Versatile ligational behavior of azopyrazolone derived from hydralazine

Article abstract of DOI:10.1080/00958972.2012.675431

Five complexes of 3-methyl-4-(phenylhydrazono)-1-phthalazinyl-2-pyrazolin- 5-one (LH) were synthesized. The ligand and complexes were characterized using elemental analyses and various analytical techniques such as IR, UV, NMR, mass spectra, magnetic susc

Full text of DOI:10.1080/00958972.2012.675431

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Versatile ligational behavior of
azopyrazolone derived from
hydralazine
Susannah Seth a & K.K. Aravindakshan b
a P.G and Research Department of Chemistry , Malabar Christian
College , Kozhikode 673001 , Kerala , India
b Department of Chemistry , University of Calicut , Kozhikode
673635 , Kerala , India
Published online: 02 Apr 2012.
To cite this article: Susannah Seth & K.K. Aravindakshan (2012) Versatile ligational behavior of
azopyrazolone derived from hydralazine, Journal of Coordination Chemistry, 65:9, 1493-1503, DOI:
10.1080/00958972.2012.675431
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Journal of Coordination Chemistry
Vol. 65, No. 9, 10 May 2012, 1493–1503
Versatile ligational behavior of azopyrazolone derived
from hydralazine
SUSANNAH SETH*y and K.K. ARAVINDAKSHANz
yP.G and Research Department of Chemistry, Malabar Christian College, Kozhikode
673001, Kerala, India
zDepartment of Chemistry, University of Calicut, Kozhikode 673635, Kerala, India
(Received 14 April 2011; in final form 21 February 2012)
Five complexes of 3-methyl-4 -(phenylhydrazono)-1-phthalazinyl-2-pyrazolin-5-one (LH) were
synthesized. The ligand and complexes were characterized using elemental analyses and various
analytical techniques such as IR, UV, NMR, mass spectra, magnetic susceptibility measure-
ments, and thermal decomposition studies such as TG/DTG. The geometries of the complexes
with special emphasis on the versatile ligational behavior of LH are discussed. All five
complexes have octahedral geometry. In four of the complexes [M(LH)Cl3] where M ¼ Fe(III)/
Cr(III) and [M(LH)(OAc)2H2O] and M ¼ Cu(II)/Ni(II), the ligand was neutral and tridentate.
Another copper complex [CuL(OAc)(H2O)2] in which the ligand is tridentate, mono-anionic
one was also obtained in an excess of aqueous solution. Antifungal studies of the compounds
are also carried out.
Keywords: Hydralazine; 3-Methyl-4 -(phenylhydrazono)-1-phthalazinyl-2-pyrazolin-5-one;
Coordination compounds; Antifungal studies
1. Introduction
1-Phthalazinyl hydrazine (hydralazine) is an antihypertensive under the trade name
apresoline, the first medicinal compound containing a hydrazino group. Druey and
Marxes [1] attributed the antihypertensive action of hydralazine and its derivatives to
the presence of NH2–NH–CR¼N–N¼C5. The ligand (LH) has been synthesized by
diazo coupling aniline with methyl acetoacetate and then cyclizing the product with
hydralazine. The ligational behavior of LH has not been reported yet and hence its
complexes with Cr(III), Fe(III), Ni(II), and Cu(II) have been synthesized and
characterized in the present investigation. Pyrazolones and their complexes exhibit
antimicrobial [2] properties. Therefore, the antifungal studies of the compounds against
Aspergillus niger are also conducted.
*Corresponding author. Email: susannahseth@yahoo.co.in
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2012 Taylor & Francis
http://dx.doi.org/10.1080/00958972.2012.675431

1494
S. Seth and K.K. Aravindakshan
2. Experimental
2.1. Reagents and apparatus
All the chemicals used for syntheses were of Analar grade. Solvents such as methanol,
acetic acid, acetone, dichloromethane and chloroform were purchased from E Merck
and used as received. Commercial ethanol was purified by distillation. Metal salts used
for synthesis of complexes were acetates of Co(II), Ni(II), and Cu(II) and chlorides of
Cr(III) and Fe(III). N-1 phthalazinylazopyrazolone, (LH) was synthesized as reported
[3]. UV-Visible spectra were recorded using 10ꢀ3 mol Lꢀ1 solutions of ligands and
complexes in methanol. The solvent, methanol was taken as a reference and scanning
was from 200 to 800 nm. Infrared (IR) spectra were recorded by making thin KBr discs
with the compound. The scanning range was 4000–400 cmꢀ1. Standardization of the
instrument was done with PS film. Fast atom bombardment (FAB) mass spectra were
obtained using Argon as the FAB gas, accelerating voltage, 10 kV, and m-nitrobenzyl
alcohol as matrix. Electrospray ionization (ESI) mass spectra were measured by
dissolution of the sample in methanol with ESI capillary set at 3.5 kV and voltage 40 V.
Nuclear magnetic resonance (NMR) spectra were obtained using CDCl3 with TMS as
internal standard. Magnetic susceptibilities were determined at room temperature on a
Sherwood Magway susceptibility instrument which was calibrated using
Hg[Co(NCS)4]. Thermogravimetric studies, TG/DTG were carried out in nitrogen
with a heating rate of 10ꢁC minꢀ1. Elemental analyses of C, H, and N were carried out
on a Vario EL III CHNS analyser. Some of the metal percentage analyses were
determined using an ICP-AES spectrometer using argon as the conductor for plasma
state at a core temperature of 9000 K. The other metal percentages were determined by
adopting standard procedure [4] as outlined below. The complex was digested with a
mixture of conc. HNO3 and 70% perchloric acid till all the white fumes subsided. It was
then made to a known volume and used for estimation of metal ions. The metals,
copper (as CuCNS), cobalt (as Hg[Co(NCS)4]), nickel (as nickel dimethyl glyoxime),
and iron (as Fe2O3) were estimated by gravimetric methods. Chromium was estimated
spectrophotometrically [5] after oxidizing to dichromate. Chloride has been estimated
by Volhard’s method by fusion with Na2CO3 followed by decomposition in HNO3.
2.2. Synthesis
2.2.1. Synthesis of methyl-2-phenylhydrazono-3-oxobutyrate. Aniline (0.01 mol) was
diazotized by dissolving in 1 : 1 HCl and adding NaNO2 (0.01 mol) solution keeping the
temperature at ꢂ0–5ꢁC. This diazonium chloride solution was added dropwise with
stirring to a well-cooled ethanolic solution (0.01 mol) of methyl acetoacetate. The pH was
kept at 7. The orange oily liquid was stirred for 0.5 h keeping the temperature low and the
solidified product was filtered, washed with water, dried and recrystallized from meth-
anol. This product was dried over anhydrous MgSO4 and verified for purity (TLC).
2.2.2. Synthesis of LH. Methyl-2-phenylhydrazono-3-oxobutyrate (phenylazo
methyl acetoacetate) solution (0.003 mol) was prepared in glacial acetic acid.
Hydralazine hydrochloride (0.003 mol) in minimum distilled water was added dropwise
to the solution. One drop of conc. H2SO4 was also added and the mixture was kept

Azopyrazolone
1495
under reflux for 10 h on a steam bath. The product was checked for cyclization using
neutral FeCl3 solution which imparts a deep red color indicating the presence of
pyrazolone (aromatic-OH) moiety. The ligand thus obtained (figure 1) was filtered,
dried, purified by recrystallization from methanol, and kept in a desiccator over
anhydrous MgSO4.
2.2.3. Synthesis of metal complexes. The metal complexes were synthesized by mixing
solutions of metal salts and ligand in methanol in 1 : 2 or 1 : 3 molar ratio for divalent
and trivalent metals, respectively. To a boiling methanolic solution of the ligand
(0.02 mol) an aqueous solution of the metal ion (0.01 mol) was added dropwise. The
resultant mixture was refluxed on a steam bath for 3 h. The precipitated complexes were
filtered while warm, washed with water and acetic acid successively, and dried over
anhydrous MgSO4 in a desiccator. Copper(II) gave two complexes, different in color,
stoichiometry, spectral, and TG data [6]. The brown complex was obtained when the
solvent for the ligand was diluted to a 25% solution with water. Both copper complexes
were analyzed and characterized. All the complexes were paramagnetic.
2.3. Antifungal studies
The antifungal activities of the compounds were evaluated by the well diffusion method
against the fungus A. niger, cultured on potato dextrose agar. The stock solution
(10ꢀ2 mol Lꢀ1) was prepared by dissolving the compounds in ethanol and the solutions
were serially diluted to find minimum inhibitory concentration values. The concentra-
tion of the compounds used in this study was 2000 ppm. In a typical procedure, a well
was made on the agar medium inoculated with microorganisms. The well was filled with
the test solution using a micropipette and the plate was incubated 24 h for the fungus
at 30ꢁC. During this period, the test solution diffused and growth of the inoculated
Figure 1. Schematic representation of the preparation of LH.

1496
S. Seth and K.K. Aravindakshan
microorganisms was affected. The inhibition zone was developed and the diameter
measured. The experiment was done in triplicate for accuracy.
3. Results and discussion
Arylazo pyrazolin-5-ones are shown [7] to exist in the hydrazone form. On the basis of
detailed investigations, LH was also assigned a hydrazone structure. Elemental
percentages of the compound were in good agreement with the molecular formula
C18N6OH14. The analytical and electronic spectral details of the compounds are shown
in table 1.
3.1. Molar conductance
The molar conductances of the metal complexes in methanol were below
14.00 Ohmꢀ1 cm2 molꢀ1 showing that they were non-electrolytes. A value of 60–
115 Ohmꢀ1 cm2 molꢀ1 is expected [8] for a 1 : 1 electrolyte.
3.2. Electronic spectral studies and magnetic behavior
The electronic spectrum of the ligand does not have an absorption band at ꢂ270–280,
characteristic of an azo structure. Hence it must exist in the hydrazone form. Electronic
spectra of the compounds predict geometry to some extent. The extinction coefficients
are given in (mol L )
ꢀ1 ꢀ1 cmꢀ1. The spectrum of the ligand was characterized by two
bands; an intense absorption at 308 nm (E ꢂ 104) due to ꢀ–ꢀ* transition and a weak to
moderate absorption band at 380 nm (E ꢂ 600) due to the n–ꢀ* transition. The
complexes were paramagnetic with ꢁeff values expected for the proposed geometry.
Cr(III) complex was dark green. The magnetic moment of 3.72 B.M. suggests an
octahedral geometry [9] and electronic spectral bands at 400 nm (E ¼ 54) due to
4
4
4
4A2g(P) ! T1g(F) and 576 nm (E ¼ 15,000) due to A2g(F) ! T2g(F) transitions [10]
gave additional support to octahedral complex. Fe(III) complex showed spectral bands
which overlapped with CT bands. Bands at 630 nm (E ¼ 55) could be due to
6A1g ! T1g transition and that at 412 nm (E ¼ 50) may be assigned [11] to
4
6A1g ! T2g. The magnetic moment value of 5.91 B.M. indicated high-spin octahedral
4
geometry. The spectrum of Ni(II) complex had bands at 386 nm (E ¼ 550) and 676 nm
(E ¼ 175) due to 3A2g ! T1g(P) and 3A2g ! T1g(F) transitions, respectively. The ꢂ2/ꢂ1
ratio for the chelate is 1.73, in the usual range (1.6–1.82) for octahedral Ni(II). The
magnetic moment value of 2.95 B.M. also pointed to octahedral geometry for Ni(II)
complexes. Assignments of Cu(II) d–d transitions are more complicated because of the
relatively low symmetry (i.e., less than cubic). However, in cubic environment, the d9
configuration makes Cu(II) subject to Jahn–Teller distortions, giving an unsymmetrical
3
3
2
2
2
2
2
2
band. Three transitions, B1g ! A1g, B1g ! B2g, and B1g ! Eg, are possible in
octahedral Cu(II), but only two transitions are observed at 514 nm and 314 nm for
[Cu(LH)(OAc)2H2O]. The electronic spectra and magnetic moment suggest octahedral
Cu(II). The probable assignments are 514 nm (E ¼ 240) a charge transfer band and
314 nm (E ¼ 360), probably a ligand-based transition. The magnetic moment of the

Azopyrazolone
1497

1498
S. Seth and K.K. Aravindakshan
Table 2. Important IR spectral bands (cmꢀ1) and their assignments.
Compound
ꢂ(OH)water
ꢂ(NH)
ꢂC¼O
ꢂC¼N
ꢂM–N
ꢂM–O
LH
[Cr(LH)Cl3]
[Fe(LH)Cl3]
[Ni(LH)(OAc)2H2O]
[CuL(OAc)(H2O)2]
[Cu(LH)(OAc)2H2O]
3177b
3175b
3167b
3180b
nil
1698s
1556s
1554s
1550s
1547s
1547s
1454m
1498m
1507m
1499m
1498m
1498m
557m
578m
581m
582m
582m
507m
510m
509m
490m
507m
3419b
3420b
3422b
3174b
s, sharp; b, broad; m, medium.
complex was 1.76 B.M. The brown CuL(OAc)(H2O)2 exhibited normal magnetic
moment of 2.1 B.M., slightly higher than spin only value (1.73 B.M.), indicating the
distorted octahedral geometry [12]. This complex shows broad asymmetric bands in the
2
2
region 680 nm (E ¼ 50) and at 512 nm (E ¼ 250) assignable to B1g ! A1g and charge
2
2
transfer transition, respectively. The former band may be due to Eg ! T2g due to
Jahn–Teller effect, suggesting a distorted octahedral geometry for these complexes. The
value of transition ratio ꢂ2/ꢂ1 is 1.32.
3.3. IR spectral studies
The IR spectrum showed a broad band at 3177 cmꢀ1 assigned to NH stretch (hydrogen
bonded) as observed in phenylhydrazono ketones. Two strong bands at 1698 cmꢀ1
indicated [13] C¼O (exocyclic) conjugated with C¼N. The band at 1546 cmꢀ1 could be
attributed to 4C–NH–N ¼ (not cyclic) [14]. In the IR spectra of the complexes, the
band at ꢂ1550 cmꢀ1 is a clear indication of chelated C¼O, suggesting involvement of
carbonyl oxygen of pyrazolone in coordination. The band at 1698 cmꢀ1 in the ligand
spectrum disappears in spectra of the complexes. The bands around 1400 cmꢀ1 indicate
C¼N; lower bands at 580 and 520 cmꢀ1 were due to ꢂM–N and ꢂM–O, respectively [15].
The important IR spectral bands and their assignment are entered in table 2.
3.4. 1H NMR spectrum
1
The H NMR spectrum of LH shows a low-field signal at ꢂ14 ppm for acidic proton.
Other signals were at 7.47, 7.45, 8 ppm due to phthalazinyl protons as shown in the
spectrum, very much in accord with reported [16] values. Other resonances were at
7.25–7.30 ppm (unsymmetrical pattern – phenyl) and 2.5 ppm (ꢀCH3). The absence of a
signal at ꢂ6.48 ppm (C-4 proton) [17] also indicated a hydrazone structure.
3.5. Mass spectra
The mass spectrum of LH showed all the expected peaks. The molecular ion peak was
present at m/z 330, though with a low-percentile value. It is expected to have a low value
due to the bulky pendant-like phthalazinyl (C8H5N2) which gets easily detached. All the
other expected peaks were present in the spectrum at m/z 93 (b.p., C6H8NþH2), 77

Azopyrazolone
1499
(C6Hþ5 ), 128 (C8H5N2þ), 203 (M–C8H5N2)þ, etc. The base peak and m/z 93 and the
absence of (M–N2) peak clearly point to a hydrazone [18] structure rather than an azo
structure. Based on the mass spectrum, the structure of LH has been confirmed. Mass
spectra of the two copper complexes showed the parent ion at 488 and 528 for the
brown colored and green colored complexes, respectively. Both spectra showed
fragment peaks due to the detachment of C8H5N2(phthalazinyl) and
C4N2OH3(pyrazolonyl). The mass spectrum of the brown colored copper complex
agreed well with the structural formula [CuL(OAc)(H2O)2]. The values of prominent
m/z peaks were 488 (Mþ), 469 (M–H2O), 450 (M–twoH2O), 301 [M–(C8H5N2 þ OAc)],
279
(M–C8H5N2–OAc–H2O),
203
[M–(C8H5N2 þ C4N2OH3 þ OAc)],
243
[M–(C8H5N2 þ C5N2H3–H2O)]
–
base peak, 185 [M–(C8H5N2 þ C5N2H3 þ H2O–
OAc)], 92 (C6H5NþH), 77 (C6Hþ5 ), etc. Additional M þ 1, M þ 2, etc. peaks were
also present. The mass spectrum of green copper complex agreed well with the
structural formula [CuLH(OAc)2H2O]. The prominent m/z values are 528 (Mþ),
474 (M–CH3COO),
416
(M–2xCH3COO),
154-Basepeak
[þM–
(2xCH3COO þ H2O þ C8N2H5 (phthalazinyl) þC6H5N2], 107 (C6H5Nþ2 ), 78(C6H5) .
3.6. Thermal data
The decomposition patterns of [CuL(OAc)(H2O)2] and [Cu(LH)(OAc)2H2O] are
summarized in table 3. As can be observed from the TG traces, both Cu(II) complexes
are stable to 200ꢁC. In both cases, the coordinated H2O and the CH3COOꢀ were lost at
about same temperature, ꢂ200ꢁC. The complex in which LH was a mono-anionic
ligand (L) retained this ligand to a temperature of 900ꢁC. This was expected because of
the stronger covalent attachment of L to Cu(II) in the former than a dative bond made
by LH to Cu(II) in the latter. The decomposition patterns agree with the structural
formulas suggested for the Cu(II) complexes.
3.7. Antifungal activity
All the compounds synthesized have been tested for their antifungal activity against
A. niger. Aspergillus niger is less likely to cause human disease than some other
Aspergillus species, but, if large amounts of spores are inhaled, a serious lung disease,
aspergillosis, can occur. Aspergillus niger is also one of the most common causes of
otomycosis, a fungal ear infection, which can cause pain, temporary hearing loss, and,
in severe cases, damage to the ear and tympanic membrane. Currently, the available
drug [19] is amphotericin B. In this study, amphotericin B has been used as control.
Amphotericin B is also commonly used in tissue cultures to prevent fungi from
contaminating cell cultures. Mammalian and fungal membranes both contain sterols, a
primary membrane target for amphotericin B. Because mammalian and fungal
membranes are similar in structure and composition, this is one mechanism by which
amphotericin B causes cellular toxicity. The objective of the present antifungal study
was to find the possibility of another potential drug comparable with the control but
less toxic. The results are presented in table 4. All the synthesized compounds exhibited
some antifungal activity. All the complexes, except that of Ni(II), showed more activity
than ligand. These complexes also disturb the respiration process of the cell and thus
block the synthesis of proteins, which restricts further growth of the organism. The

1500
S. Seth and K.K. Aravindakshan

Azopyrazolone
1501
Table 4. Antifungal activities of the compounds against A. niger.
Inhibition zone (mm)
Compound
Trial 1
Trial 2
Trial 3
LH
[Cr(LH)Cl3]
[Fe(LH)Cl3]
[Ni(LH)(OAc)2(H2O)]
[CuL(OAc)(H2O)2]
[Cu(LH)(OAc)2H2O]
Amphotericin B
Ethanol (solvent)
19
23
26
15
20
35
30
20
20
22
25
16
21
35
30
21
20
22
26
14
20
36
31
20
Figure 2. Tentative structure of the Cu(II) complex with L.
Figure 3. Tentative structures of M ¼ Fe(III)/Cr(III) complexes.
green copper chelate, [Cu(LH)(OAc)2H2O], was better than the control medicine
against the fungal strain.
4. Conclusion
From the above discussion, the versatile nature of LH is obvious. Phenylazo
pyrazolones can be tridentate when N-1 of the pyrazolone has a substituent with
suitable hetero atom. Thus in the present case nitrogen of phthalazinyl takes part in

1502
S. Seth and K.K. Aravindakshan
Figure 4. Tentative structures of M ¼ Ni(II)/Cu(II) complexes.
coordination making it a tridentate neutral ligand. One exception has been observed in
the case of brown copper(II) complex [CuL(OAc)(H2O)2] in which it acts as a tridentate
mono-anionic ligand. Both structures have been confirmed by mass spectral and TG
analyses. Therefore, based on the different physico-chemical evidence, the complexes
are assigned octahedral geometry (figures 2–4). The green copper chelate
[Cu(LH)(OAc)2H2O] has more activity than the current drug against A. niger. In vivo
studies can be performed to develop the pharmaceutical compatibility.
Acknowledgments
The authors thank the Department of Chemistry, University of Calicut for IR and
magnetic susceptibility measurements. Other facilities provided, CHN, ICP-AES, TG/
DTG by SAIF, Kochi, ESI mass spectra by CDRI Lucknow, 1H NMR spectrum by the
Department of Chemistry, Madurai Kamaraj University are also gratefully acknowl-
edged. Susannah Seth thanks the UGC for teacher fellowship.
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