Synthesis, characterization, DFT modeling and biological studies of new Co(II), Ni(II) and Cu(II) 4,6-bis(4-chlorophenyl)-2-amino-1,2-dihydropyridine-3-carbinitrile complexes

Article abstract of DOI:10.1007/s13738-017-1188-8

Three new metal complexes of 4,6-bis(4-chlorophenyl)-2-amino-1,2-dihydropyridine-3-carbinitrile (L) with Co(II), Ni(II) and Cu(II) were synthesized and characterized with physicochemical and spectroscopic techniques. The data suggest that (L) acts as a bidentate ligand bound to the divalent metal ions through amino N and carbinitrile N atoms having [M(L)₂(H₂O)₂]²⁺ formula (M?=?metal ions). The theoretical parameters, model structures, charges and molecular orbitals of all possible complexes have been determined using density functional theory. The energy gap of free ligand is ?E?=?0.12565?eV, and this value is greater than energy gap of complexes, which indicates that the complexes are more reactive than free ligand. Also, ?E of Co(II) complex is lower than other complexes, which indicates that Co(II) complex is more reactive than Ni(II) and Cu(II) complexes. The antibacterial and antifungal activities of the ligand, metal salts and its complexes were tested against some microorganisms (bacteria and fungi). The complexes showed increased antibacterial and antifungal profile in comparison with the free ligand.

Full text of DOI:10.1007/s13738-017-1188-8

J IRAN CHEM SOC
DOI 10.1007/s13738-017-1188-8
ORIGINAL PAPER
Synthesis, characterization, DFT modeling and biological studies
of new Co(II), Ni(II) and Cu(II) 4,6‑bis(4‑chlorophenyl)‑2‑amino
‑1,2‑dihydropyridine‑3‑carbinitrile complexes
W. A. Zordok1,2 · S. A. Sadeek1 · A. F. El‑Farargy1
Received: 7 April 2017 / Accepted: 23 August 2017
© Iranian Chemical Society 2017
Abstract Three new metal complexes of 4,6-bis(4-
chlorophenyl)-2-amino-1,2-dihydropyridine-3-carbinitrile
(L) with Co(II), Ni(II) and Cu(II) were synthesized and
characterized with physicochemical and spectroscopic
techniques. The data suggest that (L) acts as a bidentate
ligand bound to the divalent metal ions through amino N
and carbinitrile N atoms having [M(L)2(H2O)2]2+ formula
(M = metal ions). The theoretical parameters, model struc-
tures, charges and molecular orbitals of all possible com-
plexes have been determined using density functional theory.
The energy gap of free ligand is ∆E = 0.12565 eV, and this
value is greater than energy gap of complexes, which indi-
cates that the complexes are more reactive than free ligand.
Also, ∆E of Co(II) complex is lower than other complexes,
which indicates that Co(II) complex is more reactive than
Ni(II) and Cu(II) complexes. The antibacterial and antifun-
gal activities of the ligand, metal salts and its complexes
were tested against some microorganisms (bacteria and
fungi). The complexes showed increased antibacterial and
antifungal profle in comparison with the free ligand.
Introduction
Pyridine is common but vital heterocyclic compounds in
organic synthesis, especially as synthetic intermediates and
agrochemicals. Pyridine derivatives, such as alkoxy pyridine
compounds, aminopyridine and its derivatives, substituted
fused pyridine compounds, have already been applied widely
in the felds of agrochemical products [1]. Pyridine deriva-
tives have gained considerable attention due to their cen-
tral role as the versatile building blocks in the synthesis of
natural products and active pharmaceuticals [2–4]. Moreo-
ver, pyridine derivatives play individual role in bactericide,
acaricide, and phytocide [5]. Copper is one of the essential
transition elements, which plays a vital role in various bio-
logical processes, such as hemoglobin biosynthesis, nerve
impulse regulation and various enzymatic reactions in bio-
logical systems when present in optimum concentrations. An
improper balance of the Cu(II) ion is responsible for various
diseases, such as Alzheimer’s, Menkes and Wilson disease
and infammatory disorders [6]. Metal complexes of some
pyridine derivatives have shown antimicrobial activities in
recent years [7, 8]. The enhancement of the antimicrobial
activity of certain chemicals can be achieved by the addi-
tion of metals. The role of metals in antimicrobial activity
is shown in many studies [9–13].
Keywords Pyridine derivative · Metal complexes ·
Spectra · DFT · Antimicrobial study
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-017-1188-8) contains supplementary
material, which is available to authorized users.
The 4,6-bis(4-chlorophenyl)-2-amino-1,2-dihydropyri-
dine-3-carbinitrile (L) new compound was synthesized in
our laboratory, and the literature research has shown that no
work is reported on it with transition metal ions. We report
here the study of the reaction of L with Co(II), Ni(II) and
Cu(II) and interpreting the nature of these interactions using
the following techniques IR, UV–Vis, 1H NMR, mass spec-
tra, thermal analysis, elemental analysis, magnetic properties
and molar conductivity as well as some results of bioac-
tivity tests are also included. All prepared complexes were
* W. A. Zordok
wazordok@yahoo.com
1
Department of Chemistry, Faculty of Science, Zagazig
University, Zagazig, Egypt
2
Department of Chemistry, University College
of Quanfudha, Umm Al-Qura University, Umm al-Quwain,
Kingdom of Saudi Arabia
Vol.:(0123456789)
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J IRAN CHEM SOC
investigated theoretically by using density functional theory
(DFT) method by applying the GAUSSIAN 98 W package
of programs [14] at B3LYP/CEP-31G [15] level of theory.
used for this purpose. IR spectra were recorded on FTIR
460 PLUS (KBr disks) in the range from 4000 to 400 cm−1,
1
and H NMR spectra were recorded on Varian Mercury
VX-300 NMR spectrometer using DMSO-d6 as a solvent.
TG-DTG measurements were taken under N2 atmosphere
with rate fow 30.0 mL/min within the temperature range
from room temperature to 800 °C using TGA-50H Shi-
madzu, and the mass of sample was accurately weighted out
in an aluminum crucible. Electronic spectra were obtained
using UV-3101PC Shimadzu. The solid refection spectra
were recorded with KBr pellets. Mass spectra were recorded
on GCMS-QP-1000EX Shimadzu (ESI-70 eV) in the range
from 0 to 1090. Magnetic measurements were taken on a
Sherwood Scientifc magnetic balance using Gouy method
using Hg[Co(SCN)4] as a calibrant. Molar conductivities of
the solution of the ligand and metal complexes in DMF at
1 × 10−3 M were measured on CONSORT K410. All meas-
urements were taken at ambient temperature with freshly
prepared solution.
Materials and methods
Chemicals
All chemicals and solvents used for the preparation of the
compounds were of analytical reagent grade, commercially
available from diferent sources and used without further
purifcation. 4-Chloroacetophenone, 4-benzaldehyde, ethyl
cyanoacetate, ammonium acetate, glacial acetic acid, etha-
nol, acetone and all solvents were purchased from Fluka
Chemical Co. and AgNO3, BaCl2, FeCl3·6H2O, CoCl3·6H2O,
NiSO4·8H2O and Cu(CH3COO)2·H2O from Aldrich Chemi-
cal Co.
Preparation of 4,6‑bis(4‑chlorophenyl)‑2‑amino‑1,2‑d
ihydropyridine‑3‑carbinitrile (L)
Antimicrobial investigation
A mixture of 5,7-bis(4-chlorophenyl)-tetrazolopyridine-
8-carbonitrile (0.01 mol), zinc dust (0.01 mol) and glacial
acetic acid (10 ml) was stirred at room temperature for 2 h
and then heated on water bath at 80 °C for 8 h. The reaction
mixture was poured into water and extracted with chloro-
form, and the extract was evaporated under reduced pressure.
The formed solid compound was recrystallized using etha-
nol as a solvent. The proposed formula of L (C18H11N3Cl2,
M.Wt. = 340.00 g) is in good agreement with mass spectrum
(M+) at m/z = 339.0 (25%) and also confrmed by IR and 1H
NMR spectral data.
Antibacterial activity of the ligand and its metal complexes
was investigated by a previously reported modifed method
of Beecher and Wong [16] against diferent bacterial species,
such as Staphylococcus aureus (S. aureus), Bacillus subtilis
(B. subtilis), Escherichia coli (E. coli) and Pseudomonas
aeruginosa (P. aeruginosa), and antifungal screening was
studied against two species, Candida albicans and Asper‑
gillus fumigatus. The tested microorganisms isolates were
isolated from Egyptian soil and identifed according to the
standard mycological and bacteriological keys for identifca-
tion of fungi and bacteria as stock cultures in the Microbi-
ology Laboratory, Faculty of Science, Zagazig University.
The nutrient agar medium for antibacterial (0.5% peptone,
0.1% beef extract, 0.2% yeast extract, 0.5% NaCl and 1.5%
agar–agar) and Czapek-Dox medium for antifungal (3%
sucrose, 0.3% NaNO3, 0.1% K2HPO4, 0.05% KCl, 0.001%
FeSO4 and 2% agar–agar) were prepared [17], then cooled to
47 °C and seeded with tested microorganisms. Sterile water
agar layer was poured, solidifed and then poured the pre-
pared growth medium for fungi and bacteria (plate of 12 cm
diameter, 15 ml medium plate). After solidifcation, 5-mm-
diameter holes were punched by a sterile cork borer. The
investigated compounds, i.e., ligand and its complexes, were
introduced in petri dishes (only 0.1 ml) after dissolving in
DMF at 1.0 × 10−3 M. These culture plates were then incu-
bated at 37 °C for 20 h for bacteria and at 30 °C for 7 days
for fungi. The activity was determined by measuring the
diameter of the inhibition zone (in mm). Bacterial growth
inhibition was calculated with reference to the positive con-
trol, i.e., ampicillin, amoxycillin and cefaloxin.
Preparation of the metal complexes
The purple solid complex [Co(L)2(H2O)2]Cl2·8H2O was
prepared by adding 0.5 mmol (0.136 g) of cobalt chloride
hexahydrate in 20 ml acetone drop wisely to a stirred sus-
pended solution 1 mmol (0.340 g) of L in 50 ml acetone. The
reaction mixture was stirred for 15 h at 35 °C in a water bath.
The purple solid complex was fltered of and dried under
vacuum over anhydrous CaCl2. Dark yellow [Ni(L)2(H2O)2]
SO4·8H2O and light green [Cu(L)2(H2O)2](CH3COO)2
solid complexes were prepared in similar manner described
above by using acetone as a solvent and NiSO4·8H2O,
Cu(CH3COO)2·H2O in 1:2 molar ratio (M:L).
Elemental C, H and N analysis was carried out on a Per-
kin Elmer CHN 2400. The percentage of the metal ions were
determined gravimetrically by transforming the solid prod-
ucts into metal oxide or metal sulfate and also determined by
using atomic absorption method. Spectrometer model PYE-
UNICAM SP 1900 ftted with the corresponding lamp was
1 3

J IRAN CHEM SOC
Results and discussion
New complexes [Co(L)2(H2O)2]Cl2·8H2O, [Ni(L)2(H2O)2]
SO4·8H2O and [Cu(L)2(H2O)2](CH3COO)2 with a color
characteristic of the metal ions formed in the reaction of L
with Co(II), Ni(II) and Cu(II) in acetone as a solvent at room
temperature. The complexes were characterized through
their elemental analysis, IR, UV–Vis, 1H NMR, mass spec-
tra, melting point, molar conductivity, magnetic properties
as well as thermogravimetric analyses. The results enable us
to characterize the complexes and make an assessment of the
bonding and structures inherent in them.
The IR spectroscopic and thermogravimetric data confrm
the presence of water molecules (hydrated and coordinated)
in the composition of the complexes. The molar conductivi-
ties of solutions of free L ligand and the corresponding metal
complexes (10−3 M in DMF) were found at 10.50, 180.00,
195.00 and 170.80 S cm2 mol−1 (Table 1), which reveals that
all the complexes are electrolytes. Also, qualitative reactions
revealed the presence of chloride, sulfate and acetate ions
outside the coordination sphere [18]. The magnetic moments
(as B.M.) of the complexes were measured at room tempera-
ture and the measured magnetic moment for Co(II), Ni(II)
and Cu(II) complexes found at 4.81, 3.72 and 1.73 B.M.,
respectively.
Spectroscopic studies
IR absorption spectra
The mid-infrared spectra of L and their metal complexes
were recorded from KBr disks. The spectral bands shown
in Fig. S1 were resolved and assigned to their vibrational
modes and are compiled in Table S1. As expected, the
absorption bands characteristic of L unit is observed in the
complexes with small changes in band intensities and wave
number. Before discussing the assignments of the infrared
spectra, the proposed structures of the complexes must be
considered. Here, metal ions react with L forming complexes
of monomeric structure where the metal ions are six coordi-
nated (Scheme 1), and the equatorial positions may be occu-
pied by the four nitrogen atoms of the two carbinitrile and
two amino groups of L, and the axial positions are occupied
by the oxygen atoms of the two water molecules. The struc-
tures of these complexes possess two planes of symmetry
and twofold axis and hence may belong to C2ν symmetry.
The C2ν complexes [M(L)2(H2O)2]2+ are expected to dis-
play 219 vibrational fundamentals, which are distributed
between A1, A2, B1 and B2 motions; all are monodegenerate
[19–21] and IR and Raman active, except for the A2 mode
which is only Raman active.
The infrared spectra of metal complexes exhibit broad
bands at 3422 and 3455 cm−1, corresponding to the ν H2O
1 3

J IRAN CHEM SOC
Scheme 1 The coordination
mode of L with M. M = Co(II),
Ni(II) and Cu(II)
2+
Cl
Cl
OH2
M
NC
CN
H2N
N
N
NH2
OH2
Cl
Cl
vibration, which confrms the presence of water molecules
in the complexes [22, 23]. The N–H vibration appears in the
region of 3389–3152 cm−1 [22]. The two bands observed
at 3192 and 2205 cm−1 in the spectrum of free ligand have
been assigned to the stretching vibration ν(N–H) and the car-
binitrile group ν(C≡N), respectively. The shift of the char-
acteristic peaks of ν(N–H) and ν(C≡N) vibrations to a lower
values (Table 2) indicates the coordination of ligand through
nitrogen atoms of amino and carbinitrile groups [24, 25].
The spectra of the isolated solid complexes showed a
group of bands with diferent intensities which are charac-
teristics for ν (M–O) and ν (M–N). The ν(M–O) and ν(M–N)
bands were observed at 600, 502 cm−1 for Co(II), at 625,
511 cm−1 for Ni(II) and 650, 509 cm−1 for Cu(II). According
to the above discussion, the L is coordinated to metal ions
as a bidentate ligand through nitrogen atoms of amino and
carbinitrile groups.
UV–visible solid refection Spectra
Figure S2 shows the electronic solid refection spectra of L
and their metal complexes in the wavelength interval from
200 to 800 nm. The free ligand refected at 255 and 298 nm
may be attributed to π–π* and n–π* internal ligand transi-
tions [26].
The shift of the refection bands to lower or higher val-
ues in case of Co(II), Ni(II) and Cu(II) complexes indicated
the formation of their metal complexes. Also, the new solid
complexes showed new bands in the range from 431 to
527 nm, which may be assigned to the ligand to metal charge
transfer. The electronic spectrum of Co(II) complex gives
band at 621 nm. The band is assigned to 4T1g(F) → 4T1g(P)
transition typifed octahedral geometry [27]. Ni(II) com-
plex has two bands 522 and 634 nm, which may be assigned
3
3
3
3
to A2g → T1g(P) and A2g → T1g(F) transition [28].
Table 2 The inhibition diameter zone values (mm) for L and its metal complexes
Compounds
Microbial species
Bacteria
Fungi
E. coli
P. aeruginosa
B. subtilis
S. aureus
C. Albicans
A. Fumigatus
L
10 0.22
20 + 2 0.22
18 + 1 0.22
20 + 2 0.22
0
12 0.11
19 + 2 0.11
15NS 0.11
16 + 1 0.11
0
0
0
0
15 0.09
20 + 1 0.09
19 + 1 0.09
20 + 1 0.09
0
0
0
0
18 0.05
21NS 0.05
19NS 0.05
21NS 0.05
0
0
0
0
14 0.01
16NS 0.01
15NS 0.01
19 + 1 0.01
0
0
0
0
16 0.10
16NS 0.10
20NS 0.10
19NS 0.10
0
0
0
0
L/Co(II)
L/Ni(II)
L/Cu(II)
CoCl2·6H2O
NiSO4·6H2O
Cu(OCOCH3)2·H2O
Control (DMSO)
Standard
0
8
0
0.33
Ampicillin
Amoxicillin
Cefaloxin
0
0
0
0
0
28 0.40
22 0.11
27 1.15
0
0
0
0
0
0
0
18 1.73
16 0.52
24 0.34
Statistical signifcance PNS, P not signifcant, P > 0.05; P+1 P signifcant, P < 0.05; P+2 P highly signifcant, P < 0.01; P+3 P very highly signif-
cant, P < 0.001; Student’s t test (paired)
1 3

J IRAN CHEM SOC
Cu(II) complex has band 627 nm, which may be assigned to
and DTG curves, and Table S2 shows the maximum temper-
ature values for decomposition along with the corresponding
weight loss values for each step of the decomposition reac-
tion. The obtained data strongly support the proposed chemi-
cal formulas for complexes. The thermal decomposition of
L started at 50 °C and fnished at 350 °C with one stage
and is accompanied by a weight loss 82.30%, corresponding
exactly to the loss of 5C2H2 + HCN + 2NCCl, which is very
close to calculated value 82.35%. The maximum rate of mass
lose is indicated by DTG peak at 316 °C.
2B1g → 2Eg transition [29].
1H NMR spectra
The formation of the metal complexes was also confrmed by
1H NMR spectra. Figure S3 represents the 1H NMR spectra
of L and their metal complexes. On comparing main peaks
of L with its complexes, it is observed that all the peaks of
the free ligand are present in the spectra of the complexes
with chemical shift upon binding of ligand to the metal
The thermal decomposition of the two complexes
[Co(L)2(H2O)2]Cl2·8H2O and [Ni(L1)2(H2O)2]SO4·8H2O
exhibits two main degradation steps. The first stage of
decomposition occurs within the temperature ranges 30–150
and 30–96 °C with maximum temperature at 82, 110 and
82 °C, respectively, accompanied by a weight loss of 7.25
and 7.11%, corresponding to the loss of 4H2O in agreement
with the theoretical value of 7.28 and 7.09%.
1
ion [30]. The H NMR spectrum of L showed peak at δ
6.89 ppm corresponding to –NH2 of amine group and at
1
7.08–8.14 ppm for –CH aromatic. Comparison of the H
NMR spectra of complexes with that of ligand shows a sig-
nifcant perturbation of the chemical shift of the aromatic
protons (7.04–7.17 ppm) and also exhibits new peak in the
range 3.32–3.39 ppm, due to the presence of water mol-
ecules in the complexes.
The second decomposition stage is associated with the
remaining molecular unit. This step occurs at three maxima
220, 297, 412 °C and 242, 329, 433 °C, accompanied by a
weight loss of 75.74 and 77.46%, giving CoO + 2C NiSO4
as a fnal product.
Thermal analysis
Thermogravimetric (TGA) and diferential thermogravimet-
ric (DTG) analyses for L and their isolated solid complexes
were carried out to get information about the thermal stabil-
ity of these new compounds and to suggest a general scheme
for thermal decomposition as well as to ascertain the nature
of associated water molecules. Figure 1 represents the TGA
For Cu(II) complex, the thermal decomposition exhibits
one main degradation step within the temperature range of
100–450 °C with a mass loss 82.77% agreement with the
theoretical value 83.11% forming cupper oxide as a fnal
product (Table S2). The infrared spectra of the fnal product
Fig. 1 TGA and DTG diagram for a L, b [Co(L)2(H2O)2]Cl2·8H2O, c [Ni(L)2(H2O)2]SO4·8H2O and d [Cu(L1)2(H2O)2](CH3COO)2
1 3

J IRAN CHEM SOC
of the thermal analysis for all above complexes supported
this conclusion.
important factor that controls the antimicrobial activity.
On chelation, the polarity of the metal ion will be reduced
to a greater extent due to overlap of ligand orbital and
partial sharing of the positive charge of the metal ion
with donor groups. Further, it increases the delocalization
of π-electrons over the whole chelate ring and enhances
the lipophilicity of the complexes [34]. This increased
lipophilicity enhances the penetration of complexes into
the lipid membranes and blocks the metal binding sites in
enzymes of microorganisms.
Mass spectra
The idea of mass spectrometer builds up on the separation
of fragments ions dependent on the variation of these ions
with the ratio of mass to charge (m/z). Mass spectrum of L
(Figure S4) show that L gives a well-defned parent peak at
m/z = 339 (RI = 25%) and at m/z = 341 (RI = 12%). The
mass fragmentation of L and the molecular ion peaks of
diferent suggested fragments are shown in Scheme 2. The
mass spectra of Co(II), Ni(II) and Cu(II) complexes dis-
played molecular ion peaks at m/z 987, 1012 and 895 amu,
respectively, which refer to M.Wt. with the abundance of 12,
11, 10%, respectively.
Computational details
Computational method
Fragmentation pattern of the complex [Ni(L)2(H2O)2]
SO4·8H2O is given as an example in Scheme 3. The molec-
ular ion peak [a] appeared at m/z = 1012 (11%) losses
SO4·8H2O to give [b] at m/z = 772 (14%), and it also losses
SO4 to give [c] at m/z = 916 (34%). The molecular ion peak
[a] losses 4H2O to give [d] at m/z = 844 (45.64%), and it
losses C12H8Cl2·SO4 to give [e] at m/z = 694 (24%). The
molecular ion peak also losses C24H16Cl4·SO4 to give [f]
at m/z = 472 (12%). The molecular ion peak [a] gave frag-
ment [g] at m/z = 646 (18%), [h] at m/z = 424 (21%), [i] at
m/z = 868 (67%), [j] at m/z = 328 (12%), [k] at m/z = 450
(17%), [l] at m/z = 632 (10%) and also [m] at m/z = 702
(21%).
The geometric parameters and energies were computed
by DFT at the B3LYP/CEP-31G level of theory, using the
GAUSSIAN 98 W package of the programs, on geometries
that were optimized at CEP-31G basis set. The atomic
charges were computed using the natural atomic orbital
populations. The B3LYP is the keyword for the hybrid
functional [34], which is a linear combination of the gradi-
ent functionals proposed by Becke [35] and Lee et al. [36],
together with the Hartree–Fock local exchange function
[37]. The high basis set was chosen to detect the energies
at a highly accurate level.
Antimicrobial activity
Structural parameters and models
The susceptibility of certain strains of bacterium such
as S. aureus, B. subtilis, E. coli and P. aeruginosa was
investigated, antifungal screening was studied against
two species Candida albicans and Aspergillus fumigatus
toward L, and its complexes were determined by measur-
ing the size of the inhibition diameter. As assessed by
color, the complexes remain intact during biological test-
ing (Table 2; Fig. 2). A comparative study of ligand and
their metal complexes showed that the metal complexes
exhibit higher antibacterial activity for Gram-positive and
Gram-negative and antifungal activity. The newly synthe-
sized Co(II) and Cu(II) complexes have highly significant
against E. coli compared with free ligand. Co(II) complex
has highly significant against P. aeruginosa (Table 2).
The results are promising compared with the previous
studies [31–33]. Such increased activity of metal chelate
can be explained on the basis of the oxidation state of the
metal ion, overtone concept and chelation theory. Accord-
ing to the overtone concept of cell permeability, the lipid
membrane that surrounds the cell favors the passage of
only lipid-soluble materials in which liposolubility is an
4,6‑Bis(4‑chlorophenyl)‑2‑amino‑1,2‑dihydropyr
idine‑carbinitrile (L)
Table S3 shows equilibrium geometric parameters bond
lengths (Å), bond angles (°), dihedral angles (°) and charge
density of L ligand by using DFT/B3LYP/CEP-31G, and
Scheme 4 shows the optimized geometry of L as obtained
from B3LYP/CEP-31G calculations. The two benzene
rings are in the same plane of the pyridine ring, so, the
structure is completely planner. This observation is sup-
ported by the values of calculated dihedral angles. The
following are the dihedral angles: C13C9C15N16 is 0.00°
and C8C9C15N16 is 180.00°, which confrms –CN group
in the same plane of molecule. The value of bond angle
C9C15N16 is 152.54° refecting on sp hybridization of
C15. The values of bond distances are compared well with
that of obtained experimental data [38–40].
There is a signifcant builtup of charge density on the
nitrogen atoms of amino and cyano groups, so L molecule
reacts as bi-dentate through Namino and Ncyano atoms with
dipole µ = 1.366 and the energy value is −136.23 au.
1 3

J IRAN CHEM SOC
+
+
+
CN
CN
N
NH2
[i] 215 (10 %)
N
NH2
Cl
N
NH2
[h] 117 (6 %)
Cl
[j] 228 (5 %)
+
l
CN
C
6
C
4
N
H
4
C
H
6
l
C
C
C
4
l
2
H
6
+
CNH
N
C
H 2
[g] 85 (34 %)
N
l
C
H 4
C 6
+.
+
2
N
Cl
Cl
C
6
H
N
NH2
[k] 212 (22 %)
N
4
C
C
l
l
N
C
H
[f] 91 (45 %)
4
H
6
C
2
2
CN
+
Cl
N
NH2
+.
Cl
[a] m/z 339 (25 %)
NH2
l
2
C
CN
CN
N
N
NH2
[e] 323 (17%)
Cl
C
N
l
[b] 269 (12 %)
+
C
Cl
+
CN
N
NH2
N
NH2
[d] 313 (12%)
Cl
Cl
[c] 304 (11%)
Scheme 2 Fragmentation pattern of L
1 3

J IRAN CHEM SOC
+.
S
+
Cl
O
SO4 .8H2O
+.
4
.
8
H
NC
OH2
2 O
N
OH2
OH2
H2N
Ni
CN
CN
Ni
NC
CN
N
Cl
N
Ni
OH2
NC
NH2
NH2
N
NH2
H2N
N
(
H2N
2
OH2
OH2
C
N
[k] 450 (17 %)
6
H
[l] 632 (10 %)
[m] 702 (21 %)
4
C
l
)
Cl
.
8
H
2
O
.
S
Cl
+
O
OH2
4
Cl
l
NC
C
l
2
-
C
N
4
(
4
Ni
H2N
C
+.
6H
CN
N
C
l
4
)
.
8
H
O
Cl
.
S
O4
2
OH2
OH2
NH2
+.
Cl
CN
+.
Cl
Cl
N
Cl
[j] 328 (12 %)
Ni
NC
NH2
SO4 .8H2O
OH2
Cl
H2N
N
O
OH2
H2
8
.
N
NC
NH2
O4
S
O
H
8
NC
4
2
CN
O
S
OH2
Ni
OH2
Ni
H2N
N
Cl
NC
NH2
N
NH2
[b] 772 (14 %)
Cl
N
OH2
Cl
Cl
[a] m/z (1012) (11 %)
+.
S
O4
Cl
(
[i] 868 (67 %)
2
C
ClH
O
2
H
+
H
8
.
)
l
Cl
Cl
Cl
C
8
4
)
H
H
.
6
S
C
2
O
O
2
(
CN
Ni
N
+
OH2
S
O
4
Cl
H2N
CN
N
OH2
Cl
4
H
2
H2N
Ni
Cl
O
CN
8
H
OH2
CN
2
O
H2N
CN
N
OH2
OH2
H2N
N
H2N
Cl
N
Ni
CN
[g] 646 (18 %)
OH2
H2N
Cl
N
[c] 916 (37 %)
[e] 694 (24 %)
Cl
+.
N
Cl
-
+
O
S
H
H2N
CN
O
+
2
O
S
4
.
8
4
CN
H
2
N
4
Ni
OH2
OH2
OH2
O
CN
H2N
N
OH2
Ni
H2N
CN
H2N
CN
Ni
N
OH2
Cl
CN
H2N
OH2
N
H2N
N
Cl
[d] 844 (34 %)
[h] 424 (21 %)
[f] 472 (12 %)
Scheme 3 Fragmentation pattern of [Ni(L)2(H2O)2]SO4·8H2O
1 3

J IRAN CHEM SOC
Fig. 2 Statistical representation for biological activity of L and its metal complexes
The Co(II) L complexes
Description of the structure of [Co(C18H11N3OCl2)2
(Cl)2] Scheme 5 shows the optimized geometrical struc-
ture of the complex with the atomic numbering scheme,
and selected bond distances and angles are given in Table 3.
The Co(II) at a crystallographic inversion center is in a dis-
torted octahedral environment. In the equatorial plane, the
metal ion Co(II) is coordinated by four atoms (one nitrogen
atom of amino group N6a, one chloride ion and two nitro-
gen atoms of cyano groups N2a and N2b). In the axial plane,
the Co(II) is bonded with one chloride ion and one nitrogen
atom of amino group N6b. The bond angle between Cl1CoCl2
The Co(II) is chelated with two molecules of L through
four coordinate bonds (N-amino and N-cyano atoms)
from each molecule. The experimental data show that the
result complex is six coordinates, so other two coordinated
bonds may be with water molecules or chloride ions. In
this part, we study theoretically the two proposed struc-
tures of [Co(L)2(Cl)2] and [Co (L)2(H2O)2]Cl2 and show
the structure which is more stable to support the obtained
experimental data.
1 3

J IRAN CHEM SOC
Scheme 4 The optimized geo-
metrical structure of 4,6-bis(4-
chlorophenyl)-2-amino-1,2-di-
hydropyridine-3-carbinitrile (L)
by using B3LYP/CEP-31G
Scheme 5 Optimized geometrical structure of trans-isomer of [Co(L)2(Cl)2] complex by using B3LYP/CEP-31G
is 96.70° [41–43], so the two chloride ions are lying per-
pendicular to each other. Also, the bond angle N6aCoN2b is
89.65° and N2aCoN2b is 160.01° [44, 45] so that the two
ligand molecules are perpendicular to each other and not
occupy the same plane. The distances between metal ion of
Co(II) and the nitrogen atoms of cyano groups Co–N2a and
Co–N2b are 1.788 and 1.789 Å, respectively [46], while the
distances between Co(II) and the nitrogen atoms of amino
groups Co–N6a and Co–N6b are 2.010 and 2.014 Å, respec-
tively [44, 45]. The octahedral coordination environment is
completed by two chloride ions. The distances between Co
and Cl are 2.172 and 2.173 Å [42, 43]. The bond angles
around the Co(II) vary from 75.13° to 169.34°; these val-
ues agree with these expected for a distorted octahedron.
1 3

J IRAN CHEM SOC
Table 3 Equilibrium geometric parameters bond lengths (Å), bond angles (°) and charge density of [Co (L)2(Cl)2] and [Co (L)2(H2O)2]2+ com-
plexes by using DFT/B3LYP/CEP-31G (X = Cl, OH2O)
X = Cl
X = OH O
X = Cl
X = OH O
X = Cl
X = OH O
2
2
2
Bond length (Å)
Co –N6b
Co–N2b
2.014
1.789
2.010
1.998
1.790
1.988
Co–N2a
Co–X1
Co–X2
1.788
2.172
2.173
1.789
1.837
1.836
C5b–N6b
C5a–N6a
C3b–N2b
C3a–N2a
1.528
1.526
1.147
1.147
1.529
1.529
1.147
1.147
Co–N6a
Bond angle (°)
N6a Co N2a
N6a Co N6b
N6a Co N2b
N2a Co N6b
N2a Co N2b
Charges
Co
N7b
N6b
N2b
C8b
75.13
84.79
89.65
90.47
160.01
75.56
95.22
92.14
94.05
163.24
N2a Co X1
N2a Co X2
N2b Co N6b
N6a Co X2
N6a Co X1
95.74
97.47
75.04
90.04
169.34
91.31
100.07
75.48
89.62
166.48
X1 Co X2
X1 Co
X2 Co N6b
X1 Co N2b
X2 Co N2b
96.70
89.86
169.12
97.89
95.39
89.48
88.88
165.81
101.37
91.05
0.076
0.154
C3b
C5b
N2a
N6a
N7a
0.259
0.305
−0.089
−0.249
−0.204
0.253
0.312
−0.225
−0.273
−0.269
C8a
C3a
C5a
X1
−0.032
0.236
0.310
−0.159
−0.284
−0.079
0.276
0.308
−0.311
−0.312
−0.271
−−0.272
−0.173
−0.074
−0.269
−0.273
−0.227
−0.089
X2
X = Cl
X = OH O
2
Energies and dipole moment
Total energy/au
Total dipole moment/D
LUMO+1
−432.30
9.86
−0.25037
−0.25047
−0.28859
−0.35401
0.03812
−438.88
16.85
−0.25026
−0.25074
−0.28693
−0.35352
0.03619
LUMO
HOMO
HOMO−1
Energy gap ∆E
The energy of this complex is −432.308 au and the dipole
moment is relatively weak 9.86D, so this complex is less
stable.
all these reasons, the hydrated complex is more stable than
chloride complex and Co(II) favors the completion of the
octahedron structure by two molecules of water more than
two chloride ions [49].
Description of the structure of [Co(L)2(H2O)2]2+ The
complex consists of two units of L and two water molecules
with Co(II) as shown in Scheme 6. The complex is six
coordinates with distorted octahedral environment around
the metal ion, and the angles around the Co(II) vary from
75.48° to 166.62° as given in Table 3.
The Ni(II) L complexes
The Ni(II) complex consists of four coordinate bonds with
two L and two coordinated bonds which may be with two
water molecules or one sulfate ion. In this part, we study the-
oretically the two possible structures such as [Ni(L)2(SO4)]
and [Ni(L)2(H2O)2]SO4 and detect which is more stable than
other.
The bond distances between Co(II) and surrounded
coordinated nitrogen atoms of L in hydrated complexes are
shorter than that in chloride complex as given in Table 3, so
that the Co(II) is bonded strongly with surrounded coordi-
nated atoms of L in hydrated complex [47, 48] more than
that in chloride complex. Also, the stability of complex can
be refected from the charges accumulated on the coordi-
nated atoms. The charges on N atoms of amino and cyano
groups in hydrated complex are more negative than that in
chloride complex. In hydrated complex, the energy of this
complex is −438.888 au and highly dipole (16.859D). For
Description of the structure of [Ni(L)2(SO4)] The Ni(II)
is coordinated by two N atoms of amino groups and two
N atoms of cyano groups of two L as shown in Scheme 7.
The distances between central metal ion Ni(II) and N atoms
of amino groups Ni–N6b and Ni–N6a bond lengths are
1.978 and 1.976 Å, respectively [50, 51], and the distances
between Ni(II) and N atoms of cyano groups Ni–N2b and
1 3

J IRAN CHEM SOC
Scheme 6 Optimized geometrical structure of trans-isomer of [Co(L)2(H2O)2]2+ complex by using B3LYP/CEP-31G
Scheme 7 Optimized geometrical structure of trans-isomer of [Ni(L)2(SO4)] complex by using B3LYP/CEP-31G
1 3

J IRAN CHEM SOC
Ni–N2a bond lengths are 1.776 and 1.777 Å, respectively
[52, 53]. The octahedral coordination environment is com-
pleted by two oxygen atoms of sulfate group. The distances
between Ni(II) and two oxygen atoms of sulfate group OSO4
are 1.830 and 1.831 Å [54]. The bond angles around the
Ni(II) as given in Table 4 vary from 75.81° to 167.25°; these
values difer from these expected for a regular octahedron.
In the axial plane, the Ni(II) bonded with one N-amino N6b
and one oxygen atom of sulfato group O1, and the bond angle
O1NiN6a is 162.90°. This plane is perpendicular to the equa-
torial plane occupied by other atoms represented by (N2b,
N6a, N2a and O2 of sulfato group). The bond angle N2bNiN6a
is 90.24° and N2aNiN2b is 165.85°. The sulfato group is not
lying in the same plane but out of plane in twisting form.
The bond angle O1NiO2 is 77.27°, so the oxygen atom O1
of sulfato group is lying trans with respect to one N6b of
amino group, while other oxygen atom O2 of sulfato group
is lying trans with respect to N2b of cyano group of the other
ligand molecule with angle equal to 167.25°. The energy of
the complex is −449.034 au and the dipole moment is weak
(9.159D), so this complex is less stable.
Description of the structure of [Ni(L)2(H2O)2]2+ The two
L molecules are perpendicular to each other, and they are
not lying in the same plane as observed in Scheme 8, and
the bond angle of N6bNiN6a is 94.78° and that of N6bNiN2a
is 92.44°, which confrm that the two L molecules do not
exist in the same plane. The two water molecules bonded
with Ni(II) do not exist in trans position to each other but
exist as cis to each other, and this observation was con-
frmed by the bond angle O1NiO2 of 90.49°. The Ni–N2b and
Ni–N2a bond lengths are 1.780 and 1.781 Å, respectively
[52, 53], which are shorter than Ni–N6b and Ni–N6a (1.981
and 1.980 Å, respectively) [50, 51], and the bond distances
between Ni(II) and the oxygen atoms of the two water mol-
ecules which completed the octahedral structure OH O are
2
1827 and 1.828 Å [55, 56] as given in Table 4. Also the
angles around the central metal ion Ni(II) vary from 75.70°
to 166.62°; these values agree with a distorted octahedron
like sulfate complex.
The Ni(II) is bonded strongly with surrounded oxygen
atoms and nitrogen atoms of L in hydrated complex more
than that in sulfate complex. Also, the charge accumulated
Table 4 Equilibrium geometric parameters bond lengths (Å), bond angles (°) and charge density of [Ni(L)2(SO4)] and [Ni (L)2(H2O)2]2+ com-
plexes by using DFT/B3LYP/CEP-31G (X = OSO , OH O
)
4
2
X = OSO
X = OH O
X = OSO
X = OH O
X = OSO
X = OH O
4
2
4
2
4
2
Bond length (Å)
Ni–N6b
Ni–N2b
Ni–N6a
Ni–N2a
1.978
1.776
1.976
1.777
1.981
1.780
1.980
1.781
C3a–N2a
Ni–X1
Ni–X2
1.147
1.831
1.830
1.146
1.827
1.828
C5b–N2b
C3b–N6b
C5a–N6a
1.532
1.147
1.530
1.146
1.529
1.147
Bond angle (°)
N6a Ni N2a
N6a Ni N6b
N6a Ni N2b
N2a Ni N6b
N2a Ni N2b
Charges
Ni
N7b
N6b
N2b
C8b
75.98
95.49
90.42
101.97
165.85
75.70
94.78
94.49
92.44
164.17
N2a Ni X1
Ni X2
N2b Ni N6b
N6a Ni X2
N6a Ni X1
93.98
94.85
75.81
99.26
162.90
100.93
90.73
75.78
89.82
166.62
X1 Ni X2
X1 Ni N6b
X2 Ni N6b
X1 Ni N2b
X2 Ni N2b
77.27
94.33
95.07
90.19
167.25
90.49
88.12
165.82
90.98
99.64
0.031
−0.268
−0.115
−0.245
−0.047
0.069
−0.269
−0.276
−0.219
−0.081
C3b
C5b
N2a
N6a
N7a
0.181
0.293
−0.087
−0.257
−0.276
0.283
0.309
−0.222
−0.277
−0.269
C8a
C3a
C5a
X1
−0.037
0.166
0.292
−0.529
−0.538
−0.081
0.283
0.310
−0.316
−0.315
X2
X = OSO
X = OH O
4
2
Energies and dipole moment
Total energy/au
Total dipole moment/D
LUMO+1
−449.03
9.15
−0.25051
−0.25099
−0.31311
−0.35780
0.06212
−490.04
18.87
−0.25039
−0.25055
−0.30583
−0.35763
0.05528
LUMO
HOMO
HOMO−1
Energy gap ∆E
1 3

J IRAN CHEM SOC
Scheme 8 Optimized geometrical structure of trans-isomer Of [Ni (L)2(H2O)2]+2 complex by using B3LYP/CEP-31G
on N atoms of amino groups (N6a and N6b) is −0.277 and
−0.276 and on N atoms of cyano groups (N2a and N2b) is
−0.222 and −0.219 in hydrated complex, while that on N6a
and N6b of amino groups is −0.257 and −0.115 and on N2a
and N2b of cyano groups is −0.087 and −0.245, in sulfate
complex. There is a strong interaction between Ni(II), which
has charge equal to +0.069, and more negative oxygen atoms
and nitrogen in hydrated complex greater than that in sulfate
complex, at which Ni(II) has less positively charge (+0.031)
in sulfate complex. The energy of this complex is −490.048
au and highly dipole 18.87D. For all these reasons, the
hydrated complex is more stable than sulfate complex and
Ni(II) favors the coordination of two molecules of water
more than one sulfate group to complete the octahedron
structure.
can be chelated with metal ion through one oxygen atom and
behaves as monodentate ligand or chelated with metal ion
through two oxygen atoms and behaves as bidentate ligand
as reported [57].
In this part, we study theoretically the all possible struc-
tures can be obtained [Cu(L)2(CH3COO)(H2O)](CH3COO),
[Cu(L)2(CH3COO)](CH3COO) and [Cu(L)2(H2O)2]
(CH3COO)2. The three complexes have been constructed
to investigate which is more stable, show all crystal struc-
ture properties for both complexes and also detect the exact
structure of them.
Description
of
the
structure
of
[Cu(L)2(CH3
COO)]+ Table S4 lists selected inter atomic distances and
angles for all investigated complexes. The complex consists
of two units of 4,6-bis(4-chlorophenyl)-2-amino-1,2-dihy-
dropyridine-3-carbinitrile molecule and one acetate group
as bi-dentate ligand with Cu(II) ion, as shown in Scheme 8.
The Cu–N6b and Cu–N6a bond lengths are 1.987 and
1.994 Å, respectively [58–61], also the Cu–N2b and Cu–N2a
are 1.798 and 1.797 Å, respectively [62–64], and the bond
distance between Cu–O1 and Cu–O2 of acetate ion is 1.837
and 1.841 Å, respectively [65, 66]. Also the angles around
the central metal ion Cu(II) with surrounding atoms vary
The Cu(II) L complexes
The Cu(II) like Co(II) and Ni(II) was chelated with two mol-
ecules of 4,6-bis(4-chlorophenyl)-2-amino-1,2-dihydropyr-
idine-3-carbinitrile through four coordinate bonds (N atom
of amino group and N atom of cyano group) from each mol-
ecule, and two coordinated bonds may be with two water
molecules or one acetate ion CH3COO−. The acetate group
1 3

J IRAN CHEM SOC
from 63.09° to 157.57°; and these values difer legally from
these expected for a regular octahedron. The energy of this
complex is −473.616603210 au, while the dipole moment is
1.098D (Scheme 9).
between N2aCuN2b is 167.77° ≈ 180°, so the two 4,6-bis(4-
chlorophenyl)-2-amino-1,2-dihydropyridine-3-carbinitrile
molecules are not lying in the same plane, and they are
perpendicular to each other with angle equal to 90°. The
angle between O1CuO2 is 89.69°, and this value refects that
the two water molecules are perpendicular to each other as
observed in Scheme 11.
Description of the structure of [Cu(L)2(CH3COO)
(H2O)]+ In this complex as shown in Scheme (10), there
are two units of 4,6-bis(4-chlorophenyl)-2-amino-1,2-dihy-
dropyridine-3-carbinitrile molecule and six-coordination
sphere is completed by bonding with one acetate group as
monodentate ligand and one water. The Cu–N6b and Cu–N6a
bond lengths are 1.995 and 2.000 Å, respectively [70], the
Cu–N2b and Cu–N2a bond lengths are 1.797 and 1.798 Å,
respectively [62], and the bond distance between Cu–O2
of acetate ion and Cu–O1 of water molecule is 1.804 and
1.846 Å, respectively [66–68]. Also from the values of
angles around the central metal ion Cu(II), the structure is
expected distorted octahedron. The energy of this complex
is −461.888107928 au, while the dipole moment is 4.037D
as reported in Table S4.
The complex is six coordinates with distorted octahedral
environment around the metal ion. The metal ion Cu(II) is
coordinated to one N atom of amino group and one N atom
of cyano group of 4,6-bis(4-chlorophenyl)-2-amino-1,2-di-
hydropyridine-3-carbinitrile ligand and two oxygen atoms of
two water molecules. The Cu–N6b and Cu–N6a bond lengths
are 1.998 and 1.897 Å, respectively [68, 69], and are longer
than those of Cu–N2b and Cu–N2a (1.801 and 1.807 Å,
respectively) [64], and the bond distance between Cu(II)
and oxygen atom of water molecule is 1.846 and 1.847 Å
for Cu–O1 and Cu–O2, respectively [67, 68], and all the bond
distances and bond angles are listed in Table S4.
The charge accumulated on N6a and N6b of amino groups
is −0.267 and −0.268 and N2a and N2b of cyano groups is
−0.163 and −0.161; in acetate complex, the charge accumu-
lated on N6a and N6b of amino groups is −0.254 and −0.259
Description of the structure of [Cu(L)2(H2O)]2+ The bond
angle between N6bCuN6a is 89.38° (≈90°) and also the angle
Scheme 9 Optimized geometrical structure of trans-isomer of [Cu(L)2(CH3COO)]+ complex by using B3LYP/Cep-31G
1 3

J IRAN CHEM SOC
Scheme 10 Optimized geometrical structure of trans-isomer of [Cu(L)2(CH3COO)(H2O)]+ complex by using B3LYP/Cep-31G
and N2a and N2b of cyano groups are −0.136 and −0.183;
in acetate-hydrated complex and in hydrated complex, the
charge accumulated on the N6a and N6b of amino groups
is −0.284 and −0.254 and N2a and N2b of cyano groups is
−0.283 and −0.262. There is a strong interaction between
central metal ion Cu(II) which has charge equal to +0.241 in
case of hydrated complex, while in case of acetate complex
the charge accumulated on Cu(II) is 0.121 and in acetate-
hydrated complex the charge accumulated on Cu(II) is 0.064.
The energy of the hydrated complex is more negative than
acetate −491.038974906 au and a highly dipole 11.712D.
For all these reasons, the hydrated complex is more stable
than other complexes and Cu(II) favors the coordination of
two molecules of water to complete the octahedron structure.
Molecular orbitals
Molecular orbitals play also an important role in the electric
and optical properties, as well as in UV–Vis [69]. An elec-
tronic system with greater values of HOMO–LUMO gap
should be less reactive than one having a small energy gap
[70]. The energy gap ΔE of the studied complexes varied
between 0.03619 for Co(II) complex which is more reactive
and 0.07541 eV for Cu(II) complex which is less reactive,
so electron movement between these orbitals could be easily
occurred so that we observe a peak around 250 nm in the
UV–Vis spectra for all studied complexes.
The nodal properties of molecular orbitals of syn-
thesized complexes in Fig. 3 are illustrative and suggest
1 3

J IRAN CHEM SOC
Scheme 11 Optimized geometrical structure of trans-isomer of [Cu(L)2(H2O)2]2+ complex by using B3LYP/Cep-31G
orbital delocalization, strong orbital overlap and low num-
ber of nodal planes. These features lead to UV–Vis spec-
trum characterized by low-energy, high-intensity bands and
the presence of charge transfer transitions. These features
exist in the spectra of all newly prepared complexes and
difer according to the nature of 4,6-bis(4-chlorophenyl)-
2-amino-1,2-dihydropyridine-3-carbinitrile complexes.
The diferent MOs show a diferent extent of localization
on the diferent fragments of the complex, and the above
rationalization is valid for MO analysis of all the studied
complexes. The energy diference between HOMO and
LUMO (energy gap, ∆E) for the prepared complexes var-
ied according to the type of ligand as given in Tables 3, 4
and S4. The Cu(II) complex has greater value of energy
barrier more than others complexes, while Co(II) com-
plex has lower value less than others and all synthesized
complexes have lower energy gap less than free ligand
4,6-bis(4-chlorophenyl)-2-amino-1,2-dihydropyridine-
3-carbinitrile (L), and then, these complexes more reac-
tive than free ligand.
Conclusion
The 4,6-bis(4-chlorophenyl)-2-amino-1,2-dihydropyridine-
3-carbinitrile (L) has two donating centers Namino and Ncyano
,
and when chelated with metal ions such as Co(II), Ni(II)
and Cu(II), six-coordinated bonds are formed: four with two
L molecules and other two with two water molecules. The
hydrated complex is more stable than other complexes for
following reasons: (1) in hydrated complexes, there are more
negative charges accumulated on oxygen atoms and large
positive charge is formed over central metal ion; (2) hydrated
complexes are highly dipole greater than other complexes;
the product complexes are treated as distorted octahedral
complexes; and (3) hydrated complexes have lower energy
values less than other studied complexes. The value of
energy gap of the free ligand is greater than all new com-
plexes, while the all hydrated complexes have lower energy
gap less than others. Also the value of energy gap for Co(II)
complex is smaller than other complexes, so this complex is
more reactive than other complexes, while Cu(II) complex is
less reactive than other complexes. The diferent MOs show
1 3

J IRAN CHEM SOC
Fig. 3 Molecular orbital
surfaces and energy levels of
all studied complexes by using
B3LYP/Cep-31G
6. J.R.J. Sorenson, Biology of Copper Complexes (Humana Press,
New York, 1987)
a diferent extent of localization on the diferent fragments
of the complex, and the above rationalization is valid for MO
analysis of all the studied complexes.
7. N. Büyükkidan, C. Yenikaya, H. Ilkimen, C. Karahan, C. Darcan,
E. Sahin, Russ. J. Coord. Chem. 39, 96–103 (2013)
8. C. Yenikaya, M. Poyraz, M. Sari, F. Demirci, H. Ilkimen, O. Buy-
ukgungor, Polyhedron 28, 3526–3532 (2009)
9. A.C. Gonzalez Baro, E.E. Castellano, O.E. Piro, B.S. Parajon
Costa, Polyhedron 24, 49–55 (2005)
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