A new pyrimidine-derived ligand, n-pyrimidine oxalamic acid, and its Cu(II), Co(II), Mn(II), Ni(II), Zn(II), Cd(II), and Pd(II) complexes: Synthesis, characterization, electrochemical properties, and biological activity

Article abstract of DOI:10.1080/00958971003646506

A new heterocyclic compound N-(5-benzoyl-2-oxo-4-phenyl-2H-pyrimidin-1-yl)-oxalamic acid has been synthesized from N-amino pyrimidine-2-one and oxalylchloride. Bis-chelate complexes of the ligand were prepared from acetate/chloride salts of Cu(II), Co(II), Mn(II), Ni(II), Zn(II), Cd(II), and Pd(II) in methanol. The structures of the ligand and its metal complexes were characterized by microanalyses, IR, AAS, NMR, API-ES, UV-Vis spectroscopy, magnetic susceptibility, and thermogravimetric analyses. An octahedral geometry has been suggested for all the complexes, except for Pd(II) complex, in which the metal center is square planar. Each ligand binds using C(2)=O, HN, and carboxylate. The cyclic voltammograms of the ligand and the complexes are also discussed. The new synthesized compounds were evaluated for antimicrobial activities against Gram-positive, Gram-negative bacteria and fungi using the microdilution procedure. The Cu(II) complex displayed selective and effective antibacterial activity against one Gram-positive spore-forming bacterium (Bacillus cereus ATCC 7064), two Gram-positive bacteria (Staphylococcus aureus ATCC 6538 and S. aureus ATCC 25923) at 40-80 μg mL^-1, but poor activity against Candida species. The Cu(II) complex might be a new antibacterial agent against Gram-positive bacteria.

Full text of DOI:10.1080/00958971003646506

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A new pyrimidine-derived ligand,
N-pyrimidine oxalamic acid, and its
Cu(II), Co(II), Mn(II), Ni(II), Zn(II),
Cd(II), and Pd(II) complexes: synthesis,
characterization, electrochemical
properties, and biological activity
Mehmet Sönmez a , Metın Çelebı a , Abdulkadır Levent a , İsmet
Berber b & Zühre Şentürk a
a Department of Chemistry , Yüzüncü Yıl University , 65080 Van,
Turkey
b Department of Biology , Sinop University , 57000 Sinop, Turkey
Published online: 08 Mar 2010.
To cite this article: Mehmet Sönmez , Metın Çelebı , Abdulkadır Levent , İsmet Berber & Zühre
Şentürk (2010) A new pyrimidine-derived ligand, N-pyrimidine oxalamic acid, and its Cu(II), Co(II),
Mn(II), Ni(II), Zn(II), Cd(II), and Pd(II) complexes: synthesis, characterization, electrochemical
properties, and biological activity, Journal of Coordination Chemistry, 63:5, 848-860, DOI:
10.1080/00958971003646506
To link to this article: http://dx.doi.org/10.1080/00958971003646506
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Journal of Coordination Chemistry
Vol. 63, No. 5, 10 March 2010, 848–860
A new pyrimidine-derived ligand, N-pyrimidine oxalamic acid,
and its Cu(II), Co(II), Mn(II), Ni(II), Zn(II), Cd(II),
and Pd(II) complexes: synthesis, characterization,
electrochemical properties, and biological activity
¨
MEHMET SONMEZ*y, METIN C
¸
ELEBIy, ABDULKADIR LEVENTy,
_
¨
¨
ISMET BERBERz and ZUHRE SENTURKy
ꢀ
yDepartment of Chemistry, Yuzuncu Y|l University, 65080 Van, Turkey
¨
¨
¨
zDepartment of Biology, Sinop University, 57000 Sinop, Turkey
(Received 19 June 2009; in final form 27 October 2009)
A
new heterocyclic compound N-(5-benzoyl-2-oxo-4-phenyl-2H-pyrimidin-1-yl)-oxalamic
acid has been synthesized from N-amino pyrimidine-2-one and oxalylchloride. Bis-chelate
complexes of the ligand were prepared from acetate/chloride salts of Cu(II), Co(II), Mn(II),
Ni(II), Zn(II), Cd(II), and Pd(II) in methanol. The structures of the ligand and its metal
complexes were characterized by microanalyses, IR, AAS, NMR, API-ES, UV-Vis spectros-
copy, magnetic susceptibility, and thermogravimetric analyses. An octahedral geometry
has been suggested for all the complexes, except for Pd(II) complex, in which the metal
center is square planar. Each ligand binds using C(2)¼O, HN, and carboxylate. The cyclic
voltammograms of the ligand and the complexes are also discussed. The new synthesized
compounds were evaluated for antimicrobial activities against Gram-positive, Gram-negative
bacteria and fungi using the microdilution procedure. The Cu(II) complex displayed selective
and effective antibacterial activity against one Gram-positive spore-forming bacterium
(Bacillus cereus ATCC 7064), two Gram-positive bacteria (Staphylococcus aureus ATCC
6538 and S. aureus ATCC 25923) at 40–80 mg mLꢀ1, but poor activity against Candida species.
The Cu(II) complex might be a new antibacterial agent against Gram-positive bacteria.
Keywords: N-aminopyrimidine; Metal complexes; Cyclic voltammetry; Biological activity
1. Introduction
Pyrimidine derivatives have therapeutic applications; the presence of a pyrimidine ring
system in nucleic acids, vitamins, coenzymes, and antibiotics is a possible reason
for their biological activity [1, 2]. Pyrimidine, as a ligand, provides potential binding
sites for metal ions, and information on their coordinating properties is important
to understand the role of metal ions in biological systems [3]. Considerable attention has
been given to metal(II) complexes of ligands containing N-pyrimidine, due to their
structural richness, electrochemical properties, and models for biological systems [4–7].
Purines and pyrimidines and their derivatives are growth factor analogs and have been
*Corresponding author. Email: vansonmez@hotmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ꢁ 2010 Taylor & Francis
DOI: 10.1080/00958971003646506

Pyrimidine-derived ligand
849
used for treatment of bacterial, viral, and fungal infections [8]; pyrimidines and their
complexes display effective and selective antimicrobial activity against bacteria, fungi,
and viruses [9–11]. Metal(II) complexes of polydentate Schiff-base ligands of N-
aminopyrimidines [6] acts as a bidentate or tridentate monobasic donor for Cu(II),
Co(II), Ni(II), Mn(II), and Fe(III), coordinating through nitrogen of the azomethine
group and oxygen of the hydroxyl group.
The goal of this study is to prepare and characterize a pyrimidine-derived ligand
and its metal complexes with Cu(II), Co(II), Mn(II), Ni(II), Zn(II), Cd(II), and Pd(II).
In continuation of the study, all synthesized compounds have been investigated for their
electrochemical properties and antimicrobial activity.
2. Experimental
2.1. Materials
All chemicals used in this study were obtained commercially and used without
purification. 1-Amino-5-benzoyl-4-phenyl-1H-pyrimidine-2-one (N-aminopyrimidine)
was prepared according to the literature method [12].
2.2. Physical measurements
Elemental analyses (C, H, N, S) were performed with a Leco CHNS model 932
elemental analyzer. IR spectra were obtained using KBr pellets (4000–400 cmꢀ1) on a
Bio-Rad-Win-IR spectrophotometer. Electronic spectra in the 200–900 nm range
were recorded in DMF on a Unicam UV2-100 UV-Vis spectrophotometer. Magnetic
measurements were carried out by the Gouy method using Hg[Co(SCN)4] as calibrant.
Molar conductances of the Schiff base and metal complexes were determined in DMF
1
at room temperature using a Jenway model 4070 conductivity meter. The H- and
13C-NMR spectra of the Schiff base were carried out using a Bruker 300 MHz
Ultrashield TM-NMR instrument. LC/MS-API-ES mass spectra were recorded with
an Agilent model 1100 MSD mass spectrophotometer. Thermogravimetric (TGA)
measurements were obtained by a Shimadzu-50 thermal analyzer. The atomic
absorption measurements for the determination of cobalt and nickel ion were carried
out using a Thermo Solar System Atomic Absorption Spectrophotometer. For AAS,
cobalt and nickel were measured using the following settings: flame type, air–acetylene;
wavelength, 240.7 and 232.0 nm, respectively; lamp current, 75%; fuel flow,
0.9 L minꢀ1
; burner height, 12.0 mm; band pass, 0.5 nm; measurement, 4 s.
Electrochemical measurements were performed on a BAS 100 W electrochemical
analyzer (Bioanalytical System, USA) using a three-electrode system, glassy carbon
working electrode (ꢀ ¼ 3 mm, BAS), platinum wire as auxiliary electrode, and Ag/AgCl
(NaCl 3M, Model RE-1, BAS, USA) as reference electrode. The reference electrode was
separated from the bulk solution by a fritted-glass bridge filled with the solvent/
supporting electrolyte mixture. Before each experiment, the glassy carbon electrode was
polished manually with alumina (ꢀ ¼ 0.01 mm). Cyclic voltammetric experiments were
recorded at room temperature in DMSO (in case of Pd(II) complex, in DMF) and ionic
strength was maintained at 0.1 M Lꢀ1 with LiClO4 as the supporting electrolyte.

850
M. Sonmez et al.
¨
The solutions were deoxygenated by a stream of high purity nitrogen for 15 min prior
to the experiments, and during the experiments nitrogen flow was maintained over the
solution.
2.3. Synthesis of the ligand
The ligand N-(5-benzoyl-2-oxo-4-phenyl-2H-pyrimidin-1-yl)-oxalamic acid (N-POAH)
was prepared by the condensation of N-aminopyrimidine and oxalylchloride.
N-aminopyrimidine (1 mM) was dissolved in hot toluene (40 mL), followed by the
addition of pyridine (2 mM) to this solution. To the mixture was slowly added a
solution of oxalylchloride (1 mM) in dry toluene (10 mL). A pale yellow precipitate
formed at once. This resulting mixture was stirred at room temperature for 6 h and
the precipitate was filtered. The solid product was warmed in water (30 mL) with
stirring for 1 h, filtered, washed with water and diethyl ether, and then dried in vacuum
over P2O5. The product was finally recrystallized from acetonitrile yielding pale yellow
crystals of N-POAH (0.280 g, 78%); m.p.: 283ꢁC. Anal. Calcd (%) for C19H13N3O5
(363):C, 62.81; H, 3.58; N, 11.57. Found: C, 63.19; H, 3.72; N, 11.58. Selected IR data
(ꢀ, cmꢀ1): 3440 (OH/NH), 1712 (COOH), 1680 (Ph-CO–), 1658 (–C¼O)pyrimidine, 1613
1
(NH–C¼O)amide; H-NMR (CDCl3), ꢁ 12.4 (bs, 1H, COOH), 9.1 (s, 1H, NH), 8.7 (s,
1H, C(6)H, 6.8–7.9 (m, 10H, Harm); 13C-NMR (CDCl3), ꢁ 191.3 (OC–Ar), 173.7
(ꢀCOOH), 157.7 (–CO–NH–), 153.9 (–C2, pyrimidine ring), 151.7 (–C6, pyrimidine
ring), 116.8 (–C5), 128.8–137.0 (C, phenyl). UV-Vis (in DMF, nm): 202, 212, 279, 285,
343. LC-MS, m/z 362 [M]þ.
2.4. Synthesis of the complexes
[Cu(N-POA)2] ꢂ 2H2O: 1 mM (0.363 g) of N-POAH was dissolved in chloroform
and methanol mixture (50 mL; 1 : 1, v/v) and a solution of 0.5 mM (0.100 g) of
Cu(CH3COO)2 ꢂ H2O in 15 mL methanol was added dropwise with continuous stirring.
The mixture was stirred for 1 h at 60ꢁC. The precipitated green compound was removed
by filtration, washed with diethyl ether and cold methanol, and dried in a vacuum
desiccator. Yield: 0.210 g (76%); m.p.: 248ꢁC. Anal. Calcd (%) for C38H28CuN6O12
(823.54): C, 55.37; H, 3.40; N, 10.20; Cu, 7.72. Found: C, 55.70; H, 3.60; N, 10.40; Cu,
8.03. Selected IR data (ꢀ, cmꢀ1): 3423 ꢀ(NH–OH/H2O), 1668 ꢀ(Ph–CO), 1650 ꢀ(C¼O),
1594 ꢀ(C¼O $ C¼N). meff: 1.95 BM. ꢁM (10ꢀ3 M, in DMF, S cm2 Mꢀ1): 6.9. UV-Vis
(in DMF, nm): 226, 243, 280, 323, 362, 393, 511, 697. API-ES, m/z: 701
[(2LþCu)ꢀ2CO2]þ (65Cu isotope).
The complexes [Co(N-POA)2] ꢂ 3H2O, [Ni(N-POA)2] ꢂ 2H2O, [Mn(N-POA)2] ꢂ 2H2O,
[Zn(N-POA)2] ꢂ 2H2O, and [Cd(N-POA)2] ꢂ 2H2O were synthesized following the above
procedure using Co(CH3COO)2 ꢂ 4H2O (0.5 mM, 0.125 g), Ni(CH3COO)2 ꢂ 4H2O
(0.5 mM, 0.124 g), Mn(CH3COO)2 ꢂ 4H2O (0.5 mM, 0.123 g), Zn(CH3COO)2 ꢂ 2H2O
(0.5 mM, 0.110 g), and CdCl2 ꢂ 2H2O (0.5 mM, 0.110 g) instead of Cu(CH3COO)2 ꢂ H2O.
In the case of [Pd(N-POA)2] ꢂ 3H2O, 0.5 mM (0.089 g) of PdCl2 was dissolved by boiling
in 5 mL concentrated HCl, cooling, and then diluting with 15 mL distilled water.
To this solution was added, with stirring solution of N-POAH (1 mM, 0.363 g) dissolved
in 50 mL chloroform/methanol mixture (1: 1, v/v). After addition was complete,

Pyrimidine-derived ligand
851
the mixture was refluxed for 30 h. The compound was then filtered, washed with diethyl
ether, followed by hot methanol and dried in a vacuum desiccator.
[Co(N-POA)2] ꢂ 3H2O: Orange. Yield: 0.190 g (69%); m.p.: 300ꢁC5 Anal. Calcd (%)
for C38H30CoN6O13 (836.93): C, 54.49; H, 3.61; N, 10.03; Co, 7.04. Found: C, 54.05; H,
4.12; N, 10.29; Co, 6.54. Selected IR data (ꢀ, cmꢀ1): 3332–3400 ꢀ(NH, OH/H2O), 1663
ꢀ(Ph-CO), 1637 ꢀ(C¼O), 1605 ꢀ(C¼O $ C¼N). meff: 4.13 BM. ꢁM (10ꢀ3 M, in DMF,
S cm2 Mꢀ1): 2.7. UV-Vis (in DMF, nm): 244, 274, 307, 360, 404, 637, 669, 782. API-ES,
m/z: 784.0 [2LþCo]þ (60Co isotope).
[Ni(N-POA)2] ꢂ 2H2O: Light brown. Yield: 0.190 g (70%); mp: 225ꢁC. Anal. Calcd
(%) for C38H28N6NiO12 (818.7): C, 55.70; H, 3.44; N, 10.25; Ni, 7.17. Found: C, 55.82;
H, 4.01; N, 10.90; Ni, 8.07. Selected IR data (ꢀ, cmꢀ1), 3378–3440 ꢀ(NH, OH/H2O),
1664 ꢀ(Ph-CO), 1645 ꢀ(Ph-CO), 1594 ꢀ(C¼O $ C¼N). meff: 3.10 BM. ꢁM (10ꢀ3 M, in
DMF, S cm2 Mꢀ1): 4.6. UV-Vis (in DMF, nm): 236, 285, 330, 372, 407, 526, 652.
API-ES, m/z: 782 [2LþNi]þ (58Ni isotope).
[Mn(N-POA)2] ꢂ 2H2O: Yellow. Yield: 0.235 g (87%); m.p.: 300ꢁC5 Anal. Calcd (%)
for C38H28MnN6O12 (815): C, 55.96; H, 3.46; N, 10.30; Mn, 6.74. Found: C, 55.90; H,
3.71; N, 10.30; Mn, 5.98. Selected IR data (ꢀ, cmꢀ1): 3431 (NH, OH/H2O), 1666
ꢀ(Ph-CO), 1638 (C¼O), 1615 ꢀ(C¼O $ C¼N). meff: 5.62 BM. ꢁM (10ꢀ3 M, in DMF,
S cm2 Mꢀ1): 2.8. UV-Vis (in DMF, nm): 211, 271, 297, 363, 389, 532, 570.
[Zn(N-POA)2] ꢂ 2H2O: Cream. Yield: 0.210 g (76%); m.p.: 300 ꢁC5 Anal. Calcd (%)
for C38H28N6O12Zn (822.4): C, 55.44; H, 3.40; N, 10.21; Zn, 7.95. Found: C, 55.60; H,
3.72; N, 10.60; Zn, 6.18. Selected IR data (ꢀ, cmꢀ1): 3428 ꢀ(OH/H2O–NH), 1662
1
ꢀ(Ph-CO), 1654 ꢀ(C¼O), 1615 ꢀ(C¼O $ C¼N). H-NMR (DMSO), ꢁ 9.1 (s, NH), 8.7
(s, C–H pyrimidine), 7.0–8.3 (m, Harm), 3.5 (m, H2O); 13C-NMR (DMSO), ꢁ 192.7,
170.1, 159.7, 155.0, 146.7, 120.8–133.6, 119.3. meff: Dia. ꢁM (10ꢀ3 M, in DMF, S
cm2 Mꢀ1): 2.9. UV-Vis (in DMF, nm): 274, 297, 308, 329, 394.
[Cd(N-POA)2] ꢂ 2H2O: Light yellow. Yield: 0.190 g (65%); m.p.: 300ꢁC5 Anal. Calcd
(%) for C38H28CdN6O12 (872.4): C, 52.27; H, 3.20; N, 9.63; Cd, 12.88; Found: C, 52.56;
H, 3.50; N, 9.69; Cd, 11.35. Selected IR data (ꢀ, cmꢀ1): 3430 (OH/H2O–NH), 1666
1
ꢀ(Ph-CO), 1627 ꢀ(C¼O), 1600 ꢀ(C¼O $ C¼N). H-NMR (DMSO), ꢁ 9.3 (s, NH), 8.9
(s, C–H pyrimidine), 6.8–8.3 (m, Harm), 3.5 (m, H2O); 13C-NMR (DMSO), ꢁ 193.1,
176.5, 162.1, 157.4, 151.7, 122.5–137.6, 117.9. meff: Dia. ꢁM (10ꢀ3 M, in DMF, S
cm2 Mꢀ1): 4.6. UV-Vis (in DMF, nm): 274, 293, 313, 364, 406.
[Pd(N-POA)2] ꢂ 3H2O: Orange-brown. Yield: 0.150 g (51%); m.p.: 235ꢁC. Anal. Calcd
(%) for C38H30N6O13Pd (884.4): C, 51.57; H, 3.42; N, 9.50. Found: C, 51.33; H, 3.46;
N, 10.04. Selected IR data (ꢀ, cmꢀ1): 3406 ꢀ(OH/H2O–NH), 1677 ꢀ(-Ph-C¼O), 1663
ꢀ(C¼O), 1597 ꢀ(C¼O $ C¼N). 1H-NMR (DMSO), ꢁ 9.2 (s, NH), 8.9 (s, C–H
pyrimidine), 7.2–8.7 (m, Harm), 3.4 (m, H2O); 13C-NMR (DMSO), ꢁ 191.3, 173.1,
161.7, 153.3, 146.4, 127.8–139.6, 116.3. meff: Dia. ꢁM (10ꢀ3 M, in DMF, S cm2 Mꢀ1):
18.9. UV-Vis (in DMF, nm): 205, 280, 340, 502. API-ES, m/z: 885 [(2LþPd)þ3H2O]þ
(
106Pd isotope).
2.5. Biological assay
2.5.1. Compounds. Test compounds were dissolved in DMSO (12.5%) at an initial
concentration 1280 mg mLꢀ1 and then serially diluted in culture medium.

852
M. Sonmez et al.
¨
2.5.2. Cells. Bacterial strains were supplied from American Types Culture Collection.
Candida strains were obtained from Refik Saydam Hifzisihha Research Institute,
Ankara, Turkey.
2.6. Antibacterial assay
The compounds were screened for their antibacterial activity against four
Gram-positive (Staphylococcus aureus ATCC 6538, S. aureus ATCC 25923, Bacillus
cereus ATCC 7064 and Micrococcus luteus ATCC 9345) and one Gram-negative
(Escherichia coli ATCC 4230) bacteria as described by Clause [13] with minor
modifications. Ampicillin trihydrate was used as reference antibacterial agent.
The solutions of the compounds and reference drug were dissolved in DMSO at
2560 mg mLꢀ1. The twofold dilution of compounds and reference drug were prepared
(1280, 640, 320, 160, 80, 40, 20, 10, 5 4 mg mLꢀ1). Antibacterial activities were
performed in Mueller–Hinton broth (Difco) medium at pH 7.2 with an inoculum of
(1–2) ꢃ 103 cells mLꢀ1 by the spectrophotometric method and an aliquot of 100 mL was
added to each tube of serial dilution. The chemical compounds-broth medium serial
tube dilutions inoculated with each bacterium were incubated on a rotary shaker
at 37ꢁC for 18 h at 150 rpm. The minimum inhibitory concentrations (MICs) of each
compound were recorded as lowest concentration of each chemical compounds
in the tubes with no growth (i.e. no turbidity) of inoculated bacteria.
2.7. Antifungal assay
Antifungal activities were tested against three yeast (Candida albicans ATCC 14053,
C. krusei ATCC 6258 and C. parapsilosis ATCC 22019) strains according to the
guidelines in NCCLS approved standard document M27-A using the microdilution
broth procedure [14]. Fluconazole was used as reference antifungal agent.
Test compounds and reference drug were dissolved in DMSO at 2560 mg mLꢀ1 and
twofold dilution of the compounds and reference drug were prepared (1280, 640, 320,
160, 80, 40, 20, 10, 5 4 mg mLꢀ1). Antifungal activities of the yeast strains were
performed in RPMI 1640 Medium (Sigma), which were buffered to pH 7.0 with 0.165 M
morpholinopropanesulfonic acid (Sigma), as outlined in document M27-A. Stock yeast
inoculum suspensions were adjusted to (0.5–2.5) ꢃ 103 cells mLꢀ1 by spectrophoto-
metric method and 100 mL aliquot was added to each tube of the serial dilution.
The broth medium serial tube dilutions inoculated with yeast were incubated on a
rotary shaker at 37ꢁC for 18 h at 150 rpm. MICs of each compound were recorded
as lowest concentration of each chemical compounds in the tubes with no growth
(i.e. no turbidity) of inoculated yeast.
3. Results and discussion
3.1. Synthesis of the ligand and metal complexes
The new ligand N-POAH, whose structure is given in figure 1, was synthesized by 1 : 1
condensation of oxalylchloride with N-aminopyrimidine in dry toluene. The ligand is

Pyrimidine-derived ligand
853
H
O
O
C
O
C
O
N
O
C
N
OH
O
C
OH
NH
Ph
N
Ph
Ph
N
O
Ph
N
O
Figure 1. Structure of the ligand (N-POAH).
soluble in DMSO, DMF, CHCl3, CH3CN, CH2Cl2, and partly soluble in H2O, MeOH,
EtOH, however, insoluble in n-hexane and diethyl ether.
Complexes with deprotonated forms of N-POAH; [Cu(N-POA)2] ꢂ 2H2O, [Co(N-
POA)2] ꢂ 3H2O, [Mn(N-POA)2] ꢂ 2H2O, [Ni(N-POA)2] ꢂ 2H2O, [Zn(N-POA)2] ꢂ 2H2O,
[Cd(N-POA)2] ꢂ 2H2O, and [Pd(N-POA)2] ꢂ 3H2O were obtained from a refluxing
mixture of the respective ligand and appropriate metal salts in 1 : 2 molar ratio
in methanol. The complexes presented in figures 2 and 3 were formed in a reaction of
equimolar amounts of an acetate/chloride salts of Cu(II), Co(II), Mn(II), Ni(II), Zn(II),
Cd(II), and Pd(II) in with N-POAH in methanol solution. The complexes are soluble in
dipolar aprotic solvents but sparingly soluble in common organic solvents.
3.2. Characterization of the N-POAH and metal complexes
3.2.1. IR spectra. N-POAH may exist in two tautomeric forms (figure 1) and may
form intermolecular-hydrogen bonds,–N¼C–O–Hꢂ ꢂ ꢂO¼C–OH. In IR spectra of
N-POAH, characteristic bands appeared at 1712, ꢄ3440, 3059, 1680, 1658, 1613 cmꢀ1
corresponding to ꢀ(COOH), ꢀ(OH/NH), ꢀ(C–H pyrimidine ring), ꢀ(C¼O benzoyl),
ꢀ(C¼O), (–CO–NH–), respectively [15–17]. Condensation was supported by elimination
of HCl from oxalylchloride and N-aminopyrimidine. The absence of ꢀ(NH2) at 3300
and 3170 cmꢀ1 suggests the structure of N-pyrimidine oxalamic acid. The IR spectra
of the complexes were compared with that of the free ligand. The disappearance of
the band at 1712 cmꢀ1 due to carboxylate suggests the coordination of oxygen
after deprotonation. Similarly, the shifting of 1658 cmꢀ1 ꢀ(C¼O) in ligand to
1627–1650 cmꢀ1 in complexes indicates that keto group in the ring is also coordinating
[15]. The ligand shows a broad band at 3400–3320 cmꢀ1 due to asymmetric
and symmetric –NH stretching frequency of –NH. The complexes show 15–60 cmꢀ1
shift, indicating coordination through the amide nitrogen; the amidic ꢀN–H
(NH–C¼O $ N¼C–OH) vibration of the ligand at 1615 cmꢀ1 shifts to lower frequency
after complexation, between 1590 and 1600 cmꢀ1. The observed shift in C¼N stretch
after complexation confirms coordination of imine nitrogen to metal [10–12].
In spectra of the complexes bands at 426–465 and 488–548 cmꢀ1 are due to ꢀ(M–N)
and ꢀ(M–O), respectively [10, 11]. Broad bands of the complexes in the ꢄ3400 cmꢀ1

854
M. Sonmez et al.
¨
O
O
O
C
C
M
C
N
Ph
O
NH
O
O
Ph
N
nH2O
N
Ph
O
NH
O
Ph
N
C
O
O
M= Cu(II), Ni(II), Mn(II), Co(II), Zn(II), and Cd(II)
Figure 2. Suggested structures of M(II) complexes of N-POAH.
O
O
O
C
C
O
N
Ph
NH
O
Ph
N
Pd
3H2O
N
Ph
NH
O
Ph
N
O
C
C
O
O
O
Figure 3. Suggested structure of the Pd(II) complex of N-POAH.
region are assigned to the ꢀ(OH) vibration of water [17]; water content was also
identified by thermal analyses.
3.2.2. UV-Vis spectral study. In the UV-Vis, the complexes show bands at approx-
imately 325 nm and weaker bands in the range 350–410 nm. The weak bands were
attributed to intramolecular charge transfer transitions from the pꢂ orbital on the
carboxylate (phenolate) oxygen to empty d orbitals of the metal. The intense 320–
330 nm bands were assigned to ꢂ ! ꢂ* (intraligand) transitions [17].
The electronic absorption spectrum of [Cu(N-POA)2] ꢂ 2H2O has an absorption
2
2
at 697 nm, ascribed to T2g ! Eg of the distorted octahedral environment [18]. The
effective magnetic moment (meff : 1.92 BM) is typical for distorted octahedral
Cu(II) chelates.
The high spin octahedral Co(II) and Ni(II) complexes exhibit magnetic moment
values of 4.2 and 3.1 BM, respectively, and three transitions each in the electronic
spectra. The magnetic moment for [Co(N-POA)2] ꢂ 3H2O is near the spin-only value.
The electronic spectrum shows three d–d bands of weak intensity. The first band
4
4
(782 nm) is assigned to the transition T2g ! T1g(F), the second band (669 nm) is
4
assigned to 4A2g ! T1g(F), the third (637 nm), split into three components, is assigned
4
4
to T1g(P) ! T1g(F). The band observed at 404 nm is assigned to Co ! L charge

Pyrimidine-derived ligand
855
Table 1. The MICsa of N-POAH and its metal complexes [Cd(II), Pd(II), Cu(II), Co(II), Mn(II), Zn(II)]
against Gram-negative and Gram-positive bacterial strains.
B. cereus
ATCC 7064
S. aureus
ATCC 6538
S. aureus
ATCC 25923
E. coli
ATCC 4230
M. luteus
ATCC 9345
Compound
N-POAH
640
40
160
80
80
640
160
320
640
320
5
160
40
640
640
160
640
320
640
640
640
20
160
160
160
640
160
320
320
320
10
[Cu(N-POA)2]ꢂ2H2O
[Co(N-POA)2]ꢂ3H2O
[Mn(N-POA)2]ꢂ2H2O
[Ni(N-POA)2]ꢂ2H2O
[Zn(N-POA)2]ꢂ2H2O
[Cd(N-POA)2]ꢂ2H2O
[Pd(N-POA)2]ꢂ3H2O
Ampicillin
160
640
160
640
320
320
5
160
640
160
320
640
320
10
aThe MICs values were determined as mg mLꢀ1 active compounds in medium.
transfer [18]. [Ni(N-POA)2] ꢂ 2H2O exhibits three spectral bands at 407, 526,
and 652 nm. The first is due to charge transfer, the last two bands are assigned to
3
3
3
3
octahedral spin allowed A2g ! T1g(F) and A2g ! T2g(F) transitions. The room
temperature meff 3.1 BM and the spectral data support octahedral geometry [19].
[Mn(N-POA)2] ꢂ 2H2O gave three peaks at 363, 389, and 532 nm and room
temperature meff 5.62 BM. The first two bands are due to the effect of metal on the
ꢂ–ꢂ* electronic transition of the free ligand. However, the band at 532 nm is identified
to d–d electronic transition for high-spin octahedral configuration.
The d8 square planar [Pd(N-POA)2] ꢂ 3H2O complex is expected to exhibit three
1
1
1
1
spin-allowed d–d transitions corresponding to A1g ! A2g, A1g ! B1g and
1
1A1g ! Eg, respectively. However, the strong CT band, L!M at ca 380 nm in this
complex, tails into the visible region, obscuring d–d bands [20].
1
3.2.3. NMR spectral study. DMSO-d6 was used as a solvent to measure the H-,
13C-NMR spectra of the N-POAH and its Zn(II), Cd(II) and Pd(II) complexes. Slightly
broad and medium resonances at ꢁ 12.4 and 9.1 ppm are due to COOH proton and NH
of the ligand. The singlet at ꢁ 8.7 ppm is due to pyrimidine ring (C(6)-H) proton. In the
spectra of N-POAH, the phenyl multiplet was at ꢁ 6.8–7.9 ppm. 13C-NMR spectra of the
ligand have a cluster of peaks at ꢁ 191.3, 173.7, 153.9, 151.7, 116.8 ppm due to benzoyl
carbon, carbon of the carboxyl group, C(2)-, C(6)-, C(5)-pyrimidine ring, respectively.
The spectrum of the ligand show peaks at ꢁ 118.55–136.91 ppm due to phenyl carbons
and one at ꢁ 157.7 ppm, which may be attributed to –CO–NH–.
The complexes were also investigated by 1H-and 13C-NMR in DMSO-d6 where
the data (given in section 2) are in agreement with coordination through the carboxylate
(disappearance of the H(1) signal in) and the peaks characteristic for water molecules
were observed around ꢁ 3.52 ppm.
3.3. Mass spectra
In the mass spectra of the ligand and its metal complexes, peaks are attributable to the
molecular ions; m/z: 362 [L]þ, m/z: 701 [(2LþCu)ꢀ2CO2]þ, m/z: 784 [2LþCo]þ, m/z:

856
M. Sonmez et al.
¨
782 [2LþNi]þ, m/z: 885 [(2LþPd)þ3H2O]þ. The spectrum of the Pd(II) complex
is shown in ‘‘Supplementary material’’.
3.4. Thermal decomposition
The thermal behavior was studied using TGA and DTA techniques under nitrogen
at 30–1100ꢁC. The complexes decompose in two or three steps into MO as final product
from which the metal content can be calculated via AAS technique and compared with
that obtained from the elemental analysis. For all complexes, the analytical data show a
weight loss, which occurs in the temperature range 42–103ꢁC, corresponding to loss
of crystal water. This weight loss is 4.2% in the case of Cu(II) complex, in agreement
with the empirical formula [Cu(N-POA)2] ꢂ 2H2O (theoretical weight loss 4.4%).
For the [Ni(N-POA)2] ꢂ 2H2O complex, the weight loss is equal to 4.6% (theoretical
weight loss 4.4%) and is equal to 6.7% for the [Co(N-POA)2] ꢂ 3H2O complex
(theoretical weight loss 6.5%).
For Cu(II) complex, the initial weight loss at 43–101ꢁC, with corresponding
endothermic peak at 67ꢁC, is interpreted as loss of coordinated water. The second
step of decomposition corresponds to the loss of ligand from the anhydrous complex at
101–850ꢁC with an exothermic peak at 313ꢁC. The third step of decomposition occurred
at 850–1000ꢁC, associated with exothermic peak at 924ꢁC leading to CuO and C.
3.5. Electrochemical studies
Redox properties of N-POAH and its metal complexes were investigated at glassy
carbon electrode in DMSO (except for Pd(II) complex, which was studied in DMF)
containing 0.1 M Lꢀ1 LiClO4 by cyclic voltammetry.
In the potential range of ꢀ2.3 þ 1.2 V at scan rate of 100 mV sꢀ1, the cyclic
voltammogram of N-POAH has four cathodic waves (Ic, IIc, IIIc, and IVc) with their
anodic partners (Ia, IIa, IIIa, and IVa) (Supplementary material). The difference
between cathodic and anodic peak potentials reveals that the electrode reaction is
not reversible. Such irreversibility is observed at the entire scan rates of investigation
(10–500 mV sꢀ1). At scan rate above 50 mV sꢀ1, Ia, and IIa were fused into only one
broad peak. The cathodic wave IIc was also in the form of a peak and was easily
measurable. Hence, all subsequent work is based on measurement of the magnitude of
this step. A plot of logarithm of peak current versus logarithm of scan rate gave a
straight-line (correlation coefficient 0.999) with a slope of 0.52, very close to the
theoretical value of 0.5, which is expected for an ideal reaction of solution species [21],
so in this case the process had a diffusive component. A slightly negative shift in the
peak potential was observed, which confirms the irreversibility of the process, with the
simultaneous increase in the peak current when the scan rate was increased. With the
reported data concerning electrochemical behavior of 1-amino-5-benzoyl-4 phenyl-1H-
pyrimidine-2-one, at a hanging mercury drop electrode in aqueous and non-aqueous
methanol, we assume that reductions of N-POAH are located on the secondary amino
and the carbonyl of pyrimidine ring at positions 1 and 2, respectively.
On the cathodic side, the cyclic voltammogram of Cu(II) complex (Supplementary
material) shows four cathodic peaks (I0c, II0c, III0c, and IV0c) in addition to the ligand
peaks. On the reverse scan, oxidation waves Ia, Iia, and IIIa are absent; however, there

Pyrimidine-derived ligand
857
is a new oxidation step (IV0a) at more positive potential. Wave IV0c, which was near
the cathodic window of the LiClO4/DMSO system, only appeared when waves I0c, II0c
and III0c were present on the initial scan. By scanning to less negative potentials than
wave IV0c, the absence of oxidation wave IV0a on the reverse scan indicates that IV0a is
due to a product formed at potential of wave IV0c. The reduction wave of IV0c may be
attributable to [[CuIL2]]/[Cu0L2], with associated response (oxidation wave IV0a) in the
reverse scan. However, when the scan was limited to less negative potentials than
the potential of wave IV0c, one sharp and well-defined oxidation peak (I0a) with a
shoulder (II0a) and a small one (III0a) (at more positive potential) were produced.
If successive cyclic scans are made, the main oxidation peak increased as the number of
scans increased. We should bear in mind that [22, 23] after one-electron reduction
corresponding to [[CuIIL2]]/[[CuIL2]], part of [[CuIL2]] decomposes into copper
metal (reaction 1). Therefore, it may be assumed that the corresponding anodic
waves (I0a–III0a) are associated with the reoxidation of electrodeposited copper metal
to free Cuþ and Cu2þ according to reaction 2 shown as follows:
½CuIL2ꢅ $ Cuþ 2L þ eꢀ $ Cu0þ2L
ð1Þ
ð2Þ
Cu0 ꢀ eꢀ $ Cuþ ꢀ eꢀ $ Cu2þ
In the cyclic voltammogram of the complex with Co(II), in addition to ligand waves
Ic (ꢀ1.14 V) and IIc (ꢀ1.55 V), there is an ill-defined reduction wave III0c (ꢀ1.59 V)
and one broad oxidation peak at þ0.62 V. The cathodic wave III0c (ꢀ1.59 V)
corresponds to the reduction of complexed CoII to Co0. Finally, Co0 is oxidized to
coordinated CoII because this peak disappears when the sweep is limited to less negative
potentials than the potential of wave III0c (ꢀ1.59 V). After the first voltammetric cycle,
the current intensities of the waves decreased rapidly, which may be explained
by a rapid decomposition reaction, yielding a solid product that deposit at the electrode
surface.
For the Mn(II) complex, when the potential was first scanned in the negative
direction, in addition to ligand waves Ic (ꢀ1.43 V) and IIc (ꢀ1.53 V), one irreversible
reduction wave III0c (ꢀ2.13 V) was observed with a corresponding anodic wave III0a
(ꢀ0.40 V). Reversing the scan before reduction wave III0c shows the absence of III0a
(ꢀ0.40 V). When the scan was initiated in the positive direction, two-step oxidation
processes (I00a (þ0.51 V) and II0a (þ0.72 V)) with corresponding cathodic waves
(I0c (þ0.40 V) and II0c (þ0.59 V)) were observed. Since the difference of anodic and
cathodic potentials was about 100 mV, this process was quasi-reversible. Reductive and
oxidative processes (III0c/III0a and I0a, II0a/I0c, II0c) are based on the manganese center.
The electrochemical behavior of nickel(II) complex is similar to that of N-POAH,
with anodic waves shifted to lower positive potential. This suggests that the oxidation of
the Ni(II) complex is a ligand-based process. In the case of complexes with Zn(II)
and Cd(II), very poorly defined anodic waves were observed.
The cyclic voltammograms of Pd(II) complex were recorded in DMF containing
0.1 M Lꢀ1 LiClO4. N-POAH in DMF from ꢀ2.3 to þ1.5 V shows three cathodic
(ꢀ1.40, ꢀ1.540, and ꢀ1.82 V) and two anodic (þ0.26 and þ 0.987 V) waves. On the
cathodic side, the Pd(II) complex shows two new waves (ꢀ0.75 and ꢀ2.10 V), which can
be attributed to PdII/PdI and PdI/Pd0 reduction.
The electrochemical data upon the electrode potentials are reported in table 2.

858
M. Sonmez et al.
¨
Table 2. Voltammetric results in V vs. Ag/AgCl.
Compound
Ec
Ea
N-POAH
[Cu(N-POA)2] ꢂ 2H2O I0c:þ0.11, II0c:ꢀ0.26, III0c:ꢀ0.57, Ic:ꢀ1.35,
Ic:ꢀ1.23, IIc:ꢀ1.55, IIIc:ꢀ1.89, IVc:ꢀ2.05
IIc:ꢀ1.55, IIIc:ꢀ1.85, IVc:ꢀ2.03, IV0c:ꢀ2.20 IVa:þ0.82, IV0a: þ1.2
IaþIIa:þ0.04, IIIa:þ0.52, IVa:þ1.00
I0a:þ0.05, II0a:þ0.22, III0a:þ0.42,
[Co(N-POA)2] ꢂ 3H2O Ic:ꢀ1.14, IIc:ꢀ1.55, III0c:ꢀ1.95
[Mn(N-POA)2] ꢂ 2H2O II0c:þ0.59, I0c:þ0.40, Ic:ꢀ1.43, IIc:ꢀ1.53,
III0c:ꢀ2.13
I0a:þ0.62
III0a:ꢀ0.40 I0a:þ0.51, II0a:þ0.72
[Ni(N-POA)2] ꢂ 2H2O Ic:ꢀ1.31, IIc:ꢀ1.54, IIIc:ꢀ1.92, IVc:ꢀ2.10
[Zn(N-POA)2] ꢂ 2H2O Ic:ꢀ1.42, IIc:ꢀ1.55, IIIcþIVc:ꢀ2.05
[Cd(N-POA)2] ꢂ 2H2O Ic:ꢀ1.40, IIc:ꢀ1.52, IIIc:ꢀ1.88, IVc:ꢀ2.07
[Pd(N-POA)2] ꢂ 3H2O I0c:ꢀ0.75, Ic:ꢀ1.40, IIc:ꢀ1540, IIIc:ꢀ1.82,
IV0c:ꢀ2.10
IaþIIa:ꢀ0.20, IIIa:þ0.29, IVa:þ0.68
I0a:þ0.26, II0a:þ0.61
ꢀ denotes 100 mV sꢀ1; Ec, cathodic; and Ea, anodic.
A plot of logarithm of peak current significantly correlates with the logarithm of scan
rate for Cu(II), Ni(II), and Pd(II) complexes with slopes of 0.47 (correlation coefficient
0.997), 0.44 (correlation coefficient 0.996), and 0.51 (correlation coefficient 0.965),
respectively, showing that redox processes are predominantly diffusion-controlled in the
whole scan rate range studied. Due to poorly resolved signal obtained by cyclic
voltammetry, the effect of potential scan rate on Co(II), Mn(II), Cd(II), and Zn(II)
complexes was not evaluated.
3.6. Biological results
Antimicrobial activities of the newly synthesized compounds were screened against
four Gram-positive (S. aureus ATCC 6538, S. aureus ATCC 25923, B. cereus ATCC
7064 and M. luteus ATCC 9345), one Gram-negative (E. coli ATCC 4230) bacteria and
three yeast (C. albicans ATCC 14053, C. krusei ATCC 6258 and C. parapsilosis ATCC
22019) strains by using broth microdilution. Ampicillin trihydrate for bacteria and
fluconazole for yeast were used as reference drugs. MICs against bacterial and fungal
strains are shown in table 1. The ligand and complexes exhibit weak activity against the
tested microorganisms with MICs in the range of 160–640 mg mLꢀ1, except for the
Cu(II) complex. The Cu(II) complex displayed selective and effective antibacterial
activity against one Gram-positive spore-forming bacterium (B. cereus ATCC 7064),
two Gram-positive bacteria (S. aureus ATCC 6538, S. aureus ATCC 25923) at
40–80 mg mLꢀ1, and poor activity against other bacterial strains (E. coli ATCC 4230,
M. luteus ATCC 9345). The Co(II) complex was moderate inhibitor against one
Gram-positive bacterium as S. aureus ATCC 25923 (MIC value 80 mg mLꢀ1).
The Cu(II) complex had more antibacterial activity than uncomplexed ligand and
other complexes. The activity of complexes was enhanced by coordination. The data are
in agreement with the previous studies that Cu(II) complexes of the various compounds
have greater activity toward microorganisms than the free ligands [24–26]. Generally,
chelation/coordination of the metal results in higher capability to penetrate
microorganisms through the lipopolysaccharide layer of the cell membrane [27, 28].

Pyrimidine-derived ligand
859
Only the Cu(II) complex exhibited weak antifungal activity (MICs, 640 mg mLꢀ1
against C. albicans ATCC 14053, C. krusei ATCC 6258 and C. parapsilosis ATCC
22019.
)
4. Conclusion
Synthesis, spectroscopic characterization, electrochemical study, and antimicrobial
investigation of a substituted pyrimidine ligand and its mononuclear complexes have
been presented. We evaluated in vitro antibacterial and antifungal activities of new
synthesized various metal complexes of N-POAH which had weak antimicrobial effects
against tested microorganisms, except [Cu(N-POA)2] ꢂ 2H2O which had good antibac-
terial activity. The reason for higher antibacterial activity can be ascribed to the effect
of copper on vital cell process, such as deactivating several structural enzymes which
play important roles in metabolic pathways of the microorganisms.
Acknowledgment
We are grateful to Scientific and Research Council of Turkey (TBAG 105T145) for the
support of this research.
References
[1] A. Darwanto, L. Ngo, L.C. Sowers. Adv. Mol. Toxicol., 2, 153 (2008).
[2] R. Hilal, Z.M. Zaky, S.A.K. Elroby. Spectrochim. Acta A, 63, 740 (2006).
[3] S.I. Mostafa, M.A. Kabil, E.M. Saad, A.A. El-Asmy. J. Coord. Chem., 59, 279 (2006).
[4] F.A. French, E.J. Blanz Jr, D.A. French. J. Med. Chem., 13, 1117 (1970).
[5] J.H. Cory, A.E. Fleischeher. Cancer Res., 39, 4600 (1979).
[6] T. Hitoshi, N. Tamao, A. Hideykki, F. Manalou, M. Takayuki. Polyhedron, 16, 3787 (1997).
´ ´ ´ ´ ´ ´
[7] P. Arranz-Mascaros, M.D. Gutierrez-Valero, R. Lopez-Garzon, M.D. Lopez-Leon, M.L. Godino-
Salido, A. Santiago-Medina, H. Stoeckli-Evans. Polyhedron, 27, 623 (2008).
[8] M.T. Madigan, J.M. Martinko, J. Parker. Brock Biology of Microorganisms, 8th Edn, Prentice-Hall, Inc.,
Upper Saddle River, New Jersey, USA (1997).
[9] M.A. Girasolo, C. Di Salvo, D. Schillaci, G. Barone, A. Silvestri, G.J. Ruisi. Organomet. Chem., 690,
4773 (2005).
_
[10] M. Sonmez, I. Berber, E. Akbas¸. Eur. J. Med. Chem., 41, 101 (2006).
¨
[11] N.R. Mohamed, M.M.T. El-Saidi, Y.M. Ali, M.H. Elnagdi. Bioorg. Med. Chem., 15, 6227 (2007).
[12] Y. Akc¸ amur, B. Altural, E. Sar|p|nar, G. Kollenz, O. Kappe, K. Peters, E. Peters, H. Schering.
J. Heterocylic Chem., 25, 1419 (1988).
[13] G.W. Clause. Understanding Microbes: A Laboratory Textbook for Microbiology, W.H. Freeman and
Company, New York, USA (1989).
[14] A. Villanova. National Committee for Clinical Laboratory Standards, 17, 1 (1997).
[15] H.L. Hu, C.W. Yeh, J.D. Chen. Eur. J. Inorg. Chem., 4696 (2004).
[16] K. Nakamoto. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley, New York
(1986).
[17] G. Asgedom, A. Streedhara, J. Kivikoski, E. Kolehmainen, C.P. Rao. J. Chem. Soc., Dalton Trans., 93
(1996).
[18] A.B.P. Lever. Inorganic Electronic Spectroscopy, Elsevier, Amsterdam (1984).
[19] B.N. Figgis, J. Lewis. Progress in Inorganic Chemistry, Vol. 6, Wiley Interscience, New York (1964).
[20] S.S. Kandil, S.M.A. Katip, N.H.M. Yarkandi. Transition Met. Chem., 32, 791 (2007).

860
M. Sonmez et al.
¨
[21] E. Laviron. J. Electroanal. Chem., 112, 11 (1980).
[22] P. Zanello. Inorganic Electrochemistry; Theory, Practice and Application, The Royal Society of
Chemistry, Cambridge (2003).
[23] M. Aguilar-Martinez, R. Saloma-Aguilar, N. Macias-Ruvalcaba, R. Cetina-Rosado,
A. Navarrete-Vazquez, V. Gomez-Vidales, A. Zantella-Dehesa, R.A. Toscano, S. Hernandez-Ortega,
J.M. Fernandez-G. J. Chem. Soc., Dalton Trans., 2346 (2001).
[24] X.Y. Xu, J. Gao, M.Y. Wang, W.X. Ma, H.B. Song, K.P. Wainwright. J. Coord. Chem., 58, 669 (2005).
¨
[25] A.A. Massoud, V. Langer, L. Ohrstrom, M.A.M. Abu-Youssef. J. Coord. Chem., 62, 519 (2009).
[26] K.V. Sharma, V. Sharma, R.K. Dubey, U.N. Tripathi. J. Coord. Chem., 62, 493 (2009).
[27] Z.H. Chohan, H. Pervez, A. Rauf, C.T. Supuran. Met. Based Drugs, 8, 42 (2002).
[28] Z.H. Chohan, C.T. Supuran, A. Scozzafava. J. Enzyme Inhib. Med. Chem., 18, 1 (2003).