Synthesis, X-ray crystal structure, spectroscopic, electrochemical and antimicrobial studies of a new dinuclear cobalt(III) complex

Article abstract of DOI:10.1016/j.ica.2016.12.004

A new dinuclear Co(III) complex, [Co₂(L¹)₂(L²)₂] (HL¹= (E)-1-(2-aminophenyl) ethanone oxime, HL²= 2-(2-hydroxyphenyl)-4-methyl-1,2-dihydroquinazoline 3-oxide, H is the deprotonatable hydrogen) has been synthesized via complexation of Co(II) nitrate hexahydrate with HL¹and HL². The structure of the Co(III) complex was characterized by infrared, UV–Vis spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Elemental analysis was in good agreement with the proposed structure. The spectroscopic data of the Co(III) complex was compared with the ligand HL². In the crystal structure, each complex links with two other molecules into an infinite 2-D layer supramolecular structure through intermolecular hydrogen bonding and π···π stacking interactions. Moreover, the electrochemical property of the Co(III) complex was studied by cyclic voltammetry. Electron paramagnetic resonance (EPR) spectroscopy of the dinuclear Co(III) complex was also investigated. In addition, the antimicrobial activity of HL²and the Co(III) complex were also studied.

Full text of DOI:10.1016/j.ica.2016.12.004

Inorganica Chimica Acta 457 (2017) 34–40
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
Synthesis, X-ray crystal structure, spectroscopic, electrochemical and
antimicrobial studies of a new dinuclear cobalt(III) complex
Lan-Qin Chai a, , Kuan-Hao Mao a, Jian-Yu Zhang a, Kong-Yan Zhang a, Hong-Song Zhang b,
⇑
⇑
a School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China
b Lanzhou University Second Hospital, Lanzhou, Gansu 730030, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 October 2016
Received in revised form 29 November 2016
Accepted 2 December 2016
Available online 7 December 2016
A
new dinuclear Co(III) complex, [Co2(L1)2(L2)2] (HL1 = (E)-1-(2-aminophenyl) ethanone oxime,
HL2 = 2-(2-hydroxyphenyl)-4-methyl-1,2-dihydroquinazoline 3-oxide, H is the deprotonatable hydro-
gen) has been synthesized via complexation of Co(II) nitrate hexahydrate with HL1 and HL2. The structure
of the Co(III) complex was characterized by infrared, UV–Vis spectroscopy, elemental analysis, and single-
crystal X-ray crystallography. Elemental analysis was in good agreement with the proposed structure.
The spectroscopic data of the Co(III) complex was compared with the ligand HL2. In the crystal structure,
each complex links with two other molecules into an infinite 2-D layer supramolecular structure through
Keywords:
Quinazoline-type ligand
Dinuclear Co(III) complex
Spectroscopic studies
Crystal structure
intermolecular hydrogen bonding and
pꢀꢀꢀp stacking interactions. Moreover, the electrochemical property
of the Co(III) complex was studied by cyclic voltammetry. Electron paramagnetic resonance (EPR) spec-
troscopy of the dinuclear Co(III) complex was also investigated. In addition, the antimicrobial activity of
HL2 and the Co(III) complex were also studied.
Cyclic voltammetry
Ó 2016 Elsevier B.V. All rights reserved.
1. Introduction
ligands [20–22], herein we report on a new dinuclear cobalt(III)
complex, [Co2(L1)2(L2)2] (HL1 = (E)-1-(2-aminophenyl) ethanone
Oxime-type compounds are known to be versatile ligands in
coordination chemistry. Transition metal complexes with oxime-
type ligands have attracted remarkable attention because of their
interesting structures and a variety of applications [1–3], such as
highly efficient catalysts [4,5], redox-active sensors [6], ionic ferro-
electrics [7], development of new supramolecular architectures
with interesting properties [8], and high selectivity recognition
[9] and biological activities [10,11]. The quinazoline ring system
along with many alkaloids is a widely recognized moiety in synthe-
sis and medicinal application [12], such as it was found in HIV
reverse transcriptase inhibitors [13]. Some of them or transition
metal complexes with quinazoline analogue ligands are used as
biological models in understanding the structure of biomolecules
and biological processes [14–16]. Cobalt(III) complexes have been
widely investigated in coordination chemistry and biological
chemistry [17–19], but cleavage of two CAN bonds of Schiff
base-type have not been observed when the quinazoline-type
ligands react with d-block transition metal salts.
oxime, HL2 = 2-(2-hydroxyphenyl)-4-methyl-1,2-dihydroquinazo-
line 3-oxide, H is the deprotonatable hydrogen), formed unexpect-
edly in the reaction of the ligand with cobalt(II) nitrate
hexahydrate. The DI-Co(III) complex was characterized using sev-
eral spectroscopic techniques including X-ray crystallography, IR
and UV–Vis spectroscopy. Furthermore, the redox behavior was
studied using cyclovoltammetry and electron paramagnetic reso-
nance (EPR) techniques.
2. Experimental section
2.1. Materials and physical measurements
All chemicals were analytical grade reagents from Tianjin
Chemical Reagent Factory and used without purification. C, H,
and N analyses were carried out with a GmbH VariuoEL V3.00
automatic elemental analysis instrument. Elemental analysis for
Co was determined by an IRIS ER/SꢀWP–1 ICP atomic emission
spectrometer. IR spectra were recorded on a VERTEX-70 and Nico-
let Instrument Corporation NEXUS 670 FT-IR spectrophotometer,
with samples prepared as KBr pellets. UV–Vis absorption spectra
were recorded on a Shimadzu UV–2550 spectrometer. Cyclic
voltammetry measurements were performed using CHI660b
In continuation to our recent studies on nickel(II) and cobalt(II)
mononuclear transition metal complexes with quinazoline-type
⇑
Corresponding authors.
E-mail addresses: chailanqin@163.com (L.-Q. Chai), jijiuyish@163.com
(H.-S. Zhang).
http://dx.doi.org/10.1016/j.ica.2016.12.004
0020-1693/Ó 2016 Elsevier B.V. All rights reserved.

L.-Q. Chai et al. / Inorganica Chimica Acta 457 (2017) 34–40
35
Table 1
voltammetric analyzer, a three electrode arrangement made up of
Crystallographic data and structure refinement parameters of the Co(III) complex.
a glassy carbon working electrode, a platinum wire auxiliary elec-
trode and a Ag/AgNO3 reference electrode was used in DMF con-
taining 0.05 mol Lꢁ1 tetrabutylammonium perchlorate at scan
Empirical formula
C46H42Co2N8O6
Molecular weight, g molꢁ1
920.73
rates of 100 mV sꢁ1 1H NMR spectra were measured on Mercury
.
Temperature (K)
Crystal system
Space group
291.89(10)
Monoclinic
P21/c
Plus (400 MHz or 300 MHz) spectrometers. Chemical shifts of 1H
NMR were expressed in parts per million relative to the singlet
(d = 7.26) for CDCl3 and TMS as internal standard. MS (ESI) were
measured on Bruker Esquire 6000 mass spectrometer. Electron
paramagnetic resonance (EPR) spectrum was measured on a Bru-
ker ER-A300-9.5/12 spectrometer. Single-crystal X-ray structure
determination was carried out on an Agilent SuperNova Dual area
detector diffractometer. Melting points were obtained by use of a
microscopic melting point apparatus made by Beijing Taike Instru-
ment Limited Company and are uncorrected.
Unit cell dimensions (Å, °)
a
13.5716(10)
b
16.7080(7)
c
14.4286(12)
b
114.437(9)
2978.6(4), 2
1.027
0.599
Volume (Å3), Z
Calculated density (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
952
Independent reflections (Rint
)
0.0524
h Range for data collection (°)
Index ranges
Reflections collected/unique
Data/restraints/parameters
3.469–26.019
ꢁ16 6 h 6 15; ꢁ18 6 k 6 20; ꢁ17 6 l 6 17
2.2. Synthesis and structural characterization of HL2
13,236/3946
5858/0/290
Final R indices [I > 2
R indices (all data)
Goodness-of-fit (F2)
r
(I)]
R1 = 0.0466, wR2 = 0.1321
R1 = 0.0784, wR2 = 0.1475
1.097
The synthetic route of quinazoline-type ligand 2-(2-hydrox-
yphenyl)-4-methyl-1,2-dihydroquinazoline 3-oxide (HL2) is shown
in Scheme 1.
Largest diff. peak and hole/e Åꢁ3 0.435 and ꢁ0.389
(E)-1-(2-Aminophenyl) ethanone oxime (HL1) was synthesized
according to an analogous method reported earlier [20–22]. Yield,
w = 1/[r2 (Fo2) + (0.0680P)2 + 5.6700P], where P = (Fo2 + 2F2c)/3.
94.7%. m.p. 106–107 °C. IR (KBr)
m
/cmꢁ1: 3389 (NAOH), 3248
(NAH), 3133 (ArAH), 1602 (C@N). 1H NMR (300 MHz, CDCl3): d
11.30 (s, 1H, NOH), 7.63–7.25 (m, 4H, ArH), 5.82 (s, 2H, NH2),
2.56 (s, 3H, CH3). Anal. calcd. for C8H10N2O (150.18): C, 63.98; H,
6.71; N, 18.65. Found (%): C, 64.04; H, 6.78; N 18.73.
analysis were obtained. Yield: 64.2%. IR (KBr)
1604 (C@N), 1284 (ArAO), 579 (CoAN), 472 (CoAO). Anal. calcd. for
46H42Co2N8O6 (920.73): C, 60.01; H, 4.60, N, 12.17; Co, 12.80.
m
/cmꢁ1: 3435 (OAH),
C
Found (%): C, 60.04; H, 4.65; N, 12.21; Co, 12.85.
2-(2-hydroxyphenyl)-4-methyl-1,2-dihydroquinazoline 3-oxide
(HL2) was synthesized by modification of the reported method
[22–24]. To an ethanol solution (5 mL) of salicylaldehyde
(122.1 mg, 1.0 mmol) was added an ethanol solution (3 mL) of
HL1 (150.2 mg, 1.0 mmol). After stirring at 55–60 °C for 12 h, the
mixture was filtered, precipitates were collected on a suction filter
to give yellow crystalline solid (163.3 mg). Yield: 75.3%. m.p. 212–
2.4. X-ray crystallography
X-ray diffraction measurement for the Co(III) complex was per-
formed on an Agilent SuperNova Dual diffractometer with graphite
monochromated Mo-Ka radiation (k = 0.71073 Å) at 291.89(10) K.
Data reduction and cell refinement were performed using OLEX2
[25]. The structure was solved by using Fourier difference tech-
niques and refined by full-matrix least square methods on F2 data
[26]. The non-hydrogen atoms were generated anisotropically. All
hydrogen atoms were assigned geometrically and positioned
isotropically. The detailed crystallographic data and structure
refinement parameters of the Co(III) complex are listed in Table 1.
213 °C. IR (KBr) m
/cmꢁ1: 3393 (OAH), 3128 (NAH), 1610 (C@N),
1291 (ArAO). 1H NMR (400 MHz, CDCl3, 25 °C, TMS): d = 11.04
(br, 1H, OH), d = 7.36–7.32 (m, 1H, CHatom), d = 7.27–7.16 (m, 3H,
CHatom), d = 7.00–6.90 (m, 3H, CHatom), d = 6.72–6.67 (m, 1H,
3
CHatom), d = 6.39 (d, 1H, JHH = 3.2 Hz, NH), d = 4.97 (d, 1H,
3JHH = 2.4 Hz, CH), d = 2.43 (s, 3H, CH3) ppm. ESI-MS: calcd for [M
+H]+ 255.11, found 255.20. Anal. calcd. for C15H14N2O2 (254.28):
C, 70.85; H, 5.55; N, 11.02. Found (%): C, 70.90; H, 5.59; N, 11.07.
3. Results and discussion
2.3. Synthesis of the Co(III) complex
3.1. Synthesis
A solution of Co(II) nitrate hexahydrate (2.41 mg, 0.01 mmol) in
methanol (2 mL) was added dropwise to a solution of (E)-1-(2-
Aminophenyl) ethanone oxime (1.60 mg, 0.01 mmol) and 2-(2-
hydroxyphenyl)-4-methyl-1,2-dihydroquinazoline 3-oxide (2.50 mg,
0.01 mmol) in ethylacetate (4 mL) at room temperature. The color
of the mixing solution turned red-brownish immediately from
light yellow. The solvent was partially evaporated for half amount
at ambient temperature. After half a month several clear light
brown block-like single crystals suitable for X-ray crystallographic
As shown in Scheme 2, a new dinuclear Co(III) complex, [Co(L1)
(L2)]2 was obtained, which was formed in the course of complexa-
tion of HL1 and HL2 by Co(II) nitrate hexahydrate. The metal com-
plex is stable in atmospheric conditions. The ligands and both
complex are soluble in common organic solvents such as ethyl
acetate, chloroform, and DMF, and insoluble in n-hexane, diethyl
ether, and petroleum ether at ambient temperature. The structure
of the Co(III) complex was characterized by elemental analysis, IR,
Scheme 1. Synthesis route to the ligand HL2.

36
L.-Q. Chai et al. / Inorganica Chimica Acta 457 (2017) 34–40
Scheme 2. Synthesis route to the dinuclear Co(III) complex.
UV–Vis, EPR spectroscopy, as well as single-crystal X-ray crystal-
lography. Elemental analysis was in good agreement with the pro-
posed structure.
Surprisingly, the oxime moiety of the ligand HL1 is deprotonated,
the ligand HL2 is transformed to a tridentate dianionic Schiff base,
so two central Co(III) ions are present in the symmetric unit. The
crystal structure of the dinuclear Co(III) complex was depicted in
Fig. 1, and relevant bond lengths and angles are summarized in
Table 2. The metal-ligand bond lengths and angles are within nor-
mal values when compared with those observed in similar cobalt
(III) complexes [27]. The dihedral angels between every two metal
chelating rings adjacent to each other for the Co(III) complex are
56.33°, 54.78° and 50.27°, respectively (the plane defined by
Co1AO1AC1AC6AC7AN1, the adjacent plane defined by
Co1AN3AC16AC21AC22AN4, and the other adjacent plane
defined by Co1AN1AC8AC13AC14AN2). As a result, distorted
octahedral geometries are observed around both Co(III) cations
across the dinuclear unit. These structural features display that
the valence of cobalt ion is trivalent [28–31]. In addition, the latter
electron paramagnetic resonance (EPR) experiment also proved
that cobalt ion is trivalent.
3.2. X-ray crystal structures of [Co(L1)(L2)]2
X-ray structural analysis reveals that the dinuclear Co(III) com-
plex forms a novel 2:1 ligand to metal stoichiometry, and crystal-
lizes in the monoclinic system with
P 21/n space group.
As shown in Fig. 2, Co(III) complex exhibits an interesting sym-
metry, which is not obvious or even expected considering its
dimeric nature. Both metal centers are six-coordinated, presenting
a N4O2 coordination sphere. The ligand unit of the Co(III) complex
behaves as a cis-N3O1 tetradentate agent via one Schiff base nitro-
gen (N1), two imine nitrogen (N2 and N3), and one deprotonated
phenolic oxygens (O3), which are in the equatorial positions. The
coordination environment around Co(III) is best regarded as a
slightly distorted octahedral geometry with the distances of the
apical O1 and N4 to the N3O1 basal plane being 1.904(3) Å and
1.895(3) Å [32]. The four N3O1 donor atoms of the ligand unit are
Fig. 1. Crystal structure of the Co(III) complex with atoms numbering. All hydrogen
atoms are ignored for clarity. Displacement ellipsoids for non-H atoms are drawn at
the 30% probability level.
Table 2
Selected bond lengths (Å) and angles (°) of the Co(III) complex.
Bond
Lengths
Bond
Lengths
Co(1)AO(1)
Co(1)AN(1)
Co(1)AN(3)
Bond
1.869(3)
1.901(4)
1.987(4)
Angles
Co(1)AO(3)
Co(1)AN(2)
Co(1)AN(4)
Bond
1.898(3)
1.907(4)
1.949(4)
Angles
O(1)ACo(1)AO(3)
O(1)ACo(1)AN(2)
O(1)ACo(1)AN(4)
O(3)ACo(1)AN(2)
O(3)ACo(1)AN(4)
N(1)ACo(1)AN(3)
N(2)ACo(1)AN(3)
N(4)ACo(1)AN(3)
N(2)AO(3)ACo(1)
C(8)AN(1)ACo(1)
C(14)AN(2)ACo(1)
O(2)AN(4)ACo(1)
89.30(14)
90.47(15)
171.81(15)
94.93(14)
83.11(15)
93.92(16)
176.68(18)
83.72(17)
121.0(2)
115.4(3)
124.9(3)
117.0(3)
O(1)ACo(1)AN(1)
O(1)ACo(1)AN(3)
O(3)ACo(1)AN(1)
O(3)ACo(1)AN(3)
N(1)ACo(1)AN(2)
N(1)ACo(1)AN(4)
N(2)ACo(1)AN(4)
C(1)AO(1)ACo(1)
C(7)AN(1)ACo(1)
O(3)AN(2)ACo(1)
C(16)AN(3)ACo(1)
C(22)AN(4)ACo(1)
91.81(16)
92.73(17)
178.89(16)
86.03(15)
85.06(15)
95.78(16)
93.23(16)
124.0(3)
124.6(3)
118.4(3)
112.6(3)
129.2(4)
Fig. 2. Coordination configuration of the Co(III) complex.

L.-Q. Chai et al. / Inorganica Chimica Acta 457 (2017) 34–40
37
approximately coplanar (plane equation: ꢁ0.4472(13) x + 0.1536
(13) y ꢁ0.8812 (6) z = ꢁ4.0152 (71)). The central cobalt ion is in
the N3O1 basal plane, deviating from the mean plane by 0.037
(3) Å [33].
HL2 shows a strong band at 1291 cmꢁ1 assigned for
m
(ArAO) of
the quinazoline ring, shifted to 1284 cmꢁ1 of the Co(III) complex.
The ArAO stretching frequency shifts lower, indicating that CoAO
bonds are formed between Co(III) and oxygen of the phenol [37].
The OAH stretch of HL2 appears at about 3393 cmꢁ1, while the
infrared spectrum of the Co(III) complex shows the expected
Molecules of Co(III) complex are connected by two pairs of
C19–H19ꢀ ꢀ ꢀO3 and C23AH23BꢀꢀꢀCg6(C8AC13) intermolecular
hydrogen bonds (Fig. 3, Table 3), as well as weak
p
ꢀꢀꢀ
p
stacking
strong absorption due to
dence of OAH group from oxime. The band at 579 cmꢁ1 due to
(CoAN) and another band at 472 cmꢁ1 due to
(CoAO) are also
m
(OAH) at 3435 cmꢁ1, which is the evi-
interactions (Table 4), which play a principal role in stabilizing
m
the crystal structure of [Co(L1)(L2)]2. The distance of
p
ꢀꢀꢀ
p
stacking
m
interaction between the neighboring benzene ring centroid for Cg5
observed in the Co(III) complex. These results conform to the struc-
(C1AC6) ꢀꢀꢀCg7 (C16AC21) is 3.958(4) Å. As shown in Fig. 4, with
tural data obtained by X-ray crystallography.
the help of intermolecular hydrogen bonds and
pꢀꢀꢀp stacking
interactions, adjacent moleculars are linked together to display
an infinite two-dimensional (2-D) supramolecular frameworks
3.3.2. UV–Vis absorption spectra
UV–Vis aborption spectra of HL2 and the Co(III) complex were
determined in 5 ꢂ 10ꢁ5 mol Lꢁ1 CH2Cl2 solution. As shown in
Fig. 5, absorptions of the Co(III) complex were obviously different
from those of HL2. Compared with the Co(III) complex, three
absorptions were observed at 234, 259, and 376 nm, respectively
along the bc-plane [34]. All hydrogen bonds and
p p stacking
ꢀꢀꢀ
interactions made the structure of the crystal stabilization with
the dicobalt cores Co1ꢀꢀꢀCo2 intermetallic distance of 3.671(1) Å
and the nearest CoꢀꢀꢀCo distance of 8.781(12) Å [35].
(e
= 19,874, 13,166, and 2930 molꢁ1 L cmꢁ1) in the spectrum of
3.3. Spectral investigation
HL2. The absorption was at 234 nm of HL2 shifts to 264 nm
= 19,996 molꢁ1 L cmꢁ1) in the Co(III) complex, which can be
assigned to
p⁄ transition of phenyl rings [38,39]. A new uncon-
spicuous absorption peak at 452 nm (
= 1024 molꢁ1 L cmꢁ1) was
(e
3.3.1. IR spectra
p-
The main FT-IR spectra of HL2 and the Co(III) complex in the
e
400–4000 cmꢁ1 region are shown as Supporting information
observed in the Co(III) complex, which could be attributed to
metal-to-ligand charge transfer (MLCT) transitions [40]. These
observations were in line with common spectral features of d-
(Fig. S1). HL2 exhibits a characteristic C@N stretch at 1610 cmꢁ1
,
while C@N of the Co(III) complex is observed at 1604 cmꢁ1 [36].
Fig. 3. Intermolecular hydrogen bonds and
p
ꢀꢀꢀp
stacking interactions of the Co(III) complex.
Table 3
Hydrogen bonding distances (Å) and angles (°) of the Co(III) complex.
DAHꢀ ꢀ ꢀA
d (DAH)
d (Hꢀ ꢀ ꢀA)
d (DꢀꢀꢀA)
DAHꢀ ꢀ ꢀA
Symmetry codes
C19AH19ꢀ ꢀ ꢀO3
0.93
0.96
2.470
2.830
3.295(7)
3.641(7)
148
142
ꢁx, 1/2 + y, 1/2 ꢁ z
x, 1/2ꢁy, ꢁ1/2 + z
C23AH23BꢀꢀꢀCg6
Cg6 is the centroids for benzene ring C8AC9AC10AC11AC12AC13.
Table 4
pꢀꢀꢀp stacking interaction of the Co(III) complex.
RingI RingJ
CgIꢀꢀꢀCgJ
3.958(4)
Inter-plane angle
11.1(3)
CgI–Perp
ꢁ3.289(3)
CgJ–Perp
ꢁ3.585(3)
Slippage
–
Cg5ꢀꢀꢀCg7
Cg5 and Cg7 are the centroids for benzene ring C1AC2AC3AC4AC5AC6 and C16AC17AC18AC19AC20AC21, respectively. CgIꢀꢀꢀCgJ is the distance between ring centroids.
The inter-plane angle is that between the planes of the rings I and J. CgI-Perp is the perpendicular distance of CgI on ring J. CgJ-Perp is the perpendicular distance of CgJ on ring I.
Slippage is the distance between CgI and perpendicular projection of CgJ on ring I.

38
L.-Q. Chai et al. / Inorganica Chimica Acta 457 (2017) 34–40
Fig. 4. View of the 2-D supramolecular frameworks of the Co(III) complex along the bc-plane.
Fig. 5. UV–Vis absorption spectra: HL2 (dashed line) and the Co(III) complex (solid
line) in CH2Cl2 (5 ꢂ 10ꢁ5 mol Lꢁ1).
Fig. 6. X-band EPR spectrum of the cobalt(III) complex at liquid nitrogen
temperature.
block metal complexes. The spectral studies reveal an octahedral
geometry of the Co(III) ion with 3d6 electronic configuration.
3.3.3. EPR spectroscopy
Electron paramagnetic resonance (EPR) spectroscopy of the din-
uclear Co(III) complex was recorded using powdered sample at liq-
uid nitrogen temperature. As shown in Fig. 6, EPR spectrum for the
Co(III) complex has no paramagnetic signal at 110 K, hence it
suggests that the existence of the Co(III) ion which is in consistent
with our conclusion, not only the cobalt ion of the cobalt complex
is trivalent but also Co(III) is a low-spin state. The low-spin Co(III)
ion is expected to reduce the stronger regular geometric prefer-
ences than the high-spin Co(II) ion [41]. The change in the
spin state usually could be associated with the coordination
environment around the metal center, owing to an electron is
added to the antibonding dz2 orbital of the transition metal ion
in the Co(III) complexes [42]. Further investigations will demon-
strate how this can be accompanied by structural changes in the
redox behavior of small molecules [43]. The cobalt(III) ion in
low-spin state with a t62g configuration is diamagnetic in nature
and so EPR is silent, whereas cobalt(II) exist in both low spin
Fig. 7. Cyclic voltammogram of the Co(III) complex in DMF solution. Scan rate
100 mV sꢁ1
.

L.-Q. Chai et al. / Inorganica Chimica Acta 457 (2017) 34–40
39
Table 5
Antimicrobial activities of HL2 and the Co(III) complex.
Compound
Inhibition Zone concentration (mm)
E. coli
S. aureus
0.3
0.625
1.25
2.5
5.0
0.3
0.625
1.25
2.5
5.0
HL2
Complex
Amoxicillin
6
10
12
6
11
13
8
11
15
8
13
16
9
14
17
7
13
14
7
13
15
8
15
17
9
16
18
10
16
20
(S = 1/2) and high spin (S = 3/2) states and is paramagnetic, there-
fore EPR spectroscopy is recorded to distinguish the valence and
spin state of cobalt ion (S = 1/2 and 3/2) [44]. Work along this line
is in progress in our laboratories.
and possible delocalization of p-electron within the whole chelate
ring. Further, it enhances the lipophilic character of the central
atom. These observations are similar to previous reports on inter-
esting antimicrobial activities of related complexes [51–52].
3.4. Electrochemistry studies
4. Conclusion
A new dinuclear Co(III) complex, [Co2(L1)2(L2)2] derived from
HL1 and HL2 have been synthesized and structurally characterized.
The electrochemical property of dinuclear Co(III) complex has
been studied in DMF containing 0.05 mol Lꢁ1 tetrabutylammonium
perchlorate (TBAP) over the potential range from ꢁ3.0 to 1.0 V vs.
Ag/AgNO3 by cyclic voltammetry (CV) using a three-electrode sys-
tem under oxygen-free conditions with the scanning rate was
100 mV sꢁ1 [45,35]. As shown in Fig. 7, the Co(III) complex exhibits
two reversible redox waves, which are assigned to Co(III)/Co(II)
and Co(II)/Co(I) redox processes [46]. The first pair of oxidation–
reduction peaks corresponding to Co(III)/Co(II) couples,
Epa1 = 0.621 V, Epc1 = ꢁ2.086 V, and the average formal potential
E1/2 is ꢁ0.733 V. The second pair of oxidation–reduction
peaks corresponding to Co(II)/Co(I) couples, Epa2 = ꢁ0.264 V,
Epc2 = ꢁ2.413 V, and E1/2 is ꢁ1.339 V. The peak-to-peak separation
between the anodic and cathodic (4Ep) is 2.707, 2.149 V, respec-
tively. The proportion of the peak current (ipa1/ipc1) is 0.770
In FT-IR spectra of the Co(III) complex,
m(CoAN) and m(CoAO)
absorption frequencies have been observed. The X-ray crystal
structure of the Co(III) complex reveals that it is a dinuclear struc-
ture and has a slight distortion toward octahedral geometry. In the
crystal structure, an infinite 2-D supramolecular structure is
formed through intermolecular hydrogen bonding and
pꢀꢀꢀp stack-
ing interactions. Moreover, the quasi-reversible one-electron Co
(III)/Co(II) and Co(II)/Co(I) redox waves were determined by cyclic
voltammetry, which is also confirmed by the integrated results of
EPR experiment. EPR spectroscopy of the Co(III) complex was silent
hence it suggests that the existence of the low-spin state of Co(III)
transition metal ion. These results conform to the structural data
obtained by X-ray crystallography. In addition, the activity data
showed the metal complex to be more antibacterial than the
quinazoline-type ligand HL2.
(ipa1 = ꢁ24.074
current over cathodic peak current (ipa2/ipc2) is 0.290
(ipa2 = 8.311 A). These characteristics suggest
lA, ipc1 = 31.264 lA), and the ratio of anodic peak
lA, ipc2 = ꢁ28.484
l
that it is a quasi-reversible electrode process [47] and give ample
evidence for being a Co(III) complex [38,42,48]. Simultaneously,
the result is also supported by the EPR measurement of the exis-
tence of low-spin state of Co(III) in the complex [43,44].
Acknowledgments
The authors express their sincere thanks to the financial sup-
port by the Fundamental Research Funds for the Gansu Province
Universities (No. 214152), the Natural Science Foundation of Gansu
Province in China (No. 1508RJZA082), and Graduate Student Exper-
imental Innovation and Technology Project of Lanzhou Jiaotong
University.
3.5. Antimicrobial activity
The antimicrobial activity of HL2 and the Co(III) complex were
tested against Escherichia coli as Gram-negative bacteria and Sta-
phylococcus aureus as Gram-positive bacteria by the disc diffusion
method. The process culture of bacteria used Sabouraud dextrose
agar. The agar was poured into petri dishes and microorganisms
were introduced on the surface of agar plates individually. The
plates were placed on a leveled surface and incubated for 24 h at
37 °C, soon afterwards the diameters of the inhibition zones were
measured. The blank sterile discs measuring 5 mm in diameter
were dissolved in dimethyl sulfoxide (DMSO) and soaked in a
known concentration of the test compounds, such as the concen-
trations were 0.3, 0.625, 1.25, 2.5 and 5.0 mg mLꢁ1. The obtained
results were compared with Amoxicillin as reference standards
with different concentrations [49].
Appendix A. Supplementary data
CCDC 1408207 contains the supplementary crystallographic
data of the Co(III) complex for this paper. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.ica.2016.12.004.
References
[1] H. Furukawa, K.E. Cordova, Science 341 (2013) 974–986.
[2] J.M. Xiao, W. Zhang, Inorg. Chem. Commun. 12 (2009) 1175–1178.
[3] G. Dilber, H. Kantekin, N. Yayli, R. Abbasog˘lu, J. Coord. Chem. 64 (2011) 3679–
3692.
[4] S.S. Sun, C.L. Stern, S.T. Nguyen, J.T. Hupp, J. Am. Chem. Soc. 126 (2004) 6314–
6326.
[5] K.C. Gupta, A.K. Sutar, Coord. Chem. Rev. 252 (2008) 1420–1450.
[6] C. Goze, C. Leiggener, S.X. Liu, L. Sanguinet, E. Levillain, A. Hauser, S. Decurtins,
Chem. Phys. Chem. 8 (2007) 1504–1512.
[7] Y. Sui, D.P. Li, C.H. Li, X.H. Zhou, T. Wu, X.Z. You, Inorg. Chem. 49 (2010) 1286–
1288.
The diameter of inhibition zones of HL2 and the Co(III) complex
are presented in Table 5, the dinuclear Co(III) complex demon-
strated enhanced more antimicrobial activities than quinazoline-
type ligand HL2 under the same conditions and HL2 has a weak
biological activity [50]. As observed in Table 5, this increase in
the antibacterial activity of the metal complex with increase in
concentration can be explained on the basis of the chelation the-
ory. Chelation reduces the polarity of the metal atom mainly due
to partial share of positive charge of metal atom with donor groups
[8] G. Magadur, J.S. Lauret, G. Charron, F. Bouanis, E. Norman, V. Huc, C.S. Cojocaru,
S. Gomez-Coca, E. Ruiz, T. Mallah, J. Am. Chem. Soc. 134 (2012) 7896–7901.
[9] J. Dhuguru, W.J. Liu, W.G. Gonzalez, W.M. Babinchak, J. Miksovska, R. Landgraf,
J.N. Wilson, J. Org. Chem. 79 (2014) 4940–4947.

40
L.-Q. Chai et al. / Inorganica Chimica Acta 457 (2017) 34–40
[10] M. Rajasekar, S. Sreedaran, R. Prabu, V. Narayanan, R. Jegadeesh, N. Raaman, A.
K. Rahiman, J. Coord. Chem. 63 (2010) 136–146.
[11] Z.H. Chohan, S.H. Sumrra, M.H. Youssoufi, T.B. Hadda, Eur. J. Med. Chem. 45
(2010) 2739–2747.
[12] P. Zhichkin, E. Kesicki, J. Treiberg, L. Bourdon, M. Ronsheim, H.C. Ooi, S. White,
A. Judkins, D. Fairfax, Org. Lett. 9 (2007) 1415–1418.
[13] Co Inc., Merck, European Patent EP 0530994 A1: Quinazoline derivatives as
inhibitors of HIV reverse transcriptase, Bulletin 10 (1993) 03.
[14] R. Alonso, A. Caballero, P.J. Campos, D. Sampedro, M.A. Rodriguez, Tetrahedron
66 (2010) 4469–4473.
[31] Y. Suenaga, C.G. Pierpont, Inorg. Chem. 44 (2005) 6183–6191.
[32] P. Pattanayak, J.L. Pratihar, D. Patra, P. Brandão, V. Felix, Inorg. Chim. Acta 418
(2014) 171–179.
[33] R. Taherlo, M. Salehi, Inorg. Chim. Acta 418 (2014) 180–186.
[34] W.K. Dong, J. Zhang, Y. Zhang, N. Li, Inorg. Chim. Acta 444 (2016) 95–102.
[35] Y.I. Cho, D.M. Joseph, M.J. Rose, Inorg. Chem. 52 (2013) 13298–13300.
[36] W.K. Dong, S.J. Xing, Y.X. Sun, J. Coord. Chem. 65 (2012) 1212–1220.
[37] L.Q. Chai, G. Wang, Y.X. Sun, W.K. Dong, L. Zhao, X.H. Gao, J. Coord. Chem. 65
(2012) 1621–1631.
[38] L.Q. Chai, J.J. Huang, H.S. Zhang, Y.L. Zhang, J.Y. Zhang, Y.X. Li, Spectrochim.
Acta Part A 131 (2014) 526–533.
[39] W.K. Dong, L.C. Zhu, Y.J. Dong, J.C. Ma, Y. Zhang, Polyhedron 117 (2016) 148–
154.
[15] Y.C. Chen, D.Y. Yang, Tetrahedron 69 (2013) 10438–10444.
_
´
_
[16] E.M. Olasik, K.B. Swiatkiewiz, E. Zurek, U. Krajewska, M. Rózalski, T.J. Bartczak,
Arch. Pharm. Pharm. Med. Chem. 337 (2004) 239–246.
[17] M. Kumar, R.I. Kureshy, A.K. Shah, A. Das, N.H. Khan, S.H.R. Abdi, H.C. Bajaj, J.
Org. Chem. 78 (2013) 9076–9084.
[40] C.J. Dhanaraj, J. Johnson, J. Joseph, R.S. Joseyphus, J. Coord. Chem. 66 (2013)
1416–1450.
[18] H. Chun, I. Bernal, Cryst. Growth Des. 1 (2001) 143–149.
[19] M. Alimi, A. Allam, M. Selkti, A. Tomas, P. Roussel, E. Galardon, I. Artaud, Inorg.
Chem. 51 (2012) 9350–9356.
[20] L.Q. Chai, G. Liu, Y.L. Zhang, J.J. Huang, J.F. Tong, J. Coord. Chem. 66 (2013)
3926–3938.
[41] J. McCrea, V. McKee, T. Metcalfe, S.S. Tandon, J. Wikaira, Inorg. Chim. Acta 297
(2000) 220–230.
[42] M. Salehi, M. Hasanzadeh, Inorg. Chim. Acta 426 (2015) 6–14.
[43] M. Kügler, J. Gałe˛zowska, F. Schendzielorz, S. Dechert, S. Demeshko, I. Siewert,
Eur. J. Inorg. Chem. 2015 (2015) 2695–2706.
[21] L.Q. Chai, H.S. Zhang, J.J. Huang, Y.L. Zhang, Spectrochim. Acta Part A 137
(2015) 661–669.
[44] A. Ray, G.M. Rosair, R. Kadam, S. Mitra, EPR and DNA binding studies,
Polyhedron 28 (2009) 796–806.
[22] L.Q. Chai, J.J. Huang, J.Y. Zhang, Y.X. Li, J. Coord. Chem. 68 (2015) 1224–1237.
[23] L.Q. Chai, J.Y. Zhang, L.C. Chen, Y.X. Li, L.J. Tang, Res. Chem. Intermed. 42 (2016)
3473–3488.
[24] Aus dem Chemisch-Phamazeutischen Forschungsinstisut Clhj (Klausenburg),
Rumänien. Eine neue synthese für chinazolin-N3-oxyde und 1.2-dihydro-
chinazolin-N3-oxyde, KöVENDI und KIRCZ. 98 (1965) 1049–1059.
[25] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, J. Appl.
Cryst. 42 (2009) 339–341.
[45] L.Q. Chai, Y.X. Li, L.C. Chen, J.Y. Zhang, J.J. Huang, Inorg. Chim. Acta 444 (2016)
193–201.
[46] K.R. Grunwald, M. Volpe, P. Cias, G. Gescheidt, N.C.M. Zanetti, Inorg. Chem. 50
(2011) 7478–7488.
[47] S.K. Verma, V.K. Singh, J. Coord. Chem. 68 (2015) 1072–1087.
[48] F.L.S. Bustamante, J.M. Metello, F.A.V. Castro, C.B. Pinheiro, M.D. Pereira, M.
Lanznaster, Inorg. Chem. 52 (2013) 1167–1169.
[49] B. Shaabani, A.A. Khandar, H. Mobaiyen, N. Ramazani, S.S. Balula, L. Cunha-
Silva, Polyhedron 80 (2014) 166–172.
[26] G.M. Sheldrick, Acta Crystallogr. A 64 (2008) 112–122.
[27] V. Chandrasekhar, A. Dey, A.J. Mota, E. Colacio, Inorg. Chem. 52 (2013) 4554–
4561.
[50] B. Shaabani, A.A. Khandar, F. Mahmoudi, M.A. Maestro, S.S. Balula, L. Cunha-
Silva, Polyhedron 57 (2013) 118–126.
[28] C. Dey, R. Das, P. Pachfule, P. Poddar, R. Banerjee, Cryst. Growth Des. 11 (2011)
139–146.
[29] S.S. Qian, X.S. Cheng, Z.L. You, H.L. Zhu, Synth. React. Inorg. Met.-Org. Nano-
Met. Chem. 43 (2013) 1465–1470.
[51] A.K. Parhi, Y.Z. Zhang, K.W. Saionz, P. Pradhan, M. Kaul, K. Trivedi, D.S. Pilch, E.J.
LaVoie, Bioorg. Med. Chem. Lett. 23 (2013) 4968–4974.
[52] A.K. Ghosh, M. Mitra, A. Fathima, H. Yadav, A.R. Choudhury, B.U. Nair, R. Ghosh,
Polyhedron 107 (2016) 1–8.
[30] S.E. Cheyne, L.F. McClintock, A.G. Blackman, Inorg. Chem. 45 (2006) 2610–
2618.