Novel bioactive vic-dioxime ligand containing piperazine moiety: Synthesis, X-ray crystallographic studies, 2D NMR applications and complexation with Ni(II)

Article abstract of DOI:10.1016/j.poly.2010.08.006

A new vic-dioxime ligand bearing an important pharmacophore substituent, anti-1-(4-benzylpiperazine-1-yl) phenylglyoxime (LH₂) (Scheme 1), has been synthesized and its nickel(II) complex was obtained by the reaction of NiCl₂·6H₂

Full text of DOI:10.1016/j.poly.2010.08.006

Polyhedron 29 (2010) 2991–2998
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Novel bioactive vic-dioxime ligand containing piperazine moiety: Synthesis,
X-ray crystallographic studies, 2D NMR applications and complexation with Ni(II)
Aytek Yılmaz a, Bilge Taner a, Pervin Deveci a, Aslıhan Yılmaz Obalı a, Ug˘ur Arslan b, Ertan Sßahin c,
a
a,
⇑
_
H. Ismet Uçan , Emine Özcan
a Selcuk University, Faculty of Science, Department of Chemistry, Konya, Turkey
b Selcuk University, Selcuklu Medical Faculty, Department of Clinical Microbiology, Konya, Turkey
c Atatürk University, Faculty of Arts and Sciences, Department of Chemistry, Erzurum, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A new vic-dioxime ligand bearing an important pharmacophore substituent, anti-1-(4-benzylpiperazine-
1-yl) phenylglyoxime (LH2) (Scheme 1), has been synthesized and its nickel(II) complex was obtained by
the reaction of NiCl2ꢀ6H2O and the ligand. The characterization of the newly formed compounds was per-
formed by elemental analysis, FT-IR, 1D NMR (1H, 13C, DEPT), 2D NMR (HMBC), ESI mass-spectrometry,
TG/DTA, X-ray crystallography. The antibacterial activity was also studied against Staphylococcus aureus
ATCC 25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Lactobacillus acidophilus
RSHM 06029, Escherichia coli ATCC 25922, E. coli ATCC 35218, Pseudomonas aeruginosa ATCC 27853. The
antimicrobial test results indicated that all the compounds have mild antibacterial activity against both
Gram negative and Gram positive bacterial species.
Received 6 July 2010
Accepted 7 August 2010
Available online 18 August 2010
Keywords:
vic-Dioxime
Nickel(II) complexes
Piperazine moiety
1D and 2D NMR
Crystal structure
Antimicrobial activity
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
electrodes [15], and voltammetry [16–18] have been used to study
Ni(II)–oxime complexes. Nickel also finds a place in a variety of
vic-Dioximes and their metal complexes constitute a class of
compounds which have attracted considerable attention for their
rich analytical and electrochemical properties [1,2] and their po-
tential applications in many important chemical processes in the
fields of medicine [3], bioorganic systems [4], catalysis [5] and
metallurgy [6]. In view of the excellent properties of the vic-diox-
ime ligands, several groups including our own have reported the
syntheses and X-ray crystal structure analyses of a series of com-
plexes of these ligands with transition metal ions such as nickel(II),
copper(II), cobalt(II), cobalt(III) [7,8]. Although the cobaloximes
have acquired an independent research field among the oxime
complexes because of their usage as model compounds for the
study of vitamin B12 coenzyme [9–11], the nickel oximes are also
of continuing interest since their first discovery by Tschugaev.
Many papers that describe the spectral and the structural proper-
ties of nickel oximes [8,12] have appeared in recent years and
many analytical procedures such as spectrophotometry [13],
thermal decomposition [14], potentiometry using nickel selective
thin film materials, often alloyed with other elements as a contact
material in semiconductor devices [19].
Like oximes, the chemical properties of piperazine derivatives
have been intensively investigated in several research areas be-
cause of their versatile metal complexing capabilities [20] and
their fundamental pharmacological applications. Piperazines and
substituted piperazines are important compounds that exhibit var-
ious biological activity ranging from antiemetic to anxiolytic, to
opioid agonists, or to bradykinin antagonists [21,22]. Due to the
broad pharmacological interest in oxime and piperazine deriva-
tives and their great potential for important applications, attach-
ment of piperazine moiety on a vic-dioxime compound can lead
to new vic-dioxime derivatives with important pharmacological
properties (Scheme 1). As an extension of this idea of this present
contribution, we have enlarged our work to design and to success-
fully synthesize a new vic-dioxime ligand bearing piperazine moi-
ety and its Ni(II) complex as a new class of synthetic antimicrobial
agents a long with their in vitro antimicrobial activity. In this pa-
per, LH2 and its Ni(II) complex are novel and have been character-
ized using elemental analysis, FT-IR, 1D NMR (1H, 13C, DEPT), 2D
NMR (HMBC), ESI mass-spectrometry, TG/DTA, X-ray crystallogra-
phy. To the best of our knowledge, this is the first manuscript
which includes synthesis, antibacterial activity and enhanced char-
acterization of LH2 and its Ni(II) complex.
⇑
Corresponding author. Tel.: +90 332 2233859.
E-mail address: emineozcann@gmail.com (E. Özcan).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.08.006

2992
A. Yılmaz et al. / Polyhedron 29 (2010) 2991–2998
Scheme 1. Routes for the synthesis of the ligand and its Ni(II) complex.
Table 1
2. Experimental
Crystal data and structure refinement
2.1. Physical measurements
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C19H22N4O2
286.4
293(2)
0.71073
Monoclinic
P21/c
Elemental analyses (C, H, and N) were determined using a
LECO-932 CHNSO model analyzer. 1H NMR and 13C NMR spectra
were recorded on a Bruker GmbH Dpx-400 MHz High Performance
Digital FT-NMR spectrometer with DMSO-d6 as the solvent with
Me4Si as an internal reference. The IR spectra of solid samples were
recorded in a range from 600 to 4000 cmꢁ1 on a Perkin–Elmer
Spectrum 100 FT-IR spectrometer (Universal/ATR Sampling Acces-
sary). Thermal measurements were carried out on a Setaram Lab-
sys TG–DTA Instruments thermal analysis system in dinitrogen
atmospheres, applying a heating rate of 10 °C minꢁ1 in a tempera-
ture range from 25 to 1073 °C.
15.1911(4)
5.9128(2)
20.0082(5)
90
99.329(5)
90
719.8(12)
4
1.27
0.085
719.8
2.1–26.4°
ꢁ19 6 h 6 18,
ꢁ6 6 k 6 7,
ꢁ25 6 l 6 25
34,255
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢁ1
F(0 0 0)
)
2.2. X-ray crystallography
h Range for data collection
Index ranges
For the crystal structure determination, the single-crystal of the
compound LH2 was used for data collection on a four-circle Rigaku
R-AXIS RAPID-S diffractometer (equipped with a two-dimensional
Reflections collected
area IP detector). The graphite-monochromatized Mo K
(k = 0.71073 Å) and oscillation scans technique with
a
radiation
Independent reflections (Rint
Maximum and minimum transmission
Refinement method
)
3683 (0.167)
0.927 and 0.873
full-matrix least-squares on F2
1704/0/228
0.971
R1 = 0.065, wR2 = 0.163
0.201 and ꢁ0.213
D
x = 5° for
each image were used for data collection. The lattice parameters
were determined by the least-squares method on the basis of all
Data/parameters
Goodness-of-fit (GOF)on F2
reflections with F2 > 2 (F2). Integration of the intensities, correc-
r
R indices [F2 > 2
r
(F2)]
Largest difference in peak and hole (e Åꢁ3
)
tion for Lorentz and polarization effects and cell refinement were
performed using CrystalClear (Rigaku/MSC Inc., 2005) software
[23]. The structure was solved by direct methods using SHELXS-97
[24] and refined by a full-matrix least-squares procedure using
the program SHELXL-97 [24]. H atoms were positioned geometrically
and refined using a riding model. The final difference Fourier maps
showed no peaks of chemical significance. Relevant crystal data
and details of the structure determinations are given in Table 1.
Crystallographic data (excluding structure factors) for the struc-
tures reported in this article have been deposited with the Cam-
bridge Crystallographic Data Center with supplementary
publication number CCDC 776609. Copies of the data can be ob-
tained free of charge on application to CCDC, 12 Union Road, Cam-
bridge CB2 1EZ, UK (fax: +44 1223 336 033; e-mail:
deposit@ccdc.cam.ac.uk).
2.3. Antibacterial activity
The minimal inhibitory concentration (MIC) was determined by
broth microdilution methods according to CLSI (Clinical and Labo-
ratory Standards Institute) guidelines (2009) in MHB (Becton Dick-
inson, Sparks, MD) with an inoculum of approximately
5 ꢂ 105 colony-forming units (CFU)/ml. The in vitro antibacterial
activity of the compounds was evaluated against standard strains;
Staphylococcus aureus ATCC (American Type Culture Collection)
25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC
29212, Lactobacillus acidophilus RSHM 06029, Escherichia coli ATCC
25922, E. coli ATCC 35218, Pseudomonas aeruginosa ATCC 27853.

A. Yılmaz et al. / Polyhedron 29 (2010) 2991–2998
2993
The antibacterial was performed in Mueller–Hinton broth (MHB)
(Becton Dickinson, Sparks, MD). All the synthesized compounds
were weighed (10.24 mg) and dissolved in DMSO (10 ml) to pre-
in common organic solvents such as methanol, dichloromethane
and DMSO was washed with cold water. Yield: 78%. M.p.: 238 °C.
Anal. Calc. for C38H42N8O4Ni (732): C, 62.29; H, 5.74; N, 15.30.
pare the stock solutions. The serial dilution from 256 to 0.25
lg/
Found: C, 62.22; H, 5.81; N, 15.25%. FT-IR (m
max/cmꢁ1): 3036 (Ar–
ml was made in a 96-wells plate. To each well 100 l of a bacterial
l
CH), 2942–2819 (CH), 1770 (O–Hꢀ ꢀ ꢀO), 1567 (C@N), 1494 and
1389 (CH), 1004 (N–O); 1H NMR (DMSO-d6): d (ppm) = 16.06 (s,
2H, O–Hꢀ ꢀ ꢀO), 7.43–7.18 (m, 20H, Ar–H), 3.27 (s, 4H, Ar–CH2–N),
2.97 (t, 8H, –CH2–), 2.15 (t, 8H, –CH2–); 13C NMR (DMSO-d6): d
(ppm) = 152.45 ((CH2)2N–C@N–OH), 145.21 Ar–C@N–OH, 138.39,
131.51, 129.98, 129.80, 129.43, 128.81, 128.52, 127.61 (Ar–C),
62.59 (Ar–CH2–N), 52.96 (–CH2–), 49.19 (–CH2–).
suspension, obtained from a 24 h culture, containing ꢃ5 ꢂ 105 col-
ony-forming units (CFU)/mL was added. The plate was incubated at
35 °C for 24 h. The data were reported as MICs, the lowest concen-
tration of antibiotics and compounds inhibiting visible growth
after 24 h of incubation at 35 °C. For quality control of the method
ampicilline (IE Ulugay, Turkey), Genta (IE Ulugay, Turkey) and Pip-
eracilline (Wyeth) were tested as antimicrobial agent. These exper-
iments were carried out in duplicate.
3. Results and discussion
2.4. Synthesis
3.1. Crystal structure of ligand
anti-Chlorophenylglyoxime was synthesized as described [25].
Other reagents purchased from Merck, were reagent grade and
were used as received.
The X-ray structure of the ligand was determined in order to
confirm the assigned structure and to establish conformation of
the molecule. ORTEP drawing of the structure with atomic num-
bering is shown in Fig. 1, and the selected geometric parameters
are given in Table 2. Ligand crystallizes in the monoclinic space
group P21/c with four molecules in the unit cell. The asymmetric
unit contains one molecule. The molecular structure was formed
2.4.1. Synthesis of the ligand LH2 (1)
1-Benzylpiperazine (0.35 mL, 2 mmol) was dissolved in abso-
lute ethanol (15 mL) and the solution containing anti-chloro-
phenylglyoxime (0.19 g, 1 mmol), in absolute ethanol (20 mL)
was added slowly to this solution at room temperature with con-
stant stirring. The reaction mixture was stirred continuously for
3 h at room temperature. Water was added drop-wise until a white
precipitate formed. The precipitated ligand was filtered off, washed
with cold water, dried and crystallized from water–ethanol (1:3).
The ligand is soluble in dichloromethane, ethanol, DMSO and
DMF. Yield: 53%. M.p.: 170 °C. Anal. Calc. for C19H22N4O2 (338): C,
67.46; H, 6.51; N, 16.56. Found: C, 67.41; H, 6.49; N, 16.52%. FT-
Table 2
Selected bond lengths (Å) and angles (°), and hydrogen bonds for the ligand.
Bond lengths
N2–C9
N3–C12
N4–C13
N1–C7
1.462(4)
1.276(5)
1.278(5)
1.479(4)
N2–C12
N1–C11
N3–O2
C6–C7
1.405(4)
1.469(5)
1.412(4)
1.504(4)
Bond angles
C9–N2–C12
N4–C13–C12
C6–C7–N1
IR (m
max/cmꢁ1): 3233 (O–H), 3033 (Ar–CH), 2947–2807 (CH),
1630 (C@N), 1494 and 1353 (CH), 989 (N–O); MS (EIMS), m/z:
115.3(3)
110.0(3)
120.8(4)
N4–C13–C14
C14–C13–C12
O1–N4–C13
128.5(3)
121.4(3)
113.4(4)
320 [MꢁOH2]+, 291, 103, 77.51; 1H NMR (DMSO-d6):
d
(ppm) = 11.74 (s, 1H, O–H), 9.24 (s, 1H, O–H), 7.73–7.19 (m, 10H,
Ar–H), 3.43 (s, 2H, Ar–CH2–N), 3.07 (t, 4H, –CH2–), 2.31 (t, 4H, –
CH2–); 13C NMR (DMSO-d6): d (ppm) = 155.52 ((CH2)2N–C@N–
OH), 148.11 (Ar–C@N–OH), 138.54, 131.54, 129.84, 129.73,
129.54, 128.86, 128.72, 127.64 (Ar–C), 62.87 (Ar–CH2–N), 52.70
(–CH2–), 46.60 (–CH2–).
Hydrogen bonds
D–Hꢀ ꢀ ꢀA
d(Hꢀ ꢀ ꢀA)
0.82
0.82
d(Dꢀ ꢀ ꢀA)
3.229(4)
2.837(5)
2.858(4)
<(DHA)
154
132
O1–Hꢀ ꢀ ꢀN2a
O1–Hꢀ ꢀ ꢀN4a
O2–Hꢀ ꢀ ꢀN1b
0.82
171
a
Symmetry transformations used to generate equivalent atoms: ꢁx, 2 ꢁ y, ꢁz.
Symmetry transformations used to generate equivalent atoms: ꢁx, 1/2 + y, 1/
b
2 ꢁ z.
2.4.2. Synthesis of Ni(II) complex (2)
An ethanol solution (5 mL) of the NiCl2ꢀ6H2O (0.05 g,
0.21 mmol) was added to an ethanol solution (10 mL) of
1
(0.14 g, 0.42 mmol) while stirring at 50 °C for 15 min. A distinct
change in color and a decrease in the pH value (ꢃ2) of the solution
were observed. Potassium hydroxide (0.42 mmol) in ethanol
(20 mL) was added (pH ꢃ6) and the reaction mixture was cooled
to room temperature. The red product was precipitated at room
temperature and filtered off and then the precipitate that is soluble
Fig. 1. The molecular structure of the ligand showing the atom numbering scheme.
The thermal ellipsoids are plotted at the 40% probability level.
Fig. 2. Packing diagram with the H-bonding geometry of ligand down the b-axis.

2994
A. Yılmaz et al. / Polyhedron 29 (2010) 2991–2998
Fig. 3. 1H NMR spectrum of ligand in DMSO-d6 at 25 °C (400 MHz).
Fig. 4. The 13C NMR and DEPT spectra of ligand.
by combining phenyl, ethanedial dioxime, piperazine and benzyl
groups respectively. As expected, the phenyl moieties are planar.
The dihedral angles between the mean planes of two phenyl rings
are 21.7(1)°. Piperazine (N1/C8/C9/N2/C10/C11) ring adopts the
chair conformation. The puckering parameters of this ring are
is the characteristic six-membered ring arrangement in oximes,
resulting in classical oxime dimmers. With the other oxime group,
the crystal structure of the ligand formed an oximeꢀ ꢀ ꢀN (pipera-
zine) motif that generated an infinite chain which is parallel to
the c-axis (Fig. 2).
Q = 0.583(3) Å, h = 176.5(3)°,
U = 184(5)° [26]. N1 and N2 atoms
are displaced from the C8/C9/C10/C11 mean plane by 0.340(2)
and ꢁ0.306(2) Å. Piperazine itself has the ideal chair conformation
with N–H bonds in the equatorial positions [27]. The glyoxime
moiety is not planar and the bond lengths in the oxime group
are in harmony with the values in the previously solved structure
[28]. Oxime groups possess stronger hydrogen-bonding capabili-
ties than alcohols, phenols and carboxylic acids [29]. The hydro-
gen-bond systems in the crystals of oximes have been analyzed
and a correlation between a pattern of hydrogen-bonding and N–
O bond lengths have been suggested [30]. In parallel, hydrogen
bonds are the main driving forces for oxime non-covalent interac-
tions and oxime functionality can be stereoelectronically adjusted
for precise directed assembly of homomeric intermolecular oxi-
meꢀ ꢀ ꢀoxime and oximeꢀ ꢀ ꢀN–heterocycle molecular motifs [31].
Our compound formed a head-to-head R22(6) motif as well, which
3.2. FT-IR analysis of ligand and its Ni(II)complex
In the IR spectrum of ligand, the strong
(NO) characteristic stretching vibrations bands were observed at
3233, 1630, and 989 cmꢁ1, respectively. In the IR spectrum of Ni(II)
m(OH), m(C@N) and
m
complex, disappearance of the sharp intense m(–NOH) stretching
vibration band at 3233 cmꢁ1. The IR spectra of complex showed
a weak deformation band at ca. 1770 cmꢁ1, indicative of intramo-
lecular hydrogen bonded bending vibrations (O–Hꢀ ꢀ ꢀO) associated
with the square-planar vic-dioxime complexes. As
m
(NO) stretching
vibrations of ligand shift to slightly higher frequencies, the
m
(C@N)
stretching vibrations shift to slightly lower frequencies, and it indi-
cates the coordination of the azomethine nitrogen to the metal
center. Yuksel et al. [8] showed that vic-dioxime ligand form
square-planar Ni(II) complex in which the ligands chelate via nitro-

A. Yılmaz et al. / Polyhedron 29 (2010) 2991–2998
2995
Fig. 5. 2D HMBC spectrum of ligand.
Table 3
13C NMR, DEPT and HMBC spectral data and assignments.
Chemical shifts
DEPT
HMBC
Assignments
155.52
148.11
138.54
131.54
129.84–128.72
127.64
62.87
C
C
C
C
CH
CH
CH2
CH2
CH2
9.24
11.74
C8
C9
C4
C10
7.40, 3.43
7.70, 7.37
7.19–7.73
7.25, 3.43
7.25, 3.07
3.43, 3.07
2.31
C11, C13, C2, C1,C12
C3
C5
C6
C7
52.70
46.60
gen and oxygen donor atoms. IR band in 510 cmꢁ1 region was
attributed to (Ni–N). The FT-IR spectra of the compounds exhibited
two medium intensity absorption signals at between 3000 and
3100 cmꢁ1 result from phenyl group. Additionally, the strong and
very strong CH2 stretching bands were observed at 2944 and
2824 cmꢁ1
.
In order to study the binding properties of the dioxime ligand and
the metal ion in complex, the IR spectrum of the free oxime ligand is
compared to the Ni(II) complex. In the IR spectrum of the ligand,
O–H stretching vibration is observed at 3233 cmꢁ1 as a broad
absorption band. C@N and N–O stretching vibrations are obtained
at 1630 and 989 cmꢁ1 respectively. In the IR spectrum of Ni(II) com-
plex, disappearance of the sharp intense
m(–NOH) stretching vibra-
tion band at 3233 cmꢁ1, shift in the
m(C@N) stretching band to lower
Fig. 6. The Ni(II) complex of (a) 1H NMR spectrum and (b) 13C NMR spectrum.

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A. Yılmaz et al. / Polyhedron 29 (2010) 2991–2998
to –CH2 protons (Ar–CH2–N) are observed at 3.43 ppm as a singlet
while the other –CH2 protons are observed at 2.31 and 3.07 ppm as
a triplet. Aromatic protons in the structure are also observed at
7.19–7.73 ppm as a multiplet. (Fig. 3).
13C NMR spectrum shows 13 different carbon atoms which are
consistent with the proposed structure of ligand on the basis of
molecular symmetry. In the 13C NMR, carbon resonances of
hydroxyimino groups (–C@N–OH) are observed at 155.52 and
148.11 ppm as expected for vic-dioximes [8]. Distortionless
enhancement of NMR signals by polarization transfer (DEPT) is
used to discriminate better different types of carbons present in li-
gand. The DEPT spectrum (Fig. 4) gives the CH2 peaks at 46.60,
52.70, 62.87 ppm and the CH peaks at 127.64, 128.72, 128.86,
129.54, 129.73, 129.84 ppm. The carbons recorded in 13C NMR
but are nulled in DEPT are carbons without any attached
hydrogens.
More detailed information about the structure of ligand is pro-
vided by 2D HMBC spectrum (Fig. 5) and specific assignments of
protons and carbons are made as follows (Table 3).
The HMBC spectrum (Fig. 5) shows that Ha and Hb protons ex-
hibit long range coupling with hydroxyimino carbons at 155.52
(C8) and 148.11 (C9) ppm, respectively. Other correlations are also
in accordance with the proposed structure (Table 3).
3.3.2. 1H and 13C NMR spectrum of the Ni(II) complex
1H NMR spectrum of the vic-dioxime complexes can be evalu-
ated to determine the isomer formed, since the various chemical
environments show two O–Hꢀ ꢀ ꢀO bridge protons in the cis-form,
only one of which is in the trans-structure [33]. In the 1H NMR
spectrum of Ni(II) complex (Fig. 6a), the resonance of intramolecu-
lar bonding (O–Hꢀ ꢀ ꢀO) protons are observed at 16.06 ppm, which
disappear by D2O exchange. Since only one signal occurs at
16.06 ppm for the complex, the trans-form of this complex is con-
firmed (Scheme 1). This is in agreement with similar vic-dioxime
complexes in the literatures [9,10,34,35]. In the 13C NMR spectra
(Fig. 6b), quaternary carbon signals of the hydroxyiminocarbon
(C@N–O) appeared at 152.45 and 145.21 ppm. The other chemical
shifts (1H- and 13C NMR) observed for complex are very similar to
those which are found for ligand.
Fig. 7. TG/DTG diagram of (a) ligand and (b) Ni(II) complex.
frequency, and the appearance of the broad O–Hꢀ ꢀ ꢀO deformation
vibration at ca. 1770 cmꢁ1 are indicative of formation of complex
and N,N0-chelation in this complex [8].
3.3. NMR characterizations
3.4. Thermal analysis
3.3.1. 1H, 13C NMR, DEPT and HMBC spectrum of ligand
In the 1H NMR spectrum of LH2 in DMSO-d6, the deuterium
exchangeable protons of the @N–OH groups show chemical shifts
at 11.74 and 9.24 ppm as singlets which indicate an (E; E)-struc-
ture for the vic-dioxime [32]. The chemical shifts which belong
The synthesized vic-dioxime ligand melts at 170–171 °C with
simultaneous decomposition. The first mass loss was observed at
174 °C in the TG profile. The TG/DTG profiles of the ligand are
shown in Fig. 7a. From the TG curve, it appeared that the sample
Scheme 2. Mechanism of decomposition of LH2.

A. Yılmaz et al. / Polyhedron 29 (2010) 2991–2998
2997
Fig. 8. GC–MS spectrum of ligand.
Scheme 3. Decomposition of Ni(II) complex.
Table 4
Antibacterial activities of LH2 and its Ni(II) complex as MIC values (
l
g/ml).
S. mutans RSHM
E. faecalis ATCC
L. acidophilus RSHM
S. aureus ATCC
E. coli ATCC
E. coli ATCC
P. aeruginosa ATCC
676
29212
06029
25923
35218
25922
27853
Piperacilline
Ampicilline
Gentamycin
LH2
4
32
0,5
256
128
2
64
2
64
64
0,5
16
2
32
32
2
0,5
1
128
128
4
2
128
1
64
128
2
128
0,5
64
128
0,5
128
128
Ni(II)
128
complex
decomposes in two stages over the temperature range 25–800 °C
The first decomposition occurs between 174 and 314 °C with a
mass loss of 69.7% (calculated 69.5%) and the second decomposi-
tion starts at 314 °C and ends at 800 °C with a 30.2% (calculated
30.5%) mass loss.
Mechanism of decomposition for the ligand is possible as
shown by Scheme 2. The theoretical mechanism given in Scheme
2 is in agreement with that of Burakevich et al. [25], who studied
with phenylglyoxime in 1971. The theoretical mechanism dealt
with in Scheme 2 is confirmed by the GC–MS data in Fig. 8. The
peaks observed at 321, 303, 201, 103, 77, 51 m/z are responsible
for the evolved radical moiety. The molecular ion is not detected
in the mass spectra of the ligand, probably due to this high thermal
instability in the ionization beam.
the absence of water or other adsorptive molecules. The first
decomposition occurs between 235 and 278 °C with 35.7% (calcu-
lated 35.8%) mass loss, the second decomposition occurs between
285 and 410 °C with 24.9% (calculated 25.6%) mass loss and the
third decomposition occurs between 486 and 900 °C with 28.3%
(calculated 28.1%) mass loss. The mass losses found experimentally
are very close to the theoretical values.
From these results it was found that the Ni(II) complex was con-
verted to the corresponding NiO as shown in Scheme 3 [14,36–38].
The oxide yielded at the end of pyrolysis was confirmed by TG/DTG
data given in Fig. 7b.
3.5. Biological activity
The TGA curve of the Ni(II) complex shows three stages of
decomposition within the temperature range of 25–900 °C
(Fig. 7b). The complex shows no mass loss up to 235 °C, indicating
The synthesized vic-dioxime ligand and its Ni(II) complex
exhibited highest antimicrobial activity against S. aureus, S. mutans,
E. faecalis, L. acidophilus, E. coli ATCC 25922, E. coli ATCC 35218 and

2998
A. Yılmaz et al. / Polyhedron 29 (2010) 2991–2998
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P. aeruginosa in 128, 256, 64, 32, 64, 64, 128 and 128, 128, 64, 32,
128, 128, 128 g/ml concentrations respectively (Table 4). A com-
parative study of MIC values of the ligand and its Ni(II) complex
indicates that the free ligand has a better activity than has the me-
tal complex against E. coli and LH2 exhibited antibacterial activity
l
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in 64
Ni(II) complex was observed in 128
However, Ni(II) complex shows high bactericidal activity against S.
mutans (MIC = 128 g/ml) as compared to free ligand. Both of the
l
g/ml concentration, whereas the antibacterial activity of
_
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l
compounds have same MIC values against test microorganisms
for S. aureus, E. faecalis, L. acidophilus, and P. aeruginosa. The present
investigations of antimicrobial screening data revealed that the
newly synthesized compounds exhibited mild activity compared
to that of the control drugs. Moreover, we will synthesize novel
piperazine moiety compounds, and try our best to discover their
structure–activity relationships.
4. Conclusions
We have described the preparation, characterization and bio-
logical activities of a novel vic-dioxime ligand and its Ni(II) metal
complex which were substituted peripherally with bioactive piper-
azine moiety. The spectroscopic analysis confirmed the composi-
tion and the structure of the newly obtained compounds. It was
concluded from TG/DTG studies that the thermal stability of the
Ni(II) complex is higher than that of the ligand since the free
@C@NOH groups in the ligand participate in some internal redox
decomposition processes. The antibacterial data given for the com-
pounds presented in this paper allowed us to state that the vic-
dioxime ligand generally has a better activity than the Ni(II) com-
plex and all the compounds have mild antibacterial activity against
both Gram negative and Gram positive bacterial species.
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