Mononuclear copper(II) complexes of bis-triazole-based macrocyclic Schiff base hydrazones: Direct synthesis, EPR studies, magnetic and thermal properties

Article abstract of DOI:10.1007/s13738-013-0303-8

Mononuclear copper(II) complexes of 1,2,4-triazole-based Schiff base macrocyclic hydrazones, III and IV, have been reported. The prepared amorphous complexes have been characterized by spectroscopic methods, electron spray ionization mass spectrometry, an

Full text of DOI:10.1007/s13738-013-0303-8

J IRAN CHEM SOC
DOI 10.1007/s13738-013-0303-8
ORIGINAL PAPER
Mononuclear copper(II) complexes of bis-triazole-based
macrocyclic Schiff base hydrazones: direct synthesis,
EPR studies, magnetic and thermal properties
Hamid Khanmohammadi
Edward J. Reijerse
•
Malihe Erfantalab
•
Received: 26 March 2013 / Accepted: 20 June 2013
Ó Iranian Chemical Society 2013
Abstract Mononuclear copper(II) complexes of 1,2,4-
triazole-based Schiff base macrocyclic hydrazones, III and
IV, have been reported. The prepared amorphous com-
plexes have been characterized by spectroscopic methods,
electron spray ionization mass spectrometry, and elemental
analysis data. Electrochemical studies of the complexes in
DMSO show only one quasi-reversible reduction wave at
Introduction
During the past decade great attention has been devoted to
the construction of transition metal complexes of hetero-
cycle-based ligands due to their interesting chemical and
physical properties as well as their biological importance
[1–5]. 1,2,4-Triazole-based ligands constitute a dominant
class of these compounds which have attracted a great
number of researchers in recent years [6, 7]. This is due to
the key role played by 1,2,4-triazole group which has
unique structural characteristics such as (i) bridging capa-
bility and (ii) structural flexibility [7, 8]. On the other hand,
the electronic properties of 1,2,4-triazole-based ligands are
also unique. The tendency of 1,2,4-triazole moiety to
coordinate with metal ions is dependent on the presence of
other groups, such as phenolic and azomethine groups [9–
11]. Hence, the incorporation of 1,2,4-triazole unit into
acyclic and/or macroacyclic Schiff bases is of considerable
interest due to their capabilities to bind with various metal
ions and also their possibility of generating magnetically
interesting complexes [7, 12–14].
?
0.43 V (DE = 70 mV) and ?0.42 V (DE = 310 mV)
for III and IV, respectively, which is assigned to the
Cu(II) ? Cu(I) reduction process. Temperature depen-
dence of magnetic susceptibilities of III and IV has been
measured within an interval of 2–290 K. The values of v
M
-
3
3
-1
-3
at 290 K are 1.72 9 10 cm mol and 1.71 9 10 for
III and IV, respectively, which increases continuously
upon cooling to 2 K. EPR spectra of III and IV in frozen
DMSO and DMF were also reported. The trend
g [ g\ [ g suggests the presence of an unpaired elec-
||
e
tron in the dx2-y2 orbital of the Cu(II) in both complexes.
Furthermore, spectral and antimicrobial properties of the
prepared complexes were also investigated.
Keywords 1,2,4-Triazole ꢀ Schiff base ꢀ Macrocyclic
copper(II) complex ꢀ Magnetic properties ꢀ EPR study
Prior to this work, other groups, most notably Alcade
et al. [15] have reported the synthesis and structural char-
acterization of several metal-free triazole-based macrocy-
cles. Foroughifar et al. [16] and Abbas [17] have reported
synthesis and spectral characterization of metal-free 1,2,4-
triazole and thiadiazole-based Schiff base macrocyclic
ligands via condensation reaction of various dicarbonyles
with triazole and/or thiadiazole-based diamines, Fig. 1a.
However, attempts to prepare the metal-free Schiff base
macrocycles from 3,5-diacetyl-1,2,4-triazole were unsuc-
cessful [18–21]. The first dinuclear metal complexes of
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-013-0303-8) contains supplementary
material, which is available to authorized users.
H. Khanmohammadi (&) ꢀ M. Erfantalab
Department of Chemistry, Arak University,
Arak 38156-8-8349, Iran
e-mail: h-khanmohammadi@araku.ac.ir
1
,2,4-triazole-based Schiff base ligand of that dicarbonyl
E. J. Reijerse
Max Planck Institute for Chemical Energy Conversion,
M u¨ lheim an der Ruhr, Germany
have been reported by Torres and co-workers [22–24], but
none of them were structurally characterized to date.
123

J IRAN CHEM SOC
Fig. 1 Reported triazole and
tiadiazole-based Schiff base
macrocyclic ligands
Y
Y
O
S
O
O
O
N
N
N
N
N
N
N
S
S
R
S
R
X
N
N
S
S
N
N
N
N
X
N
(
a)
X = (CH ) , (CH )
2 3
2
2
Y = (CH ) , (CH )
2 3
2
2
R = 3-pyridyl, 4-pyridyl
Ph
H
N
Ph
N
N
N
N
N
N
(
CH )
n(CH2)
2 n
N
N
N
H
Ph
Ph
L , n=1
1
(
b)
L , n=2
2
Binuclear Pb(II) complexes of symmetric [2 ? 2] 1,2,4-
triazole-based Schiff base macrocycles, Ln (n = 1,2),
Fig. 1b, were formed by cyclocondensation of 3,5-diacetyl-
of III and IV also exhibited a half-field, DM = 2, transition
with a seven line pattern, demonstrating interaction between
s
two copper (II) centers.
1
,2,4-triazole with diamine components in the presence of
In addition, in vitro antimicrobial activities of III and IV
were screened against Escherichia coli (E. coli), Staphy-
lococcus aureus, and Candida albicans using disc diffusion
method. The data showed that the antimicrobial activities
of III and IV are too low, probably due to their low sol-
ubility in DMSO. Spectral property of the prepared com-
plexes in DMSO and DMF were also evaluated.
Pb(II) ion [18]. Up to now, based on our knowledge, almost
all transition metal complexes of triazole-based Schiff-base
macrocyclic ligands have been prepared via transmetala-
tion procedure and attempts to direct synthesis of mono-
nuclear complex of 1,2,4-triazole-based Schiff-base ligands
in the presence of transition metal ions were not successful
[
18].
In order to try to direct synthesis of Cu(II) complexes of
new 1,2,4-triazole-based Schiff base macrocycles and also to
investigate the influence of the substituents on the electronic
and magnetic properties of the resulting complexes, we
developed direct synthesis of 1,2,4-triazole-based copper(II)
complexes. Here we report the synthesis of mononuclear
copper(II) complexes of bis-1,2,4-triazole-based Schiff base
macrocycles, III and IV, by cyclocondensation of N,N’-
ethylene-bis(3-formyl-5-methylsalicylaldimine)copper(II),
CuL, with 1,2,4-triazole-based diamines, I and II, in MeOH,
Fig. 2. The powder XRD data indicated that the prepared
complexes are amorphous. The complexes were character-
ized by electron spray ionization mass (ESI–MS) spec-
trometry. Variable temperature magnetic measurements
were also carried out on complexes in the temperature range
Experimental section
General information
All chemicals and solvents were of analytical grade and
purchased commercially. 4-Amino-3-(4-pyridyl)-5-mer-
capto-1,2,4-triazole [25], N,N’-ethylene-bis(3-formyl-5-
methylsalicylaldimino)copper(II), CuL, [26], and bis(4-
amino-1,2,4-triazolepyridylsulfanyl)ethane, I, [17] were
1
prepared as described previously. H NMR spectra were
obtained with a Bruker Avance 300 MHz spectrometer.
Electronic spectral measurements were carried out using a
Perkin-Elmer Lambda spectrophotometer in the range
200–600 nm. Thermal analyses were performed on a Per-
kin-Elmer Thermogravimetric Analyzer TG/DTA 6300
instrument. Elemental analyses were performed on an
Elementar Vario EL III elemental analyzer. Infrared
spectra were recorded as pressed KBr discs, using a
2
–290 K. Furthermore, the EPR spectra of III and IV
exhibited well-resolved features characteristic of mononu-
clear Cu(II) complexes which is also supported by the
magnetic data. However, the EPR spectra of frozen-solution
1
23

J IRAN CHEM SOC
Fig. 2 Triazole-based Schiff
base macrocyclic complexes
Unicam Galaxy Series FT-IR 5000 spectrophotometer
-
microorganisms were introduced onto the surface of agar
plates individually. The blank sterile discs measuring
6.4 mm in diameter were soaked in a known concentration
of the test compounds. Then the soaked discs were
implanted on the surface of the plates. A blank disc was
soaked in the solvent (DMSO) and implanted as negative
control on each plate along with the standard drugs. The
plates were incubated at 37 °C (24 h) and 27 °C (48 h) for
bacterial and fungal strain, respectively.
1
(
400–4,000 cm ). Electron paramagnetic resonance
EPR) was obtained from frozen solutions at 10–50 K with
(
a Bruker ELEXSYS E500 spectrometer operating at
X-band utilizing microwave frequencies around 9.5 GHz.
The concentrations of copper complexes were in range of
-
4
-3
1
9 10 M–2 9 10 M in DMSO and DMF solvents.
The g , g\, A , and A\ parameters were evaluated using
k
k
Easy Spin software [27, 28]. The variable temperature
magnetic measurements were carried out in a supercon-
ducting quantum interference device (SQUID) magne-
tometer in the range 2–290 K and the data were simulated
using julX [27, 28]. The positive electrospray mass spectra
Synthesis of bis(4-amino-1,2,4-triazolepyridylsulfanyl)-
1,3-methylbenzene, II
(
ESI–MS) in DMF: Methanol (50:50) solutions were
1
,3-Bis(bromomethyl)benzene (0.264 g, 1 mmol) was
recorded on a Q-ToF Ultima, Waters apparatus. Electro-
chemical measurements were recorded on an Autolab 30 V
potentiostat/Galvanostat of Eco Chemical Company. All
readings were taken using a three-electrode potentiostatic
added to an alkaline (0.112 g, 2 mmol of KOH), solution of
4
2
-amino-3-(4-pyridyl)-5-mercapto-1,2,4-triazole (0.386 g,
mmol) in ethanol (50 mL). The reaction mixture was
stirred and heated under reflux for 1 h. The solvent was
removed in vacuum and the remaining solid was collected
-
3
system in DMSO with 0.1 mol cm tetrabutylammonium
perchlorate (TBAP, electrochemical grade, Acros) as sup-
porting electrolyte. A three-electrode assembly composed
of a glassy carbon working electrode, a platinum auxiliary
electrode, and Ag–AgCl reference electrode was used with
and washed with water. Yield: 81 %, m.p. = 208–209 °C.
1
H NMR (d -DMSO, ppm): 8.72 (dd, 4H, J = 6.00 Hz),
6
7
6
3
.98 (dd, 4H, J = 6.00 Hz), 7.56 (s, br, 1H), 7.29 (m, 3H),
-
.23 (s, 4H), 4.46 (s, 4H). IR (KBr, cm ); IR (KBr, cm );
1
-1
-
3
-3
sample concentrations of 1 9 10 molcm . X-ray dif-
,340, 3,267 t(NH2), 1,602 t(C=C), 1,556 t(C=C–N), 1,232
fraction studies were performed in a X-Pert PW 3710
˚
t(N–N), 825 t(NCN). Anal. Calcd. for C H N S : C, 54.08;
H, 4.13; N, 28.67; S, 13.13. Found: C, 54.23; H, 4.28; N,
22
20 10 2
powder diffractometer with Cu-K radiation (1.5406 A) at
a
4
0 kV and 35 mA current.
2
8.34; S, 13.01.
Procedure for biological activity study
General procedure for the synthesis of copper(II)
Newly prepared copper(II) complexes were screened for
their activity against E. coli, S. aureus, and C. albicans
strains by disc diffusion method as gram-negative, gram-
positive, and fungal organisms, respectively.
complexes, III and IV
A solution of diamine, I and/or II, (0.5 mmol) in
MeOH:CH COOH (5:1) (5 mL) was added to a suspension
3
0
The muller hinton agar and subro dextrose agar were
used to culture bacterial and fungal, respectively. The
culture media was poured into sterile plates and
of
N,N -ethylene-bis(3-formyl-5-methylsalicylaldimino)
copper(II) (1 mmol) and copper perchlorate (1 mmol) in
methanol (15 mL) at 60 °C. The mixture was heated for
123

J IRAN CHEM SOC
a -1
Table 1 Tentative assignments of some selected IR frequencies (cm ) and UV–Vis data of the prepared complexes
-
-1
-1
Compound t(C–O) t(C=N/C=C)
t (phenol ring) t(ClO
4
)
t(Cu–N) and (Cu–O)
k
max (nm) (e (M cm )) in DMSO
III
IV
a
1,309
1,307
1,637, 1,606, 1,448 1,572
1,637, 1,602, 1,446 1,574
–
–
684, 586, 509
696, 584, 513
275 (49,967), 419 (22,077), 596 (1,333)
275 (69,165), 423 (30,000), 607 (1,500)
KBr discs
-
absorption band at 1,686 cm together with the appear-
1
1
5–17 h at same temperature. The isolated green solid was
filtered and washed well with warm absolute methanol.
ance of new t(C=N) absorption band in the IR spectra of
III and IV at 1,637–1,640 cm clearly indicated that a
cyclic Schiff-base had formed. The bands located at 1,541,
-
1
Complex III
-
91, and 700 cm in the IR spectra of III and IV can be
1
9
The isolated green solid was recrystallized from DMF. IR
-
assigned to t(C=C) and t(C=N ) of the in plane ring
py
1
(
KBr, cm ); 1,652 (shoulder), 1,637 t(C=N), 1,606,
1
6
2
,572, 1,539, 1,448, 1,383, 1,309, 1,236, 991, 831, 705,
-
1
-1
84, 586, 509. UV–Vis kmax (nm)(e (M cm )) in DMF:
75 (49,967), 419 (22,077), 596 (1,333). Anal. Calc. for
C H N O S Cu. 0.5 DMF: C, 54.47; H, 4.08; N, 21.17;
36 30 12 2 2
S, 7.76; Cu, 7.69 %. Found: C, 54.61; H, 4.43; N, 21.17; S,
-
4
-1
cm .
7
.71; Cu, 7.94 %. g = 2.23, A = 560 9 10
k
k
leff = 2.00 ± 0.05 BM.
Complex IV
-1
IR (KBr, cm ); 1,637 t(C=N), 1,602, 1,574, 1,541, 1,446,
,379, 1,307, 1,234, 1,091, 991, 775, 696, 623, 584, 513. UV–
1
-1
-1
Vis kmax (nm)(e (M cm )) in DMSO: 275 (69,165), 423
30,000), 607 (1,500). Anal. Calc. for C H N O S Cu. 0.5
(
4
2 34 12 2 2
CH OH: C, 57.84; H, 4.11; N, 19.05; S, 7.27; Cu, 7.20 %.
3
Found: C, 57.80; H, 4.43; N, 18.62; S, 7.10; Cu, 7.14 %.
-1
-
4
g = 2.23, A = 500 9 10 cm
.
leff = 1.99 ± 0.05
k
BM.
k
Result and discussion
New macrocyclic copper(II) complexes, III and IV, have
been prepared by direct synthesis. The complexes are
amorphous solids, air stable, and moderately soluble in
DMSO and DMF at ambient temperature. ESI(?)-MS data
provided evidence for the presence of mononuclear com-
plexes in solution.
-5
Fig. 3 The absorption spectra of (a) 1.0 9 10
-
M of III
5
(
b) 2.0 9 10 M of IV in mixture of DMSO: CCl
4
Table 2 Zone inhibition of the prepared compounds
Compounds Staphylococcus
aureus (mm)
Escherichia
coli (mm)
Candida
albicans (mm)
Infrared spectra
III
3
–
–
–
–
In the absence of X-ray crystal structure data, infrared
spectroscopic data were used to find relatively narrow
bonding pattern of the amorphous complexes. The posi-
tions of some of the prominent bands in the IR spectra of
the prepared compounds and their assignments based on
extensive data available for related compounds [29, 30] are
given in Table 1. The total absence of CuL t(C=O)
IV
4
–
DMSO
–
–
Standard
drugs
Penicillin 33 mm
Gentamicin
18 mm
Nistatin 25 mm
–
Indicates bacteria are resistant to the compounds. Zone of inhibition
are reported in mm of diameter. Discs were inoculated with 5 mg of
the compounds dissolved in DMSO
1
23

J IRAN CHEM SOC
deformation and out of plane ring deformation mode,
respectively [29, 31]. The coordination mode of the ligands
is supported by the appearance of m(Cu–N) and m(Cu–O)
of III may be assigned to a coordinated DMF molecule
[34], as was confirmed by their disappearance after drying
of III at 150 °C over night.
-
1
bands at 480–580 cm
[32, 33]. These bands are in
accordance with data found in the literature and strongly
support the hypothesis that the metal ion is coordinated
through the imine nitrogen and phenolic oxygen atoms.
The total absence of perchlorate bands in the IR spectra of
III and IV implies that the complexes have no counter ions.
Electronic spectra of III and IV
The electronic spectra of III and IV in DMSO display three
main features at 260–280, 410–430, and 590–610 nm,
Table 1. The intense absorption band located at
260–280 nm can be assigned to the moderate-energy
-
1
-1
The bands at 1,645 cm and 706 cm in the IR spectrum
Fig. 4 TGA-DTA analyses curve of IV (see supplementary data)
Table 3 Thermal analyses data
for III and IV
a
Compound, M.F.
M. Wt.)
Dissociation Temperature
stages
Weight loss,
range in TG (°C) found
calculated) (%)
Decomposition
assignment
Td
(°C)
(
(
III C36
H
30
N
12
O
2
S
2
Cu. Stage I
Stage II
50–250
4.50 (4.42)
50.66 (49.90)
–
The loss of
0.5 mol DMF
307
0
.5DMF (826.93)
250–370
370–550
The loss of
16 12 9 2
C H N S
Stage III
The loss of
remaining
organic parts
IV C42
H
34
N
12
O
2
S
2
Cu. Stage I
50–200
2.20 (1.82)
The loss of
0.5 mol
287
0
.5MeOH (882.50)
CH
The loss of
HN
The loss of
3
OH
Stage II
Stage III
Stage IV
200–310
310–390
390–550
13.97 (14.44)
28.89 (29.30)
–
C
3
4
S
9 7 5
C H N S
The loss of
remaining
organic parts
a
Decomposition temperature
123

J IRAN CHEM SOC
(
p ? p*) transition of the aromatic rings while the second
low inhibition of complexes may be due to their low sol-
ubility in DMSO.
band at 410–430 nm is due to low-energy (p ? p*) tran-
sition involving the p-electrons of the azomethine groups
[
35]. The low-intensity band at ca. 600 nm is due to the d–
Thermal properties
d transition of Cu(II) ion.
The UV–Vis spectra of III and IV were also recorded in
mixture of DMSO/CCl to study the effect of a non-polar
In order to obtain more insight into the structure of III and
IV, thermal studies of the prepared complexes have been
carried out using TGA/DTA techniques. The thermo-
gravimetric studies have been made in the temperature
4
solvent on solvent–solute interactions and tautomeric
equilibrium in solution, Fig. 3. Upon the addition of CCl4,
the intensity of absorption band at 410–430 nm, in pure
DMSO, was decreased gradually and simultaneously the
intensity of band at 260–280 was increased with isosbestic
points at 386 nm and 384 nm for III and IV, respectively,
indicating the establishment of equilibrium between vari-
ous tautomers. The position of band was also shifted to
lower wavelength during the addition of CCl4.
range 25–550 °C under N atmosphere.
2
The TG curve of III refers to three stages of mass
loses within the temperature range 50–550 °C. The first
stage at 50–250 °C with a mass loss of 4.50 % (calc.
4.42 %) corresponds to the loss of DMF. The second
stage at 250–370 °C with a mass loss of 50.66 % (calc.
49.90 %) corresponds to the loss of C H N S frag-
16
12 9 2
ment, accompanied by an exotherm in the DTA curve,
and the thermal decomposition of the complex. Another
stage of decomposition at the temperature range
370–550 °C is roughly assigned to the loss of the
remaining organic part of the complex (See supporting
information).
Antibacterial and antifungal activities
The investigation of antibacterial screening data revealed
that III and IV did not show any antibacterial activity
against E. coli, S. aureus, and C. albicans (Table 2). The
Fig. 5 Positive ion ESI mass spectra of (a) III, (b) IV in DMF: Methanol (50:50) solution
1
23

J IRAN CHEM SOC
Table 4 Relevant magnetic data for the prepared copper(II) com-
plexes, III and IV
parts of complex, C HN S 13.97 % (calc. 14.44 %) and
3 4
C H N S 28.89 % (calc. 29.30 %) fragments, respectively.
9 7 5
3
3
a
a
R
The fourth stage at the temperature range 390–550 °C is
assigned to the loss of the remaining organic part of the
Complexes
v
mol ), 290 K mol ), 2 K
M
(cm
-
v
M
(cm
-1
g
1
complex. The comparison of T (decomposition tempera-
d
-
3
3
-5
-5
III
IV
a
1.72 9 10
1.71 9 10
0.20
2.162 1.56 9 10
2.142 1.61 9 10
ture) showed that the thermal stability of the complexes
-
0.178
increases in order III > IV (Table 3).
The best fit parameters
Electron spray ionization mass spectra
The TG curve of IV, refers to four stages of mass loses
within the temperature range 50–550 °C (Fig. 4). In the
first stage, methanol molecule was released 2.20 % (calc.
Electrospray ionization mass spectra, ESI–MS, were found
to be fully compatible with the proposed structure of III
and IV, Fig. 5. The ESI–MS of III and IV exhibit similar
features and containing two types of positively charged
species: m/z 812.3 (m/z 812.12 calculated for
1
.82 %). The second and third stages at temperature range
of 200–310 °C and 310–390 °C indicate the loss of organic
Fig. 6 Thermal evolution of the
magnetic susceptibility for
(
a) III and (b) IV
123

J IRAN CHEM SOC
?
[
C H N O S Cu ? Na] ) and m/z 828.0 (m/z 828.10
36 30 12 2 2
?
calculated for [C H N O S Cu ? K] ) for III and also
3
6 30 12 2 2
m/z 888.3 (m/z 888.16 calculated for [C H N O S
2 34 12 2 2-
4
?
Cu ? Na] ) and m/z 904.0 (m/z 904.13 calculated for
?
[
C H N O S Cu ? K] ) for IV. The numbers of peaks,
42 34 12 2 2
m/z values and the relative peak heights observed for all
cations are in excellent agreement with the calculated
spectral patterns obtained by taking into consideration the
relative abundances of the isotopes of the constituent
elements.
Magnetic properties
The temperature dependence of magnetic susceptibilities of
III and IV were measured in the range 2–290 K. The
values of vM at 290 and 2 K are given in Table 4. The
magnetic moment (l ) of III and IV at 290 K is
eff
2
.00 ± 0.05 BM and 1.99 ± 0.05 BM, respectively,
slightly larger than the spin-only value (1.73 BM) for one
isolated Cu(II) center. This deviation may be arising from
spin–orbit interaction which consistent with the common
behavior of copper(II) ion with square pyramidal geometry
[
36–40]. The plot of vM vs T and also v T vs T for III and
M
IV are depicted in Fig. 6 (vM is the magnetic susceptibility
per one copper atom). The vM values of III and IV
Fig. 7 Cyclic voltammgram for (a) III and (b) IV in DMSO
(
-3
0.1 mol cm TBAP, glassy carbon, Ag–AgCl, 100 mV/s)
increases
continuously
-1
upon
cooling
-3
from
-
3
2
3
1
2
2
.72 9 10 cm mol
and 1.71 9 10
at 290 K to
3
-
3
-1
-2
-1
.21 9 10 cm mol and 2.15 9 10 cm mol
at
0 K, respectively. Upon further cooling, the v values
M
Table 5 Voltammetric data for III and IV versus Ag/AgCl in
DMSO-TBAP
3
-1
exponentially increase up to 0.20 cm mol and 0.178 at
K for III and IV, respectively, indicating the predomi-
2
a
Complexes
E
pc
E
1/2
E
oa
Process
nance of interaction between copper(II) ions through the
solvent bridge.
2
?
?
?
III
IV
a
?0.36
?0.12
?0.40
?0.27
?0.43
?0.42
Cu /Cu
2
?
The magnetic data were analyzed using the program
julX [27]. The best-fit parameters of III are g = 2.162 and
Cu /Cu
E
1/2 values (vs. SEC) were taken as the average of the anodic and
-
R = 1.56 9 10 . R is the agreement factor defined as
5
cathodic peaks potentials
Fig. 8 The EPR spectra of III
and IV
1
23

J IRAN CHEM SOC
Table 6 EPR parameters of III and IV in frozen DMSO
the versatile coordination behavior of the present 1,2,4-
triazole-based macrocyclic Schiff base ligands.
Complexes
g
||
g
\
A (G)
k
III
IV
2.23
2.23
2.01
2.06
199
175
Electron paramagnetic resonance
The X-band EPR studies were performed in frozen DMSO
solution of III and IV at 6–50 K. The EPR spectrum of III
is characterized by a well-resolved mononuclear Cu(II)
X ꢀ
ꢁ
X ꢀ
The best-fit parameters of IV are g = 2.145 and with
ꢁ
2
2
ðv TÞ ꢁ ðv TÞ Þ =
ðv TÞ
M
obs
M
calc
M
obs
complex signal, Fig. 8. The observed g , g\, and A values
k
|
|
i
i
are 2.23, 2.01, and 199 G, respectively, Table 6. The EPR
parameters of are consistent with the assumption that (i) the
copper ion located in an axial symmetry environment and
-
5
R = 1.61 9 10
.
(
ii) the ground state orbital is dx2–y2 (2.00 & g\ \ g ) [42,
||
Electrochemical analysis
44–47]. Besides allowed transitions, DM
s
= ± 1, around
160 mT weak signals (so called half-field) was observed
Electrochemical investigation of III and IV were carried
-
corresponding to the DM = ± 2 forbidden transition,
s
which indicates a magnetic coupling between the two
1
out in DMSO at a concentration of 1 mmolL , Fig. 7 and
Table 5. Only one quasi-reversible reduction wave at
Cu(II) ions [42], Fig. 9.
?
0.43 V (DE = 70 mV) and ?0.42 V (DE = 310 mV)
The EPR spectrum of IV is containing a much broader
signal including a g \ 2 contribution as well as a half-field
signal, indicative of dimer formation and/or aggregation of
the complex. To monitor the aggregation behavior, the
EPR spectrum was recorded on freshly prepared and
was observed for III and IV, respectively, assigned to the
Cu(II) ? Cu(I) processes [41, 42]. The values are some-
what higher than those of square planer Salen-type cop-
per(II) complexes, CuN O , indicating that the chelating
2
2
-
4
-3
ligands tend to destabilize copper(II) by p-delocalization of
electron density from metal center [43]. Furthermore,
Patterson and Holm [43] have shown that the redox prop-
erties of the copper(II) are influenced by coordination
number, stereochemistry, and the hard/soft character of the
ligand donor atoms. Therefore, the higher positive values
1-week-old solutions of 1 9 10 M and 1 9 10 M of IV
in DMSO, Fig. 10 (see also supporting information).
Judging from the intensity of the g \ 2 contribution in EPR
spectra, the level of aggregation in IV seems to increase
over time. To verify the effect of the solvent, the EPR
-
3
spectrum of 1 9 10 M freshly prepared solution of IV in
the strongly coordinable solvent, DMF, was recorded.
2
?
1?
of Cu /Cu redox potentials of III and IV may be due to
Fig. 9 The EPR and half-field
spectra of s compound IV and
their simulation diagrams
123

J IRAN CHEM SOC
Fig. 10 The time-dependent
EPR spectra of IV copper
complex in DMSO and DMF
solvents
Clearly, aggregation of IV is significantly diminished due
to saturation of coordination sphere of metal center with
DMF. In fact, the EPR spectrum of IV in DMF is quite
similar to that of III in same solvent, Figs. 8 and 10.
(Max Planck Institute for Chemical Energy Conversion) and
Zhe-Ming Wang (State Key Laboratory of Rare Earth Materials
Chemistry and Applications) for their help in magnetic measurements
Electronic supplementary material.
References
Conclusion
1
. K. Tenza, M.J. Hanton, A.M.Z. Slawin, Organometallics 28,
4852 (2009)
In the present study direct synthesis of new mononuclear
Cu(II) complexes of 1,2,4-triazole-based macrocyclic
Schiff base hydrazones have been reported. The powder
XRD studies in various temperatures showed that the
prepared complexes, III and IV, are amorphous. Electron
spray ionization mass spectra of III and IV are in agree-
ment with the presence of mononuclear complex in DMF/
MeOH solution. The magnetic moment of III and IV at
2
3
. U. Beckmann, S. Brooker, Coord Chem Rev 254, 17 (2003)
. T. R u¨ ther, M.C. Done, K.J. Cavell, E.J. Peacock, B.W. Skelton,
A.H. White, Organometallics 20, 5522 (2001)
4
5
. D.W.J. Kwong, O.Y. Chan, R.N.S. Wong, S.M. Musser, L. Vaca,
S.I. Chan, Inorg Chem 36, 1276 (1997)
. P.M. Guha, H. Phan, J.S. Kinyon, W.S. Brotherton, K. Sreenath,
J.T. Simmons, Z. Wang, R.J. Clark, N.S. Dalal, M. Shatruk, L.
Zhu, Inorg Chem 51, 3465 (2012)
6
. J.A. Kitchen, S. Brooker, Coord Chem Rev 252, 2072 (2008)
2
90 K is slightly larger than the spin-only value for one
7. J. Olgu ´ı n, S. Brooker, Coord Chem Rev 255, 203 (2011)
8
9
. M.H. Klingele, S. Brooker, Coord Chem Rev 241, 119 (2003)
. H. Liu, J. Tian, Y. Kou, J. Zhang, L. Feng, D. Li, W. Gu, X. Liu,
D. Liao, P. Cheng, J. Ribas, S. Yan, J Chem Soc, Dalton Trans
isolated Cu(II) center which may be arising from weak
spin–orbit interaction in square pyramidal structures. The
interaction between the copper(II) ions is clearly recog-
nizable in the EPR spectra of complexes in frozen DMSO.
It seems probable that the interaction between two cop-
per(II) ions is derived from the cooperative exchange
through the coordinated bridging solvents.
4
8, 10511–10517 (2009)
10. P.A. Vigato, S. Tamburini, L. Bertolo, Coord Chem Rev 251,
311 (2007)
1
1
1
1. J.G. Haasnoot, Coord Chem Rev 200–202, 131 (2000)
´
2. A. Noble, J. OlguIn, R. Cl e´ rac, S. Brooker, Inorg Chem 49, 4560
(
2010)
3. B. Shivarama Holla, B. Veerendra, M.K. Shivananda, B. Poojary,
1
Acknowledgments We are grateful to the Arak University
Eur J Med Chem 38, 759 (2003)
14. H. Khanmohammadi, M. Erfantalab, Spectrochim. Acta (A) 86,
39 (2012)
(
(
I. R. Iran) and Max Planck Institute for Bioinorganic Chemistry
Germany) for financial support of this work. We thank Dr. Eckhard Bill
1
23

J IRAN CHEM SOC
1
5. E. Alcalde, M. Gisbert, C. Alvarez-Rtia, S. Garcia-Granda, Tet-
rahedron 52, 15189 (1996)
31. J. Madejov a´ , L. Jankovi cˇ , M. Pentr a´ k, P. Komadel, Vib Spectrosc
57, 8 (2011)
1
6. N. Foroughifar, A. Mobinikhaledi, S. Ebrahimi, H. Moghanian,
M.A. Bodaghi Fard, M. Kalhor, Tetrahedron Lett 50, 836 (2009)
7. A.A. Abbas, Tetrahedron 60, 1541 (2004)
32. G.A. Van Albada, I. Mutikainen, U. Turpeinen, J. Reedijk,
Polyhedron 26, 2728 (2007)
1
1
33. B.T. Op‘t Holt, M.A. Vance, L.M. Mirica, D.E. Heppner, T.D.P.
Stack, E.I. Solomon, J Am Chem Soc 131, 6421 (2009)
34. Y.J. Kim, C.R. Park, Inorg Chem 41, 6211 (2002)
35. J. Lisowski, P. Starynowicz, Inorg Chem 38, 1351 (1999)
36. N.R.S. Kumar, M. Nethiji, K.C. Patil, Polyhedron 10, 365 (1991)
37. V. Katovi c´ , L.T. Taylor, D.H. Busch, Inorg Chem 10, 458 (1971)
38. G.G. Mohamed, C.M. Sharaby, Spetrochim. Acta (A) 66, 949
(2007)
39. E.N. Baker, D. Hall, T.N. Waters, J. Chem. Soc. (A) 92, 406
(1970)
40. R.C. Elder, M.C. Hill, Inorg Chem 18, 729 (1979)
41. C.C. Chou, C.C. Su, H.L. Tsai, K.H. Lii, Inorg Chem 44, 628
(2005)
42. G.E. Gurr, Acta Crystallogr B 24, 1511 (1968)
43. G.S. Patterson, R.H. Holm, Bioinorg. Chem. 4, 257 (1975)
44. A.W. Addison, H.M.J. Hendriks, J. Reedijk, L.K. Thompson,
Inorg Chem 20, 103 (1981)
45. M. Ciampolini, N. Nardi, Inorg Chem 5, 41 (1966)
46. G. Albertin, E. Bordignon, A.A. Orio, Inorg Chem 14, 1411
(1975)
8. C.D. Brandt, J.A. Kitchen, U. Beckmann, N.G. White, G.B.
Jameson, S. Brooker, Supramol Chem 19, 17 (2007)
9. U. Beckmann, J.D. Ewing, S. Brooker, Chem Commun 15, 1690
1
2
2
2
2
2
(2003)
0. C.V. Depree, U. Beckmann, K. Heslop, S. Brooker, J Chem Soc,
Dalton Trans 7, 3071 (2003)
1. U. Beckamann, S. Brooker, C.V. Depree, J.D. Ewing, B. Mou-
baraki, K.S. Murray, J. Chem. Soc. Dalton Trans. 7, 1308 (2003)
2. J.M. Alonso, M.R. Martin, J. de Mendoza, T. Torres, Heterocy-
cles 26, 989 (1987)
3. J.A. Duro, J.M. Ontoria, A. Sastre, W. Schafer, T. Torres, J Chem
Soc, Dalton Trans 94, 2595 (1993)
0
4. B. Cabezo n, A. Sastre, T. Torres, W. Schafer, J.J. Borras-Al-
menar, E. Coronado, J Chem Soc, Dalton Trans 35, 2305 (1995)
5. J.R. Reid, N.D. Heindel, J Heterocycl Chem 13, 925 (1976)
¯
6. H. Okawa, S. Kida, Bull Chem Soc Jpn 45, 1759 (1972)
7. S. Stoll, A. Schweiger, J Magn Reson 178, 42 (2006)
8. E. Bill. Available online at: www.cec.mpg.de
9. F. Bentiss, M. Lagrene’e, J.P. Wignacourt, E.M. Holt, Polyhe-
dron 21, 403 (2002)
2
2
2
2
2
47. M. Duggan, N. Ray, B. Hathaway, G. Tomlinson, P. Briant, K.
Plein, J Chem Soc, Dalton Trans 20, 1342 (1980)
3
0. K.J. Schenk, S. Meghdadi, M. Amirnasr, M.H. Habibi, Polyhe-
dron 26, 5448 (2007)
123