Synthesis and spectral characterization of Cu(II) complexes of some thio-Schiff bases of acyl pyrazolone analogues

Article abstract of DOI:10.1080/00958972.2010.489946

A series of tridentate pyrazolone-based thio-Schiff bases were synthesized by the interaction of 4-acyl/aroyl pyrazolones with thiosemicarbazide in an ethanolic medium. All of these ligands were characterized on the basis of elemental analysis, infrared (IR), ¹H- and ¹³C-NMR data. Nuclear magnetic resonance (NMR) suggests the amine-one form of ligand in solution at room temperature. Copper Schiff-base complexes, [Cu(L)(H₂O)], have been prepared by the interaction of the aqueous solution of copper sulfate pentahydrate with hot ethanolic solution of the appropriate ligand. The resulting complexes have been characterized by elemental analysis, metal content determination, molar conductance, fast atom bombardment mass spectra, magnetic measurements, thermogravimetric analysis (TGA), IR, and electronic spectral studies. Thermal stability, heat capacity, and activation energy of thermal degradation for these complexes were determined by TGA, differential thermal analysis, and differential scanning calorimetry. Suitable structures are proposed for these complexes.

Full text of DOI:10.1080/00958972.2010.489946

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Synthesis and spectral characterization
of Cu(II) complexes of some thio-Schiff
bases of acyl pyrazolone analogues
Ravindra J. Yadav a , Komal M. Vyas a & R.N. Jadeja a
a Department of Chemistry, Faculty of Science , The Maharaja
Sayajirao University of Baroda , Vadodara–390002, Gujarat, India
Published online: 11 Jun 2010.
To cite this article: Ravindra J. Yadav , Komal M. Vyas & R.N. Jadeja (2010) Synthesis and spectral
characterization of Cu(II) complexes of some thio-Schiff bases of acyl pyrazolone analogues,
Journal of Coordination Chemistry, 63:10, 1820-1831, DOI: 10.1080/00958972.2010.489946
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Journal of Coordination Chemistry
Vol. 63, No. 10, 20 May 2010, 1820–1831
Synthesis and spectral characterization of Cu(II) complexes
of some thio-Schiff bases of acyl pyrazolone analogues
RAVINDRA J. YADAV, KOMAL M. VYAS and R.N. JADEJA*
Department of Chemistry, Faculty of Science, The Maharaja Sayajirao University of
Baroda, Vadodara – 390002, Gujarat, India
(Received 22 April 2009; in final form 3 February 2010)
A series of tridentate pyrazolone-based thio-Schiff bases were synthesized by the interaction of
4-acyl/aroyl pyrazolones with thiosemicarbazide in an ethanolic medium. All of these ligands
were characterized on the basis of elemental analysis, infrared (IR), 1H- and 13C-NMR data.
Nuclear magnetic resonance (NMR) suggests the amine-one form of ligand in solution at room
temperature. Copper Schiff-base complexes, [Cu(L)(H2O)], have been prepared by the
interaction of the aqueous solution of copper sulfate pentahydrate with hot ethanolic solution
of the appropriate ligand. The resulting complexes have been characterized by elemental
analysis, metal content determination, molar conductance, fast atom bombardment mass
spectra, magnetic measurements, thermogravimetric analysis (TGA), IR, and electronic
spectral studies. Thermal stability, heat capacity, and activation energy of thermal degradation
for these complexes were determined by TGA, differential thermal analysis, and differential
scanning calorimetry. Suitable structures are proposed for these complexes.
Keywords: Acyl pyrazolone; Copper complexes; Thio-Schiff base; Thiosemicarbazone
1. Introduction
The interest in sulfur donor chelating agents has grown very rapidly. Most of the
early investigations on these systems were centered on their use as analytical reagents.
Interest in complexes of these ligands now covers a full gamut of areas ranging from
general metal–sulfur bonding and electron delocalization in transition metal complexes
to potential biological activity and practical application in fields as diverse as rubber
technology and agriculture. Complexes of transition metals containing ligands with
N, S or N, S, and O donors are known to exhibit interesting stereochemical,
electrochemical, and electronic properties [1, 2]. Derivatives of semicarbazones and
thiosemicarbazones are among the most widely studied nitrogen and oxygen/sulfur
donors [3, 4]. Particularly, thiosemicarbazones have emerged as an important class
of sulfur ligand for transition metal ions. The real impetus toward developing
their coordination chemistry was their physicochemical properties and significant
biological activities [5, 6]. Compounds containing a thiosemicarbazone component have
shown broad spectrum chemotherapeutic properties, including antimalarial [7],
*Corresponding author. Email: rajendra_ jadeja@yahoo.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ꢀ 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.489946

Thio-Schiff bases of acyl pyrazolone
1821
antitumor [8], antibacterial [9], antitrypanosomal [10], and antiviral [11] activities.
Thiosemicarbazones and their metal complexes have attracted attention because of
their wide ranging biological activities, analytical applications, specific structures, and
chemical properties [12–27]. Thiosemicarbazones usually react as chelating ligands by
bonding through the sulfur and the hydrazinic nitrogen through ligand deprotonation.
Metal complexes of first and second raw transition elements are of interest of many
researchers [28, 29], especially those involving [MoO]þ2 or [MoOS]þ2 core are studied
to mimic xanthine oxidase [30, 31].
The coordination behavior of Schiff bases of acyl pyrazolones is of interest of many
researchers including us [32–35]. However, there are scanty reports on thio-Schiff bases
of this class of ligands, especially thiosemicarbazones which are potentially tridentate
ligands having NSO donors. Moreover, the interesting pharmacological properties of
the thio-Schiff bases are believed to be due to the presence of sulfur. We have
synthesized and characterized the thio-Schiff-base ligands of acyl pyrazolones and
mononuclear Cu(II) complexes [CuL(H2O)].
2. Experimental
2.1. Materials
All the chemicals used in this study were of the best quality. Pyrazolones (3-methyl-1-(30-
chloro phenyl)-2-pyrazolin-5-one and 3-methyl-1-(40-methyl phenyl)-2-pyrazolin-5-one)
were gifted from Nutan Dye Chem Pvt. Ltd., Sachin, Surat, and used after crystallization
from alcohol. 1,4-Dioxane was obtained from Sisco Chem Pvt. Ltd., Mumbai, and used
as supplied. Thiosemicarbazide obtained from Loba Chemie Pvt. Ltd., Mumbai, was
used without purification. Absolute ethanol was obtained from Baroda Chemical
Industries Ltd., Baroda. Calcium hydroxide and acetyl chloride were supplied by
Suvidhinath Laboratories, Baroda. Benzoyl chloride was obtained from Gayatri
Minerals & Chemicals, Baroda. Sodium acetate was obtained from Qualigens Fine
Chemicals, Mumbai. Copper(II) sulfate was supplied by Suvidhinath Laboratories,
Baroda. The solvents used in this study were purified by the following standard
procedures.
2.2. Instruments
Elemental analyses (C, H, and N) were performed on a model 2400 Perkin Elmer
elemental analyzer. Infrared (IR) spectra were recorded on a Perkin Elmer Fourier
transform IR (FT-IR) spectrum RX 1 spectrometer as KBr pellets. Nuclear magnetic
resonance (NMR) spectra were recorded on an AVANCE-II-500 Bruker FT-NMR
instrument at Central Salt & Marine Chemicals Research Institute (CSMCRI),
Bhavnagar, Gujarat, India. Electronic spectra were recorded on a Perkin Elmer
Lambda 35 UV-Vis spectrometer. Specific conductivities of the complexes were
measured on an Elico CM 180 conductivity meter. Room temperature magnetic
susceptibilities were measured by a Gouy balance using Hg(II) tetrathiocyanato
cobaltate(II) as a calibrant. Diamagnetic corrections were estimated from Pascal
tables. Fast atom bombardment (FAB) mass spectra were recorded on a JEOL SX

1822
R.J. Yadav et al.
102/DA-6000 at room temperature using m-nitro benzyl alcohol as a matrix.
A simultaneous TG/DTA (thermogravimetry/differential thermal analysis) was carried
out on a SII EXSTAR6000 TG/DTA 6300. The experiments were performed in N2 at a
heating rate of 10ꢀC minꢁ1 in the temperature range 25–560ꢀC using an Al2O3 crucible.
The sample sizes ranged in mass from 4.5 to 10 mg. The differential scanning calorimetry
(DSC) was recorded using DSC 292ꢁ01, TA Instrument, USA. The DSC curves were
obtained at a heating rate of 5ꢀC min in N2 over the temperature range of 25–400ꢀC
using an aluminum crucible.
2.3. Synthesis of ligands
2.3.1. Preparation of 4-acetyl-3-methyl-1-(30-chloro phenyl)-2-pyrazolin-5-one. 3-Methyl-
1-(30-chloro phenyl)-2-pyrazolin-5-one (AMC) (20.85 g, 0.1 mol) was dissolved in a hot
dioxane (80 cm3) in a flask equipped with a stirrer, separating funnel, and reflux
condenser. Calcium hydroxide (14.81 g, 0.2 mol) was added to this solution, followed by
acetyl chloride (10 mL) added dropwise with caution, as this reaction was exothermic.
During this addition, the whole mixture was converted into a thick paste. After
complete addition, the reaction mixture was refluxed for 2 h, and then poured into a
cold dilute hydrochloric acid (200 cm3, 2 mol). Thus, the colored crystals obtained were
separated by filtration, washed with acidified water, and dried [35, 36]. Yield 74.92%,
m.p. 72ꢀC.
2.3.2. Preparation
of
4-acetyl-3-methyl-1-(40-methyl
phenyl)-2-pyrazolin-5-
one. 4-Acetyl-3-methyl-1-(40-methyl phenyl)-2-pyrazolin-5-one (APT) was prepared
analogously from 3-methyl-1-(40-methyl phenyl)-2-pyrazolin-5-one (20.1 g, 0.1 mol) and
yellow crystals were obtained. Yield 75.19%, m.p. 91ꢀC.
2.3.3. Preparation
of
4-benzoyl-3-methyl-1-(40-methyl
phenyl)-2-pyrazolin-5-
one. 4-Benzoyl-3-methyl-1-(40-methyl phenyl)-2-pyrazolin-5-one (BPT) was prepared
analogously from 3-methyl-1-(40-methyl phenyl)-2-pyrazolin-5-one (20.1 g, 0.1 mol) and
instead of acetyl chloride, benzoyl chloride (10 mL) was used; yellow crystals were
obtained. Yield 75.99%, m.p. 106ꢀC. The synthesis of these compounds is summarized
in scheme 1.
2.3.4. Preparation of thiosemicarbazones (AMC-TS, APT-TS, and BPT-TS). An
identical procedure was used in the preparation of all the thiosemicarbazones
(scheme 2). The thiosemicarabazones were prepared by refluxing 1 : 1 mole ratio of
4-acetyl/benzoyl-2-pyrazolin-5-one and thiosemicarbazide in ethanol for 2 h. The
thiosemicarbazones thus obtained were filtered and dried [37].
The physical properties are given in table 1. All the data were in good agreement with
the proposed structure.
2.3.5. Preparation of Cu(II) complexes. The following general procedure was used in
the synthesis of copper complexes (scheme 3). Copper sulfate pentahydrate was
dissolved in minimum hot ethanol. The hot ethanolic ligand solution in slight excess
over the metal was added dropwise with constant stirring. To the resultant mixture,

Thio-Schiff bases of acyl pyrazolone
1823
CH3
N
Dioxane
+
+ Ca(OH)2
CH3 / C6H5COCl
O
Ca-complex
2M HCl
N
Reflux
O
R2
CH3
C
CH3 / C6H5
R1
N
O
N
R2
where R1 = H and R2 = Cl for AMC
R1 = CH3 and R2 = H for APT
R1
Scheme 1. Preparation of acetyl/benzoyl pyrazolones. R1 ¼ H and R2 ¼ Cl for AMC; R1 ¼ CH3 and R2 ¼ H
for APT.
O
NH2
C6H5 / H3C
NH
C
S
CH3
C
CH3 / C6H5
CH3
C
N
Ethanol
Reflux
N
NH2–NH–CS–NH2
+
O
N
N
O
N
R2
R2
R1
R1
where R1 = H and R2 = Cl for AMC-TS
R1 = CH3 and R2 = H for APT-TS and BPT-TS
Scheme 2. Preparation of ligands. R1 ¼ H and R2 ¼ Cl for AMC-TS; R1 ¼ CH3 and R2 ¼ H for APT-TS
and BPT-TS.

1824
R.J. Yadav et al.
Table 1. Melting point, elemental analysis (C, H, and N) and yield of the ligands.
Elemental analysis (%)a
Ligands
m.p. (ꢀC)
Carbon
Hydrogen
Nitrogen
Yield (%)
AMC-TS
APT-TS
BPT-TS
200
205
214
48.20 (48.22)
55.05 (55.42)
62.79 (62.44)
4.30 (4.98)
5.49 (5.64)
5.19 (5.24)
21.30 (21.62)
22.80 (23.08)
18.26 (19.16)
74.92
75.19
75.99
aCalculated values are given in parentheses.
NH2
C6H5 / H3C
NH
C
CH3
C
N
S
N
CuSO
O
4
N
Cu-complexes
Ethanol
Reflux
R2
R1
Scheme 3. Preparation of Cu(II) complexes.
2 g of sodium acetate was added and the mixture was refluxed for 1 h. The resulting
solution was then concentrated to half of its original volume and cooled. The product
obtained was filtered and washed several times with hot water and finally with ethanol
and dried at 45ꢀC. The yields of the complexes were almost quantitative. The physical
properties of complexes are depicted in table 2.
3. Results and discussion
3.1. Characterization of the ligands
3.1.1. IR spectra. The important absorption frequencies for the ligands are listed in
table 3. All show a sharp band at ꢂ1590 cmꢁ1 due to ꢀ(C¼N) coordinated þ ꢀ(C¼O).
There is some contribution from aromatic vibrations and also azomethine ꢀ(C¼N) at
ꢂ1620 cmꢁ1. The ligands show a band at ꢂ3300 cmꢁ1 due to ꢀ(N–H). The band for
ꢀ(N–N) is observed at ꢂ950 cmꢁ1 [38].
The ligands show very complicated spectra, especially in the 1500–1650 cmꢁ1 region
from the presence of C¼O, –NH2, and more than one C¼N. Therefore, the correct

Thio-Schiff bases of acyl pyrazolone
1825
Table 2. Analytical data and physical properties of complexes.
Effective
magnetic
moments,
ꢂeff (B.M.)
Molar
conductance,
ÃM
m.p.
(ꢀC)
Complexes
Color
Yield (%)
Ma(%)
[Cu(AMC-TS) ꢃ (H2O)]
[Cu(APT-TS) ꢃ (H2O)]
[Cu(BPT-TS) ꢃ (H2O)]H2O
Green
Green gold
Garland
86.61
72.27
47.71
5250 15.25 (15.75)
248 15.88 (16.55)
242 14.61 (14.27)
24.0
12.0
4.0
1.71
1.72
1.68
aCalculated values are given in parentheses.
Table 3. Important IR frequencies (cmꢁ1) of ligands.
ꢀ(C¼N)
coordinated þ
ꢀ(C¼O)
ꢀ(C¼N)
ꢀ(C¼S) þ ꢁ(NH) þ
ꢃ(NH2)
Ligands
ꢀ(N–H)
azomethine
ꢀ(C¼S)
ꢀ(N–N)
AMC-TS 3305 (w, s)
APT-TS 3314 (w, s)
1587
1581
1570
1616
1613
1620
766 (s, s) 464 (w, s)
767 (s, s) 475 (w, s)
758 (s, s) 471 (w, s)
1286 (s, s)
1285 (s, s)
1283 (s, s)
965
952
932
BPT-TS
3306 (w, s)
assignments to the observed bands in this region are difficult; tentative assignments
based on the previous work are given in table 3.
C¼S having proton adjacent is relatively unstable and tends to change to a stable
C–S by enethiolization [39]. The IR spectra of ligands show intense bands at ꢂ760 cmꢁ1
and a weak band at ꢂ470 cmꢁ1, assigned to C–S stretching vibrations (table 3). A
strong band at ꢂ1280 cmꢁ1 due to a coupled vibration of ꢀ(C¼S) þ ꢁNH þ ꢁNH2 is also
observed in the IR spectra.
3.1.2. 1H-NMR spectra. 1H-NMR spectra of ligands 1–3 are summarized in
‘‘Supplementary material.’’ The signal due to methyl protons appeared as a singlet in
the range of ꢁ 2.0–2.3 ppm. In some cases signals of CH3 groups overlapped and it is
difficult to assign each signal to a particular methyl, and no attempt has been made for
such assignment [35].
A singlet corresponding to one proton for all such ligands is observed at
ꢁ 10.04–10.08 ppm and disappears on deuterium exchange assigned to thiol
group (–SH). However, when ligand exists in –NH–CS– form, this signal may be
assigned to –NH. A downfield signal corresponding to one proton for all ligands is
observed at ꢁ 12.04–12.12 ppm and also disappeared when a D2O exchange experiment
was carried out. It can be assigned either to –OH or –NH, strongly deshielded because
of hydrogen bonding with the other atom (N/O). Integration of this signal matches with
one proton, which suggests that only one tautomeric form of the ligands exists in
solution [40].
For the convenience of identification, the protons in the ligands are assigned as
follows (scheme 4).
3.1.3. 13C-NMR spectra. In 13C-NMR spectra of APT-TS ligand, the carbons
of methyl appear at ꢁ 14.41–20.52 ppm. Carbons of benzene rings are present at
ꢁ 129.21–132.97 ppm. A total of 11 signals were observed, as expected for p-substituted

1826
R.J. Yadav et al.
Hf
He
Hd
NH2
NH
C
S
CH3
C
N
N
O
N
Hb
Hc
Ha
H=R2
CH3 /Hg
Scheme 4. Proton numbering scheme for interpretation of NMR.
benzene ring of pyrazolone. One signal was observed around ꢁ 40.0 ppm, which was
associated with the carbon of the heterocyclic ring. The most deshielded signal
(ꢁ 164.43) can be assigned to C¼S and the next signal (ꢁ 147.34) to C¼O of the
heterocyclic ring. The singlet at ꢁ 118.10–136.64 ppm is assigned to the carbon of C–N,
upfield due to the electron-donating methyl attached to it [35].
3.1.4. Mass spectra. The direct analysis in real time mass spectrometry (DART–MS)
of APT-TS (figure S1 in Supplementary material) was recorded on a JEOL-AccuTOF
JMS-T100LC mass spectrometer having DART source. Dry helium was used for
ionization at 350ꢀC. The molecular ion peak at m/z ¼ 304.15 matches well the calculated
value of 303.28.
3.2. Characterization of Cu(II) complexes
Cu(II) complexes of all five ligands were synthesized by the reaction of CuSO4 and the
respective ligands in ethanol. Molar conductivities show ÃM values (table 2) lower than
those expected for 1 : 1 electrolytes, confirming the non-electrolytic nature of complexes
[41]. Magnetic moment measurements of the complexes show ꢂeff of ꢂ1.70 (table 2),
which corresponds to one unpaired electron and is expected from mononuclear Cu(II)
complexes (d9) with some orbital contribution. The metal and C, H, and N analyses
of these complexes (table 2) suggest a molecular formula [Cu(L)(H2O)], where
L ¼ deprotonated form of the respective ligand.

Thio-Schiff bases of acyl pyrazolone
1827
Table 4. Important IR frequencies (cmꢁ1) of metal complexes.
ꢀ(C¼N)
coordinated þ
ꢀ(C¼O)
ꢀ(C¼N)
ꢀ(C¼N)
ꢀ(M–S) azomethine
Complexes
ꢀ(O–H)
cyclic
ꢀ(M–N)
[Cu(AMC-TS) ꢃ (H2O)]
[Cu(APT-TS) ꢃ (H2O)]
3444 (m, br) 1574 (s, br) 1596 (m, s) 513 (w, br) 494 (w, s) 1625 (w, s)
3445 (m, br) 1572 (s, br) 1596 (m, s) 514 (w, br) 492 (w, s) 1624 (w, s)
[Cu(BPT-TS) ꢃ (H2O)]H2O 3441 (m, br) 1566 (s, br) 1598 (m, s) 513 (w, br) 490 (w, s) 1624 (w, s)
Table 5. Electronic spectral data of complexes.
Complexes
d–d maxima (nm)
d–d maxima (cmꢁ1
)
" (molar absorptivity)
[Cu(AMC-TS) ꢃ (H2O)]
[Cu(APT-TS) ꢃ (H2O)]
[Cu(BPT-TS) ꢃ (H2O)]H2O
557.04
571.09
577.02
17952
17510
17330
192
218
318
3.2.1. IR spectra. Spectra of the metal complexes (table 4) indicate that the ligands are
tridentate, coordinating through the nitrogen of azomethine group, sulfur of mercapto,
and oxygen of enol.
Bands at ꢂ760 and ꢂ470 cmꢁ1 in spectra of the ligands, mainly due to C¼S stretch,
disappear on complexation. During complexation, C¼S is converted into C–Sꢁ. The
ligand band at ꢂ1280 cmꢁ1 also disappears due to the change of 1N–C–N2 to
1N–C¼N2. From the spectral and analytical data, the ligands are doubly charged
tridentate by losing the protons from mercapto and hydroxyl.
3.2.2. Electronic spectral analysis. Electronic spectra of all the complexes were
recorded in dimethylformamide (DMF), and the data are presented in table 5. For
2
2
2
2
square planer Cu(II), the expected transitions are B1g ! A1g and B1g ! Eg with
respective absorptions at 505–520 and 665–650 nm. Due to Jahn–Teller (J-T)
distortions, square planar Cu(II) complexes give a broad absorption between 600 and
700 nm and the peak at 505–520 nm merges with the broad band [42], and thus only one
broad band is observed. All the complexes under this study exhibit a broad band in the
region of 550–600 nm.
3.2.3. FAB mass spectra. Mass spectra were obtained at electron beam energy of
70 eV. The simplest event that occurs is the removal of a single electron from the
molecule in gas phase by an electron of the electron beam to form a molecular ion, a
radical cation (Mþ). A special reference of exact masses of isotopes was taken. The FAB
mass spectrum (figure S2 in Supplementary material) of [Cu(APT-TS) ꢃ (H2O)] was
recorded in m-nitro benzyl alcohol as a matrix. The parent ion peak can be observed at
m/z ¼ 365 with relative abundance 100% (table 6). This is formed by the complex, and
in the place of water molecule a proton is associated. So the parent ion is [Cu-APT-
TS]þ. A peak corresponding to ligand, C14H21N5OS appears at m/z ¼ 307 with 51%
relative abundance. Peaks at m/z ¼ 365, 366, 307, and 277 with relative abundance
100%, 89%, 51%, and 63%, respectively, strongly indicate the formation of [Cu-APT-
TS]. The peaks corresponding to the m-nitro benzyl alcohol and the associated products

1828
R.J. Yadav et al.
Table 6. Mass spectral fragmentation of [Cu(APT-TS) ꢃ (H2O)].
Molecular formula
of the fragment
m/z (relative abundance)
365 (100%)
366 (89%)
307 (51%)
277 (63%)
[C14H19N5OSCu]þ
[C14H20N5OSCu]þ
[C14H21N5OS]þ
[C7H12N5OSCu]þ
Table 7. Thermoanalytical results (TG, DTG, DTA) of Cu(II) complexes.
TG
range
(ꢀC)
Mass loss
estimation
(Calcd %)*
DTGmax
(ꢀC)
Peak temp.
in DTA (ꢀC)
Complexes
Assignment
[Cu(AMC-TS) ꢃ (H2O)]
50–121
209–500
78
245
79(ꢁ) 245(ꢁ)
227(ꢁ) 290(ꢁ)
52(þ) and
4.44 (4.93)
77.72 (78.26)
17.22 (16.81) Loss of ligand molecule
Leaving CuO residue
4.03 (4.90)
81.66 (82.68)
12.89 (12.42) Loss of ligand molecule
Leaving CuO residue
Loss of one coordinated
H2O
[Cu(APT-TS) ꢃ (H2O)]
40–210
220–550
224
360
Loss of one coordinated
H2O
[Cu(BPT-TS) ꢃ (H2O)]H2O 40–220
100
260
6.75 (7.70)
Loss of one coordinated
and one hydrated H2O
255–525
155(ꢁ), 265(ꢁ) 77.0 (78.25)
13.86 (14.05) Loss of ligand molecule
Leaving CuO residue
DTG, derivative thermogravimetry; (ꢁ) exothermic; (þ) endothermic; (*) total mass loss.
are observed at m/z ¼ 136, 137, 154, and 289 with high relative abundance. The natural
abundances of 63Cu and 65Cu are 69.1% and 30.9%, respectively. Therefore, mass
spectral peaks of copper complexes and fragment ions having at least one copper atom
must exhibit isotope distribution pattern in the abundance ratio 2 : 1 [43]. All the mass
spectral peaks of the complexes in this study exhibit isotope distribution patterns arising
from the molecular/fragment ions containing copper (figure S2 in Supplementary
material). In addition to the molecular ion peak at 366, peaks at m/z ¼ 428, 483, 522,
etc., are due to the combination of molecular ion with other fragments of copper and/or
matrix and their fragments. The peak at m/z ¼ 428 is due to [M þ Cu]þ, also showing
isotopic pattern due to the presence of copper ion, while m/z ¼ 522 peak in the FAB
mass spectra of the [Cu(APT-TS) ꢃ (H2O)] is due to the combination of molecular ion
with matrix, i.e., m-nitro benzyl alcohol.
3.3. Thermal studies
The thermoanalytical results of Cu(II) complexes summarized in table 7 are in good
agreement with the proposed structures. The following stability order of complexes is
observed:
½CuðBPT ꢁ TSÞ ꢃ ðH2OÞꢄH2O 4 ½CuðAPT ꢁ TSÞ ꢃ ðH2OÞꢄ 4 ½CuðAMC ꢁ TSÞ ꢃ ðH2OÞꢄ

Thio-Schiff bases of acyl pyrazolone
1829
NH
2
H
C
3
N
C
S
CH
C
3
N
Cu
N
OH
O
2
N
Scheme 5. Structure of the metal complexes.
All the complexes contain coordinated water, in addition to that [Cu(BPT-
TS) ꢃ (H2O)]H2O contain one hydrated water. The Cu(II) complexes decomposed in
several steps are summarized in table 7. The final product of the thermal decomposition
CuO was determined by the elemental analysis.
4. Conclusion
This study provides a general way of synthesizing mononuclear [CuL]H2O and
[CuL(H2O)]H2O complexes (where L is the dianion of the ONS donor Schiff base)
which can undergo reversible and facile transformations because of the combined
presence of hard (O and N) and soft (S) donors in the Schiff base skeleton. Binegative
Schiff bases satisfy the 2þ charge of the metal leading to the formation of uncharged
complexes which are stable and easy to isolate from the reaction medium. Interaction of
CuSO4 ꢃ 5H2O with AMC-TS, APT-TS, or BPT-TS resulted in the formation of
complexes with square planar stereochemistry: Schiff base nitrogen, enolic oxygen, and
sulfur coordinate Cu(II). One coordinated water is present in all the complexes.
Spectroscopic data confirm the proposed structure. From thermal study, [Cu(BPT-
TS) ꢃ (H2O)]H2O is more stable due to the 4-benzoyl stable resonance structure [44].
From all the structural characterizations, structure provided in scheme 5 has been
proposed for metal complexes
Supplementary material
Thermodynamic data of the thermal decomposition of Cu(II) complexes, TGA, DTA,
and DSC curves along with discussion and mass spectra of one ligand (APT-TS) and its

1830
R.J. Yadav et al.
Cu(II) complexes is available as a supplementary material in the online version of
this article.
Acknowledgments
Financial assistance for carrying out this work was provided by University Grants
Commission, New Delhi, in terms of minor research project to R.N. Jadeja is gratefully
acknowledged. The authors are also thankful to Head of the Department of Geology
for providing TG/DTA facility.
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