Some new IIB group complexes of an imidazolidine ligand: Synthesis, spectral characterization, electrochemical, thermal and antimicrobial properties

Article abstract of DOI:10.1007/s12039-013-0555-y

An imidazolidine Schiff base ligand, (E)-N-(4-nitrobenzylidene)-2-(2-(4- nitrophenyl) imidazolidine- 1-yl) ethaneamine (L) has been synthesized by a condensation reaction between N′-(2-aminoethyl)- ethane-1,2-diamine and 4-nitrobenzaldehyde in 1:2 ratio a

Full text of DOI:10.1007/s12039-013-0555-y

c
J. Chem. Sci. Vol. 126, No. 1, January 2014, pp. 227–238. ꢀ Indian Academy of Sciences.
Some new IIB group complexes of an imidazolidine ligand: Synthesis,
spectral characterization, electrochemical, thermal and antimicrobial
properties
MORTEZA MONTAZEROZOHORIa,∗, SAYED ALIREZA MUSAVIa, ASGHAR NAGHIHAb
and SOMAYEH VEYSEHc
aDepartment of Chemistry, Yasouj University, Yasouj 75918-74831, Iran
bDepartment of Animal Sciences, Faculty of Agriculture, Yasouj University, Yasouj 75918-74831, Iran
cApplied Geological Research Center of Iran, No 7, Sarbazane Gomnam Blvd, Samad Naghdi 31746-74841,
Iran
e-mail: mmzohori@mail.yu.ac.ir; mmzohory@yahoo.com
MS received 24 June 2013; revised 28 October 2013; accepted 5 November 2013
Abstract. An imidazolidine Schiff base ligand, (E)-N-(4-nitrobenzylidene)-2-(2-(4-nitrophenyl) imidazo-
lidine-1-yl) ethaneamine (L) has been synthesized by a condensation reaction between Nꢁ-(2-aminoethyl)-
ethane-1,2-diamine and 4-nitrobenzaldehyde in 1:2 ratio and then characterized by physical and spectral data.
Some new complexes with general formula of MLX2(wherein M is Zn(II),Cd(II) and Hg(II) and X is chloride,
bromide and/or iodide) have been prepared and characterized by physical and spectroscopic studies such as ele-
mental analysis, molar conductance measurements, FT-IR, 1H and 13C NMR and UV–Visible electronic spectra.
The spectral data indicate that the ligand is coordinated to zinc(II) as a bidentate ligand in imidazolidine form
but it binds to other metal salts as bis-imine tridentate ligand. Furthermore, cyclic voltammetry technique was
applied for recording the electrochemical behaviour of the ligand and its complexes. Cyclic voltamogram of
the ligand showed that it is reduced at four cathodic potentials and then oxidized only in two anodic potentials
in reverse direction. The electrochemical behaviour of ligand is affected by coordination. Thermal analysis of
ligand and its complexes revealed that they are decomposed via 3-4 thermal steps. Moreover, some activation
thermodynamic parameters such as A, E*, ꢀH*, ꢀS* and ꢀG* were calculated based on TG/DTA plots using
Coats–Redfern relation. The Schiff base ligand and its complexes have also been tested in vitro to evaluate their
antimicrobial activities.
Keywords. Schiff base; spectroscopic; cyclic voltammetry; antibacterial; antifungal; thermogravimetry.
epoxides.11–15 Furthermore, many biological properties,
such as DNA cleavage activity,16 biomimetic enzyme
models,17–19 tumour growth inhibitors, antivirus, anti-
HIV, antifungal and antibacterial activities20–24 have
also been reported for these type of compounds. A
literature survey indicates that though many reports
exist on the Schiff bases, their complexes and bio-
logical applications but the synthesis and investiga-
tion of some properties such as electrochemical, ther-
mal and biological behaviour of N2 and N3 donor
Schiff bases and their IIB group element complexes are
scanty.
In continuation of our previous studies on transi-
tion metal Schiff base complexes,25–30 here we report
the synthesis and spectral characterization of a new
series of MLX2 complexes in which M is Zn(II),
Cd(II) and Hg(II); X is Cl−, Br−, I− and L is Schiff
base ligand, (E)-N-(4-nitrobenzylidene)-2-(2-(4-nitro-
phenyl)imidazolidin-1-yl) ethaneamine. Furthermore,
1. Introduction
The wide variety of possible structures for the Schiff
base ligands depending upon the parent aldehydes and
amines has resulted in the fast development of the
chemistry of them and their complexes. Schiff base
ligands as a highlighted class of organic compounds
generally contain O and N donor atoms that are used
for coordination to the metal ions.1–6 In recent years,
the Schiff base complexes have been found as one
important group of the coordination compounds due
to their valuable biochemical, analytical and antimicro-
bial properties.7–10 The Schiff base complexes are also
applied as catalysts for a broad range of organic con-
version including epoxidation of olefins, decarboxyla-
tion of arylacetic acids, hydroxylation of alkanes, poly-
merization of lactides and asymmetric ring opening of
∗For correspondence
227

228
Morteza Montazerozohori et al.
the electrochemical, antibacterial, antifungal and ther- 2.2 Synthesis of (E)-N-(4-nitrobenzylidene)-2-(2-(4-
mal behaviour of all compounds were investigated.
nitrophenyl)imidazolidine-1-yl) ethaneamine
as an imidazolidine Schiff base ligand
A solution of 4-nitrobenzaldehyde (0.302 g, 2 mmol)
in methanol (20 mL) was added drop-wise to methano-
lic solution of Nꢁ-(2-aminoethyl)-ethane-1,2-diamine
(0.103 g, 1 mmol) (10 mL) at room temperature and
then the reaction mixture was vigorously stirred. After
3 h, the ligand as a cream precipitate was filtered and
washed twice with cooled methanol and then dried
on the vacuum apparatus. Some important FT/IR, UV-
visible, 1HNMR and 13CNMR data are listed in below:
2. Experimental
2.1 Materials and methods
All solvents, Nꢁ-(2-aminoethyl)-ethane-1,2-diamine, 4-
nitrobenzaldehyde, zinc, cadmium and mercury salts
and other chemicals were provided from Aldrich and/or
Merck chemical companies and used without any fur-
ther purification. For biological tests, the solid medium
of nutrient agar (Merck, Germany) was used for prepar-
ing the nutrient plates while Mueller Hinton broth
(Scharlab) was applied as the liquid culture media.
Sabouraub dextrose agar (Oxoid, Hampshire, England)
was used as solid media for preparing the plates in anti-
fungal studies. The Escherichia coli (ATCC 25922),
Pseudomonas aereuguinosa (ATCC 9027), Staphylo-
coccus aureus (ATCC 6538) and Bacillus subtilis
(ATCC 6633) were used as Gram-negative or posi-
tive bacterial strains in antibacterial activity evalua-
tions. The FT-IR spectra of compounds were recorded
on the FT/IR-JASCO-680 model in the range of 400–
4000 cm−1 using KBr disks. Elemental analysis (C, N
and H) was carried out by a CHNS-932(leco) elemen-
tal analyzer. UV-Visible spectra of compounds were
recorded by a JASCO-V570 spectrometer in the range
IR(KBr, cm−1): 3434(m), 3209(m), 3101(w), 3071(w),
2941(w), 2886(w), 2848(w), 1645(s), 1601(s),
1518(vs), 1346(vs), 1293(w), 1106(w), 1065(w),
1013(w), 943(w), 851(s), 830(m), 749(s), 692(s),
462(w).UV-Vis [(DMF), λ(nm) (ε,
M
−1 cm−1)]:
278(16991). 1H NMR (CDCl3,ppm): 8.33(s, 1H),
8.30(d, 2H, J = 8.76 Hz), 8.18(d, 2H, J = 8.76 Hz),
7.88(d, 2H, J = 8.80 Hz), 7.69(d, 2H, J = 8.60 Hz),
4.40(s, 1H), 3.76–2.61(m, 8Hethylenic and HNH).13C
NMR (CDCl3, ppm): 159.56, 148.56, 141.44, 129.98,
129.82, 128.72, 123.98, 123.72, 82.37, 61.10, 53.51,
53.46, 45.30.
2.3 Synthesis of MLX2 complexes (M = Zn(II), Cd(II)
and Hg(II) and X = Cl−, Br−, I−)
of 200–800 nm in DMF solution. H and 13C NMR
1
Imidazolidine Schiff base ligand (0.369 g, 1 mmol) was
dissolved in 20 mL of absolute ethanol and then gradu-
ally added to methanolic solution of chloride, bromide
and/or iodide salts of zinc (II), cadmium (II) and mer-
cury (II) (1 mmol) and the mixture was continuously
stirred at room temperature. The resultant precipitates
were filtered off and washed with cooled ethanol and
then recrystallized from dichloromethane/ethanol mix-
ture solvent (1:1) and finally dried on the vacuum appa-
ratus. Some important FT/IR, UV-visible, 1HNMR and
13CNMR data are listed in below:
spectra were obtained by use of a Brucker DPX FT-
NMR spectrometer at 400 MHz in DMSO-d6 and/or
CDCl3 solvents using TMS as internal standard. Molar
conductivities of the Schiff base ligand and its metal
complexes were measured in DMF solution (1.0 ×
10−3 M) by means of a Metrohm 712 conductometer
at room temperature. The melting points or decompo-
sition temperature (◦C) of the ligand and its complexes
were recorded by a Kruss instrument. Thermogravimet-
ric analyses of the compounds have been studied by use
of STA 1500, Rheo Metric Scientific instrument in the
range of room temperature to 600◦C. Cyclic voltam- [ZnLCl2]. IR(KBr, cm−1): 3500(m), 3253(s), 3103(w),
metric (CV) measurements were performed using a 3068(w), 2957(w), 2935(w), 2852(w), 1649(s),
three-electrode configuration cell connected to Sama 1602(s), 1522(vs), 1348(vs), 1218(w), 1106(w),
500 (electroanalysis system) equipped with glassy car- 1064(w), 1018(w), 916(w), 855(s), 832(s), 747(s),
bon as working electrode, Pt-disk as an auxiliary elec- 693(s), 584(w), 492(w).UV-Vis [(DMF), λ(nm) (ε,
trode and a silver wire as the reference electrode. 50 mL M−1 cm−1)]: 279(20096).1H NMR (DMSO-d6, ppm):
of sample solutions (10−3 M) in acetonitrile as well as 8.43(s, 1H), 8.30(d, 2H, J = 8.76 Hz), 8.11(d, 2H, J
(n-Bu)4NPF6 (TBAHFP) (10−3 M) as supporting elec- = 8.72 Hz), 7.94(d, 2H, J = 8.88 Hz), 7.69(d, 2H, J
trolyte were used for the CV record under argon atmo- = 8.64 Hz), 4.41(s, 1H), 3.90–2.50(m, 8Hethylenic and
sphere. A potential window of −2.0 to 0.5 V with a scan
H
NH). 13C NMR (DMSO-d6, ppm): 160.03, 149.13,
rate of 0.1 VS−1 was considered for electrochemical 148.45, 147.14, 141.59, 129.34, 128.79, 123.88,
investigation. 123.05, 81.16, 59.87, 53.08, 52.68, 44.80.

Some new IIB group complexes of an imidazolidine ligand
229
[ZnLBr2]. IR(KBr, cm−1): 3445(m), 3252(s), 3102(w),
3069(w), 2954(w), 2933(w), 2850(w), 1647(s),
1602(s), 1522(vs), 1347(vs), 1217(w), 1106(w),
1083(w), 1014(w), 916(w), 854(s), 831(s), 746(s),
692(s), 582(w), 491(w).UV-Vis [(DMF), λ(nm) (ε,
M−1 cm−1)]: 279(15586).1H NMR (CDCl3, ppm):
8.70(s, 2H), 8.37(d, 4H, J = 8.80 Hz), 8.14(d, 4H,
J = 8.90 Hz), 4.60(m, 4H), 3.37(m, 2H), 3.30(m, 2H),
3.10(m, 1H).13C NMR (CDCl3, ppm): 163.85, 155.65,
145.30, 130.49, 124.12, 59.62, 49.65.
NMR(CDCl3, ppm): 163.36, 149.54, 139.80, 129.86,
124.02, 59.71, 50.25.
2.4 Biological activity
Antibacterial and antifungal activities of ligand and its
complexes were tested in vitro. For these antimicro-
bial investigations, two Gram-negative bacterial strains
such as Escherichia coli and Pseudomonas aeruginosa;
two Gram-positive bacterial strains such as Staphylo-
coccus aureus and Bacillus subtillis and also the fungus
of Candid albicans were selected as a typical fungal
strain. The biological activities of all compounds were
confirmed by determination of the minimum inhibitory
concentration (MIC) values by sample dilution and disk
diffusion methods. In MIC method that was used for
antibacterial studies, a series of sample solutions with
various concentrations (500 to 15.63 μg/mL) were pre-
pared in DMSO in the sterile test tubes. For the bioassay
of the organisms, Muller Hinton broth as basal media
was added to the test tubes containing 0.1 mL of bac-
terium and then, these test tubes were incubated at 37◦C
[ZnLI2]. IR(KBr,cm−1): 3435(m), 3251(s), 3102(w),
3069(w), 2938(w), 2884(w), 2842(w), 1647(s),
1601(s), 1520(vs), 1438(w), 1346(vs), 1217(w),
1105(w), 1083(w), 1009(w), 934(w), 851(s), 834(m),
746(s), 692(s), 583(w), 479(w).UV-Vis [(DMF), λ(nm)
(ε, M−1 cm−1)]: 277(17528).1H NMR (CDCl3, ppm):
8.71(s, 2H), 8.37(d, 4H, J = 8.84 Hz), 8.16(d, 4H, J =
8.84 Hz), 4.06(m, 4H), 3.31(m, 4H), 3.14(m, 1H).13C
NMR (CDCl3, ppm): 165.95, 151.70, 140.50, 130.79,
124.02, 58.33, 48.78.
[CdLCl2]. IR(KBr, cm−1): 3443(m), 3278(s), 3102(w), for 24 h. For preparation of solid media in disk dif-
3071(w), 2947(w), 2861(w), 2842(w), 1638(s), fusion method, 15 mL of nutrient agar for antibacte-
1599(s), 1517(vs), 1444(w), 1347(vs), 1215(w), rial and sabouraub dextrose agar for antifungal stud-
1101(w), 1011(w), 941(w), 849(m), 830(m), 747(s), ies were poured into each petri-plate. Then 0.1 mL of
690(s), 509(w), 479(w).UV-Vis [(DMF), λ(nm) (ε, inoculums of the microorganism (18 h old culture) was
M
−1 cm−1)]: 274(14802).1H NMR(DMSO-d6, ppm): swabbed evenly on surface of solid medium and kept
8.63(s, 2H), 8.29(d, 4H, J = 8.44 Hz), 8.08(d, 4H, J = for suitable adsorption for 15 min. Sterile paper disks
8.48 Hz), 3.12(bs, 4H), 2.93(m, 4H), 3.11(m, 1H).13C (6 mm in diameter) were saturated with a desired solu-
NMR (DMSO-d6, ppm): 161.76, 148.57, 141.21, tion of test compounds that has been prepared in DMSO
129.37, 123.69, 59.14, 49.11.
(500 μg/mL) and then placed on the agar plates. All
the plates were incubated at 37◦C for 24 h and then
the diameters of inhibition zones of the growth were
measured by a vernier caliper.
[CdLI2]. IR(KBr, cm−1): 3444(m), 3275(s),
3100(w), 3071(w), 2921(w), 2870(w), 1639(s),
1601(s), 1520(vs), 1423(w), 1344(vs), 1219(w),
1101(w), 1010(w), 935(w), 851(s), 837(s), 746(s),
693(s), 577(w), 491(w).UV-Vis [(DMF), λ(nm) (ε,
3. Results and discussion
M
−1 cm−1)]: 275(18437).1H NMR(CDCl3, ppm):
The (E)-N-(4-nitrobenzylidene)-2-(2-(4-nitrophenyl)
imidazolidin-1-yl) ethaneamine as a new imidazolidine
Schiff base ligand was prepared by a condensation
reaction between 4-nitrobenzaldehyde and Nꢁ-(2-
aminoethyl)-ethane-1, 2-diamine in 2:1 molar ratio
in dry methanol. Then, some of its new complexes
of zinc, cadmium and mercury halides were well-
synthesized and their structures were confirmed by
elemental analysis and also by FT/IR, UV-visible,1H
and 13C NMR spectral data. Figure 1 illustrates the
suggested structure of free ligand and its complexes.
The resultant complexes (tables 1 and 2) are coloured
solids and are suggested to be as non-electrolyte
complexes as evidenced by their molar conductivities
8.61(s, 2H), 8.37(d, 4H, J = 8.80 Hz), 8.17(d, 4H,
J = 8.76 Hz), 4.60(bt, 2H), 3.88(bd,2H), 3.38(m, 2H),
3.25(m, 2H), 2.59(m, 1H).13C NMR (CDCl3, ppm):
165.50, 148.15, 140.48, 131.04, 123.98, 59.73, 49.87.
[HgLI2]. IR(KBr, cm−1): 3446(m), 3215(s), 3102(w),
3074(w), 2901(w), 2881(w), 2852(w), 1639(s),
1600(s), 1519(vs), 1461(w), 1340(vs), 1217(w),
1104(w), 1008(w), 917(w), 849(m), 838(m), 747(s),
686(s), 528(w), 487(w).UV-Vis [(DMF), λ(nm) (ε,
M−1 cm−1)]: 279(19540).1H NMR(CDCl3, ppm):
8.59(s, 2H), 8.33(d, 4H, J = 8.76 Hz), 8.04(d, 4H, J =
8.80 Hz), 3.95(t, 4H), 3.25(bs, 4H), 2.49(bs, 1H).13C

230
Morteza Montazerozohori et al.
(a)
(b)
(c)
e
e
f
e
k
j
g
g
g
f
h
f
i
i
k
i
h
k
d
d
h
d
j
j
6
7
6
6
7
8
7
8
9
9
5c
5c
c'
5c
N
N
NH
N
N
NH
N
NH
N
l
l
l
4
4
4
3b
3b
10m
3b
Zn
10m
n
11
11
12n
13o
12n
13o
Cl
Cl
M
2a
2a
o
3'b'
3'b'
2a
n'
b'
12'n'
13'o'
12'n'
13'o'
X
X
2'a'
2'a'
1
a'
1
o'
14
1
14
O2N
O2N
O2
N
NO2
NO2
NO2
Figure 1. Proposed structure for ligand (a), ZnLCl2 complex (b) and MLX2 wherein M = Zn(II), X = Br−, I−; M = Cd(II),
Hg(II) and X = Cl−, Br−, I−.
(5–28 ꢁ−1 cm2 mol−1) of their solutions (10−3 M) in
dry DMF.31 All compounds are very stable at room
temperature in the solid state. The decomposition tem-
peratures of the complexes were evaluated in the span
of 145–241◦C. Elemental analyses and other physical
properties of the ligand and its complexes are summa-
rized in table 1. The results of the elemental analyses
are in a good agreement with the proposed formula.
proves that the azomethine nitrogen atoms are coor-
dinated to the metal ions. In the ligand spectrum, the
stretching vibration of N–H is appeared as a broad peak
at 3210 cm−1 because of its involvement at probable
hydrogen bonding. This vibration is more sharp and
shifted to higher vibrational frequencies in the com-
plexes spectra except for the complexes of entries 6 and
8.33 The absorption frequencies of aromatic, aliphatic
and azomethine CH bonds are observed at 3101 and
3071, 2941, 2886 and 2848 cm−1, respectively. These
absorption peaks have not considerable shift to the
higher or lower frequencies in all complexes spec-
tra. The very strong stretching vibrations at 1518 and
1346 cm−1 are attributed to the asymmetric (νasym) and
symmetric stretching (νsym) of –NO2 groups that they
shift a few wavenumbers to lower or higher frequencies
in the complexes spectra. One of the important absorp-
tion frequencies in the complexes spectra confirming
their synthesis is the vibrational frequency of M–N
bond that appeared at the range of 530–584 cm−1 in the
complexes spectra.34,35 This characteristic absorption
peak is not observed in the ligand spectrum (table 2).
Electronic spectra of the ligand and its complexes
were recorded in DMF at room temperature and their
spectral data including the λmax values are tabulated
3.1 Infra-red and electronic spectra
The characteristic frequencies of the ligand and its
complexes spectra are tabulated in table 2. In the
IR spectrum of ligand, the vibrational frequencies
assigned to the parent amine and aldehyde com-
pounds were not found. On the other hand, appear-
ance of a strong absorption frequency at 1645 cm−1
attributed to the vibrational stretching of the azome-
thine group, ν(C=N),32 indicates that the titled ligand
has been successfully synthesized via a condensation
reaction. This absorption frequency is smoothly shifted
towards higher frequencies in zinc complexes while
shifted to lower frequencies in the cadmium and mer-
cury complexes spectra. Observation of these changes
in the vibrational frequencies of azomethine groups
Table 1. Analytical and physical data of the imidazolidine Schiff base ligand and its zinc (II), cadmium (II) and mercury
(II) complexes.
Compound
Colour
Melting point
(dec.)
Yield (%)
Found (calcd.) (%)
N
ꢂM
(cm2 ꢁ−1M−1
)
C
H
1
2
3
4
5
6
7
Ligand
ZnLCl2
ZnLBr2
ZnLI2
CdLCl2
CdLI2
Cream
Cream
Cream
Cream
Cream
Cream
Cream
108*
224
235
241
220
229
145
68
75
76
80
72
85
80
58.3 (58.53)
42.3 (42.75)
36.3 (36.36)
31.2 (31.40)
38.9 (39.12)
29.2 (29.39)
26.1 (26.24)
18.8 (18.96)
13.5 (13.85)
11.7 (11.78)
10.3 (10.17)
12.8 (12.67)
9.5 (9.52)
5.1 (5.18)
3.4 (3.79)
3.1 (3.22)
2.5 (2.78)
3.2 (3.47)
2.4 (2.60)
2.2 (2.32)
5
10
15
19
18
28
13
HgLI2
8.4 (8.50)
*melting point

Some new IIB group complexes of an imidazolidine ligand
231
Table 2. Vibrational (cm−1) and electronic (nm) spectral data of the imidazolidine Schiff base ligand and its complexes.
Compound νNH
νCHarom
νCHaliph
νCHimin
νC=N νC=C
ν(-NO2)
νM–N λmax
1
2
3
4
5
6
7
Ligand
ZnLCl2
ZnLBr2
ZnLI2
CdLCl2
CdLI2
3210
3253
3252
3251
3278
3275
3214
3101, 3071
3103, 3068 2957, 2935
3102, 3069 2954, 2933
3102, 3069
3102, 3071
3100, 3071
3102, 3074
2941
2886, 2848
2852
1645
1649
1647
1647
1638
1639
1639
1601
1602
1602
1601
1599
1601
1600
1518, 1346
1522, 1348
1522, 1347
1520, 1346
1517, 1347
1520, 1344
1519, 1340
–
278
279
279
277
274
275
279
584
582
583
581
577
571
2850
2938
2947
2921
2901
2884, 2842
2861, 2842
2870
HgLI2
2881, 2852
in table 2. In the UV-visible spectrum of the ligand, In the spectra of the ligand and ZnLCl2 complex, the
two types of internal electronic transition (IT) assign- signal of HNH is overlapped by the signals of ethylenic
ing to π–π* electron transfer of aromatic rings and hydrogens and appeared at the range of 2.6–2.78 ppm
π–π* transition localized within the azomethine chro- and 3.2 ppm, respectively.36 In the 1H NMR spectra of
mophores are expected. Though it seems that these other complexes, this signal was observed in the range
absorption bands are overlapped with each other and of 2.49–3.14 ppm because of the structural change of
therefore one absorption band is appeared at 278 nm ligand in other complexes with respect to free ligand
in the electronic spectrum of the ligand. This absorp- and ZnLCl2 complex. The hydrogens of aromatic rings
1
tion band has not considerably changed in the elec- in the H NMR spectrum of ligand were appeared in
ꢁ
tronic spectra of the complexes. Electronic configura- the range of 7.69 to 8.30 ppm; Ha and a protons were
tion of IIB transition metal ion is d10 and therefore found at 8.30 ppm as doublet signal with J = 8.76 Hz
ꢁ
the d–d electronic transition are not expected for them. due to coupling with hydrogens of Hb and b . Protons
ꢁ
In the electronic spectra of the titled complexes, the of Ho and o were appeared at 8.18 ppm as a doublet
ꢁ
bands of charge transfer transition (MLCT) were also peak due to coupling with hydrogens of Hn and n . Two
not observed probably due to its overlap with π–π* doublet peaks at 7.88 and 7.69 ppm with J = 8.8 Hz
ꢁ
ꢁ
electronic transitions of the ligand.
and J = 8.6 Hz were assigned to Hb and b and Hn and n
,
respectively. The signals of the ethylenic hydrogens
were appeared at 2.61–3.76 ppm range as eight individ-
ual multiplet peaks due to formation of imidazolidine
ring leading to the asymmetrical character in ligand
structure. In the 1H NMR spectra of the complexes, the
signals of aromatic ring hydrogens were observed at
7.69–8.37 ppm and the signals of ethylenic hydrogens
were appeared at 2.50–4.60 ppm range. 1H NMR spec-
tra of the complexes showed the signals of Ha and a and
Ho and o as doublet peaks in the range of 8.29–8.37 ppm
except for entry 2. The same pattern was observed for
Hb and b and Hn and n at 8.04–8.17 ppm. The ethylenic
hydrogens of He,d, j, k were found as a multiplet peaks
at 3.12–4.60 ppm range. For the complex of entry 6,
Hd and j and He and k showed different chemical shifts
such that their peaks were appeared at 4.04 ppm and
3.88 ppm as a broad triplet and doublet, respectively.
3.2 1H and 13C NMR spectra
1
The H and 13C NMR spectral data of the ligand and
its metal complexes have been listed in the section 2.3.
1
The H NMR of ligand, ZnLCl2 and HgLI2 as typi-
cal spectra are exhibited in figure 2 and other spectra
are found as supplementary information (figures S1–
S12). The spectral data based on figure 1 show that
the structure of free ligand and coordinated one in
ZnLCl2 complex are not symmetric. Existence of an
imidazolidine ring in the structure of ligand both in
free form and in ZnLCl2 complex is well-confirmed
by a signal appeared at 4.40 and 4.41 ppm assigned
to imidazolidine C–H and also by a signal at 82.37
and 81.16 ppm attributed to C10 of imidazolidine ring
ꢁ
ꢁ
ꢁ
ꢁ
1
in H and 13C NMR spectra of ligand and its ZnLCl2
1
complex, respectively.36 These signals are not observed
The H NMR spectra of entries 4, 5 and 7 included
multiplet peaks at 2.93–3.31 ppm range for Hf, g, h, i
1
at the H and 13C NMR spectra of other Schiff base
.
complexes. According to 1H NMR spectrum of ligand,
the signal of proton resonance of azomethine group
(Hc) as a characteristic group of Schiff base compound
is appeared at 8.33 ppm as a singlet peak.37 Due to
binding of the azomethine nitrogen to metal centres, the
azomethine proton is more deshielded so that its signal
shifts to downfield region in the complexes spectra.
In the complexes spectra of entries 3 and 6, the signals
of Hf and h and Hg and i were observed at 3.37–3.38 ppm
and 3.25–3.30 ppm as multiplet peaks, respectively.
In some cases, it seems that the chemical shifts of
ethylenic hydrogens are affected by the spatial position
of HNH in the complexes structures and therefore are
appeared at different chemical shifts with respect to

232
Morteza Montazerozohori et al.
Figure 2. 1H NMR (a, b and c) of the ligand, ZnLCl2 and HgLI2, respectively.

Some new IIB group complexes of an imidazolidine ligand
233
TMS. The 13C NMR spectrum of the ligand showed the
azomethine carbon (C5) resonance as functional
group at 159.56 ppm. This peak is shifted to
160.03–165.95 ppm in its complexes suggesting
well-coordination of the azomethine nitrogens to
metal ions. In the 13C NMR spectrum of the ligand,
the resonance signals of aromatic carbons are sug-
gested to be appeared at 148.56(C1,14), 141.44(C4,11),
ion is zinc and halide is chloride, the coordination of
imidazolidine Schiff base ligand is possible as shown in
figure 1b but when the metal ion and/or halide anions
is changed to more voluminous and polarizable ones,
the electronic and steric effects prevent the coordination
of ligand as imidazolidine form. Therefore, imidazoli-
dine ring of ligand is opened during the coordination of
ligand as shown in figure 1c.
ꢁ
ꢁ
ꢁ
129.98(C12), 129.82(C12 ), 128.72(C3,3 ), 123.98(C2,2 ),
ꢁ
123.72(C13,13 ); imidazolidine carbon(C10) is found
3.4 Thermal investigation
at 82.37 ppm and the ethylenic carbons resonance
are observed as four individual peaks at 61.10(C8),
53.51(C6), 53.46(C9) and 45.30(C7) ppm. In the
13C NMR spectrum of ZnLCl2 complex containing
the retained structure of ligand, the peaks of aroma-
tic ring carbons and imidazolidine carbon may be as-
signed as 149.13(C1), 148.45(C14), 147.14(C4),
Thermal behaviour (TG/DTA) of the titled compounds
were investigated at the heating rate of 10 (◦C/min)
under nitrogen atmosphere from room temperature to
600◦C. TG/DTA plots of the ligand, zinc and mercury
iodide complexes as illustrative diagrams in figure 3.
Thermal analysis data including thermal decomposi-
tion steps, mass loss (%) and thermodynamic activation
parameters of each decomposition steps of the ligand
and its complexes have been derived and tabulated in
table 3 based on TG/DTA plots.
The TG diagrams confirm the absence of water
molecules in the complex structures. The TG/DTA
plots of ligand and its complexes indicate that they are
decomposed in four successive thermal steps except for
ZnLBr2 that is decomposed in three thermal steps. First
thermal step in the TG plots of all compounds may be
assigned to thermal elimination of nitro-groups. In the
next thermal steps, the ligand and its complexes lose
38.58–81.9% of total mass up to 600◦C attributed to
other organic segments as suggested in table 3.
ꢁ
ꢁ
ꢁ
141.59(C11), 129.34(C12,12), 128.79(C3,3), 123.88(C2,2 ),
ꢁ
123.05(C13,13 ) and 81.16 (C10) ppm, respectively.
On the other hand, the ethylenic carbons signals are
observed as four characteristic peaks at 59.87(C8),
53.08(C6), 52.68(C9) and 44.80(C7) ppm. In the13C
NMR spectra of other complexes, seven signals of
carbon resonances assigned to seven types of carbons
in the symmetric structures of them are obviously
observed. For these complexes, the azomethine car-
bon signals appeared at 161.76–165.95 ppm range
show a downfield shift with respect to one in free
ligand. Finally, the signals attributed to (C1), (C4),
(C3), (C2), (C6) and (C7) are found in the ranges
of 148.15–155.65, 139.80–145.30, 129.37–131.04,
123.69–124.12, 58.33–58.73 and 48.78–50.25 ppm in
the complexes spectra, respectively.
Moreover, the thermodynamic activation parameters
of thermal decomposition steps of the ligand and its
complexes including Arrhenius constant (A), activation
energy (E*), enthalpy (ꢀH*), entropy (ꢀS*) and Gibbs
free energy (ꢀG*) of thermal steps were evaluated
3.3 Coordination mode
With regard to spectral data, it is suggested that the li- using Coats–Redfern relation based on TG plots.40,41
gand is formed as imidazolidine Schiff base (figure 1a) Activation parameters evaluation of the ligand and its
not as a simple bis-azomethine ligand. This type of complexes may be carried out to suggest the ther-
Schiff base ligand has been previously reported by Yue mal stability of them. The resultant values showed
et al.36 The titled imidazolidine Schiff base is coordi- that the activation energies (E*) in the different steps
nated to zinc chloride without ring opening of the imi- of thermal decomposition processes are found in the
dazolidine and acts as a bidentate N2-ligand that along range of 22.57–352.69 kJmol−1 indicating relatively
with chloride anions forms pseudo-tetrahedral geo- high thermal stability of the compounds. The values of
metry around the zinc ion. Coordination of the li- the activation entropy (ꢀS*) are evaluated as negative
gand to other metal salts is accompanied with imidazo- numbers for all thermal decomposition steps of com-
lidine ring opening so that the ligand is coordinated to pounds except for the first thermal steps of ligand, zinc
metal centers as a tridentate bis-azomethine amine li- and cadmium iodide complexes and are found in the
gand such that five coordinated complexes are formed range of −266 − 409 Jmol−1 k−1. The negative values
along with halide anions similar to some other previ- suggest an associated mechanism at rate determining
ous reports.38,39 The change in coordination mode of step of thermal decomposition process similar to many
the ligand may be due to electronic and steric effect of reports in the literature in this matter. All evaluated
metal ion and its halide anions so that where the metal ꢀH* and ꢀG* values for the compounds are positive

234
Morteza Montazerozohori et al.
cyclic voltammetry technique in the potential win-
dow of −2.00 to 0.5 V in dry acetonitrile solution
containing (n-Bu)4NPF6(TBAHP) as supporting elec-
trolyte (10−3 M). The cyclic voltammogarms of lig-
and, zinc chloride and mercury iodide complexes have
been illustrated in figure 4 as representative diagrams
while all electrochemical data considered as poten-
tial window have been tabulated in table 4. Cyclic
voltammogram of ligand showed four cathodic and two
anodic potential peaks. The cathodic peaks(E were
)
pc
found at −0.81 V(I), −0.95 V(II), −1.35 V(III) and
−1.64 V(IV) while two anodic peaks(E ) were appeared
pc
at −0.74 V and −0.87 V in relative to I and II
cathodic potential peaks. The cathodic peaks appeared
at −0.81 V and −0.95 V may be corresponded to the
reduction of two different nitro-groups in the ligand
structure (as shown in figure 1) to nitro-anion radi-
cals and then to nitroso groups in one step, respec-
tively. These reduction steps are quasi-reversibly fol-
lowed (potential difference(ꢀEp) values are 0.070 V
and 0.080 V, respectively) by two anodic peaks as men-
tioned above. The irreversible cathodic peaks appeared
at −1.35 V and −1.64 V may be attributed to the reduc-
tion of the nitroso groups to the hydroxyl amine and
then to amine groups, respectively.42,43 Based on elec-
trochemical data in table 4, it seems that in zinc chlo-
ride and bromide complexes, the reduction of one nitro-
group to nitroso group have occurred via two differ-
ent steps (peaks IIa, IIb) (instead of one step observed
in free ligand as mentioned above) with anodic and
cathodic shifts for (I, IIa) and IIb with respect to free
ligand as shown in table 4 while other reduction peaks
(III and IV) are seen in a model similar to free li-
gand. The electrochemical behaviour of coordinated
ligand in zinc iodide is similar to free ligand but with an
anodic shift in its potential values. The anodic shift in
potential values of ligand in zinc complexes is due to its
coordination to metal centre and then induction of po-
sitive charge on ligand structure that facilitates its redox
behaviour. Voltammograms of cadmium chloride and
cadmium iodide complexes also show the same electro-
chemical behaviour as observed for the free ligand but
with a cathodic shift in redox potential values confirm-
ing a well-coordination of ligand. The cathodic shift
may be because of an induction of negative charge on
ligand structural surface because of an efficient π- back
bonding from cadmium ion as an electron-rich metal
ion to ligand π* orbitals(π* of iminic bond(C=N))
after initial coordination.44–46 For mercury iodide com-
plex, a electrochemical behaviour similar to coordi-
nated ligand in the cadmium complexes is observed
but the fourth reduction is not observed suggesting a
high cathodic shift to out of studied potential window.
Figure 3. TG/DTA diagrams of ligand (a), zinc iodide
complex (b) and mercury iodide complex (c).
numbers in the range of 17.5 to 348.53 kJmol−1 and 134
to 249 kJmol−1, respectively indicating endothermic
character of all thermal decomposition steps.
3.5 Cyclic voltammetry
The electrochemical behaviour of the Schiff base li-
gand and its complexes (10−3 M) were studied by

Some new IIB group complexes of an imidazolidine ligand
235
Table 3. Thermal analysis data including thermal decomposition steps, mass loss (%) and thermodynamic activation
parameters of thermal steps of ligand and its complexes.
Total
mass
Thermal
Mass
Compound step(◦C) loss(%) loss(%) E∗(kJmol−1
)
A(s−1
)
ꢀS∗(kJmol−1
)
ꢀH∗(kJmol−1 ꢀG∗(kJmol−1
)
Ligand
160–240
240–340
340–470
470–600
11.3
8.3
8.5
56.3
239.34
33.66
54.42
96.25
129.66
64.66
108.37
175.70
54.21
31.15
135.91
94.95
26.21
100.50
46.47
352.69
22.57
48.10
79.10
39.31
34.98
50.84
67.34
5.32 × 1023
2.99
2.05 × 102
–2.41 × 102
–2.20 × 102
–1.90 × 102
–5.26 × 101
–1.98 × 102
–1.76 × 102
3.42 × 101
235.39
29.08
48.84
89.26
125.33
59.22
101.39
171.31
49.34
25.83
128.96
90.85
21.44
94.77
39.82
348.53
17.57
42.04
72.22
35.51
29.69
44.59
60.34
1.38 × 102
1.62 × 102
1.96 × 102
2.49 × 102
1.53 × 102
1.89 × 102
2.49 × 102
1.53 × 102
1.70 × 102
1.88 × 102
2.47 × 102
1.45 × 102
1.68 × 102
1.96 × 102
2.43 × 102
1.44 × 102
1.77 × 102
2.18 × 102
2.46 × 102
1.34 × 102
1.88 × 102
2.22 × 102
2.49 × 102
4.61 × 101
1.99 × 103
1.95 × 1010
6.16 × 102
1.18 × 104
6.75 × 1014
2.23 × 102
8.06 × 10−1
7.03 × 105
1.90 × 107
5.63 × 10−1
3.03 × 105
8.50 × 10−1
2.29 × 1034
1.69 × 10−1
3.79
28.2
ZnLBr2
ZnLI2
200–310 11.04
38.58
58.13
310–430
430–600
210–285
285–340
340–415
3.04
24.5
9.04
4.9
–2.06 × 102
–2.53 × 102
–1.42 × 102
–1.10 × 102
–2.55 × 102
–1.47 × 102
–2.55 × 102
4.09 × 102
3.1
415–600 51.09
180–275 13.88
CdLCl2
CdLI2
HgLI2
46.38
59.46
81.90
275–360
360–455
455–600
210–265
265–380
380–500 15.00
500–600
120–230
4.00
3.00
25.5
8.13
8.43
–2.66 × 102
–2.41 × 102
–2.10 × 102
–2.15 × 102
–2.49 × 102
–2.36 × 102
–2.24 × 102
27.9
4.79
1.92 × 102
5.85 × 101
1.35
230–435 43.41
435–520 14.10
520–600
7.68
19.6
3.57 × 101
Furthermore, two new reversible redox potentials are two Gram-negative and two Gram-positive bacterial
observed at mercury iodide complex voltammogram as strains including Escherichia coli, Pseudomonas aerug-
Iꢁ and IIꢁ peaks that may be attributed to Hg(II)/(I) and inosa, Staphylococcus aureus and Bacillus subtillis bac-
Hg(I)/(0) redox pairs, respectively.
teria and also for their inhibitory effects on the growth
of Candid albicans using disc diffusion and MIC meth-
ods. The antibacterial activities of the ligand and its
complexes as inhibition zone (mm) of the bacterial
and fungal growth have been classified in table 5 and
also depicted as column diagram in figure 5. The solu-
tions with concentration of 500 μg/mL of Schiff base
ligand and its complexes in DMSO were applied in
disc diffusion technique. The effective material on each
disk was estimated to be 25 μg. The MIC method
was also peformed for all the compounds by use of
the sample solutions with 15.63, 31.25, 62.50, 125,
250, 500 μg/mL concentrations. The results showed
that the synthesized complexes are more antimicrobial
active as compared with their parent Schiff base li-
gand against the same bacteria and fungi under the same
experimental conditions. An increase in the inhibitory
effect of the complexes as compared with the free li-
gand may be discussed based on Overtone’s concept
and Tweedy’s chelation theory.47,48 The cell membrane
has been made from lipid layers that are permeable only
for lipid-soluble materials. The antibacterial activity of
3.6 Antibacterial and antifungal activity
The Schiff base ligand and its metal complexes were
tested in vitro for their antibacterial activities against
Figure 4. The cyclic voltammograms of ligand, ZnLCl2
and HgLI2 in dry acetonitrile.

236
Morteza Montazerozohori et al.
Table 4. The cyclic voltammetric data of imidazolidine Schiff base ligand and its complexes.
Compound
Ligand
Peak
Epc (V)
Epa (V)
ꢀEp (V)
I
II
III
IV
I
IIa
IIb
III
V
–0.81
–0.95
–1.35
–1.64
–0.69
–0.88
–1.01
–1.45
–1.65
–0.61
–0.88
–1.02
–1.5
–1.77
–0.76
–0.89
–1.45
–1.6
–0.88
–0.99
–1.45
–1.76
–0.92
–1.05
–1.66
–1.83
0.2
–0.74
–0.87
–
0.070
0.080
–
–
–
ZnLCl2
ZnLBr2
–0.64
–0.79
–0.95
–
0.050
0.090
0.060
–
–
–
I
–0.51
–0.76
–0.91
–
0.100
0.120
0.110
–
IIa
IIb
III
IV
I
–
–
ZnLI2
CdLCl2
CdLI2
HgLI2
–0.67
–0.82
–
0.090
0.070
–
II
III
IV
I
–
–
–0.79
–0.94
–
0.090
0.050
–
II
III
IV
I
–
–
–0.83
–0.98
–
0.090
0.070
–
II
III
IV
Iꢁ
–
–
0.32
–0.29
–1.02
–1.16
–
0.120
0.120
0.070
0.070
–
IIꢁ
I
–0.41
–1.09
–1.23
–1.67
II
III
a compound is depended on its liposolubility charac- metal ion and π-electron delocalization within whole of
ter. After coordination of organic ligand to metal cen- the ligand chelating ring that would certainly enhance
tre, the polarity of the metal ion considerably is reduced the lipophilic character of the central metal ion. The
due to overlap of its valence orbitals with the ligand increased lipophilicity character causes more diffusion
orbitals. This leads to a decrease in positive charge of of the complexes into cell membrane and blocks the
Table 5. Antibacterial and antifungal activities of 25 μg/disk of the imidazolidine Schiff bases ligand and its complexes
based on inhibition zone of the bacterial and fungal growth (mm) and their MIC values (μg/mL).
Gram-negative bacteria
Gram-positive bacteria
Candida
albicans
zone
Compound Escherichia coli
MIC zone
(μg/mL) (mm) (μg/mL)
Pseudomonas aereuguinosa Bacillus subtillis Staphylococcus aureus
MIC
zone
(mm)
MIC
zone
MIC
zone
(mm)
(μg/mL) (mm) (μg/mL)
(mm)
Ligand
ZnLCl2
ZnLBr2
ZnLI2
CdLCl2
CdLI2
500
250
500
250
125
500
125
11.50
15.50
12.20
15.20
16.19
11.50
17.66
500
500
500
500
125
250
125
6.80
8.44
7.90
8.60
10.60
9.80
500
250
500
500
125
65.50
65.50
14.46
17.00
15.00
14.80
17.70
23.80
23.40
500
250
500
125
250
250
62.50
10.00
12.00
11.50
16.20
15.90
16.00
21.90
17.40
24.80
21.80
18.50
22.20
17.80
26.50
HgLI2
10.70

Some new IIB group complexes of an imidazolidine ligand
237
Figure 5. The inhibiton zone of the growth of bacteria and fungus (mm) (the numbers refer to entries of the tables).
metal coordination sites of the enzymes in the bacte- Hg(I)/(0). TG/DTA plots of ligand and its complexes
ria and/or fungi structures. In the case of antibacte- have revealed that there are no water molecules in the
rial studies, it was observed that HgLI2 complex is the complex structure. Thermal analyses data of the ligand
most active compound against Staphylococcus aureus and its complex indicated that they are decomposed and
with a MIC value of 62.5 μg/mL. The growth of lose 38.58–81.9% of total mass from the room tem-
Escherichia coli and Pseudomonas aereuguinosa was perature to 600◦C. Finally, the antibacterial/antifungal
more efficiently inhibited by CdLCl2 and HgLI2 com- activities of the compounds were screened against two
plexes (MIC = 125 μg/mL) with respects to other com- Gram-negative and positive bacterial strains and also
pounds. Among the investigated compounds, HgLI2 a fungus. All complexes have shown more antibacte-
and CdLI2 complexes showed higher activities against rial/antifungal active compounds as compared with the
Bacillus subtillis with respect to others. The antifungal free ligand.
activities of the ligand and its complexes were checked
by disc diffusion method and the results revealed that
the inhibitory effect of the ligand was enhanced after
Supplementary information
its chelation to metal ions. In this investigation, it was
Figures S1–S12 as supplementary information can be
recognized that HgLI2 complex efficiently prevents the
seen at www.ias.ac.in/chemsci website.
growth of Candid albicans as compared with free li-
gand. Finally, zinc chloride, zinc bromide, cadmium
chloride, zinc and cadmium iodide were found in the
next positions in the antifungal activity point of view
with respect to free ligand.
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