Synthesis, characterization and crystal structure of some bidentate heterocyclic Schiff base ligands of 4-toluoyl pyrazolones and its mononuclear Cu(II) complexes

Article abstract of DOI:10.1016/j.molstruc.2011.01.024

We depict the synthesis of a new set of six bidentate heterocyclic Schiff base ligands, formed by the condensation of three different 4-toluoyl pyrazolones with various aromatic amines in ethanolic medium. All of these ligands have been characterized on the basis of elemental analysis, IR, ¹H NMR, ¹³C NMR and Mass spectral data. The molecular geometries of three of these ligands have been determined by single crystal X-ray study. It reveals that these ligands exist in amine-one tautomeric form in the solid state. The reaction of these ligands with copper(II) resulted in the formation of mononuclear complexes having the general composition [CuL ₂(H₂O)₂] with two water molecules at axial positions. These complexes have been characterized on the basis of elemental analysis, Cu-estimation, molar conductivity, magnetic measurements, IR, UV-Visible, FAB-Mass, TG-DTA-DSC data, cyclic voltametric measurements and ESR spectral studies. ESR spectra and magnetic susceptibility measurements indicates distorted octahedral stereochemistry of Cu(II) complexes, while non-electrolytic behaviour of complexes indicates the absence of counter ion.

Full text of DOI:10.1016/j.molstruc.2011.01.024

Journal of Molecular Structure 990 (2011) 110–120
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, characterization and crystal structure of some bidentate heterocyclic
Schiff base ligands of 4-toluoyl pyrazolones and its mononuclear Cu(II) complexes
b
c
Komal M. Vyas a, R.N. Jadeja a, , Vivek K. Gupta , K.R. Surati
⇑
a Department of Chemistry, Faculty of Science, The MS University of Baroda, Vadodara 390 002, India
b Department of Physics, Jammu University, Jammutawi 180 006, India
c Department of Chemistry, Sardar Patel University, Vallabhvidyanagar 388 120, India
a r t i c l e i n f o
a b s t r a c t
Article history:
We depict the synthesis of a new set of six bidentate heterocyclic Schiff base ligands, formed by the con-
densation of three different 4-toluoyl pyrazolones with various aromatic amines in ethanolic medium. All
of these ligands have been characterized on the basis of elemental analysis, IR, 1H NMR, 13C NMR and
Mass spectral data. The molecular geometries of three of these ligands have been determined by single
crystal X-ray study. It reveals that these ligands exist in amine-one tautomeric form in the solid state.
The reaction of these ligands with copper(II) resulted in the formation of mononuclear complexes having
the general composition [CuL2(H2O)2] with two water molecules at axial positions. These complexes have
been characterized on the basis of elemental analysis, Cu-estimation, molar conductivity, magnetic mea-
surements, IR, UV–Visible, FAB–Mass, TG–DTA–DSC data, cyclic voltametric measurements and ESR
spectral studies. ESR spectra and magnetic susceptibility measurements indicates distorted octahedral ste-
reochemistry of Cu(II) complexes, while non-electrolytic behaviour of complexes indicates the absence of
counter ion.
Received 1 December 2010
Received in revised form 1 January 2011
Accepted 3 January 2011
Available online 22 January 2011
Keywords:
Bidentate Schiff base ligands
Cu(II) complexes
Acyl pyrazolone
Crystal structures
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
one can develop synthetic strategies to influence the one, two or
three-dimensional arrangement in the crystal in a more directed
The design of new coordination supramolecules and polymers
based on transition metal compounds and multidentate organic li-
gands has attracted much interest in recent years [1]. Current
interest in the coordination chemistry of b-diketones toward sev-
eral metal ions [2] particularly in the development of the relatively
new class of 4-acyl, 5-pyrazolones [3], having a pyrazole ring fused
to a chelating carbonyl, has emerged from several points of view.
Acylation is one of the fundamental reactions in organic chemis-
try and can be carried out by wide variety of reagents. Pyrazolone-5
derivatives, especially 4-acyl pyrazolone form an important class of
organic compounds and their derivatives represent a big scientific
and applied interest in analytical applications, catalysis, dye and
extraction metallurgy, etc. [4–6] because they display several differ-
ent coordination modes, with respect to classical b-diketonate. Fur-
thermore, 4-acyl pyrazolone derivatives have the potential to form
different types of coordination compounds due to the several elec-
tron-rich donor centers [7,8] and tautomeric effect of the enol form
and keto form [9]. Complexescontaining these ligands are known for
almost every transition and main group metal [10]. Dependent on
the nature of the metal and the coordination behaviour of the ligand
way [11].
They are also known to show extensive solid state tautomerism
and the insertion of substituents with special conjugated system to
them leads to formation of compounds with intense stable colour
[12]. Schiff bases are important ligands in coordination chemistry
and find extensive application in different fields [13]. Among them,
the Schiff base derivatives of 1-phenyl 3-methyl 5-pyrazolone and
their metal complexes have been widely studied because of the
high pharmaceutical activities [14].
As a part of our continuing interest in pyrazolones chemistry,
we synthesized a number of such compounds [15–18]. Now we re-
port on the successful synthesis of a series of Cu(II) complexes con-
taining pyrazolone based Schiff base ligands.
2. Experimental
2.1. Materials
The compounds 5-methyl-2-phenyl-2, 4-dihydro-pyrazol-3-one;
5-methyl-2-m-tolyl-2,4-dihydro-pyrazol-3-one and 2-(3-chloro-phe-
nyl)-5-methyl-2,4-dihydro-pyrazol-3-one were obtained from Nutan
Dye Chem Pvt. Ltd., Sachin, Surat and were used after recrystallization.
Para toluidine, para bromo aniline and dioxane were obtained from
⇑
Corresponding author. Tel.: +91 265 2795552.
E-mail address: rajendra_jadeja@yahoo.com (R.N. Jadeja).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.01.024

K.M. Vyas et al. / Journal of Molecular Structure 990 (2011) 110–120
111
Sisco-Chem. Pvt. Ltd., Mumbai and used after purification following a
standard procedure [19]. Absolute alcohol was obtained from Baroda
Chem. Industries Ltd., Baroda, and was used after distillation. Calcium
hydroxide and copper acetate were obtained from LOBA Chem. Pvt.
Ltd., Mumbai.
reflux a microcrystalline yellow compound was separated, which
was isolated by filtration and dried in air and finally purified by crys-
tallized in appropriate solvent.
2.4.2. 4-[(4-Bromo-phenylimino)-p-tolyl-methyl]-5-methyl-2-phenyl-
2,4-dihydro-pyrazol-3-one [PMP-BA]:
2.2. Techniques
Equimolar (10 mmol) ethanolic solution (50 mL) of 5-Methyl-
4-(4-methyl-benzoyl)-2-phenyl-2,4-dihydro-pyrazol-3-one
and
Elemental analysis (C, H, N) were performed on a model 2400
Perkin–Elmer elemental analyzer. Infrared (IR) spectra were re-
corded on a model RX 1 FTIR Perkin–Elmer as KBr pellets. 1H
NMR spectra were recorded with Bruker AV 400 MHz using CDCl3
as a solvent and TMS as an internal reference. The electronic spec-
tra were recorded on a model Perkin Elmer Lambda 35 UV–VIS
spectrometer. Mass spectra (EI)/(FAB) of the compounds were
recorded at SAIF, CDRI, Lucknow. A simultaneous TG/DTA was
recorded on EXSTAR6000 TG/DTA6300 model. DSC was carried
out on universal V3.0G TA instrument in the range 0–400 °C at
Department of Chemistry, Vallabhvidyanagar. Specific conductivity
of the Schiff base complexes was measured on a model Elico CM
180 conductivity meter. GC–MS of all the ligands recorded on Trace
GC ultra DSQ II. Copper was determined by EDTA after decompos-
ing the complexes with HNO3. ESR spectrum of Copper(II) complex
was recorded on X-band instrument at ESR laboratory, IIT, Bombay,
at room temperature and liquid nitrogen temperature for polycrys-
talline and solution state, respectively. Magnetic susceptibility
measurements of the complexes were carried out by Gouy balance
using [HgCo(CN)4] as the calibrant. Cyclic voltametry measure-
ments were performed on a CH 600C/CH instruments, USA.
para bromo aniline was refluxed for 6 h in round bottom flask. Dur-
ing the reflux a microcrystalline yellow compound was separated,
which was isolated by filtration and dried in air and finally purified
by crystallized in appropriate solvent.
2.4.3. 2-(3-Chloro-phenyl)-5-methyl-4-(p-tolyl-p-tolylimino-methyl)-2,
4-dihydro-pyrazol-3-one [MCPMP-T].
2.4.4.
4-[(4-Bromo-phenylimino)-p-tolyl-methyl]-2-(3-chloro-phe-
nyl)-5-methyl-2-phenyl-2, 4-dihydro-pyrazol-3-one [MCPMP-BA].
It wasprepared analogouslyfrom2-(3-Chloro-phenyl)-5-methyl-
4-(4-methyl-benzoyl))-2,4-dihydro-pyrazol-3-one and obtained
yellow crystals were filtered and dried.
CH3/Br
H3C
C
N
2.3. Synthesis of 4-toluoyl pyrazolones [TP]
N
Cu-acetate
Ethanol
O
Cu(II)-complex
Toluoylation reaction of all three pyrazolones was carried out
by following the standard method reported in our previous articles
[15–18].
N
2.4. Synthesis of Schiff base ligands
Cl/H
2.4.1. 5-Methyl-2-phenyl-4-(p-tolyl-p-tolylimino-methyl)-2,4-
dihydro-pyrazol-3-one[PMP-T]:
CH3/H
Equimolar (10 mmol) ethanolic solution (50 mL) of 5-Methyl-4-
(4-methyl-benzoyl)-2-phenyl-2,4-dihydro-pyrazol-3-one and p-
toluidine was refluxed for 6 h in round bottom flask. During the
Scheme 1. Synthesis of Cu(II)-complex.
Table 1
Summary of crystallographic data.
Compound
PMP-BA
24H20BrN3O1
MCPMP-T
MCPMP-BA
Chemical formula
Formula weight
a (Å)
b (Å
c (Å)
C
C25H22ClN3O1
415.91
C24H19BrClN3O
480.78
446.34
9.281(4)
18.444(9)
12.598(6)
90.000
104.761(8)
90.000
4
2085(3)
9835
2288
0.0603
342
Monoclinic
P21/n
CH3/Br
7.3549(3)
10.7278(5)
13.7950(6)
78.158(4)
85.465(3)
84.840(4)
2
1058.92(8)
7881
4752
0.0244
359
Triclinic
P-1
1.304
7.1797(14)
10.419(2)
14.336(3)
107.185(3)
92.247(3)
94.151(3)
2
1019.8(3)
6507
4654
0.0259
271
Triclinic
P-1
1.566
a
(°)
H3C
C
b (°)
N
c
(°)
Z
V (Å3)
N
Reflection collected
Independent reflections
R(int)
O
N
Number of parameters
Crystal system
Space group
qcalcd. (g cmꢀ3
)
1.422
1.991
Abs coeff,
l
(cmꢀ1
)
0.202
2.168
F (0 0 0)
Temp (°C)
GOF on F2
912
23
0.944
436
23
1.000
488
23
1.001
Cl/H
CH3/H
R1/wR2 ([I > 2
R1/wR2 (all data)
r
(I)]
0.0585/0.1351
0.1251/0.1654
0.0525/0.1172
0.0974/0.1415
0.0516/0.1188
0.0695/0.1352
Fig. 1. The common structure for Schiff base ligands.

112
K.M. Vyas et al. / Journal of Molecular Structure 990 (2011) 110–120
solution was added to a hot ethanolic solution of the corresponding
Schiff bases. After the complete addition little amount of sodium
acetate was added and the mixture was refluxed for 4 h. A crystal-
line solid was obtained, which was isolated by filtration, washed
with hot water and dried in air.
2.4.5. 5-Methyl-2-p-tolyl-4-(p-tolyl-p-tolylimino-methyl)-2,4-dihy-
dro-pyrazol-3-one [PTPMP-T].
2.4.6.
4-[(4-Bromo-phenylimino)-p-tolyl-methyl]-5-methyl-2-p-tolyl-
2,4-dihydro-pyrazol-3-one [PTPMP-BA]:
The synthesis of the Cu(II) complexes can be summarized in
Scheme 1.
It was prepared analogously from 5-methyl-4-(4-methyl-ben-
zoyl)-2-p-tolyl-2,4-dihydro-pyrazol-3-one and obtained yellow crys-
tals were filtered and dried.
The structure drawing of all the Schiff bases can be summarized
in the following common structure (Fig. 1).
2.6. Single crystal X-ray structure determination of Schiff base ligands.
A crystal having good morphology was chosen for three-dimen-
sional intensity data collection using Bruker SMART CCD area-
detector diffractometer, equipped with low-temperature device,
2.5. Synthesis of Cu(II) complexes.
All the Cu(II) complexes of Schiff base were prepared by the fol-
lowing method. The metal salt was dissolved in water and the
by using graphite–monochromated Mo K
corrected for Lorentz and polarization factors but no absorption
a radiation. Data were
Fig. 2. ORTEP view of the molecule: (a) PMP-BA, (b) MCPMP-T, and (c) MCPMP-BA, showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50%
probability level and H atoms are shown as small spheres of arbitrary radii.

K.M. Vyas et al. / Journal of Molecular Structure 990 (2011) 110–120
113
Table 2
Analytical data and the IR band assignments for Schiff base ligands.
Ligands
Formula Weight(g
molꢀ1
Colour Yield
(%)
Melting point
(°C)
Elemental analysis (%),
found (calcd)
IR frequencies(cmꢀ1
)
)
C
H
N
vC@N
vC@O (pyrazolone
vC@N
vNAH
(cyclic)
ring)
(azomethane)
PMP-T
381.47
446.35
Yellow 74.42
Yellow 71.59
Yellow 51.93
Yellow 61.29
Yellow 53.18
Yellow 54.27
188
194
120
190
152
212
78.68
6.01
12.51
1570
1570
1587
1586
1594
1570
1621
1618
1620
1638
1622
1608
1230
1229
1227
1226
1235
1216
3130
3125
3210
3175
3210
3135
(78.74) (6.03) (12.59)
64.50 4.42 10.71
(64.57) (4.48) (10.76)
72.00 5.25 11.53
(72.02) (5.29) (11.55)
60.02 3.91 10.03
(60.00) (3.95) (10.00)
78.94 6.34 12.12
(78.98) (6.32) (12.15)
65.19 4.75 10.61
(65.21) (4.78) (10.63)
PMP-BA
MCPMP-T 415.92
MCPMP-
BA
PTPMP-T
480.78
395.50
460.37
PTPMP-
BA
Table 3
Physical and analytical data of the Cu(II) complexes.
Complexes
Formula weight (g molꢀ1
)
Colour
Yield (%)
Melting point (°C)
Analysis (%) Found(calcd)
KM
(X
ꢀ1 cm2 molꢀ1
)
leff (BM)
C
H
N
M
Cu-PMP-T
860.47
990.20
929.36
1058.92
888.52
1018.26
Brown
Green
Brown
Green
Green
Green
43.39
30.86
50.10
39.90
35.19
38.94
>270
>266
>250
290
69.65
(69.68)
58.11
(58.12)
64.50
(64.51)
54.31
(54.33)
70.18
(70.19)
58.86
5.54
(5.57)
4.22
(4.23)
4.93
(4.94)
3.75
(3.77)
5.83
(5.84)
4.50
9.74
(9.75)
8.45
(8.47)
9.02
(9.03)
7.90
(7.92)
9.43
(9.44)
8.23
7.46
(7.37)
6.55
(6.40)
7.50
(7.37)
6.10
(5.99)
7.21
(7.14)
6.46
6.00
1.78
1.79
1.81
1.80
1.76
1.79
Cu-PMP-BA
4.00
6.00
5.00
Cu-MCPMP-T
Cu-MCPMP-BA
Cu-PTPMP-T
Cu-PTPMP-BA
>290
>280
10.00
16.00
(58.88)
(4.51)
(8.24)
(6.23)
rized in Table 1. An ORTEP [21] view of the all the compounds with
atomic labelling are shown in Fig. 2. The geometry of the molecule
has been calculated using the software PLATON [22] and PARST
[23].
R
R
R
H
C
3. Results and discussion
C
N
H
C
N
N
3.1. Physicochemical properties of the synthesized compounds
N
N
N
N
O
N
O
N
All these complexes are intensively coloured, air and moisture
free crystalline solids. They are insoluble in common organic sol-
vents and only soluble in DMF and DMSO. Molar conductance val-
ues of the complexes soluble in DMF (10ꢀ3 M solution at room
temperature), indicate that the complexes have molar ratio of
metal: ligand as 1:2. The lesser molar conductance values (6–
OH
Cl/H
Cl/H
Cl/H
16
X
ꢀ1 cm2 molꢀ1) indicate that they are all non-electrolytic in
CH3/H
CH3/H
CH3/H
nature [24]. The elemental analyses data concur well with the
planned formulae for the ligands and also recognized the
[ML2(H2O)2] composition of the metal(II) complexes. The analytical
and physical data of the Schiff base ligands and their complexes are
shown in Table 2 and Table 3, respectively.
imine-one
(I)
imine-ol
(II)
amine-one
(III)
Fig. 3. The existence of different tautomeric forms in the ligands.
correction was made. The crystal structure was solved by direct
methods using SHELXS86 software [20]. All non-hydrogen atoms
of the molecule were obtained from the E-map. Full-matrix least-
squares refinement was carried out using SHELXL97 software
[20]. All the hydrogen atoms were located on a difference electron
density map and their positional and isotropic thermal parameters
were included in the refinement. Atomic scattering factors were ta-
ken from International Tables for X-ray Crystallography (1992, Vol.
C, Tables 4.2.6.8 and 6.1.1.4). The crystallographic data are summa-
3.2. IR spectral studies
The bonding modes of the ligands coordinated to Cu(II) ion
were further elucidated by comparison of IR spectra of ligands
and Cu-complexes.
The molecular structures of the ligands are shown in Fig. 2a–c.
The ligands used in present study can undergo keto–enol tauto-
merization and exist in one of the following form as shown in
Fig. 3.

114
K.M. Vyas et al. / Journal of Molecular Structure 990 (2011) 110–120
Table 4
IR band assignments for Cu(II) complexes.
Complexes
m(OH) coordinated H2O
vC@N (cyclic)
vC@N (azomethane)
vCAO
vMAO
vMAN
Cu-PMP-T
Cu-PMP-BA
Cu-MCPMP-T
Cu-MCPMP-BA
Cu-PTPMP-T
Cu-PTPMP-BA
3431
3431
3432
3425
3428
3409
1564
1563
1584
1584
1570
1568
1214
1214
1214
1212
1212
1213
1478
1476
1475
1474
1482
1481
483
483
485
485
489
482
550
534
545
534
536
532
bidentate manner. The IR band assignments for the complexes
are listed in Table 4.
Table 5
1H NMR spectral data for the ligands recorded in CDCl3.
Ligands
Methyl protons
(d ppm)
Aryl protons
(d ppm)
ANH*
(d ppm)
3.3. 1H and 13C NMR spectra of ligands
PMP-T
[1.60, 2.18, 2.43]
Singlet
9H
1.61, 2.44]
Singlet
6H
[1.60, 2.25, 2.43]
Singlet
9H
[1.58, 2.43]
Singlet
6H
[1.20, 2.18, 2.42, 3.71]
Singlet
12H
[6.70–8.04]
Multiplet
13H
[6.66–8.04]
Multiplet
13H
[6.71–8.14]
Multiplet
12H
[6.64–8.09]
Multiplet
12H
[6.68–7.88]
Multiplet
12H
[6.64–7.88]
Multiplet
13H
12.84
Singlet
1H
12.89
Singlet
1H
12.79
Singlet
1H
12.68
Singlet
1H
12.80
Singlet
1H
12.81
Singlet
1H
The 1H and 13C spectra of all the ligands were recorded in CDCl3 at
roomtemperatureand the 1H NMR data are presented in Table 5. The
proton NMR spectrum of one of the ligand (PMP-T) is shown in Fig. 4.
The signals due to methyl protons (two in the case of PMP-BA,
MCPMP-BA; three in the case of PMP-T, MCPMP-T, PTPMP-BA and
four in the case of PTPMP-T) appeared as singlet in the range d
1.20–3.73 ppm. In some cases signals of CH3 groups are overlapped
and all of these signals are so closely spaced that it is difficult to as-
sign each signal to a particular methyl group unambiguously [15].
Moreover, such assignment will not contribute to establish the
geometry of the ligands; therefore, no attempt has been made for
such assignment. In the aromatic region, a few doublets and in few
cases some overlapping doublets/multiplets are observed in the
range d 6.56–8.14 ppm. These doublets/multiplets are due to aryl
protons of three benzene rings. Another singlet corresponding to
one proton for all compounds is observed in the range d 12.80–
12.84 ppm. This signal disappeared or weakened when a D2O ex-
change experiment was carried out. It can be bonding with the other
atom (N/O). It may be noted that the integration of this signal per-
fectly matches with one proton and there is no other fragment(s)
of this signal, which suggests that only one tautomeric form of the li-
gands exist in solution under the experimental conditions. We have
not done any temperature dependent experiments. Comparing with
thesolid state study, we prefer to assign thissignal to ANH, however,
assignment of this peak to AOH cannot be ruled out provided solid
state structural evidence is not considered [15].
PMP-BA
MCPMP-T
MCPMP-BA
PTPMP-T
PTPMP-BA
[1.21, 2.43, 3.73]
Singlet
9H
*
Not observed when spectra taken in CDCl3 + D2O.
The IR spectra of all ligands exhibit two characteristic bands in
the ranges 3100–3200 cmꢀ1 and 1600–1640 cmꢀ1, which can
either be assigned to OAH and C@N respectively for the tautomeric
imine-ol (Fig. 3, II) form or mNAH and C@O, respectively for the
amine-one form (Fig. 3, III) of the ligands [16]. We assigned this
band to NAH and C@O for the later form based on the information
obtained from crystallographic studies. The strong band at 1570–
1595 cmꢀ1 is observed in all ligands, is assigned to
C@N of the pyr-
m
m
m
m
m
In the 13C NMR spectra, the carbon atoms of the methyl groups
appear in the range d 16.1–21.5 ppm. The carbon atoms of the
m
three benzene rings exhibit signals in the range
d 117.0–
azolone ring, which also bears out that ligands exist as the keto
form in solid state, consisting with the crystal structure. The IR
band assignments of ligands are listed in Table 2.
136.5 ppm and the number of signals varies from seven to four-
teen. Nine signals were observed for ligand PTPMP-BA, as expected
for all p-substituted benzene rings because of symmetry [16].
However, nine signals (for ligand PMP-T), 11 signals (for ligand
PMP-BA) and seven signals (for ligand PTPMP-T) were observed in
the 13C NMR spectra of different ligands. Some of the signals
might be overlapped as indicated by the intensity of a few sig-
nals. The other two ligands MCPMP-T and MCPMP-BA, where
one of the benzene rings is m-substituted, show twelve and four-
teen signals, respectively, as expected because of the loss of sym-
metry [16,17].
The ligands as well as its corresponding complexes show
absorption in the region 3000–2900 cmꢀ1, which may be due to
mCAH. In the IR spectra of the complexes, it can be obviously ob-
served that the NAH stretching vibrations disappear; indicating
de-protonation of NAH group in metal complexes and a new band
attributed to mCAO appears at 1470–1485 cmꢀ1. In addition, the
new bands at about 480–490 cmꢀ1 and 530–550 cmꢀ1 are assigned
to CuAN [25] and CuAO [26] vibrations, respectively. There are
other changes like the absorption bands of C@O and C@N slightly
shift to the lower wave number, suggesting the coordination
through the oxygen atom of pyrazolone ring and azomethane
nitrogen to the central metal atom. All complexes show band in
the region 3400–3435 cmꢀ1, which may be due to the presence
of coordinated water molecules. As shown by TGA of all the com-
plexes, this band may be assigned to the two coordinated water
molecules. The wave number of cyclic C@N does not change in
all the complexes, indicates no coordination via C@N cyclic. By
comparing the IR spectra of ligands and metal complexes, it is easy
to predict that the ligand binds to the metal ion via N and O, i.e.
3.4. Molecular structure of ligands
The molecular structures of three ligands (PMP-BA, MCPMP-T
and MCPMP-BA) were determined from single crystal X-ray
studies. ORTEP diagrams of these ligands with the atom number-
ing schemes are shown in Fig. 2. Important bond lengths and an-
gles for all the compounds are listed in Table 6. Existence of acyl
pyrazolone derivatives in different tautomeric forms (Fig. 3) in
solid state is well known phenomenon and thus many studies

K.M. Vyas et al. / Journal of Molecular Structure 990 (2011) 110–120
115
Fig. 4. 1H NMR spectrum of PMP-T.
Table 6
Selected bond lengths and angles in the ligands.
3.5. Electronic spectral studies
Compound
PMP-BA
MCPMP-T
MCPMP-BA
Bond distances (Å) with esd’s in parentheses
Electronic spectra serve as a tool to distinguish the geometry
of the complexes. In order to shed some light on the geometrical
structure of the complexes, the spectra of all the complexes were
recorded in DMF in liquid phase at room temperature. The
absorption spectra of all the Cu(II) complexes show two bands
within the range 400–900 nm assignable to Jahn–Teller distor-
tion. The band between 400–500 nm is due to the intraligand
N1AC5
N1AN2
N2AC3
N2AC6
C3AO3
1.311(5)
1.397(4)
1.374(4)
1.415(4)
1.238(4)
1.450(5)
1.496(5)
1.333(5)
1.506(6)
1.371(5)
1.394(6)
1.391(6)
1.305(3)
1.405(2)
1.380(3)
1.411(3)
1.246(2)
1.438(3)
1.496(3)
1.343(3)
1.495(3)
1.365(3)
1.373(3)
1.387(3)
1.309(4)
1.404(4)
1.382(4)
1.415(4)
1.245(4)
1.391(5)
1.481(5)
1.345(4)
1.520(5)
1.380(5)
1.393(5)
1.391(5)
C3AC4
C5AC12
C13AN21
C17AC20
C18AC19
C7AC8
transition (p ? p transition) and the other band around 715 nm
is due to the d–d transition in the metal complexes, which can
4
be assigned as the T2g(F) ? 4T1g(F) transition, relieving that the
C17AC18
Cu(II) complex exists in the octahedral geometry [27]. Electronic
spectral data of the complexes with their tentative assignments
are listed in Table 8.
Bond angles (°) with esd’s in parentheses
C5 N1 N2
C3 N2 N1
C3 N2 C6
N1 N2 C6
O3 C3 N2
O3 C3 C4
N2 C3 C4
N1 C5 C12
C11 C6 N2
N21 C13 C4
N21 C13 C14
106.4(3)
112.6(3)
128.5(3)
118.4(3)
126.6(3)
129.5(3)
103.9(3)
118.4(4)
118.9(3)
117.6(3)
121.3(3)
106.51(16)
111.87(17)
129.35(18)
118.68(17)
125.7(2)
129.6(2)
104.67(17)
117.8(2)
106.9(3)
112.2(3)
129.2(3)
118.6(3)
126.2(3)
129.4(3)
104.3(3)
118.8(3)
120.7(3)
118.1(3)
121.0(3)
3.6. Mass spectral studies
The mass spectra of all bidentate Schiff base ligands are in good
agreement with proposed structure. Melting point of each ligand is
high, as a result of this; the mass spectra were carried out by EI. The
electronic impact mass spectra of PMP-T Schiff base (Fig. 5) shows a
molecular ion peak at m/z = 381 with a relative intensity near to
100%, which is equivalent to its molecular weight. The other peaks
appeared in the mass spectrum (abundance range 1–100%) is attrib-
uted to the fragmentation of PMP-T molecule obtained from the
rupture of different bonds inside the molecule. The mass spectral
assignments for all the ligands are shown in Table 9.
120.8(2)
118.4(2)
121.3(2)
have been made to establish the geometry of these derivatives
including ours [15–18]. The single crystal X-ray diffraction study
on this compound clearly indicates that the present compound
exists in amine-one from without any ambiguity. The Hydrogen
bonding geometry parameters of the ligands are also shown in
Table 7.
The FAB–Mass spectra of all the complexes (Table 10) were re-
corded in m-nitro benzyl alcohol as a matrix. The [Cu(PMP-
T)2(H2O)2] complex gives a parent ion peak at m/z = 824. This is
formed by the complex when two water molecules are removed.

116
K.M. Vyas et al. / Journal of Molecular Structure 990 (2011) 110–120
Table 7
Hydrogen–bonding geometry (esd’s in parentheses). Cg1 denotes the centroid of the C6AC11 ring (for MCPMP-T, PMP-BA) and C14AC19 ring (for MCPMP-BA).
Ligand
D–Hꢂ ꢂ ꢂA
D–H (Å)
Hꢂ ꢂ ꢂA (Å)
Dꢂ ꢂ ꢂA (Å)
D–Hꢂ ꢂ ꢂA (°)
MCPMP-BA
N21AH21ꢂ ꢂ ꢂO3
C20AH20Cꢂ ꢂ ꢂCg1i
N21AH21ꢂ ꢂ ꢂO3
C26H26ꢂ ꢂ ꢂCg1
N21AH21ꢂ ꢂ ꢂO3
C15H15ꢂ ꢂ ꢂCg1
0.86
0.96
0.83(3)
0.96(2)
0.85(3)
0.86(3)
1.96
2.93
1.99(3)
2.72(2)
1.98(4)
2.69(3)
2.692(4)
3.306(4)
2.711(3)
3.620(3)
2.695(4)
3.485(5)
142
128
145(3)
158(2)
142(3)
153(3)
MCPMP-T
PMP-BA
Symmetry code: (i) 1 + x, y, z (ii) 1 + x, y, z for MCPMP-T and PMP-BA (i) 1 ꢀ x, 2 ꢀ y, 1 ꢀ z for MCPMP-BA.
thermo gravimetric characteristics have been estimated. Thermal
behaviour of all complexes explains as follows.
Table 8
Electronic spectral data of the complexes.
The TG curve follows the decrease in sample mass with increase
in temperature. In the present investigation heating rates were
suitably controlled at 10 °C minꢀ1 and mass loss followed up to
30–800 °C. The complexes slowly started decomposition between
150–280 °C. The first mass loss up to 300 °C is attributed to the re-
moval of two coordinated water molecules. This process is accom-
panied by exothermic process at around 200–350 °C in DTA curves
of all complexes. The mass loss occurring at temperature 350–
600 °C corresponds to the pyrolysis of the one organic ligand mol-
ecule. The subsequent temperature range 600–800 °C the mass loss
is due to the pyrolysis of another organic ligand molecule. The final
product of the thermal decomposition CuO was determined by ele-
mental analysis.
Complexes
Intraligand transition
d–d transition
kmax (nm)
e
kmax (nm)
e
Cu-PMP-T
Cu-PMP-BA
Cu-MCPMP-T
Cu-MCPMP-BA
Cu-PTPMP-T
Cu-PTPMP-BA
490
499
498
487
408
427
752
523
591
490
567
704
715
714
712
712
712
715
300
148
118
100
42
88
So, the parent ion peak is [Cu(PMP-T)2]. A peak corresponding to
ligand appears at m/z = 380. The fragmentation pattern for the li-
gand PMP-T and its Cu(II) complex is presented in Scheme 2 and
the spectra are shown in Figs. 5 and 6, respectively.
3.7.1. General scheme of degradation of Cu (II) complexes from TG
ꢀðLn
½CuðLnÞ ðH2OÞ ꢁ ꢀ2!H2O½CuðLnÞ2ꢁ !Þ CuO
3.7. Thermal studies
2
2
Thermal analyses of all the complexes were carried out by the
TG, DTA and DSC techniques. The experimental results revealed
that the degradation occurred in multiple stages, following a com-
plex mechanism. For each stage the kinetic parameters and the
From the above results it is confirmed that copper(II) complexes
contain two coordinated water molecules. Also degradation of li-
gand molecules with two stage, respectively. The TG–DTA curve
of one of the complexes is shown in Fig 7.
Fig. 5. The Mass spectra of ligand PMP-T.
Table 9
Mass spectral data of ligands.
Ligands
m/z (observed)
Assignments
C
25H23N3O+, C18H16N3O+, C18H16N3O+, C17H13N3O+, C12H10N3O+, C11H7N3O+, C7H7+, C3N2O+
PMP-T
PMP-BA
MCPMP-T
MCPMP-BA
PTPMP-T
PTPMP-BA
381, 305, 290, 276, 212, 197, 91, 80
446, 366, 340, 275, 260, 197, 91, 80
415, 380.5, 324, 304, 274, 197, 91, 80
480, 445.5, 365.5, 274.5, 259, 197, 91, 80
395, 350, 304, 289, 213, 197, 91, 80
460, 380, 378, 369, 289, 197, 91, 80
C24H20N3O+, C24H20N3O+, C16H10N3OBr+, C17H12N3O+, C16H10N3O+, C11H7N3O+, C7H7+, C3N2O+
C25H22N3OCl+, C25H22N3O+, C18H15N3OCl+, C19H18N3O+, C17H12N3O+, C11H7N3O+, C7H7+, C3N2O+
C24H19N3OBrCl+, C24H19N3OBr+, C24H19N3O+, C17H12N3O+, C16H11N3O+, C11H7N3O+, C7H7+, C3N2O+
C26H25N3O+, C23H16N3O+, C19H18N3O+, C18H15N3O+, C19H18N3O+, C11H7N3O+, C7H7+, C3N2O+
C25H22N3OBr+, C25H22N3O+, C11H8N3OBr+, C18H15N3OBr+, C18H15N3O+, C11H7N3O+, C7H7+, C3N2O+

K.M. Vyas et al. / Journal of Molecular Structure 990 (2011) 110–120
117
Table 10
Mass spectral data of Cu(II) complexes.
Complexes
m/z (observed)
Assignments
[Cu(PMP-
T)2(H2O)2]
[Cu(PMP-
824, 809, 670, 640, 580, 380,
275, 169
954, 794, 611,582, 445,
422,275,169
893, 823, 641, 611, 499, 414,
275, 169
[Cu(C25H22N3O)2]+, [Cu(C19H17N3O)2]+, [Cu(C49H41N6O)]+, [Cu(C25H22N3O)2]+, [Cu(C16H8N3O)2]+, (C25H22N3O)+,
[Cu(C8N6O)]+, [Cu(C4N3O)]+
[Cu(C24H19N3OBr)2]+, [Cu(C24H19N3O)2]+, [Cu(C17H11N3O)2]+, [Cu(C16H9N3OBr)2]+, (C24H19N3OBr)+,
[Cu(C16H9N3O)2]+, [Cu(C8N6O)]+, [Cu(C4N3O)]+
BA)2(H2O)2]
[Cu(MCPMP-
T)2(H2O)2]
[Cu(MCPMP-
BA)2(H2O)2]
[Cu(PTPMP-
T)2(H2O)2]
[Cu(PTPMP-
BA)2(H2O)2]
[Cu(C25H21N3OCl)2]+, [Cu(C25H21N3O)2]+, [Cu(C18H14N3O)2]+, [Cu(C17H11N3O)2]+, [Cu(C10H4N3OCl)2]+,
(C25H21N3O)+, [Cu(C8N6O)]+, [Cu(C4N3O)]+
1022, 951, 862, 791, 579, 479, [Cu(C24H18N3OClBr)2]+, [Cu(C24H18N3O)2]+, [Cu(C24H18N3OCl)2]+, [Cu(C24H18N3OBr)2]+, [Cu(C16H8N3O)2]+,
275, 169
852, 762, 640, 488, 394, 306,
275, 169
982, 822, 742, 488, 459, 275,
169
(C24H18N3OClBr)+, [Cu(C8N6O)]+, [Cu(C4N3O)]+
[Cu(C26H24N3O)2]+, [Cu(C23H15N3O)2]+, [Cu(C18H14N3O)2]+, [Cu(C12H10N3O)2]+, [Cu(C5H3N3O)2]+,
(C26H24N3O)2+,[Cu(C8N6O)]+, [Cu(C4N3O)]+
[Cu(C25H21N3OBr)2]+, [Cu(C25H21N3O)2]+, [Cu(C12H10N3O)2]+, [Cu(C23H15N3O)2]+, (C25H21N3OBr)+, [Cu(C8N6O)]+,
[Cu(C4N3O)]+
[Cu(C25H22N3O)22H2O]
860.50
-2H2O
-36.029
[Cu(C25H22N3O)2]
m/z=824(824.471)
3
H
0
C
-
2
-
1
5
9
.
0
6
3
0
.
-154.21 -2C6H5
5
3
-
[Cu(C49H41N6O2)]
(809.43)
[Cu(C24H19N3O)2]
(794.40)
[Cu(C19H17N3O)2]
(670.261)
-C6H5
-77.105
H 3
C
2
-
[Cu(C43H36N6O2)]
(732.32)
[Cu(C18H14N3O)2]
(640.192)
-2C7H7
-182.26
-60.138 -4CH3
[Cu(C29H22N6O2)]
(550.05)
[Cu(C16H8N3O)2]
(580.054)
-Cu(C4N3O)
-169.60
-304.39
-4C6H4
[C25H22N3O]
(380.446)
[Cu(C8N6O2)]
(275.66)
3
-91.13 -C7H7
[C19H17N3O]
(303.34)
-C4N3O
-106.064
[C24H19N3O]
(365.412)
[C18H15N3O]
(289.31)
[Cu(C4N3O)]
(169.6)
-15.034 -CH3
-77.105 -C6H5
-77.105 -C6H5
[C18H14N3O]
(288.306)
-63.54
-Cu
[C18H14N3O]
(288.307)
[C12H10N3O]
(212.205)
[C4N3O]
(106.06)
-C7H7
-91.13
-91.13 -C7H7
-15.034 -CH3
[C11H7N3O]
(197.17)
[C11H7N3O]
(197.17)
[C11H7N3O]
(197.17)
-
1
5
-
1
1
.
7
-117.15
5
.
1
-C8H7N
7
-
C
1
N
1
H
-
H 7
N
C 8
-
[C3N2O]
(80.01)
Scheme 2. Fragmentation pattern for ligand PMP-T and its Cu-complex.
Thermal stability measured by TG order of stability is as follows.
Differential scanning calorimetry (DSC) is the most widely used
thermo analytical technique for studying and characterizing a wide
variety of materials. Fig. 8 shows the DSC curve of one of the repre-
sentative complexes. The area of the exothermic and endothermic
[Cu(MCPMP-T)2(H2O)2] > [Cu(PMP-T)2(H2O)2] > [Cu(PTPMP-T)2
(H2O)2] > [Cu(PMP-BA)2(H2O)2] > [Cu(MCPMP-BA)2(H2O)2]

118
K.M. Vyas et al. / Journal of Molecular Structure 990 (2011) 110–120
Fig. 6. The FAB–Mass spectra of [Cu(PMP-T)2(H2O)2].
8.500
8.000
7.500
7.000
6.500
6.000
5.500
5.000
4.500
4.000
3.500
55.00
600.0
500.0
400.0
300.0
200.0
100.0
0.0
50.00
45.00
40.00
35.00
30.00
25.00
20.00
15.00
10.00
5.00
0.00
100.0
200.0
300.0
400.0
500.0
Temp Cel
Fig. 7. The TG–DTA curve of the complex [Cu(PMP-T)2(H2O)2].
peak corresponding to the heat of fusion and the peak temperature
corresponds to the phase change. The melting (Tp), transition tem-
perature (T1, T2), heat of reaction (dH), and entropy (dS) of the com-
plexes calculated from DSC results are given in Table 11.
3.8. ESR studies of Cu(II) complexes
As we could not get well-shaped single crystals, the EPR spectra
were recorded only for powder and solution samples for the com-
plex [Cu(PMP-T)2(H2O)2] at RT and LNT. The powder sample was
recorded in quartz tube to avoid Mn(II) or Fe(II) impurities and
solution spectra was recorded in DMF solution in capillary tube.
The solution spectrum was recorded to confirm that the complex
does not undergo structural change in solution.
The powder as well as the solution ESR spectra of the complex
[Cu(PMP-T)2(H2O)2] was studied. Hamiltonian parameters g||, g\,
A||, A\ and Aiso were also calculated. Complex [Cu(PMP-T)2(H2O)2]
shows the g|| = 2.18 and g\ = 2.11, for Cu(II) g|| indicates covalence
with g|| < 2.3 for covalent complexes and g|| P 2.3 for ionic [28] g||
Fig. 8. The DSC curve of the complex [Cu(PMP-BA)2(H2O)2].

K.M. Vyas et al. / Journal of Molecular Structure 990 (2011) 110–120
119
Table 11
Thermoanalytical data of the complexes.
Complexes
TG range
(°C)
DTA max Ts
T1
(°C)
T2
(°C)
Tp
(°C)
D
EÃ
dHÃ
D
SÃ
Mass loss (%) obs. Assignments
(calcd.)
(°C)
(°C)
(kJ molꢀ1
)
(kJ molꢀ1
)
(J Kꢀ1 molꢀ1
)
[Cu(PMP-T)2
(H2O)2]
50–350
325
272
158
279
157
246
272
249
0.784
25.0
0.10
4.19 (4.18)
Loss of two coordinated
water molecules
Loss of one PMP-T ligand
Remaining CuO residue
350–600
600–800
352
–
271
–
308
–
285
–
0.821
59.03
–
0.20
–
44.33 (44.33)
8.81 (8.82)
[Cu(PMP-BA)2
(H2O)2]
50–350
335
196
205
199
0.879
0.807
3.52
0.01
3.62 (3.63)
Loss of two coordinated
water molecules
Loss of one PMP-BA ligand
Remaining CuO residue
350–600
600–800
351
–
277
–
312
–
283
–
97.97
–
0.34
–
45.09 (45.07)
7.66 (7.65)
[Cu(MCPMP-T)2
(H2O)2]
50–350
332
167
255
222
0.908
0.938
145.1
0.65
3.87 (3.87)
Loss of two coordinated
water molecules
Loss of one MCPMP-T ligand
Remaining CuO residue
350–600
600–800
389
–
293
–
321
–
293
–
150.0
–
0.51
–
44.67 (44.75)
8.16 (8.17)
[Cu(MCPMP-BA)2
(H2O)2]
50–350
321
150
177
164
0.926
0.896
28.73
0.17
3.41 (3.40)
Loss of two coordinated
water molecules
Loss of one MCPMP-BA
ligand
350–600
360
287
317
306
98.06
0.31
45.30 (45.40)
600–800
50–350
–
–
–
–
–
–
7.16 (7.17)
4.03 (4.05)
Remaining CuO residue
[Cu(PTPMP-T)2
(H2O)2]
315
240
249
289
269
0.913
0.892
137.1
0.50
Loss of two coordinated
water molecules
Loss of one PTPMP-T ligand
Remaining CuO residue
350–600
600–800
406
–
269
304
289
150.4
0.51
44.54 (44.51)
8.53 (8.55)
3
7
value of the complex of 2.18 indicates covalency for MAL bond.
The nature of ligand is evaluated from G value,
a2 ¼ ꢀðA =0:036Þ þ ðg ꢀ 2:0023Þ þ ðg? ꢀ 2:0023Þ þ 0:04
jj
jj
b2 ¼ ðgjj ꢀ 2:0023ÞE=ðꢀ8ka2
Þ
gjj ꢀ 2
G ¼
ffi 4:0
g? ꢀ 2
The a
2 = 0.80 its state that Cu(II) complex have covalent bond-
ing and b2 = 0.67 suggest that in-plane
in complex.
p-bonding is also present
For G < 4.0, the ligand forming the complex is regarded as a
strong field ligand. For [Cu(PMP-T)2(H2O)2], G = 3.5 it indicates
octahedral stereochemistry of complex [28].
The RT solution ESR consists of four asymmetrical but equally
spaced hyperfine lines characteristic of the Cu(II) nuclear hyperfine
interaction (Cu = I = 3/2 for 63Cu and 65Cu). From these solution ESR
spectra, we have calculated values of g|| = 2.15, g\ = 2.10,
A|| = 205.33 Â 10ꢀ4, A\ = 185.26 Â 10ꢀ4. The ratio of g||/A|| is used
to find the structure of a complex. In present Cu(II) complexes,
the ratio obtained is in the range 104.70 cmꢀ1, which is due octa-
hedral copper(II) complexes [28,29].
3.9. Cyclic voltametric study
The redox properties of 1 mM solution of all the complexes have
been investigated in DMF containing 0.1 M tetraethylammonium
tetrafluoroborate as a supporting electrolyte at a platinum working
electrode. The cyclic voltametric results are given in Table 12.
For the complexes a negative scan initiated at 400 mV in the
potential range 1200 to ꢀ1000 mV yielded quasireversible couple
corresponding Cu(II)/(I) redox process. In both complexes peak
potential increases as scan rate is increased [30–31].
The frozen solution spectrum of the complex is axial with
g|| > g\ > 2.0, suggesting the presence of a dx2–y2 ground state [28].
Molecular orbital co-efficient,
a
2 (covalent in-plane
r
-bonding)
The cyclic voltametry of the ligands has also been investigated.
The spectra clearly indicates that the ligands are having irrevers-
ible nature within the range 50–300 mV.
and b2 (covalent in-plane
p-bonding) were calculated by using the
following equations [28].
3.10. Germination study
Table 12
N-acylated compounds [32] show growth inhibitory activity
with seedling of wheat, rye and barely. Schiff bases [33] show
remarkable activities on plant hormone such as the auxins on root
growth. There are many reports in literature on seed germination
inhibition but there in no reports on the effect of toluoyl pyrazo-
lones on seed germination. We have studied the effect of one of
Cyclic voltametric measurements of Cu(II) complexes.
Complexes
Epc (mV)
Epa (mV)
D
EP (V)
EI/2
Cu-PTPMP-T
Cu-PTPMP-BA
ꢀ0.200
ꢀ0.202
0.102
0.120
302
322
0.151
0.161
Table 13
Inhibition activity of ligand PMP-T on wheat seed germination.
Days
Blank
Water + alcohol (cm)
Water + alcohol + ligand (cm)
Inhibition (%)
7
14
21
28
12.20
14.00
18.00
24.80
12.90
14.20
18.20
25.00
–
100
7.2
51.42
55.55
50.40
10.00
12.50

120
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the Schiff base (PMP-T) used in the present study on the germina-
tion of wheat (Triticum aestivum L.).
The germination study of seed was carried out in a pot experi-
ments. In 1st pot, seeds were grown only in water as blank. In 2nd
pot, seeds were grown in water + alcohol mixture and in 3rd pot 1%
ligand PMP-T was dissolved in alcohol and was mixed with soil and
then seeds were grown in that soil using water. The identical con-
ditions were provided to all the three pots. The length of the plants
were measured every 7 days interval. The results obtained are tab-
ulated below (Table 13) clearly indicating up to 50% inhibition by
the PMP-T.
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This data can be obtained free of charge at www.ccdc.cam.ac.uk/
conts/retrievel.html or from the Cambridge Crystallographic Data
Center, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223/
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The authors are thankful to University Grants Commission, New
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search project to RNJ. They are also thankful to Head, Department
of Chemistry for providing necessary facilities required to carry out
this work. The award of Alembic Research Fellowship to KMV is
also gratefully acknowledged.
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