Nanospheres of copper(iii) 1,2-dicarbomethoxy-1,2-dithiolate and its composite with water soluble carbon nanotubes

Article abstract of DOI:10.1039/c3nj00368j

We report here the synthesis and structural characterization of a new discrete bis-dithiolene complex, [PPh₄][Cu(DMED)₂] (1; DMED = 1,2-dicarbomethoxy-1,2-dithiolate), involving the reaction between a copper polysulfide precursor with activated acetylene. 1 is stable, showing a sulfur-based radical character, as observed by electronic, EPR and cyclic voltammetric studies. This complex, possessing terminal -COOCH₃ groups, forms nanospheres by hydrogen bonding in a mixture of solvents containing water as one of the components. These nanospheres further aggregate with water soluble (carboxylated) carbon nanotubes (wsCNTs). These nano-composites are assisted by hydrogen bonding between the carboxylic acid groups of the wsCNTs and the peripheral -COOCH₃ groups of the coordinated dithiolenes of the nanospheres, which is promoted by water molecules. Interaction between the nanospheres on wrapping with wsCNTs, in forming the nano-composites, showed a perturbed EPR signal of the sulfur radical originating from the oxidised dithiolate ligand of the discrete complex 1.

Full text of DOI:10.1039/c3nj00368j

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Nanospheres of copper(III) 1,2-dicarbomethoxy-1,2-
dithiolate and its composite with water soluble
carbon nanotubes†
Cite this: DOI: 10.1039/c3nj00368j
Kumud Malika Tripathi,a Ameerunisha Begum,a Sumit Kumar Sonkara and
Sabyasachi Sarkar*b
We report here the synthesis and structural characterization of a new discrete bis-dithiolene complex,
[PPh4][Cu(DMED)2] (1; DMED = 1,2-dicarbomethoxy-1,2-dithiolate), involving the reaction between a
copper polysulfide precursor with activated acetylene. 1 is stable, showing a sulfur-based radical
character, as observed by electronic, EPR and cyclic voltammetric studies. This complex, possessing
terminal –COOCH3 groups, forms nanospheres by hydrogen bonding in a mixture of solvents containing
water as one of the components. These nanospheres further aggregate with water soluble (carboxy-
lated) carbon nanotubes (wsCNTs). These nano-composites are assisted by hydrogen bonding between
the carboxylic acid groups of the wsCNTs and the peripheral –COOCH3 groups of the coordinated
dithiolenes of the nanospheres, which is promoted by water molecules. Interaction between the nano-
spheres on wrapping with wsCNTs, in forming the nano-composites, showed a perturbed EPR signal of
the sulfur radical originating from the oxidised dithiolate ligand of the discrete complex 1.
Received (in Montpellier, France)
8th April 2013,
Accepted 12th June 2013
DOI: 10.1039/c3nj00368j
www.rsc.org/njc
metallic nano-particles,16 have been actively made to explore
future applications utilizing their novel chemical, electrical and
1. Introduction
mechanical properties.17 Armed with unique properties, CNTs
are ideal components for the fabrication of novel CNT-based
composites. These composites have several important applica-
tion prospects in the field of aerospace sciences,18 energy storage
devices, chemical sensors,19 photo-catalysis16 and in biological
systems.20,21 Zheng et al. reported the self-assembly of the CuO–
CNT composite (nano-microspheres) showing the enhanced
cycling and rate performance as anode materials in lithium-
ion batteries.22 CNT based drug delivery systems are a promising
nano-platform for cancer therapeutics.23 Non-covalent interactions
between CNTs and DNA, proteins and certain organization proper-
ties of such systems have also been reported.24 The practical
application of water soluble CNTs (wsCNTs) and wsCNT-conjugates
are, in general, growing fast. CNT-based magnetic nano-composite
materials are the centre of attention in recent research because of
their immense applications in a broad area ranging from techno-
logical applications to biomedicine.25
Self-assembly or self-organization is one of the basic underlying
principles of nano-science and technology, which directs the
formation of nanocrystals, nanoparticles or larger aggregates of
different shapes and sizes.1–8 For example, the self-assembly of
diphenylalanine, in the formation of peptide nano-tubes, their
nanocrystalline building blocks and most recently the self-assembly
of polyhedra such as octapod-nanocrystals into ordered super
structures or into dense packings are known.9,10 Self-assembly,
leading to ordered supramolecular structures, may involve non-
covalent sub-chemical bonds such as van der Waals interactions,
hydrogen bonding, hydrophobic interactions, p–p stacking, donor–
acceptor interactions or electrostatic attraction.11
The development of nano-composite materials with advanced
photo-physical, magnetic and electrical properties have shown
wide spread interest. The fabrication of carbon nanotubes
(CNTs) based nano-composites with various materials, such as
organic molecules,12 biomolecules,13 polymers,14 dendrimers,15
These complexes show unusual magnetic properties that
depends upon the nature of the transition metal atoms26,27 and are
widely used as bio-catalysts28–30 and exhibit interesting optical
properties.31,32 We have reported a nickel(II) dithiolene complex
with terminal ester (–COOCH3) substituents that undergoes solvent
controlled self-assembly, resulting in the formation of different
a Department of Chemistry, Indian Institute of Technology, Kanpur – 208016,
Uttar Pradesh, India
b Department of Chemistry, Bengal Engineering and Science University, Shibpur,
Botanic Garden, Howrah – 711103, West Bengal, India. E-mail: abya@iitk.ac.in
† CCDC 893236. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3nj00368j
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nanocrystalline shapes in different solvent mixtures. The pre-
sent complex, with potential hydrogen bonding groups
(viz., –COOCH3), interacts more efficiently with functionalized
carbon quantum dots than the –CRN substituted analogue.33
Furthermore, 1,2-dithiolene coordinated transition metal com-
plexes are known to undergo ligand centered oxidation/reduction
involving dianionic to neutral to dipositive complexes and sulfur
based radicals.31–33 Radical based metal–dithiolate systems are
expected to show unprecedented spectroscopic properties, which
are sometimes strikingly similar to that of the biological active
sites.34 Copper–dithiolene complexes show unusual properties
such as very intense electronic transitions in the near-IR region
and they exhibit different oxidation states connected through
reversible processes.35,36
To the best of our knowledge, transition metal complex and
wsCNT-based formation of nano-composites by a self-assembly
process is not reported in the literature. So, the report pre-
sented here is the synthesis of a new bis-dithiolene complex
[PPh4][Cu(DMED)2], (1; DMED = 1,2-dicarbomethoxy-1,2-dithiolate),
along with its X-ray crystal structure, spectroscopic and electro-
chemical properties. We also report that 1 spontaneously
aggregates to nano-spheres on interacting with water, and these
nano-spheres further aggregate, with the assistance of water
molecules, to nano-composites with wsCNTs.
Scheme 2 Synthesis of copper(III) 1,2-dicarbomethoxy-1,2-dithiolate.
(s; nS(S–S));. Anal. calcd (%) for C48H40CuP2S8: C 57.72, H 4.04;
found: C 57.82, H 3.83.
2.2.2. Synthesis of copper(III) 1,2-dicarbomethoxy-1,2-dithio-
late: [PPh4][Cu(DMED)2]. The reaction of [PPh4]2[Cu(S4)2] with a
slight excess of DMAD proceeds readily at room temperature to
afford copper(III) 1,2-dicarbomethoxy-1,2-dithiolate, 1, as shown in
Scheme 2. The reaction between the metal polysulfide and DMAD
occurs through the formation of a bipolar intermediate.40 The
electron-withdrawing –COOCH3 group renders the acetylenic
carbon atoms more susceptible to nucleophilic attack by the lone
2ꢀ
2ꢀ
pairs of the S4 ligands.41 A pair of such types of S4 ligands is
available to react with the acetylene moiety, leading to the
formation of 1 (Scheme 2). [PPh4]2[Cu(S4)2] (1 g, B1 mM) was
taken in acetonitrile (50 mL) in a round bottom flask. DMAD
(1 mL, B7 mM) was added and the mixture stirred at room
temperature for 3 h. The dark brown colour of the solution
changed to reddish brown. The solution was filtered and diethyl
ether (500 mL) was added to the filtrate and shaken well. The clear
red coloured solution was decanted from the precipitated solid of
1 in a flask. The solution was left overnight to yield dark red single
crystals suitable for X-ray diffraction. Total yield: 0.52 g: 62%.
2. Experimental section
2.1. Materials
All reactions were carried out under ambient conditions. The
starting materials, cupric acetate and tetraphenylphosphonium
bromide were purchased from Spectrochem and ferrous sulfide
was obtained from Lancaster. Dimethyacetylenedicarboxylate
(DMAD) was purchased from Sigma-Aldrich (USA). All solvents used
were of reagent grade and were distilled using standard techniques.
Molecular formula:
C36H32CuO8PS4; molecular weight:
815.37; FT-IR (KBr): n = 2947 (w), 1829 (s), 1727 (s; n(CQO)),
1587 (w), 1546 (s), 1481 (m), 1435 (m; n(CQC)), 1239 (s), 1107 (m),
1073 (m), 1027 (m), 942 (w), 752 (w), 852 (s), 762 (m), 750 (s),
724 (s), 687 (s), 526 (s; n (S–S)); UV-vis (CH3CN): lmax (e) = 713
(1402), 1459 (3131); EPR (298 K): g = 2.022, g1 = 2.068, g2 = 2.022,
g3 = 1.978. Anal. calcd (%) for C36H32CuO8PS4: C 53.03, H 3.96;
found: C 52.89, H 3.88.
2.2.3. Synthesis of water soluble carbon nanotubes (wsCNTs).
The wsCNTs used here were synthesized by the oxidative treatment
of CNTs with nitric acid using a previously reported method,20,21
which results in the incorporation of a sufficient number of
electrophilic carboxylic acid groups as ‘‘surface defects’’ that makes
the CNTs and other nano-carbons42–50 soluble in water. The
removal of trace amounts of nitric acid was carried out by
repeatedly evaporating out the aqueous solution of wsCNTs in a
water bath to drive away any residual nitric acid, which was
confirmed by the Griess reagent test.51
2.2. Synthesis
2.2.1. Synthesis of copper(II) polysulfide: [PPh4]2[Cu(S4)2].
Copper polysulfide, as the precursor complex, was synthesized by
the reaction of copper acetate in methanolic potassium polysulfide
solution, following a modified procedure reported earlier,37,38 as
shown in Scheme 1, which lead to the formation of a soluble metal
polysulfide. Polysulfide ions are able to coordinate with metal
centers. Polysulfides can adjust their chain length according
to the geometric preferences of the host metal. Such metal poly-
sulfides are generally reactive, can easily undergo conversion,
involving scission or insertion into the S–S bonds.39
Molecular formula: C48H40CuP2S8; molecular weight: 996.96;
yield: 3.7 g, 95%; FT-IR (KBr): n = 3057 (w), 1584 (w), 1482 (s),
1435 (w), 1186 (w), 1153 (s), 994 (w), 754 (s), 721 (s), 687 (s), 524
2.3. Characterization
2.3.1. Electron microscopy. Field emission scanning electron
microscopic measurements were carried out on the SUPRA 40VP
(FE-SEM) (CARL ZEISS NTS GmbH, Oberkochen (Germany))
equipped with an energy dispersive X-ray (EDX) facility. In a
typical preparation, crystals of 1 was powdered finely in a
passel–mortar, dissolved in a mixture of H2O–CH3CN (1 : 1)
Scheme 1 Synthetic route for the synthesis of copper(II) polysulfide.
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and sonicated for 5 min. From this mixture, 5 mL of solution
was placed on a brass stub. The samples prepared by such
treatment were dried for 3 h under a table lamp (60 W, placed
0.5 m away) and then subjected to FESEM analysis. Transmis-
sion electron microscopy (TEM) and its high resolution
(HRTEM) analysis were carried out using a Tecnai 20 G2
200 kV, STWIN model with an acceleration voltage of 200 kV.
The samples were prepared for TEM measurements by placing
a small drop of the sample (diluting the sample prepared for
SEM) onto a carbon coated copper grid.
2.3.2. Raman/infrared and UV-Vis absorption spectroscopy.
Raman spectroscopic measurements were carried out with a Raman
spectrometer; WITEC MODEL with 514 nm excitation wavelength.
The infrared spectra of the complexes were recorded out on a Bruker
Vertex 70, FT-IR spectrophotometer using KBr pellets. Electronic
spectral measurements were carried out in acetonitrile on a Perkin
Elmer Lambda 35 UV-Vis spectrophotometer. Elemental analyses of
the complexes were determined using a CE-440 elemental analyzer,
EAI Exeter analytical, INC.
Fig. 1 Raman spectra of (a) raw CNTs and (b) wsCNTs; (c) TEM image of wsCNTs,
(d) HRTEM image of the wsCNTs, showing the inter-planar distance between the
graphitic carbons.
2.3.3. Electron paramagnetic resonance spectroscopy/
magnetism and cyclic voltammetry. The X-band EPR spectral
measurements were recorded in the solid state with a Bruker
EMX spectrometer at a typical microwave frequency of 9.87 GHz
and a microwave power of 0.200 mW. The modulation amplitude
was 5 G and the time constant was 10 ms. For the measure-
ments, powdered samples were placed into EPR Wilmad 5 mm
o.d. quartz tubes centred into the rectangular cavity.
Cyclic voltammetric measurements were carried out with a BASi
Epsilon-EC, Bioanalytical systems, Inc. Cyclic voltammograms (CV)
were measured for 10ꢀ3 M solutions of the compounds in aceto-
nitrile (CH3CN) with 0.2 M [Bu4N][ClO4] as the supporting electro-
lyte with a platinum disc working electrode, Ag/AgCl reference
electrode and a platinum wire as the auxiliary electrode. All
electrochemical experiments were performed under an argon atmo-
sphere at 298 K. The magnetic measurements were carried out by a
ADS DMS EV7 vibrating sample magnetometer (VSM).
spectra of the raw (as produced) and wsCNTs are displayed in
Fig. 1(a) and (b), respectively. The Raman spectrum of the raw
CNTs, before acid treatment, showed characteristic D-band
(corresponding to the vibrations of sp3 hybridized carbon)
and G-band (corresponding to the vibrations of sp2 hybridized
carbon) bands at B1354 and B1606 cmꢀ1, respectively. After
oxidative treatment with nitric acid the intensity and area of the
D-band increases with respect to the G-band, as demonstrated
in Fig. 1(b). This clearly shows the enhancement of sp3 hybridised
carbon atoms in terms of enhanced ‘‘surface defects’’ due
to the incorporation of carboxylic acid groups. Both peak
positions (D and G bands) are shifted towards lower wave
numbers, at B1337 and B1592 cmꢀ1, which corresponds to
the weakening of the graphitic structure of the wsCNTs as a
result of the oxidative treatment.49
The structure and morphology of wsCNTs used here were
characterized by high resolution TEM analysis. The TEM images
in Fig. 1(c) show the presence of tubular like structures of CNTs
with diameters in the range of 20–30 nm. The high resolution TEM
image (Fig. 1(d)) shows the inter-planer distance between the
graphitic carbons, with a d-spacing of 0.34 nm.20,21,49
2.3.4. Single crystal measurements. Single crystals of 1
suitable for X-ray diffraction were obtained by recrystallization
from CH3CN. The intensity data were collected on a Bruker AXS
Smart APEX CCD diffractometer with graphite monochromated
Mo-Ka radiation (0.71073 Å). Data reduction and absorption
corrections were done using a SAINTPLUS program package
supplied by Bruker. The structure was solved by direct and
conventional Fourier methods and refined on F2 by the full-
3.2. Structure of copper(III) 1,2-dicarbomethoxy-1,2-dithiolate
matrix least-squares technique using the SHELXTL program Complex 1 crystallizes in the monoclinic system in space group
package.52 All non-hydrogen atoms were refined anisotropically P21/c. The asymmetric unit of complex 1 has two half [Cu(DMED)2]
and the H-atoms were fixed at idealized positions in the anions, with the Cu atoms lying on the inversion centers, and one
riding mode.
tetraphenylphosphonium cation in a general position. Geometrical
parameters of both half anions show very little difference. An
ORTEP view of the two half anions is displayed in Fig. 2. The
X-ray crystal structure determination study indicates that the Cu(III)
complex has a square planar geometry. The important crystal-
lographic data parameters, and the selected bond lengths and
3. Results and discussion
3.1. Characterization of the water soluble carbon nanotubes
(wsCNTs)
Incorporation of the high density electrophilic (carboxylic angles are summarized in Table 1 and 2, respectively. The
groups) groups on the surface of the CNTs as ‘‘surfacial copper(III) centre is tetra coordinated in a square planar fashion
defects’’ was characterized by Raman spectroscopy. The Raman with four thiolate donors from two DMED ligands.
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Table 2 Selected bond lengths [Å] and angles [1] for the Cu(III) complexa
Cu(1)–S(1)
Cu(2)–S(3)
S(1)–C(1)
S(3)–C(7)
S(2)#1–Cu(1)–S(2)
S(2)–Cu(1)–S(1)
S(1)–Cu(1)–S(1)#1
S(4)–Cu(2)–S(3)#2
S(4)–Cu(2)–S(3)
C(2)–S(1)–Cu(1)
C(7)–S(3)–Cu(2)
2.1829(12)
2.1669(15)
1.740(4)
1.735(4)
180
92.28(4)
180.0
88.16(5)
91.84(5)
102.40(17)
103.09(16)
Cu(1)–S(2)
Cu(2)–S(4)
S(2)–C(2)
S(4)–C(8)
S(2)#1–Cu(1)–S(1)
S(2)–Cu(1)–S(1)#1
S(4)#2–Cu(2)–S(4)
S(4)#2–Cu(2)–S(3)
S(3)#2–Cu(2)–S(3)
C(1)–S(2)–Cu(1)
C(8)–S(4)–Cu(2)
2.1750(14)
2.1801(12)
1.753(4)
1.747(4)
87.72(4)
87.72(4)
180.0
88.16(5)
180.0
102.68(18)
103.85(17)
a
#1 and #2 characters in the atom labels show that these atoms are at
equivalent positions (1 ꢀ x, ꢀy, 1 ꢀ z) and (ꢀx, ꢀy, ꢀz) respectively.
Fig. 2 ORTEP view of the two half anions of the Cu(III) 1,2-dicarbomethoxy-1,2-
dithiolate complex, showing 50% probability thermal ellipsoids with a partial
atom labelling scheme.
Table
1
Crystallographic dataa for Cu(III) 1,2-dicarbomethoxy-1,2-dithiolate
complex
Complex
1
Formula
Formula weight
Crystal system
Space group
Temperature (K)
Z
a (Å)
b (Å)
c (Å)
a (1)
C36H32CuO8PS4
815.37
Monoclinic
P21/c
100(2) K
4
17.928(5)
10.121(5)
21.863(5)
90
Fig. 3 Electronic spectrum of the Cu(III) 1,2-dicarbomethoxy-1,2-dithiolate
complex in CH3CN.
b (1)
113.697(5)
90
3633(2)
1.491
1.91 to 25.50
18 850
6753
0.0616
1.062
0.0535, (0.1353)
g (1)
V (Å3)
dcalcd (g cmꢀ3
y range (1)
)
Reflections collected
Unique reflections
Rint
GOF (F2)
R1,b (wR2 )
c
Scheme 3 Resonating structures of dithiolenes resulting from ligand-based
P
P
P
a
b
c
2
redox processes.
Mo Ka radiation. R1
=
8F0| ꢀ |Fc8/ |F0|. wR2 = { [w(F0
ꢀ
P
Fc2)2]/ [w(F02)2]}1/2
.
the presence of a sulfur based radical in the coordinated
dithiolene. The dithiolene complexes exist in different oxidation
states, and these oxidation states are connected through a
ligand-based reversible redox process, which forms sulfur-based
radicals as depicted in Scheme 3. The square-planar geometry of
the complex facilitates the high degree of electron delocalization
in the five membered rings. This low-energy electronic absorp-
tion band is assigned for the p–p* transition between the HOMO
and LUMO, which occurs at low energy. This type of electronic
transition, known as IVCT (intervalence charge transfer) bands,
is well known.57–59
The average Cu–S bond lengths in the anionic copper(III) and
copper(II) dithiolene complexes are in the range of 2.16–2.18
and 2.25–2.28 Å, respectively.53–56 The Cu–S bond lengths in
complex 1 are almost equal and in the range 2.1829(12)–
2.1669(15) Å, suggesting the oxidation state of copper is three.
The lack of variation in the bond lengths indicates that the
electron in the radical form is uniformly distributed through-
out the entire molecule.
3.3. Electronic spectral measurements
The electronic absorption spectrum of 1 (in CH3CN) in the
region of 600–2200 nm is displayed in Fig. 3. It exhibits a band
3.4. Electrochemistry
at 1459 nm in the near-IR region with high intensity (e, 3131) The cyclic voltammograms of 1 in CH3CN at various scan rates
and a band at 713 nm (e, 1402). The band at l = 1459 nm is are displayed in Fig. 4. This complex undergoes a reversible
characteristic of copper–dithiolenes.57 This band arises due to reduction at E1/2 = ꢀ0.31 V and a quasi-reversible reduction at
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Fig. 6 Field dependence of meff of 1.
Fig. 4 Cyclic voltammograms of 1 (2 mM) in CH3CN with supporting electrolyte,
tetrabutylammonium perchlorate (TBAP, 0.2 M) at various scan rates (50–500 mV sꢀ1).
intensity absorption band at 1459 nm, supports the presence
of such a radical species.58
3.6. Magnetic measurement
E1/2 = ꢀ1.38 V vs. Ag/AgCl. The reduction at E1/2 = ꢀ0.31 V is
assigned to S-based radical reduction, forming the dithiolate,
as it is observed in all transition metal complexes containing
S-based radical ligands. This electrochemical observation
clearly supports the coordination of S-based radical to the
copper centre in 1.58,60
The quasi-reversible reduction at E1/2 = ꢀ1.38 V may be related
to the metal centred reduction from Cu(III) to Cu(II), leading to the
instability of the system. The irreversible oxidation at Epa = 0.847 V
vs. Ag/AgCl is assigned to the oxidation of the dithiolene sulfur.
Complex 1 is a Cu(III) d8 system with a square planar geometry,
which is diamagnetic.53,54 However its magnetic measurement
exhibits meff values in the range of 1.32–1.24 BM (Fig. 6) based
on a varied magnetic field. Such a low magnetic moment value
(less than that of an unpaired electron) may be correlated with
the presence of a sulfur based radical with large spin–orbit
coupling.
3.7. Self-assembly of 1 with water
1 is not soluble in water as such and its solution with CH3CN
alone did not show any aggregation. However, when 1 was
dissolved in a CH3CN and H2O mixture (1 : 1) aggregation took
place. SEM images of the nanospheres of 1 at low and high
magnifications are shown in Fig. 7, which indicate the spherical
morphology with a poly-dispersed nature. 1 formed nanospheres
with diameters in the range B400 nm to B1600 nm. The EDX
analysis of these nanospheres (Fig. 8) indicates that all the
constituent elements of 1 are present within the expected ratio
3.5. Electron paramagnetic resonance (EPR) spectroscopic
measurements
1 has a square planar Cu(III) geometry with a d8 system, which is
not EPR active. However, it shows a room temperature EPR
signal that lacks the simple Cu(II) EPR signature (Fig. 5). This
consists of three lines with g values (g1 = 2.068, g2 = 2.022, and
g3 = 1.978). The average hgi value of 2.022 clearly suggests its
radical character and that is from the sulfur based radical.57–63
The electronic spectrum, with the appearance of a high
Fig. 7 Nanospheres of 1 in a mixture of CH3CN and H2O, (a) and (c) low
magnification SEM images of nanospheres of 1, (b) size distribution histogram
of the nanospheres, (d) high resolution SEM image of nanospheres of 1 on a
brass matrix.
Fig. 5 The X-band EPR spectrum of 1 due to sulfur radicals at 298 K.
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Fig. 8 EDX analysis of the nanospheres of 1.
of the elements. The nanospheres on re-dissolution in aceto-
nitrile shows an identical electronic spectrum of 1, confirming
that upon aggregation the basic nature of 1 is preserved.
3.8. Nano-composites of 1 with wsCNT and water
The nano-composite of 1 and water soluble carbon nanotubes
(wsCNTs) was prepared by reacting 1 with wsCNTs in a H2O–
CH3CN mixture (1 : 1). The multi-walled CNTs were made water
soluble through the introduction of –COOH groups by oxidative
treatment with nitric acid as described.20,21 1 mg of wsCNTs
was added to 2 mL of distilled water and sonicated for 1 min,
wherein the wsCNTs were completely dissolved. In the mean-
time, 1 (1 mg) was dissolved in 2 mL of acetonitrile. The two
solutions were then mixed and sonicated for 5 min. and
allowed to age for six days under an argon atmorsphere. A
couple of drops of this solution was then deposited onto a brass
stub and dried under the exposure of a 60 W lamp (1.5 feet
away) for SEM measurements. The SEM images of the compo-
sites of wsCNTs with nanospheres of 1 at low and high
magnifications are displayed in Fig. 9. Ligands containing
–COOCH3 groups in the Cu(III) 1,2-dicarbomethoxy-1,2-dithio-
late complex are capable of hydrogen bonding with the –COOH
groups of the wsCNTs. Nanospheres of the Cu(III) complex were
wrapped in the wsCNTs network to interact and decorate the
smooth surfaces of nanospheres. Fig. 9(b) shows the wrapping
of the nanospheres in the CNTs network. The interactions of
wsCNTs with 1 are shown in Fig. 9(c) and (d), which clearly
demonstrate that the wsCNTs are abundantly present on the
surface. The TEM images of the composites of wsCNTs with
nanospheres of 1 are shown in Fig. 9(e) and (f). TEM images
confirm the interaction of the wsCNTs with the nanospheres of
complex 1 and reveal the abundance of the wsCNTs on the
surface of the nanospheres.
Fig. 9 (a) SEM images of the nanocomposite of 1 with wsCNTs at lower
magnification, (b and c) high resolution SEM image of the nano-composite of
complex 1 with wsCNTs, (d) zoomed image of a portion of the nano-composite,
(e and f) TEM images of the nano-composite of 1 with wsCNTs.
Fig. 10 Solid state X-band EPR spectrum of the nano-composites of Cu(III) 1,2-
The interactions of the nano-composites of wsCNTs and the
Cu(III) 1,2-dicarbomethoxy-1,2-dithiolate complex was further
studied by EPR measurements, which showed a decrease in the
intensities with hgi close to 2.002, confirming the presence of
free radicals even under the formation of the nano-composite.
The EPR spectrum of the nano-composites of 1 with wsCNTs
is shown in Fig. 10, the spectrum of the nano-composites is
similar to the EPR of 1 under similar measurement conditions
(298.4 K in solid state), as shown in Fig. 5. The signal intensity
dicarbomethoxy-1,2-dithiolate complex and wsCNTs.
material’s composition.63,64 The EPR spectrum of the nano-
composites also shows slight broadening, which reveals the
interaction between 1 and the wsCNTs.65
4. Conclusions
is related to the radical concentration that decreases in the The discrete copper(III) 1,2-dicarbomethoxy-1,2-dithiolate complex
nano-composites, which could be due to the radical scavenger showed strong aggregation to create nanospheres upon its inter-
nature of CNTs and also as a result of the change in the action with water due to hydrogen bonding. These nanospheres
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Paper
18 J. Nijuguna and K. Pielichowski, Adv. Eng. Mater., 2003,
5, 769.
19 R. H. Baughman, A. A. Zakhidov and W. A. D. Heer, Science,
2002, 297, 787.
20 S. Tripathi, S. K. Sonkar and S. Sarkar, Nanoscale, 2011,
3, 1176.
21 M. Roy, S. K. Sonkar, S. Tripathi, M. Saxena and S. Sarkar,
J. Nanosci. Nanotechnol., 2012, 12, 1754.
22 S.-F. Zheng, J.-S. Hu, L.-S. Zhong, W.-G. Song, L.-J. Wan and
Y.-G. Guo, Chem. Mater., 2008, 20, 3617.
23 W. Wu, S. Wieckowski, G. Pastorin, M. Benincasa,
C. Klumpp, J.-P. Briand, R. Gennaro, M. Prato and
A. Bianco, Angew. Chem., Int. Ed., 2005, 44, 6358.
24 R. R. Johnson, A. T. C. Johnson and M. L. Klein, Small, 2010,
6, 31.
were further wrapped by wsCNTs. Such wrapping by the
wsCNTs into a nano-spherical Cu(III) complex can be clearly
visualized by electron microscopy, and such an interaction led
to the perturbation of the EPR signature of the starting copper
dithiolate complex, where the diamagnetic Cu(III) complex
exists with the oxidized radical part of the 1,2-dicarbo-
methoxy-1,2-dithiolate ligand. The role of water in the self-
aggregation of 1, followed by further aggregation with wsCNTs
to create larger aggregates, could be useful in the exploring
the size dependent properties of pure inorganic and also
composite materials.
Acknowledgements
K. M. T. thanks the CSIR for the doctoral fellowship; S. K. S.
thanks IIT Kanpur for the senior teaching assistantship; A. B.
thanks DST, New Delhi, for the award of the fast track scheme
for young scientists. S. S. acknowledges the funding from DST
(SR/S1/IC-06/2010).
25 H. Jarei, H. Ghourchian, K. Eskandari and M. Zeinali, Anal.
Biochem., 2012, 421, 446.
ˇ
`
´ˇ
´ˇ
´
26 K. Mrkvova, J. Kamenıcek, Z. Sindelar, L. Kvıtek,
ˇ
`
J. Mrozinski, M. Nahorska and Z. Zak, Transition Met.
Chem., 2004, 29, 238.
27 D. Belo and M. Almeida, Coord. Chem. Rev., 2010, 254, 1479.
28 A. T. Coomber, D. Beljonne, R. H. Friend, J. L. Bredas,
A. Charlton, N. Robertson, A. E. Underhill, M. Kurmoo and
P. Day, Nature, 1996, 380, 144.
29 R. Cammack, V. M. Fernandez, K. Schneider and
J. R. Lancaster, The Bioinorganic Chemistry of Nickel, VCH,
New York, 1988.
Notes and references
1 A. P. Alivisatos, Science, 1996, 271, 933.
2 X. Lu, X. Shi and T. Min, Inorg. Chem., 2011, 50, 2175.
3 W. Mamdouh, R. E. A. Kelly, M. Dong, L. N. Kantorovich and
F. Besenbacher, J. Am. Chem. Soc., 2008, 130, 695.
4 G. M. Whitesides and B. Grzybowski, Science, 2002,
295, 2418.
30 D. Sellmann, D. H. Ussinger, F. Knoch and J. M. Moll, J. Am.
Chem. Soc., 1996, 118, 5368.
31 G. A. Reynolds and K. H. Drexhage, J. Appl. Phys., 1975,
46, 4852.
32 C.-M. Liu, D.-Q. Zhang, Y.-L. Song, C.-L. Zhan, Y.-L. Li and
D.-B. Zhu, Eur. J. Inorg. Chem., 2002, 1591.
33 A. Begum, S. K. Sonkar, M. Saxena and S. Sarkar, J. Mater.
Chem., 2011, 21, 19210.
5 G. M. Whitesides, E. E. Simanek, J. P. Mathias, C. T. Seto,
D. N. Chin, M. Mammen and D. M. Gordon, Acc. Chem. Res.,
1995, 28, 37.
6 M. Grzelczak, J. Vermant, E. M. Furst and L. M. Liz-Marzan,
ACS Nano, 2010, 4, 3591.
7 J. Aizenberg, A. J. Black and G. M. Whitesides, Nature, 1999,
398, 495.
34 U. T. Mueller-Westerhoff, B. Vance and D. I. Yoon, Tetra-
hedron, 1991, 47, 909.
´
´
´
´
8 N. Perez-Hernandez, D. Fort, C. Perez and J. D. Martın,
35 J. A. McCleverty, Prog. Inorg. Chem., 1968, 10, 49.
36 J. R. Ferraro and J. M. Williams, Introduction to Synthetic
Electrical Conductors, Academic Press, New York, 1987.
37 K. N. Udpa and S. Sarkar, Polyhedron, 1987, 6, 627.
38 A. Begum, G. Moula and S. Sarkar, Chem.–Eur. J., 2010,
16, 12324.
39 R. J. Pafford and T. B. Rauchfuss, Inorg. Chem., 1998,
37, 1974.
40 C. M. Bolinger and T. B. Rauchfuss, Inorg. Chem., 1982,
21, 3947.
41 M. G. Kanatzidis and D. Coucouvanis, Inorg. Chem., 1984,
23, 403.
42 S. K. Sonkar, M. Roy, D. G. Babar and S. Sarkar, Nanoscale,
2012, 4, 7670.
43 S. K. Sonkar, M. Ghosh, M. Roy, A. Begum and S. Sarkar,
Mater. Express, 2012, 2, 105.
44 M. Ghosh, S. K. Sonkar, M. Saxena and S. Sarkar, Small,
2011, 7, 3170.
Cryst. Growth Des., 2011, 11, 1054.
9 M. Reches and E. Gazit, Science, 2003, 300, 625.
10 K. Miszta, J. D. Graaf, G. Bertoni, D. Dorfs, R. Brescia,
S. Marras, L. Ceseracciu, R. Cingolani, R. V. Roij,
M. Dijkstra and L. Manna, Nat. Mater., 2011, 10, 872.
11 A. Begum, M. Saxena, S. K. Sonkar and S. Sarkar, Indian J.
Chem., 2011, 50A, 1257.
12 B. Valter, M. K. Ram and C. Nikolini, Langmuir, 2002,
18, 1535.
13 J. Li, Q. Liu, Y. Liu, S. Liu and S. Yao, Anal. Biochem., 2005,
346, 107.
14 D. Baskaran, J. W. Mays and M. S. Bratcher, Chem. Mater.,
2005, 17, 3389.
15 S. Campidelli, C. Sooambar, E. L. Diz, C. Ehli, D. M. Guldi
and M. Prato, J. Am. Chem. Soc., 2006, 128, 12544.
16 W.-J. Ong, M. M. Gui, S.-P. Chai and A. R. Mohamed, RSC
Adv., 2013, 3, 4505.
17 S.-H. Baek, B. Kim and K.-D. Suh, Colloids Surf., A, 2008,
316, 292.
45 M. Saxena and S. Sarkar, Diamond Relat. Mater., 2012, 24, 11.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem.

View Article Online
Paper
NJC
46 P. K. Chaudhury, P. Dubey, M. Saxena and S. Sarkar, Adv. 57 M. Bose, G. Moula, A. Begum and S. Sarkar, Inorg. Chem.,
Sci. Lett., 2011, 4, 558. 2011, 50, 3852.
47 S. K. Sonkar, M. Saxena, M. Saha and S. Sarkar, J. Nanosci. 58 K. Ray, T. Petrenko, K. Weighardt and F. Neese, Dalton
Nanotechnol., 2010, 10, 4064. Trans., 2007, 1552.
48 D. G. Babar, S. K. Sonkar, K. M. Tripathi and S. Sarkar, 59 P. Ghosh, A. Begum, D. Herebian, E. Bothe, K. Hildenbrand,
J. Nanosci. Nanotechnol., 2013 (accepted).
49 P. Dubey, S. K. Sonkar, S. Majumder, K. M. Tripathi and
S. Sarkar, RSC Adv., 2013, 3, 7306.
50 P. Dubey, D. Muthukumaran, S. Dash, R. Mukhopadhyay
and S. Sarkar, Pramana, 2005, 65, 681.
51 S. Roy and S. Sarkar, J. Chem. Soc., Chem. Commun., 1994,
275.
52 G. A. Sheldrick, Acta Crystallogr., 2008, A64, 112.
T. Weyhermuller and K. Wieghardt, Angew. Chem., 2003,
115, 581.
60 O. M. Usov, Y. Sun, V. M. Grigoryants, J. P. Shapleigh and
C. P. Scholes, J. Am. Chem. Soc., 2006, 128, 13102.
61 K. Ray, S. DeBeer George, E. I. Solomon, K. Wieghardt and
F. Neese, Chem.–Eur. J., 2007, 13, 2783.
62 K. Ray, T. Weyhermuller, F. Neese and K. Wieghardt, Inorg.
Chem., 2005, 44, 5345.
ˇ
`
´ˇ
`ˇ
´
53 K. Mrkvova, J. Kamenıcek, Z. Sindelar and L. Kvıtek, Transition 63 L. Dennany, P. Sherrell, J. Chen, P. C. Innis, G. G. Wallace
Met. Chem., 2004, 29, 238. and A. I. Minett, Phys. Chem. Chem. Phys., 2010, 12, 4135.
54 X. Ribas, J. C. Dias, J. Morgado, K. Wurst, E. Molins, E. Ruiz, 64 M. J. Martınez-Morlanes, P. Castell, V. Martınez-Nogues,
´
´
´
´
M. Almeida, J. Veciana and C. Rovira, Chem.–Eur. J., 2004,
10, 1691.
M. T. Martinez, P. J. Alonso and J. A. Puertolas, Compos. Sci.
Technol., 2011, 71, 282.
55 V. Madhu and S. K. Das, Polyhedron, 2004, 23, 1235.
56 X. Ren, J. Ma, C. Lu, S. Yang, Q. Meng and P. Wu, Dalton
Trans., 2003, 1345.
65 V. Gupta, B. K. Gupta, R. K. Kotnala, T. N. Narayanan,
V. Grover, J. Shah, V. Agrawal, S. Chand and V. Shanker,
J. Colloid Interface Sci., 2011, 362, 311.
c
New J. Chem.
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013