S. Lhuachan, S. Siripaisarnpipat, N. Chaichit
FULL PAPER
Complex 1 by Chemical Synthesis: In this synthesis the mol ratio
of Cu:tscac is 1:2. A 6 solution of NH3 was added to a solution
of CuCl (1.5 mmol in 6 HCl) until the pH of the solution was
4Ϫ5. After adding thiosemicarbazone (3.0 mmol in 50 mL acetone)
dropwise with stirring at room temperature, the reaction mixture
formed two layers. Concentrated ammonium chloride solution was
then added to the two layers until a single layer formed. The reac-
tion mixture became pale yellow and was then filtered. Upon slow
evaporation for 12Ϫ24 hours at room temperature, yellow octahed-
ral crystals were formed. The product was collected, washed with
water and acetone and dried in an oven at 60Ϫ70 °C. Yield: 40%
(0.109 g). The infrared spectrum shows the presence of the tscac
added to the reaction mixture otherwise the electrolysis will
not occur. Therefore the hydrogen gas must be formed from
the protons in the hydrochloric acid not in the ligand.
Conclusion
It can be concluded from the electrolysis data (see Exp.
Sect.) that the electrolysis of copper in the presence of acet-
onethiosemicarbazone occurs as follows [Equation (1) and
(2)]:
1
ligand in the yellow product. H NMR (500 MHz, [D6]DMSO, 25
°C): δ ϭ 2.00 (m, 12 H, CH3), 7.63 and 8.86 (br, 4 H, NH2), 10.92
(s, 2 H, NH).
(1)
(2)
Complex 2 by Chemical Synthesis: This complex was prepared in a
similar procedure to that described above, but using a mol ratio of
Cu:tscac of 1:1. After slow evaporation of the solvent from the pale
yellow solution for 1Ϫ2 days at room temperature, colorless needles
were formed. The product was filtered, washed with water and acet-
one, and dried in an oven at 60Ϫ70 °C. Yield: 38% (0.132 g). The
infrared spectrum shows the presence of tscac in the product. This
complex turns green when exposed to air for several weeks. 1H
NMR (500 MHz, [D6]DMSO, 25 °C): δ ϭ 2.00 (m, 12 H, CH3),
7.98 and 8.47 (s, 4 H, NH2), 10.31 and 11.41 (s, 2 H, NH).
Alternatively the complexes may be prepared by chemical
synthesis as outlined below
Experimental Section
Complex 1 by Electrochemical Synthesis: The electrochemical ox-
idation of a copper anode in an acidic solution containing acetone
(50 mL), 6 HCl (0.5 mL), acetonethiosemicarbazone (1.5 mmol)
and ammonium chloride (0.5 g) for half hour at 4.5 V and 40 mA
led to the dissolution of 47.4 mg of copper as the CuI ion. The
reaction mixture became pale yellow and was then filtered to re-
move insoluble impurities. The solvent was then slowly evaporated
from the filtrate at room temperature. After 6 hours, yellow crystals
formed. These were then filtered off, washed with water and acet-
one successively and dried in an oven at 60Ϫ70 °C. Yield: 98%
(0.266 g). The infrared spectrum shows the presence of tscac in the
yellow crystals. The electrochemical efficiency of this reaction was
evaluated (see above).
Materials and Instruments: All chemicals are commercially available
(BDH Co., Carlo Erba, Merck Co., Fluka, May & Baker Co. Ltd.,
Mallinckvodt Co.) and used without further purification. The
infrared spectra were measured as KBr discs on a PerkinϪElmer
1
Model SYSTEM 2000 spectrophotometer. H NMR spectra were
recorded on a JEOL Model JNM-A500 FT NMR 500 MHz spec-
trometer with deuterated dimethyl sulfoxide (DMSO) as solvent
and internal standard. X-ray analyses were carried out using a Sie-
mens Smart CCD diffractometer.
The electrochemical cell consists of a platinum cathode and the
sacrificial copper anode immersed in an ammonium chloride solu-
tion containing acetonethiosemicarbazone. The complexes were
prepared using the method described by Mabrouk and co-
workers[9] with slight modification. After each electrolysis the elec-
trochemical efficiency(Ef) was determined. The electrochemical ef-
ficiency is defined as mol of metal dissolved per Faraday of electri-
city. The amount of electricity used for each experiment in this
study is equal to 72 coulomb or 7.5 ϫ 10Ϫ4 Faradays. Theoretically,
this amount of electricity dissolves Cuϩ 7.5 ϫ 10Ϫ4 mol or Cu2ϩ
3.75 ϫ 10Ϫ4 mol. Therefore, the Ef for Cuϩ and Cu2ϩ must be
close to 1 and 0.5 mol·FϪ1. This means that after electrolysis the
Ef for one-electron transfer must be close to 1 and for two-electron
transfer to 0.5. The variation of voltage, current and time was per-
formed in order to determine the optimum electrolysis conditions.
The electrochemical conditions described below are the optimum
conditions for each complex.
Complex 2 by Electrochemical Synthesis: The electrochemical ox-
idation of a copper anode in an acidic solution containing acetone
(50 mL), 6 HCl (0.5 mL), acetonethiosemicarbazone (1.5 mmol)
and ammonium chloride (0.5 g) for one hour at 3.5 V and 40 mA
led to the dissolution of 94.8 mg of copper as the CuI ion. The
reaction mixture was pale yellow solution and then was filtered to
remove the impure particles. The reaction mixture became pale
yellow and was then filtered to remove insoluble impurities. The
solvent was then slowly evaporated from the filtrate at room tem-
perature. After 8 hours, pale yellow crystals had formed. These
were then filtered off, washed with water and acetone successively
and dried in an oven at 60Ϫ70 °C). Yield: 69% (0.273 g). The
infrared spectrum shows the presence of coordination between Cu
and tscac. The electrochemical efficiency of this reaction was evalu-
ated (see above). This complex did not give a suitable crystal for
the collection of X-ray diffraction data.
Acetonethiosemicarbazone (tscac): The ligand was prepared using
the method described by Sunner[10] with a slight modification.
Thiosemicarbazide (2 mmol) was added to acetone (50 mL) and the
mixture was heated and stirred until a white precipitate had
formed. The compound was collected (yield 98%) and recrystal-
X-ray Crystallographic Study: The diffraction data for all com-
plexes with appropriate size crystals were collected at 298(2) K on
a 1 K Bruker Smart CCD area detector diffractometer using ω ro-
lized from a mixture of water and acetone. 1H NMR (500 MHz, tation scans with a scan width of 0.3° and graphite-monochrom-
˚
[D6]DMSO, 25 °C): δ ϭ 1.89 (s, 3 H, CH3), 1.90 δ (s, 3 H, CH3), ated Mo-Kα radiation (λ ϭ 0.71073 A). For data collection and
7.49 (br, 1 H, NH2), 7.95 (br, 1 H, NH2) and 9.87 (br, 1 H, NH) data integration, the SMART and SAINT programs were used[11]
ppm.
and empirical absorption correction was performed with the pro-
266
Eur. J. Inorg. Chem. 2003, 263Ϫ267
Lhuachan, Sanchai
