Supramolecular structure, spectroscopic, thermal studies and antimicrobial activities of Schiff base complexes

Article abstract of DOI:10.1007/s11164-016-2641-5

Metal(II) complexes of 4-(((2-hydroxynaphthalen-1-yl)methylene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HL) were prepared, and their compositions and physicochemical properties were characterized on the basis of elemental analysis, with<

Full text of DOI:10.1007/s11164-016-2641-5

Res Chem Intermed
DOI 10.1007/s11164-016-2641-5
Supramolecular structure, spectroscopic, thermal
studies and antimicrobial activities of Schiff base
complexes
1
1
•
A. Z. El-Sonbati
1
•
A. A. El-Bindary
2
•
M. A. Diab
E. E. Abdo
•
M. I. Abou-Dobara
1
Received: 22 April 2016 / Accepted: 5 July 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract Metal(II) complexes of 4-(((2-hydroxynaphthalen-1-yl)methylene)
amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HL) were prepared,
and their compositions and physicochemical properties were characterized on the
1
basis of elemental analysis, with HNMR, UV–Vis, IR, mass spectroscopy and
thermogravimetric analysis. All results confirm that the novel complexes have a 1:1
(
M:HL) stoichiometric formulae [M(HL)Cl2] (M = Cu(II)(1), Cd(II)(5)),
Cu(L)(O NO)(OH ) ](2), [Cu(HL)(OSO )(OH ) ]2H O(3), [Co(HL)Cl (OH ) ]3-
H O(4), and the ligand behaves as a neutral/monobasic bidentate/tridentate forming
[
2
2 2
3
2 3
2
2
2 2
2
a five/six-membered chelating ring towards the metal ions, bonding through
azomethine nitrogen, exocyclic carbonyl oxygen, and/or deprotonated phenolic
oxygen atoms. The XRD studies show that both the ligand and Cu(II) complex (1)
show polycrystalline with monoclinic crystal structure. The molar conductivities
show that all the complexes are non-electrolytes. On the basis of electronic spectral
data and magnetic susceptibility measurements, a suitable geometry has been pro-
posed. The trend in g values (g [ g [ 2.0023) suggest that the unpaired electron
ll
\
on copper has a d
2
2
character, and the complex (1) has a square planar, while
x Ày
complexes (2) and (3) have a tetragonal distorted octahedral geometry. The
molecular and electronic structures of the ligand (HL) and its complexes (1–5) have
been discussed. Molecular docking was used to predict the binding between HL
ligand and the receptors of the crystal structure of Escherichia coli (E. coli) (3t88)
and the crystal structure of Staphylococcus aureus (S. aureus) (3q8u). The activa-
tion thermodynamic parameters, such as activation energy (E ), enthalpy (DH),
a
entropy (DS), and Gibbs free energy change of the decomposition (DG) are
&
A. Z. El-Sonbati
elsonbatisch@yahoo.com
1
2
Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
Botany Department, Faculty of Science, Damietta University, Damietta, Egypt
123

A. Z. El-Sonbati et al.
calculated using Coats–Redfern and Horowitz–Metzger methods. The ligand and its
metal complexes (1–5) showed antimicrobial activity against bacterial species such
as Gram positive bacteria (Bacillus cereus and S. aureus), Gram negative bacteria
(E. coli and Klebsiella pneumoniae) and fungi (Aspergillus niger and Alternaria
alternata); the complexes exhibited higher activity than the ligand.
Keywords Schiff base Á Molecular docking Á DNA binding Á Molecular structure Á
Thermodynamic parameters
Introduction
Schiff base complexes of transition metals are of particular interest to inorganic
chemists since their wide range of diverse biological activities and their chemical,
structural, and spectral properties are often strongly dependent on the nature of the
ligand structure [1, 2]. Also a Schiff base chromophore possesses substantial
harmonic phonons, which give substantial contributions to their coordination ability
with different ligands [3]. Metal chelation is involved in many biological processes,
where the coordination can occur between a different metal ion and a wide range of
ligands [4]. In recent years, metal-based drugs have gained much importance in the
medicinal field. They are in use as medicines for the treatment of diabetes, cancer,
and anti-inflammatory and cardiovascular disease [5–7].
Schiff bases derived from 2-hydroxy-1-napthaldehyde have been extensively
studied due to their wide range of applications in medicinal fields [10], and they
form stable complexes with metal ions due to the presence of a phenolic hydroxyl
group at their o-position, which coordinates to the metal ion via deprotonation.
Many Schiff bases derived from 2-hydroxynaphthaldehyde have been studied by
NMR spectroscopy and X-ray analysis in the solid state [8–11]. The UV–Vis spectra
of some 2-hydroxyl Schiff bases have been investigated in polar and non-polar
solvents [12–14]. The absorption band at[400 nm belongs to a keto-amine form of
the Schiff base. The results showed that the enol-imine form is dominant in a non-
polar solvent while the keto-amine form is dominant in a polar solvent for such
Schiff bases. Recently, the UV–Vis spectroscopic study for quantitative analysis of
undefined mixtures of the substituted Schiff bases of 2-hydroxynaphthaldehydes has
been based on the chemometric approach [13]. Schiff bases can be incorporated into
crown ether structures to form interesting cation binding ligands. In such structures
the cation can occupy the crown cavity depending on the donor atom and cation
character or form the Schiff base complex through the imine group. Some crown
ether-containing ortho hydroxylated Schiff bases have been synthesized and their
complexation properties with transition metal cations have been investigated [15].
However, the crown ether moieties carrying only oxygen and nitrogen donor atoms
exist in these compounds. Schiff bases have been reported to possess remarkable
antibacterial and antifungal activities. The C=N linkage in azomethine derivatives is
an essential structural requirement for biological activity [16, 17].
Recently we have reported the synthesis, characterization and biological
activities of some metal(II) complexes of Schiff bases [16]. We have synthesized
1
23

Supramolecular structure, spectroscopic, thermal studies…
the novel Schiff base ligand 4-(((2-hydroxynaphthalen-1-yl)methylene)amino)-1,5-
dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HL) containing carbonyl and
azomethines as potential chelating sites. In order to explore the ligational behavior
of this ligand, we have prepared a series of its Cu(II), Co(II) and Cd(II) complexes
and characterized them by various physicochemical techniques and studied their
antimicrobial activities. Study of the docking of the Schiff base ligand, as well as
molecular and electronic structures of the ligand (HL) and its complexes are
discussed
Experimental
Materials
All reagents and chemicals required were Analytical Grade (AR), purchased
commercially. All the solvents were purified by distillation and used. All reactants
(
2-hydroxy-1-naphthaldehyde and 4-aminoantipyrine) were procured from Sigma
Aldrich. Calf thymus DNA (CT-DNA) was purchased from SRL (India). Organic
solvents were spectroscopically pure from BDH and included ethanol, methanol,and
dimethylformamide.
Preparation of Schiff base ligand (HL)
The Schiff base ligand of 4-(((2-hydroxynaphthalen-1-yl)methylene)amino)-1,5-
dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (HL) was prepared according to
the previous procedure [16]. An ethanolic solution of 4-aminoantipyrine
(
(
0.1 m mol) was added slowly to the solution of 2-hydroxy-1-naphthaldehyde
0.1 m mol) in ethanol with constant stirring and addition of two drops of
piperidine. The mixture was refluxed for 4 h in in a water bath. After concentration
of the solution, the precipitate was separated, filtered, washed with ethanol, and
dried in vacuum over anhydrous CaCl [18]. Recrystallization from ethanol afforded
2
pure crystals, Yield: 70 %. The purity of ligand was checked by TLC. Our synthetic
route of Schiff base ligand is shown in Fig. 1.
Preparation of the complexes
The metal complexes (1–5) of the different metal ions under study were prepared
and purified by recrystallization when possible (Fig. 2). The following synthetic has
been employed. Ethanolic solution of CuCl Á2H O, CuSO Á5H O, Cu(NO ) Á6H O,
2
2
4
2
3 2
2
CoCl Á6H O and CdCl ÁH O (0.001 mol) was added slowly to the ligand (HL)
2
2
2
2
(
0.001 mol) in ethanol, and the reaction mixture was further refluxed. The colored
precipitates were filtered through a sintered glass crucible and washed several times
with hot ethanol, ether, and finally dried in vacuum over anhydrous calcium chloride
in desiccators. The results of elemental analysis as well as some physical properties
and the suggested chemical formula are listed in Table 1.
123

A. Z. El-Sonbati et al.
3
H C
CHO
CH
3
OH
N
N
H
2
N
3
H C
+
Refluxed
CH
3
N
N
O
N
OH
O
(A)
3
H C
CH
3
N
N
N
O
H
O
(
B)
3
H C
H
3
C
CH
3
CH
3
N
N
N
N
HN
N
O
O
H
O
O
(C)
(
D)
3
H C
CH
3
N
N
N
3
H C
O
H
CH
3
O
N
O
N
H
H
O
N
N
O
N
O
N
3
H C
(E)
CH
3
(
F)
H
O
3
C
H
3
C
CH
3
CH
3
N
N
N
N
H
N
N
O
O
H
O
O
O
O
H
H
O
N
N
N
N
N
N
H
3
C
3
H C
CH
3
CH
3
(H)
(G)
Fig. 1 The structure route of Schiff base ligand (HL)
1
23

Supramolecular structure, spectroscopic, thermal studies…
(
1)
H3C
CH3
N
H
C
N
N
OH
O
Cu
Cl
(2)
Cl
CH3
H3C
(5)
d
N
l
o
c
H
C
n
H3C
CH3
o
N
O
y
2
l
N
H
c
k
H
C
N
2
.
i
2
u
l
q
O
C
t.
C
u
u
N
O
p
C
p
N
,
O
N
h
OH2
4
O
x
OH
s
C
d
O
y
l
lu
k
f
c
i
r
e
Cl
u
q
Cl
O
.
t
O 2
p p ,
h
H
6
.
d l
2
)
4
3
x
wly
s
c o
O
O
u
n
.H 2
l
t. slo
N
(
f
o
e
l
C
2
u
r
C
,p
p
Cd
h
4
t
x
h
lus
n
H3C
ref
o
CH3
o
N
N
N
CH
O
OH
re
C
ly
HL
o
flu
o
O
4
w
n
s
C
2
S
l
o
c
x
l
u
s
old
C
t.
4
h
.6
p
,p
H
,
p
pt.
h
2
O
8
x
quic
flus
t
kly
re
o
h
n
o
H3C
H3C
CH3
CH3
CH
CH
N
N
N
N
2
H2O
3H2O
N
N
H2O
H2O
OH
OH
Cu
Co
Cl
O
O
O3SO
H2O
Cl
OH2
H2O
(3)
(4)
Fig. 2 Structure of the metal complexes (1–5)
Microbiological investigation
The newly synthesized Schiff base ligand (HL) and its metal complexes were
screened for their antibacterial and antifungal activities using nutrient agar and
DOX agar media, respectively, by the agar well dilution method [19, 20]. In vitro,
123

A. Z. El-Sonbati et al.
1
23

Supramolecular structure, spectroscopic, thermal studies…
antibacterial activity of the test compounds was tested against two local Gram
positive bacterial strains, Bacillus cereus and Staphylococcus aureus and two local
Gram negative bacterial strains, Escherichia coli and Klebsiella pneumoniae and
antifungal activities were carried out against two local fungal strains, Aspergillus
niger and Alternaria alternata. The stock solutions of each test compound were
-
1
prepared using concentrations of of 50, 100, and 150 lg mL . By using a sterile
cork borer (10 mm diameter), wells were made in agar media plates previously
seeded with the test microorganism. Then 200 ll of each compound was applied in
each well. The agar plates were kept at 4 °C for at least 30 min to allow the
diffusion of the compound to agar medium. The plates were then incubated at 37 or
3
0 °C for growth of bacteria and fungi, respectively. The diameters of inhibition
zone were determined after 24 h and 7 days for bacteria and fungi, respectively,
taking into consideration the control values (DMF).
DNA binding experiments
The binding properties of the ligand to CT-DNA have been studied using electronic
absorption spectroscopy. The stock solution of CT-DNA was prepared in 5 mM
Tris–HCl/50 mM NaCl buffer (pH 7.2), which has a ratio of UV absorbances at 260
and 280 nm (A260/A280) of ca. 1.8–1.9, indicating that the DNA was sufficiently free
of protein [21], and the concentration was determined by UV absorbance at 260 nm
-
1
-1
(
e = 6600 M cm ) [22]. Electronic absorption spectra (300–700 nm) were
carried out using 1 cm quartz cuvettes at 25 °C by fixing the concentration of ligand
or complex (1.00 9 10 mol L ), while gradually increasing the concentration of
-
3
-1
-
CT-DNA (0.00–1.30 9 10 mol L ). An equal amount of CT-DNA was added to
4
-1
both the compound solutions and the references buffer solution to eliminate the
absorbance of CT-DNA itself. The intrinsic binding constant K of the compound
with CT-DNA was determined using the following equation [23]:
b
½
DNAŠ
½DNAŠ
1
¼
þ
;
ð1Þ
ðea À efÞ ðeb À efÞ Kbðea À efÞ
where [DNA] is the concentration of CT-DNA in base pairs, e is the molar
a
extinction coefficient observed for the Aobs/[compound] at the given DNA con-
centration, e is the molar extinction coefficient of the free compound in solution,
f
and e is the molar extinction coefficient of the compound when fully bonded to
b
DNA. In plots of [DNA]/(e –e ) versus [DNA], K is given by the ratio of the slope
a
f
b
to the intercept.
Measurements
Elemental microanalyses of the separated ligand and solid chelates for C, H, and N
were performed on a Perkin-Elmer (2400) CHNS analyzer. The analyses were
repeated twice to check the accuracy of the analyzed data. Infrared spectra were
1
recorded as KBr discs using a Pye Unicam SP 2000 spectrophotometer. The H-
NMR spectrum was obtained with a Bruker WP 300 MHz using DMSO-d as a
6
123

A. Z. El-Sonbati et al.
solvent containing TMS as the internal standard. Mass spectra were recorded by the
EI technique at 70 eV using a MS-5988 GS-MS Hewlett-Packard.Ultraviolet–
visible (UV–Vis) spectra of the compounds were recorded using a Perkin-Elmer AA
800 spectrophotometer model AAS. The magnetic moment of the prepared solid
complexes was determined at room temperature using the Gouy’s method.
Mercury(II) (tetrathiocyanato)cobalt(II), [Hg{Co(SCN) }], was used for the cali-
4
bration of the Gouy tubes. Diamagnetic corrections were calculated from the values
given by Selwood [24] and Pascal’s constants. Magnetic moments were calculated
coor. 1/2
using the equation, leff. = 2.84 [TvM
and its copper complex powder forms was recorded on X-ray diffractometer in the
] . X-ray diffraction analysis of the ligand
o
range of diffraction angle 2h = 5°–80°. This analysis was carried out using Cu Ka
˚
radiation (k = 1.540598 A). The applied voltage and the tube current were 40 kV
and 30 mA, respectively. The diffraction peaks in powder spectra were indexed, and
the lattice parameters were determined with the aid of the computer program [25].
The value of interplanar spacing, d, and Miller indices, hkl, for each diffraction peak
were determined by using the CHEKCELL program [26]. Thermal studies were
computed on a Simultaneous Thermal Analyzer (STA) 6000 system using the
thermogravimetric analysis (TGA) method. Thermal properties of the samples were
-
1
analyzed in the temperature range up to 1000 °C at a heating rate of 10 °C min
under dynamic nitrogen atmosphere. ESR measurements of powdered samples were
recorded at room temperature (Tanta University, Egypt) using an X-band
spectrometer utilizing a 100 kHz magnetic field modulation with diphenylpicryl-
hydrazyle (DPPH) as a reference material. The molecular structures of the ligands
were optimized by HF method with a 3–21G basis set. The molecules were built
with the Perkin Elmer ChemBioDraw and optimized using the Perkin Elmer
ChemBio3D software [27, 28].
In the study simulation of the actual docking process, in which the ligand–protein
pair-wise interaction energies was calculated, was done using Docking Server [29].
The MMFF94 Force field was for used energy minimization of ligand molecules
using Docking Server. Gasteiger partial charges were added to the ligand atoms.
Non-polar hydrogen atoms were merged, and rotatable bonds were defined. Docking
calculations were carried out on a crystal structure of HL ligand protein model.
Essential hydrogen atoms, Kollman united atom type charges, and solvation
parameters were added with the aid of AutoDock tools [30]. Auto Dock parameter
set- and distance-dependent dielectric functions were used in the calculation of the
van der Waals and the electrostatic terms, respectively.
Results and discussion
Metal complexes
The Schiff base 4-(((2-hydroxynaphthalen-1-yl)methylene)amino)-1,5-dimethyl-2-
phenyl-1,2-dihydro-3H-pyrazol-3-one (HL) analogues were carried out according to
a convenient one-step procedure, that is, by the condensation of 4-amino-1-phenyl-
2
,3-dimethylpyrazolin-5-one and 2-hydroxy-1-naphthaldehyde in ethanol, which
1
23

Supramolecular structure, spectroscopic, thermal studies…
provided excellent yield (*70 %). The elemental analyses data confirmed the
assigned composition of the Schiff base and its complexes. The Schiff base is
soluble in all common organic solvents and strong polar solvents such as DMF and
DMSO. All the complexes (1–5) are stable at room temperature, insoluble in water,
but soluble in ethanol, DMF, and DMSO.
All the complexes were prepared by direct reaction between ligand (HL) and the
hydrated copper(II) chloride, nitrate, sulfate, cadmium, and cobalt(II) chlorides in
ethanol to yield the complexes (1–5) (Fig. 2).
The products were purified by washing with dry ethanol, and gave elemental
analyses compatible with the suggested formulae given in Table 1 according to the
following general equations:
CuCl2 Á 2H2O þ HL ! ½CuðHLÞCl2Š;
ð2Þ
ð3Þ
ð4Þ
ð5Þ
ð6Þ
CuðNO Þ Á6H O þ HL ! ½CuLðO NOÞH OŠ þ HNO ;
3
2
2
2
2
3
CuSO4 Á 5H2O þ HL ! ½CuðHLÞðOSO3Þð3H2Oފ 2H2O;
Â
Ã
CoCl Á 6H O þ HL ! CoðHLÞCl ðH OÞ 3H O;
2
2
2
2
2
2
CdCl Á H O þ HL ! ½CdðHLÞCl Š:
2
2
2
L is the deprotonated ligand.
-
1
2
-1
The observed molar conductance (Km = 6.4–11.6 O cm mol ) of all the
-
3
complexes in 10 molar solution in DMF suggest the non-electrolytic nature of
these complexes [31]. Such a non-zero molar conductance value for each of the
complexes in the present study is most probably due to the strong donor capacity of
DMF, which may lead to the displacement of anionic ligands and change of
electrolyte type [31].
Formulation of the complexes was based on their elemental analytical data, molar
conductance values, and magnetic susceptibility data. Cu(II), Co(II) and Cd(II)
complexes showed 1:1 metal–ligand stoichiometry (Table 1).
Structure of the ligand and its metal complexes
The ESI mass spectrum of the Schiff base ligand (HL) showed a molecular ion peak
recorded at m/z = 357, which is equivalent to its molecular weight. Generally, the
fragmentation of mass spectra of the ligand showed four main pathways as shown in
Scheme 1.
Introduction of a hydroxyl group at the ortho position to the azomethine linkage
raises the possibility of phenolimine–quinoneamine tautomerism. It has been
reported that the tautomeric equilibrium depends on the extent of conjugation,
nature, and position of the substituent and polarity of the solvent, and this
phenomenon has drawn considerable attention both from the theoretical and
experimental point views [32]. Anonove et al. [32] explained this type of
tautomerism exhibited by 2-hydroxy-1-naphthaldehyde Schiff base and arrived at
the conclusion that the compound exists in the quinonoid form. The ligand under
123

A. Z. El-Sonbati et al.
H3C
H3C
CH3
N
N
N
N
N
N
CH
–
CH3
CH
O
O
OH
–C6H5
OH
m/e=265(74.23%)
m/e=357(100%)
–
C H
6
5
H C
3
H C
3
C
N
N
C
N
N
N
N
C
O
C
C
O
–
C H O
C
C
CH
4
3
m/e=121(33.893%)
OH
m/e=188(52.66%)
-
C H N
4 3
N
N
C
O
m/e=65(18.207%)
Scheme 1 The fragmentation of mass spectra of the ligand
investigation is also capable of exhibiting phenolimine–quinoneamine tautomerism
(
Fig. 1b, d). On the basis of the spectral data, a phenolimine structural form
-1
-
1
[
established (Fig. 1b).
3921 cm
(p ? p*) and 31,940 cm
(n ? p*)] of the ligand has been
The infrared spectrum of HL ligand gives interesting results and conclusions. In
the spectrum of 4-aminoantipyrine, a pair of medium intensity bands present at
-
1
*
spectra of all the complexes. Furthermore, no strong absorption band was observed
3150 to 3400 cm corresponds to t(NH ), but these were absent in the infrared
2
1
23

Supramolecular structure, spectroscopic, thermal studies…
-
1
at *1760 cm indicating the absence of a t(C=O) group of 4-aminoantipyrine
33]. This indicated that the coordination of the carbonyl group of 4-aminoan-
[
tipyrine and the amino group of 4-aminoantipyrine might have taken place [34].
These results provide strong evidence for the formation of a ligand frame [35]. A
-
1
strong absorption band in the *1643 cm may be attributed to the t(C=N) group.
The lower value of t(C=N) may be explained on the basis of a drift of the lone pair
density of azomethine nitrogen towards the metal atom [16].
Infrared spectrum of the ligand was in a broad absorption band located at
-
1,
*
3210 cm which could be attributed to hydrogen bonded phenolic t(O–H). The
low frequency bands indicated that the hydroxy hydrogen atom was involved in
(
B , D) tautomerism through hydrogen bonding (Fig. 1). The region between
-
219 and 1323 cm was due to C–OH stretching, to C–OH in plane or out of plane
1
1
bending and out-of-plane C–OH bending vibrations. The strong band at 1620 cm
-
1
was due to a carbonyl stretching vibration mode. An intramolecular hydrogen bridge
linking of the C=N and carbonyl groups to the OH moiety was found to be a
characteristic feature of this compound class (Fig. 1b). The five/six membered
intramolecular hydrogen bonding ring is shown in Fig. 1b. The IR spectrum of the
ligand shows an intense carbonyl band (tC=OÁÁÁH), (tC=O)/tC=NÁÁÁH)(tC=N)
formed with extensive five/six membered intramolecular hydrogen bonding, and
this has been confirmed by El-Sonbati et al. [20].
-
1
IR spectrum of the ligand shows a broad band located at *3210 cm due to the
stretching vibration of some hydrogen bonding. El-Sonbati et al. [16, 20] made
detailed studies for the different types of hydrogen bonding, which are favorable in
the molecule under investigation:
1.
2.
3.
4.
Intramolecular hydrogen bond between the nitrogen atom of the –C=N–/C=O
system and hydrogen atom of the hydroxy hydrogen atom (Fig. 1b).
Intramolecular hydrogen bond between the oxygen atoms of the –C=O/
C=O(exocyclic) system and the hydrogen atom of the NH atom (Fig. 1d).
Intermolecular hydrogen bonding is possible forming cyclic dimmer through
OHÁÁÁN=C (F) (Fig. 1).
Intermolecular hydrogen bonding is possible forming cyclic dimmer through
NHÁÁÁO=C(exocyclic) (H) or OHÁÁÁO=C (G) (Fig. 1).
By comparing the infrared spectrum of the ligands of its complexes, the
following features for some of the prepared complexes were observed.
The exocyclic carbonyl absorption band t(CO) was shifted to frequencies higher
by 25–10 cm for all complexes (1–5) indicating that the carbonyl group was
-
1
coordinated to the metals ions (Fig. 2). New bands were found in the spectra of
1,
-
complexes in the regions 560–585 and 417–452 cm which were assigned to t(M–
O) and t(M–N) stretching vibrations, respectively.
-
1
A strong band observed at *1760 cm in the free ligand was attributed to
t(C=O) of the exocyclic carbonyl oxygen. The infrared spectrum of the coordination
-
1
ligand showed a considerable negative shift of 15–20 cm
absorption of the exocyclic carbonyl oxygen group, indicating a decrease in the
in the t(C=O)
stretching force constant of C=O as a consequence of coordination through the
123

A. Z. El-Sonbati et al.
exocyclic carbonyl oxygen atom of the ligand. This band shifted in all the
complexes (1–5) indicating the participation of the exocyclic carbonyl oxygen in
-
1
bonding with metal ions. A medium-to-strong intensity band at cm in the free
ligand was attributed to the t(C=N) stretch of the azomethine group. Coordination
of the Schiff base to the metal ions through the nitrogen atom is expected to reduce
electron density in the azomethine link and lower the t(C=N) absorption frequency.
This band shifted to a lower wavenumber side in all the complexes (1–5) indicating
the participation of the azomethine nitrogen in coordination with metal ions.
The broad band due to the internally hydrogen-bonded phenolic –OH group
-
1
disappeared from the region 3300–3000 cm
indicating deprotonation and
formation of a metal–oxygen bond. Consequently, the band due to t(C–O) was
-
1
increased by *25 cm in the metal complex (2) and this adequately supported the
bond formation by phenolate oxygen.
Moreover, the IR spectrum of the [CuL(O NO)OH )] (2) complex reflects that
2
2
the HL acts as a monobasic tridentate ligand coordinating via the oxygen atom of
phenolic (OH), azomethine nitrogen, and exocyclic carbonyl oxygen, while
[
(
Cu(HL)Cl ] (1), [Cu(HL)(OSO )(OH ) ]2H O (3), [Co(HL)(Cl )(OH ) ]3H O
2 2 2 3 2 2 2 2 2
4) and [Cd(HL)Cl ] (5) complexes reflect that the HL acts as a neutral bidentate
2
ligand coordinating via the azomethine nitrogen and exocyclic carbonyl oxygen.
Apart from these bands, the non-ligand bands of low intensity appearing in the
-
1
region 560–585 and 417–452 cm could be assigned to t(M–O) and t(M–N)
vibrations, respectively [16]. The above mode of bonding suggested by infrared
spectral studies was reinforced by the proton NMR spectral study of the Cd(II)
complex.
Additionally, the IR spectra of the complexes show the bands due to coordinated
anions. In the spectrum of complex (2), three additional bands, which were not
present in the spectrum of free ligand, were observed. Of these, the band
-
1
*
1030 cm was assigned to the t mode of the nitrate group. The bands at 1470
2
-1
and 1260 cm are the two split bands of t and t , respectively, of the coordinated
nitrate group. The magnitude of t -t is about 200 cm in the complex (2), which
4
1
-
1
4
1
indicated that the nitrate group was coordinated to the copper(II) ion in bidentate
-
1
fashion [36]. The sulphato complex (3) showed IR bands in 1130 and 1110 cm
-1
-
1
(t3), 965 cm (t ) and 665 cm (t ) indicating the unidentate [37] nature of
sulpate group. The spectra of complexes, which contain water molecules, showed a
1
4
-
1
broad band *3475 to 3380 cm , assigned to t(OH) of crystallization water
involved in the complexes [20]. Moreover, the spectra of complexes containing
-
1
coordinated water molecules showed an additional two bands *965 and 650 cm
,
owing to q (H O) and q (H O), respectively [20, 38]. The appearance of the latter
r
2
w
2
two modes indicated coordinated water rather than hydrated water.
1
The H NMR spectrum of the ligand was recorded in DMSO-d (Fig. 3). The
6
signal at d(14.965 ppm)(s. 1H) is assigned to phenolic proton of (–OH–) group The
downward shift of the proton is presumably due to strong hydrogen bonding [16].
The signal at d(10.657 ppm; s. 1H) is assigned to the azomethine proton, in the
Schiff base ligand (Table 2). The aromatic proton at d(7.169–8.097 ppm; m. H)
shifted downfield in the complexes. A sharp singlet at d(2.437) was assigned to
methyl proton. On the basis of the spectral values, a hydrogen bonded phenolimine
1
23

Supramolecular structure, spectroscopic, thermal studies…
1
Fig. 3 H NMR spectra of (a) ligand (HL) and (b) Cd(II) complex (5)
123

A. Z. El-Sonbati et al.
1
Table 2 H NMR spectral data
of Schiff base ligand (HL) and
its Cd(II) complex (5)
1
Compound
H NMR data (ppm)
HL
14.965 (s, 1H, Phenolic OH)
1
7
2
0.657 (s, 1H, HC=N)
.169–8.097 (m, 12H, ArH)
3
.437 (m,C–CH )
5
14.966 (s, 1H, Phenolic OH)
1
7
2
0.664 (s, 1H, HC=N)
.760–8.100 (m, 12H, ArH)
3
.456 (m,C–CH )
structure has been proposed for the ligand. The above in the spectrum of the Cd(II)
complex (Fig. 3), with the presence of an –OH (14.966 ppm) proton signal is a clear
indication that phenolic oxygen is not bonded to the metal ion. A careful
comparison of the position of other signals in this complex with those of the ligand
indicated a downward shift of the other protons by *d(0.10–0.25 ppm) in the metal
complexes. Thus, the azomethine proton signal observed at d(10.664 ppm) in the
complex was shifted down field by 0.007 ppm.
The IR spectrum showed that the ligand (HL) acted as monobasic bidentate/
tridentate through the (–C=N) and (C=O)/proton displacement from the phenolic
OH moiety groups forming a five/six membered structure (Fig. 1).
The X-ray diffraction (XRD) patterns powder forms of HL and Cu(II) complexes
1) are presented in Fig. 4. The XRD of HL and Cu(II) complex (1) show many
(
diffraction peaks, which indicated the polycrystalline phase. The average crystallite
size (n) can be calculated from the XRD pattern according to Debye–Scherrer
Eq. [28, 39]:
Kk
n ¼ b
:
ð7Þ
cos h
=2
1
The equation uses the reference peak width at angle (h), where k is the wavelength
˚
of X-ray radiation (1.541874 A), K is constant taken as 0.95 for organic compounds
[
40] and b1/2 is the width at half maximum of the reference diffraction peak mea-
sured in radians. The dislocation density, d, is the number of dislocation lines per
unit area of the crystal. The value of d is related to the average particle diameter (n)
by relation [39, 40]:
1
d ¼
:
ð8Þ
2
n
The value of n was calculated and found to be 315 nm and 630 nm and the value of
-
4
-4
-2
d was 33.78 9 10 and 15.86 9 10 nm for ligand (HL) and Cu(II) complex
1), respectively. The diffraction peaks in powder spectra were indexed, and the
(
lattice parameters were determined with the aid of the CRYSFIRE computer pro-
gram [40–43]. The values of interplanar spacing (d) and Miller indices (hkl) for
each diffraction peak before and after refinement are determined by using the
CHEKCELL program [40–43]. The values of d and corresponding hkl for HL and
1
23

Supramolecular structure, spectroscopic, thermal studies…
(A) 25000
(2)
2
1
1
0000
5000
0000
(1)
5
000
0
(
3) (4)
(
5) (6) (7) (8)
(9 )( 10)
(11)
6
8
10 12 14 16 18 20 22 24 26 28 30
θ°
2
(
B) 650
(
1)
6
5
5
4
4
3
3
2
2
1
1
00
50
00
50
00
50
00
50
00
50
00
(
2)
(
5)
(
7)
(20)
(
4)
(
19)
(8)
(
3)
(
10)
(14)
(12)
(15)
16)(17)(18)
11 () 13)
(
6)
(9)
(
(
(21)
5
0
0
6
8
10 12 14 16 18 20 22 24 26 28 30
θ°
2
Fig. 4 X-Ray diffraction pattern for a ligand (HL) and b complex (2) in powder forms
Cu(II) complex (1) are listed in Tables 3 and 4, respectively. The results show that
the HL ligand and Cu(II) complex (1) have monoclinic crystal structure with space
group P2 and P21/C, respectively. The lattice parameters are estimated as:
)
a ¼ 8:6156 A; b ¼ 13:5885 A; c ¼ 7:4372 A˚
˚
˚
for ligand:
a ¼ 90 ; c ¼ 114 ; b ¼ 90ꢀ
ꢀ
ꢀ
and
)
˚
˚
˚
a ¼ 15:5084 A; b ¼ 18:5706 A; c ¼ 7:0558 A
for CuðIIÞ complex:
a ¼ 90 ; c ¼ 114 ; b ¼ 90ꢀ
ꢀ
ꢀ
123

A. Z. El-Sonbati et al.
Table 3 Crystallographic data
for HL Schiff base ligand
˚
˚
Peak no.
2hobs. (°)
d
obs. (A)
d
cal. (A)
ðh
k
lÞ
1
2
3
4
5
6
7
8
9
6.5255
13.0339
17.3054
18.6222
19.5618
20.8833
21.7006
22.7498
26.3207
26.651
13.53541
6.786964
5.120178
4.760963
4.534377
4.2504
13.59033
6.773119
5.12683
0
1 0
1ꢀ
1
2
2
3
0
1
0
2
0
4
0
0
1
0
1
1
0
0
2
1
1ꢀ
1ꢀ
4.765656
4.529578
4.244241
4.089748
3.906405
3.38655
0
2ꢀ
4.09204
1
3.905636
3.383302
3.342115
3.034828
2
2ꢀ
1
1
0
1
3.343187
3.033946
2ꢀ
29.4075
0
Table 4 Crystallographic data
for Cu(II) complex (1)
˚
˚
Peak no.
2hobs. (°)
d
obs. (A)
d
cal. (A)
ðh
k
lÞ
1
2
3
4
5
6
7
8
9
7.7015
11.2895
13.0047
13.5337
15.4656
15.8558
16.3792
17.558
11.47002
7.831436
6.802132
6.537418
5.724865
5.584846
5.407538
5.047057
4.727594
4.642085
4.422805
4.318254
4.237004
4.073697
3.921423
3.868906
3.703365
3.507757
3.441082
3.274389
3.129856
11.48707
7.838002
6.801712
6.548589
5.726797
5.588647
5.407147
5.051366
4.723883
4.642655
4.42488
1ꢀ
1ꢀ
2ꢀ
1ꢀ
2ꢀ
1ꢀ
1
2
1
1
1
2
1
2
3
4
4
3
2
3
4
4
1
0
1
2
2
0
0
0
2
1
1
2
1
0
0
0
1
1
1
0
1
1
2
2
2
2
0
2ꢀ
18.7549
19.1035
20.0602
20.5511
20.9496
21.7995
22.657
2ꢀ
1
1
1
1
1
1
1
1
1
1
2
2
0
1
2
3
4
5
6
7
8
9
0
1
0
1ꢀ
4.31576
2ꢀ
3ꢀ
4.236494
4.074177
3.938893
3.868706
3.703437
3.505687
3.43856
1
2ꢀ
22.9687
24.0145
25.371
1ꢀ
4ꢀ
1ꢀ
2ꢀ
2ꢀ
25.8711
27.2131
28.4953
3.274285
3.129459
0
Molecular structures of the ligand and its complexes
The forms A–D of ligand (HL) are shown in Fig. 1. Primary calculations reveal that
the form (A) is more stable and reactive than other forms (Fig. 1). The selected
geometrical structures of the Schiff base ligand (HL) [form (A)] and its complexes
1
23

Supramolecular structure, spectroscopic, thermal studies…
Fig. 5 Optimized structure for Schiff base (HL)
(
(
1–5) are shown in Figs. 5 and 6. The bond lengths and bond angles for ligand
HL)[form (A)] and its metal complexes (1–5) are listed in Tables 5, 6, 7, 8, 9 and
1
0. The form (A) is more reactive than the other forms as reflected from energy gap
values (Table 11). The HOMO–LUMO energy gap, DE, which is an important
stability index, is applied to develop theoretical models for explaining the structure
and conformation barriers in many molecular systems [16, 39]. The value of DE for
form (A), form (B), form (C), and form (D) was found to be 3.229, 3.678, 5.143, and
3
.440 eV, respectively, so the form (A) is more stable than the other forms. The
HOMO and LUMO of the Schiff base ligand (HL) and its complexes (1–5) are
shown in Fig. 7. The calculated quantum chemical parameters are given in
Table 11. Additional parameters such as DE, absolute electronegativities, v,
chemical potentials, Pi, absolute hardness, g, absolute softness, r, global
electrophilicity, x, global softness, S, and additional electronic charge, DNmax
have been calculated according to the following equations [20, 39]:
,
DE ¼ ELUMO À EHOMO
;
ð9Þ
ÀðEHOMO þ ELUMOÞ
v ¼
g ¼
;
ð10Þ
ð11Þ
2
ELUMO À E
HOMO
;
2
1
r ¼ g
;
ð12Þ
ð13Þ
ð14Þ
Pi ¼ Àv;
1
S ¼ 2
;
g
2
Pi
x ¼ 2g
;
ð15Þ
123

A. Z. El-Sonbati et al.
Fig. 6 Optimized structures for complexes (1–5)
1
23

Supramolecular structure, spectroscopic, thermal studies…
Table 5 The selected geometric parameters for HL [form (A)]
˚
Bond lengths (A)
Bond angles (°)
C(27)–H(46)
C(26)–H(45)
C(25)–H(44)
C(24)–H(43)
C(22)–H(42)
O(21)–H(41)
C(18)–H(40)
C(17)–H(39)
C(14)–H(38)
C(13)–H(37)
C(12)–H(36)
C(11)–H(35)
C(10)–H(34)
C(9)–H(33)
C(9)–H(32)
C(9)–H(31)
C(8)–H(30)
C(8)–H(29)
C(8)–H(28)
C(18)–C(17)
C(15)–C(17)
C(16)–C(15)
C(27)–C(15)
C(26)–C(27)
C(25)–C(26)
C(24)–C(25)
C(16)–C(24)
C(20)–C(16)
C(19)–C(20)
C(18)–C(19)
C(7)–C(14)
C(13)–C(14)
C(12)–C(13)
C(11)–C(12)
C(10)–C(11)
C(7)–C(10)
N(3)–C(2)
1.104
1.103
1.104
1.099
1.09
H(37)–C(13)–C(14)
H(37)–C(13)–C(12)
C(14)–C(13)–C(12)
H(36)–C(12)–C(13)
H(36)–C(12)–C(11)
C(13)–C(12)–C(11)
H(35)–C(11)–C(12)
H(35)–C(11)–C(10)
C(12)–C(11)–C(10)
H(38)–C(14)–C(7)
H(38)–C(14)–C(13)
C(7)–C(14)–C(13)
H(34)–C(10)–C(11)
H(34)–C(10)–C(7)
C(11)–C(10)–C(7)
H(30)–C(8)–H(29)
H(30)–C(8)–H(28)
H(30)–C(8)–N(3)
H(29)–C(8)–H(28)
H(29)–C(8)–N(3)
H(28)–C(8)–N(3)
C(14)–C(7)–C(10)
C(14)–C(7)–N(4)
C(10)–C(7)–N(4)
C(5)–N(4)–N(3)
120.169
119.783
120.044
120.491
120.518
118.99
0.967
1.104
1.104
1.103
1.103
1.103
1.103
1.101
1.112
1.113
1.112
1.113
1.114
1.112
1.335
1.341
1.354
1.347
1.338
1.337
1.342
1.353
1.363
1.36
119.573
120.111
120.314
120.887
116.816
122.266
116.055
121.952
121.961
109.053
103.771
112.568
109.375
110.706
111.122
116.414
119.602
123.965
102.355
130.25
C(5)–N(4)–C(7)
N(3)–N(4)–C(7)
123.336
120.903
120.707
118.389
119.413
120.476
120.111
116.69
H(45)–C(26)–C(27)
H(45)–C(26)–C(25)
C(27)–C(26)–C(25)
H(44)–C(25)–C(26)
H(44)–C(25)–C(24)
C(26)–C(25)–C(24)
H(41)–O(21)–C(19)
H(40)–C(18)–C(17)
H(40)–C(18)–C(19)
C(17)–C(18)–C(19)
H(46)–C(27)–C(15)
H(46)–C(27)–C(26)
C(15)–C(27)–C(26)
H(39)–C(17)–C(18)
1.343
1.349
1.342
1.34
1.34
1.343
1.349
1.277
1.345
1.364
1.273
1.363
118.513
119.305
122.182
121.386
117.701
120.913
118.565
C(1)–C(2)
C(5)–C(1)
N(4)–C(5)
N(3)–N(4)
123

A. Z. El-Sonbati et al.
Table 5 continued
˚
Bond lengths (A)
Bond angles (°)
C(1)–N(23)
C(22)–N(23)
C(20)–C(22)
C(19)–O(21)
C(2)–C(9)
1.263
1.26
H(39)–C(17)–C(15)
C(18)–C(17)–C(15)
H(43)–C(24)–C(25)
H(43)–C(24)–C(16)
C(25)–C(24)–C(16)
C(17)–C(15)–C(16)
C(17)–C(15)–C(27)
C(16)–C(15)–C(27)
C(20)–C(19)–C(18)
C(20)–C(19)–O(21)
C(18)–C(19)–O(21)
C(15)–C(16)–C(24)
C(15)–C(16)–C(20)
C(24)–C(16)–C(20)
C(16)–C(20)–C(19)
C(16)–C(20)–C(22)
C(19)–C(20)–C(22)
H(42)––C(22)–N(23)
H(42)–C(22)–C(20)
N(23)–C(22)–C(20)
C(1)–N(23)–C(22)
C(1)–C(5)–N(4)
121.917
119.518
113.024
123.716
123.26
1.355
1.369
1.508
1.485
1.279
1.216
N(3)–C(8)
119.967
117.84
N(4)–C(7)
C(5)–O(6)
122.194
118.769
126.037
115.187
115.132
120.217
124.651
119.346
121.281
119.373
113.455
121.079
125.454
131.352
111.093
123.024
125.744
107.971
103.753
112.395
110.294
110.827
111.344
114.409
115.901
129.133
104.075
128.703
127.049
106.932
135.358
117.706
C(1)–C(5)–O(6)
N(4)–C(5)–O(6)
H(33)–C(9)–H(32)
H(33)–C(9)–H(31)
H(33)–C(9)––C(2)
H(32)–C(9)–H(31)
H(32)–C(9)–C(2)
H(31)–C(9)–C(2)
C(2)–N(3)–N(4)
C(2)–N(3)–C(8)
N(4)–N(3)–C(8)
N(3)–C(2)–C(1)
N(3)–C(2)–C(9)
C(1)–C(2)–C(9)
C(2)–C(1)–C(5)
C(2)–C(1)–N(23)
C(5)–C(1)–N(23)
1
23

Supramolecular structure, spectroscopic, thermal studies…
Table 6 The selected geometric parameters for complex (1)
˚
Bond lengths (A)
Bond angles (°)
C(26)–H(49)
C(25)–H(48)
C(24)–H(47)
C(23)–H(46)
C(22)–H(45)
C(22)–H(44)
C(22)–H(43)
C(21)–H(42)
C(20)–H(41)
C(19)–H(40)
C(18)–H(39)
C(17)–H(38)
C(15)–H(37)
C(15)–H(36)
C(15)–H(35)
C(8)–H(34)
O(7)–H(33)
C(4)–H(32)
C(3)–H(31)
C(16)–C(21)
C(20)–C(21)
C(19)–C(20)
C(18)–C(19)
C(17)–C(18)
C(16)–C(17)
C(4)–C(3)
1.104
1.102
1.104
1.095
1.113
1.112
1.112
1.103
1.103
1.103
1.103
1.102
1.114
1.112
1.113
1.106
0.969
1.104
1.104
1.35
H(41)–C(20)–C(21)
H(41)–C(20)–C(19)
C(21)–C(20)–C(19)
H(40)–C(19)–C(20)
H(40)–C(19)–C(18)
C(20)–C(19)–C(18)
H(39)–C(18)–C(19)
H(39)–C(18)–C(17)
C(19)–C(18)–C(17)
H(42)–C(21)–C(16)
H(42)–C(21)–C(20)
C(16)–C(21)–C(20)
H(38)–C(17)–C(18)
H(38)–C(17)–C(16)
C(18)–C(17)–C(16)
C(21)–C(16)–C(17)
C(21)–C(16)–N(12)
C(17)–C(16)–N(12)
H(37)–C(15)–H(36)
H(37)–C(15)–H(35)
H(37)–C(15)–N(13)
H(36)–C(15)–H(35)
H(36)–C(15)–N(13)
H(35)–C(15)–N(13)
C(16)–N(12)–N(13)
C(16)–N(12)–C(11)
N(13)–N(12)–C(11)
Cu(28)–O(27)–C(11)
H(45)–C(22)–H(44)
H(45)–C(22)–H(43)
H(45)–C(22)–C(14)
H(44)–C(22)–H(43)
H(44)–C(22)–C(14)
H(43)–C(22)–C(14)
C(15)–N(13)–C(14)
C(15)–N(13)–N(12)
C(14)–N(13)–N(12)
C(22)–C(14)–C(10)
C(22)–C(14)–N(13)
C(10)–C(14)–N(13)
O(27)–C(11)–N(12)
120.102
119.658
120.239
120.442
120.451
119.1
119.759
120.125
120.111
121.625
116.571
121.801
116.885
121.11
121.986
116.73
122.132
121.093
108.537
107.194
110.153
108.596
112.416
109.79
1.343
1.34
1.34
1.342
1.349
1.334
1.341
1.356
1.347
1.338
1.336
1.342
1.353
1.365
1.361
1.341
2.16
119.902
121.169
113.226
111.086
111.688
105.669
111.73
C(1)–C(3)
C(2)–C(1)
C(26)–C(1)
C(25)–C(26)
C(24)–C(25)
C(23)–C(24)
C(2)–C(23)
C(6)–C(2)
103.97
112.214
111.109
123.706
135.261
99.062
C(5)–C(6)
C(4)–C(5)
Cu(28)–Cl(30)
Cu(28)–Cl(29)
O(27)–Cu(28)
N(9)–Cu(28)
C(11)–O(27)
2.158
1.819
1.312
1.247
134.701
126.7
98.297
168.433
123

A. Z. El-Sonbati et al.
Table 6 continued
˚
Bond lengths (A)
Bond angles (°)
C(14)–C(22)
N(12)–C(16)
N(13)–C(15)
C(14)–C(10)
N(13)–C(14)
N(12)–N(13)
C(11)–N(12)
C(10)–C(11)
N(9)–C(10)
C(8)–N(9)
1.507
1.281
1.47
O(27)–C(11)–C(10)
N(12)–C(11)–C(10)
Cl(30)–Cu(28)–Cl(29)
Cl(30)–Cu(28)–O(27)
Cl(30)–Cu(28)–N(9)
Cl(29)–Cu(28)–O(27)
Cl(29)–Cu(28)–N(9)
O(27)–Cu(28)–N(9)
C(14)–C(10)–C(11)
C(14)–C(10)–N(9)
C(11)–C(10)–N(9)
Cu(28)–N(9)–C(10)
Cu(28)–N(9)–C(8)
C(10)–N(9)–C(8)
H(48)–C(25)–C(26)
H(48)–C(25)–C(24)
C(26)–C(25)–C(24)
H(47)–C(24)–C(25)
H(47)–C(24)–C(23)
C(25)–C(24)–C(23)
H(46)–C(23)–C(24)
H(46)–C(23)–C(2)
C(24)–C(23)–C(2)
H(34)–C(8)–N(9)
H(34)–C(8)–C(6)
N(9)–C(8)–C(6)
86.55
81.959
110.925
109.108
112.711
113.474
120.667
87.562
1.372
1.252
1.347
1.272
1.458
1.286
1.279
1.364
1.367
115.718
121.936
122.037
90.222
C(6)–C(8)
C(5)–O(7)
111.046
127.671
121.092
120.871
118.025
119.328
120.585
120.083
111.803
124.189
123.996
116.827
113.7
129.458
110.921
118.415
126.065
115.519
120.075
123.96
H(33)–O(7)–C(5)
C(2)–C(6)–C(5)
C(2)–C(6)–C(8)
C(5)–C(6)–C(8)
C(6)–C(5)–C(4)
C(6)–C(5)–O(7)
C(4)–C(5)–O(7)
115.843
118.919
119.596
121.481
121.522
117.407
121.069
118.393
122.193
H(32)–C(4)–C(3)
H(32)–C(4)–C(5)
C(3)–C(4)–C(5)
H(49)–C(26)–C(1)
H(49)–C(26)–C(25)
C(1)–C(26)–C(25)
H(31)–C(3)–C(4)
H(31)–C(3)–C(1)
1
23

Supramolecular structure, spectroscopic, thermal studies…
Table 6 continued
˚
Bond lengths (A)
Bond angles (°)
C(4)–C(3)–C(1)
C(1)–C(2)–C(23)
C(1)–C(2)–C(6)
C(23)–C(2)–C(6)
C(3)–C(1)–C(2)
C(3)–C(1)–C(26)
C(2)–C(1)–C(26)
119.414
114.146
120.09
125.742
120.464
116.906
122.629
and
Pi
:
DNmax ¼ À
ð16Þ
g
The value of DE for complexes (1–5) was found to be 1.742, 1.428, 0.492, 0.218,
and 2.532 eV, respectively, so the complex (4) is more stable than the other
complexes.
Electronic spectra
The electronic spectrum of Co(II) complex (4) display bands
-1
4
4
-1
4
4
T (F) ? T (F) (*94,500 cm ), T (F) ? A (F) (*14,450 cm ) and
1
g
2g
1g
2g
4
4
-1
T (F) ? T (P) (*21,250 cm ) transitions. This indicates that this complex
1
g
1g
-
1
has octahedral geometry. The value of Dq (945 cm ) was calculated from the
-
1
transition energy ratio diagram using the t /t2 ratio (1.471 cm ) [44]. The
3
naphelaxetic parameter b (0.84) was readily obtained by using the relation
-
1
b = B(complex)/B (free ion), where B free for the Co(II) complex is 1120 cm
45]. From the position of the bands, the chelates are octahedral with largely
[
covalent bonds between the organic ligand and the metal ion [20]. The magnetic
susceptibility measurements lie in the 4.91 B.M. range, corresponding to three
unpaired electrons (normal range for octahedral Co(II) complexes is 4.3–5.2 B.M.),
and is an indication of octahedral geometry [46].
Magnetic moment values for Cu(II) complexes (1–3) recorded at room
temperature lie in the range 1.89–2.04 B.M. corresponding to one unpaired electron
on a Cu(II) ion in an ideal square planar and/or octahedral environment (Table 1).
2
2
The electronic spectrum of complex (1) showed two bands at B1g ? A
(
1g
-
1
2
2
-1
17,825 cm ) and B1g ? E (22,270 cm ), transitions, for square planar
geometry [47, 48]. The observed magnetic moment of 1.72 B.M. further supported
the electronic results. Also, the electronic spectra of six-coordinated Cu(II)
2
complexes have either D4h or C4v symmetry, and the E and T levels of the D free
g
2g
ion term will split into B , A , B , E levels, respectively. Copper complexes (2
g
1
g
1g
2g
and 3) under study display bands in the range 13,210–15,720 and 15,590–
-
6,660 cm . These bands were assigned to the following transitions in order of
1
1
increasing energy [49, 50].
123

A. Z. El-Sonbati et al.
Table 7 The selected geometric parameters for complex (2)
o
Bond angles ( )
˚
Bond lengths (A)
O(30)–H(53)
O(30)–H(52)
C(26)–H(51)
C(25)–H(50)
C(24)–H(49)
C(23)–H(48)
C(22)–H(47)
C(22)–H(46)
C(22)–H(45)
C(21)–H(44)
C(20)–H(43)
C(19)–H(42)
C(18)–H(41)
C(17)–H(40)
C(15)–H(39)
C(15)–H(38)
C(15)–H(37)
C(8)–H(36)
1.001
1.049
1.104
1.103
1.103
1.1
O(33)–N(31)–O(32)
O(33)–N(31)–O(29)
O(32)–N(31)–O(29)
H(43)–C(20)–C(21)
H(43)–C(20)–C(19)
C(21)–C(20)–C(19)
H(42)–C(19)–C(20)
H(42)–C(19)–C(18)
C(20)–C(19)–C(18)
H(41)–C(18)–C(19)
H(41)–C(18)–C(17)
C(19)–C(18)–C(17)
H(44)–C(21)–C(16)
H(44)–C(21)–C(20)
C(16)–C(21)–C(20)
H(40)–C(17)–C(18)
H(40)–C(17)–C(16)
C(18)–C(17)–C(16)
C(21)–C(16)–C(17)
C(21)–C(16)–N(12)
C(17)–C(16)–N(12)
H(39)–C(15)–H(38)
H(39)–C(15)–H(37)
H(39)–C(15)–N(13)
H(38)–C(15)–H(37)
H(38)–C(15)–N(13)
H(37)–C(15)–N(13)
H(47)–C(22)–H(46)
H(47)–C(22)–H(45)
H(47)–C(22)–C(14)
H(46)–C(22)–H(45)
H(46)–C(22)–C(14)
H(45)–C(22)–C(14)
C(15)–N(13)–C(14)
C(15)–N(13)–N(12)
C(14)–N(13)–N(12)
C(22)–C(14)–C(10)
C(22)–C(14)–N(13)
C(10)–C(14)–N(13)
C(16)–N(12)–N(13)
C(16)–N(12)–C(11)
119.767
85.234
119.608
120.157
119.609
120.224
120.552
120.544
118.899
119.614
120.195
120.191
121.687
115.988
122.302
115.471
122.255
122.273
116.091
122.421
121.414
107.296
108.199
109.943
108.901
109.994
112.359
107.12
1.113
1.112
1.112
1.1
1.103
1.103
1.103
1.103
1.114
1.113
1.112
1.098
1.101
1.105
1.348
1.342
1.34
C(4)–H(35)
C(3)–H(34)
C(16)–C(21)
C(20)–C(21)
C(19)–C(20)
C(18)–C(19)
C(17)–C(18)
C(16)–C(17)
O(33)–Cu(28)
N(31)–O(33)
N(31)–O(32)
O(29)–N(31)
O(7)–Cu(28)
O(30)–Cu(28)
Cu(28)–O(29)
O(27)–Cu(28)
N(9)–Cu(28)
C(11)–O(27)
C(26)–C(1)
1.339
1.342
1.352
1.814
1.359
1.565
1.35
110.925
110.774
104.669
110.732
112.336
123.317
135.702
99.822
2.003
1.849
1.828
1.828
1.575
1.231
1.349
1.34
131.812
127.91
C(25)–C(26)
C(24)–C(25)
C(23)–C(24)
C(2)–C(23)
1.338
1.341
1.348
99.849
124.265
119.276
1
23

Supramolecular structure, spectroscopic, thermal studies…
Table 7 continued
o
Bond angles ( )
˚
Bond lengths (A)
C(14)–C(22)
N(12)–C(16)
N(13)–C(15)
C(14)–C(10)
N(13)–C(14)
N(12)–N(13)
C(11)–N(12)
C(10)–C(11)
N(9)–C(10)
C(8)–N(9)
1.504
1.283
1.469
1.361
1.253
1.346
1.275
1.457
1.286
1.498
1.626
1.789
1.35
N(13)–N(12)–C(11)
O(27)–C(11)–N(12)
O(27)–C(11)–C(10)
N(12)–C(11)–C(10)
Cu(28)–O(33)–N(31)
H(53)–O(30)–H(52)
H(53)–O(30)–Cu(28)
H(52)–O(30)–Cu(28)
N(31)–O(29)–Cu(28)
Cu(28)–O(27)–C(11)
O(33)–Cu(28)–O(7)
O(33)–Cu(28)–O(30)
O(33)–Cu(28)–O(29)
O(33)–Cu(28)–O(27)
O(33)–Cu(28)–N(9)
O(7)–Cu(28)–O(30)
O(7)–Cu(28)–O(29)
O(7)–Cu(28)–O(27)
O(7)–Cu(28)–N(9)
O(30)–Cu(28)–O(29)
O(30)–Cu(28)–O(27)
O(30)–Cu(28)–N(9)
O(29)–Cu(28)–O(27)
O(29)–Cu(28)–N(9)
O(27)–Cu(28)–N(9)
C(14)–C(10)–C(11)
C(14)–C(10)–N(9)
C(11)–C(10)–N(9)
Cu(28)–N(9)–C(10)
Cu(28)–N(9)–C(8)
C(10)–N(9)–C(8)
115.935
165.505
83.352
83.209
68.443
71.707
92.777
163.598
68.151
110.038
58.207
C(6)–C(8)
C(5)–O(7)
101.626
60.481
C(6)–C(2)
C(5)–C(6)
1.628
1.336
1.34
147.768
118.049
134.033
102.169
91.013
C(4)–C(5)
C(3)–C(4)
C(1)–C(3)
1.349
1.355
C(1)–C(2)
107.588
100.414
93.252
118.053
144.439
66.744
77.83
116.292
117.217
126.192
101.862
122.904
131.553
120.548
120.231
119.221
119.915
120.46
H(50)–C(25)–C(26)
H(50)–C(25)–C(24)
C(26)–C(25)–C(24)
H(49)–C(24)–C(25)
H(49)–C(24)–C(23)
C(25)–C(24)–C(23)
H(48)–C(23)–C(24)
H(48)–C(23)–C(2)
C(24)–C(23)–C(2)
H(36)–C(8)–N(9)
119.625
115.786
122.346
121.867
116.09
123

A. Z. El-Sonbati et al.
Table 7 continued
o
Bond angles ( )
˚
Bond lengths (A)
H(36)–C(8)–C(6)
N(9)–C(8)–C(6)
Cu(28)–O(7)–C(5)
C(8)–C(6)–C(2)
C(8)–C(6)–C(5)
C(2)–C(6)–C(5)
O(7)–C(5)–C(6)
O(7)–C(5)–C(4)
C(6)–C(5)–C(4)
H(35)–C(4)–C(5)
H(35)–C(4)–C(3)
C(5)–C(4)–C(3)
H(51)–C(26)–C(1)
H(51)–C(26)–C(25)
C(1)–C(26)–C(25)
H(34)–C(3)–C(4)
H(34)–C(3)–C(1)
C(4)–C(3)–C(1)
C(23)–C(2)–C(6)
C(23)–C(2)–C(1)
C(6)–C(2)–C(1)
C(26)–C(1)–C(3)
C(26)–C(1)–C(2)
C(3)–C(1)–C(2)
115.606
128.152
112.218
126.282
118.103
115.505
117.624
124.144
118.221
119.334
121.615
119.049
121.239
117.165
121.596
115.841
120.125
124.029
121.658
118.382
119.955
117.469
119.309
123.222
2
2
2
2
B1g ! A1gðt1Þ;
B1g ! B2gðt2Þ
The complex of Cd(II) is diamagnetic. In analogy with those described for the
Cd(II) complex containing N–O donor Schiff bases and according to the empirical
formulae of this complex, a square planar geometry was proposed for the Cd(II)
complex [51].
ESR spectroscopy
ESR spectra of the polycrystalline were recorded at room temperature and presented
in Table 12. The values of g factors were assessed following the method described
by Searl et al. [52]. The g tensor values of Cu(II) complex can be used to derive the
ground state. In tetragonal and square planar complexes, the unpaired electron lies
2
in the d
2
2
orbital giving B as the ground state with the g [ g [ 2.0023 [20].
x Ày
1g
ll
\
From the observed values for complexes (1–3), it is clear that g [ g . These data
ll
\
are in agreement with those obtained from the electronic spectra and confirm the
1
23

Supramolecular structure, spectroscopic, thermal studies…
Table 8 The selected geometric parameters for complex (3)
o
Bond angles ( )
˚
Bond lengths (A)
O(31)–H(61)
O(31)–H(60)
O(30)–H(59)
O(30)–H(58)
O(29)–H(57)
O(29)–H(56)
C(26)–H(55)
C(25)–H(54)
C(24)–H(53)
C(23)–H(52)
C(22)–H(51)
C(22)–H(50)
C(22)–H(49)
C(21)–H(48)
C(20)–H(47)
C(19)–H(46)
C(18)–H(45)
C(17)–H(44)
C(15)–H(43)
C(15)–H(42)
C(15)–H(41)
C(8)–H(40)
O(7)–H(39)
C(4)–H(38)
C(3)–H(37)
C(16)–C(21)
C(20)–C(21)
C(19)–C(20)
C(18)–C(19)
C(17)–C(18)
C(16)–C(17)
C(4)–C(3)
1.081
1.088
1.068
1.25
O(32)–S(33)–O(36)
O(32)–S(33)–O(35)
O(32)–S(33)–O(34)
O(36)–S(33)–O(35)
O(36)–S(33)–O(34)
O(35)–S(33)–O(34)
H(47)–C(20)–C(21)
H(47)–C(20)–C(19)
C(21)–C(20)–C(19)
H(46)–C(19)–C(20)
H(46)–C(19)–C(18)
C(20)–C(19)–C(18)
H(45)–C(18)–C(19)
H(45)–C(18)–C(17)
C(19)–C(18)–C(17)
H(48)–C(21)–C(16)
H(48)–C(21)–C(20)
C(16)–C(21)–C(20)
H(44)–C(17)–C(18)
H(44)–C(17)–C(16)
C(18)–C(17)–C(16)
Cu(28)–O(32)–S(33)
H(61)–O(31)–H(60)
H(61)–O(31)–Cu(28)
H(60)–O(31)–Cu(28)
H(59)–O(30)–H(58)
H(59)–O(30)–Cu(28)
H(58)–O(30)–Cu(28)
H(57)–O(29)–H(56)
H(57)–O(29)–Cu(28)
H(56)–O(29)–Cu(28)
C(21)–C(16)–C(17)
C(21)–C(16)–N(12)
C(17)–C(16)–N(12)
H(43)–C(15)–H(42)
H(43)–C(15)–H(41)
H(43)–C(15)–N(13)
H(42)–C(15)–H(41)
H(42)–C(15)–N(13)
H(41)–C(15)–N(13)
C(16)–N(12)–N(13)
115.267
113.457
115.449
87.909
1.132
1.079
1.09
97.365
122.263
129.984
109.495
120.444
126.203
122.635
111.157
115.069
118.949
125.897
128.395
100.426
131.179
117.719
112.387
129.857
121.204
83.093
1.091
1.114
1.078
1.1
1.108
1.13
1.108
1.109
1.116
1.104
1.09
1.168
1.151
1.099
1.13
0.967
1.103
1.096
1.426
1.376
1.333
1.331
1.349
1.343
1.338
1.337
1.34
78.195
148.923
134.231
111.033
102.063
58.116
153.166
116.446
101.157
135.222
123.565
78.856
C(1)–C(3)
C(2)–C(1)
C(26)–C(1)
C(25)–C(26)
C(24)–C(25)
C(23)–C(24)
C(2)–C(23)
C(6)–C(2)
1.351
1.335
1.317
1.337
1.35
97.921
119.332
100.985
120.149
127.687
142.175
1.373
1.345
C(5)–C(6)
123

A. Z. El-Sonbati et al.
Table 8 continued
o
Bond angles ( )
˚
Bond lengths (A)
C(4)–C(5)
1.339
1.792
1.933
1.903
1.931
1.849
1.409
1.264
1.583
1.39
C(16)–N(12)–C(11)
N(13)–N(12)–C(11)
Cu(28)–O(27)–C(11)
H(51)–C(22)–H(50)
H(51)–C(22)–H(49)
H(51)–C(22)–C(14)
H(50)–C(22)–H(49)
H(50)–C(22)–C(14)
H(49)–C(22)–C(14)
C(15)–N(13)–C(14)
C(15)–N(13)–N(12)
C(14)–N(13)–N(12)
C(22)–C(14)–C(10)
C(22)–C(14)–N(13)
C(10)–C(14)–N(13)
O(27)–C(11)–N(12)
O(27)–C(11)–C(10)
N(12)–C(11)–C(10)
O(31)–Cu(28)–O(30)
O(31)–Cu(28)–O(29)
O(31)–Cu(28)–O(32)
O(31)–Cu(28)–O(27)
O(31)–Cu(28)–N(9)
O(30)–Cu(28)–O(29)
O(30)–Cu(28)–O(32)
O(30)–Cu(28)–O(27)
O(30)–Cu(28)–N(9)
O(29)–Cu(28)–O(32)
O(29)–Cu(28)–O(27)
O(29)–Cu(28)–N(9)
O(32)–Cu(28)–O(27)
O(32)–Cu(28)–N(9)
O(27)–Cu(28)–N(9)
C(14)–C(10)–C(11)
C(14)–C(10)–N(9)
C(11)–C(10)–N(9)
Cu(28)–N(9)–C(10)
Cu(28)–N(9)–C(8)
C(10)–N(9)–C(8)
96.352
116.553
112.384
109.838
106.109
111.976
101.344
121.063
104.765
90.377
O(31)–Cu(28)
O(30)–Cu(28)
O(29)–Cu(28)
Cu(28)–O(32)
O(27)–Cu(28)
N(9)–Cu(28)
C(11)–O(27)
C(14)–C(22)
N(12)–C(16)
N(13)–C(15)
C(14)–C(10)
N(13)–C(14)
N(12)–N(13)
C(11)–N(12)
C(10)–C(11)
N(9)–C(10)
C(8)–N(9)
1.809
1.407
1.219
1.418
1.295
1.365
1.295
1.292
1.359
1.364
1.759
1.717
1.566
1.444
151.893
106.749
118.828
95.37
85.009
166.882
83.465
83.425
C(6)–C(8)
64.311
C(5)–O(7)
84.853
O(32)–S(33)
S(33)–O(36)
S(33)–O(35)
S(33)–O(34)
69.112
73.986
151.272
53.14
79.986
122.012
135.405
132.91
85.974
93.894
120.722
127.514
77.294
125.631
116.605
109.324
118.063
110.829
125.215
128.232
116.282
H(54)–C(25)–C(26)
H(54)–C(25)–C(24)
1
23

Supramolecular structure, spectroscopic, thermal studies…
Table 8 continued
o
Bond angles ( )
˚
Bond lengths (A)
C(26)–C(25)–C(24)
H(53)–C(24)–C(25)
H(53)–C(24)–C(23)
C(25)–C(24)–C(23)
H(52)–C(23)–C(24)
H(52)–C(23)–C(2)
C(24)–C(23)–C(2)
H(40)–C(8)–N(9)
H(40)–C(8)–C(6)
N(9)–C(8)–C(6)
H(39)–O(7)–C(5)
C(2)–C(6)–C(5)
C(2)–C(6)–C(8)
C(5)–C(6)–C(8)
C(6)–C(5)–C(4)
C(6)–C(5)–O(7)
C(4)–C(5)–O(7)
H(38)–C(4)–C(3)
H(38)–C(4)–C(5)
C(3)–C(4)–C(5)
H(55)–C(26)–C(1)
H(55)–C(26)–C(25)
C(1)–C(26)–C(25)
H(37)–C(3)–C(4)
H(37)–C(3)–C(1)
C(4)–C(3)–C(1)
C(1)–C(2)–C(23)
C(1)–C(2)–C(6)
C(23)–C(2)–C(6)
C(3)–C(1)–C(2)
C(3)–C(1)–C(26)
C(2)–C(1)–C(26)
115.446
122.142
122.95
114.906
101.744
125.902
132.184
122.76
122.377
114.01
110.78
117.705
124.161
117.897
117.819
122.551
119.341
118.579
118.4
123.019
121.286
113.149
125.42
119.735
119.209
121.034
106.795
124.24
128.506
115.716
122.692
121.56
square planar geometry for complex (1) and the tetragonal geometry for complexes
2
(
2) and (3). The term of the fundamental state is thus defined by the orbital d
2
.
x Ày
The ESR spectrum of the copper(II) complex (1) has been reported such that g
ll
can be used as a measure of the covalent character of the metal–ligand bond. If the
value is more than 2.3, the metal–ligand bond is essentially ionic, and the value less
than 2.3 is indicative of covalent character [53]. Apart from this, the covalency
2
parameter (a ) has been calculated using the Kivelson and Neinant equation [45].
2
The covalency parameter (a = 0.58) indicates considerable covalent character for
the metal–ligand bond [54]. Also, the trend g [ g [ 2.0023 observed for this
ll
\
123

A. Z. El-Sonbati et al.
Table 9 The selected geometric parameters for complex (4)
o
Bond angles ( )
˚
Bond lengths (A)
O(32)–H(55)
O(32)–H(54)
O(31)–H(53)
O(31)–H(52)
C(26)–H(51)
C(25)–H(50)
C(24)–H(49)
C(23)–H(48)
C(22)–H(47)
C(22)–H(46)
C(22)–H(45)
C(21)–H(44)
C(20)–H(43)
C(19)–H(42)
C(18)–H(41)
C(17)–H(40)
C(15)–H(39)
C(15)–H(38)
C(15)–H(37)
C(8)–H(36)
O(7)–H(35)
C(4)–H(34)
C(3)–H(33)
C(16)–C(21)
C(20)–C(21)
C(19)–C(20)
C(18)–C(19)
C(17)–C(18)
C(16)–C(17)
C(4)–C(3)
1.15
H(43)–C(20)–C(21)
H(43)–C(20)–C(19)
C(21)–C(20)–C(19)
H(42)–C(19)–C(20)
H(42)–C(19)–C(18)
C(20)–C(19)–C(18)
H(41)–C(18)–C(19)
H(41)–C(18)–C(17)
C(19)–C(18)–C(17)
H(44)–C(21)–C(16)
H(44)–C(21)–C(20)
C(16)–C(21)–C(20)
H(40)–C(17)–C(18)
H(40)–C(17)–C(16)
C(18)–C(17)–C(16)
H(55)–O(32)–H(54)
H(55)–O(32)–Co(28)
H(54)–O(32)–Co(28)
H(53)–O(31)–H(52)
H(53)–O(31)–Co(28)
H(52)–O(31)–Co(28)
C(21)–C(16)–C(17)
C(21)–C(16)–N(12)
C(17)–C(16)–N(12)
H(39)–C(15)–H(38)
H(39)–C(15)–H(37)
H(39)–C(15)–N(13)
H(38)–C(15)–H(37)
H(38)–C(15)–N(13)
H(37)–C(15)–N(13)
C(16)–N(12)–N(13)
C(16)–N(12)–C(11)
N(13)–N(12)–C(11)
Co(28)–O(27)–C(11)
H(47)–C(22)–H(46)
H(47)–C(22)–H(45)
H(47)–C(22)–C(14)
H(46)–C(22)–H(45)
H(46)–C(22)–C(14)
H(45)–C(22)–C(14)
C(15)–N(13)–C(14)
120.119
119.578
120.302
120.533
120.526
118.939
119.752
120.179
120.063
122.21
1.15
1.149
1.15
1.104
1.102
1.104
1.094
1.11
1.113
1.113
1.1
115.689
122.067
116.647
120.971
122.345
120.177
114.473
124.711
122.792
122.353
114.316
116.273
123.83
1.103
1.103
1.103
1.102
1.111
1.113
1.113
1.105
0.969
1.104
1.104
1.349
1.343
1.34
119.876
104.323
107.721
113.487
109.895
110.846
110.356
123.74
1.34
1.342
1.349
1.334
1.342
1.356
1.347
1.338
1.336
1.342
1.353
1.364
1.359
1.341
1.193
C(1)–C(3)
C(2)–C(1)
129.021
103
C(26)–C(1)
C(25)–C(26)
C(24)–C(25)
C(23)–C(24)
C(2)–C(23)
C(6)–C(2)
109.707
106.664
107.101
112.573
109.306
110.557
110.485
115.539
C(5)–C(6)
C(4)–C(5)
O(32)–Co(28)
1
23