Deposition and characterization of Cu9S5 nanocrystals from unsymmetrical [(Hex)(Me)NC(S)NC(O)C6H3(NO 2)2 -3,5]2Cu(II) and [(Et)(Bu)NC(S)NC(O)C 6H4-4-NO

Article abstract of DOI:10.3906/kim-1305-47

Cu₉ S₅ nanocrystals were synthesized from unsymmetrical [(Hex)(Me)NC(S)NC(O)C₆H₃ (NO ₂)₂ -3,5]₂ Cu(II) and [(Et)(Bu)NC(S)NC(O)C ₆H₄ -4-NO₂ ]

Full text of DOI:10.3906/kim-1305-47

Turk J Chem
Turkish Journal of Chemistry
(2014) 38: 413 – 422
¨
http://journals.tubitak.gov.tr/chem/
˙
c
⃝ TUBITAK
doi:10.3906/kim-1305-47
Research Article
Deposition and characterization of Cu9 S5 nanocrystals from unsymmetrical
[(Hex)(Me)NC(S)NC(O)C6 H3 (NO2)2 -3,5]2 Cu(II) and
[(Et)(Bu)NC(S)NC(O)C6 H4 -4-NO2 ]2 Cu(II) complexes by colloidal thermolysis
method
Sohail SAEED1,2,∗, Rizwan HUSSAIN2
1Department of Chemistry, Research Complex, Allama Iqbal Open University, Islamabad, Pakistan
2National Engineering & Scientific Commission, Islamabad, Pakistan
Received: 21.05.2013
•
Accepted: 14.10.2013
•
Published Online: 14.04.2014
•
Printed: 12.05.2014
Abstract:Cu9 S5 nanocrystals were synthesized from unsymmetrical [(Hex)(Me)NC(S)NC(O)C6 H3 (NO2)2 -3,5]2 Cu(II)
and [(Et)(Bu)NC(S)NC(O)C6 H4 -4-NO2 ]2 Cu(II) complexes by colloidal thermolysis in the presence of surfactant
oleylamine. The unsymmetrical copper complexes were synthesized by the reaction of copper(II) acetate with N -
[hexyl(methyl)carbamothioyl]-3,5-dinitrobenzamide and N -[ethyl(butyl)carbamothioyl]-4-nitrobenzamide. The com-
plexes were used as single-source precursors for the preparation of Cu9 S5 nanocrsytals. The Cu9 S5 nanocrystals
were characterized by X-ray powder diffraction and transmission electron microscopy.
Key words: Cu9 S5 nanocrystals, p-XRD, crystallites, TEM, colloidal thermolysis, thiourea derivatives
1. Introduction
The emerging nanotechnology involves the development and utilization of nanostructures and devices with a
size range from 1 nm (molecular size) to about 20 nm. Most of the inorganic materials reported for photovoltaic
applications are either toxic or use less-abundant elements such as lead, cadmium, indium, or gallium. Relatively
less toxic, abundant, and thus cheaper materials may be more promising even with overall lower efficiencies for
photovoltaic applications.1 Recent estimates of the annual electricity potential as well as material extraction
costs and environmental friendliness led to the identification of inorganic or organic based materials that could
be used in photovoltaic applications on a large scale. The most promising and efficient materials include iron
and copper sulfide.2,3 The properties and application of semiconducting nanostructured materials extensively
depend on their crystal phase, size, composition, and shape as well as the processing technique for the production
of highly tuned nanocrystals.4
Semiconducting nanostructured copper sulfides thin films and nanoparticles have been investigated for
many uses including as p-type semiconductors in solar cells,5−7 nanoscale switches,8e and cathodic materials
for lithium rechargeable batteries.9 Vaughan et al.10 reported that in 1940 only the end member (Cu2 S) and
CuS were known in the Cu–S system. By 1974 nine more copper sulfide phases had been identified,11e and
in 2006 a total of 14 copper sulfide phases were recognized.12 Some important known and promising forms of
copper sulfide include chalcocite (Cu2 S), djurleite (Cu31 S16 or Cu1.94 S), digenite (Cu9 S5 or Cu1.8 S), anilite
∗Correspondence: sohail262001@yahoo.com
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SAEED and HUSSAIN/Turk J Chem
(Cu7 S4 or Cu1.75 S), covellite (CuS), and villamaninite (CuS2).13 Semiconducting nanostructured thin films
of copper sulfide have been prepared by various methods including RF-reactive sputtering,14 spray pyrolysis,15
successive ionic layer adsorption and reaction,16 chemical bath deposition,17e and chemical vapor deposition.18
Acylthioureas containing different heterocyclic moieties and alkyl substituents are important ligands for
the preparation of metal complexes and these precursors can be easily applied for the deposition of metal
sulfide nanoparticles using different capping agents. Arslan and co-workers19,20 reported the complexation of
copper(II) and zinc(II) with acylthiourea ligands and concluded that the coordination was through multifunction
S,O-donor atoms, using infrared spectroscopy and X-ray diffractions studies. Binzet and co-workers21 reported
that the complexes of methylthiourea have coordination through sulfur donor atoms.
We have previously reported biologically active acylthiourea derivatives containing benzothiazole, thi-
azole, and pyrimidine moieties and their metal complexes.22−24 As part of our long-standing interest in the
coordination chemistry of acylthioureas bearing different heterocyclic moieties, we here explore the prepa-
ration of copper sulfide nanocrystals from single-source precursors bis[N -[hexyl(methyl)carbamothioyl]-3,5-
dinitrobenzamide]copper(II) and bis[N -[ethyl(butyl)carbamothioyl]-4-nitrobenzamide]copper(II). These unsym-
metrical single-source precursors can be easily prepared in high yield from comparatively inexpensive and only
mildly hazardous starting materials, making them ideal for the potential large-scale production of copper sulfide
semiconducting nanostructured thin films and nanocrystals.
2. Experimental
2.1. Materials and physical measurements
4-Nitrobenzoyl chloride (≥98.0%), N -hexylmethylamine (99%),N -butylethylamine (99%), sodium thiocyanate
(99%), copper(II) nitrate trihydrate (99.5%), tetrabutylammonium bromide (TBAB) (≥98%), oleylamine-
approx. C18 content 80%–90%, and 3,5-dinitrobenzoyl chloride (≥98.0%) were purchased from Sigma-Aldrich.
Elemental analysis of the ligands was performed using a PerkinElmer CHNS/O 2400. Infrared spectra were
recorded on a Specac single reflectance attenuated total reflectance (ATR) instrument (4000–400 cm−1 , res-
olution 4 cm−1). Atmospheric pressure chemical ionization mass spectrometry (MS-APCI) of the copper
complexes was recorded on a Micromass Platform II instrument. Metal analysis of the complexes was carried
out by Thermo iCap 6300 inductively coupled plasma optical emission spectroscopy (ICP-OES). Melting points
were recorded on a Barloworld SMP10 melting point apparatus. Thermal stability of the copper complexes was
studied by thermogravimetery in an inert atmosphere, at sample heating rate of 10 ◦ C/min, with a DuPont
2000 ATG. X-ray powder diffraction (p-XRD) studies were performed on an Xpert diffractometer using Cu-Kα
radiation. The samples were mounted flat and scanned between 20◦ and 65◦ with a step size of 0.05 with vari-
ous count rates. The diffraction patterns were then compared to the documented patterns in the International
Center Diffraction Datae (ICDD) index. Transmission electron microscopy (TEM) samples were prepared by
evaporating a drop of a dilute suspension of the sample in n-hexane on a carbon-coated copper grid. The excess
solvent was allowed to dry completely at room temperature. TEM images were collected on a Philips CM200
transmission electron microscope using an accelerating voltage of 200 kV.
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SAEED and HUSSAIN/Turk J Chem
2.2. Synthesis of the copper complexes
Bis[N -[hexyl(methyl)carbamothioyl]-3,5-dinitrobenzamide]copper(II)
[(Hex)(Me)NC(S)NC(O)C6 H3 (NO2)2 -3,5]2 Cu(II)
To a 250-mL double-necked round-bottomed flask containing 3,5-dinitrobenzoyl chloride (0.01 mol)
dissolved in anhydrous acetone (75 mL) and 0.3 mole% of tetrabutylammonium bromide (TBAB) in acetone was
added dropwise a suspension of sodium thiocyanate in acetone (45 mL) and the reaction mixture was refluxed
for 45 min. After cooling to room temperature, a solution of N -hexylmethylamine (0.01 mol) in acetone (25
mL) was added and the resulting mixture refluxed for 2 h. The reaction mixture was poured into 5 times its
volume of cold water, whereupon the acylthiourea precipitated. The solid product of acylthiourea was washed
with water and purified by recrystallization from ethyl acetate. Light yellow in semisolid state. Mp: 98–99 ◦ C.
Yield: 3.3 g (78%). IR (νmax , cm−1): 3176 (NH), 2959, 2877 (C–H), 1685 (C=O), 1262 (C=S). 1 H NMR (400
MHz, CDCl3) in δ (ppm) and J (Hz): δ 9.11 (t, 1H, J = 1.8), 8.83 (d, 2H, J = 1.8), 8.38 (bs, 1H, CONH),
3.90 (t, 2H, N–CH2), 3.01(s, 3H, CH3), 2.57(m, 2H, –CH2 –), 1.83 (m, 2H, –CH2 –), 1.66 (m, 2H, –CH2 –),
1.27 (m, 2H, –CH2 –), 0.90 (t, 3H, CH3). Anal. calcd. for C15 H20 N4 O5 S: C, 48.90; H, 5.47; N, 15.21; S, 8.70.
Found: C, 48.87; H, 5.49; N, 15.20; S, 8.70.
In the second step, a solution of copper nitrate (0.005 mol) in methanol (25 mL) was added dropwise to a
solution of the acylthiourea ligand in a 1:2 ratio with a small excess of acylthiourea in ethanol (25 mL) at room
temperature, and the resulting mixture was stirred for 3 h. The reaction mixture was filtered, washed with
ethanol, and recrystallized from a THF:acetonitrile mixture (1:1, v : v). Green. Yield: 3.9 g (81%). IR (νmax
,
cm−1): 2926, 2856 (Ar–H), 1508 (C–O), 1537 (C–N), 1121 (C–S); Anal. calcd. fore C30 H38 N8 O10 S2 Cu:
C, 45.13; H, 4.80; N, 14.04; S, 8.05; Cu, 7.96. Found: C, 44.78; H, 4.87; N, 14.00; S, 8.06; Cu, 7.72. Mass
(MS-APCI) (m/z): 798 [M+, C30 H38 N8 O10 S2 Cu].
Bis[N -[ethyl(butyl)carbamothioyl]-4-nitrobenzamide]copper(II)
[(Et)(Bu)NC(S)NC(O)C6 H4 -4-NO2 ]2 Cu(II)
To a 250-mL double-necked round-bottomed flask containing 4-nitrobenzoyl chloride (0.01 mol) dissolved
in anhydrous acetone (75 mL) and 0.3 mole% of tetrabutylammonium bromide (TBAB) in acetone was added
dropwise a suspension of sodium thiocyanate in acetone (45 mL) and the reaction mixture was refluxed for 45
min. After cooling to room temperature, a solution of N -butylethylamine (0.01 mol) in acetone (20 mL) was
added and the resulting mixture refluxed for 2 h. The reaction mixture was poured into 5 times its volume of
cold water, whereupon the acylthiourea precipitated. The generated solid product of acylthiourea was washed
with water and purified by recrystallization from the ethanol. Yellow. Mp: 89–90 ◦ C. Yield: 3.3 g (90%). IR
(νmax , cm−1): 3233 (NH), 2931, 2852 (C–H), 1691 (C=O), 1256 (C=S). 1 H NMR (400 MHz, CDCl3) in δ
(ppm): 8.45 (s, 1H, CONH), 8.12 (d, 2Hmeta , p-nitrophenyl), 7.35 (d, 2Hortho , p-nitrophenyl), 3.82 (t, 2H,
CH2), 3.54 (m, 2H, CH2), 1.85 (m, 2H, CH2),1.65 (m, 2H, CH2), 0.98 (t, 3H, CH3), 0.91 (t, 3H, CH3);
Anal. calcd. for C14 H19 N3 O3 S: C, 54.35; H, 6.19; N, 13.58; S, 10.36. Found: C, 54.32; H, 6.35; N, 13.57; S,
10.37. In the second step, a solution of copper nitrate (0.005 mol) in methanol (25 mL) was added dropwise
to a solution of the acylthiourea ligand in a 1:2 ratio with a small excess of acylthiourea in ethanol (25 mL)
at room temperature, and the resulting mixture was stirred for 3 h. The reaction mixture was filtered, washed
with ethanol, and recrystallized from a THF:acetonitrile mixture (1:1, v : v). Dark brown. Mp: 175–176 ◦ C.
Yield: 3.3 g (78%). IR (νmax , cm−1): 2928, 2855 (Ar–H), 1508 (C–O), 1535 (C–N), 1140 (C–S); Anal. calcd.
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SAEED and HUSSAIN/Turk J Chem
fore C28 H36 N6 O6 S2 Cu: C, 49.43; H, 5.33; N, 12.35; S, 9.43; Cu, 9.34. Found: C, 49.51; H, 5.56; N, 12.22; S,
9.45; Cu, 9.05. Mass (MS-APCI) (m/z): 680 [M+, C28 H36 N6 O6 S2 Cu].
2.3. Synthesis of copper sulfide nanocrystals
Copper sulfide nanocrystals were prepared by pyrolyzing the copper complexes as precursors in oleylamine by
colloidal thermolysis. In a typical reaction, 15 mL of oleylamine was refluxed under vacuum at 90 ◦ C for 45 min,
and then it was purged with nitrogen gas for 30 min at the same temperature. Then about 0.25 g of precursor
was added to hot oleylamine and the reaction temperature was slowly increased to a desired point (170 and 230
◦ C) and the temperature was maintained for 1 h and the mixture was allowed to cool to room temperature.
The black precipitate generated during the process was separated by centrifugation at 25,000 rpm.
3. Results and discussion
The synthetic pathway for unsymmetrical acylthiourea derivatives and their copper complexes described in this
communication is outlined in the Scheme. The acylthiourea ligands and copper complexes were synthesized
according to the reported procedures25−33 with minor modifications. The use of phase transfer catalyst is a
well known method and is extensively applied in heterogeneous reaction systems.34,35e To improve the yield of
aroylthiourea ligands, we used TBAB as phase transfer catalyst in our designed reactions. The reaction proceeds
via nucleophilic addition of the secondary amine to the acylisothiocyanate. IR spectra of acylthiourea ligands
and the copper complexes in the region 4000–400 cm−1 were compared and assigned on careful comparison.
N, N′ -disubstituted thioureas behave both as monodentate and bidentate ligands, depending upon the reaction
conditions.36 The characteristic bands of N, N′ -disubstituted thioureas are 3233–3276 (NH), 2852–2959 Ph
(CH), 1691–1685 (C=O), and 1262–1256 (C=S), and there is a slight shift of (C=O) and (C=S) groups’
stretching frequencies due to coordination of the ligands to the copper atom.
As is well known, acythioureas usually act as bidentate ligands to transition-metal ions through the
acyl oxygen and sulfur atoms.37−40 The IR spectra of the copper(II) complexes show significant changes when
compared with the IR spectra of the corresponding acylthiourea ligands. The IR spectra of the complexes show
absorption bands at υmax : 2855–2926 Ph (CH), 1508 (C–O), 1537–1535 (C–N), and 1140–1121 (C–S) cm−1
.
The most prominent changes are the N–H stretching frequency at ∼3200 cm−1 in the free acylthiourea ligands,
which disappears completely, in full agreement with both ligands and copper complexes and the complexation
reaction. The spectroscopic data clearly indicate the loss of the proton originally bonded to the nitrogen
atom of the (NH–CO) amide groups. Another prominent change is observed for the carbonyl functional group
stretching vibrations. The stretching frequencies due to the carbonyl functional groups (1691 and 1685 cm−1
)
in the free acylthiourea ligands are shifted towards lower frequencies upon complexation, indicating that ligands
are coordinated to copper(II) ion through the O,S-donor atoms.41−45 IR spectroscopic data of the complexes
with the values of the free acylthiourea ligands indicate that the coordination of acylthiourea ligands to the
copper atom has a significant effect on υ(N-H), υ(C=O), and υ(C=S) frequencies.
3.1. Thermal decomposition studies of copper(II) complexes
The TGA pattern of the complex [(Hex)(Me)NC(S)NC(O)C6 H3 (NO2)2 -3,5]2 Cu(II) shows 2-step decomposi-
tion (Figure 1a). The first step starts at 164 ◦ C and is accomplished at 335 ◦ C with weight loss of 67.24%. The
major part of the complex degraded sharply in the first region (164–335 ◦ C). In the second step, the decom-
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SAEED and HUSSAIN/Turk J Chem
Copper complexes
[(Hex)(Me)NC(S)NC(O)C6H3(NO2)2-3,5]2Cu(II) NO2
[(Et)(Bu)NC(S)NC(O)C6H4-4-NO2]2Cu(II)
R1
R2
H
R3
NO2 Hexyl Methyl
H Butyl Ethyl
R
R’
H
NO2
Scheme
position starts at 343 ◦ C and is accomplished at 586 ◦ C. The decomposition ends at about 600 ◦ C to leave a
residue of 21.01% of the initial mass, which is slightly higher than the 17.34% calculated for complete conversion
to copper sulfide material. The residual weight remains the same from 550 ◦ C to higher temperatures, which
indicates the expected stable phase of copper sulfide. TGA of the complex [(Et)(Bu)NC(S)NC(O)C6 H4 -4-
NO2 ]2 Cu(II) shows 2-step decomposition with rapid weight loss between 243 and 324 ◦ C and the second step
between 331 and 442 ◦ C as shown in Figure 1b. The major part of the complex degraded sharply in the region
of 270–300 ◦ C. The decomposition ends at about 600 ◦ C to leave a residue amount of 18.63%, which is very
close to the accumulative mass of decomposed product copper sulfide (calcd. 18.77%). Arslan and co-workers
reported the mechanism of thermal decomposition of some thioureas and their metal complexes.46−50
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SAEED and HUSSAIN/Turk J Chem
Figure 1. TGA of copper complex [(Hex)(Me)NC(S)NC(O)C6 H3 (NO2)2 -3,5]2 Cu(II) (a) and [(Et)(Bu)NC(S) NC(O)
C6 H4 -4-NO2 ]2 Cu(II) (b).
3.2. X-ray diffraction and transmission electron microscopic characterization of digenite Cu9 S5
nanocrystals deposited from [(Hex)(Me)NC(S)NC(O)C6 H3 (NO2)2 -3,5]2 Cu(II)
The XRD pattern for the Cu9 S5 nanocrystals synthesized from precursor [(Hex)(Me)NC(S)NC(O)C6 H3 (NO2)2 -
3,5]2 Cu(II) is shown in Figure 2. The synthesis of copper sulfide nanocrystals was carried out at 170 ◦ C and
230 ◦ C. No deposition was obtained below 170 ◦ C (Figure 2a). At 230 ◦ C (Figure 2b) the XRD pattern of
Cu9 S5 (digenite) nanocrystals shows diffractions of rhombohedral Cu9 S5 and the space group R-3m (166) with
major diffraction peaks of (0015), (107), (1010), (0114), (110), and (205) planes (ICDD: 026-0476) as shown in
the Table. In the XRD pattern, an extra peak ‘x’ was also observed. This peak may be due to some impurity
present but unfortunately its nature could not be identified. The TEM image (Figure 3) showed the deposited
Cu9 S5e crystallites are rectangular and irregular shaped. There was a certain degree of agglomeration and size
of the particles could be approximated to 250–600 nm in length.
Table. Powder X-ray crystal data of the decomposed material from complexes.
Copper sulfide, Cu9S5e [ICDD:026-0476]
Crystal system
Space group
Cell volume
Z
Rhombohedral
R-3m
˚
638.44 A
3
3
a = 3.919 A
α = 90.00◦
β = 90.00◦
˚
˚
b = 3.919 A
Cell parameters
c = 48.000 A γ = 120.00◦
˚
hkl matched with
˚
No. Pos. [2θ]
d-spacing d(A)
Cu9S5
0015
107
1
2
3
4
5
6
7
8
27.8572
29.3357
30.2301
32.2793
35.9058
41.5629
46.2976
54.8994
3.2000
3.0420
2.9540
2.7710
2.4990
2.1710
1.9594
1.6710
018
1010
1013
0117
110
205
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SAEED and HUSSAIN/Turk J Chem
Figure 2. XRD pattern of Cu9 S5 nanocrystals prepared at (a) 170 ◦ C (b) 230 ◦ C from [(Hex)(Me)NC(S)NC(O)C6 H3
(NO2)2 -3,5]2 Cu(II).
Figure 3. TEM image of Cu9 S5 nanocrystals from [(Hex)(Me)NC(S)NC(O)C6 H3 (NO2)2 -3,5]2 Cu(II).
3.3. X-ray diffraction and transmission electron microscopic characterization of digenite Cu9 S5
nanocrystals deposited from [(Et)(Bu)NC(S)NC(O)C6 H4 -4-NO2 ]2 Cu(II)
The XRD pattern for the Cu9 S5 nanocrystals synthesized from precursor [(Et)(Bu)NC(S)NC(O)C6 H4 -4-
NO2 ]2 Cu(II) is shown in Figure 4. The synthesis of copper sulfide nanocrystals was carried out at 170 ◦ C
and 230 ◦ C. No deposition was obtained below 170 ◦ C (Figure 4a). At 230 ◦ C (Figure 4b) the XRD pattern
of Cu9 S5 (digenite) nanocrystals shows diffractions of rhombohedral Cu9 S5 and the space group R-3m (166)
with major diffraction peaks of (0015), (107), (1010), (110), and (205) planes (ICDD: 026-0476). The TEM
image (Figure 5) showed that the deposited particles are in trigonal shaped and size of the particles could be
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SAEED and HUSSAIN/Turk J Chem
approximated to 17–450 nm in length. Reaction time, temperature, concentration, and the selection of reagents
and surfactants play an important role to control the size, shape, and quality of the particles. Generally the
particle size increases with an increase in reaction time and temperature.51
Figure 4. XRD pattern of Cu9 S5 nanocrystals prepared at (a) 170 ◦ C (b) 230 ◦ C from [(Et)(Bu)NC(S)NC(O)C6 H4 -
4-NO2 ]2 Cu(II).
Figure 5. TEM image of Cu9 S5 nanocrystals from [(Et)(Bu)NC(S)NC(O)C6 H4 -4-NO2 ]2 Cu(II).
4. Conclusions
A new approach has been introduced to synthesize Cu9 S5 nanocrystals from single source precursors [(Hex)(Me)
NC(S)NC(O)C6 H3 (NO2)2 -3,5]2 Cu(II) and [(Et)(Bu)NC(S)NC(O)C6 H4 -4-NO2 ] 2 Cu(II) by colloidal ther-
molysis. The prepared Cu9 S5 nanocrystals are rectangular and trigonal shaped crystallites 250–600 nm and
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SAEED and HUSSAIN/Turk J Chem
17–450 nm in length, respectively. These newly synthesized copper complexes may also be useful as applicable
precursors for the deposition of TOPO capped (tri-n-octylphosphineoxide) nanoparticles of copper sulfide.
Acknowledgment
Dr Sohail Saeed would like to acknowledge the Higher Education Commission (HEC), Government of Pakistan,
for its financial support.
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