New 5-bromo-2-hydroxybenzaldehyde S-ethylisothiosemicarbazone and its mixed-ligand Cu(II) complex with imidazole: Synthesis, characterization and DFT calculation

Article abstract of DOI:10.2478/s11532-013-0313-5

A new Schiff base ligand of 5-bromo-2-hydroxybenzaldehyde S-ethyl-isothiosemicarbazone (H₂L) was synthesized and its mixed-ligand Cu(II) complex was also prepared by reaction of Cu(NO ₃)₂·3H₂O with H₂L and imidazole. Their structures were fully characterized by elemental analysis, FT-IR, molar conductivity and UV-Vis methods. The analytical data suggest that the metal, H₂L and imidazole ratios in the Schiff base complex are 1:1:1. Single crystal diffraction was also used to better understand the molecular structure of the Cu(II) complex. The results of physico-chemical analyses of the Schiff base complex reveal the coordination geometry around the central atom is square planar. The H₂L ligand (NNO donor) is coordinated to the metal center as a tridentate bionegatively agent. Another position of the square planar geometry is occupied by the imidazole ligand. Furthermore, computational studies of the new complex were performed by carrying out DFT calculations. Geometry optimization and natural band analysis of the complex is discussed in further detail. [Figure not available: see fulltext.]

Full text of DOI:10.2478/s11532-013-0313-5

Cent. Eur. J. Chem. • 11(11) • 2013 • 1844-1851
DOI: 10.2478/s11532-013-0313-5
Central European Journal of Chemistry
New 5-bromo-2-hydroxybenzaldehyde S-ethyl-
isothiosemicarbazone and its mixed-ligand
Cu(II) complex with imidazole: synthesis,
characterization and DFT calculation
Research Article
Reza Takjoo1*, Alireza Akbari2, Mehdi Ahmadi2,
Hadi Amiri Rudbari3, Giuseppe Bruno4
1Department of Chemistry, School of Sciences,
Ferdowsi University of Mashhad, Mashhad 91775-1436, Iran
2Department of Chemistry, Payame Noor University (PNU),
19395-4697 Tehran, Iran
3Department of Chemistry, Isfahan University of Technology,
Isfahan 84156-83111, Iran
4Department of Inorganic Chemistry,
Analytical Chemistry and Physical Chemistry, University of Messina,
Salita Sperone, 98199 Messina, Italy
Received 19 December 2012; Accepted 8 July 2013
Abstract:
A new Schiff base ligand of 5-bromo-2-hydroxybenzaldehyde S-ethyl-isothiosemicarbazone (H2L) was synthesized and its mixed-ligand
Cu(II) complex was also prepared by reaction of Cu(NO3)2•3H2O with H2L and imidazole. Their structures were fully characterized by
elemental analysis, FT-IR, molar conductivity and UV–Vis methods. The analytical data suggest that the metal, H2L and imidazole ratios
in the Schiff base complex are 1:1:1. Single crystal diffraction was also used to better understand the molecular structure of the Cu(II)
complex. The results of physico-chemical analyses of the Schiff base complex reveal the coordination geometry around the central atom
is square planar. The H2L ligand (NNO donor) is coordinated to the metal center as a tridentate bionegatively agent. Another position of
the square planar geometry is occupied by the imidazole ligand. Furthermore, computational studies of the new complex were performed
by carrying out DFT calculations. Geometry optimization and natural band analysis of the complex is discussed in further detail.
Keywords: Schiff base • Isothiosemicarbazone • Cu(II) complex • Crystal structure • DFT
© Versita Sp. z o.o.
as significant active sites [5]. In addition, a large number
of copper(II) complexes with Schiff base ligands have
1. Introduction
There has been increasing interest in research on also been prepared and their catalytic abilities have
copper complexes because of their photophysical been investigated [6].
behavior [1], as well as electrochemical and corrosion
The chemistry of imidazole derivatives has attracted
inhibiting properties [2,3]. Copper complexes show attention due to its wide application in medicine [7],
great potential in the area of organic chemistry [4]. and its presence in important biological building-
From a bioinorganic perspective, copper complexes blocks such as histidine and histamine [8,9], antifungal
have been extensively studied due to their similarity to drugs [10], fuel cell membranes [11] and luminescent
metalloproteins. This has introduced copper compounds materials [12]. The most important property is that the
* E-mail: r.takjoo@um.ac.ir
1844

R. Takjoo et al.
interaction of small molecules such as imidazole with ethanol and chloroform and dried in vacuo over silica
DNA has shown suitable quality in recent years [13]. gel.
The facile redox behavior of Cu(II) has made the ion
Yield: 2.48 g (82%). M.p. 137oC. FT-IR (film): νas
an intriguing target for artificial nuclease design [14]. = 3286 (NH2), νsy = 3203 (NH2), ν = 3062 (OH), 2854-
In this work, we have described the syntheses and 293 (CH), 1639 (ν(C=N) + δ(NH2)), 1600 & 1516 (C=N
characterizations of 5-bromo-2-hydroxybenzaldehyde + C=C), 1473 (C=C), 1184 (C-O), 1080 (N-N), δ = 648
1
S-ethyl-isothiosemicarbazone ligand and (5-bromo-2- (CH). H NMR (100 MHz, DMSO-d6): δ = 11.7 (s, 1H,
hydroxybenzaldehyde S-ethyl-isothiosemicarbazonato- O1H), 10.8 (s, H, N3bH), 8.4 (d, 1H, C7H), 7.9 (d,
N,N’,O)-(imidazole)-copper(II)
complex
(Cu(L)Im, 1H, N2bH), 7.7 (d, 1H, C5), 7.4 (dd, 1H, C3), 7.1 (s,
Im:imidazole) as two new compounds by spectral 2H, N3H2), 6.8 (d, 1H, C2), 3 (q, 2H, C9), 1.3 (t, 3H,
properties and micro analysis. The solid-state structure C10). Anal. Calc. for C10H12BrN3OS: C, 39.75; H, 4.00;
of the Cu(II) complex was also investigated. In addition, N, 13.91. Found: C, 39.31; H, 4.06; N, 13.76%. UV/
we use density functional theory to predict geometry Vis (methanol): λ
(lg ε max): 224 nm (4.43), 240 nm
max
optimization and natural band analysis. More recently, (4.35), 298 nm (4.28), 344 nm (4.22). Molar conductivity
DFT (Density Functional Theory) calculations were (1.0Í10-3 M; methanol): 23 Ω-1 cm2 mol-1.
used to investigate natural band behavior [15,16].
Preparation
Preparation
hydroxybenzaldehyde
hydroxybenzaldehy
of
(5-bromo-2-
S-ethyl-
2.3.
of
2. Experimental procedure
isothiosemicarbazonato-N,N’,O)-
isothiosemicarbazonato-N,N’,O)-(imidazole)
(imidazole)-copper(II)
copper(II)
2.1. Physical measurements
H2L (0.30 g, 1 mmol) was dissolved in 5 mL of ethanol
and added dropwise to a 5 mL ethanolic solution of a
mixtureofCu(NO3)2•3H2O(0.24g, 1mmol)andimidazole
(0.07 g, 1 mmol) at room temperature. The solution
color gradually turned back to red after three hours.
The clear solution was put in a refrigerator to produce
suitable crystals. The appropriate single crystals were
obtained after one week. They were separated and
washed several times with cold ethanol and dried in
vacuo over silica gel.
All solvents and metal salt were of analytical reagent
grades and used without any further purification. The
infrared spectra were recorded on an 8400-SHIMADZU
FT-IR spectrometer. Solid samples were examined as
KBr discs. The electronic spectra were recorded on a
SHIMADZU model 2550 UV–Vis spectrophotometer
at concentrations of 2×10-5 and 1×10-3 M. 1H NMR
spectra were recorded on a Bruker BRX 100 AVANCE
spectrometer in DMSO-d6. C, H and N elemental
analyses were performed on a Thermo Finnigan
Flash Elemental Analyzer 1112EA instrument. Electric
conductance measurements were carried out with a
Metrohm 712 Conductometer at a concentration of
1×10-3 M in methanol. Diffraction data were measured
using a Bruker APEX II CCD diffractometer.
Yield: 0.24 g (55%). M.p. 186oC. FT-IR (film): ν =
3409 (NH)Im, 3117 (N3H), 3039-3050 (CH)Im, 2854-
2931 (CH)ar, 1597 & 1497 (C=N + C=C), 1452 (C=C),
1157 (C-O), 1064 (N-N), δ = 656 (CH). Anal. Calc. for
C13H14BrCuN5OS: C, 36.16; H, 3.27; N, 16.22. Found:
C, 36.51; H, 3.16; N, 16.06%. UV/Vis (methanol): λ
max
(lg ε max): 222 nm (4.36), 242 nm (4.4), 340 nm(4.06),
392 nm(4.22), 580 nm (2.3). Molar conductivity
(1.0×10-3 M; methanol): 11 Ω-1 cm2 mol-1.
2.2.
Preparation
Preparation
of
of
5-bromo-2-
S-ethyl-
hydroxybenzaldehy
hydroxybenzaldehyde
isothiosemicarbazone (H L)
isothiosemicarbazone (H L)
2
2
2.4. Crystal structure determination
Thiosemicarbazide (0.91 g, 10 mmol) was treated
with ethyl iodide (1.72 g, 11 mmol) in 10 ml ethanol
for 1 h at 90°C until all solid vanished. 5-bromo-2-
hydroxybenzaldehyde (2.01 g, 10 mmol) was added
to the reaction and reflux continued for one hour extra.
A yellow precipitate was filtered off. After completely
drying, it was dissolved in 50 mL of chloroform, and
10 mL of aqueous Na2CO3•10H2O (2.68 g, 10 mmol) was
added to neutralize hydrogen iodide in constant stirring
at room temperature. The two layers were separated
and the organic layer left to stand overnight. A colorless
precipitate separated. It was washed several times with
Data were collected at room temperature with a Bruker
APEX II CCD area-detector diffractometer using Mo
Ka radiation (λ = 0.71073 Å). Data collection, cell
refinement, data reduction and absorption correction
were performed using multi scan methods with Bruker
software[17].Thestructurewassolvedbydirectmethods
using SIR2004 [18]. The non hydrogen atoms were
refined anisotropically by the full matrix least squares
method on F2 using SHELXL [19]. All the hydrogen
(H) atoms were placed at the calculated positions and
constrained to remain on their parent atoms. The crystal
1845

New 5-bromo-2-hydroxybenzaldehyde S-ethyl-isothiosemicarbazone
and its mixed-ligand Cu(II) complex with imidazole: synthesis,
characterization and DFT calculation
data, data collection parameters, and structure solution Table 1. Crystal data and structure refinement for Cu(II)-complex.
and refinement details for the determined structure is
reported in Table 1.
Empirical formula
C
13H14BrCuN5OS
Formula weight
Temperature
431.80
296(2) K
2.5. Computational methods
The geometry of the copper(II) structure was optimized
at the DFT level by using the B3LYP method [20,21]
with the Gaussian 98 program [22]. In the unrestricted
calculations, the 6-311++G(d,p) basis set was employed
on C, H, N, S and O atoms and LANL2DZ [23] was
selected on the central ion. The full optimization of the
initial geometry was modified by frequency calculation
that does not show any imaginary frequency, confirming
geometry optimization was carried out successfully. In
addition, natural band orbital (NBO) analysis was done
with the NBO code included in Gaussian 98 [24].
Wavelength
0.71073 Å
Triclinic, P-1
Crystal system, space group
a = 7.5705(3) Å
b = 8.9644(3) Å
α = 76.946(2)°
β = 88.597(2)°
Unit cell dimensions
c = 12.9346(5) Å δ = 70.021(2)°
Volume
802.33(5) Å3
Z, Calculated density
2, 1.787 Mg m-3
Absorption coefficient
F(000)
3.989 mm-1
430
Crystal size
0.14×0.08×0.05 mm
2.49° to 27.55°
Theta range for data collection
-9<=h<=9, -11<=k<=11,
-16<=l<=16
3. Result and discussion
Limiting indices
Reflections collected / unique
15392 / 3698 [R(int) = 0.0238]
In
ethanol,
the
reaction
of
5-bromo-2-
Completeness to theta = 27.55
Refinement method
99.8%
hydroxybenzaldehyde
S-ethyl-isothiosemicarbazone
(H2L) with copper(II) nitrate trihydrate and imidazole,
using a (1:1:1 ) molar ratio, yields a new Cu(II) mixed-
ligand complex. The molar conductivities of the ligand
and the complex are 23 and 11 Ω-1 cm2 mol-1 in methanol
respectively, indicating H2L is neutralized successfully
and a neutral Cu(II) complex is formed [26]. The two
new compounds have good solubility in DMF and
DMSO, less solubility in common organic solvents like
methanol, acetone, chloroform and diethyl ether, and
are insoluble in benzene and n-hexane.
Full-matrix least-squares on F2
Data / restraints / parameters
3698 / 0 / 200
1.023
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
R1 = 0.0307, wR2 = 0.0907
R1 = 0.0406, wR2 = 0.0969
0.608 and -0.662 e. Å-3
Largest diff. peak and hole
conjugation of ν(C=N) + ν(C=C) stretching vibrations
[33]. The stretching vibration of the C-O band appears at
1157 cm-1 which shows a 27 cm-1 blue shift as compared
to the free ligand, modifying coordination through the
oxygen atom that is also supported by elimination of the
ν(O-H) peak [34].
3.1. Spectral properties
All spectra of the H2L and Cu(II) complex are
presented in the supplementary material. H2L has two
characteristic IR absorption bands at 3286 cm-1 and
3203 cm-1, indicative of asymmetric and symmetric
vibrations of the NH2 group respectively [27]. The OH
stretching vibration is located at 3062 cm-1 [28]. The
IR spectrum of ligand also exhibited four strong bands
related to ν(C=N) + δ(NH2) at 1639 cm-1, ν(C=N)
+ ν(C=C) at 1600 cm-1, 1516 cm-1 and ν(C=C) at
1473 cm-1. A band with medium intensity at 1184 cm-1
is assigned to the ν(C-O) vibration band [29,30]. The
IR spectrum of the complex shows two sharp bands at
3409 cm-1 and 3117 cm-1 attributed to ν(NH) of imidazole
and deprotonated NH2 respectively, in agreement
with the coordination of the Schiff base to the metal
ion through the thioamide nitrogen and imidazole
nitrogen atoms respectively [31,32]. Two intensive
bands at 1597 cm-1 and 1497 cm-1 are ascribed to the
In the UV-Vis spectrum of H2L, the two bands at
224 nm and at 240 nm are attributed to the π→π*
transitionofthebenzeneringof5-bromo-salicylaldehyde.
The azomethine and thioamide chromophore n→π*
transitions are observed at 298 nm and 344 nm,
respectively [35]. For the Cu(II) complex, the two
bands at 222 nm and 242 nm in the UV-Vis spectrum
are attributed to the π→π* transition of the aromatic
ring. The lower energy band at 340 nm is related to
the n→π* transition [36]. Similar to other square planar
Cu(II) complexes, the fourth band at 392 nm reveals
coordination of the ligand to metal center. The high
epsilon value of log ɛ= 4.22 confirms this band is due
to MLCT (metal to ligand) and LMCT (ligand to metal)
charge transfer transitions [37]. Three spin transitions
are possible for four-coordinated Cu(II) complexes
1846

R. Takjoo et al.
Scheme 1. The two tautomeric forms of H2L with numbering view used for the assignment of 1H NMR.
2
2
that are assigned as follows: A1g→2B1g, B2g→2B1g and nitrogen and the anionic thioaminenitrogen atoms. The
2Eg→2B1g. The high intensity charge transfer bands remaining site of the square planar geometry is occupied
2
2
masked A1g→2B1g and B2g→2B1g transitions and only by imidazole.
the Eg→2B1g transition displays at 580 nm with a low
intensity of log ɛ = 2.3 [38].
The donor-copper bonds are Cu1-O1, Cu1-N1,
Cu1-N3 and Cu1–N4 with bond lengths of 1.892(2) Å,
2
The 1H NMR spectrum of H2L was recorded in 1.956(2) Å, 1.920(3) Å and 1.981(2) Å, respectively,
DMSO solvent. Two tautomeric forms of H2L along which conform with observed values in this class
with their numbering are depicted in Scheme 1. The copper(II) complex [39]. The bond distances and bond
1H NMR spectrum shows a broad peak at 11.7 ppm, angles found in the aromatic ring and S-ethyl fragments
corresponding to the OH proton resonance; two singlet are in good agreement with corresponding values
signals due to the N3bH and N2bH resonance at 10.8 ppm for the related compound [40]. The bond distances
and 7.9 ppm; and a broad signal recorded at 7.1 ppm C8-N2 = 1.332(3) Å and C8-N3 = 1.315(3) Å are
corresponds to N3H2, which corroborate the existence between the double and single C-N bond comparing
of both tautomeric forms in solution. The OH, N3bH, with some transition metal complexes with tridentate
N2bH and N3H2 signals disappear in the presence of S-alky-lisothiosemicarbazones, indicating
a
large
D2O, which is evidence of their exchangeability. A sharp electron delocalization in the iosthiosemicarbazone
single peak appears at 8.4 ppm, corresponding to the fragment [41]. The four bond angles N3-Cu1-N4, N3-
azometinic proton. The signals of aromatic protons Cu1-N1, N1-Cu1-O1 and O1-Cu1-N4 around the
corresponding to C5, C3 and C2 appear at 7.7, 7.4 copper(II) center are 96.84(9)o, 80.64(9)o, 92.92(9)o and
and 7.1 ppm as a doublet, doublet- doublet and singlet 89.92(9)o respectively. The significant discrepancy
respectively. Finally, the C9 and C10 protons appear as between N3-Cu1-N1 and the other angles is due to
triplet and quartet peaks at 3 and 1.3 ppm.
formation of a five membered chelating ring. This
observation is also noted in a related copper(II)
complex [42]. It is interesting that the imidazole ring
3.2. Crystal structure of Cu(II) complex
The best resolution of the structure of the Cu(II) complex is shifted toward the O atom, as shown by the angle
was achieved by single crystal X-ray diffraction. An O1-Cu1-N4 of 89.92(9)o compared with N3-Cu1-N4 of
ORTEP diagram of molecular structure and a unit cell 96.84(9)o. This phenomenon may be due to steric
of the complex by 30% thermal ellipsoids are presented effects. The weak interactions between C13 with C7 and
in Fig. 1. Selected bond lengths and angles around N1 make a dimer that associates with other molecules
the central ion are summarized in Table 2. [Cu(L) through hydrogen bonding. The dimer has an inversion
Im] crystallizes in the triclinic P-1 space group with center and one molecule (sym. Code x,y,z) converts to
unit cell parameters a = 7.5705(3) Å, b = 8.9644(3) Å, another (-x,-y,-z) via inversion at [0,0,0]. These dimers
c = 12.9346(5) Å , α = 76.946(2)o, β = 88.597(2)o, form a one-dimensional chain with N5 and N2 interaction
γ = 70.021(2)o with two molecules in the unit cell. The along the ab plane bisector (Fig. 2).
complex has the expected square planar arrangement
around the central metal ion. The S-ethyl fragment is in 3.3. Geometry optimization and NBO analyses
the trans position with respect to the N3 atom, indicating The geometry of the Cu(II) complex was optimized
that the ligand coordinated to the metal center is in the completely. Some important bond lengths and angles
syn configuration. The ligand behaves as a NNO donor around the central ion of the Cu(II) complex are shown
tridentate bi-negative agent. The coordination is through in Table 2. Generally, the calculated bond lengths
the anionic phenol oxygen atom, the neutral azomethine and angles are fairly consistent with the X-ray crystal
1847

New 5-bromo-2-hydroxybenzaldehyde S-ethyl-isothiosemicarbazone
and its mixed-ligand Cu(II) complex with imidazole: synthesis,
characterization and DFT calculation
Figure 1. ORTEP drawing of the molecular structure and unit cell of the complex [Cu(L)Im].
Figure 2. Crystal packing diagram (sym. code i: x,y,z ii: -x,-y,-z).
Table 2. Selected bond lengths (Å) and angles (o) in the experimental and at the B3LYP/6-311++G calculation.
type
Exp.
Calc.
Type
Exp.
Calc.
Cu1-O1
Cu1-N4
Cu1-N1
Cu1-N3
S1-C8
S1-C9
O1-C1
N1-N2
N1-C7
N2-C8
N3-C8
C7-C6
1.892(2)
1.981(2)
1.956(2)
1.920(3)
1.756(3)
1.803(3)
1.295(3)
1.391(3)
1.275(3)
1.332(3)
1.315(3)
1.436(4)
1.937
2.063
1.987
1.969
1.788
1.837
1.309
1.371
1.295
1.319
1.335
1.439
O1-Cu1-N4
O1-Cu1-N1
O1-Cu1-N3
N4-Cu1-N1
N4-Cu1-N3
N1-Cu1-N3
C8-S1-C9
89.92(9)
92.92(9)
171.11(9)
175.91(9)
96.84(9)
80.64(9)
104.1(2)
127.9(2)
109.0(2)
112.2(2)
122.8(2)
124.2(2)
88.7
92.4
172.3
178.2
98.9
79.8
102.8
128.0
110.2
110.6
123.5
125.5
Cu1-O1-C1
N1-N2-C8
Cu1-N3-C8
N2-C8-N3
N1-C7-C6
structure result. Maximum deviations are 0.082 Å and effects of the chemical environment [43]. The dipole
2.3o for the Cu1-N4 bond and the N4-Cu1-N1 angle, moment of the Cu(II) complex was evaluated to be
respectively, at the B3LYP/6-311++G(d,p) level. The 11.74 Debye into the XY plane, which shows that all
deviations between experiments and calculations may electronegative atoms (Cu, N, O, Br and S) lie in the
be due to choice of an approximate basis set in the plane frame in the square planar environment and they
calculations. The X-ray crystal diffraction was applied do not show significant displacement toward the Z axis.
in the solid state, whereas the theoretical calculations Table 3 presents additional results obtained from the
were performed in the gas phase without considering NBO analysis. There are more spin densities around the
1848

R. Takjoo et al.
Figure 3. Contour plots of the HOMO and LUMO orbitals of the Cu(II) complex.
Table 3. Electron population, spin densities and charge of central
composition [Cu(L)Im] were prepared. The ligand and
ion, nitrogen and oxygen atoms.
the metal complex were characterized by elemental
analysis, FT-IR and UV–Vis spectroscopy. In addition,
X-ray diffraction was employed for characterization
of the metal complex. From the X-ray diffraction and
spectral properties, it was concluded that the ligand
is coordinated to metal as tridentate, bi-negatively
chelating through the azomethine-N and deprotonated
phenolic-O and deprotonated thioamide-N atoms and
one imidazole ligand was also coordinated to the metal
ion. Finally, DFT calculations were applied successfully
to predict the structural geometry and interpret the
atom
Electron population
of the valence core
spin
densities
Charge
Cu1
O1
N4
N1
N3
4S (0.32), 3d (9.39)
2S (1.67), 2p (5.08)
2S (1.36), 2p (4.17)
2S (1.31), 2p (3.99)
2S (1.40), 2p (4.47)
0.512
0.109
0.058
0.177
0.116
0.080
-0.324
0.001
-0.005
0.230
copper atom as compared to the nitrogen and oxygen natural band analysis. The geometry of the complex can
donor atoms. The formal charges calculated from the be reproduced with minimum discrepancy with X-ray
natural population analysis on the central ion, O1, N1, crystallography information. NBO analysis predicted
N3 and N4 were found to be 0.08 a.u., -0.324 a.u., a formal charge of 0.08 a.u. on the central ion Cu(II),
0.001 a.u., -0.005 a.u. and 0.23 a.u. respectively, which indicating electron transmission from donor atoms
indicate that donor atoms transmit electrons toward the N and O. Finally, the Cu(II) complex is air stable and
central atom.. The calculated formal charge of Cu(II) soluble in most solvents, which may lead to increasing
is much lower than the expected +2, indicating charge interest in research on its biological and catalytic
donation of donor atoms toward the central ion. No activities.
bonds were detected between the central ion and donor
atoms N1 and N2 in the NBO analysis, which may be
due to weak interactions between Cu(II) with N1 and N2 Supplementary data
atoms [44]. Fig. 3 depicts the HOMO and LUMO orbitals
of the copper(II) complex. As can be seen in Fig. 3, a Crystallographic data for the structural analysis was
substantial contribution of electron density is localized deposited in the Cambridge Crystallographic Data
toward the tridentate NNO donor ligand and the central Centre, CCDC No. 879871 for the Cu(II) complex. A
ion in the HOMO orbital. The majority of the LUMO is copy of this information may be obtained free of charge
also located on the ligand, though a little is also located from The Director, CCDC, 12 Union Road, Cambridge,
on the Cu(II) atom. However, the HOMO and LUMO Cb2 1EZ, UK (fax: +44 1223 336 033); e-mail: deposit@
act primarily as electron donor and electron acceptor ccdc.cam.ac.uk.
respectively. The transition state from the HOMO to the
LUMO can be predicted by a combination of inter-ligand
and MLCT charge transfer [45].
Acknowledgements
We thank the Department of Chemistry, at Ferdowsi
4. Conclusion
University of Mashhad and Payame Noor University
(PNU) for financial assistance received. We thank
A new asymmetric tridentate NNO donor Schiff base the Università di Messina (Italy) for the provision of a
ligand (H2L) and its copper(II) complex with the general diffractometer.
1849

New 5-bromo-2-hydroxybenzaldehyde S-ethyl-isothiosemicarbazone
and its mixed-ligand Cu(II) complex with imidazole: synthesis,
characterization and DFT calculation
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