Synthesis, magnetic, and spectral studies of mixed-ligand complexes of nickel(II) involving some chelating 4-oximino-2-pyrazoline-5-one derivatives

Article abstract of DOI:10.1081/SIM-120019997

The synthesis, magnetic and spectral studies of mixed-ligand complexes of nickel(II) derived from chelating 4-oximino-2-pyrazoline-5-one derivatives, viz., 4-benzoytoxime-3-methyl-1-phenyl-2-pyrazoline-5-one (bomppH), 4-acetyloxime-3-methyl-1-phenyl-2-pyrazoline-5-one (aomppH) and 3-methyl-1-phenyl-4-propionyloxime-2-pyrazoline-5-one (mppopH), and certain heterocyclic ligands, viz., 3-methyl-1-phenyl-2-pyrazoline-5-one (mpp), 4-amino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one (adpp), 2,3-dimethyl-1-phenyl-3-pyrazoline-5-one (dpp), 2,3-dimethyl-4-methylaminomethanesulfonate sodium-1-phenyl-3-pyrazoline-5-one (dmspp), benzimidazole (bzl) and benzothiazole (bzt) are described. The complexes, which have been characterized by conductance measurements, electron spin resonance, magnetic measurements, thermogravimetric analyses, electronic and infrared spectral studies have the general formulas [Ni(A-A)₂(L)₂] and [Ni(A-A)₂(L-L)] where, (A-A)H = bomppH, aomppH, or mppopH, L = mpp, dpp, bzl or bzt and L - L = adpp or dmspp. All the complexes were found to be non-electrolytes and octahedral structures have been proposed for them.

Full text of DOI:10.1081/SIM-120019997

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Synthesis, Magnetic, and Spectral Studies of
Mixed‐Ligand Complexes of Nickel(II) Involving Some
Chelating 4‐Oximino‐2‐pyrazoline‐5‐one Derivatives
R. C. Maurya a , R. Verma a & D. Sutradhar a
a Coordination Chemistry Laboratory , Department of P. G. Studies and Research in
Chemistry , R. D. University , Jabalpur, 482‐001, India
Published online: 15 Feb 2007.
To cite this article: R. C. Maurya , R. Verma & D. Sutradhar (2003) Synthesis, Magnetic, and Spectral Studies of Mixed‐Ligand
Complexes of Nickel(II) Involving Some Chelating 4‐Oximino‐2‐pyrazoline‐5‐one Derivatives, Synthesis and Reactivity in
Inorganic and Metal-Organic Chemistry, 33:3, 435-451, DOI: 10.1081/SIM-120019997
To link to this article: http://dx.doi.org/10.1081/SIM-120019997
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 33, No. 3, pp. 435–451, 2003
Synthesis, Magnetic, and Spectral Studies of
Mixed-Ligand Complexes of Nickel(II)
Involving Some Chelating 4-Oximino-
2-pyrazoline-5-one Derivatives
*
R. C. Maurya, R. Verma, and D. Sutradhar
Coordination Chemistry Laboratory, Department of P. G. Studies and
Research in Chemistry, R. D. University, Jabalpur, India
ABSTRACT
The synthesis, magnetic and spectral studies of mixed-ligand complexes
of nickel(II) derived from chelating 4-oximino-2-pyrazoline-5-one
derivatives, viz., 4-benzoyloxime-3-methyl-1-phenyl-2-pyrazoline-5-
one (bomppH), 4-acetyloxime-3-methyl-1-phenyl-2-pyrazoline-5-one
(aomppH) and 3-methyl-1-phenyl-4-propionyloxime-2-pyrazoline-5-one
(mppopH), and certain heterocyclic ligands , viz., 3-methyl-1-phenyl-2-
pyrazoline-5-one (mpp), 4-amino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-
one (adpp), 2,3-dimethyl-1-phenyl-3-pyrazoline-5-one (dpp), 2,3-
dimethyl-4-methylaminomethanesulfonate sodium-1-phenyl-3-pyrazo-
line-5-one (dmspp), benzimidazole (bzl) and benzothiazole (bzt) are
*
Correspondence: R. C. Maurya, Coordination Chemistry Laboratory, Department of
P. G. Studies and Research in Chemistry, R. D. University, Jabalpur 482-001, India;
E-mail: rcmaurya@sancharnet.in.
435
DOI: 10.1081/SIM-120019997
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

436
Maurya, Verma, and Sutradhar
described. The complexes, which have been characterized by conduct-
ance measurements, electron spin resonance, magnetic measurements,
thermogravimetric analyses, electronic and infrared spectral studies have
the general formulas [Ni(A–A)2(L)2] and [Ni(A–A)2(L–L)] where,
(A–A)H = bomppH, aomppH, or mppopH, L = mpp, dpp, bzl or bzt and
L–L = adpp or dmspp. All the complexes were found to be non-elec-
trolytes and octahedral structures have been proposed for them.
Key Words: Mixed-ligand Ni(II) chelates; Spin free octahedral
symmetry; 4-Oximino-2-pyrazoline-5-one derivatives; Nuclear
hyperfine coupling; trans-Octahedral structure; cis-Octahedral structure.
INTRODUCTION
In continuation of our interest to synthesize and characterize novel
metal complexes involving chelating molecules,[1] our studies have been
extended so as to observe the ligational behaviour of chelating 4-oximino-
2-pyrazoline-5-one derivatives in the presence of some 5-pyrazolones, ben-
zothiazole or benzimidazole, towards nickel(II).
The chelating behaviour of 4-oximino-2-pyrazoline-5-ones,[2–4] viz., 4-
oximino-1-phenyl-3-methyl-2-pyrazoline-5-one, 4-oximino-3-methyl-2-py-
razoline-5-one, 4-oximino-3-phenyl-2-pyrazoline-5-one, 4-oximino-1,3-
diphenyl-3-methyl-2-pyrazoline-5-one is well established. They coordinate
through the cyclic carbonyl oxygen and oximino nitrogen, thus behaving as
bidentate O, N donors.
Substituted pyrazolones have been well established as mono-, bi and
tridentate ligands.[5] The ligational behaviours of benzothiazole, benzimi-
dazole and their derivatives have been reported earlier from our Coordi-
nation Chemistry Laboratory[6–8] by Maurya et al. and also by others.[9–11]
Monomeric complexes of nickel(II) cobalt(II) and chromium(III) with 4-
oximino-1-phenyl-3-methyl-2-pyrazoline-5-one, 4-oximino-3-methyl-2-py-
razoline-5-one, 4-oximino-3-phenyl-2-pyrazoline-5-one and 4-oximino-1,3-
diphenyl-2-pyrazoline-5-one have been prepared and characterized by Shah et
al.[2] The same group of workers has carried out structural studies on
oxovanadium(IV), chromium(III), manganese(II), cobalt(II), nickel(II), cop-
per(II) and zinc(II) chelates of 4-formyloxime-3-methyl-1-phenyl-2-pyrazo-
line-5-one.[12] The chelates have been isolated in the solid state and cha-
racterized as monomers by different physico-chemical studies. Structural
studies[3] on Fe(II), Mn(II), Zn(II), VO(IV) and UO2(VI) complexes of some
4-oximino-2-pyrazoline-5-ones have also been carried out by the same group
of workers. Pyridine and 3-picoline adducts of Ni(II) and Zn(II) chelates with
some 4-oximino-2-pyrazoline-5-ones (mixed-ligand complexes) have been

Mixed-Ligand Complexes of Nickel(II)
437
Figure 1. Structures of oximes.
synthesized and characterized by the same group of workers,[4] and they are
suggested to have trans-octahedral structures with axial pyridine/3-picoline.
However, there is no report on the synthesis and characterization fo mixed-
ligand complexes of Ni(II) involving the chelating molecules 4-benzoylox-
ime-3-methyl-1-phenyl-2-pyrazoline-5-one (bomppH), 4-acetyloxime-3-
methyl-1-phenyl-2-pyrazoline-5-one (aomppH) and 3-methyl-1-phenyl-4-
Figure 2. Structures of ligands.

438
Maurya, Verma, and Sutradhar
propionyloxime-2-pyrazoline-5-one (mppopH). It was, therefore, thought of
interest to synthesize mixed-ligand complexes of Ni(II) with the aforemen-
tioned oxime derivatives along with 3-methyl-1-phenyl-2-pyrazoline-5-one
(mpp), 4-amino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one (adpp), 2,3-
dimethyl-1-phenyl-3-pyrazoline-5-one (dpp),2,3-dimethyl-4-methylamino-
methanesulphonate sodium monohydrate 1-phenyl-3-pyrazoline-5-one
(dmspp), benzimidazole (bzl) and benzothiazole (bzt). The structures of the
oxime derivatives and other ligands used in the present study are shown in
Figures 1 and 2, respectively.
EXPERIMENTAL
Materials
Nickel(II) chloride hexahydrate (Polypharm Pvt. Ltd., Bombay), acetyl
chloride (B. D. H. Chemicals, Bombay), benzoyl chloride (Robert Johnson,
India), propionyl chloride, 3-methyl-1-phenyl-2-pyrazoline-5-one (Kempha-
sol, Bombay), hydroxylamine hydrochloride (Loba Chemie, Bombay), 2,3-
dimethyl-1-phenyl-3-pyrazoline-5-one (B. D. H. Chemicals, England),
4-amino-2,3-dimethyl-1-phenyl-3-pyrazoline-5-one (Aldrich Chemicals
Company, U. S. A.), 2,3-dimethylaminomethanesulphonate sodium mono-
hydrate-1-phenyl-3-pyrazoline-5-one (Indian Drugs and Pharmaceuticals Ltd.,
Hyderabad), benzimidazole (Wilson Laboratories, Bombay), benzothiazole (E.
Merck, Germany) were used as such. All other chemicals were of A. R. grade.
4-Benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-one (bmpp), 4-acetyl-3-methyl-
1-phenyl-2-pyrazoline-5-one (ampp) and 3-methyl-1-phenyl-4-propionyl-2-
pyrazoline-5-one (mppp) were prepared by the method reported by Jensen.[13]
Preparation of Oxime Derivatives of
bmpp, ampp, and mppp
These oximes were prepared by following the general method[14] given
below: A solution of hydroxylamine hydrochloride (5 mmol, 0.347 g) and
sodium hydroxide (5 mmol, 0.200 g) in 60 mL aqueous/ ethanol (1:1) were
added to a solution of bmpp, ampp or mppp (5 mmol) in 40 mL ethanol. The
mixture was refluxed for two hours. On cooling, a crystalline product was
obtained which was filtered by suction, washed several times with water and
finally with ethanol. The oxime of bmpp was precipitated by pouring the
reaction mixture in excess (150 mL) of distilled water. Melting point (colour):
bmppoxime 155 °C (brown), amppoxime 170 °C (yellowish brown) and
mpppoxime 160 °C (light brown)), and yields are 70–75%.

Mixed-Ligand Complexes of Nickel(II)
Preparation of Mixed-Ligand Complexes
439
The complexes were prepared by refluxing the combined solutions of
aqueous (5 mL) nickel(II) chloride hexahydrate (10 mmol, 2.377 g), ethanolic
( ꢀ 25 mL) bomppH (20 mmol, 5.860 g), aomppH (20 mmol, 4.620 g) or
mppopH (20 mmol, 4.900 g), and ethanolic ( ꢀ 20 mL) mpp (20 mmol, 3.480
g), dpp (20 mmol, 3.76 g), adpp (10 mmol, 2.030 g), dmspp (10 mmol, 3.510),
bzl (20 mmol, 2.360 g) or bzt (20 mmol, 2.700 g) for 30–60 minutes. During
this time coloured crystals were precipitated. They were filtered by suction,
washed several times with ethanol and dried in vacuo.
Analyses
Carbon, hydrogen and nitrogen were determined microanalytically at
the Central Salt and Marine Chemicals Research Institute, Bhavnagar,
India. The nickel content in each of the complexes was determined gravi-
metrically as nickel dimethylglyoximate.[15]
Physical Methods
Solid state IR spectra were recorded in Nujol mulls on a Perkin-Elmer
model 1620 FI-IR spectrophotometer at the National Chemical Laboratory,
Pune, India. ESR spectra were recorded on an EPR-112 spectrometer
using powdered samples at the Regional Sophisticated Instrumentation
Centre, Indian Institute of Technology, Madras. Electronic spectra of the
complexes were recorded on a Shimadzu model UV-160 spectropho-
tometer. Magnetic measurements were performed by Gouy’s method using
mercury(II) tetrathiocyanatocobaltate(II) as the calibrant at the Central
Salt and Marine Chemicals Research Institute, Bhavnagar. Conductance
measurements were performed at room temperature in dimethylformamide
using a Toshniwal conductivity bridge and dip-type cell with a smooth
platinum electrode of cell constant 1.3. Thermogravimetric cruves were
recorded by heating the sample at the rate of 15 °C min–1, up to 740 °C
on a thermal analyzer at the Regional Sophisticated Instrumentation Cen-
tre, Nagpur.
RESULTS AND DISCUSSION
The Ni(II) chelates were synthesized according to the following
equations:
NiCl2ꢁ6H2O þ 2ðbomppHÞ þ 2L ! ½NiðbomppÞ2ðLÞ2Š þ 2HCl þ 6H2O

440
Maurya, Verma, and Sutradhar

Mixed-Ligand Complexes of Nickel(II)
441
Where L = mpp (1), dpp (4), bzl (5) or bzt (6).
NiCl2ꢁ6H2O þ 2ðA-AÞH þ 2mpp
! ½NiðA-AÞ2ðmppÞ2Š þ 2HCl þ 6H2O
Where (A-A)H = aomppH (2) or mppopH (3)
NiCl2ꢁ6H2O þ 2bomppH þ L-L
! ½NiðbomppÞ2ðL-Lފ þ 2HCl þ 6H2O
Where L–L = adpp (7) or dmspp (8).
The resulting products are non-hygroscopic, coloured solids. The ele-
mental analyses of these complexes are given in Table 1, while the colours,
decomposition temperatures and percent yields are given in Table 2. These
compounds were characterized on the basis of conductance and magnetic
measurements, thermogravimetric analysis, electron spin resonance, infrared
and electronic spectral studies as described below in detail.
Conductance Measurements
The observed molar conductances of these complexes in 10–3 mo-
lar dimethylformamide solutions are found in the range 5–39 ohm–1
cm2mol–1. These data, which are comparable to our previous results,[16]
indicate the non-electrolytic nature of these complexes. Such a non-zero
molar conductance value for each of the complex in the present study is
most probably due to the strong donor capacity of dimethylformamide
which may lead to the displacement of anionic ligands and change of
electrolyte[17] type.
Electron Spin Resonance Spectra
Room temperature X-band ESR spectra of two representative com-
pounds, [Ni(bompp)2(bzl)2] (5) and [Ni(bompp)2(adpp)] (7) (Figures 3 and
4), were recorded on powdered samples using a microwave frequency of
9.45–9.47 GHz with the field set at 3300 G and the scan range of 2.0 KG.
Both parallel and perpendicular features of 61Ni were resolved in both
spectra, which are characteristic of axial symmetry.[18] Nuclear hyperfine
coupling is observed in the g perpendicular regions with four components
clearly resolved. The observed g? and gk values are given in Table 2. The
deviation of g values from the free electron value (2.0036) may be due to
angular momentum contributions[19] in the complexes.

442
Maurya, Verma, and Sutradhar

Mixed-Ligand Complexes of Nickel(II)
443
Figure 3. ESR spectrum of [Ni(bompp)2(bzl)2] (5).
Figure 4. ESR spectrum of [Ni(bompp)2(adpp)] (7).

444
Maurya, Verma, and Sutradhar
Magnetic Measurements
The observed magnetic moments of these mixed-ligand complexes are
given in Table 2. The effective magnetic moments, 3.05–3.23 B.M., support
the presence of two unpaired electrons. These results suggest a spin-free
octahedral[20] symmetry for Ni(II) ion. The possibility of spin-paired octa-
hedral complexes is ruled out as the d8 arrangement in a very strong octa-
hedral fields may result in tetragonal[21] distortion, making the complexes
diamagnetic. The square-planar geometry may be viewed as resulting from
the strong tetragonal elongation of an octahedral geometry. Again, this
geometry leads to diamagnetism. In the tetrahedral geometry, the ground state
term has a built-in orbital contribution and the van Vleck equation[22] pre-
dicts m ꢀ 4.0 B. M. In reality, regular tetrahedron complexes exhibit m ꢀ
3.6–4.0 B. M. This again rules out the possibility of tetrahedral complexes.
Thermogravimetric Analysis
The thermogravimetric analysis of a representative complex
[Ni(bompp)2(dpp)2] (Figure 5) was carried out in the temperature range
Figure 5. TG curve of [Ni(bompp)2(dpp)2] (4).

Mixed-Ligand Complexes of Nickel(II)
445
from room temperature to 700 °C. It shows a mass loss (observed 37%,
theoretical 36.95%) at 340 °C corresponding to the loss of two molecules of
dpp. The mass losses observed before this temperature could not be
correlated. The second weight loss in the temperature range 340–500 °C
(observed 51.4%, theoretical 53%) corresponds to the elimination of two
molecules of bompp. The final residue to be NiO. Thus, the overall ther-
mogravimetric results support the conclusion derived from the infrared
spectral studies given below.
Infrared Spectral Studies
The important IR spectral bands and their tentative assignments are
presented in Table 1. The IR spectra of the three oximino derivatives
(bomppH, aomppH and mppopH) have a strong band at 1690–1710 cm–1
which is assigned to n(C=O) (cyclic). In the spectra of all the complexes,
this band is shifted to the lower frequency side and is observed at 1621–
1650 cm–1, indicating the coordination of the cyclic carbonyl oxygen of the
oxime ligands to the metal ion. This is in agreement with the results
reported elsewhere.[2] The ligands mpp, adpp, dpp and dmspp exhibit a
strong band for n(C=O) (cyclic carbonyl) at 1620–1650 cm–1. The
coordination of the respective ligand to the metal is inferred by the
shifting of this band to lower wave numbers[23] and then appearing in the
region 1535–1551 cm–1. All the complexes display a band in the range
1592–1616 cm–1, which is assigned to n(C=N) (cyclic) of both oximino
derivatives as well as of mpp. Based on our previous results[24] on pyra-
zolone-based ligands, it appears that this mode does not undergo any
appreciable change after complexation, suggesting the reluctance of the
n(C=N) (cyclic) nitrogen of the oximino derivatives and mpp to participate
in bonding. The coordination of the oximino nitrogen in all the complexes
is inferred by the appearance of a strong band due to the n(C=N) mode in
the region 1462–1516 cm–1. This assignment is based on previous reports
of such complexes.[2–4] A medium-intensity band at 1061–1092 cm–1,
assignable to n(N–O), suggests bond formation through the nitrogen of the
oximino group.[2–4]
In the IR spectrum of [Ni(bompp)2(adpp)] (compound 7), the ap-
pearance of two bands at 3300 and 3200 cm–1 are assigned as nas(N–H)
and ns(N–H) for the coordinated amino nitrogen of adpp. The characteristic
n(C–N) (exocyclic) band in free dmspp is observed at 1300 cm–1 which
undergoes a shift[25] to lower wave numbers and appears at 1265 cm–1 in
[Ni(bompp)2(dmspp)] (compound 8), indicating bonding of the exocyclic
nitrogen of dmspp to nickel(II).

446
Maurya, Verma, and Sutradhar
The characteristic band for coordinated tertiary nitrogen of bzl and bzt
is the n(C=N) mode, which should appear above 1600 and 1620 cm–1,
respectively. This band seems to be merged with the n(C=O)(cyclic)
mode of the oximino derivatives at 1628 and 1650 cm–1, respectively.
The imidazole-NH nitrogen and thiazole-S were found to be reluctant
towards coordination.
We have concluded, using the overall IR data, that 1) oximino
derivatives in all the complexes behave as mononegative bidentate ligands,
2) mpp, dpp, bzl or bzt behave as monodentate ligands and 3) adpp or
dmspp behave as bidentate ligands.
Electronic Spectra
The electronic spectra of these compounds (in 10ꢂ3 M DMF solutions)
recorded in the range 350–800 nm, display two absorption bands at 440–
3
3
3
3
460 and 530–560 nm assignable to A2g(F)! T1g(P) and A2g(F) ! T1g
(F), respectively, in agreement with the results reported elsewhere.[26–28]
This suggests an octahedral geometry around Ni(II) ion. Considering the
low[29] molar extinction coefficients (10–30 L molꢂ1 cm–1) of the
electronic spectral bands, the possibilities of tetrahedral and square-planar
geometries are ruled out. An electronic spectral band of a tetrahedral or
square-planar complex has a high[29] molar extinction coefficient ( ꢀ 50–
600 L molꢂ1 cm–1). The electronic spectrum of one representative com-
pound is shown in the Figure 6.
Figure 6. Electronic spectrum of [Ni(bompp)2(mpp)2] (1).

Mixed-Ligand Complexes of Nickel(II)
CONCLUSIONS
447
Satisfactory analytical data as well as all the studies presented above
suggest that the present complexes may be formulated as [Ni(bompp)2(L)2]
(where L = mpp, dpp, bzl or bzt, [Ni(A-A)2(mpp)2] {where (A–A)H = aompp
Figure 7. Proposed octahedral structure of complexes.
(continued )

448
Maurya, Verma, and Sutradhar
Figure 7. Continued.
H or mppopH} and [Ni(bompp)2(L–L)] (where L–L = adpp or dmspp).
Considering the well documented square-pyramidal structure of [Cu(4-
Menp)2(py)][30] (np = o-nitrosophenol, finding a natural place in the family of
carbonyl oximes, py = pyridine) having the oxime nitrogen trans to the other
oxime nitrogen by crystal structure determination, and the monomeric trans-
octahedral structure of [Ni(4-Menp)2(py)2][30] with axial py, a trans-
octahedral structure (having oxime nitrogen trans to oxime nitrogen) as
shown in Figure 7 has been proposed for each of the complexes (1)–(6).
Moreover, following the definitely known cis-octahedral structure of
Na[Fe(Ynp)3] (Y is H2C=CH–C6H4–COO– attached to the 4-position of

Mixed-Ligand Complexes of Nickel(II)
449
the np ring), where the oxime nitrogen is trans to carbonyl oxygen, it is
reasonable to propose a similar cis-octahedral structures for complexes (7)
and (8) as shown in Figure 7.
ACKNOWLEDGMENTS
We are thankful to Professor S. D. Tripathi, Vice-chancellor of this
University, for encouragement, and Professor K. K. Mishra, Head, De-
partment of Chemistry, for laboratory facilities and helpful discussion.
Analytical facilities provided by the Central Drug Research Institute, Luck-
now, India, and the Regional Sophisticated Instrumentation Centre, Indian
Institute of Technology, Chennai, India, are gratefully acknowledged.
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Received: April 21, 1998
Accepted: November 13, 2002
Referee I: H. V. R. Dias
Referee II: K. H. Dahmen