nm is attributed to the
Fig. 11. Fluorescence spectra of (a) HgS1 and (b) HgS2.
Fig. 10. UV–Vis absorption spectra of (a) HgS1 and (b) HgS2.
Fig. 12. FT-IR spectra of (a) HgS1 and (b) HgS2.

24
S.H. Dar et al. / Polyhedron 96 (2015) 16–24
recombination of trapped electrons/holes in some surface defect
states of the HgS particles.
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/10.
1016/j.poly.2015.04.020.
4.5. Infrared spectral studies on HgS1 and HgS2 nanoparticles
The infrared spectra of HgS1 and HgS2 are shown in
Fig. 12(a) and (b), respectively. The IR spectrum of HgS1 shows a
band at 3429 cmꢁ1, which is due to the N–H vibration. The bands
observed at 2922 and 2853 cmꢁ1 are assigned to masym and msym
vibrations of –CH2–, respectively. From the results of the IR analy-
sis, it is suggested that ethylenediamine should exist in HgS1. The
lack of bands due to the dithiocarbamate ligand exhibits their
absence in HgS1. No characteristic band was observed in the IR
spectrum of HgS2. This confirms the absence of the dithiocarba-
mate ligand and ethylenediamine in the mercury sulfide (HgS2).
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CCDC 1040880 and 1040881 contain the supplementary crys-
tallographic data for (1) and (2). These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12 Union Road,