Thermal, spectral and biological investigation of new nickel complexes with imidazole derivatives

Article abstract of DOI:10.1007/s10973-018-7133-y

Four new Ni(II) complexes with acrylate and imidazole (Him) or imidazole derivatives [2-methylimidazole(2-MeIm)/5-methylimidazole(5-MeIm)/2-ethylimidazole(2-EtIm)] as ligands were prepared and characterized. All coordination compounds were characterized b

Full text of DOI:10.1007/s10973-018-7133-y

Journal of Thermal Analysis and Calorimetry
https://doi.org/10.1007/s10973-018-7133-y(0123456789(). -, vo Vl
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Thermal, spectral and biological investigation of new nickel complexes
with imidazole derivatives
Ioana Dorina Vlaicu Rodica Olar Gina Vasile Sc a˘ e t¸ eanu3 • Luigi Silvestro4 • Martin Maurer4 •
1 •
2 •
5
2
Nicolae St a˘ nic a˘
•
Mihaela Badea
Received: 22 November 2017 / Accepted: 24 February 2018
Ó Akad e´ miai Kiad o´ , Budapest, Hungary 2018
Abstract
Four new Ni(II) complexes with acrylate and imidazole (Him) or imidazole derivatives [2-methylimidazole(2-MeIm)/5-
methylimidazole(5-MeIm)/2-ethylimidazole(2-EtIm)] as ligands were prepared and characterized. All coordination com-
pounds were characterized by elemental analysis, infrared (FTIR) and ultraviolet-visible-near-infrared (UV-Vis-NIR)
spectroscopy, mass spectroscopy, magnetic moments measurements and thermal analysis (TG). The resulted complexes
were formulated as follows: [Ni(HIm) (acr) ] (1), [Ni(2-MeIm) (acr) (H O)]ÁH O (2), [Ni(5-MeIm) (acr) ]ÁH OÁ (3),
2
2
2
2
2
2
2
2
2
[
Ni(2-EtIm) (acr) (H O)]ÁH O (4). On the basis of magnetic moments measurements and on UV–Vis–NIR spectra, for all
2
2
2
2
Ni(II) complexes was proposed an octahedral stereochemistry. Acrylate ions act as bidentate in complexes (1) and (3);
meanwhile, in (2) and (4) they behave as bidentate and unidentate. Antimicrobial activity of complexes was investigated on
ATCC reference and clinical microbial strains. The MIC (minimum inhibitory concentration) values revealed moderate
antimicrobial activity of complex (1) against Enterococcus faecium and of complex (2) against Pseudomonas aeruginosa
and Bacillus subtilis.
Keywords Imidazole derivative Á Nickel complex Á Thermal analysis Á Acrylate
Introduction
potential biological activities of resulted complexes, the
more so as the azole ligands are reported for antimicrobial,
antiviral, antidiabetic, anticancer activities [1]. Complexes
with azole-type ligands are in our interest for several years,
and their biological potential has been evidenced in some
papers [2–7].
The coordination chemistry of carboxylates and azoles is
very interesting and lately has gained interest having in
view the versatility of carboxylate anions, and due to
Imidazole core, found in many bioactive heterocyclic
compounds, has the potential to generate new species used
for treatment of cancer, metabolic disorders and infectious
diseases [8]. Beside organic compounds based on imida-
zole nucleus with proven pharmacological activities [8],
there are reported imidazole-containing metal complexes
with significant biological properties. So far, bis(ac-
etato)tetrakis(imidazole) copper(II) complex presents
anticonvulsant activity against strychnine [9] and hypo-
glycemic effect [10]. The hypoglycemic effect, but
less pronounced, has been manifested also by bis(ac-
etato)bis(l-acetato)tetrakis(N-methylimidazole) copper(II)
hexaaquo and bis(acetato)bis(1,2-dimethylimidazole)cop-
per(II) [10]. Other complexes with general formula
[Cu(dien)(B)(NO )](NO ) (dien = diethylenetriamine,
&
Mihaela Badea
e_m_badea@yahoo.com
1
2
National Institute of Materials Physics, Atomistilor Str.
05A, POB MG-7, 077125 M a˘ gurele, Ilfov, Romania
4
Department of Inorganic Chemistry, Faculty of Chemistry,
University of Bucharest, 90-92 Panduri Str.,
0
50663 Bucharest, Romania
3
Department of Soil Sciences, University of Agronomical
Sciences and Veterinary Medicine, 59 M a˘ r a˘ s¸ ti Str.,
0
11464 Bucharest, Romania
4
5
3S-Pharmacological Consultation and Research GmbH, 1
Koenigsbergerstrasse, 27243 Harpstedt, Germany
‘‘Ilie Murgulescu’’ Physical Chemistry Institute, Romanian
Academy, 202 Splaiul Independentei, 77208 Bucharest,
Romania
3
3
123

I. D. Vlaicu et al.
B = imidazole/2-ethylimidazole) have presented activity
against colon cancer cells (HT-29) [11]. Also, complexes
of copper(II) with carboxylate and imidazole ligands have
been studied as models for copper proteins that contain
both functionalities in the side chain [12, 13].
Some researches present the synthesis and characteri-
zation of complexes with ligands that bear both carboxylate
and imidazole groups to build coordination polymers.
Consequently, there are reported [19] three coordination
polymers of Cu(II), Co(II) and Ni(II) with 2-(3-methox-
yphenyl)-1H-imidazole-4,5-dicarboxylic acid that present
1D column-like structure and display a 3D supramolecular
network generated by pÁÁÁp stacking or hydrogen bond
interactions. Interesting structures and properties were
obtained also in the case of employment in coordination
compounds of 1H-imidazole-4,5-dicarboxylic acid, 1H-
imidazole-2-carboxylic acid [20], 2-propyl-4,5-imida-
zoledicarboxylate [21], 2-(4-carboxyphenyl)-1H-imida-
zole-4,5-dicarboxylic acid and 2-(2-carboxyphenyl)-1H-
imidazole-4,5-dicarboxylic acid [22].
Complexes of the type [Cd(valp) (imidazole) ], [Co(-
2
2
valp) (imidazole) ] (valp = valproate) exhibit cytotoxic
2
2
specificity, a significant cancer cell inhibitory rate against
tumor cell lines (HeLa, Hep-G2, A2780, LS-174, B16,
MS1, MRC-5), and present antibacterial activity against
Gram-positive and Gram-negative bacteria [14].
In addition to those mentioned above, there are reported
two categories of complexes that present imidazole core
and carboxylates: (i) mixed ligand complexes based on
imidazole/imidazole derivative and various carboxylates
and (ii) complexes with ligands that present grafted both
imidazole and carboxylate groups.
In our ongoing interest to synthesize and characterize
mixed complexes with unsaturated carboxylates and azole-
type ligands [3–5], we report herein the synthesis and
characterization of four new Ni(II) complexes with acrylate
(acr) and imidazole (Him) or imidazole derivatives (2-
methylimidazole(2-MeIm)/5-methylimidazole(5-MeIm)/2-
ethylimidazole(2-EtIm)) as ligands, as follows:
Accordingly, complexes Zn(im) (L2) (im = imidazole,
2
2
L2 = 3-(4-methoxyphenyl)acrylate),
Zn(im) (L3)
2 2
(
L3 = methylenedioxy)benzoate) and [Cd(im) (L3)2]2-
2
4
H O contain imidazole coordinated in a monodentate
2
fashion with their neutral nitrogen groups; meanwhile,
carboxylate acts as monodentate, chelating bidentate and
bridging bidentate. In all complexes, beside classical
hydrogen bonds, there appear intra- and intermolecular
weak interactions C–HÁÁÁO, CH ÁÁÁO, CH ÁÁÁO, C–HÁÁÁp,
[
[
[
[
Ni(HIm) (acr) ] (1)
2 2
Ni(2-MeIm) (acr) (H O)]ÁH O (2)
2
2
2
2
Ni(5-MeIm) (acr) ]ÁH O (3)
2
2
2
2
3
Ni(2-EtIm) (acr) (H O)]ÁH O (4)
2
2
2
2
CH ÁÁÁp, O–HÁÁÁp and p–p which are responsible for high-
3
dimensional ordered supramolecular network [15].
The complexes were characterized by elemental analy-
sis, infrared (FTIR) and near-infrared–ultraviolet–visible
(NIR–UV–Vis) spectroscopy, mass spectroscopy, magnetic
moments measurements and thermal analysis (TG).
The versatility of carboxylate was allowed in the case of
some systems formed from copper(II) acrylate/methacry-
late and imidazole to obtain more than one product from
the same synthesis [16]. Hence, complexes bis(acrylate)-
bis(imidazole) copper(II) (purple) and binuclear
0
tetrakis(l -acrylate-O,O )-bis(imidazole)-dicopper(II)
Experimental
2
(
green) resulted from the system Cu (acrylate) (H O) and
2 4 2 2
imidazole; meanwhile, bis(methacrylate)-bis(imidazole)-
0
Materials and methods
copper(II) (purple) and tetrakis(l -a-methacrylate-O,O )-
2
bis(imidazole)-dicopper(II) (green) were obtained after
All chemicals were purchased from Acros Organics
reaction between Cu (methacrylate) (H O) and imidazole.
2
[NiCO Á2Ni(OH) Á6H O], Sigma-Aldrich (imidazole and
4
2
2
3
2
2
Moreover, for the reported complexes the interconversion
of the two corresponding complexes with different struc-
tures in methanol solution was observed, while this
behavior does not occur in anhydrous methanol. A cop-
per(II) dimer, [Cu (Ac) (EtImH) ] (Ac = acetate,
imidazole derivatives) and Merck Schuchardt OHG
(acrylic acid), were of reagent grade and were used without
further purification.
The chemical analyses (C, H, N) were performed on a
PerkinElmer PE 2400 analyzer. Nickel content was estab-
lished using a Shimadzu AA 6300 spectrometer.
IR spectra, in KBr pellets, were recorded with a Bruker
2
4
2
EtImH = 2-ethylimidazole), with relatively high thermal
stability (close to 175 °C) probably because the presence of
strong intermolecular hydrogen bridge has been reported
-
1
Tensor 37 spectrometer in the range 400–4000 cm
.
[
17]. Other studies [18] present the synthesis and structural
UV–Vis–NIR spectra were recorded in the range
200–1500 nm, on a Jasco V 670 spectrophotometer, by
diffuse reflectance technique, with Spectralon as standard.
Magnetic measurements were recorded at room tem-
perature, on a Lake Shore’s fully integrated vibrating
sample magnetometer (VSM) system 7404 and calibrated
characterization of trinuclear copper(II) complexes of the
type Cu (acrylate) (OH)(imH) and Cu (methacrylate) (-
3
5
3
3
5
OH)(imH) (imH = imidazole) with one copper ion in a
3
distorted trigonal bipyramidal configuration and two cop-
per ions in a distorted square planar configuration.
1
23

Thermal, spectral and biological investigation of new nickel complexes with imidazole…
with a Ni sphere. The molar magnetic susceptibilities were
calculated and corrected for the atomic diamagnetism.
Mass spectrometry measurements were taken using a
Thermo Finnigan MAT-900S mass spectrometer with
FAB (Cs-gun, Thermo Finnigan) ionization source oper-
ating in positive ion mode. Samples were dissolved in a
matrix of nitrobenzyl alcohol containing 1% of
hydrochloric acid at 30%. Molecular ion scanning range
[Ni(5-MeIm) (acr) ]ÁH O. Analysis, found: Ni, 15,44;
2
2
2
C, 43,85; H, 5,37; N, 14,78%; calculated for NiC H
4 20-
1
N O (F.W. = 383,03): Ni, 15,32; C, 43,90; H, 5,26; N,
4
5
14,63%.
[Ni(2-EtIm) (acr) (H O)]ÁH O; Analysis, found: Ni,
2
2
2
2
13,61; C, 44,90; H, 6,16; N, 13,13%; calculated for
NiC H N O (F.W. = 429,09): Ni, 13,67; C, 44,78; H,
16 26 4 6
6,10; N, 13,06%.
(
m/z) was 60–1450.
The obtained complexes are soluble in water, methanol,
ethanol, dimethylformamide and dimethylsulfoxide.
The heating curves (TG and DTA) were recorded using
a Labsys 1200 SETARAM instrument, over the tempera-
ture range of 30–900 °C using a heating rate of
-
1
1
0 °C min . The measurements were taken in synthetic
Results and discussion
3
-1
air atmosphere (flow rate 16.66 cm min ), by using
alumina crucibles.
As an extension of previously reported studies [3–5] and
considering our interest regarding complexes with unsatu-
rated carboxylates and azole-type ligands, new Ni(II)
complexes with acrylate (acr) and imidazole (Him) or
imidazole derivatives (2-methylimidazole(2-MeIm)/5-
methylimidazole(5-MeIm)/2-ethylimidazole(2-EtIm)) as
ligands were synthesized and characterized and formulated
as [Ni(HIm) (acr) ] (1), [Ni(2-MeIm) (acr) (H O)]ÁH O
The X-ray powder diffraction patterns were collected on
a DRON-3 diffractometer with a nickel filtered Cu Ka
˚
radiation (k = 1.5418 A) in 2h range of 5–70°, a step
width of 0.05° and an acquisition time of 2 s per step.
The antimicrobial activities of the complexes were
determined against ATCC reference and clinical microbial
strains, i.e., Gram-positive (Bacillus subtilis ATCC 6683,
Enterococcus faecium E5), Gram-negative (Klebsiella
2
2
2
2
2
2
(2), [Ni(5-MeIm) (acr) ]ÁH O (3), [Ni(2-EtIm) (acr) (H
2
2
2
2
2
2-
pneumoniae IC
5922, Pseudomonas aeruginosa ATCC 27857) and fun-
gus Candida albicans 1760.
13420, Escherichia
coli
ATCC
O)]ÁH O (4). The characterization and biological activity of
2
2
above-mentioned complexes are presented in the following
sections.
The qualitative screening was performed by an adapted
disk diffusion method, while the quantitative assay of the
antimicrobial activity was performed by the liquid-medium
microdilution method as previously reported [5].
Infrared spectra
In order to establish the nature of donor atoms and coor-
dination mode of ligands, the infrared spectra of the ligands
and the metal complexes have been recorded. The main
absorption bands of imidazole, 2-methylimidazole,
5-methylimidazole and 2-ethylimidazole as well as for
their complexes are listed in Table 1.
Synthesis of complexes
All the complexes were obtained following the general
procedure: A suspension of NiCO Á2Ni(OH) (3 mmol) in
3
2
3
methanol (50 cm ) and acrylic acid (18 mmol) was stirred
at 50 °C for 2 days. The solution of nickel acrylate
obtained after filtration was then mixed with imidazole/
imidazole derivative (15 mmol), stirred 2 h at room tem-
perature and let to slow evaporation for a few days when
the complex precipitate. The sparingly soluble product was
filtered off, washed several times with methanol and air-
dried.
All complexes spectra display the characteristic vibra-
tion bands of imidazole-type ligands [23, 24]. The funda-
mental stretching vibration mode characteristic of the
-
1
secondary amine group, m(NH), occurs around 3140 cm
in complexes spectra, similar to spectra of uncoordinated
ligands. In the complexes spectra, the strong band around
-
1
1640 cm is assigned to the vibration mode m(C=N). This
band is shifted to lower wavenumbers by 35–40 cm
-
1
[
Ni(HIm) (acr) ]. Analysis, found: Ni, 17,12; C, 42,84;
2
compared to the spectra of free imidazole/imidazole
derivatives. These aspects indicate the coordination of
imidazole/imidazole derivatives to metal by pyridine-type
nitrogen atom.
2
H, 4,32; N, 16,42%; calculated for NiC H N O
2 14 4 4
1
(
F.W. = 336,96): Ni, 17,42; C, 42,77; H, 4,19; N, 16,63%.
[
Ni(2-MeIm) (acr) (H O)]ÁH O. Analysis, found: Ni,
2
2
2
2
1
4,52; C, 41,85; H, 5,71; N, 13,78%; calculated for
The two band characteristics of the vibration modes
m (COO) and m (COO) of the acrylate anion appear in the
NiC H N O (F.W. = 401,04): Ni, 14,64; C, 41,93; H,
4
1
4
22
6
as
s
-
1
5
5
,53; N, 13,97%.
1530–1580 and 1330–1420 cm ranges. The coordination
mode of acrylate anion can be assigned by comparing to
the sodium acrylate spectrum, using the values of differ-
Exp.(%)/calc.(%): Ni, 14,52/14,64; C, 41,85/41,93; H,
,71/5,53; N, 13,78/13,97.
ence D = m (COO) - m (COO) [25, 26]. Thus,
a
as
s
123

I. D. Vlaicu et al.
-1
Table 1 Characteristic absorption bands (cm ) in IR spectra of ligands and complexes
HIm
2-MeIm
5-MeIm
2-EtIm
(1)
(2)
(3)
(4)
Assignments
–
–
–
–
–
3450 w
3131 w
2920 w
2880 w
1640 s
1573 vs
–
3383 w
3145 w
2926 w
2877 w
1639 m
1572 vs
–
3445 vs
3150 w
2920 w
2880 w
1637 vs
1577 vs
–
m(OH
2
)
3
–
–
1
–
1
–
–
124 m
3136 m
3136 m
3153 w
3120 w
2920 w
2880 w
1629 m
1569 vs
1545 s
1520 w
1385 m
m(CH), m(NH)
–
–
–
mas(CH
2
)
–
–
–
m (CH )
s 2
669 m
541 s
1676 m
1676 m
1673 w
m(C=N)
mas(COO)
–
–
–
–
–
–
1596 vs
1596 vs
d(NH), m(CC), m(CN)
m(C=C) aliph
–
–
–
–
1520 w
1427 vs
–
–
1384 m
1424 vs
1360 m
1280 m
1237 m
1150 w
960 w
875 w
822 w
770 w
625 w
s
m (COO)
1
361 s
–
1
1
9
8
–
7
6
–
–
–
1268 s
1230 w
1150 w
950 m
885 w
–
1272 s
1192 s
1145 w
937 m
875 w
831 s
1273 m
–
2
d(CH )
243 w
146 s
36 vs
95 m
1206 w
1155 vs
942 s
875 w
–
1206 w
1155 vs
942 s
875 w
–
1243 w
1153 m
956 s
875 w
–
m(CN), d(CH)
1195 m
961 w
875 w
–
m(CC), m(CN), d(CH)
d(CH), d(imidazole ring)
p(CH), d(imidazole ring)
r 2
q (OH )
56 s
19 s
756 vs
627 w
756 vs
627 w
751 vs
625 w
760 m
647 m
746 m
679 s
740 w
621 m
p(CH)
p(NH)
vs—very strong, s—strong, m—medium, w—weak (band intensity in FTIR spectra); HIm—imidazole; 2-MeIm—2-methylimidazole; 5-MeIm—
-methylimidazole; 2-EtIm—2-ethylimidazole; (1)—[Ni(HIm) (acr) ]; (2)—[Ni(2-MeIm) (acr) (H O; (3)—[Ni(5-MeIm) (acr) ]ÁH O;
O)]ÁH
4)—[Ni(2-EtIm) (acr) (H O; m—stretching; d—in-plane bending; p—out-of-plane bending; q—rocking
O)]ÁH
5
2
2
2
2
2
2
2
2
2
(
2
2
2
2
difference between the vibration modes of the acrylate
-
1
anion, D, in the range of 144–153 cm and in the range of
-
12–217 vs. 203 cm for sodium acrylate indicates both
1
2
bidentate and unidentate nature for complexes [Ni(2-
MeIm) (acr) (H O)]ÁH O (2) and [Ni(2-EtIm) (acr) (H
2
2
2
2
2
2
2-
O)]ÁH O (4). For complexes [Ni(HIm) (acr) ] (1) and
(2)
1)
2
2
2
[
Ni(5-MeIm) (acr) ]ÁH O (3), the difference D of 184 and
2
2
2
(
-
88 cm , respectively, indicates the bidentate nature of
1
1
(3)
this ligand.
(4)
-
1
The broadband around 3400 cm that appears in the
complex combinations (2)–(4) can be assigned to the
stretching vibration m(OH) corresponding to the water
molecules, their presence being confirmed by the chemical
and thermal analysis. For complexes (2) and (4), the band
2
00
500
1000
1500
Wavelength/nm
-
1
around 830 cm
assigned to vibration mode q (H O)
Fig. 1 UV–Vis–NIR spectra of complexes (1)–(4)
r
2
indicates that water molecules are also involved in the
coordination process [27].
octahedral stereochemistry [28]. In addition, a strong
ultraviolet band due to the intraligand transition appears in
-
1
Magnetic and electronic spectral data
the 41,000–46,000 cm range. The absorptions bands for
the metal complexes together with crystal-field parameters
(calculated using K o¨ nig’s formulas [29]) are listed in
Table 2.
The characteristics of the metal–ligand bond and the
symmetry of coordination polyhedron were established on
the basis of observed transitions in the UV–Vis–NIR
spectra.
The low value of the splitting parameters is generated by
the ligands’ low field associated with the presence of the
oxygen donor atoms. This assumption is supported by the
values of the nephelauxetic parameter which corresponds
All complexes exhibit UV–Vis–NIR spectra (Fig. 1),
characteristic of d–d transitions for Ni(II) ion in an
1
23

Thermal, spectral and biological investigation of new nickel complexes with imidazole…
Table 2 UV–Vis–NIR absorption bands, crystal-field parameters and magnetic moments for complexes (1)–(4)
-1
Complex
Absorption maxima/cm
Assignments
Crystal-field parameters
lef/B.M.
-1
-1
1
0Dq/cm
B/cm
b
[
Ni(HIm) (acr)
2
2
] (1)
41,670
p ? p*
9640
845
0.81
2.98
3
3
3
3
3
3
25,975
22,220
15,625
13,515
A
A
A
A
A
2g ? T1g (P)
1
2g ? A1g
3
2g ? T1g (F)
1
2g ? E
g
3
9
300
2g ? T2g
[
[
Ni(2-MeIm)
Ni(5-MeIm)
2
(acr)
2
(H
2
O)]ÁH
2
O (2)
40,000
p ? p*
9125
9637
858
845
0.82
0.81
3.46
3.00
3
3
25,315
14,925
13,515
A
A
A
A
2g ? T1g (P)
3
3
3
3
2g ? T1g (F)
1
2g ? E
g
3
8
620
2g ? T2g
2
(acr)
2
]ÁH
2
O (3)
41,670
p ? p*
3
3
25,975
22,470
15,625
13,515
A
A
A
A
A
2g ? T1g (P)
3
3
3
3
1
2g ? A1g
3
2g ? T1g (F)
1
2g ? E
g
3
9
380
2g ? T2g
[
Ni(2-EtIm)
2
(acr)
2
(H
2
O)]ÁH
2
O (4)
45,455
p ? p*
8990
900
0.86
3.44
3
3
25,640
23,810
14,815
13,420
A
A
A
A
A
2g ? T1g (P)
3
3
3
3
1
2g ? A1g
3
2g ? T1g (F)
1
2g ? E
g
3
7
810
2g ? T2g
to a high degree of ionicity of metal–ligand bonds as a
result of the interaction with the acrylate anion.
The values of magnetic moment lie in the 2.80–3.50 B.
M. range, which is characteristic for octahedral complexes
of nickel (II) [30].
Proposed coordination for nickel(II) complexes
(1)–(4)
Taking into account all experimental data, the most prob-
able coordination is presented in Fig. 3. On the basis of
higher intensity of d–d transition bands which suggests a
lower symmetry, for complexes (1)–(3) it was considered a
cis position of imidazole derivatives.
Mass spectra
The mass spectra were recorded in positive ionization
mode and contain peaks corresponding to pseudomolecular
Thermal behavior of complexes
?
ion [Ni(L acr ? H] ion at m/z: 337/365/365/393 for
2
2
complexes (1)/(2)/(3)/(4), respectively. Also, some other
?
fragments were evidenced: [NiL acr] (m/z: 265/-/293/
The results concerning the thermal decomposition of the
new complexes are presented in Table 3.
2
?
?
3
21), [NiLacr ? H] (m/z: 269/283/-/297), [NiLacr] (m/
2
z: 197/211/211/225) as well as the protonated ligands
?
L ? H] (m/z: 69/83/83/97). Figure 2 illustrates mass
Thermal decomposition of [Ni(HIm) (acr) ] (1)
2
2
[
spectrum of complex (3).
These data together with that obtained from elemental
and thermal analysis confirm the complexes formulation.
According to the TG curve (Fig. 4), the complex
[Ni(HIm) (acr) ] (1) is stable up to 270 °C indicating the
2
2
absence of any lattice or coordinated water/methanol
molecules. The first mass loss step corresponds to oxidative
degradation of both imidazole molecules. The DTG curve
shape indicates this step is not a single one but an overlap
123

I. D. Vlaicu et al.
8
3.1
222.0
293.0
211.0
257.0
224.0
1
40.0
259.0
2
96.0
1
42.0 157.0
75.0
341.1
1
225.0
236.1 261.0
8
1.1
2.1
304.0 339.1
8
4.1
100
159.0
365.0
8
6
0
80
120
140
160 180
200 220
m/z/Da
240
260 280
300
320 340
360
Fig. 2 Mass spectrum of complex (3)
of at least two processes. The same information is provided
by DTA curve which exhibits at least two exothermic
effects. The IR spectrum of the intermediate residue iso-
lated at 380 °C displays only the characteristic bands of
acrylate ion [25]. The second exothermic decomposition
step corresponds to oxidative degradation of acrylate ions,
a complex process according to both DTG and DTA
curves. The final residue was identified, using powder
X-ray diffraction, as nickel (II) oxide.
O
O
O
O
O
O
Ni
N
Ni
N
O
N
O
HN
H3C
N
CH3
N
H
HN
NH
(
1)
(
3)
HN
OH2
O
H5C2
Thermal decomposition of [Ni(2-MeIm) (acr) (H O)]ÁH O (2)
2
2
2
2
O
N
O
Ni
N
O
O
O
O
Ni
N
N
The thermal decomposition of title compound (Fig. 5)
starts with water molecules release. Although TG curve
indicates only one process, both DTG and DTA curves
show successive elimination. The high temperature
observed for this process suggests that apart from the fact
that one molecule is coordinated, the lattice water is
H2O
O
N
CH3
H
C2H5
CH3
NH
2)
NH
(
(4)
Fig. 3 Proposed coordination of complexes (1)–(4)
Table 3 Thermal
decomposition data (in air flow)
for complexes (1)–(4)
Complex
Step
1.
Thermal effect
Temp./°C
Dmexp/%
Dmcalc/%
[
Ni(HIm) (acr)
2
2
] (1)
Exothermic
Exothermic
270–380
380–490
40.2
37.4
22.4
9.1
40.4
37.4
22.2
9.0
2
.
Residue (NiO)
1. Endothermic
[
Ni(2-MeIm)
2
(acr)
2
(H
2
O)]ÁH
2
O (2)
140–250
260–392
392–580
2
3
.
.
Miscellaneous
Exothermic
40.8
31.4
18.7
4.9
40.9
31.5
18.6
4.7
Residue (NiO)
1. Endothermic
[
[
Ni(5-MeIm)
2
(acr)
2
]ÁH
2
O (3)
126–160
250–350
350–460
460–655
2
3
4
.
.
.
Endothermic
Exothermic
Exothermic
21.6
21.2
32.6
19.7
4.5
21.4
21.4
33.0
19.5
4.2
Residue (NiO)
1. Endothermic
Ni(2-EtIm)
2
(acr)
2
(H
2
O)]ÁH
2
O (4)
67–135
135–220
220–455
455–860
2
3
4
.
.
.
Endothermic
Exothermic
Exothermic
4.4
4.2
45.0
28.6
17.5
44.8
29.4
17.4
Residue (NiO)
1
23

Thermal, spectral and biological investigation of new nickel complexes with imidazole…
Fig. 4 Thermoanalytical curves
(
[
1
TG, DTG and DTA) of
Ni(HIm) (acr) ] in air flow at
0 °C min
TG
0
0
0
.4
.2
.0
0
2
2
30
-
1
–
–
–
–
20
40
60
80
2
1
0
0
DTG
–
–
–
0.2
0.4
0.6
DTA
0
–
10
–
100
–0.8
0
200
400
600
800
1000
Temperature/°C
Fig. 5 Thermoanalytical curves
TG, DTG and DTA) of [Ni(2-
MeIm) (acr) (H O in air
O)]ÁH
flow at 10 °C min
40
30
(
TG
0
0.5
2
2
2
2
-
1
DTG
2
0
0
–
–
–
–
20
40
60
80
0
.0
1
0
–
–
–
–
0.5
1.0
DTA
10
20
–1.5
–
30
0
200
400
600
800
1000
Temperature/°C
involved in hydrogen bonds. According to the mass loss,
the next step corresponds to 2-methylimidazole molecule
release. The IR spectrum of intermediate isolated at 392 °C
exhibits only the characteristic pattern of acrylate ion. DTA
curve exhibits an endothermic effect followed by an
exothermic one. In the last step, the acrylate ion oxidative
degradation occurs, leading to nickel oxide as the final
residue according to powder X-ray diffractogram pattern.
discussed complexes, suggesting that is not coordinated at
nickel ion.
The second step which is endothermic corresponds to
the loss of one molecule of imidazole derivative. IR
spectrum of intermediate isolated at 350 °C (Fig. 7a)
contains both 5-methylimidazole and acrylate ion charac-
teristic bands. As temperature increases, the second mole-
cule of 5-methylimidazole undergoes oxidative
degradation. According to both DTG and DTA curves, this
step is not a single one but an overlapping of two processes.
The acrylate intermediate formation at 460 °C was con-
firmed through IR spectrum (Fig. 7b). The last step cor-
responds to oxidative degradation of acrylate ions, the final
residue being nickel oxide.
Thermal decomposition of [Ni(5-MeIm) (acr) ]ÁH O (3)
2
2
2
The complex [Ni(5-MeIm) (acr) ]ÁH O (3) decomposes in
2
2
2
four steps (Fig. 6). First, water molecule is released in a
lower-temperature range compared with the previously
123

I. D. Vlaicu et al.
Fig. 6 Thermoanalytical curves
TG, DTG and DTA) of [Ni(5-
MeIm) (acr) O in air flow
]ÁH
at 10 °C min
0.3
0.2
(
50
40
TG
0
20
40
60
80
2
2
-
2
1
0
0
–
–
.1
3
2
0
0
–
–
–
–
DTG
.0
0.1
0.2
10
0
DTA
–
–
–
–
0.3
0.4
0.5
0.6
–
–
–
10
20
30
0
200
400
600
800
1000
Temperature/°C
different complexes [6, 7, 31]. The imidazole derivative
molecules undergo oxidative degradation in the third
exothermic step as IR spectrum of intermediate indicates.
The remaining nickel acrylate undergoes oxidative
decomposition leading to NiO.
As a general observation, for [Ni(R-imid) (acr) ] moiety
2
2
there was evidenced a correlation between the molecular
weight of imidazole derivative and the initial and final
decomposition temperature. Thus, as the molecular weight
increases, this moiety starts to decompose at lower tem-
peratures, while the final temperature of decomposition
increases.
(
a)
(
b)
Microbiological assay
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber/cm–1
The antimicrobial activity of complexes was investigated
on ATCC reference and clinical microbial strains. Since in
the first step, the qualitative screening, all compounds
present diameters of inhibition zone of about 8 mm, it was
proceeded to the quantitative assay. The MIC (minimum
inhibitory concentration) values revealed moderate
antimicrobial activity, as follows:
Fig. 7 IR spectra of intermediates isolated at 350 °C (a) and 460 °C
b)
(
Thermal decomposition of [Ni(2-EtIm) (acr) (H O)]ÁH O (4)
2
2
2
2
•
•
complex (1) against Enterococcus faecium, (MIC
-
Although the thermal behavior of complex (4) is quite
similar to the previously discussed complexes, there are
some differences which are worth highlighting (Fig. 8).
Thus, the different nature of water molecules is better
evidenced on all thermoanalytical curves (TG, DTG and
DTA) which exhibit two successive endothermic steps.
This behavior was evidenced for other similar [5] or
1
2
50 lg mL );
complex (2) against Pseudomonas aeruginosa (MIC
-
1
2
2
50 lg mL
)
and
Bacillus
subtilis
(MIC
-
1
50 lg mL ).
1
23

Thermal, spectral and biological investigation of new nickel complexes with imidazole…
Fig. 8 Thermoanalytical curves
60
0.6
0.4
(
TG, DTG and DTA) of [Ni(2-
EtIm) (acr) (H O in air
O)]ÁH
flow at 10 °C min
TG
0
2
2
2
2
-
1
4
2
0
0
0.2
–
20
DTG
0
–
–
–
–
–
.0
0.2
0.4
0.6
0.8
1.0
–
–
40
60
DTA
0
–
20
40
–
80
–
–1.2
0
200
400
600
800
1000
Temperature/°C
with pyrazole derivatives.
013;113:1337–43.
J
Therm Anal Calorim.
Conclusions
2
3
4
. Vlaicu ID, Constand M, Olar R, Marinescu D, Grecu MN, Lazar
V, Chifiriuc MC, Badea M. Thermal stability of new biologic
active copper (II) complexes with 5,6-dimethylbenzimidazole.
J Therm Anal Calorim. 2013;113:1369–77.
. Badea M, Vlaicu ID, Olar R, Constand M, Bleotu C, Chifiriuc
MC, M a˘ ru ¸t escu L, Lazar V, Grecu MN, Marinescu D. Thermal
behaviour and characterisation of new biologically active Cu(II)
complexes with benzimidazole as main ligand. J Therm Anal
Calorim. 2014;118:1119–33.
The new complexes of Ni (II) with acrylate and imidazole
Him) or imidazole derivatives (2-methylimidazole (2-
(
MeIm)/5-methylimidazole (5-MeIm)/2-ethylimidazole (2-
EtIm)) have been synthesized and characterized. Spectral
data indicate an octahedral stereochemistry for all com-
plexes and bidentate coordination mode for acrylate in
complexes (1) and (3) and both unidentate and bidentate in
5
6
7
. Olar R, Vlaicu ID, Chifiriuc MC, Bleotu C, St a˘ nic a˘ N, Vasile
Sc a˘ e ¸t eanu G, Silvestro L, Dulea C, Badea M. Synthesis, thermal
analysis and biological characterisation of some new nickel (II)
complexes with unsaturated carboxylates and heterocyclic
N-donor ligands. J Therm Anal Calorim. 2017;127:731–41.
. Olar R, Calu L, Badea M, Chifiriuc MC, Bleotu C, Velescu B,
Stoica O, Ioni ¸t a˘ G, St a˘ nic a˘ N, Silvestro L, Dulea C, Uivarosi V.
Thermal behaviour of some biologically active species based on
complexes with a triazolopyrimidine pharmacophore. J Therm
Anal Calorim. 2017;127:685–96.
. Calu L, Badea M, Cerc Koro sˇ ec R, Bukovec P, Daniliuc C,
Chifiriuc MC, M a˘ ru ¸t escu L, Ciulic a˘ C, S¸ erban G, Olar R. Ther-
mal behaviour of some novel biological active complexes with a
triazolopyrimidine pharmacophore. J Therm Anal Calorim.
2017;127:697–708.
(
2) and (4). Thermal analysis (TG, DTA) of these com-
plexes confirms the complexes composition and allows the
number and nature of the water molecule determination. A
correlation between the stability of the anhydrous com-
pounds and the molecular weights of imidazole derivatives
has been established.
The MIC (minimum inhibitory concentration) values
revealed moderate antimicrobial activity of complex (1)
against Enterococcus faecium and of complex (2) against
Pseudomonas aeruginosa and Bacillus subtilis.
Acknowledgements The authors thank to Mariana Carmen Chifiriuc
from Faculty of Biology, University of Bucharest for the help with
antimicrobial assay. I.D. Vlaicu acknowledges the financial support to
the Sectorial Operational Programme Human Resources Development
8. Narasimhan B, Sharma D, Kumar P. Biological importance of
imidazole nucleus in new millenium. Med Res Chem.
2011;20:1119–40.
(
SOP HRD), financed from the European Social Fund and by the
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etato)tetrakis(imidazole)copper(II) in delaying the onset and
reducing the mortality rate of strychnine- and thiosemicarbazide-
induced convulsions. Biol Trace Elem Res. 2004;101:87–95.
0. Abdul-Ghani A-S, Abu-Hijleh A-L, Nahas N, Amin R. Hypo-
glycemic effect of copper (II) acetate imidazole complexes. Biol
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Kyriakidis DA. Antiproliferative activity of mixed-ligand dien-
Cu(II) complexes with thiazole, thiazoline and imidazole
derivatives. J Inorg Biochem. 2002;88:25–36.
Romanian Government under the contract number SOP HRD/107/1.5/
S/82514. This work was partially supported by University of
Bucharest.
1
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