Novel boron compounds of 2,3- and 2,5-pyridinedicarboxylic acids

Article abstract of DOI:10.1016/j.ica.2011.11.006

The (Hea)[B(ph)₂(2,3-pydc)] (1) and (Hea)[B(ph) ₂(2,5-pydc)] (2) boron compounds (2,3-H₂pydc = 2,3-pyridinedicarboxylic acid, 2,5-H₂pydc = 2,5-pyridinedicarboxylic acid, Hea = ethanolammonium) were synthesized a

Full text of DOI:10.1016/j.ica.2011.11.006

Inorganica Chimica Acta 383 (2012) 169–177
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Novel boron compounds of 2,3- and 2,5-pyridinedicarboxylic acids
b
c
d
e
f
Alper Tolga Çolak a, , Yüksel Sßahin , Okan Zafer Yesßilel , Ferdag˘ Çolak , Filiz Yılmaz , Murat Taßs
⇑
a Department of Chemistry, Faculty of Arts and Sciences, Dumlupınar University, 43820 Kütahya, Turkey
b Department of Chemistry, Faculty of Arts and Sciences, Adnan Menderes University, 09010 Aydın, Turkey
c Department of Chemistry, Faculty of Arts and Sciences, Eskißsehir Osmangazi University, 26480 Eskißsehir, Turkey
d Department of Biology, Faculty of Arts and Sciences, Dumlupınar University, 43820 Kütahya, Turkey
e Department of Chemistry, Science Faculty, Anadolu University, 26470 Eskißsehir, Turkey
f Department of Chemistry, Faculty of Arts and Sciences, Giresun University, 28049 Giresun, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The (Hea)[B(ph)2(2,3-pydc)] (1) and (Hea)[B(ph)2(2,5-pydc)] (2) boron compounds (2,3-H2pydc =
2,3-pyridinedicarboxylic acid, 2,5-H2pydc = 2,5-pyridinedicarboxylic acid, Hea = ethanolammonium)
were synthesized and characterized by elemental analysis, spectroscopic measurements (UV–Vis, 11B
NMR, 13C NMR, 1H NMR and IR spectra) and single crystal X-ray diffraction technique. Compound 1
and 2 crystallize in the monoclinic space group P21/c. The crystal packing of compound 1 is stabilized
Received 16 February 2011
Received in revised form 28 October 2011
Accepted 2 November 2011
Available online 15 November 2011
through strong intermolecular hydrogen bonding and C–Hꢀ ꢀ ꢀ
p interactions, resulting in a 3D framework.
Keywords:
The individual molecules of 2 are connected by the N–Hꢀ ꢀ ꢀO and O–Hꢀ ꢀ ꢀO hydrogen bonds leading to two-
dimensional hydrogen bonded layer. The in vitro antibacterial and anticandidal activities of (1) and (2)
were evaluated by disc diffusion method and MIC tests. Both new complexes showed antimicrobial activ-
ity against MRSA and clinical and standard yeast isolates.
2,3-Pyridinedicarboxylate
2,5-Pyridinedicarboxylate
Boron compound
Diphenylborinic acid
Antimicrobial activity
MIC
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
divergent function groups, which possibly form bridging hydrogen
bonds, are interesting and have potential for self-assembly. In addi-
The chemistry of elemental boron, its compounds and crystal-
line phases based on them is currently a vast and quite complicated
scientific field at the boundary of inorganic and organo-element
chemistry. Boron compounds are successfully used in various areas
of materials science, in catalysis, surface chemistry, inorganic and
organic synthesis, biochemistry, agriculture, medicine, forestry
and OLEDs [1–7]. The synthesis of boron derivatives of biomole-
cules such as amino acids, peptides, nucleosides, porphyrins and
sugars is a major area of research [8]. For the past decade chemists
have been interested in the synthesis and characterization of five-
and six-membered boron compounds with a coordinative N ? B
bond. Also such boron compounds have been prepared from pyri-
dinedicarboxylic acids [9–13]. These acids can act as both a multi-
ple proton donor and an acceptor while also using their carboxylate
oxygen and nitrogen atoms, which are highly accessible to metal
ions, to form interesting network structures [14,15]. Pyridinedicar-
boxylic acids have widely been used as organic ligands for the con-
struction of organic–inorganic hybrid materials, which have been of
great interest in recent years [16–22]. These types of ligands com-
bine the advantages of both organic multi-carboxylic acid and aro-
matic compounds. 2,3- and 2,5-pyridinedicarboxylic acids with
tion, the carboxylic groups in position 5 of the pyridine ring may be
prone to involvement in hydrogen bonds [23,24]. Organic boron
compounds can be studied by multinuclear NMR techniques. Par-
ticularly, 11B NMR provides valuable structural information due to
its sensitivity to electronic and steric effects as well as to the boron
coordination number. The structures of several new compounds
have been determined by X-ray diffraction analyses [25].
Herein, we report the synthesis, characterization and antimicro-
bial activity of two novel boron compounds, using 2,3- and
2,5-pyridinedicarboxylic acids involving coordinative N ? B bonds.
2. Experimental
2.1. Materials and measurements
All chemicals and solvents used for the syntheses were of
reagent grade. The synthesis of diphenylborinic acid was carried
out under an atmosphere of dry argon by using standard Schlenk
techniques. 1H and 13C NMR spectra were recorded with Varian
AS 400. 11B NMR spectra were recorded with a Varian AS 600
spectrometer. NMR references were (CH3)4Si and BF3ꢀEt2O.
2,3-Pyridinedicarboxylic acid and 2,5-pyridinedicarboxylic acid
(Aldrich) were used as received. Elemental analysis (C, H, and N)
was performed using a Vario EL III CHNS elemental analyzer.
⇑
Corresponding author. Tel.: +90 2742652051; fax: +90 2742652056.
E-mail address: acolak@dumlupinar.edu.tr (A.T. Çolak).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.11.006

170
A.T. Çolak et al. / Inorganica Chimica Acta 383 (2012) 169–177
FT-IR spectra were recorded in the 4000–400 cmꢁ1 region with a
Bruker Optics, Vertex 70 FT-IR spectrometer using KBr pellets. Ther-
mal analyses were performed by the Seiko S II TG-DTA-DTG system,
in a dynamic nitrogen atmosphere (200 mL/min), at a heating rate
of 3 °C/min, in the temperature range of 35–1300 °C in platinum
gen atoms were refined anisotropically. Hydrogen atoms were
added to the structure model at calculated positions. Geometric
calculations were performed with Platon [29]. Molecular drawings
were obtained using Mercury [30]. The H atom of O–H in 2-ammo-
niumethanol was found from a difference Fourier map and was re-
0
sample vessels with reference to
a-Al2O3.
fined with distance restraint of O–H = 0.8 ÅA. The remaining H
atoms including N–H atoms in 2-ammoniumethanol were refined
using a riding model with Uiso(H) = 1.2 Ueq(C).
2.2. Crystallographic analyses
2.3. Biological evaluation
Diffraction data for complexes were collected with a Bruker AXS
APEX [26] CCD diffractometer equipped with a rotation anode at
2.3.1. Antimicrobial assays
100(2) K using graphite monochrometed Mo
Ka radiation
2.3.1.1. Microorganisms and media. The antimicrobial activities
were tested against clinical microorganisms of Gram positive
(methicillin-resistant Staphylococcus aureus) and Gram negative
(Vancomycin resistant Enterococcus faecium) bacteria and yeasts
(Candida albicans (3 isolates), Candida krusei, Candida glabrata,
Candida parapsilosis and Candida tropicalis). The clinical isolates
were obtained from hospitalised patients, and were a kind gift
from the Microbiology Laboratory of the Faculty of Medicine, Uni-
versity of Eskißsehir, Osmangazi, Turkey and the State Hospital of
Kütahya, Turkey. The standard strains used in the experiment were
S. aureus ATCC 25923, Bacillus subtilis NRRL 209, Bacillus cereus
NRRL 3711, Escherichia coli ATCC 25922, Aeromonas hydrophilia
NRRL 406, Proteus vulgaris NRRL-B 123, Enterococcus fecalis ATCC
29212, Saccharomyces baulardii, Rhodotorula rubra DSM 70403
and C. albicans NRRL Y-12983. The standard strains were obtained
from the American Type Culture Collection (Rock-ville, MD, USA)
and Northern Regional Research Laboratory (USDA, Peoria, IL,
USA). Cultures of each microbial species were maintained on Nutri-
ent Agar medium and stored at 4 °C.
(l = 0.71069 Å). Diffraction data were collected over the full sphere
and were corrected for absorption. The data reduction was per-
formed with the SAINT program package. For further crystal and data
collection details see Table 2. Structure solution was found with
the SHELXS-97 [27] package using the direct-methods and was re-
fined SHELXL-97 [28] against F2 using first isotropic. All non-hydro-
H3N CH2CH2OH
3
OOC
4
HOOC
HOOC
5
6
MeOH/ -78 o
C
+
Ph2BOCH2CH2NH2
1
2
N
N
O
C
O
B
Ph
Ph
Scheme 1. Synthesis of 1.
HOCH2CH2 NH3
COO
2.3.1.2. Preparation of inoculum. Cultures less than 30 h old were
touched with a loop and transferred to sterile nutrient Broth. The
broth was incubated at 37 °C until the growth reached a turbidity
equal to or greater than that of 0.5 Mc Farland standard (at 625 nm,
0.08–0.1 absorbance). The density of microorganism suspensions
was adjusted to 0.5 Mc Farland with sterile saline. The cell suspen-
sions containing 108 CFU/mL cells for bacteria, 107 CFU/mL cells for
yeasts were prepared. Inocula of the microorganisms were
adjusted to a concentration of 105 CFU/mL for MIC assay.
COOH
MeOH/ -78 oC
4
3
2
5
6
+
Ph2BOCH2CH2NH2
1
N
HOOC
N
O
C
O
B
Ph
Ph
Scheme 2. Synthesis of 2.
15.00
100.0
TG
30.00
20.00
10.00
0.00
80.0
10.00
60.0
DTA
5.00
40.0
-10.00
-20.00
20.0
0.00
DTG
0.0
200
400
600
800
1000
1200
Temperature (°C)
Fig. 1. TG-DTA-DTG curves of 1.

A.T. Çolak et al. / Inorganica Chimica Acta 383 (2012) 169–177
171
50.00
40.00
30.00
20.00
10.00
0.00
TG
15.00
10.00
5.00
100.0
80.0
60.0
40.0
20.0
0.0
DTG
DTA
0.00
-10.00
-20.00
-5.00
200
400
600
800
1000
1200
Temperature (°C)
Fig. 2. TG-DTA-DTG curves of 2.
2.3.1.3. Assays. Agar disc diffusion method was employed for deter-
mination of the antimicrobial activity of the synthesized com-
plexes [31]. Fresh stock solutions of the complexes were
prepared in dimethylsulfoxide (DMSO) according to the three con-
Table 1
Crystal data and structure refinement parameters for 1 and 2.
1
2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C
21H21BN2O5
C21H21BN2O5
392.21
centrations (100, 150 and 200 lg/disc) for activity experiments.
392.21
293 (2)
0.71073 Mo K
monoclinic
P21/c
17.258
9.258
12.821
108.03
1948
DMSO was used as negative control. Fifteen millilitres of the nutri-
ent agar (45 °C) was poured into sterile Petri dishes (Ø 90 mm). The
plates were dried for 2 days at room temperature. The cell suspen-
sions containing 108 CFU/mL cells for bacteria, 107 CFU/mL cells for
yeasts were prepared and were evenly spread onto the surface of
the agar plates using swab sticks. The paper disc (Ø 6 mm) impreg-
nated with 10 lL of the complexes was placed on the surface of the
inoculated agar plate. The plates were preincubated for 2 h at room
temperature prior to incubation at 37 °C for 24 h for bacterial
a
monoclinic
P21/c
12.363
17.452
13.406
138.19
1928
b (Å)
c (Å)
b (°)
V (Å3)
Z
4
4
Dcalc (Mgmꢁ3
)
1.337
18030
4817
1.351
17952
4825
Total reflections
Independent reflections
Absorption correction
Refinement method
Rint
Integration
Full-matrix least-squares on F2
0.035
0.041
0.104
1.05
0.063
0.059
0.207
1.09
R[F2 > 2
wR(F2)
r
(F2)]
Goodness-of-fit on F2
0
0.36; ꢁ0.24
0.46; ꢁ0.51
D
q
(eAÅꢁ3
)
Data/restraints/parameters
4817/0/266
4825/3/291
Table 2
Selected geometric parameters (Å, °) for 1 and 2.
1
2
Bond length
B1–O1
B1–N1
B1–C1
B1–C7
1.527 (2)
1.595 (2)
1.600 (2)
1.613 (2)
1.525 (4)
1.624 (4)
1.603 (4)
1.609 (4)
Bond angles
O1–B1–N1
O1–B1–C1
N1–B1–C1
O1–B1–C7
N1–B1–C7
C1–B1–C7
97.7 (1)
110.7 (1)
113.8 (1)
110.3 (1)
108.6 (1)
114.6 (1)
97.3 (2)
110.1 (2)
111.0 (2)
108.7 (2)
109.7 (2)
118.0 (2)
Fig. 3. The molecular structure of 1 with atom-labelling scheme.

172
A.T. Çolak et al. / Inorganica Chimica Acta 383 (2012) 169–177
strains and 48 h for yeast. Vancomycin (VA; 30
mycin (E; 15 g/disc), Chloramphenicol (C; 30
(IPM; 10 g/disc), Rifampicin (RD; 5 g/disc, Kanamycin (K; 30
disc), Cefotaxime (CTX; 30 g/disc), Ampicillin (AMP; 10 g/disc),
g/disc), Streptomycin (S; 25 g/disc) and
g/disc) for bacteria and Nystatin (N; 100 U/
l
g/disc), Erythro-
g/disc), Imipenem
g/
experiment was repeated three times. Antimicrobial activity was
evaluated by measuring the zone (mm) of inhibition against the
test organisms.
l
l
l
l
l
l
l
Tetracycline (T; 15
Gentamicin (CN; 30
l
l
l
2.4. Minimal inhibitory concentration (MIC)
disc) for yeast were used as positive controls. Each assay in this
In determination of the minimal inhibitory concentration of the
complexes, tube dilution method was employed [32,33]. Sterile
tubes were filled with 1 mL of serial two fold dilutions (500–15.6
lg/mL) of the two complexes. The nutrient broth (1 mL), containing
Table 3
the microorganisms was transferred into each test tube. Tubes were
incubated at 37 °C for 48 h. Afterwards MIC was defined as the low-
est concentration of the complexes at which the microorganisms
did not demonstrate visible growth. The growth of microorganisms
was indicated by the presence turbidity and a ‘‘pellet’’ on the tube
bottom.
Selected hydrogen-bond geometric parameters (Å, °) for 1 and 2.
DꢁHꢀ ꢀ ꢀA
DꢁH
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
\DꢁHꢀ ꢀ ꢀA
Compound 1
N2–H22Aꢀ ꢀ ꢀO3i
N2–H22Bꢀ ꢀ ꢀO2i
O5–H10ꢀ ꢀ ꢀO3ii
N2–H22Cꢀ ꢀ ꢀO4iii
0.89
0.89
0.92 (2)
0.89
1.97
2.18
1.80 (2)
1.90
2.763 (1)
2.953 (1)
2.715 (2)
2.790 (1)
147
145
173 (1)
175
Compound 2
2.5. Minimal microcidal concentration (MMC)
N2–H2Cꢀ ꢀ ꢀO2i
N2–H2Aꢀ ꢀ ꢀO4ii
O5–H5ꢀ ꢀ ꢀO3iii
0.96 (4)
0.88 (1)
0.80 (4)
2.10 (4)
1.91 (2)
1.94 (4)
2.953 (4)
2.755 (4)
2.722 (3)
148 (3)
163 (3)
167 (4)
The Minimal microcidal concentration (MMC) is defined as the
concentration producing a P99.9% reduction in CFU number in the
initial inoculum. For the determination of MMC, a portion of the
Symmetrycodes:(i)ꢁx + 1, y ꢁ 1/2, ꢁz + 1/2;(ii)ꢁx + 2, ꢁy, ꢁz + 1;(iii)ꢁx + 1, ꢁy, ꢁz.
liquid (10 lL) from each tube that showed no turbidity was placed
Fig. 4. (a) Unit cell and (b) The crystal packing and inter-molecular hydrogen bonding, C–Hꢀ ꢀ ꢀp interactions of compound 1.

A.T. Çolak et al. / Inorganica Chimica Acta 383 (2012) 169–177
173
on NA. Prior to the drying of the spots, plates were inverted and
3. Results and discussion
incubated at 37 °C for 62 h. The lowest concentration that yielded
no growth after this sub-culturing was taken as the MMC. Both
MIC and MMC were confirmed by the two replicates.
3.1. NMR spectra
The treatment of 2-aminoethyl diphenylborinate whit metha-
nol at ꢁ78 °C probably led to the formation of methyl diphenylbo-
rinate and ethanolamine, causing a transesterification reaction of a
carboxylic acid group (2,3-pyridinedicarboxylic acid) with boron
(methyl diphenylborinate) to take place [10], resulting in the
formation of a boron compound. During formation of the boron
compound and ethanolamine an acid–base reaction occurred be-
tween the other carboxylic acid group of the boron compound
and ethanolamine. This acid–base reaction yielded diphenyl
[(2-(3-carboxypyridyl))-carbonyloxy-O,N] boron (Scheme 1, 1).
The synthesis of diphenyl [(2-(5-carboxypyridyl))-carbonyloxy-
O,N] boron (Scheme 2, 2) was similar to that for 1 except that
2,5-pyridinedicarboxylic acid was used in the synthesis instead
of 2,3-pyridinedicarboxylic acid.
2.6. Preparation of boron compounds
2.6.1. Synthesis of diphenyl [(2-(3-carboxypyridyl))-carbonyloxy-O, N]
boron (1) and diphenyl [(2-(5-carboxypyridyl))-carbonyloxy-O, N]
boron (2)
1 was synthesized from a mixture of 0.60 g (3.60 mmol) of
2,3-pyridinedicarboxylic acid, and methyl diphenylborinate pre-
pared from 0.90 g (4.00 mmol) of 2-aminoethyl diphenylborinate
in 40 mL methanol at ꢁ78 °C. After evaporation of the solvent
the colorless crude products were washed with a mixture of
pentane–hexane (1:1) and crystallized from ethanol at 4 °C. 2
was synthesized using the same method as described for 1 using
2,5-pyridinedicarboxylic acid instead of 2,3-pyridinedicarboxylic
acid in methanol at ꢁ78 °C.
Signals in the 13C NMR spectrum of 1 were observed at
130.3 ppm for C5, 135.6 ppm for C3, 140.6 ppm for C2, 140.9 ppm
for C6, 141.2 ppm for C4, 145.3 ppm for the ipso-C atoms of both
phenyl groups, and 162.5 ppm (C2–COO) and 166.8 ppm
(C5–COOB) for the carboxyl carbon atoms. The carbon atoms on 1
were assigned with COSY and HETCOR spectra. The C atoms
(C2–COOB) of 1 and 2 were determined due to increase in chemical
shift values of C-atoms of COOB group, when they are compared to
that of 2,3- and 2,5-pyridinedicarboxylic acids. Signals correspond-
ing to C atoms and protons of both phenyl groups were observed at
the same shift values. Due to the use of DMSO as the solvent, the
dative bond (B–N) could be eliminated by the solvent effect so that
both phenyl groups were allowed to rotate freely, given that oxy-
gen ligands have high affinities for boron [34,35]. In the 1H NMR
spectrum of 1, multiple signals in the range of 7.20–7.29 ppm were
observed from –B(C6H5)2 group protons. A broad signal at 8.15
ppm was also observed for –C(NH+3) protons, a triplet signal at
7.98 ppm for the C5-proton, a doublet at 8.23 ppm for the C4-pro-
ton and a doublet at 8.87 ppm for the C6–H proton. The B atom was
observed at 10.2 ppm in the 11B NMR spectrum of 1. The chemical
shifts in the 13C NMR spectrum of 2 were different than those ob-
served for 1. Signals in the 13C NMR spectrum of 2 were observed at
141.0 ppm for C5, 135.6 ppm for C3, 141.6 ppm for C2, 142.0 ppm
for C6, 144.2 ppm for C4, 144.6 ppm for the ipso-C atoms of both
2.6.1.1. Analytical data. Compound 1 (392.21 g/mol), Anal. Calc. for
C21H21BN2O5: C, 64.25; H, 5.35; N, 7.14. Found: C, 64.27; H, 5.28; N,
7.17%. Yield 82%, M.p. 215–217 °C. 1H (400 MHz. DMSO-d8) d
(ppm): 2.82 (t, 2H, CH2NH3), 3.55 (t, 2H CH2OH), 7.18–7.23 (m,
10 H, o-, m- and p-2C6H5), 7.98 (t, 1H, H-5), 8.15 (br, 3H, NH3),
8.23 and 8.87 (each d, each 1H, H-4 and H-6, 2J(H–H) = 8.0 Hz);
13C (100.47 MHz, DMSO-d8) d (ppm): 41.3 (CH2NH3), 57.6 (CH2OH),
127.0 (p-C6H5), 127.5 (m-C6H5), 130.3 (C-5), 131.8 (o-C6H5), 135.6
(C-3), 140.6 (C-2), 140.9 (C-6), 141.2 (C-4), 145.3 (br, i-C, C6H5),
162.5 (COOH), 166.8 (CO); 11B (86.6 MHz, DMSO-d6) d (ppm): 10.2.
2.6.1.2. Analytical data. Compound 2 (392.21 g/mol), Anal. Calc. for
C21H21BN2O5: C, 64.25; H, 5.35; N, 7.14. Found: C, 64.29; H, 5.31; N,
7.10%. Yield 80%, M.p. 217–219 °C. 1H (400 MHz. DMSO-d8) d
(ppm): 2.84 (t, 2H, CH2NH3), 3.54 (t, CH2OH), 7.19–7.30 (m, 10 H,
o-, m- and p-2C6H5), 8.17 (br, 3H, NH3), 8.41 and 8.88 (each d, each
1H, H-3 and H-4, 2J(H–H) = 8.0 Hz), 9.03 (s, 1H, H-6); 13C
(100.47 MHz, DMSO-d8) d (ppm): 41.9 (CH2NH3), 58.3 (CH2OH),
123.6 (C-3), 127.1 (p-C6H5), 127.6 (m-C6H5), 131.8 (o-C6H5),
141.0 (C-5), 141.6 (C-2), 142.0 (C-6), 144.2 (C-4), 144.6 (br, i-C,
C6H5), 163.2 (COOH), 163.9 (CO); 11B (86.6 MHz, DMSO-d6) d
(ppm): 10.8.
Fig. 5. The molecular structure of 2 with atom-labelling scheme.

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A.T. Çolak et al. / Inorganica Chimica Acta 383 (2012) 169–177
phenyl groups, and 163.2 ppm (C6-COO) and 163.9 ppm (C5-COOB)
for the carboxyl carbon atoms. Multiple signals in the 1H NMR
spectrum of compound 2 were observed in the range of 7.19–
7.30 ppm for –B(C6H5)2 group protons. There was also a broad sig-
complexes 1 and 2, respectively. The difference between the asym-
metric and symmetric carboxylate stretching
as(COOꢁ)–
s(COOꢁ) is often used for the correlation of the infrared spectra
with the structures of metal carboxylates [36,37]. These values
are approximately 228 cmꢁ1 for monodentate, 164 cmꢁ1 for ionic
and 42 cmꢁ1 for bidentate for carboxylate groups. These differ-
(
D = m
m
nal at 8.17 ppm for –C(NH+
) protons, a doublet signals at
3
8.40 ppm for the C3-proton, a doublet at 8.88 ppm for the C4-pro-
ton and a singlet at 9.03 ppm for the C6-proton. A signal at
10.08 ppm was observed in the 11B NMR spectrum of 2.
ences were determined for 1
D ,
= 236 cmꢁ1 (1571–1335 cmꢁ1
monodentate) and
2
D
= 162 cmꢁ1 (1431–1269 cmꢁ1, ionic) and for
D D = 157
= 239 cmꢁ1 (1568–1329 cmꢁ1, monodentate) and
cmꢁ1 (1440–1283 cmꢁ1, ionic). In the Na2(pydc)ꢀnH2O salt, these
3.2. FT-IR spectra
symmetric
ms(COO) and asymmetric mas(COO) stretching bands
were observed at 1402 and 1604 cmꢁ1, respectively. The absorp-
tion bands at 1335 and 1329 cmꢁ1 correspond to B–O vibration
of the compounds 1 and 2, respectively [38].
The broad bands at 3205 and 3287 cmꢁ1 are attributed to
of 2-ammoniumethanol for 1 and 2, respectively. The absorption
peaks at 3110 and 3175 cmꢁ1 are assigned to
(NH3) stretching
m(OH)
m
vibration of 2-ammoniumethanol ligand in 1 and 2, respectively.
The strong absorption bands at 1636, and 1648 cmꢁ1 are due to
3.3. Thermal analysis
m
(C@C) +
eral
as(COOꢁ) strong bands in free H2pydc are shifted to lower fre-
quencies of 1571 and 1431 cmꢁ1 and 1568 and 1440 cmꢁ1 in
m(C@N) vibration of ligands for 1 and 2, respectively. Sev-
m
The TG-DTG and DTA curves of 1 and 2 are shown in Figs. 1 and
2. The compounds 1 and 2 are thermally stable up to about 180 °C.
Fig. 6. (a) Inter-molecular hydrogen bonding of compound 2. (b) Inter-molecular C–Hꢀ ꢀ ꢀp interactions of compound 2.

A.T. Çolak et al. / Inorganica Chimica Acta 383 (2012) 169–177
175
A two-step weight loss is observed upon further heating. The DTG
curve shows two peaks at 216 and 261 °C for these stages. It is hard
to give clear interpretations concerning degradation of organic
groups because no flat plateau forms on TG curve. The rate of res-
idue which is determined as 23.1% for 1 and 24.7% for 2 at 450 °C
which is melting point for B2O3 shows that organic residues exist
in the medium beside B2O3. As a matter of fact, only B2O3 would
be expected to exist in the medium around 973 °C considering
the literature [39–41] (Theoretic B2O3 17.8%). However, a con-
stantly increasing mass loss occurs until 1300 °C starting from this
temperature. This is an indicator that B2O3 and suboxides [41]
formed of B2O3 start to evaporate above 450 °C. Thanks to FT-IR
analysis of the remaining product of 1 (Fig. S1) we may state that
12% of the product at 1300 °C is a mixture of B2O3 and C [41].
Fig. 3. The selected bond lengths and angles and hydrogen bonding
geometry are given in Tables 2 and 3. Compound 1 crystallizes in
the monoclinic space group P21/c. The crystallographic analysis re-
vealed that compound 1, (Hea)[B(ph)2(2,3-pydc)], consists of dis-
crete [Ph2B(2,3-pydc)]ꢁ anion and one protonated ea cation. The
B atom has a distorted tetrahedral coordination and is chelated
by the 2,3-pydc ligand through carboxylate O and pyridine N
atoms. The tetrahedral geometry is completed by two phenyl
groups. The B1–O1 (1.527(2) Å) and B1–N1 (1.595(2) Å) bond
distances are similar to the corresponding values found in
[B(ph)2(pdca)] [10] (H2pdca = 2,6-pyridinedicarboxylic acid),
[BLSTc] [9] (L = 9-borabicyclo[3.3.1]nonane, STc = S-trityl-(R)-cys-
teine), [Ph2C(NH2)CO2BPh2].
The crystal packing of compound 1 is stabilized through strong
intermolecular hydrogen bonding and C–Hꢀ ꢀ ꢀ
p interactions, result-
ing in
a
3D framework. The intermolecular N2–H22Aꢀ ꢀ ꢀO3i,
3.4. Description of the crystal structures
N2–H22Bꢀ ꢀ ꢀO2i, O5–H10ꢀ ꢀ ꢀO3ii, N2–H22Cꢀ ꢀ ꢀO4iii and bonds have
the Hꢀ ꢀ ꢀO distances of 1.97, 2.18, 1.80 and 1.90 Å, respectively
(Symmetry codes: (i) ꢁx + 1, ꢁy, ꢁz + 1; (ii) x, ꢁy + ½, z ꢁ ½; (iii)
ꢁx + 1, ꢁy + 1, ꢁz + 1). It is seen from Fig. 4 that the hydrogen bonds
between the Hea cations and the carboxylate groups of 2,3-pydc li-
gands, giving rise to R44ð18Þ and R22ð9Þ ring motives in the bc plane.
The details of the crystal structures are given in Table 1. The
molecular structure of 1 with the atom labelling is shown in
Table 4
The means of inhibition zone diameters of the two complexes against clinical and
standard isolates of bacteria and clinical and standard isolates of yeast (disc Ø 6 mm).
These 2D layers are held together by C–Hꢀ ꢀ ꢀ
p interactions to form
a three-dimensional network. For the C8–H8ꢀ ꢀ ꢀCg contact (Cg =
1
2
100
lg
150
22
l
g
200
25
lg
100
l
g
150
23
l
g
200
26
lg
phenyl ring, C7–C12), the distance between atom H8 and the aro-
0
matic ring centroid is 2.81 ÅA, with a C18–H18ꢀ ꢀ ꢀCg angle of 141°.
In 1, the compound anion has A ring (N1/C14–C18), B ring
(C1–C6) and C ring (C7–C12) plane and the dihedral angles between
A–B rings, A–C rings and B/C rings are 58.79(7)°, 76.20(6)° and
68.06(7)°, respectively.
Gram positive bacteria
MRSA
(clinical)
20
20
B. subtilis
B. cereus
S. aureus
12
13
12
16
15
15
20
20
20
15
15
13
18
18
15
23
22
21
The structures of 2 (Fig. 5) is similar to that of 1. The selected
bond lengths and angles and hydrogen bonding geometry are given
in Tables 2 and 3. As shown in Fig. 5, the boron ion in compound 2
is coordinated by a 2,5-pydc ligand and two phenyl groups, form-
ing a significantly distorted tetrahedral geometry. The 2,5-pydc li-
gand acts as a bidentate chelating ligand, forming a five-membered
ring [B–N1 = 1.624(4) and B–O1 = 1.524(3) Å]. The bond distances
are comparable to those of compound 1. The dihedral angle be-
tween the rings of pyridine and phenyl rings is 82.81(13),
69.54(13) and 80.92(13)°.
Gram negative bacteria
E. coli
–
7
16
9
9
8
8
–
15
8
8
–
7
8
A. hydrophilia
P. vulgaris
E. fecalis
14
8
8
20
10
10
10
18
10
9
21
11
11
12
VRE (clinical)
–
8
100
lg
150
l
g
200
lg
100
l
g
150
l
g
200
lg
N
Standard yeast
C. albicans
S. baulardii
R. rubra
18
7
18
22
9
20
25
10
23
20
8
19
22
10
20
25
13
24
19
20
21
The individual molecules of 2 are connected by the N–Hꢀ ꢀ ꢀO and
O–Hꢀ ꢀ ꢀO hydrogen bonds leading to two-dimensional hydrogen
bonded layer (see Fig. 6a). The intermolecular N2–H2Cꢀ ꢀ ꢀO2i, N2–
H2Aꢀ ꢀ ꢀO4ii and O5–H5ꢀ ꢀ ꢀO3iii bonds have the Hꢀ ꢀ ꢀO distances of
2.10, 1.91 and 1.94 Å, respectively (Symmetry codes: (i) ꢁx + 1,
y ꢁ ½, ꢁz + ½; (ii) ꢁx + 2, ꢁy, ꢁz + 1; (iii) ꢁx + 1, ꢁy, ꢁz). Some of
these interactions are illustrated in Fig. 6b. These layers are held
Clinical yeast
C. parapsilosis 18
21
12
20
10
20
20
18
25
15
24
14
22
26
21
18
12
8
21
16
12
13
20
22
20
25
18
15
16
23
28
25
20
15
10
20
15
20
19
C. tropicalis
C. krusei
C. globrata
C. albicansa
C. albicansb
C. albicansc
10
16
8
18
15
15
9
18
15
18
together by C–Hꢀ ꢀ ꢀ
p
interactions (C5–H5ꢀ ꢀ ꢀCg1 = 3.430(3) Å, 177;
N, Nystatin (100 U/disc).
C9–H9ꢀ ꢀ ꢀCg2 = 3.820(3) Å, 155° and C21–H21Aꢀ ꢀ ꢀCg3 = 3.630(3) Å,
Table 5
Antimicrobial activity of standard antibiotics against microorganisms (disc Ø 6 mm).
Antibiotic discs
VA
E
C
IPM
RD
K
CTX
AMP
T
S
CN
Gram positive bacteria
MRSA (clinic)
B. subtilis
B. cereus
S. aureus
24
22
17
20
15
30
22
25
32
29
25
20
12
30
30
39
8
8
–
10
26
9
14
35
27
25
13
20
22
20
10
17
18
20
26
18
25
21
19
20
30
10
8
29
Gram negative bacteria
E. coli
A. hydrophilia
P. vulgaris
E. fecalis
12
21
22
18
–
15
20
8
19
16
30
20
18
24
12
40
38
40
30
20
20
22
34
24
12
20
19
8
11
–
40
8
40
28
–
25
22
30
28
21
24
25
18
12
34
20
19
20
20
18
15
18
22
14
–
VRE
Vancomycin (VA; 30
lg/disc), Erythromycin (E; 15
l
g/disc), Chloramphenicol (C; 30
lg/disc), Imipenem (IPM; 10
lg/disc), Rifampicin (RD; 5
lg/disc, Kanamycin (K; 30
lg/
disc), Cefotaxime (CTX; 30
l
g/disc), Ampicillin (AMP; 10
lg/disc), Tetracycline (T; 15
l
g/disc), Streptomycine (S; 25
l
g/disc), Gentamisin (CN; 30 l
g/disc).

176
A.T. Çolak et al. / Inorganica Chimica Acta 383 (2012) 169–177
127°, Cg1 = C7–C12, Cg2 = N1/C14–C18 and Cg3 = C1–C6) and
exhibited activity against clinical MRSA with an MIC value of
31.25 g/mL. Minimum microcidal concentrations of the two com-
hydrogen bonding interactions to form
a
three-dimensional
l
network.
plexes for the microorganism species ranged from 250 to 500
lg/
mL.
Two complexes displayed anticandidal activity against all stan-
dard and clinical yeasts at three concentrations (Table 4). Two
complexes were found to be highly active against standard yeast
C. albicans and less active against R. rubra and S. baulardii. Complex
1 was found to be highly active against clinical C. albicansb and less
active against C. parapsilosis and C. krusei. It displayed low activity
3.5. Antimicrobial activities
In the present study, in vitro potential antimicrobial activity of
complexes 1 and 2 tested against microorganisms according to disc
diffusion method is presented in Table 4. Antimicrobial activity was
determined for 100, 150 and 200 lg/disc concentrations against
against C. globrata at 200 lg/disc concentration. Complex 2 was
tested microorganisms. The comparison of the obtained results
with the 11 antibacterial agents and one antifungal agent used in
the study are presented in Tables 4 and 5. Two complexes displayed
antimicrobial activity against all tested microorganisms at 150 and
found to be highly active against clinical C. albicansb and less active
against C. parapsilosis and C. albicansc. It displayed low activity
against C. krusei at 200 lg/disc concentration. Obanda et al. [4]
mentioned about fungicidal activity of boron in their study.
Minimal inhibitory concentration (MIC) and minimal microcid-
al concentration (MMC) results of the complexes against clinical
and standard Candida species are presented in Table 6. MIC of com-
plex 1 for the clinical and standard Candida species ranged from
200
crobial activity against E. coli and Vancomycin resistant E. faecium
100 g/disc concentrations. Two complexes displayed maximum
antimicrobial activity against MRSA at 200 g/disc concentration.
lg/disc concentrations. Two complexes did not display antimi-
l
l
MRSA is a resistant variation of the common bacterium S. aureus.
Inorganic and organic boron compounds possess interesting phar-
macological properties, such as hypolipidemic, anti-inflammatory,
anti-osteoporosis, and antineoplastic activities [8]. Two complexes
displayed weak antimicrobial activity against E. coli (8 mm).
Complex 1 displayed antimicrobial activity against B. subtilis, B.
cereus, S. aureus, A. hydrophilia, P. vulgaris, E. fecalis and Vancomycin
resistantE. faecium (VRE) with diameters of zone inhibition ranging
62.5 to 125
species ranged from 125 to 500
the clinical and standard Candida species ranged from 31.25 to
250 g/mL. MMC of complex 2 for the microorganism species ran-
lg/mL. MMC of the complex 1 for the microorganism
lg/mL. MIC of the complex 2 for
l
ged from 250 to 500 lg/mL.
Acknowledgments
between 10 and 20 mm at 200 lg/disc concentration. Complex 2
This work was supported by Dumlupınar University, project No.
2007/14 and by Adnan Menderes University project No. FEF-08002.
showed antimicrobial activity against B. subtilis, B. cereus, S. aureus,
A. hydrophilia, P. vulgaris, E. fecalis and Vancomycin resistant
E. faecium (VRE) with diameters of zone inhibition ranging between
Appendix A. Supplementary material
11 and 23 mm at 200 lg/disc concentration.
The MIC and MMC results of the two complexes against Gram
positive and Gram negative bacteria are given in Table 6. Minimum
Inhibitory Concentrations of the two complexes for the microor-
CCDC 770796 and 780575 contains the supplementary crystal-
lographic data for 1 and 2. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2011.11.006.
ganism species ranged from 31.25 to 125 lg/mL. Two complexes
Table 6
Minimal inhibitory concentration (MIC) and minimal microcidal concentration
(MMC) values of the complexes against clinical and standard isolates of bacteria
and clinical and standard isolates of yeast.
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