Complexes of nickel(II) with 2,3-dimethyl-4-formyl(benzhydrazide)-1-phenyl- 3-pyrazolin-5-one

Article abstract of DOI:10.1081/SIM-120030430

Nickel(II) complexes of the Schiff base 2,3-dimethyl-4-formyl- (benzhydrazide)-1-phenyl-3-pyrazolin-5-one (L) with the formulae [Ni(L) ₂ (ClO₄)]ClO₄, [Ni(L)₂(NO ₃)](NO₃), and [Ni(L)₂X₂] (X = Cl, Br, or I) have been synthesized and characterized by elemental analyses, electrical conductance in nonaqueous solvents, infrared and electronic spectra as well as magnetic susceptibility measurements. In these complexes, L acts as a neutral bidentate ligand coordinating through the azomethine nitrogen and the carbonyl oxygen of the pyrazolone ring. In the perchlorate and nitrate complexes one of the anions is coordinated to the metal ion in a bidentate fashion while in the halide complexes both the anions are coordinated. An octahedral geometry is assigned around the nickel(II) ion in all these complexes.

Full text of DOI:10.1081/SIM-120030430

Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry
ISSN: 0094-5714 (Print) 1532-2440 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt19
Complexes of Nickel(II) with
2,3‐Dimethyl‐4‐formyl(benzhydrazide)‐1‐phenyl‐3‐pyrazolin‐5‐o
K. C. Raju & P. K. Radhakrishnan
To cite this article: K. C. Raju & P. K. Radhakrishnan (2004) Complexes of Nickel(II) with
2,3‐Dimethyl‐4‐formyl(benzhydrazide)‐1‐phenyl‐3‐pyrazolin‐5‐one, Synthesis
and Reactivity in Inorganic and Metal-Organic Chemistry, 34:3, 417-428, DOI: 10.1081/
SIM-120030430
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 3, pp. 417–428, 2004
Complexes of Nickel(II) with 2,3-Dimethyl-
4-formyl(benzhydrazide)-1-phenyl-
3-pyrazolin-5-one
*
K. C. Raju and P. K. Radhakrishnan
School of Chemical Sciences, Mahatma Gandhi University,
Kottayam, Kerala, India
ABSTRACT
Nickel(II) complexes of the Schiff base 2,3-dimethyl-4-formyl-(benz-
hydrazide)-1-phenyl-3-pyrazolin-5-one (L) with the formulae [Ni(L)2
(ClO4)]ClO4, [Ni(L)2(NO3)](NO3), and [Ni(L)2X2] (X ¼ Cl, Br, or I)
have been synthesized and characterized by elemental analyses, electrical
conductance in nonaqueous solvents, infrared and electronic spectra as
well as magnetic susceptibility measurements. In these complexes,
L acts as a neutral bidentate ligand coordinating through the azomethine
nitrogen and the carbonyl oxygen of the pyrazolone ring. In the perchlor-
ate and nitrate complexes one of the anions is coordinated to the metal ion
in a bidentate fashion while in the halide complexes both the anions are
coordinated. An octahedral geometry is assigned around the nickel(II)
ion in all these complexes.
Key Words: Nickel(II); Schiff base; Hydrazines; Metal complex.
*
Correspondence: P. K. Radhakrishnan, School of Chemical Sciences, Mahatma Gandhi
University, Kottayam 686 560, Kerala, India; E-mail: mgu@vsnl.com.
417
DOI: 10.1081/SIM-120030430
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Raju and Radhakrishnan
INTRODUCTION
The interesting and varied ligand behavior of hydrazines and hydrazones
towards transition metal ions is well known.[1] The pharmacological appli-
cations of antipyrine-based ligands and their metal complexes have drawn
the attention of many investigators.[2–4] In view of these and as part of our
continuing interest on metal complexes[5–10] with Schiff bases derived from
antipyrine, we report here the synthesis and structural investigation on
nickel(II) complexes of the Schiff base 2,3-dimethyl-4-formyl(benzhydrazide)-
1-phenyl-3-pyrazolin-5-one (L). (Fig. 1)
RESULTS AND DISCUSSION
The formation of the complexes can be represented by the general
equation shown below:
NiX2 þ 2L ꢀ! NiðLÞ2X2 ðX ¼ ClO4; NO3; Cl; Br; or IÞ
All the complexes are light yellow in color and are nonhygroscopic. They
are soluble in acetonitrile, DMF, ethanol, methanol, and nitrobenzene, but
insoluble in benzene, chloroform, ethyl acetate, and toluene. The analytical
data (Table 1) indicate that the complexes have the general formula:
NiðLÞ2X2 ðX ¼ ClO4; NO3; Cl; Br; or IÞ
The molar conductance values of the complexes (Table 2) in acetonitrile,
DMF, and nitrobenzene (1023 M solution) are in the range expected for 1 : 1
electrolyte for perchlorate and nitrate complexes while the corresponding
chloride, bromide, and iodide complexes behave as nonelectrolytes.[11]
Figure 1. 2,3-Dimethyl-4-formyl(benzhydrazide)-1-phenyl-3-pyrazolin-5-one (L).

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Raju and Radhakrishnan
Table 2. Molar conductancea data of the nickel(II) complexes of L (ohm21 cm2 mol21).
Molar conductance
Compound
Acetonitrile
DMF
Nitrobenzene
[Ni(L)2(ClO4)](ClO4)
[Ni(L)2(NO3)](NO3)
[Ni(L)2Cl2]
153.72
148.23
71.37
93.33
94.42
85.64
82.35
34.04
35.14
41.72
27.45
25.25
7.68
[Ni(L)2Br2]
[Ni(L)2I2]
10.98
12.08
a1023 M solution.
Thus, the complexes may be formulated as [Ni(L)2(ClO4)](ClO4), [Ni(L)2
(NO3)](NO3), and [Ni(L)2X2] (X ¼ Cl, Br, or I).
Infrared Spectra
The important infrared spectral data of the ligand and its complexes are
presented in Table 3. The infrared spectral bands at 1674 and 1630 cm21 of
the ligand are characteristic of n(C55O) of the pyrazolone ring and benzoyl
moiety, respectively.[7] In complexes, the band at 1674 cm21 is shifted to
the region 1640–1657 cm21 indicating that the carbonyl oxygen is involved
in coordination.[7] The band corresponding to n(C55O) of the benzoyl moiety
remains practically unaltered at about 1625 cm21 indicating the noncoordina-
tion of benzoyl carbonyl in all these complexes.[12] The strong band observed
at 1571 cm21 in the ligand spectrum attributed to C55N stretching vibration is
shifted to 1551–1558 cm21 indicating the coordination of azomethine nitro-
gen in the complexes.[7] The n(N–N) band at 998 cm21 in the ligand spectrum
shifted to higher frequency (1006–1008 cm21) in the complexes which further
supports the bonding through azomethine nitrogen.[13]
In the perchlorate complex, the triply split band maxima observed at
1142, 1110, and 1020 cm21 are due to n8, n6, and n1, vibrations, respectively,
of the perchlorate group of C2v symmetry, which is indicative of bidentate
coordination,[14] but the band around 1089 cm21 is assigned to the n3 vibration
of the ionic perchlorate of Td symmetry. Thus, the presence of both ionic and
bidentately coordinated perchlorate groups is indicated in these complexes.[14]
The vibrational frequencies observed at 940 and 636 cm21 corresponding to n2
and n3 vibrations, respectively, of the perchlorate (C2v group) group and the
band at 625 cm21 due to the n4 vibration of the ionic perchlorate, which are
not present in the spectrum of the free ligand, also supports the coexistence

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Raju and Radhakrishnan
of both ionic and bidentately coordinated perchlorate groups in these
complexes.
In the nitrate complex, characteristic vibrational frequencies of both ionic
and coordinated nitrate groups are observed. The presence of a coordinated
nitrate group is indicated by the bands observed at 1,440 and 1,247 cm21
due to the n4 and n1 vibrations, respectively, of the nitrate group of C2V sym-
metry.[16] A medium band observed at 1052 cm21 due to the n2 vibration of
the nitrate group (C2V), stands as additional evidence for the presence of coor-
dinated nitrate ion. The difference in wave numbers between the two highest
frequency bands (n4 2 n1) of the C2V nitrate is about 193 cm21, which indi-
cates that the coordinated nitrate ion is bidentate.[15,16] A very strong band
at 1384 cm21 indicates the presence of an ionic nitrate group and it is due
to the n3 vibration of the nitrate group of D3h symmetry. This is supported
by another band of medium intensity observed around 830 cm21 due to the
n2 vibration of the ionic nitrate.[15]
In the far infrared spectrum of chloride, bromide, and iodide complexes,
Ni–Cl, Ni–Br, and Ni–I stretching vibrations occur at 240, 165, and
125 cm21, respectively, which are not present in the spectrum of the free ligand.
The above results, along with the conductance data, confirm that in these
complexes one of the perchlorate and nitrate ions and two of the chloride,
bromide, and iodide ions are coordinated to the metal ion. Furthermore,
n(Ni–N) and n(Ni–O) stretching vibrations are observed at about 550 and
450 cm21, respectively, in all these complexes.[17]
Electronic Spectra
Electronic spectral data of the ligand and complexes in the solid state
(using Nujol) with their tentative assignments are given in Table 4. The
electronic spectrum of the ligand shows two maxima at 23,866 and
41,153 cm21 corresponding to n ! pꢁ and p ! pꢁ transitions, respectively.
In the complexes n ! pꢁ bands are found to be blue-shifted to the region
24,510–25,839 cm21 while p ! pꢁ bands are red-shifted to the region
40,160–41,052 cm21, respectively, compared to that of the ligand. The
bands observed in the regions 21,551–21,978 cm21 and 15,527–
3
3
3
3
16,891 cm21 are attributed to A2g(F ) ! T1g(P) and A2g(F ) ! T1g(F )
consistent with octahedral geometry around nickel(II) in these com-
plexes.[18,19] In addition to this, a low energy band in the region 9191–
9541 cm21 attributable to 3A2g(F) ! T2g(F ) supports the octahedral geome-
3
try around nickel(II) in these complexes.[18,19] An intense absorption band in
the region 32,573–33,989 cm21 may be due to a charge transfer process.

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423
Table 4. Electronic spectral data and magnetic moments of the nickel(II) complexes
of L.
Compound
L
Abs. max. (cm21
)
Tentative assignment
m
eff (B.M.)
23,866
41,153
n ꢀ! pꢁ
p ꢀ! pꢁ
—
[Ni(L)2(ClO4)](ClO4)
[Ni(L)2(NO3)](NO3)
[Ni(L)2Cl2]
25,839
40,650
32,573
21,929
15,576
9,505
n ꢀ! pꢁ
3.02
3.30
3.27
2.98
3.12
p ꢀ! pꢁ
Charge transfer
3
3A2g(F) ꢀ! T1g (P)
3
3A2g(F) ꢀ! T2g (F)
3
3A2g(F) ꢀ! T2g (F)
25,125
40,160
33,364
21,739
15,600
9,191
n ꢀ! pꢁ
p ꢀ! pꢁ
Charge transfer
3
3A2g(F) ꢀ! T1g (P)
3
3A2g(F) ꢀ! T2g (F)
3
3A2g(F) ꢀ! T2g (F)
24,630
40,485
32,573
21,551
15,576
9,310
n ꢀ! pꢁ
p ꢀ! pꢁ
Charge transfer
3
3A2g(F) ꢀ! T1g (P)
3
3A2g(F) ꢀ! T1g (F)
3
3A2g(F) ꢀ! T2g (F)
[Ni(L)2Br2]
25,510
40,650
33,898
21,978
15,527
9,354
n ꢀ! pꢁ
p ꢀ! pꢁ
Charge transfer
3
3A2g(F) ꢀ! T1g (P)
3
3A2g(F) ꢀ! T1g (F)
3
3A2g(F) ꢀ! T2g (F)
[Ni(L)2I2]
24,813
41,052
33,444
21,929
16,891
9,541
n ꢀ! pꢁ
p ꢀ! pꢁ
Charge transfer
3
3A2g(F) ꢀ! T1g (P)
3
3A2g(F) ꢀ! T1g (F)
3
3A2g(F) ꢀ! T2g (F)
Magnetic Moment Data
The magnetic moments of the nickel(II) complexes are in the range 2.98
to 3.30 B.M. Typical octahedral nickel(II) complexes have magnetic
moments between 2.90 and 3.40 B.M. depending on the magnitude of the

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Raju and Radhakrishnan
orbital contribution.[20] The results indicate that these complexes probably
have octahedral geometry.[21,22]
Based on the results of the present study, the structure shown in Fig. 2
may be assigned to the complexes.
EXPERIMENTAL
Materials
The metal salts were prepared from Analar BDH nickel carbonate and the
respective 50% acids and the salts were crystallized out by evaporating the
.
solution on a steam bath. For example NiCl2 6H2O was prepared as follows.
Nickel carbonate was dissolved in hot 50% hydrochloric acid. A slight excess
of carbonate was used. The undissolved carbonate was removed by filtration.
.
The filtrate was concentrated by evaporation when crystals of NiCl2 6H2O
separated.
Preparation of the Ligand
The ligand 2,3-dimethyl-4-formyl(benzhydrazide)-1-phenyl-3-pyrazolin-
5-one was prepared and characterized as described earlier.[7]
Preparation of Complexes
Perchlorate and Iodide Complexes
.
A quantity of 0.3657 g (1 mmol) of Ni(ClO4)2 6H2O or 0.4206 g
.
(1 mmol) of NiI2 6H2O in ethyl acetate (10 mL) was added to a boiling suspen-
sion of 0.7357 g (2.2 mmol) of the ligand in ethyl acetate (100 mL). The result-
ing mixture was refluxed for about 4 hr on a steam bath. The complex
precipitated on cooling and was filtered and washed several times with hot
benzene to remove the excess ligand. The complexes were dried under
vacuum over phosphorus(V)oxide.
Chloride Complex
.
A quantity of 0.2377 g (1 mmol) of NiCl2 6H2O in methanol (10 mL) was
added to a boiling suspension of 0.7357 g (2.2 mmol) of the ligand in ethyl
acetate (100 mL). The resulting mixture was refluxed for about 3 hr on a

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425
Figure 2. [Ni(L)2X2] (X ¼ Cl, Br, or I).

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Raju and Radhakrishnan
steam bath and concentrated. The complex precipitated on cooling and was
filtered and washed several times with hot benzene to remove the excess
ligand. The complex was dried under vacuum over phosphorus(V)oxide.
Bromide and Nitrate Complex
.
A quantity of 0.3266 g (1 mmol) of NiBr2 6H2O or 0.2908 g (1 mmol) of
.
Ni(NO3)2 6H2O in acetone (10 mL) was added to a boiling suspension of
0.7257 g (2.2 mmol) of the ligand in acetone (100 mL). The mixture was
refluxed for about 3 hr on a steam bath. The resulting solution was concen-
trated. The complexes precipitated on cooling and were filtered and washed
several times with hot benzene to remove the excess ligand. The complexes
were dried under vacuum over phosphorus(V)oxide.
ANALYSES ON PHYSICAL METHODS
All the complexes were analyzed for metal and halide contents by the
standard methods[23] and the perchlorate content by the Kurz method.[24]
The molar conductances of the complexes in acetonitrile, DMF, and nitroben-
zene (1023 M solution) were measured at room temperature using a Toshniwal
conductivity bridge with a dip-type conductance cell (cell constant ¼ 1.094).
The infrared spectra of the ligand and complexes were recorded in the range
4000–400 cm21 on a Shimadzu IR–470 spectrometer. Electronic spectra of
the ligand and the complexes in the solid state were measured in the range
200–1100 nm on a Shimadzu UV 160A spectrophotometer and in the range
1100–1500 nm on a Cary 2390 UV-VIS-NIR spectrophotometer. The elemen-
tal analyses (C, H, and N) were carried out in a Heraeus CHNO rapid analyzer.
The magnetic moments were measured at room temperature by the Guoy
method using mercury(II)tetrathiocyanatocobaltate(II) as the calibrant.
ACKNOWLEDGMENTS
We wish to express our sincere thanks to the heads of the Regional
Sophisticated Instrumentation Centers at the Indian Institute of Technology,
Chennai and the Indian Institute of Technology, Mumbai, for some instrumen-
tal analyses. We also thank Mahatma Gandhi University, Kerala, for providing
laboratory facilities and the University Grants Commission for awarding
a Teacher Fellowship to one of us (KCR) under the faculty improvement
program. We also wish to express our sincere thanks to Dr. Siby Joseph and
Dr. N. T. Madhu for some fruitful discussions.

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427
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Accepted October 24, 2003
Referee I: J. Protasiewicz
Referee II: B. Guo

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