Synthesis, spectroscopic, thermal, voltammetric studies and biological activity of crystalline complexes of pyridine-2,6-dicarboxylic acid and 8-hydroxyquinoline

Article abstract of DOI:10.1016/j.molstruc.2009.07.026

Two new compounds (8-H₂Q)₂[M(dipic)₂]·6H₂O (M = Co (1) and Ni (2), 8-HQ = 8-hydroxyquinoline, dipic = dipicolinate) have been prepared and characterized by elemental analysis, spectral (IR and UV-vis), thermal a

Full text of DOI:10.1016/j.molstruc.2009.07.026

Journal of Molecular Structure 936 (2009) 67–74
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, spectroscopic, thermal, voltammetric studies and biological activity
of crystalline complexes of pyridine-2,6-dicarboxylic acid and 8-hydroxyquinoline
a,*
b
c
d
Alper Tolga Çolak , Ferda g˘ Çolak , Okan Zafer Ye ßs ilel , Orhan Büyükgüngör
a
Department of Chemistry, Faculty of Arts and Sciences, Dumlupınar University, 43820 Kütahya, Turkey
Department of Biology, Faculty of Arts and Sciences, Dumlupınar University, 43820 Kütahya, Turkey
Department of Chemistry, Faculty of Arts and Sciences, Eski ßs ehir Osmangazi University, 26480 Eski ßs ehir, Turkey
Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new compounds (8-H Q) [M(dipic) ]ꢀ6H O (M = Co (1) and Ni (2), 8-HQ = 8-hydroxyquinoline,
2
2
2
2
Received 13 February 2009
Received in revised form 29 May 2009
Accepted 21 July 2009
dipic = dipicolinate) have been prepared and characterized by elemental analysis, spectral (IR and
UV–vis), thermal analyses, magnetic measurements and single-crystal X-ray diffraction techniques. Both
1
and 2 consist two 8-hydroxyquinolinium cations, one bis(dipicolinate)M(II) anion [M = Co(II), Ni(II)]
Available online 25 July 2009
and six uncoordinated water molecules. Both 1 and 2 crystallize in the monoclinic space group C2/c. In
the compounds anion, each dipic ligand simultaneously exhibits tridentate coordination modes through
N atom of pyridine ring and oxygen atoms of the carboxylate groups. The crystal packing of 1 and 2 is a
Keywords:
Dipicolinate complexes
composite of intermolecular hydrogen bonding and C–Oꢀ ꢀ ꢀ
p interactions. The in vitro antibacterial and
8
-Hydroxyquinoline
antifungal activities of 1 and 2 were evaluated by the agar well diffusion method by MIC tests. Both
new compounds showed the same antimicrobial activity against Gram-positive bacteria and yeast and
fungi expect Gram-negative bacteria.
Antimicrobial activity
Cyclic voltammograms
Ó 2009 Elsevier B.V. All rights reserved.
1
. Introduction
of more effective anti-HIV agents and the design of insulin-mi-
metic agents [2,5–8]. Previous studies have shown that a series
Pyridine-2,6-dicarboxylic acid (dipicolinic acid, H
first discovered in a biological system in 1936 and is now known
to be a major component of bacterial spores [1]. H dipic is used
in a variety of processes as an enzyme inhibitor, plant preservative
and food sanitizer [2]. Recent investigations of the H dipic exhibit
that this acid prevents the oxidation of low density lipoprotein, the
substance, whose oxidation is involved in the pathogenesis of arte-
2
riosclerosis [3]. H dipic is a polar aromatic acid that is soluble in
2
dipic) was
of vanadium-dipicolinate complexes is effective on diabetic hyper-
glycemia and vanadium(V) can have insulin mimetic properties
when the organic ligand has been chosen appropriately [9–11].
2
2ꢁ
The [Co(dipic)
2
]
was found to be effective in reducing the hyper-
2
lipidemia of diabetes using oral administration in drinking water in
rats with streptozotocin-induced diabetes [12]. Mixed ligand com-
plexes have a key role in biological chemistry because the mixed
chelation occurs commonly in biological fluids as millions of
potential ligands are likely to compete for metal ions in vivo
[13]. Although a high number of pyridine-2,6-dicarboxylic acid
complexes of almost all transition metals is known, studies of
biologic [13–17] and electrochemical [18,19] activity with the
complexes of this ligand are rather scant and appear to be limited
to only a few examples based on transition metals. Single-crystal
X-ray structure determinations of other Co(II)–dipic, Ni(II)–
organic and chlorinated solvents in the acidic form and thus can
penetrate lipid interfaces and be solubilized in hydrophobic envi-
ronments [4]. H
2
dipic has been studied extensively as a Lewis base.
ꢁ
2ꢁ
2
H dipic and its anions (Hdipic , dipic ) have proved to be well
suited for the construction of multidimensional frameworks, due
to the presence of two adjacent O atoms of carboxylate groups as
substituents on the N-heterocyclic pyridine ring [2,5]. Among the
diversity of pyridine-2,6-dicarboxylic acid complexes known, po-
tential applications, in fields of aqueous chemistry, catalysis, bio-
chemistry, as water-soluble drugs, antitumor activity, magnetic
materials, in bleaching, bactericidal compositions, development
dipic, Cu(II)–dipic proton transfer compounds are (HIm)
2
[Co
pipz)[Ni
2
O [22] (Im = imidaz-
(dipic)
(dipic)
2
]ꢀ2H
2
O
[20], (HIm)
2
[Ni(dipic)
2
]ꢀ2H
2 2
O [20], (H
]ꢀ6H
2
]ꢀ4H
2
O [21], (HQx) [Cu(Hdipic)
2
2
ole, pipz = piperazine, HOx = 8-hydroxyquinoline).
The treatment of infectious diseases still remains an important
and challenging problem because of a combination of factors
including emerging infectious diseases and the increasing number
of multi-drug resistant microbial pathogens [23]. Decreased
*
Corresponding author.
E-mail address: acolak@dumlupinar.edu.tr (A.T. Çolak).
0
022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.07.026

6
8
A.T. Çolak et al. / Journal of Molecular Structure 936 (2009) 67–74
efficacy and resistance of pathogens to compounds has necessi-
tated development of new alternatives. In light of these problems,
the search for new antimicrobial agents has gained immense pop-
ularity in the field of drug development.
In this study, we describe the preparation, spectroscopic, ther-
mal, structural characterization, antimicrobial activities and elec-
35 °C for about 40 min in an incubator. The agar well method for
the estimation of MIC values (the lowest concentration of com-
pounds required to inhibit the growth of the tested microorgan-
isms) was applied to evaluate the antimicrobial activity. At the
same time, 10 mm wells were bored using a sterile cork borer
and impregnated with known concentrations which were previ-
trochemical studies of
nickel(II) with 8-hydroxyquinoline, (8-H
8-H Q) [Ni(dipic) O (2).
]ꢀ6H
H
2
dipic complexes of cobalt(II) and
ously determined by MIC tests (250–0.4
lg/mL for each well) from
2
Q) [Co(dipic) O (1)
2
2
]ꢀ6H
2
each compound (100 L) and the synthesized compounds 1 and 2
l
(
2
2
2
2
were placed into the wells. The plates were preincubated for 2 h at
room then the plates were incubated at 37 °C for 24 h for bacterial
strains, 48 h for yeasts and 72 h for fungi at room temperature. Tet-
2
. Experimental
racycline (30 lg/mL) for bacteria was used as positive control.
DMSO was used as negative control. Antimicrobial activity was
evaluated as zones of inhibition of growth around wells. All sam-
ples were tested in triplicate.
2
.1. Materials and equipment
All chemicals and solvents used for the synthesis were of re-
agent grade. Pyridine-2,6-dicarboxylic acid, 8-hydroxyquinoline,
Co(CH COO) O, Ni(CH COO) and OH (Aldrich)
were used as received. Elemental analyses (C, H, and N) were per-
formed using a Vario EL III CHNS elemental analyzer. Magnetic sus-
ceptibility measurements were performed at room temperature
using a Sherwood Scientific MK1 model Gouy magnetic balance.
UV–vis spectra were obtained in the methanol solutions (10
mol/L) of the complex with a Shimadzu Pharmaspec UV-1700
spectrometer in the range of 1000–190 nm. FT-IR spectra were re-
2
H
.4. Synthesis of (8-H
2
Q)
2
2 2
[Co(dipic) ]ꢀ6H O (1) and (8-
3
2
ꢀ4H
2
3
2
2
ꢀ4H O
2 5
C H
2
Q)
2 2 2
[Ni(dipic) ]ꢀ6H O (2)
A
solution of [Co(H
2
dipic)(dipic)]ꢀ3H
2
O [12] or [Ni(Hdi-
pic)
2
]ꢀ3H O [29] (1 mmol, 0.445 g) in ethanol–water (1:1; 40 mL)
2
ꢁ3
was added drop wise by stirring at room temperature to a solution
of 8-hydroxyquinoline (2 mmol, 0.290 g). After 60 min stirring at
room temperature, resulting clear red (1) and green (2) solutions
were observed. After one week, formed crystals were filtered and
washed with 20 mL of cold ethanol and dried on air. Yields 0.52 g
ꢁ
1
corded in the 4000–400 cm region with a Bruker Optics, Vertex
0 FT-IR spectrometer using KBr pellets. Diamond TG/DTA thermal
7
(
4
66%) and 0.48 g (61%). Anal. calcd. for (1) C32
8.7; H, 4.3; N, 7.1. Found: C, 48.6; H, 4.4; N, 7.2%. Anal. calcd.
for (2) C32 16Ni : C, 48.7; H, 4.3; N, 7.1. Found: C, 48.7; H
.3; N 7.1%.
34 4
H N O16Co : C,
analyzer was used to record simultaneous TG, DTG and DTA curves
in nitrogen 1 and 2 in static air atmosphere at a heating rate of
1
ꢁ1
34 4
H N O
0 K min in the temperature range 35–1000 °C using platinum
4
crucibles.
2.2. X-ray crystallography
3. Results and discussion
Data collection (1) and (2) were performed on a STOE IPDS II im-
3.1. UV–vis spectra and magnetic susceptibilities
a
age plate detector using MoK radiation (k = 0.71019 Å). Intensity
data were collected in the h range 2–25.5° at 293(2) K. Data collec-
tions: Stoe X-AREA [24]. Cell refinement: Stoe X-AREA [24]. Data
reduction: Stoe X-RED [24]. The structure was solved by direct-
methods and anisotropic displacement parameters were applied
to non-hydrogen atoms in a full-matrix least-squares refinement
Electronic absorption spectrum of 1 displays the visible asym-
4
4
metric region maximum at kmax = 556 nm ( T1g ? A2g transition).
The electronic spectrum of 2 in H O exhibits three absorption
bands at 371, 508, 617 nm and the corresponding values are
2
e
ꢁ
1
ꢁ1
43, 32, 35 L mol cm . These values were assigned to the follow-
2
ing d–d transitions; 3A2g ? T1g (P)
respectively. The
3
3
3
3
3
based on F using SHELXL-97 [25]. Molecular drawings were ob-
tained using ORTEP-III [26].
,
A
2g ? T1g and
A
2g ? T2g
,
,
ꢁ
1
D
o
value for 2 was calculated as 10941 cm
8
since
D = m for d complexes.
o 1
The complex 1 shows room temperature magnetic moments in
the range of 5.21 BM corresponding to three unpaired electrons
which suggest an octahedral geometry. This value is higher than
the spin-only value of 3.87. Because, not only the spin magnetic
moment contribute to the total magnetic moment but also orbital
magnetic moment in Co(II) complexes. For orbital angular momen-
tum to contribute, and hence for the paramagnetism to differ sig-
nificantly from the spin-only value, there must be an unfilled or
half-filled orbital similar in energy to that of the orbitals occupied
by the unpaired spins. If that is so, the electrons can make use of
the available orbital to circulate around the center of the complex
and hence generate angular momentum and a magnetic moment
2
.3. Biological activity of compounds
Microbial strains; A total of 6 microbial species including 4 bac-
teria, 1 molds and 1 yeast were used as test organisms in this
study. Staphylococcus aureus ATCC 25923, Escherichia coli ATCC
2
1
5922 Salmonella typhimurium ATCC 14028, Aspergillus niger ATCC
0949, Candida albicans (ATCC 10231) were obtained from Ameri-
can Type Culture Collection; Bacillus subtilis NRRL-B-209 from
USDA, Agriculture Research Service, Peria, USA. Bacterial and fun-
gal cultures of test organisms were maintained on Nutrient Agar
and Malt Extract Agar slants at 4 °C, respectively, and were subcul-
tured in petri dishes prior to use. Antimicrobial activity analysis of
test compounds was carried out according to modified agar well
diffusion assay [27,28]. The following test conditions were applied;
compound was dissolved in Dimethylsulfoxide (DMSO, Merck). Fif-
teen milliliters of the specified molten agar (45 °C) were poured
into sterile Petri dishes (Ø90 mm). The cell suspensions containing
[
30]. The complex 2 exhibits magnetic moment value of 2.90 BM,
which suggests an octahedral geometry.
3.2. FT- IR spectra
8
7
1
1
0 CFU/mL cells for bacteria, 10 CFU/mL cells for yeasts, and
The most significant frequencies in the IR spectrum of 1 are gi-
ven in Table S3. The strong and broad absorption bands at 3480 (1)
5
0 spore/mL of fungi were prepared and evenly spread onto the
ꢁ1
surface of the agar plates of Nutrient Agar (Fluka) for bacteria
and yeast and Potato Dextrose Agar (Merck) medium for fungi
using sterile swab sticks. The plates were dried aseptically at
and 3491 cm (2) are attributed to the
m(OH) vibrations of crystal
water molecules. The absorption bands at 3370, 3376 and 3193,
ꢁ
1
3191 cm
are related to m(NH) and m(OH) vibrations of 8-HQ

A.T. Çolak et al. / Journal of Molecular Structure 936 (2009) 67–74
69
ligands in the IR spectrum of 1 and 2. The carboxylate groups
listed in Tables S4 and S5. The crystallographic analyses revealed
that the complexes (8-H Q) [M(dipic) O (M = Co(II) and
]ꢀ6H
Ni(II)) consist of a discrete [M(dipic) anion, two protonated
8-hydroxyquinoline cations, 8-H Q and six crystal water molecules
ꢁ1
exhibited strong bonds in the region 1682–1582 cm . These
strong bands were shifted and broadened with respect to free dip-
2
2
2
ꢁ
2
2
2
]
ꢁ
icolinic acid. The presence of carboxylate COO is reflected by IR
2
spectrum in absorption bands of the asymmetric (
m
as) and symmet-
(Figs. 3 and 4). The M(II) ions has a distorted octahedral geometry
with two tridentate dipicolinate ligands. The bisdeprotonated 2,6-
pyridinedicarboxylate is coordinated to the M(II) by both the
pyridine nitrogen atom and the oxygen atoms of carboxylate
groups, creating two chelate ring. The M1–Ndipic bond distances
are 2.010(1) and 1.958(1) Å in 1 and 2, respectively, and they are
shorter than the M–Odipic bond distances (Co1–O1 = 2.155(1),
Co1–O3 = 2.168(1), Ni–O1 = 2.121(1) and Ni–O3 = 2.146(1) Å). The
M–N1 and M–O1/O3 bond distances are in agreement with the
ꢁ
1
ric
473 cm , respectively, and moreover the differences between
the asymmetric and symmetric stretches of the carboxylate groups
(m
s
)
stretch vibrations at 1615–1472 cm
and 1609–
ꢁ1
1
ꢁ1
of the complexes
D = 143 and 136 cm , respectively, suggest a
monodentate binding of the carboxylate group to the metal ion
ꢁ
1
[
31]. The absorption bands at 1589 and 1591 cm
are due to
m
(C@C)+ (C@N) vibration of dipic and 8-H Q (1) and (2) ligands.
m
2
ꢁ
1
The absorption band at 620; 428, and 630; 442 cm are attributed
to the M–O and M–N vibrations of the complexes.
corresponding values in the related structures [Co(H
pic)]ꢀ3H O [Co1–O = 2.108(2) and 2.195(2) Å, Co1–N = 2.017(3) Å]
[24], [Ni(H O) ][Ni(dipic) ]ꢀ5H O [Ni1–O = 2.114(2), 2.117(2),
2
dipic)(di-
2
3.3. Thermal analyses
2
6
2
2
2
.126(2) and 2.147(2) Å, Ni1–N = 1.964(3) and 1.967(3) Å] [32],
The TG-DTG and DTA curves of the compounds are shown in
[Ni(H O) (data) ][Ni(dipic) ]ꢀ5H O [Ni–O = 2.104(4), 2.109(3),
2
2
2
2
2
Figs. 1 and 2. The endothermic peaks of 1 (DTAmax = 91.30 °C) be-
tween 35 and 102 °C correspond to the loss of the 6-mol crystal
water molecules (found 13.80, calcd. 13.67%). The similar results
are found for 2 (DTGmax = 91 °C; found 13.30, calcd. 13.68) between
2.137(4), 2.187(4) and Ni–N = 1.952(4), 1.961(4) Å] [33], [Ni(cy-
clam)(H O) ][Ni(dipic) ]ꢀ2.5H O [Ni–O = 2.132(2), 2.146(2) and
2
2
2
2
Ni–N = 1.955(3), 1.931(3) Å] [5] and (HQx) [Cu(HDPC ]ꢀ6H O
2
2
2
[Cu–O = 2.172(1), 2.221(2) and Cu–N = 1.932(2) Å] [22]. The bond
3
5 and 120 °C. The anhydrous compound 1 is thermally stable up
distances and angles of 8-H Q ions are in agreement with the cor-
2
to about 125 °C. Three-mole decarboxylate of dipic molecules
responding values in the related structures [22,34–36]. Compari-
+
and two (8-H
2
Q) groups are lost in two steps (DTAmax = 164.7 °C,
38.6 °C; found 53.80, calcd. 53.74%) for 1 between 102 and
58 °C. One-mole decarboxylate of dipic molecules and two (8-
son of values of the M–Odipic and M–Ndipic distances for the
similar 2,6-dicarboxylate complexes can be found in Table 2. The
angle of N1–M–O1 [76.31(4) and 78.04(5)°] and N1–M–O3
[76.37(4) and 77.75(5)°] is nearly equal.
The carboxyl groups of the 2,6-pyridinedicarboxylate ligands
and water molecules are involved in intermolecular hydrogen
bonding with the carboxyl group of dipic ligands and crystal water
2
3
H
+
2
Q) groups are lost in three steps (DTGmax = 180.3 °C, 255.2 °C,
2
78.1 °C; found 43.60, calcd. 42.61%) for 2. The exothermic peaks
of 1 (DTAmax = 430.4 °C) between 358 and 480 °C correspond to
the loss of the one-mole decarboxylate of dipic molecules and re-
main dipic moiety (found 24.90, calcd. 25.60%). The exothermic
peaks of 2 (DTGmax = 423.8 °C) between 314 and 488 °C correspond
to the loss of the three-mole decarboxylate of dipic molecules and
remain dipic moiety (found 35.20, calcd. 36.76%). The final decom-
position products for 1 and 2, CoO and NiO, were identified by IR
spectroscopy (found 7.50%, calcd. 9.48%; found 8.40%, calcd.
+
2
molecules. The 8-H Q ions are involved in intra- (N2–H2ꢀꢀꢀO5 and
ii
O5–H5AꢀꢀꢀO8) and intermolecular (N2–H2ꢀꢀꢀO4 , (ii) = x + 1/2, yꢁ1/
2, z) hydrogen bonding with the nitrogen atom of pyridine ring, hy-
droxyl oxygen and water molecule. There are also intramolecular
hydrogen bonds O5–H5AꢀꢀꢀO8, O6–H6AꢀꢀꢀO3 and O7–H7AꢀꢀꢀO2.
Some of these interactions are illustrated in Fig. 3. There are also
9
.46%;), respectively.
C–Oꢀ ꢀ ꢀ
C7–O4) of carboxyl group and rings of dipic ligands (Cg1 = N(2)–
C(8)–C(9)–C(10)–C(11)–C(16) and Cg2 = C(11)–C(12)–C(13)–
p interactions between the oxygen atoms (C1–O2 and
3.4. Crystal structure of (8-H
2
Q)
2
[Co(dipic)
2
]ꢀ6H
2
O (1) and (8-
i
H
2
Q) [Ni(dipic) O (2)
2
2
]ꢀ6H
2
C(14)–C(15)–C(16)) [the contact distances: C1–O2ꢀꢀꢀCg1 = 3.325
ii
for 1, 3.926 Å for 2 (i = ꢁ½ + x, ½ ꢁ y, ½ + z), C1–O2ꢀꢀꢀCg2 = 3.950
The compounds 1 and 2 are isomorphous and crystallize in the
for 1, 3.926 Å for
2
(ii = ½ ꢁ x, ½ + y, ½ ꢁ z) and C7–
iii
monoclinic crystal system space group C2/c. Details of crystal
structures are given in Table 1. The selected bond distances and an-
gles together with the hydrogen bonding geometry for 1 and 2 are
O4ꢀꢀꢀCg2 = 3.968 for 1, 3.994 Å for 2 (iii = ½ ꢁ x, ꢁ½ + y, ½ ꢁ z).
All of these intermolecular interactions give three-dimensional
network results (Tables S4 and S5, Fig. 5.).
Fig. 1. TG, DTG and DTA curves of (1).

7
0
A.T. Çolak et al. / Journal of Molecular Structure 936 (2009) 67–74
Fig. 2. TG, DTG and DTA curves of (2).
Table 1
Crystal data and structure refinement parameters for the complexes.
1
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
32
H
34
N
4
O
16Co
C
32 34 4
H N O16Ni
789.56
293(2)
0.71073 MoK
Monoclinic
C2/c
18.355(1)
10.3518(4)
19.136(1)
90; 110.368(4); 90
3408.7(3)
4
0.59
789.34
293(2)
a
Monoclinic
C2/c
18.370(1)
10.3476(6)
19.1539(9)
90; 111.000(4); 90
3399.0(3)
4
b (Å)
c (Å)
a
, b, d (°)
3
V (Å )
Z
Absorption coefficient (mmꢁ1)
0.65
1.542
ꢁ
3
D
calc (mg m
)
1.539
Theta range for data collection (°)
Measured reflections
2.24–27.97
26829
2.24–27.98
23537
Independent reflections
Absorption correction
Refinement method
3343
3332
Integration Stoe X-RED (Stoe & Cie, 2001)
Full-matrix least-squares on F2
Final R indices [I > 2
Final R indices (all data)
r
(I)]
R
int = 0.047
= 0.030; wR
R
int = 0.038
2
= 0.030; wR = 0.081
R
1
2
= 0.079
R
1
2
Goodness-of-fit on F
1.04
0.19
1.05
0.16
0
max (e ÅA ꢁ3)
min (e ÅA ꢁ3)
D
D
q
q
0
ꢁ0.35
ꢁ0.35
ꢁ3
3
.5. Cyclic voltammetric studies
rate. At scan rate of 100 mVs–1 (1.0 ꢂ 10 M), its potential range
changes from ꢁ0.03 to ꢁ0.57 V (Epc) and ꢁ0.74 to 0.03 V (Epa). In
–
1
Cyclic voltammograms of the Co(II) and Ni(II) metal complexes
were run in DMF-0.1M NBu BF as supporting electrolyte at room
other words, at scan rates of 100 and 250 mVs (concentration:
ꢁ4
4
4
1.0 ꢂ 10 M), the anodic and cathodic peak potentials shifted to
temperature. Unless otherwise stated, all potentials quoted refer to
measurements run at scan rates of 100 and 250 mVs–1 and against
an internal ferrocene–ferrocenium standard. In order to study the
effect of the different concentrations of the metal complexes, the
electrochemical properties were investigated using the solutions
the more positive regions.
The electrochemical curves of the nickel(II) complex at 100 and
ꢁ
1
ꢁ3
250 mVs scan rates (1.0 ꢂ 10 M) are shown in Figs. S7 and S8.
As may be seen from Figs. S7 and S8 and data obtained from Table
S6, the reduction–oxidation process of the nickel(II) complex is
irreversible. While the cathodic peak potential (0.08 V) at
–3
ꢁ4
1
.0 ꢂ 10 and 1.0 ꢂ 10 M and only metal centered. Data ob-
ꢁ1
ꢁ3
tained from the electrochemical studies were given in Table S6.
The electrochemical curves of the Co(II) metal complex at scan
rates of 100 and 250 mVs–1 (1.0 ꢂ 10 M) are shown in Figs. 6
and 7. The cv curves of the Co(II) complex at different scan rates
and concentrations in dmf solution show the irreversible process
100 mVs scan rate (1.0 ꢂ 10 M) shifts to more positive region
ꢁ1
(0.11 V) at 250 mVs scan rate, the anodic peak potential shifted
to the more negative potentials at the same scan rates. Similar re-
ꢁ3
ꢁ
4
sults were also obtained when 1.0 ꢂ 10 M solution was utilized
in dmf. For the cobalt(II) and nickel(II) complexes, although the
forward peaks in reduction process in dmf solution and reverse
peaks in oxidation process in dmf solution are almost invariant,
ꢁ3
(I
pc: Ipa – 1.0). But, the cobalt(II) complex (1.0 ꢂ 10 M) shows
–1
only reversible process at 0.03 V (Ipc: Ipa = 1.0) at 250 mVs scan

A.T. Çolak et al. / Journal of Molecular Structure 936 (2009) 67–74
71
Fig. 3. The molecular structure of (8-H
i = ꢁx + 1, y, ꢁz + 3/2).
2
Q)
2
[Co(dipic)
2
]ꢀ6H
2
O (1) showing the atom numbering scheme. The thermal ellipsoids are plotted at the 30% probability level
(
Fig. 4. The molecular structure of (8-H
2
Q)
2
[Ni(dipic)
2
]ꢀ6H
2
O (2) showing the atom numbering scheme. The thermal ellipsoids are plotted at the 30% probability level.
Table 2
Comparison of the bond distances (Å) and angles (°) of the pyridine-2,6-dicarboxylic acid complexes.
Complexes
M–O
M–O
M–N
O–M–N
O–M–O
[
[
Ni(cyclam)(H
Co(H
dipic)(dipic)]ꢀ3H
O) , [17]
[Cu(Hdipic)
]ꢀ6H
O) ][Ni(dipic)
]ꢀ5H
O) ][Ni(dipic)
]ꢀ3H
O) Ni(dipic) O, [44]
]ꢀ2H
Ni(dipic)(H O) ], [45]
Ni(dipic)(bta) ], [46]
Ni(dipic)(phen)(H
O)]ꢀH
Ni(H dipic)(H O) ][Ce(dipic)
[Co(H O) ][Co(dipic)
]ꢀ8H
[Co(dipic) O, This work
]ꢀ6H
[Ni(dipic) O, This work
]ꢀ6H
2
O)
2
][Ni(dipic)
2
]ꢀ2.5H
2
O, [5]
2.132(2)
2.108(2)
2.002(2)
2.172(15)
2.147(2)
2.115(2)
2.164(3)
2.005
2.146(2)
2.195(2)
2.006(2)
2.221(16)
2.126(2)
2.115(2)
2.179(3)
2.006
1.931(3)
2.017(3)
1.905(2)
1.932(16)
1.964(3)
1.960(3)
1.974(3)
1.903
78.35(5), 78.29(5)
77.2(1), 75.7(1)
80.70(7), 80.15(7)
78.25(6), 77.65(6)
77.53(10)
78.09(6)
76.97(12), 77.64(12)
80.20, 80.41
78.39, 76.44
78.17, 77.34
76.35(12), 77.11(12)
76.50(6), 76.73(6), 75.79(6), 76.99(6)
76.31(4), 76.37(4)
78.04(5), 77.75(5)
156.70(10)
152.9(1)
2
2
O, [12]
Cu(dipic)(H
2
2
160.42(6)
155.86(5)
155.68(9)
156.17(8)
154.38(11)
160.15
154.82
155.31(6)
153.40(11)
(
[
[
[
[
[
[
[
HQx)
2
2
2
O, [22]
O, [32]
O, [32]
Ni(H
Zn(H
Ni(H
2
6
2
2
2
6
2
2
2
5
2
2
2
2
3
2.586
2.112
1.992
2
2
O, [47]
]ꢀ3H
O, [49]
2.107(2)
2.178(3)
2.153(2), 2.122(2)
2.155(1)
2.121(1)
2.132(2)
2.172(3)
2.162(2), 2.193(2)
2.168(1)
2.146(1)
1.986(2)
1.994(3)
2.010(2), 2.020(2)
2.010(1)
1.958(1)
2
2
3
3
2
O, [48]
PpzH
(
(
2
2
6
2
2
151.30(6), 152.52(6)
152.61(4)
155.79(4)
8-H
8-H
2
Q)
Q)
2
2
2
2
2
2
2

7
2
A.T. Çolak et al. / Journal of Molecular Structure 936 (2009) 67–74
reduction was detected for the metal complexes. All of the com-
plexes were sufficiently soluble in dmf to allow a cyclic voltammo-
gram to be run. In dmso solvent, the complexes show an identical
pattern of peaks. However, in generally, the potentials of all these
processes are slightly more positive in dmso than their positions in
dmf.
3.6. Antimicrobial activity
In this study, in vitro potential antimicrobial activity of H
2
dipic,
8
2 2 2 2
-HQ, [Co(H dipic)(dipic)]ꢀ3H O [12], 1, [Ni(Hdipic) ]ꢀ3H O [29], 2
were tested according to agar well diffusion method. Table 3 shows
the effect of 11 different concentrations against the growth of
Gram-positive, Gram-negative bacterial strains, yeast strain and
fungal strain. We look into compound 1 which displayed the inhib-
itory effect against all tested Gram-positive bacteria (S. aureus,
B. subtilis) and yeast and mold (C. albicans, A. niger) expect Gram-
negative bacteria (E. coli, S. typhimirium). Inhibitory effect against
Gram-positive bacteria and yeast and mold was observed in
compound 2. The main reason for the antimicrobial activity in
compounds 1 and 2 are related to presence of 8-HQ. In light of
these results, it appears that, compound 1 and 2 showed same anti-
microbial activity against tested microorganisms. In classifying the
antibacterial activity as Gram-positive or Gram-negative, it would
generally be expected that a much greater number would be active
against Gram-positive than Gram-negative bacteria [37]. The outer
membrane of Gram-negative bacteria is the first barrier capable of
limiting the penetration of antimicrobial agents. This fact is widely
known and referred to as ‘‘intrinsic resistance” of Gram-negative
bacteria [38]. Our study results had showed also the same effect.
Fig. 5. Packing diagram of (1) viewed along the a-axis.
As can be seen from Table 3, [Co(H
2
dipic)(dipic)]ꢀ3H
2
O did not
show any antimicrobial activity against tested microorganisms at
applied concentrations. Pyridine-2,6-dicarboxylic acid did not
show antimicrobial activity against E. coli, S. typhimirium but weak
antimicrobial activity against B. subtilis and C. albicans and A. niger.
8
-HQ showed good inhibitory effect against tested total microor-
ganisms [Ni(Hdipic) O showed weak or absent antimicrobial
]ꢀ3H
activity at 250 g/well. It is interesting that complexation protects
2
2
l
the microorganisms, again consistent with the free ligand being
more potent than the complex. While inert Mo compounds are
the least effective at inhibiting yeast growth, Mo-dimethylhdroxy-
lamido complex is the most effective [39]. These results show that
the formation of some Mo complexes can protect yeast from the
growth inhibition observed when either the ligand or Mo salt alone
is present [39]. But this effect was not observed for the vanadium
insulin-enhancing compounds [10–11]. These studies have re-
vealed many compounds which exhibited good antimicrobial
Fig. 6. Cyclic voltammograms of the Co(II) complex in the presence of 0.1 M
ꢁ
1
ꢁ3
NBu
4
BF
4
in DMF (sr: 100 mVs , 1 ꢂ 10 M).
effect (8-H
2
Q)
2
[Mn(dipic)
2
(dipic)]ꢀ6H
2 2 2 2
O and (8-H Q) [Zn(dipic)
(
dipic)]ꢀ6H
2
O showed good inhibition effect against Gram-positive
bacteria and fungi. No growth inhibition was observed against
tested Gram-negative bacteria [40].The activity of the new synthe-
sis complexes increases as the concentration increases because
concentration is well known to play a vital role in increasing the
degree of inhibition [13]. In a previous study, Co(III) complexes
of pyridine-2,6-dicarboxylic acid, pyridine-2,5-dicarboxylic acid,
pyridine-3,5-dicarboxylic acid, and pyridine-3,4-dicarboxylic acid
were synthesized and characterized using the ‘‘Field-Durant
3 3 3
Green” solution as starting material (K [(Co(III)(CO ) ]). The muta-
genic activity of the K[Co(III)(dipic) ] (H
2
2
dipic = pyridine-2,6-dicar-
Fig. 7. Cyclic voltammograms of the Co(II) complex in the presence of 0.1 M
ꢁ
1
ꢁ3
boxylic acid) complex was tested according to Ames [41,42] with S.
typhimurium TA 98 and TA 100 strains. Tests carried out on the
complex proved it to be a non-mutagenic compound [14].
NBu
4
BF
4
in DMF (sr: 250 mVs , 1 ꢂ 10 M).
the position and broadness of the return peak varies markedly
depending on the anion present. This suggests that close associa-
tion of the anions with the metal(II) centers may occur following
A
pyrazolate bridged binuclear Pd(II) complex [Pd2(l-
dppz) (Hida) ]ꢀCH OHꢀ2H O (dppz = 3,5-diphenylpyrazolate) with
2
2
3
2
monoprotonated iminodiacetate (Hida) and a mononuclear Pt(II)
complex containing Hdppz and 2,6-pyridinedicarboxylate
I
0
reduction on the electrode surface. No M –M (M: Co(II) and Ni(II))

A.T. Çolak et al. / Journal of Molecular Structure 936 (2009) 67–74
73
Table 3
Antibacterial and antifungal activity [Co(H
2
dipic)(dipic)]ꢀ3H
Concentrations (
50 125
2
O [29], 8-HQ, 1, [Ni(Hdipic)
2
]ꢀ3H
2
O [30], 2 as inhibition zones (mm) (well Ø10 mm).
Compound
Strains
lg/well)
2
62.5
31.2
15.6
7.8
3.9
1.9
0.9
0.4
8
-HQ
B. subtilis
S. aureus
E. coli
S. typhimirium
C. albicans
A. niger
53 ± 0.4
68 ± 0.7
32 ± 0.7
25 ± 1.4
54 ± 0.7
56 ± 0.8
48 ± 0.7
54 ± 0.9
28 ± 1.2
20 ± 1.6
50 ± 1.2
51 ± 1.5
32 ± 0.8
41 ± 0.7
22 ± 1.9
18 ± 1.2
31 ± 1.3
48 ± 1.2
26 ± 1.1
30 ± 0.5
17 ± 1.2
14 ± 1.4
20 ± 1.5
40 ± 1.4
19 ± 1.2
22 ± 0.7
12 ± 1.6
–
15 ± 1.3
31 ± 0.6
12 ± 1.3
16 ± 0.7
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
13 ± 1.1
–
–
–
11 ± 0.4
–
–
–
–
–
22 ± 1.6
14 ± 1.3
H
2
dipic
B. subtilis
S. aureus
E. coli
S. typhimirium
C. albicans
A. niger
18 ± 0.4
12 ± 0.4
–
16 ± 0.4
–
–
–
14 ± 0.4
12 ± 0.4
15 ± 0.6
–
–
–
13 ± 0.6
–
14 ± 01
–
–
–
12 ± 01
–
13 ± 0.5
12 ± 08
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
15 ± 0.4
14 ± 0.4
[
Co(H
2
dipic)(dipic)]ꢀ3H
2
O, [29]
B. subtilis
S. aureus
E. coli
S. typhimirium
C. albicans
A. niger
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1
B. subtilis
S. aureus
E. coli
S. typhimirium
C. albicans
A. niger
28 ± 1.7
38 ± 1.2
–
25 ± 1.3
29 ± 0.4
–
21 ± 0.4
20 ± 1.3
–
18 ± 1.3
15 ± 0.4
–
15 ± 0.4
12 ± 0.8
–
–
12 ± 0.9
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
26 ± 1.1
51 ± 0.4
18 ± 0.8
48 ± 0.9
15 ± 0.4
38 ± 0.3
12 ± 0.2
24 ± 0.4
–
–
18 ± 0.4
14 ± 0.8
[
Ni(Hdipic)
2
]ꢀ3H
2
O, [30]
B. subtilis
S. aureus
E. coli
S. typhimirium
C. albicans
A. niger
11 ± 0.5
–
–
–
11 ± 0.1
12 ± 0.8
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
, no inhibition of zone. All the microorganisms were resistant to the control DMSO.
(
dipic)[Pt(Hdppz)(dipic)]ꢀCH
3
OH are synthesized. Moderate lumi-
Strong hydrogen bonds between uncoordinated water, (8-H
2
Q)+
nescence property and antimicrobial activity againstB. subtilis have
been noted for both [16].
and carboxylate play important roles in the construction of the
supramolecular networks. The decrease in biological activity of li-
gands has also been observed in complex 1 and 2 which has previ-
ously been experienced in molybdenum complexes due to
complexation.
2
Mononuclear complexes M(L)Cl where M = Mn(II), Fe(II), Co(II),
Ni(II) and Cu(II) and (L = N,N-diethylpiperazinyl,2,6-pyridinedicar-
boxylate) have been synthesized. Antimicrobial activities of newly
synthesized complexes were investigated against some Gram-posi-
tive and Gram-negative bacteria such as, E. coli, S. aureus, C. albicans
and A. flavus. The activity of Mn(II), Fe(II) and Co(II) complexes have
been observed as lower than that of Cu(II) complex [15]. The anti-
microbial activity of the metal complexes generally depend on
the following factors: the chelation ability of the ligand, the nature
of nitrogen donor ligands, the total charge of the complex, the exis-
tence and the nature of the metal ion neutralizing the ionic complex
and the nuclearity of the metal center in the complex [43].
Acknowledgments
The authors are indebted to the Dumlupinar University Research
Found for support (Grant No: 2007/14). The authors would like to
thank to Prof. Dr. Mehmet Tümer (University of Kahramanmaraßs
_
Sütçü Imam) for assistance in cyclic voltammetric studies of 1
and 2.
4
. Conclusion
In summary, two new compounds (8-H
M = Co (1) and Ni (2), 8-HQ = 8-hydroxyquinoline, dipic = dipicoli-
2
Q)
2
[M(dipic)
2
]ꢀ6H
2
O
Appendix A. Supplementary data
(
nate) have been prepared and characterized by elemental analysis,
spectral (IR and UV–vis), thermal analyses, magnetic measure-
ments and single-crystal X-ray diffraction techniques. The com-
Crystallographic data for the structure reported here have been
deposited at the CCDC as supplementary data, CCDC No. 675198
and 675199. Copies of the data available at CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK. E-mail: deposit@ccdc.-cam.ac.uk. Materi-
als and equipment of cyclic voltammograms, Tables S3–S6 of bond
angles and hydrogen bond geometries of complexes, CV graphic of
2 and electronic absorption spectra of 1 and 2 as well as their pre-
cursors are also available. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.molstruc.2009.07.026.
pounds
1 and 2 are isomorphous and crystallize in the
monoclinic crystal system space group C2/c. The common bond
distances and angles of (1) and (2) are in agreement with the cor-
responding values in the literature structures. As for bond dis-
tances, M–O and M–N of (1) and (2) have showed significant
changes according to precursors. The M(II) ions has a distorted
octahedral geometry with two tridentate dipicolinate ligands.

7
4
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