Synthesis, electrochemical and structural characterization of novel azacrown ether containing macrocyclic redox-active vic-dioxime ligand and its mononuclear transition metal complexes: Application of DEPT, HSQC, HMBC-NMR and cyclic voltammetry

Article abstract of DOI:10.1016/j.poly.2011.04.008

This paper presents a new azacrown containing vic-dioxime; anti-N-(4-aminophenyl)aza-15-crown-5-glyoxime (LH₂), and its mononuclear nickel(II), copper(II), cobalt(II), cadmium(II) and zinc(II) complexes. The azacrown moieties appended at the pe

Full text of DOI:10.1016/j.poly.2011.04.008

Polyhedron 30 (2011) 1726–1731
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Polyhedron
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Synthesis, electrochemical and structural characterization of novel azacrown
ether containing macrocyclic redox-active vic-dioxime ligand and its
mononuclear transition metal complexes: Application of DEPT, HSQC,
HMBC-NMR and cyclic voltammetry
Pervin Deveci a, Bilge Taner a, Zeynel Kılıç b, Ali Osman Solak b,c, Ug˘ur Arslan d, Emine Özcan a,
⇑
a Selcuk University, Faculty of Science, Department of Chemistry, Konya, Turkey
b Ankara University, Faculty of Science, Department of Chemistry, Tandogan, Ankara, Turkey
c Kyrgyz-Turk Manas University, Faculty of Eng., Dep. of Chem. Eng., CAL Campus, Bishkek, Kyrgyzstan
d Selcuk University, Selcuklu Medical Faculty, Department of Clinical Microbiology, Konya, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
This paper presents a new azacrown containing vic-dioxime; anti-N-(4-aminophenyl)aza-15-crown-5-
glyoxime (LH2), and its mononuclear nickel(II), copper(II), cobalt(II), cadmium(II) and zinc(II) complexes.
The azacrown moieties appended at the periphery of the oxime provide solubility for the vic-dioxime
ligand and complexes in common organic solvents. The mononuclear M(LH)2 (M = Ni and Cu),
M(LH)2(H2O)2 (M = Co) and [M(LH)(H2O)(Cl)] (M = Cd and Zn) complexes have been obtained with the
metal:ligand ratios of 1:2 and 1:1. The structure of the ligand is confirmed by elemental analysis, Fourier
transform infrared (FT-IR), ultraviolet–visible (UV–Vis), mass spectrometry (MS), one-dimensional (1D)
1H, 13C NMR, distortionless enhancement by polarization transfer (DEPT) and two-dimensional (2D) het-
eronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlation (HMBC) tech-
niques. The structures of the complexes are confirmed by elemental analyses, MS, UV–Vis, FT-IR and 1H,
13C NMR techniques. Redox behaviors of the ligand and its complexes have been investigated by cyclic
voltammetry at the glassy carbon electrode in 0.1 M TBATFB in DMSO. The antibacterial activity was
studied against Staphylococcus aureus ATCC 29213, Streptococcus mutans RSHM 676, Enterococcus faecalis
ATCC 29212, Lactobacillus acidophilus RSHM 06029, Escherichia coli ATCC 25922, Pseudomonas aeruginosa
ATCC 27853. The antimicrobial test results indicate that all the complexes have low levels of antibacterial
activity against both Gram negative and Gram positive bacterial species.
Received 7 January 2011
Accepted 5 April 2011
Available online 15 April 2011
Keywords:
vic-Dioxime
Azacrown ether
Macrocyclic ligand
Metal complexes
Cyclic voltammetry
Antimicrobial activity
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
ethers, calixpyrroles, ferrocene groups, tetrathiamacrocycles or
N2O2 macrocycles and dendritic groups [8–10]. Azacrown ethers
The synthesis of vic-dioximes by Tschugaev in 1905 initiated in-
tense research activity into the coordination chemistry of these
versatile ligands [1–4]. They can form different types of coordina-
tion compounds with transition metal ions due to several electron-
rich donor centers with unique structural and chemical properties.
These complexes have been widely explored for the versatility of
their coordination geometries, technical application dependent
molecular structures, spectroscopic properties and their biochem-
ical significance [5–7]. Furthermore, the ease of functionalization
of the these ligands leads to the incorporation of versatile com-
pounds in multidentate ligand structures, usually in combination
with macrocyclic compounds such as crown ethers, azacrown
occupy a specific place among the macrocyclic compounds because
of their fascinating structures and high abilities of ligation with
both alkali and alkaline earth as well as heavy-metal guest cations
[11]. On the other hand, the study of azacrown ethers has largely
contributed to the development of host–guest interactions by
improving selective fluorescent sensors for cation detection
[12,13]. The low solubility of vic-dioxime complexes has hindered
the study of their structures and reactions. The attachments of the
crown ether groups to the vic-dioxime core significantly increases
the solubility of vic-dioximes in organic solvents, leading to signif-
icant advances in research such as biological modeling, homoge-
neous catalysis, sensors, alkaline or earth alkaline–earth metal
cation extractions and trace metal analysis. In continuation of
our interest in vic-dioxime and azacrown ether compounds
[14,15], we now wish to describe a new and efficient method for
the synthesis of an azacrown ether functionalized soluble
⇑
Corresponding author. Tel.: +90 332 2233859; fax: +90 332 2412499.
E-mail address: emineozcann@gmail.com (E. Özcan).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.04.008

P. Deveci et al. / Polyhedron 30 (2011) 1726–1731
1727
Scheme 1. Synthesis of LH2 and its complexes (Ni(LH)2, Cu(LH)2, Co(LH)2(H2O)2, [Cd(LH)(H2O)(Cl)], [Zn(LH)(H2O)(Cl)]); (i): CdCl2ꢂ2H2O or ZnCl2; (ii): NiCl2ꢂ6H2O, CuCl2ꢂ2H2O
or CoCl2ꢂ6H2O.
at 298.15 K. Samples dissolved in DMSO or CDCl3. Chemical shifts
vic-dioxime ligand and its transition metal complexes (Scheme 1).
The structure of the vic-dioxime ligand anti-N-(4-aminophe-
nyl)aza-15-crown-5 glyoxime (LH2) is characterized in detail for
were reported in ppm relative to TMS for 1H and 13C NMR spectra.
1H NMR, 13C NMR, HSQC and HMBC NMR spectra were obtained at
a base frequency of 125.71 MHz for 13C and 499.95 MHz for 1H nu-
the first time to confirm the proposed structure using NMR (1H,
clei. Two-dimensional Gradient HSQC and HMBC techniques were
13C, HSQC, HMBC and DEPT), FT-IR, UV–Vis, MS and elemental
measured using standard pulse programs provided by Varian. The
analysis. The composition of metal complexes have been identified
spectra were acquired with 512 increments in the F1 dimension
by elemental analysis, FT-IR, UV–Vis and MS. The 1H and 13C NMR
and 2048 data points in the F2 dimension. The IR spectra of solid
spectra of the Ni(LH2), [Cd(LH)(H2O)(Cl)] and [Zn(LH)(H2O)(Cl)]
samples were recorded on a Perkin–Elmer Spectrum 100 FT-IR
were also reported. Electrochemical properties of the ligand, and
spectrometer (Universal/ATR Sampling Accessary). UV–Vis spectra
its metal complexes were investigated in DMSO solution contain-
were obtained on Shimadzu UV–1700 visible recording spectro-
ing 0.1 M tetrabutylammoniumtetrafluoroborate (TBATFB) as sup-
photometers. Melting points were determined using an electro-
porting electrolyte by cyclic voltammetry. To the best of our
thermal apparatus and were uncorrected. MS spectra were
knowledge, this is the first manuscript which includes the synthe-
recorded on a Bruker Micro TOF LC–MS spectrometer. All the elec-
sis, enhanced characterization, antibacterial activity and electro-
trochemical experiments were performed using a CH Instruments
chemical properties of LH2 and its Ni(II), Cu(II), Co(II), Cd(II) and
electrochemical analyzer (model 600C series) equipped with BAS
Zn(II) complexes.
C3 cell stand. The working electrode was a bare glassy carbon disk
(BAS Model MF-2012) with a geometric area of 0.027 cm2. The ref-
erence electrodes were Ag/AgCl/KCl(sat.) in aqueous and Ag/Ag+
2. Experimental
(0.01 M) in nonaqueous media, and the counter electrode was a
Pt wire.
2.1. Chemicals
N-(4-aminophenyl)aza-15-crown-5 [16] and anti-chloro-
glyoxime [17] were prepared according to the procedures reported
in literature. All other chemicals were purchased from Merck or
Sigma–Aldrich, and used as supplied. Silica gel (70–230 mesh)
was used for chromatographic separations. All organic solvents
were dried and purified by means of the usual methods. All the
processes performed in aqueous media and the preparation of
the aqueous solutions were carried out using ultra-pure water with
2.3. Synthesis of the anti-N-(4-aminophenyl)aza-15-crown-5
glyoxime (LH2)
A
solution of N-(4-aminophenyl)aza-15-crown-5 (0.47 g,
1.50 mmol) in 10 mL diethylether was added to a stirred mixture
of anti-chloroglyoxime (0.18 g, 1.50 mmol) and triethylamine
(0.21 mL, 1.50 mmol) in diethylether (10 mL). The mixture was
also stirred at room temperature for 30 min under an N2 atmo-
sphere and monitored by TLC using methanol. The solvent was
evaporated and the residue was purified by column chromatogra-
phy on silica gel with methanol to give the vic-dioxime derivative
H2L. Yield: 0.45 g (76%) and m.p.: 118 °C. Anal. Calc. for
a resistance of ꢀ18.3 M
X
cm (Human Power 1+ Scholar purifica-
tion system).
2.2. Apparatus
Elemental analyses (C, H and N) were performed using a LECO-
932 CHNSO model analyzer. NMR experiments were performed in
a Varian Unity INOVA 500 spectrometer using 5 mm ID-PFG probe
C
18H28N4O6: C, 54.53; H, 7.12; N, 14.13. Found: C, 54.16; H, 7.05;
N, 14.26%. MS (fragments are based on the most abundant iso-
topes): m/z 397.2064 (MH)+ (Calc. 397.2082). FT-IR ( max/cmꢁ1):
m

1728
P. Deveci et al. / Polyhedron 30 (2011) 1726–1731
3400 (O–H), 3184 (N–H), 3030 (C–Harom.), 2980 (C–Haliph.), 1648
(C@N), 1514 (C@C), 988 (N–O). 1H NMR (DMSO-d6), d (ppm):
3.41 (t, 4H, CH2N), 3.48 (bs, 4H, CH2O), 3.52 (bs, 4H, CH2O), 3.58
(t, 4H, CH2O), 6.74 (dd, 2H, ArH), 6.47 (dd, 2H, ArH), 7.37 (s, 1H,
CH), 7.46 (s, 1H, NH), 10.41 (s, 1H, OH), 11.32 (s, 1H, OH). 13C
NMR (DMSO-d6), d (ppm): 52.8, 68.8, 69.7, 70.1, 71.0, 111.6,
124.7, 130.2, 143.0, 144.3, 146.4.
5.38; N, 10.78%. MS (fragments are based on 66Zn and 35Cl): m/z
515.2630 (MH)+; (Calc. 515.1163). FT-IR max/cmꢁ1): 3258
(O–H), 3210 (N–H), 3030 (C–Harom.), 2981 (C–Haliph.), 1612 (C@N),
1515 (C@C), 978 (N–O) cmꢁ1 1H NMR (DMSO-d6), d (ppm): 3.39
(s, 2H, H2O), 3.40–3.59 (m, 20H, CH2CH2O, CH2CH2N), 6.73 (dd,
2H, ArH), 6.46 (dd, 2H, ArH), 7.50 (s, 1H, NH), 7.36 (s, 1H, CH),
11.33 (s, 1H, OH), .13C NMR (DMSO-d6), d (ppm): 52.7, 68.7, 69.6,
70.1, 70.9, 111.5, 124.7, 130.1, 142.8, 144.2, 146.4.
(
m
.
2.4. Synthesis of the complexes; Ni(LH)2, Cu(LH)2, Co(LH)2(H2O)2,
[Cd(LH)(H2O)(Cl)], [Zn(LH)(H2O)(Cl)]
2.5. Electrochemical studies
A solution of NiCl2ꢂ6H2O (0.059 g, 0.25 mmol), CuCl2ꢂ2H2O
(0.043 g, 0.25 mmol) CoCl2ꢂ6H2O (0.059 g, 0.25 mmol), ZnCl2
(0.07 g, 0.50 mmol) or CdCl2ꢂ2H2O (0.114 g, 0.50 mmol) in water
(5 mL) was added to a solution of LH2 (0.19 g, 0.50 mmol) in
5 mL ethanol at room temperature. A distinct change in color and
a decrease in the pH of the solution (3.5–4.0) was observed. While
stirring at the same temperature, NaOH (1%) was added in order to
increase the pH to 7. The reaction mixture was stirred for 30 min at
room temperature. The precipitate was filtered off, washed several
times with water, and then dried in vacuum.
Glassy carbon electrodes were prepared by first polishing them
with fine wet emery papers grain size 4000 (Buehler, Lake Bluff, IL,
USA) followed by a 0.1 lm and 0.05 lm alumina slurry on a polish-
ing pad (Buehler, Lake Bluff, IL, USA), to give them a mirror-like
appearance. The electrodes were sonicated for 5 min in water
and in 50:50 (v/v) isopropyl alcohol and acetonitrile (IPA + MeCN)
solution purified over activated carbon. Before the electrochemical
experiments, the electrodes were dried with an argon gas stream
and the solutions were purged with pure argon gas (99.999%) at
least for 10 min and an argon atmosphere was maintained over
the solution during experiments. Electrochemical studies of the
compounds were performed in a solution of 1 mM LH2 and its com-
plexes, in 0.1 M TBATFB in DMSO versus an Ag/Ag+ (0.01 M) refer-
ence electrode using CV with a scan rate of 200 mV sꢁ1 between
1 V and ꢁ2.5 V.
2.4.1. Ni(LH)2
Yield: 0.16 g (75%) and m.p.: 258 °C. Anal. Calc. for C36H54N8O12-
Ni: C, 50.92; H, 6.41; N, 13.19. Found: C, 50.72; H, 6.34; N, 13.12%.
MS (fragments are based on 58Ni, 60Ni and 62Ni): m/z 849.3603
(MH)+, 850.3623 and 853.3575; (Calc. 849.3287, 850.3317 and
853.3254). FT-IR (m
max/cmꢁ1): 3132 (O–H), 3120 (N–H), 3008 (C–
2.6. Determination of antibacterial activities
H
arom.), 2992 (C–Haliph.), 1717 (O–Hꢂ ꢂ ꢂO), 1613 (Cꢂ ꢂ ꢂN), 1518
(Cꢂ ꢂ ꢂC), 976 (N–O). 1H NMR (CDCl3), d (ppm): 3.75 (m, 8H, CH2N),
3.80 (bs, 8H, CH2O), 3.83 (bs, 8H, CH2O), 3.90 (m, 8H, CH2O), 6.74
(s, 2H, CH), 6.76 (s, 2H, NH), 7.06–7.09 (m, 8H, ArH), 14.64 (s, 2H,
O–Hꢂ ꢂ ꢂO). 13C NMR (CDCl3), d (ppm): 52.06, 67.93, 69.10, 69.50,
70.36, 111.34, 125.68, 128.25, 143.50, 145.20, 146.05.
The minimal inhibitory concentrations (MIC) were determined
by broth microdilution methods in Mueller–Hinton broth (MHB)
(Becton Dickinson, Sparks, MD) with an inoculum of approximately
5 ꢃ 105 colony-forming units (CFU)/mL, according to CLSI (Clinical
and Laboratory Standards Institute) guidelines (2009). The in vitro
antibacterial activity of the complexes was evaluated against stan-
dard strains; Staphylococcus aureus ATCC (American Type Culture
Collection) 29213, Streptococcus mutans RSHM 676, Enterococcus
faecalis ATCC 29212, Lactobacillus acidophilus RSHM 06029, Esche-
richia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853.
The antibacterial activity was performed in MHB (Becton Dickin-
son, Sparks, MD). All the synthesized complexes were weighed
(10.24 mg) and dissolved in DMSO (10 mL) to prepare the stock
2.4.2. Cu(LH)2
Yield: 0.15 g (61%) and m.p.: 195 °C. Anal. Calc. for C36H54N8O12-
Cu: C, 50.61; H, 6.37; N, 13.11. Found: C, 50.55; H, 6.13; N, 13.34%.
MS (fragments are based on 63Cu and 65Cu): m/z 854.3528 (MH)+
and 856.3519; (Calc. 854.3230 and 856.3227), FT-IR (m
max/cmꢁ1):
3183 (O–H), 3142 (N–H), 3042 (C–Harom.), 2980(C–Haliph.),
1718(O–Hꢂ ꢂ ꢂO), 1614 (C@N), 1519 (C@C), 973 (N–O) cmꢁ1
.
solutions. The serial dilution from 256 to 0.25
lg/mL were made
2.4.3. Co(LH)2(H2O)2
in a 96 well plate. 100 L of a bacterial suspension, obtained from
l
Yield: 0.11 g (49%) and m.p.: >300 °C. Anal. Calc. for
a 24 h culture and containing ꢀ5 ꢃ 105 colony-forming units
(CFU)/mL was added to each well. The plate was incubated at
35 °C for 24 h. The data were reported as MICs, the lowest concen-
tration of antibiotic and complexes inhibiting visible growth after
24 h of incubation at 35 °C. For quality control of the method
ampicillin (IE Ulugay, Turkey), Genta (IE Ulugay, Turkey) and
Piperacillin (Wyeth) were tested as antimicrobial agents. These
experiments were carried out in duplicate.
C
36H58N8O14Co: C, 48.81; H, 6.60; N, 12.65. Found: C, 48.46; H,
6.65; N, 12.76%. MS (fragment is based on 59Co): 673.369 [M–
(C2H5N2O6Co)]+ (Calc. 673.462) FT-IR ( max/cmꢁ1): 3240 (O–H),
m
3140 (N–H), 3035 (C–Harom.), 2980 (C–Haliph.), 1716 (O–Hꢂ ꢂ ꢂO),
1600 (C@N), 1514 (C@C), 970 (N–O).
2.4.4. [Cd(LH)(H2O)(Cl)]
Yield: 0.10 g (35%) and m.p.: 212 °C. Anal. Calc. for
C
18H29N4O7ClCd: C, 38.32; H, 5.18; N, 9.93. Found: C, 38.51; H,
5.27; N, 10.02%. MS (fragments are based on 115Cd and 35Cl): m/z
3. Results and discussion
545.2880 (MꢁH2O)+; (Calc. 545.5514). FT-IR (
m
max/cmꢁ1): 3252
(O–H), 3210 (N–H), 3030 (C–Harom.), 2982 (C–Haliph.), 1612 (C@N),
1516 (C@C), 973 (N–O). 1H NMR (DMSO-d6), d (ppm): 3.36 (s,
2H, H2O), 3.39–3.57 (m, 20H, CH2CH2O, CH2CH2N), 6.70 (dd, 2H,
ArH), 6.39 (dd, 2H, ArH), 7.50 (s, 1H, NH), 7.36 (s, 1H, CH), 11.37
(s, 1H, OH), 13C NMR (DMSO-d6), d (ppm): 52.6, 68.9, 69.4, 70.2,
70.9, 111.3, 124.7, 130.4, 142.4, 144.1, 146.7.
3.1. FT-IR analysis
The IR spectrum of LH2 exhibits two sharp bands of medium
intensity at 1648 and 988 cmꢁ1 which are assigned to the
m
(C@N) and m(N–O) stretching vibrations, respectively [18]. A
broad band at 3184 cmꢁ1 is due to –NH stretching frequency. In
the IR spectra of all the complexes, the –NOH band of the corre-
sponding ligand observed at 3400 cmꢁ1 is absent due to hydrogen
bonding upon complexation and the azomethine frequency is
2.4.5. [Zn(LH)(H2O)(Cl)]
Yield: 0.53 g (65%) and m.p.: 189 °C. Anal. Calc. for
C18H29N4O7ClZn: C, 42.03; H, 5.68; N, 10.89. Found: C, 42.33; H,
shifted to a lower wave number, indicating the ligation of

P. Deveci et al. / Polyhedron 30 (2011) 1726–1731
1729
azomethine nitrogen to metal, which is further supported by a de-
3.4. 13C NMR spectra
crease in the N–O band by 18–10 cmꢁ1 [19]. The IR spectra of Ni(II),
Cu(II) and Co(II) complexes display a weak deformation band at
1716–1718 cmꢁ1, indicative of intramolecular hydrogen bonded
bending vibrations (O–Hꢂ ꢂ ꢂO) associated with the square-planar
and octahedral vic-dioxime complexes [20]. The IR spectra of the
Co(II), Cd(II) and Zn(II) complexes show broad bands at about
3250 cmꢁ1 which are assigned to the –OH stretching vibration of
water molecules participating in the coordination sphere.
The 13C NMR spectrum of LH2 shows eleven different carbon
atoms which are consistent with the proposed structure of ligands
on the basis of molecular symmetry (Scheme S2). In the 13C NMR
spectrum of LH2 the signals at 143.0 ppm and 146.4 ppm are as-
signed to the carbon atoms of the vic-dioxime group. Two different
frequencies of the dioxime group in 13C NMR indicate that the vic-
dioxime has an anti-structure [27]. In the 13C NMR spectra of
Ni(LH)2, [Cd(LH)(H2O)(Cl)] and [Zn(LH)(H2O)(Cl)] quaternary car-
bon signals of the hydroxyiminocarbon (C@N–O) appeared at
145.20 and 146.05 ppm for Ni(LH)2 144.1 and 146.7 ppm for
[Cd(LH)(H2O)(Cl)] and 144.2 and 146.4 ppm for [Zn(LH)(H2O)(Cl)].
The other 13C NMR chemical shifts observed for these complexes
are very similar to those which are found for ligand. Distortionless
enhancement of NMR signals by polarization transfer (DEPT) is
used to better discriminate among different types of carbons pres-
ent in the ligand. The DEPT spectrum (Fig. S4) gives the –CH2 peaks
at 52.8, 68.8, 69.7, 70.1, 71.0 ppm and the –CH peaks at 111.6,
124.7 and 143.0 ppm. The carbons recorded in 13C NMR, but nulled
in DEPT, are carbons without any attached hydrogens. More de-
tailed information about the structure of ligand is provided by
the 2D HSQC and HMBC spectrum (Figs. 1 and 2) and specific
assignments of protons and carbons are made as follows (Table
S2). The HMBC spectrum (Fig. 2), shows that O–H protons exhibit
3.2. UV–Vis spectroscopy
The UV–Vis spectra of ligand and complexes were taken in DMSO
in order to assign the geometries around the metal ions. As Fig. S1
shows, the free ligand absorption spectra reveal bands at 266 nm
and 320 nm which can be assigned to
p ?
p⁄ transitions of the aro-
matic rings and n ? p⁄ transitions of the C@N groups, respectively
[21]. In the Ni(LH)2 spectra two bands at 387 nm and 486 nm may
originate from the LMCT and d–d electron transfer, respectively.
Since no other d–d bands are observed up to 1200 nm, the simplicity
of the spectra and the corresponding band intensities suggest the
square planar rather than tetrahedral, configuration of the complex
in solution [22]. The copper(II) complex shows a broad and low en-
ergy band at 586 nm, attributed to d–d transition (2B1g ? 2A1g),
which strongly favors the square-planar geometry around the metal
ion [23,24]. The weak d–d transition of the complexes Co(LH)2-
(H2O)2, [Cd(LH)(H2O)(Cl)], [Zn(LH)(H2O)(Cl)] could not be observed.
The d–d bands should also be present in this range with low intensi-
ties, but they are masked by the stronger CT absorption band [25].
long range coupling with hydroxyimino carbons at 143.0 (C11
)
and 146.4 (C10) ppm, respectively. Other correlations are also in
accordance with the proposed structure.
3.5. Electrochemical studies
3.3. 1H NMR spectra
The electrochemical properties of the ligand, LH2 and its metal
complexes were investigated in DMSO solution containing 0.1 M
TBATFB as a supporting electrolyte by cyclic voltammetry. All the
measurements were carried out in 1 mM solutions of free ligand
and its complexes at room temperature, in the potential range
from +1 to ꢁ2.5 V with a scan rate of 200 mV sꢁ1. Typical cyclic
voltammograms of LH2 and its metal complexes are shown in
Fig. S5 (Supplementary material), and the results are summarized
in Table 1. First, we carried out the voltammetric measurements
of N-(4-aminophenyl)aza-15-crown-5 in order to compare its re-
dox behavior with those of the ligand and its metal complexes
and thus assign the nature of the redox processes. Fig. S5a indicates
that both the CV of LH2 and N-(4-aminophenyl)aza-15-crown-5
(Ac) displays two reversible waves in the positive potential region
The structure of LH2 is assigned through the combined use of pro-
ton and carbon 1D (1H NMR, 13C NMR and DEPT) and 2D (HSQC and
HMBC) NMR experiments. All the 1H and 13C NMR chemical shifts for
LH2 are given in Tables S1 and S2 in the Supplementary material,
alongwith theHMBCand HSQCcorrelations. Thenumberingscheme
for the assignments of protons is shown in Scheme S1 in the Supple-
mentary material. In the 1H NMR spectrum (Fig. S2) the aromatic
ring protons are observed at 6.74 ppm (H6) and 6.47 ppm (H7) as
two doublets of doublets (3J = 8.95 Hz and 4J = 1.87 Hz) for LH2 and
as a multipletin the region 7.06–7.09 ppm (H6, H7) for Ni(LH)2. These
signals, due to crown ether moiety, have been observed at 3.41–3.58
for LH2 and at 3.75–3.90 ppm for Ni(LH)2. For the ligands’ spectrum,
the singlets found at 7.46 ppm (H8) and 7.37 ppm (H9) have been as-
signed to the N–H and C–H groups, respectively. These peaks have
been observed at 6.76 ppm and 6.74 ppm for Ni(LH)2. In the 1H
NMR spectrum of LH2, peaks corresponding to N–OH were observed
at 10.41 ppm (H10) and 11.32 ppm (H11). These two deuterium
exchangeable singlets correspond to two nonequivalent –OH pro-
tons, which also indicate the anti-configuration of the –OH groups
relative to each other [26]. In the 1H NMR spectrum of Ni(LH)2, the
signal arising from the hydroxyimino protons disappeared after
the complexation, and a new resonance at 14.64 ppm which could
be easily identified by deuterium exchange, could be assigned to
the formation of a hydrogen bridge. In the 1H NMR spectrum of
[Cd(LH)(H2O)(Cl)] and [Zn(LH)(H2O)(Cl)] (Fig. S3) the aromatic
ring protons are observed at 6.70 ppm and 6.39 ppm for
[Cd(LH)(H2O)(Cl)] and 6.73 ppm and 6.46 ppm for [Zn(LH)(H2O)(Cl)]
as two doublets of doublets. These signals, due to crown ether
moiety, have been observed as a multiplet at 3.39–3.57 for
[Cd(LH)(H2O)(Cl)] and at 3.40–3.59 ppm for [Zn(LH)(H2O)(Cl)]. In
the 1H NMR spectrum of these complexes, peaks corresponding to
N–OH were observed at 11.37 ppm for [Cd(LH)(H2O)(Cl)] and
11.33 ppm for [Zn(LH)(H2O)(Cl)].
Fig. 1. HSQC spectrum of the LH2 in DMSO-d6 (expanded form of the azacrown
ether region is shown in the box inset).

1730
P. Deveci et al. / Polyhedron 30 (2011) 1726–1731
potentials and peak currents depending on the stability of the com-
plexes and the kinetics of the electron transfer. For Ni(LH)2, the
reduction wave (Epc = ꢁ1.53 V) corresponding to Ni(II)/Ni(I) reac-
tion is obtained [28,29] in the cathodic potential region, in addition
to the ligand peak at ꢁ1.79 V. For the Cu(II) complex, the reversible
wave at E1/2–0.07 V and an irreversible peak at ꢁ0.72 V corre-
spond to the Cu(II)/Cu(I) and Cu(I)/Cu(0) couples, respectively, in
addition to the ligand peaks at ꢁ1.28 V and ꢁ2.12 V [30,31]. The
reversible Cu(II)/Cu(I) wave has an adsorptional character with al-
most symmetric cathodic and anodic peaks with a peak separation
value of 10 mV (Table 1). The reversible character indicates that
both Cu(II) and Cu(I) complexes of LH2 are stable at the electrode
surface and in DMSO. As can be inferred from the irreversible char-
acter of the peak at ꢁ0.72 V, the Cu(I) complex is probably de-
stroyed during the reduction of Cu(I) to Cu(0) in the complex.
Comparison of the voltammetric data of Ni(LH)2 and Cu(LH)2 with
that of LH2 suggests that the reduction peaks at ꢁ1.79 V and
ꢁ1.28 V are due to oxime-based processes (Fig. S5b and c). These
ligand-based reduction processes, especially the oxime-based
reduction process of Cu(LH)2, occurs at less negative potentials
than those of LH2. This behavior was also observed in Ni(LH)2 pre-
sumably due to negative charge transfer from ligand to metal dur-
ing the formation of metal complexes [32]. For Co(LH)2(H2O)2 the
absence of the reduction peak of the imino group indicates that,
owing to the lack of transferable hydroxylic protons, the reduction
potentials of the dianionic ligands have been shifted beyond the
lower limit of the potential interval considered in the experimental
measurements [33]. The CV wave for the process Co(II)/Co(I) falls
at potentials near ꢁ1.82 V (Fig. S5d). [Cd(LH)(H2O)(Cl)] and
[Zn(LH)(H2O)(Cl)] show a CV voltammogram in line with expecta-
tions. In these complexes, the cyclic voltammetric M(II)/M(I)
reduction process was observed at ꢁ1.73 V and ꢁ1.58 V and oxime
group reductions were observed at ꢁ2.16 V and ꢁ2.23 V, respec-
tively (Fig. S5e and f). For all complex CV measurements, at differ-
ent scan rates in the range of 50–800 mV sꢁ1, the Epc values appear
to be only slightly dependent upon the scan rate. Furthermore, in
all cases a linear relationship between the cathodic peak current
(ipc) and the square root of the scan rate was observed. This
fact implies that these electrochemical processes are mainly
diffusion-controlled.
Fig. 2. HMBC correlations for LH2 in DMSO-d6.
Table 1
Voltammetric data for LH2, Ni(LH)2, Cu(LH)2, Co(LH)2(H2O)2, [Cd(LH)(H2O)(Cl),
[Zn(LH)(H2O)(Cl) in DMSO/TBATFBa (Ac = N-(4-aminophenyl)aza-15-crown-5,
Ox = anti-N-(4-aminophenyl)aza-15-crown-5 glyoxime).
Compound
LH2
Redox couple
Ac/Acꢁ
Ea or Ep (V)b
D
Ep (V)c
1/2
I
I0
0.31
0.68
0.01
0.02
–
IV
III
I
I0
III
II
I
I0
ꢁ2.10
ꢁ1.83
0.41
Ox/Oxꢁ
Ac/Acꢁ
–
Ni(LH)2
Cu(LH)2
0.22
0.11
–
–
0.20
–
–
–
0.01
–
–
–
–
–
0.08
0.12
–
0.70
Ox/Oxꢁ
ꢁ1.79
ꢁ1.53
0.40
Ni(II)/Ni(I)
Ac/Acꢁ
0.84
IV
III
IIc, IIa
II
I
I0
III
II
I
I0
III
II
I
I0
III
II
ꢁ2.12
ꢁ1.28
ꢁ0.07
ꢁ0.72
0.30
Ox/Oxꢁ
Cu(II)/Cu(I)
Cu(I)/Cu(0)
Ac/Acꢁ
Co(LH)2(H2O)2
0.71
–
Ox/Oxꢁ
Co(II)/Co(I)
ꢁ1.82
[Cd(LH)(H2O)(Cl)
[Zn(LH)(H2O)(Cl)
Ac/Acꢁ
0.36
0.68
Ox/Oxꢁ
ꢁ2.16
ꢁ1.73
0.36
3.6. Biological activity
Cd(II)/Cd(I)
–
Ac/Acꢁ
0.12
0.10
–
vic-Dioxime ligand and its metal complexes obtained higher
0.69
Ox/Oxꢁ
Zn(II)/Zn(I)
ꢁ2.23
and similar MIC values (64 and 128
lg/mL) when used against
ꢁ1.58
–
Staphylococcus aureus, Streptococcus mutans, Enterococcus faecalis,
a
+
Lactobacillus
aeruginosa.
acidophilus, Escherichia coli and Pseudomonas
Half-wave (E1/2) or peak (Ep) potentials in DMSO/TBATFB versus Fc/Fc couple
correspond approximately with the above data ꢁ0.50 V. Data was acquired by
cyclic voltammetry.
b
E1/2 = (Epa + Epc)/2 for reversible or quasi-reversible processes. Ep indicates the
cathodic peak potential for irreversible reduction processes and the anodic peak
4. Conclusion
potential for irreversible oxidation processes.
c
The peak separation (
D
Ep = Epa ꢁ Epc) values are reported at 0.200 V sꢁ1
.
We have described the preparation, characterization and bio-
logical activities of a novel vic-dioxime ligand and its Ni(II), Cu(II),
Co(II), Cd(II) and Zn(II) metal complexes which were substituted
peripherally with the azacrown ether moiety. The spectroscopic
analysis confirmed the composition and the structure of the newly
obtained compounds. The spectral and magnetic data suggested
the square-planar geometry for Ni(II) and Cu(II) complexes and
the octahedral geometry for Co(II) complex, while Cd(II) and Zn(II)
complexes have tedrahedral geometry. The redox behavior was ex-
plored by cyclic voltammetry based on the metal-centered reduc-
tion processes for all complexes. The copper complexes show
both the reduction and oxidation process. The reduction/oxidation
potential depends on the structure and conformation of the central
atom in the coordination compounds. The antimicrobial test
belonging to the N-(4-aminophenyl)aza-15-crown-5 moiety. The
main difference of these two voltammograms is the presence of
only one reduction peak in the Ac voltammogram (ꢁ2.03 V) but
two reduction peaks in the voltammogram of LH2 (ꢁ1.83 and
ꢁ2.10 V) (Table 1). Comparison of the redox data of LH2 with N-
(4-aminophenyl)aza-15-crown-5 implies that the first reduction
process probably corresponds to the imino group of oxime moie-
ties (Epc = ꢁ1.83 V) while the second reduction process corre-
sponds to the N-(4-aminophenyl)aza-15-crown-5 moiety in LH2.
The reversible waves in the positive potential region are always
observed for all complexes of LH2 with small differences in peak

P. Deveci et al. / Polyhedron 30 (2011) 1726–1731
1731
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This work was supported by the Research Found of Selcuk Uni-
versity Project Number: 08101030 under thesis.
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Appendix A. Supplementary material
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