Zinc, cadmium and mercury dithiocarboxylates: Synthesis, characterization, structure and their transformation to metal sulfide nanoparticles

Article abstract of DOI:10.1002/ejic.200601059

Reactions of M(OAc)₂·nH₂O and M(OAc) ₂(tmeda) with dithiocarboxylic acids gave [M(S₂CTol) ₂]_n (1) (M = Zn or Cd; Tol = C₆H ₄Me-4) and [M(S₂CAr)₂(

Full text of DOI:10.1002/ejic.200601059

FULL PAPER
DOI: 10.1002/ejic.200601059
Zinc, Cadmium and Mercury Dithiocarboxylates: Synthesis, Characterization,
Structure and Their Transformation to Metal Sulfide Nanoparticles
Gotluru Kedarnath,[a] Vimal K. Jain,*[a] Shamik Ghoshal,[a] Gautam K. Dey,[b]
Carol A. Ellis,[c] and Edward R. T. Tiekink*[c]
Keywords: Zinc / Cadmium / Mercury / Dithiocarboxylates / Nanoparticles
Reactions of M(OAc)2·nH2O and M(OAc)2(tmeda) with di-
thiocarboxylic acids gave [M(S2CTol)2]n (1) (M = Zn or Cd;
Tol = C6H4Me-4) and [M(S2CAr)2(tmeda)] (3) (M = Zn, Cd,
Hg; Ar = Ph or Tol), respectively, in high yields as deep-
colored crystalline solids. The former are soluble in pyridine
to give pyridine adducts [M(S2CTol)2(py)] (2). These com-
plexes were characterized by elemental analysis, UV/Vis and
geometries are found as the dithiocarboxylate ligands are ef-
fectively monodentate; evidence for the greater coordination
–
–
potential is found for S2CTol over S2CPh. Chelating dithio-
carboxylate ligands in [Cd(S2CTol)2(tmeda)] (3d) lead to an
octahedral geometry. Thermal behavior has been studied by
thermogravimetric analysis. The [M(S2CAr)2(tmeda)] com-
plexes underwent a three-step decomposition. Pyrolysis in
NMR (1H, 13C) spectroscopy. The absorptions in the elec- the temperature range 300–500 °C and solvothermal decom-
tronic spectra have been assigned to ligand-to-ligand
charge-transfer transitions. The crystal and molecular struc-
tures of the monomeric species [Zn(S2CTol)2(py)] (2),
[Zn(S2CPh)2(tmeda)] (3a), [Zn(S2CTol)2(tmeda)] (3b) and
[Cd(S2CTol)2(tmeda)] (3d) have been established by X-ray
position in ethylenediamine and hexadecylamine (HDA)
gave metal sulfide nanoparticles. The MS (M = Zn, Cd, Hg)
nanoparticles were characterized by XRD, EDAX, absorp-
tion/emission spectroscopy and electron microscopy (TEM).
Solvothermal decomposition gave hexagonal phases of nano-
crystallography. In [Zn(S2CTol)2(py)], chelating dithiocarbox- particles whereas heating in a furnace gave cubic ZnS and
ylate ligands and pyridine define a coordination geometry
intermediate between square pyramidal and trigonal bipy-
ramidal. In each of 3a and 3b, tetrahedral N2S2 coordination
HgS, and hexagonal CdS.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
particles with limited investigations on HgE. Metal organo-
chalcogenolates, [M(EPh)2(tmeda)] (M = Zn or Cd; E =
S, Se or Te),[12] thiocarboxylates [M(SCOR)2L2] (M = Zn
or Cd; L = tmeda, 2-lutidene; R = Me, tBu)[13] and
Introduction
During the past two decades considerable effort has been
made to prepare high-quality monodispersed surface-
passivated nanoparticles of II–VI semiconductors.[1] Owing
to their quantum-confinement effect, semiconductor nano-
particles exhibit remarkable size- and shape-dependent op-
tical properties which have led to their use in opto-elec-
tronic devices[2–6] and biological imaging.[7,8] Although a
wide range of synthetic routes have been developed to pre-
pare II–VI semiconductor nanoparticles,[8–11] decomposi-
tion of single-source molecular precursors in a suitable sol-
vent has proved quite successful for isolation of high-qual-
ity nanoparticles within a narrow size distribution. The area
has been dominated by ZnE and CdE (E = S, Se, Te) nano-
[Cd(SCOPh)2(2,2Ј-bipyridine)],[14]
selenocarboxylates,
[M(SeCOAr)2(tmeda)] (M = Zn or Cd),[15] xanthates
[M(S2COR)2] (M = Zn or Cd; R = Et, iPr),[16,17] dithiocar-
bamates [M(S2NRRЈ)2] (M = Zn or Cd)[18,19] and dithio-
phosphinates [M(S2PiBu2)2] (M = Zn, Cd)[20] have been
employed for the preparation of ME (M = Zn, Cd; E = S,
Se, Te) nanoparticles/thin films.
Chemistry of the zinc-triad 1,1-dithiolates has been of
considerable interest due to their numerous applications
(e.g., lubricating oil in combustion engine, vulcanization of
rubber, floating agents in metallurgy) and diverse structural
features.[21–24] Subtle changes in organic substituents on the
dithiolate group or in an auxiliary ligand often result in
different structural motifs. Thus, molecules with zero- (dis-
crete mono- and bi-nuclear complexes), one-, two- and
three-dimensional structural motifs have been isolated and
structurally characterized.[24] The 1,1-dithiolate chemistry
of the zinc-triad has been dominated by ligands of the type
A–D with relatively little attention to dithiocarboxylates
(E), Scheme 1.[25–27] With the above in mind, it was consid-
[a] Chemistry Division, Bhabha Atomic Research Centre,
Mumbai 400085, India
E-mail: jainvk@apsara.barc.ernet.in
[b] Materials Science Division, Bhabha Atomic Research Centre,
Mumbai 400085, India
[c] Department of Chemistry, The University of Texas at San An-
tonio, One UTSA Circle,
Texas 78249–0698, USA
E-mail:Edward.Tiekink@utsa.edu
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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ered worthwhile to explore the dithiocarboxylate chemistry gand protons. The absence of singlets ascribed to the SH
of zinc, cadmium and mercury with the aim of isolating proton in the spectra indicate deprotonation of the acid.
new structural motifs and also to develop a new family of The NMe2 and NCH2 protons resonances appeared as sing-
promising single-source molecular precursors for the syn- lets in the ranges 2.39–2.65 and 2.57–2.73 ppm, respectively.
thesis of MS nanoparticles. Results of this work are de- The resonance due to 2,6-protons of the aryl ring are deshi-
scribed herein.
elded with reference to the free ligand. The 13C{1H} NMR
spectra showed singlets for NMe2 and NCH2 carbon atoms
of tmeda at ca. 46.0 ppm and ca. 56.5 ppm, respectively.
The resonance due to thiocarbonyl carbon (C=S) is deshi-
elded (Ͻ20 ppm) on complexation, deshielding being
greater in cadmium complexes than the corresponding zinc
derivatives.
Structural Characteristics
The molecular structure of [Zn(S2CTol)2(py)] (2) is repre-
sented in Figure 1 (a). The molecule is disposed about a
crystallographic twofold axis which bisects the pyridine
molecule and contains the zinc atom. The zinc atom is five-
coordinate within a NS4 donor set defined by two asymmet-
rically chelating dithiocarboxylate ligands and the pyridine-
N atom. The Zn–S1 and Zn–S2 bond lengths are 2.3499(9)
and 2.6046(11) Å, respectively and this asymmetry is re-
flected in the associated C–S distances so that S1–C1 is sig-
nificantly longer than S2–C2, i.e., 1.716(3) and 1.679(3) Å,
Scheme 1.
Results and Discussion
Treatment of M(OAc)2·2H2O with p-tolyldithiocarbox-
ylic acid in methanol gave sparingly soluble orange com-
plexes of composition [M(S2Ctol)2] (1) [M = Zn (1a) or Cd
(1b)]. The complexes dissolved readily in pyridine solution,
with concomitant formation of the corresponding pyridine
adducts [Zn(S2CTol)2(py)] (2). The reaction of [M(OAc)2-
(tmeda)] with dithiocarboxylic acid in benzene afforded
deep-colored complexes of the general formula,
[M(S2COAr)2(tmeda)] (3) [Equation (1)].
(1)
The electronic spectra of these complexes in dichloro-
methane solution displayed two (Ar = Ph) and three (Ar =
Tol) absorption bands and are assigned for transitions in
thiocarbonyl group. The electronic spectra of metal dithio-
carboxylates have been reported to display characteristic
absorption maxima in the region 250–550 nm attributable
1
to π–π* and n–π* transitions.[28] The H NMR spectra ex-
Figure 1. (a) Molecular structure and (b) unit cell contents for
hibited characteristic peaks due to tmeda and dithiolate li- [Zn(S2CTol)2(py)] (2).
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respectively; the Zn–N1 distance is 2.046(3) Å. The dihedral
angle between the two ZnS2C chelate rings is 53.96(7)° and
each of these is effectively orthogonal to the pyridine ring,
dihedral angle = 79.87(10)°. The range of angles subtended
at the zinc atom extends from 72.04(2)°, for the S1–Zn–S2
chelate angle to 164.55(4)°, for S2–Zn–S2i; symmetry oper-
ation i: –x, y, 1/2 – z. The coordination geometry is interme-
diate between square pyramidal (τ = 0) and trigonal bipy-
ramidal (τ = 1) as exemplified in the value of τ of 0.61.[29]
The closely related structure of [Zn(S2CC6H2-4-OH-3,5-
tBu2)2(py)][26] also features an intermediate geometry but
one more inclined towards a square-pyramidal geometry as
judged by the τ value of 0.43. The 1,1-dithiolate ligand is
not strictly planar, there being a twist about the C1–C2
bond in 2 as seen in the value of –162.7(2)° for the S1/C1/
C2/C3 torsion angle. In the crystal structure, Figure 1 (b),
molecules pack in layers along (101). The primary contacts
within layers are π···π interactions of 3.7202(19) Å between
interdigitated C2–C7 rings (symmetry operation: 1/2 – x,
1/2 – y, –z). The interactions between successive layers are of
the type C–H···π. Thus, the C4–H···ring centroid (pyridine)
distance is 2.88 Å with an angle of 153° subtended at the
H4 atom (symmetry operation: 1/2 + x, 1/2 + y, z).
A formal decrease in the coordination number of zinc is
found in the structure of [Zn(S2CTol)2(tmeda)] (3b). The
molecule, Figure 2 (a), has twofold symmetry, with the axis
bisecting the tmeda ligand and containing zinc atom. The
zinc atom is four-coordinate with the N2S2 coordination geo-
metry defined by chelating tmeda and monodentate dithio-
carboxylate ligands. The respective Zn–S1 and Zn–S2 dis-
tances are 2.3238(7) and 3.0860(9) Å, and these distances
are significantly shorter and longer than the equivalent dis-
tances in the pyridine analog, respectively. The asymmetric
mode of coordination is reflected in the respective S1–C1
and S2–C1 bond lengths of 1.705(3) and 1.667(3) Å; the
Zn–N1 distance is 2.170(2) Å. The range of angles sub-
tended at the tetrahedrally coordinated zinc atom is
84.11(11)°, for the N1–Zn–N1i chelate angle, to 132.46(5)°
for S1–Zn–S1i; symmetry operation i: –1 – x, –y, z. The
wider angle is certainly due to the close approach of the S2
atoms. A small twist is apparent between the S2C and aro-
matic ring as seen in the S1/C1/C2/C3 torsion angle of
174.88(18)°. In the crystal structure, Figure 2 (b), the mole-
cules form chains along the c axis stabilized by Cmethyl
–
Figure 2. (a) Molecular structure and (b) unit cell contents for
[Zn(S2CTol)2(tmeda)] (3b).
H···π interactions so that the C8–H···ring centroid of C2–
C7 distance is 2.88 Å and angle at H of 130° for symmetry
operation: –1/2 – x, y, –1/2 + z.
The influence of substituting the –S2CTol ligand by 1.725(5) and 1.653(5) Å. The difference in mode of coordi-
–S2CPh was investigated by examining the crystal and mo- nation of the two 1,1-dithiolate ligands can be conveniently
lecular structure of [Zn(S2CPh)2(tmeda)] (3a). The mole- realized by considering the ∆(Zn–S) and the associated
cule, Figure 3 (a), has twofold symmetry as described for 3b ∆(C–S) values, with greater values been correlated with
but the structures are not isomorphous. To a first approxi- greater asymmetry. Thus, in 3b these compute to 0.76 and
mation, the coordination geometry for both structures is 0.04 Å, respectively, which are smaller than the values
the same. Thus, the zinc atom exists is a distorted tetrahe- found for 4a of 0.97 and 0.07 Å, respectively. Further, the
dral geometry defined by a N2S2 donor set. The Zn–S1 and Zn–N1 distance of 2.127(4) Å is shorter in the present
Zn–S2 distances of 2.3079(12) and 3.2736(14) Å are respec- structure. These results correlate in the expected fashion
tively, shorter and longer than the comparable distances in with the electron-donating ability of the methyl group in
–
3b. This is reflected in the S1–C1 and S2–C1 distances of the S2CTol ligand that makes this a comparatively better
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chelating agent. However, it is noted that there is a signifi- and “(b)” C5–H···S2ii of 3.06 Å and angle 125°; symmetry
–
cant twist about the C1–C2 bond of the S2CTol ligand as operations i: –x, 1 – y, 1 – z and ii: x, 1 – y, –1/2 + z. Or-
seen in the value of 142.8(4)° for the S1/C1/C2/C3 torsion thogonal C8–H···S2iii interactions, i.e., involving methylene-
angle, and so the negative inductive effect exerted by the H atoms, of 3.02 Å and angle 173°, link translationally re-
methyl group is not the reason for the different coordinat- lated molecules along the b-direction into chains; symmetry
ing abilities. By contrast to the previously described crystal operation iii: x, 1 + y, z.
structures, in the absence of π···π and C–H···π interactions,
The remaining structure to be described is that of
C–H···S interactions dominate the crystal packing in 3a. [Cd(S2CTol)2(tmeda)] (3d), shown in Figure 4. This struc-
Thus, in addition to a variety of intramolecular C–H···S ture is isomorphous with the zinc analog described above,
interactions, three intermolecular C–H···S interactions may but the coordination geometry is different. Here, owing to
be discerned in the stabilization of the crystal structure. A the greater propensity of the larger cadmium atom to in-
view of the unit-cell contents is shown in Figure 3 (b). Here, crease its coordination number, the coordination geometry
two C–H···S interactions are highlighted and show adjacent is based on a distorted octahedron within a N2S4 donor set.
C–H atoms of an aromatic ring bridging S1 and S2 atoms The dithiocarboxylate ligand forms nearly symmetric Cd–S
of different ligands but of the same molecule. The param- bonds of 2.6508(8) and 2.7336(9) Å, ∆(Cd–S) is only
eters associated with interaction “(a)” are C6–H···S1i of 0.08 Å; the Cd–N1 bond length is 2.416(2) Å. Distortions
3.10 Å with an angle of 164° subtended at the H6 atom, from the ideal octahedral geometry may be traced to the
acute chelate angles of 66.18(2)°, for S1–Cd–S2, and
76.15(12)°, for N1–Cd–N1i; symmetry operation i: –x, –y,
z. The CS2 and aromatic portions of the 1,1-dithiolate li-
gand are effectively co-planar as evidenced by the S1/C1/
C2/C3 torsion angle of –174.3(2)°. The crystal packing is
as described above for 3d with a C8–H···ring centroid of
C2–C7 distance is 2.94 Å and angle at H of 131° for sym-
metry operation: –1/2 – x, y, 1/2 + z.
Figure 4. Molecular structure of [Cd(S2CTol)2(tmeda)] (3d).
Thermal Studies
TG analyses were carried out to study the thermal behav-
ior and suitability of these complexes for the preparation
of metal sulfides. These complexes underwent a three-step
decomposition, exemplified for [Zn(S2CPh)2(tmeda)] (3a) in
Figure S1 (see Supporting Information), with the formation
of metal sulfides as inferred from the weight loss (e.g. 3a,
Figure 3. (a) Molecular structure and (b) unit cell contents for
[Zn(S2CPh)2(tmeda)] (3a).
calculated weight loss: 80.0% and observed weight loss:
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76.5%) and confirmed from the XRD patterns of the resi-
dues. The onset temperatures are 3a, 194 °C; 3b, 178 °C; 3c,
175 °C; 3d, 180 °C. The TG curves of the zinc complexes
showed slightly separated steps while for the cadmium and
mercury derivatives they were poorly resolved indicating in-
stability of the intermediate species. The first step, based on
percentage of weight loss (e.g. 3a, calcd. weight loss for
tmeda: 23.8% and obsd. weight loss for first step: 23.8%)
has been attributed to the elimination of tmeda. The second
and third steps can be characterized for decomposition of
dithiocarboxylate groups.
Pyrolysis of [M(S2CAr)2(tmeda)] (Ar = Ph, Tol) was car-
ried out at 350 °C under flowing nitrogen for 2 h. In each
case metal sulfides (MS; M = Zn, Cd, Hg) were formed as
confirmed by their XRD patterns (see Figure 5 and Fig-
ures S2–S3 in the Supporting Information) and EDAX
analysis (Ar = Ph) (ZnS: calcd 67.1, S 32.9; found Zn 60.2,
S 39.8. CdS: calcd Cd 77.8, S 22.2; found Cd 74.3, S 25.7.
HgS: calcd. Hg 86.2, S 13.8; found Hg 84.2, S 15.8). The
XRD patterns of ZnS and HgS were consistent with the
formation of cubic phase of the material,[30,31] whereas CdS
was isolated in the hexagonal phase.[32] The pyrolysis of
[Cd(S2CPh)2(tmeda)] (3c), carried out at 300, 400 and
500 °C, also gave hexagonal CdS with the average particle
sizes of 18, 36 and 43 nm, respectively, from the Scherrer
equation.[33] This indicates that particle size increases with
increasing decomposition temperature at a given time. The
absorption spectrum of CdS nanoparticles (obtained at
300 °C) showed a broad peak at 505 nm. The emission pro-
file displayed a band at 521 nm, which may be due to sur-
face traps (Figure 6). The particles are of 15 nm in size as
estimated from the Brus expression.[34]
Solvothermal decomposition of [M(S2CPh)2(tmeda)] (M
= Zn, Cd, Hg) was examined in different coordinating sol-
vents, such as ethylenediamine and HDA, to assess their
suitability as precursors for the preparation of MS nano-
particles. Pyrolysis of [M(S2CPh)2(tmeda)] in refluxing eth-
ylenediamine gave hexagonal phases of MS (from XRD)
nanoparticles which were isolated as cream (ZnS), yellow-
orange (CdS) and orange (HgS) powders by centrifugation
(Figure S4 in the Supporting Information). The particle
sizes, estimated from the Scherrer formula,[33] are 34 (ZnS),
29 (CdS) and 103 (HgS) nm. The mercury complex can be
pyrolyzed in ethylenediamine at a temperature as low as
57 °C with the formation of hexagonal HgS, having an
average particle size (diameter) of 21 nm. The absorption
spectra of CdS and HgS nanoparticles (obtained at 122 °C
in ethylenediamine) displayed peaks at 480 and 401 nm,
respectively. Emission profile (Figure 7) of these CdS nano-
particles exhibited a band at 518 nm (bulk CdS bandgap is
515 nm), which may be due to surface traps.
Figure 5. XRD patterns of the HgS nanoparticles prepared under
different conditions from [Hg(SC2Ph)2(tmeda)]; a) heated in a fur-
nace at 250 °C, b) heated in a furnace at 350 °C, c) thermolysis in
ethylenediamine at 125 °C and d) thermolysis in HDA at 125 °C.
Figure 6. a) Absorption and b) emission spectra of CdS nanopar-
ticles obtained by the pyrolysis of [Cd(S2CPh)2(tmeda)] in a furnace
at 300 °C under flowing nitrogen.
Nanoparticles prepared under different conditions are
known to give different phases and sizes due to different
nucleation mechanisms.[35] It is likely that in the present cir- decomposition of the complex, whereas in a coordinating
cumstances different nanoparticles are obtained owing to solvent, the coordinating ligand helps in passivating the sur-
different mechanisms of formation and temperatures. Thus, face of the particles resulting in different phases.
when the precursor is heated without solvent, initially
Pyrolysis of [Cd(S2CPh)2(tmeda)] (3c) and [Hg(S2CPh)2-
tmeda is released (as inferred from TG curve) followed by (tmeda)] (3e) was also carried out in HDA either at different
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tion and temperature with different precursor/solvent mol
ratio 1:34 (particle size is 17 nm) and 1:55 (particle size is
26 nm) also gave different particle sizes which may be due
to Ostwald ripenening.[38]
Electron Microscopy
The Selected Area Electron Diffraction (SAED) patterns
of MS nanoparticles (Figure 9; Figures S5–S6 in the Sup-
porting Information) obtained by pyrolysis of [M(S2CPh)2-
(tmeda)] in a furnace at 350 °C for M = Zn, and in ethyl-
enediamine for M = Cd (122 °C) and Hg (57 °C) revealed
the formation of crystalline material. The diffraction rings
in the SAED pattern of ZnS corresponds to the lattice pla-
nes (111), (220) and (311) which are assigned for the cubic
phase. Concentric rings in the SAED patterns of MS (M =
Cd or Hg) have been attributed to the lattice planes (100),
(002), (101), (102), (110), (103) and (112) (CdS); (101),
(102), (110), (104) and (105) (HgS), respectively, of the hex-
agonal phases of MS. The phases determined from the
SAED and XRD patterns are in agreement. The TEM im-
age of MS showed that ZnS nanoparticles [Figure S5 (Sup-
porting Information)] are spherical in shape with an average
diameter of 10 nm, while those of CdS (Figure 9) and HgS
(Figure S6, Supporting Information) are nearly spherical
with the average size of 20 and 25 nm, respectively. How-
ever, in the case of CdS, the presence of a small amount of
nanorods of 20–60 nm in length and diameter of 12–20 nm
Figure 7. a) Absorption and b) emission spectra of CdS nanopar-
ticles obtained by pyrolysis of [Cd(S2CPh)2(tmeda)] in ethylenedi-
amine at 122 °C.
temperatures and/or different concentrations of the precur-
sor. Thermolysis of 3c in HDA at 188, 188, and 225 °C
having precursor/solvent mol ratio of 1:34, 1:55, and 1:55,
respectively gave yellow-orange nanoparticles of hexagonal
CdS with particle sizes 17, 26, and 34 nm, respectively.
Their absorption spectra (Figure 8) in toluene showed exci-
ton peaks at 466, 473 and 503 nm, respectively, which are
blue shifted from bulk CdS (515 nm). The emission spectra
of the samples prepared at 188 °C of precursor: solvent mol
ratio of 1:34 and 1:55 exhibited a broad emission at 523
and 546 nm, respectively. Both absorption and emission
maxima are red-shifted with increasing size of the CdS
nanoparticles. Pyrolysis of 3e in HDA (precursor/HDA mol
ratio = 1:70) at 125 °C afforded the hexagonal phase of
HgS,[36] whereas at 160 °C it gave cubic HgS with particle
size of 26 nm and 34 nm (from the Scherrer formula[33]),
respectively.
Figure 8. Absorption spectra of CdS nanoparticles obtained by the
pyrolysis of [Cd(S2CPh)2(tmeda)] with precursor: coordinating sol-
vent mole ratio a) 1:34 (188 °C), b) 1:55 (188 °C) and c) 1:55
(225 °C).
Thermolysis of 3c in HDA at 188, 188 and 225 °C having
precursor/solvent mol ratio of 1:34, 1:55 and 1:55, respec-
tively, gave nanoparticles of hexagonal CdS with different
particle sizes. At fixed precursor/solvent mol ratio and du-
ration, particle size increases with increase of temperature.
This may be due to the growth of particles that accelerates
Figure 9. a) TEM image and b) SAED pattern of CdS nanopar-
ticles obtained by pyrolysis of [Cd(S2CPh)2(tmeda)] in ethylenedi-
amine at 122 °C. In b) the inner ring is assigned to planes (100),
(002) and (101), with the remaining rings from inner to outer corre-
with increasing temperature.[37] Thermolysis at a fixed dura- sponding to planes (102), (110), (103) and (112), respectively.
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enediamine (en), solvents were obtained from commercial sources.
[M(OAc)2(tmeda)] (M = Zn, Cd and Hg) were prepared by re-
fluxing metal acetates with an excess of tmeda in dichloromethane
under an inert atmosphere for 2 h. Dithiocarboxylic acids, RCS2H
was also observed. Co-formation of nanoparticles of dif-
ferent morphology is known and optimization of reaction
conditions can lead to the preferential deposition of one
form over another.[39] The particle sizes of ZnS and HgS
nanoparticles obtained from TEM images are in agreement
with the sizes estimated from XRD pattern using the
Scherrer formula,[33] whereas the sizes evaluated by these
techniques differs for CdS nanoparticles. This inconsistency
could be due to the deviation from spherical morphology
of the CdS particles.[40]
1
(R = Ph, p-Tol) [NMR in CDCl3 for R = Ph, H NMR: δ = 6.40
(br. s, SH), 7.39 (br., 2 H, 3,5-H), 7.57 (br., 1 H, 4-H), 8.07 (br., J
= 8.2 Hz, 2 H, 2,6-H) ppm. 13C{1H} NMR: δ = 126.7 (C-3,5),
128.2 (C-4), 133.0 (C-2,6), 143.5 (C-1), 225.2 (CS2) ppm. 1H NMR
for R = p-Tol: δ = 2.38 (s, Me-tol), 4.71 (s, SH), 7.19 (d, J = 8.3 Hz,
2 H, 3,5-H), 7.98 (d, J = 8.2 Hz, 2 H, 2,6-H) (C6H4) ppm. 13C{1H}
NMR: δ = 21.5 (Me), 126.9 (C-2,6), 129.0 (C-3,5), 141.1 (C-4),
144.2 (C-1), 224.6 (CS2) ppm] were prepared by the reaction of
RMgBr with CS2 in diethyl ether as described in the literature
method.[41]
Conclusions
Preparation of [Zn(S2CTol)2] (1a): A methanolic solution of
Zn(OAc)2·2H2O (390 mg, 1.78 mmol) was added to a benzene solu-
tion (20 mL) of HS2CTol (600 mg, 3.56 mmol), with vigorous stir-
ring which continued for 2 h under nitrogen. The solvents were
evaporated under vacuum to afford an orange residue (660 mg,
93%), m.p. 175 °C. C16H14S4Zn (399.94): calcd. C 48.0, H 3.5, S
32.1; found C 47.5, H 3.4, S 32.6. UV/Vis (CH2Cl2): λ = 334, 350
and 392 nm. 1H NMR (CDCl3): δ = 2.43 (s, CH3C6H4CS2), 7.22
(d, 7.5 Hz, C6H4), 8.28 (d, 7.5 Hz, C6H4) ppm. A portion of the
residue was recrystallized as red crystals from dichloromethane
Zinc, cadmium and mercury dithiocarboxylate com-
plexes are conveniently prepared in high yields and are
stable at room temperature for several months. The homo-
leptic derivatives are associated in the solid state and are
sparingly soluble in non-coordinating solvents. The com-
plexes with neutral donor ligands (e.g., py or tmeda) are
discrete monomers. These complexes undergo facile decom-
position both in the solid state (furnace heating) and in
solution (solvothermal) to yield metal sulfide nanoparticles.
The solvothermal decomposition affords nanoparticles at
moderately low temperatures which can be as low as 57 °C
for the preparation of HgS. Different phases (cubic/hexago-
nal) can be obtained under different experimental condi-
tions. Thus, owing to the synthetic ease and facile conver-
sion into phase pure metal sulfide nanoparticles, these com-
plexes prove to be reliable precursors for the generation of
MS, M = Zn, Cd and Hg.
1
containing few drops of pyridine. The H NMR spectrum of these
crystals, [Zn(S2CTol)2(py)] (2), showed resonances due to coordi-
1
nated pyridine: H NMR: δ = 2.73 (s, CH3C6H4CS2), 7.15 (d, J =
7.7 Hz, C6H4), 7.70 (d, J = 7 Hz, C6H4), 7.31 (br.), 8.38 (br.), 8.64
(br., py); this formulation was confirmed by an X-ray crystallo-
graphic study for red crystals grown by the slow evaporation of a
dichloromethane solution of the compound.
Preparation of [Cd(S2CTol)2] (1b): This was prepared in a manner
similar to the zinc complex in 92% yield as a red-orange crystalline
solid; m.p. 160 °C. C16H14CdS4 (446.96): calcd. C 43.0, H 3.2, S
28.7; found C 43.0, H 3.1, S 29.4. UV/Vis (CH2Cl2): λ = 321, 345,
Experimental Section
1
360 nm. H NMR (CDCl3): δ = 2.37 (s, CH3C6H4CS2), 7.12 (br.,
C6H4), 8.30 (br., C6H4) ppm.
General: Elemental analyses were carried out by Radio Chemistry
Division of B.A.R.C. 1H and 13C{1H} NMR spectra were recorded
with a Bruker DPX-300 NMR spectrometer operating at 300 and
75.47 MHz, respectively. Chemical shifts are relative to internal
chloroform resonances at δ = 7.26 ppm for 1H and δ = 77.0 ppm for
13C{1H}. UV/Vis absorption spectra were recorded with a Chemito
Spectrascan UV 2600 double beam UV/Vis spectrophotometer.
Fluorescence spectra were recorded using a Hitachi F-4500 FL
spectrofluorometer.
Preparation of [Zn(S2CTol)2(tmeda)] (3b): Solid [Zn(OAc)2(tmeda)]
(590 mg, 1.97 mmol) was added to a benzene solution (20 mL) of
HS2CTol (660 mg, 3.92 mmol), with vigorous stirring, which con-
tinued for 2 h under nitrogen. The solvent was removed under vac-
uum to yield an orange residue which was recrystallzed from
dichloromethane/toluene (1:3) mixture to give red crystals (930 mg,
91% yield), m.p. 173 °C. C22H30N2S4Zn (516.14): calcd. C 51.2, H
5.9, N 5.4, S 24.9; found C 51.3, H 5.9, N 5.4, S 25.0. UV/Vis
(CH2Cl2): λ = 307, 326, 366 nm. 1H NMR (CDCl3): δ = 2.35 (s,
CH3C6H4CS2), 2.62 (s, NMe2), 2.70 (s, NCH2), 7.10 (d, J = 7.4 Hz,
C6H4), 8.36 (d, J = 7.3 Hz, C6H4) ppm. 13C{1H} NMR (CDCl3):
δ = 21.4 (CH3-C6H4CS2), 46.2 (NMe2), 56.9 (NCH2), 127.2, 128.1,
128.7, 142.7 (C6H4), 245.0 (C=S) ppm. Red crystals for X-ray dif-
fraction were grown by the slow evaporation of a dichloromethane/
toluene (3:1) solution of the compound.
Thermogravimetric analyses (TGA) were carried out with a Nitzsch
STA PC-Luxx TG-DTA instrument, which was calibrated with
CaC2O4·H2O. TG curves were recorded at a heating rate of
5 °Cmin–1 under a flow of nitrogen. Solvents were dried and dis-
tilled before use under nitrogen. HPLC-grade toluene was used in
all experiments involving HDA as a capping agent while methanol
was used in case of ethylenediamine as the capping agent. Dimeth-
ylformamide was used in pyrolysis experiments for optical studies.
X-ray powder diffraction patterns were measured using Cu-Kα radi-
ation with a Philips PW1820 powder diffractometer. EDAX were
carried out with a Tescan Vega 2300T/40 instrument. A JEOL-
2000FX transmission electron microscope operating at accelerating
voltages up to 200 kV was used for TEM studies. The samples for
TEM and SAED were prepared by placing a drop of sample dis-
persed in acetone on a carbon-coated copper grid.
Preparation of [Zn(S2CPh)2(tmeda)] (3a): This was prepared in a
manner similar to [Zn(S2CTol)2(tmeda)] and recrystallized from
dichloromethane/toluene as dark-red crystals in 92% yield, m.p.
152 °C (dec). C20H26N2S4Zn (488.08): calcd. C 49.2, H 5.4, N 5.7,
S 26.3; found C 49.5, H 5.4, N 5.9, S 25.7. UV/Vis (CH2Cl2): λ =
302, 366 nm. 1H NMR (CDCl3): δ = 2.65 (s, NMe2), 2.73 (s,
NCH2), 7.30 (t, J = 7.7 Hz), 7.47 (t, J = 7.2 Hz), 8.44 (d, J =
7.4 Hz, Ph) ppm. 13C{1H} NMR (CDCl3): δ = 46.1 (NMe2), 56.7
(NCH2), 126.9, 127.3, 131.7, 145.4 (Ph), 245.9 (C=S) ppm. Red
crystals for X-ray crystallography were grown by the slow evapora-
Materials: Zinc, cadmium and mercury acetates, N,N,NЈ,NЈ-tetra-
methylethylenediamine (tmeda), hexadecylamine (HDA) and ethyl-
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Eur. J. Inorg. Chem. 2007, 1566–1575

Conversion of Dithiocarboxylates to Sulfide Nanoparticles
FULL PAPER
tion of a dichloromethane/toluene (3:1) solution of the compound.
found C 40.1, H 4.1, N 4.0, S 20.3. UV/Vis (CH2Cl2): λ = 315, 335,
361 nm. 1H NMR (CDCl3):
δ = 2.39 (s, NMe2), 2.38 (s,
Preparation of [Cd(S2CPh)2(tmeda)] (3c): This complex was pre-
pared in a similar fashion to its zinc analog and recrystallized from
dichloromethane/hexane or dichloromethane/toluene mixture as
orange crystals in 90% yield; m.p. 164 °C (dec). C20H26CdN2S4
(535.11): calcd. C 44.9, H 4.9, N 5.2, S 24.0; found C 45.4, H 4.8,
N 4.8, S 24.5. UV/Vis (CH2Cl2): λ = 304, 368 nm. 1H NMR
(CDCl3): δ = 2.60 (s, NMe2), 2.69 (s, NCH2), 7.32 (t, J = 7.8 Hz),
7.48 (t, J = 7.3 Hz), 8.47 (d, J = 7.7 Hz) (Ph) ppm. 13C{1H} NMR
(CDCl3): δ = 46.0 (NMe2), 56.7 (NCH2), 127.3, 128.2, 131.9, 145.4
(Ph), 249.0 (s, C=S) ppm. Red crystals for X-ray diffraction were
grown by the slow evaporation of a chloroform/toluene (3:1) solu-
tion of the compound.
CH3C6H4CS2), 2.57 (s, NCH2), 7.16 (d, J = 7.7 Hz, C6H4), 8.15
(br., C6H4) ppm.
X-ray Crystallography: Intensity data for [Zn(S2CTol)2(py)],
[Zn(S2CTol)2(tmeda)], [Zn(S2CPh)2(tmeda)] and [Cd(S2CTol)2-
(tmeda)] were measured with a Rigaku AFC12/Saturn724 CCD
fitted with Mo-Kα radiation so that θ = 27.5°. The structures were
solved by heavy-atom methods[42] and refinement was on F2 [43]
using data that had been corrected for absorption effects with an
empirical procedure,[44] with non-hydrogen atoms modeled with an-
isotropic displacement parameters, with hydrogen atoms in their
calculated positions, and using a weighting scheme of the form w
= 1/[σ2(Fo2) + (aP)2 + bP] where P = (Fo2 + 2Fc )/3. The absolute
2
Preparation of [Cd(S2CTol)2(tmeda)] (3d): This was prepared simi-
larly to [Zn(S2CTol)2(tmeda)] and recrystallized from dichloro-
methane/toluene in 90% yield as orange crystals; m.p. 176 °C.
C22H30CdN2S4 (563.16): calcd. C 46.9, H 5.4, N 5.0, S 22.8; found
C 47.3, H 5.4, N 5.1, S 23.0. UV/Vis (CH2Cl2): λ = 316, 328,
376 nm. 1H NMR (CDCl3): δ = 2.37 (s, CH3C6H4CS2), 2.57 (s,
NMe2), 2.66 (s, NCH2), 7.10 (d, J = 7.8 Hz, C6H4), 8.39 (d, J =
7.8 Hz, C6H4) ppm. 13C{1H} NMR (CDCl3): δ = 21.4 (CH3-
C6H4CS2), 46.0 (NMe2), 57.0 (NCH2), 127.7, 128.1, 142.9, 143.4
(Ph), 248.4 (C=S) ppm.
configuration of [M(S2CTol)2(tmeda)], M = Zn and Cd, was deter-
mined on the basis of differences in Friedel pairs included in the
data sets and confirmed by the near-zero value of the Flack param-
eter in each case, i.e. 0.006(12) and –0.01(3), respectively.[45] A resid-
ual electron density peak of 2.02 eÅ–3 was noted in the final differ-
ence map for [Zn(S2CPh)2(tmeda)], this was located between the
Zn and S1 atoms. A residual of 1.05 eÅ–3 was located 0.02 Å from
the Cd atom in [Cd(S2CTol)2(tmeda)]. Molecular structures shown
in Figures 1, 2, 3, and 4 were drawn at the 50% probability level
using ORTEP.[46] The DIAMOND program[47] was used for the
remaining crystallographic figures. Data manipulation and analyses
were performed with teXsan[48] and PLATON.[49] Crystallographic
data and refinement details are given in Table 1.
Preparation of [Hg(S2CPh)2(tmeda)] (3e): The complex was ob-
tained as a brown solid similarly to the previous mercury complex
in 90% yield; m.p. 78 °C (dec). C20H26HgN2S4 (623.29): calcd. C
38.5, H 4.2, N 4.5, S 20.6; found C 37.9, H 3.7, N 4.3, S 21.2. UV/
Preparation of Metal Sulfide Nanoparticles
1
Vis (CH2Cl2): λ = 298 (sh), 310 nm. H NMR (CDCl3): δ = 2.43
(a) Pyrolysis in a Furnace: A weighed quantity of a sample (ca.
200 mg) in a quartz boat, was pyrolyzed at 350 °C (unless otherwise
stated) in a furnace under flowing nitrogen for 2 h. After cooling,
the residue in the quartz boat was again weighed and characterized
by XRD and in some cases by UV/Vis spectroscopy. The pyrolysis
of 3c was carried out at three different temperatures, 300, 400 and
500 °C and the dark-red residual powder was characterized by
XRD.
(s, NMe2), 2.66 (s, NCH2), 7.38 (t, J = 7 Hz), 7.56 (t, J = 7.2 Hz),
8.19 (br., Ph) ppm. 13C{1H} NMR (CDCl3): δ = 45.2 (NMe2), 56.2
(NCH2), 126.9, 127.9, 132.7, 144.3 (Ph) ppm; the resonance due to
C=S was not resolved.
Preparation of [Hg(S2CTol)2(tmeda)] (3f): This was prepared simi-
larly to its zinc, cadmium analogs as a brown solid in 91%; m.p.
112 °C. C22H30HgN2S4 (651.34): calcd. C 40.6, H 4.6, N 4.3, S 19.7;
Table 1. Crystallographic parameters and refinement details for [Zn(S2CTol)2(py)], [Zn(S2CTol)2(tmeda)], [Zn(S2CPh)2(tmeda)] and
[Cd(S2CTol)2(tmeda)].
Parameter
[Zn(S2CTol)2·py]
[Zn(S2CTol)2(tmeda)]
[Zn(S2CPh)2(tmeda)]
[Cd(S2CTol)2(tmeda)]
Formula
Fw
C21H19NS4Zn
478.98
C22H30N2S4Zn
516.09
C20H26N2S4Zn
488.04
C22H30CdN2S4
563.12
Crystal system
Space group
a [Å]
b [Å]
c [Å]
monoclinic
C2/c
orthorhombic
Aba2
13.140(3)
23.098(5)
7.8304(15)
90
2376.6(8)
4
1.397
monoclinic
C2/c
orthorhombic
Aba2
12.644(3)
23.859(5)
7.9794(16)
90
2407.1(9)
4
1.266
17.451(6)
9.023(2)
13.979(4)
107.038(6)
2104.6(11)
4
1.570
1.512
2412
2340
18.419(4)
8.0230(16)
15.404(3)
98.251(4)
2252.9(8)
4
1.469
1.439
2582
2506
β [°]
V [Å3]
Z
µ [cm–1]
Dcalcd. [gcm–3]
Independent reflections
Observed reflections with
IϾ2σ(I)
1.442
2720
2677
1.554
2741
2717
R (obsd. data)
a, b in weighting scheme
Rw (all data)
CCDC numbers[a]
0.049
0.065, 5.371
0.127
0.034
0.052, 1.787
0.084
0.054
0.042, 42.646
0.160
0.026
0.031, 4.477
0.062
616718
616716
616717
616715
[a] The supplementary crystallographic data for this paper can be obtained free of charge from The Cambridge Crystallographic Data
Centre (CCDC) via www.ccdc.cam.ac.uk/data_request/cif.
Eur. J. Inorg. Chem. 2007, 1566–1575
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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V. K. Jain, E. R. T. Tiekink et al.
FULL PAPER
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Conversion of Dithiocarboxylates to Sulfide Nanoparticles
FULL PAPER
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