Hydrothermal and sonochemical synthesis of a nano-sized nickel(II) Schiff base complex as a precursor for nano-sized nickel(II) oxide; Spectroscopic, catalytic and antibacterial properties

Article abstract of DOI:10.1007/s11243-010-9410-x

The Ni(II) complexes [Ni(L)₂](ClO₄)₂ (1) and [Ni(L)₂(NO₃)₂] (2), where L is the Schiff base ligand of 4,5,9,13,14-pentaaza-benzo[b] triphenylene, were synthesized and characterized by physico-chemical and spectroscopic methods. Nano-sized particles of (1) were prepared both by sonochemistry (3) and solvothermal (4) methods. NiO nanoparticles were obtained by calcination of the nano-structure complexes at 500 °C. The structures of the nano-sized compounds were characterized by X-ray powder diffraction and scanning electron microscopy. The thermal stabilities of the bulk complexes (1-2) and nano-sized particles (3-4) were studied by thermogravimetric and differential scanning calorimetry. The catalytic activities of complexes of (1-4) are reported. The free Schiff base and its Ni(II) complexes have been screened for antibacterial activities against three Gram-positive bacteria. The metal complexes are more active than the free Schiff base. Electrochemical studies show that the Ni complexes undergo irreversible reduction in MeCN solution.

Full text of DOI:10.1007/s11243-010-9410-x

Transition Met Chem (2010) 35:903–910
DOI 10.1007/s11243-010-9410-x
Hydrothermal and sonochemical synthesis of a nano-sized
nickel(II) Schiff base complex as a precursor for nano-sized
nickel(II) oxide; spectroscopic, catalytic and antibacterial
properties
•
Lotf Ali Saghatforoush Robabeh Mehdizadeh
•
Firoozeh Chalabian
Received: 5 June 2010 / Accepted: 9 August 2010 / Published online: 22 August 2010
Ó Springer Science+Business Media B.V. 2010
Abstract The Ni(II) complexes [Ni(L)2](ClO4)2 (1) and
[Ni(L)2(NO3)2] (2), where L is the Schiff base ligand of
4,5,9,13,14-pentaaza-benzo[b] triphenylene, were synthe-
sized and characterized by physico-chemical and spectro-
scopic methods. Nano-sized particles of (1) were prepared
both by sonochemistry (3) and solvothermal (4) methods.
NiO nanoparticles were obtained by calcination of the
nano-structure complexes at 500 °C. The structures of the
nano-sized compounds were characterized by X-ray powder
diffraction and scanning electron microscopy. The thermal
stabilities of the bulk complexes (1–2) and nano-sized
particles (3–4) were studied by thermogravimetric and
differential scanning calorimetry. The catalytic activities of
complexes of (1–4) are reported. The free Schiff base and
its Ni(II) complexes have been screened for antibacterial
activities against three Gram-positive bacteria. The metal
complexes are more active than the free Schiff base. Elec-
trochemical studies show that the Ni complexes undergo
irreversible reduction in MeCN solution.
as a bis-chelating ligand and be prepared starting from an
already complexed phenanthroline. The diketone function-
ality can also easily be transformed to other chelating
groups such as a diamine or a dioxime. Moreover, it is also a
versatile organic linker that can form bridges through amine
condensation or a combination of coordination and con-
densation [2]. Owing to its redox activity, pdon in both a
metal-free state and in complexes with transition metals
(ruthenium, cobalt, osmium, iron, and nickel) shows strong
electrocatalytic activity for the oxidation of NADH. Many
condensation reactions between the o-quinoid moiety of
pdon and a diamine group have been reported [3]. 5,6-
Diamino-1,10-phenanthroline (Phen-diamine) is particu-
larly important in that it can either directly bridge two metal
atoms or be condensed with a variety of ortho-quinones to
form derivatives. For example, the useful bridging ligand,
tetrapyrido[3,2-a:20,300,200-h:2000,3000-j]phenazine (tpphz), is
readily formed upon condensation of phen-diamine with
pdon [4, 5]. Some Schiff bases have antibacterial, anti-
fungal and antitumor activities [6–8]. The complexation of
Schiff bases with iron, copper, zinc and other metals
influences their antimicrobial activity [9]. Since nickel is
present in the active site of urease and its complexes are
used extensively in the design and construction of new
magnetic materials, the study of nickel compounds is of
great interest in various aspects of chemistry [10].
Introduction
Schiff bases are widely employed ligands that exhibit
various denticities and functionalities [1]. 1,10-Phenan-
throline-5,6-dione (pdon) is a versatile ligand for the
assembly of metal organic materials. It can be used directly
The macroscopic properties of materials strongly depend
on both the size and the morphologies of the microscopic
particles they are made up from. This is especially true for
materials with morphological features smaller than a
micron in at least one dimension, which are commonly
called nanoscale materials, or simply nanomaterials. In
these materials, the ratio of surface area to volume is vastly
increased when compared to compounds with larger grain
sizes and quantum mechanical effects such as the ‘‘quantum
L. A. Saghatforoush (&) ꢀ R. Mehdizadeh
Department of Chemistry, Faculty of Sciences, Payame Noor
University (PNU), P.O. Box. 58168-45164, Khoy, Iran
e-mail: saghatforoush@gmail.com
F. Chalabian
Department of Biology, Islamic Azad University,
Tehran North Campus, Tehran, Iran
123

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Transition Met Chem (2010) 35:903–910
size effect’’ begin to play a significant role. Most impor-
tantly, the electronic properties of solids are altered with
such great reductions in particle size, but also a number of
other physical properties such as catalytic activities change
when compared to macroscopic systems [11, 12]. Thus, the
synthesis and characterization of nano-structures with dif-
ferent particle sizes and morphologies are very important
both from the viewpoint of basic science as well as for
technological applications [12].
conductometer. TGA were obtained on a Mettler-Toledo
TGA 851e at a heating rate of 10°Cmin-1 under a nitrogen
atmosphere. DSC thermograms were obtained on a Mettler-
Toledo DSC 822e module, which was calibrated with indium
metal (T = 156.6 0.3, DH = 28.45 0.61 Jg-1). Sam-
ples of 2–5.8 mg in solid form were placed in aluminium
pans (40 ll) with a pierced lid, and heated or cooled at a scan
rate of 10 °C min-1 under nitrogen flow. Cyclic voltammo-
grams (CVs) were obtained using an Autolab modular elec-
trochemical system (Ecochimie, Ulterecht, The Netherlands)
equipped with a PGSTAT 20 module and driven by GPES
(Ecochimie) in conjunction with a three electrode system and
a personal computer for data storage and processing. An
Ag/AgCl (Saturated KCl)/3M KCl reference electrode, a Pt
wire (counter electrode) and a glassy carbon working elec-
trode (Metrohm 0.0314 cm2) were employed for the elec-
trochemical studies. Voltammetric measurements were
performed at room temperature in MeCN solution with 0.1 M
tetrabutylammonium perchlorate as the supporting electro-
lyte. The reaction products of oxidation were analyzed by an
HB 5890B gas chromatograph equipped with an HB-5 cap-
illary column (phenyl methyl siloxane 30 m 9 320 lm 9
0.25 lm) with flame-ionization detector. An ultrasonic
generator (Dr. Hielscher UP400 S ultrasonic processor)
equipped with an H22 sonotrode with diameter 22 mm,
operating at 24 kHz with a maximum power output of
400 W, was used for the ultrasonic irradiation. The ultra-
sonic generator automatically adjusts the power level. X-ray
powder diffraction (XRD) measurements were performed
using a Philips diffractometer manufactured by X’pert with
monochromatized CuKa radiation. SEM images were
recorded using a Philips model XL30. For characterization
with a scanning electron microscope, samples were gold
coated.
Nanoparticles have attracted great interest in recent years
because of their interesting chemical and physical proper-
ties, which are different from those of either the bulk
materials or single atoms [13]. Among these materials,
metal oxide nanoparticles are of technological importance
for solar cells, chemical sensors and liquid crystal displays
[13]. Sonochemistry is the research area in which molecules
undergo a reaction due to the application of powerful
ultrasonic radiation (20 kHz–10 MHz) [14, 15]. Herein, we
describe the synthesis and characterization of new nickel(II)
complexes of a Schiff base ligand namely (4,5,9,13,
14-pentaaza-benzo[b] triphenylene). Nano-sized structures
as well as bulk compounds were prepared using sono-
chemical and solvothermal methods and we have compared
the catalytic activity of both to evaluate the interesting and
highly valuable influence of the particle size of the nickel
catalysts upon their activity. NiO nanoparticles were
obtained by calcination of the nano-structure complexes.
The antibacterial activities of the Schiff base and its com-
plexes are reported against the three Gram-positive bacteria.
Experimental
All reagents and olefins were purchased from Merck or
Fluka and used as received. Solvents used for reactions were
purified and dried by conventional methods [16]. Nickel(II)
perchlorate hexahydrate was purchased from Aldrich. 1,10-
Phenanthroline-5,6-dione was prepared according to the
reported method [17]. Caution: The perchlorate salts
reported here are potentially explosive and, therefore,
should be handled with care.
Preparation of the Schiff base ligand (L)
A solution of 2,3-diaminopyridine (0.109 g, 1 mmol) in
absolute ethanol (5 mL) was added to a solution of 1,10-
phenanthroline-5,6-dione (0.21 g, 1 mmol) in absolute
ethanol (10 mL) to give a brown solution that was gently
refluxed for about 3 h, then cooled to room temperature. A
black precipitate was removed by filtration, and the filtrate
was concentrated on a rotary evaporator. The yellow pre-
cipitate thus obtained was filtered off, washed with cooled
absolute ethanol and then recrystallized from chloroform
and dried under vacuum. Yield: 0.81 g (60%). Anal.
Found: C, 72.1. H, 3.3. N, 24.8. Calcd: C, 72.1. H, 3.2. N,
24.7%. m.p: 238 °C. FT-IR (KBr disk): 3053, 1620, 1602,
FTIR spectra were recorded using KBr disks on a Shi-
1
madzu FTIR model Prestige 21 spectrometer. The H and
13C NMR spectra were recorded on a Bruker spectrospin
Avance 400 MHz in CDCl3, and chemical shifts are indi-
cated in ppm relative to tetramethylsilane. Melting points
were determined using an electrothermal apparatus and
are uncorrected. Electrospray ionization mass spectra
(ESI–MS) were measured on a Micromass Qtof YA 263
mass spectrometer. The UV–vis spectra in the 200–900 nm
range were obtained in MeCN on a Perkin-Elmer lambda
25 spectrophotometer. Conductivity measurements were
carried out in MeCN at room temperature using a Metrohm
1
1588, 1574 cm-1. H NMR (400 MHz CDCl3) dH: 9.73
(dd, 1H, J = 1.8, J = 8.1), 9.54 (dd, 1H, J = 1.8,
J = 8.1), 9.35 (dd, 1H, J = 1.9, J = 4), 9.28–9.31(m, 2H),
123

Transition Met Chem (2010) 35:903–910
905
8.67(dd, 1H, J = 1.9, J = 8.5), 7.87(dd, 1H, J = 4,
J = 8.5), 7.82(dd, 1H, J = 4.5, J = 8.2), 7.8(dd, 1H,
J = 4.5, J = 8.1). 13C NMR (CDCl3) dC: 123.39, 123.51,
124.82, 125.89, 126.17, 13315, 133.85, 136.94, 137.47,
141.13, 142.53, 147.13, 147.29, 148.78, 151.93, 152.12,
154.68. ESI–MS: m/z = 283.09 (100%). UV–vis (kmax/nm):
374, 355, 302, 294, 264.
characterized. Anal. Found: C. 49.6, H. 2.2, N. 17.0. Calcd:
C. 49.6, H. 2.2, N. 17.0%. m.p: 307–309 °C. IR (KBr disk):
3076, 1654, 1622, 1573, 1084, 625 cm-1
.
General oxidation procedure
Oxidation reactions were performed in a stirred round-bot-
tom flask fitted with a condenser. The reactions were carried
out in air with acetonitrile as solvent and H2O2 as oxidant. In
a typical experiment, a mixture of 0.032 mmol catalyst,
10 mL solvent, 1 mmol olefin and 1 mmol n-octane as
internal standard was prepared. After the mixture was
heated to 30 °C, 0.5 mmol H2O2 was added. At appropriate
intervals, aliquots were removed and analyzed immediately
by GC. Oxidation product yields based on the starting
substrate were quantified by comparison with n-octane.
Preparation of the nickel complexes
General procedure: to an ethanol solution (5 mL) of nickel
salt (perchlorate or nitrate) (0.5 mmol), an ethanol solution
(10 mL) of L (0.283 g, 1 mmol) was added. The resulting
solution was refluxed for 2 h and then left at room tem-
perature. The product was removed by filtration, washed
with cooled absolute ethanol and recrystallized from
methanol or acetonitrile and dried in vacuo.
[Ni(L)2](ClO4)2 (1), Yield: 0.24 g (58%). Anal. Found:
C. 49.6, H. 2.2, N. 17.0, Calcd: C. 49.6, H. 2.2, N. 17.0%.
m.p: 309 °C. IR (KBr disk): 3076, 1654, 1622, 1573, 1084,
625 cm-1. K = 222 lS. UV–vis (kmax/nm): 575, 374, 357,
302, 269.
Antibacterial activity tests
The in vitro activity tests were carried out using the well
method [18]. The potencies of the components were
determined against the three Gram-positive bacteria:
Streptococcus pyogenes (RITCC 1949), Staphylococcus
aureus (RITCC 1113) and Bacillus anthracis (RITCC
1036). Microorganisms (obtained from the enrichment
culture of the microorganisms in 1 mL Muller–Hinton
broth, incubated at 37 °C for 12 h) were cultured on
Muller–Hinton agar medium. The inhibitory activity was
compared with standard antibiotic, gentamicin (10 lg).
After drilling wells on medium using a 6-mm cork borer,
100 lL of the solution of each compound was poured into
the well. The plates were incubated at 37 °C overnight. The
diameter of the inhibition zone was measured to the nearest
millimeter. Each test was carried out in triplicate, and the
average was calculated for inhibition zone diameters. A
blank containing only methanol showed no inhibition in a
preliminary test. The micro-dilution broth susceptibility
assay was used for the evaluation of minimal inhibitory
concentration (MIC). After incubation at 37 °C for 24 h,
the first tube without turbidity was determined as the MIC.
[Ni(L)2(NO3)2](2), Yield: 0.215 g (58%). m.p: 308 °C.
CHN. Found: C. 54.6, H. 2.5, N. 22.5. Calcd: C. 54.5, H.
2.4, N. 22.4%. IR (KBr disk): 3076, 1634, 1619, 1590,
1492, 1356, 1211, 826 cm-1. K = 65 lS. UV–vis (kmax/nm):
760, 558, 374, 358, 300, 268.
Preparation of [Ni(L)2](ClO4)2 (3) nano-structures
by sonochemical method
Ten microliters of a 0.1 M solution of Ni(ClO4)2.6H2O in
MeOH was positioned in a high-density ultrasonic probe,
operating at 24 kHz with a maximum power output of
400 W. Into this solution, 10 mL of a 0.2 M solution of the
ligand L was added dropwise. The obtained precipitate was
filtered off, washed with methanol and then dried in air.
Anal. Found: C. 49.6, H. 2.3, N. 17.0. Calcd: C. 49.6, H.
2.2, N. 17.0%. m.p: 308–309 °C. IR (KBr disk): 3076,
1654, 1622, 1573, 1084, 625 cm-1
.
Preparation of [Ni(L)2](ClO4)2 (4) nano-structures
by solvothermal method
Results and discussion
The mononuclear complexes (1) and (2) were obtained by
the reaction of Ni(X)2. 6H2O (X=ClO4, NO3) with L (molar
ratio = 1:2, Fig. 1a, b). The analytical data for complexes
are in good agreement with the calculated values. The solid
compounds were stable at room temperature in air. The 1H
NMR spectrum of the free Schiff base ligand in chloroform
displays eight signals assigned to the aromatic protons of L.
Ni(ClO4)2.6H2O (0.182 g, 0.5 mmol) and ligand
L
(0.283 g, 1 mmol) were dissolved in EtOH (15 mL) or a
mixture of H2O and EtOH. The solution was charged into a
Teflon-lined stainless steel autoclave and heated at 150 °C
for 24 h. After the autoclave was cooled immediately to
room temperature, the product was filtered off, dried and
123

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Transition Met Chem (2010) 35:903–910
The 13C NMR spectrum of L in chloroform displays 17
distinct signals assigned to the aromatic carbon atoms. The
infrared spectra of the free ligand and its complexes were
recorded in the region 4000–400 cm-1. The spectra of the
complexes show a band at 1,634–1,654 cm-1, attributable
to the imine groups, but no bands due to m(C=O) vibrations.
The spectra exhibit medium bands at 1,619–1,622 cm-1 as
expected for the ring vibrations of the coordinated phe-
nanthroline and at 1,573–1,590 cm-1 as expected for pyr-
idine [19]. The FTIR spectra of all the complexes,
compared with the free ligand, indicate that the m(C=N)
band at 1,602 cm-1 is shifted to higher frequency by
20 cm-1 in the complexes, indicating that the ligand is
coordinated to the metal through the nitrogen atom of the
phenanthroline group [19]. The IR spectra of the perchlo-
rate complexes showed absorptions attributable to per-
chlorate at approximately 1,084 and 622 cm-1 [20]. The
lack of splitting of these bands suggests that the perchlorate
anions are not coordinated [19]. The complex (2) shows
bands at 1,492 cm-1 (m1), 1,356 cm-1 (m5), 1,211 cm-1
(m2), and 826 cm-1 (m6) indicating coordination of the
nitrate groups [21, 22]. The separation of *136 cm-1
between m1 and m5 indicates unidentate coordination of the
nitrate [21]. The molar conductivity data at room temper-
ature show that complex (1) is a 1:2 electrolyte, while
complex (2) shows non-electrolytic nature [23]. The
absorption spectra of compounds (1) and (2) were studied
in acetonitrile. All of the complexes exhibit three absorp-
tion bands at 250–270 nm and 350–380 nm, due to the
ligand centered p–p* transitions [24] or charge transfer
(CT) transitions. The presence of a band at 575 nm in the
spectrum of complex (1), which is assigned to a d–d
transition, suggests that the coordination geometry at the
metal atom could be distorted from square planar [25]. The
presence of d–d bands at 558 and 760 nm in the spectra of
complex (2) can be assigned to octahedral geometry around
the metal center [26].
N
O
N
O
N
a
Reflux
N
N
N
N
+
H2N
NH2
N
L
b
N
N
N
N
N
N
N
N
N
(ClO4)2
Ni
N
(1)
ONO2
Ni
N
N
N
N
N
N
N
N
N
N
ONO2
(2)
by ultrasound
c
(3)
Calcination
in air
Ni(ClO4)2
L
NiO nanostructures
+
(4)
by hydrothermal
Fig. 1 (a) Syntheses and structure of the Schiff base ligand.
(b) Suggested structures of Ni (II) complexes. (c) The formation of
nanocompounds and synthetic methods
the nano-structures are indistinguishable from complex (1).
Fig. 1c gives an overview of the methods used for prepa-
ration of the nano-structures and their conversion to NiO
by calcination. The XRD pattern of bulk complex (1) is the
same as those of complexes of (3) and (4) prepared by
the sonochemical and solvothermal methods, respectively.
The obtained data indicate that the compounds obtained by
both hydrothermal and sonochemical processes have an
amorphous phase. The size of the particles is 58–82 nm,
which is in agreement with that observed by scanning
Cyclic voltammograms (CVs) of complexes (1) and (2)
were recorded in acetonitrile with 0.1 M tetrabutylammo-
nium perchlorate as supporting electrolyte in the potential
range -2 to ?0.1 V. Complex (1) exhibits an irreversible
redox processes with one oxidation (Ea = -0.103 V) and
one reduction peak (Ec = -0.601 V) related to the NiII/
NiIII couple. In addition, in complex (1), anodic and
cathodic peaks (Ea = -0.71 V and Ec = -0.95 V) are
observed at nearly the same potential values as the corre-
sponding free ligand and may be due to irreversible redox
process of the ligand. Complex (2) exhibited one irre-
versible reduction peak related to the NiII/NiI couple in
addition to the ligand peaks (Table 1).
Table 1 Electrochemical data for nickel (II) complexes in CH3CN
solution
Complex
Epa(V)
Epc(V)
DEa(mV)
ipa/ipc
Eb1/2
(1)
(2)
(3)
(4)
-0.103
–
-0.601
-0.677
-0.601
-0.607
498
–
0.46
–
-0.35
–
-0.103
-0.112
498
495
0.53
0.55
-0.35
-0.35
Peak potentials E1/2 = 1/2(Epa ? Epc)
a
DEp = Epc-Epa at scan rate 100 mV
Nano-structured complexes (3 and 4) were obtained by
both ultrasonic irradiation in a methanol solution and
solvothermal reaction in an ethanol solution. IR spectra of
b
Data from cyclic voltammetric measurements; E1/2 is calculated as
average of anodic (Epa) and cathodic (Epc)
123

Transition Met Chem (2010) 35:903–910
907
patterns match with the standard patterns of face centered
cubic NiO [27]. These nano-structures show the most
crystallinity because of the existence of sharp peaks in the
XRD pattern. The phase purity of the as-prepared face-
centered cubic NiO nano-structures is completely obvious,
and all diffraction peaks are perfectly indexed to the faced-
centered cubic NiO structure with the lattice parameters
˚
of a = 4.1769 A, Z = 4 and S.G = Fm3m in JCPDS card
file No. 4-835. No characteristic peaks of impurities were
detected in the XRD pattern. The broadening of the peaks
indicated that the particles were of nanometer scale.
Figure 4 shows an SEM image of the NiO nano-structures
obtained from calcination of compound (1) under air.
To examine the thermal stabilities of the nano-sized
structures and the corresponding bulk sample (1), thermal
gravimetric analyses and differential scanning calorimetry
were carried out between 25 and 850 °C in a static atmo-
sphere of nitrogen. Enthalpy changes and decomposition
temperatures of the free Schiff base and its nickel(II)
complexes are tabulated in Table 2. The TGA data indicate
that the nickel complex (1) start decomposition at 316 °C.
There is no mass loss up to 200 °C, indicating that either
water or solvent molecules are absent in these complexes.
On the basis of the DSC data, the nano-sized structures of
compounds (3) and (4) start to decompose at 285 °C and
289 °C, respectively.
For the catalytic investigations, we chose olefin oxida-
tion, with the aim of obtaining epoxides as they are one of
the most useful synthetic intermediates for the preparation
of oxygen-containing natural products, epoxy resins and
many others. Catalytic olefin epoxidation was performed
at 30 °C under air in acetonitrile containing the olefin,
oxidant and catalyst in a 1: 0.5: 0.032 M ratios. The only
product of alkene oxidation by these systems was the
Fig. 2 SEM images of nano-structures: (a) complex (3) was prepared
by ultrasound and (b) complex (4) was prepared by solvothermal
electron microscopy, as shown in (Fig. 2a, b). Thermal
decomposition of the nano-sized structures of (3 and 4) in
air at 500 °C produced NiO nano-structures as established
by their powder XRD patterns (Fig. 3). The obtained
Fig. 3 XRD pattern NiO nano-
structures
123

908
Transition Met Chem (2010) 35:903–910
catalyzed by these nickel complexes was investigated by
UV–vis spectroscopy (Fig. 5). The initial spectrum chan-
ges after adding H2O2. The change in the spectra may be
attributed to the rapid coordination of hydrogen peroxide to
the nickel(II) and probably the reaction mechanism is
improved via the formation of an intermediate oxo-metal
species, as reported earlier for similar Schiff base com-
plexes [28–31]. In the meantime, in order to check the
stability of the catalysts in the reaction media, the IR
spectra of the catalyst before and after the reaction were
recorded. There were no differences in the IR spectra,
hence the catalysts appear to be stable during the exami-
nation period [28–32]. Nitrogenous ligands are reported to
lengthen and weaken the M–O bond in the oxidized form
of the catalyst by donating electron density into the M–O
antibonding orbital, which can account for the improved
reactivity [33, 34].
Fig. 4 SEM image of NiO nano-structures
Table 2 Thermoanalytical (enthalpy changes and decomposition
temperatures) results of free Schiff base ligand and related Ni (II)
complexes
Antibacterial activities (zone of growth inhibition and
minimal inhibitory concentrations) of the free Schiff base,
its nickel complexes and of gentamicin (as a standard
compound) are shown in Table 4. The organisms used in
the present investigation were Streptococcus pyogenes
(RITCC 1940), Staphylococcus aureus (RITCC 1885) and
Bacillus anthracis (RITCC 1036) as Gram-positive bacte-
ria. The data show that the free Schiff base has moderate
activity against S. pyogenes and S. aureus and high activity
toward B. anthracis. All of the Ni(II) complexes have strong
activity against S. aureus, plus good activity (inhibitory
Compound
Ta ( °C)
DHa(Jg-1
)
Tbd( °C)
L
238.32
316.83
314.35
284.57
286.31
16.93
47.79
54.15
73.82
74.26
299
320
320
290
290
(1)
(2)
(3)
(4)
a
Data obtained from first DSC cycle
Data obtained from TGA; 10 °C min-1 under N2 gas
b
corresponding alkene oxide. The results of oxidation of
alkenes and alkanes in the presence of these complexes as
catalysts are summarized in Table 3. The final yields were
typically obtained after 2 h. It can be seen that the nano-
size catalysts are much more reactive than the parent bulk
materials composed of micrometer or larger particles.
Maximum conversion of alkenes or alkanes with the nano-
catalysts is obtained within the first 5 min at room tem-
perature. The presence of the oxidant H2O2 is essential for
the reaction to proceed. The progress of olefin epoxidation
3
2.5
2
1.5
1
Table 3 Epoxidation of alkenes and alkane with H2O2 catalyzed by
Ni (II) complexes
Conversion (%)
Catalyst Styrene oxide 4-methylstyrene oxide Cyclooctanone
None
(1)
0
0
0
0.5
0
91.2
90
92.7
86
98
99
94.4
80
97
97
(2)
(3)
96.5
97
(4)
550
650
750
850
Conditions: catalyst, 0.032 mmol; substrate, 1 mmol; n-octane,
1 mmol; solvent, 10 mL; H2O2, 0.5 mmol, Temperature 30 °C, time
reaction 2 h for bulk complex and first 5 min for nanocomplex
Fig. 5 Transition absorption spectrum (solid line) of complex (1),
spectrum (dotted line) obtained after addition of H2O2 to complex (1)
123

Transition Met Chem (2010) 35:903–910
909
Table 4 Antibacterial activities
(zone of growth inhibition and
minimal inhibitory
concentrations) of Schiff base
ligand and nickel (II) complexes
and gentamicin (as a standard
compound)
Method
Main
compounds
Microorganisms
Streptococcus
pyogenes (?)
Bacillus
anthracis (?)
Staphylococcus
aureus (?)
Growth inhibitory zone [mm]
L
16
15
17
18
20
13
25
25
25
25
25
25
17
20
19
20
32
12.5
25
25
25
25
17
(1)
25
(2)
29
(3)
30
(4)
30
Standard
gentamicin
13
Minimum inhibitory concentration
(mg/ml)(MIC)
L
25
(1)
(2)
(3)
(4)
12.5
6.25
6.25
6.25
Acknowledgments We are grateful to Payame Noor University for
financial support of this work.
zones[15 mm) against B. anthracis and S. pyogenes. The
antibacterial activities for the free Schiff base are lower than
those for the complexes against S. aureus and S. pyogenes,
except for complex (1) which has lower activity against
S. pyogenes. [6]. In comparison with complex (1), the
nanocomplexes (3) and (4) have good activity against all
tested Gram-positive bacteria; this is probably because of
the diminished the size of particle in these complexes. All
the compounds exhibit greatest activity against S. pyogenes
and S. aureus and among the complexes, the antibacterial
activities of (2), (3) and (4) are the same. The quantitative
assays gave MIC values in the region 6.25–100 mg mL-1
(Table 4), in agreement with the above obtained results.
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