A new mixed-ligand copper(II) complex of (E)-N′-(2- hydroxybenzylidene) acetohydrazide: Synthesis, characterization, NLO behavior, DFT calculation and biological activities

Article abstract of DOI:10.1016/j.molstruc.2014.05.024

A tridentate hydrazone Schiff base ligand, (E)-N′-(2- hydroxybenzylidene)acetohydrazide [HL], and its mixed-ligand Cu(II) complex [CuL(phen)], have been synthesized and characterized by elemental analyses, FT-IR, molar conductivity, UV-Vis spectroscopy. The structure of the complex has been determined by X-ray diffraction. This complex has square pyramidal geometry and the positions around central atom are occupied with donor atoms of Schiff base ligand and two nitrogens of 1,10-phenanthroline. Computational studies of compounds were performed by using DFT calculations. The linear polarizabilities and first hyperpolarizabilities of the studied molecules indicate that these compounds can be good candidates of nonlinear optical materials. It is in accordance with experimental data. In addition, invitro antimicrobial results show that these compounds specially [CuL(phen)] have great potential of antibacterial activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Listeria monocytogenes bacteria and antifungal activity against Candida Albicans in comparison to some standard drugs.

Full text of DOI:10.1016/j.molstruc.2014.05.024

Journal of Molecular Structure xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
A new mixed-ligand copper(II) complex of
(E)-N0-(2-hydroxybenzylidene) acetohydrazide: Synthesis,
characterization, NLO behavior, DFT calculation and biological activities
a
b
c
d
S. Yousef Ebrahimipour a, , Iran Sheikhshoaie , Aurelien Crochet , Moj Khaleghi , Katharina M. Fromm
⇑
a Department of Chemistry, Shahid Bahonar University of Kerman, 7616914111, Kerman, Iran
b FriMat, University of Fribourg, Chemin du Musée 6, CH-1700 Fribourg, Switzerland
c Department of Biology, Shahid Bahonar University of Kerman, 7616914111, Kerman, Iran
d Department of Chemistry, University of Fribourg, Chemin du Musée 9, CH-1700 Fribourg, Switzerland
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
ꢀ
Crystal structure of a new mixed
ligand Cu(II) complex has been
determined by single crystal X-ray
diffraction analysis.
ꢀ
The electronic nature of the
compounds have been investigated
via DFT calculations.
ꢀ
ꢀ
NBO, vibrational and UV-Vis spectral
analysis were carried out.
The antimicrobial activities of
compounds were evaluated against
microorganisms.
a r t i c l e i n f o
a b s t r a c t
A tridentate hydrazone Schiff base ligand, (E)-N0-(2-hydroxybenzylidene)acetohydrazide [HL], and its
mixed-ligand Cu(II) complex [CuL(phen)], have been synthesized and characterized by elemental analy-
ses, FT-IR, molar conductivity, UV–Vis spectroscopy. The structure of the complex has been determined
by X-ray diffraction. This complex has square pyramidal geometry and the positions around central atom
are occupied with donor atoms of Schiff base ligand and two nitrogens of 1,10-phenanthroline. Compu-
tational studies of compounds were performed by using DFT calculations. The linear polarizabilities and
first hyperpolarizabilities of the studied molecules indicate that these compounds can be good candidates
of nonlinear optical materials. It is in accordance with experimental data. In addition, invitro antimicro-
bial results show that these compounds specially [CuL(phen)] have great potential of antibacterial activ-
ity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Listeria monocytogenes bacteria
and antifungal activity against Candida Albicans in comparison to some standard drugs.
Article history:
Received 29 March 2014
Received in revised form 9 May 2014
Accepted 9 May 2014
Available online xxxx
Keywords:
Cu(II) complex
ONO donor
DFT calculation
Antimicrobial activity
Crystal structure
Ó 2014 Elsevier B.V. All rights reserved.
Introduction
applications [1,2]. Copper(II) complexes can act as efficient
catalysts in many chemical processes. Also many reports
Nowadays, copper(II) Schiff base complexes have attracted
great attention in coordination chemistry due to their different
have shown that they are suitable candidates for NLO materials
[3,4].
⇑
Corresponding author. Tel./fax: +98 (341) 3222033.
E-mail addresses: ebrahimipour@uk.ac.ir, ebrahimipour@ymail.com (S. Yousef Ebrahimipour).
http://dx.doi.org/10.1016/j.molstruc.2014.05.024
0022-2860/Ó 2014 Elsevier B.V. All rights reserved.
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2
S. Yousef Ebrahimipour et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
In bioinorganic chemistry, major interest of researches on Cu(II)
1489,
25 °C, ppm): d = 11.7 (s, 1H; O1H), 10.9 (s, 1H; N4H), 8.1 (s, 1H;
C7), 6.8–7.7 (m, 4H; C5), 2.1 (s, 3H; C1, C3). UV/Vis (DMSO), kmax
nm (
, L molꢁ1 cmꢁ1): 284(39,558), 293(36,306), 326(27,715).
m(CAO) 1315, m
(NAN) 1114. 1H NMR (100 MHz, DMSO-d6,
complexes have been focused on their similarity of structures to
metaloproteins and providing models for the metal-containing
sites in these proteins and enzymes such as superoxide dismutases
[5,6]. This metalloenzyme plays a key role in the protection of cell
against potentially toxic derivatives of biological activated oxygen.
Superoxide dismutases carry one copper and one adjacent ion in
active catalytic center [7–9].
,
e
Preparation of (1,10-phenanthroline)[(E)-N0-(2-hydroxybenzylidene)
acetohydrazide] copper(II) [CuL(phen)]
Also heterocyclic ligands like 1,10-phenanthroline and their
complexes have been in concentration due to their wide range of
biological properties such as DNA binding, anti-microbial, anti-
cancer and antioxidant activities [10–13]. There are few report of
mixed ligand Cu(II) complexes with hydrazone ONO Schiff base
and 1,10-phenanthroline [14] therefore investigation of properties
of this class of compounds can be useful for development of appli-
cations of them in different areas.
In our previous work we discussed that biochemical activity of
mixed ligand complexes of Cu(II) complex with CuL1L2 formula
depends on non-covalent interaction between aromatic units [15].
Based upon, hydrazone derivative compound, (E)-N0-(2-hydrox-
ybenzylidene)acetohydrazide [HL], and its mixed ligand Cu(II)
complex were prepared and characterized by various physico-
chemical methods. DFT calculations have been performed to inves-
tigate detailed experimental spectroscopic data and NLO
properties of synthesized compounds. Also, the biological activities
of the mentioned compounds as antimicrobial agents especially
against Gram-positive and Gram-negative bacteria were
investigated.
Cu(OAc)2ꢂ4H2O (0.1 mmol, 0.02 g) was added to a solution of
[HL] (0.1 mmol, 0.018 g) and NaOH (0.2 mmol, 0.01 g) in 5 mL of
boiling ethanol and the mixture was refluxed in a water bath for
10 min. 1,10-Phenanthroline (0.1 mmol, 0.02 g) was added to the
resulting dark-green colored solution which was further refluxed
for ca. 1 h. After cooling, the precipitate was separated and then
recrystallized from dichloromethane–methanol to give green sin-
gle crystal and were dried in a vacuum desiccator over CaCl2.
Yield: 0.030 g, 72%. m.p.:>300 °C. Molar conductance (10ꢁ3 M,
DMSO) 17.0 ohmꢁ1 cm2 molꢁ1
(419.92 g molꢁ1): C, 60.06; H, 3.84; N, 13.34. Found: C, 60.17; H,
3.71; N, 13.45%. FT-IR (KBr), cmꢁ1
(C@N) 1612, (C@Cring) 1512,
, L molꢁ1
. Anal. Calc. for C21H16CuN4O2
:
m
m
m
(CAO) 1303, m(NAN) 1103. UV/Vis (DMSO, kmax, nm (e
cmꢁ1): 282(35,901), 319(17,097), 389(10,138), 652(192).
Computational methods
The geometry of the synthesized compounds was fully opti-
mized without any symmetry constraints using density functional
theory (DFT), B3LYP exchange correlation functional and 6-
31+G(d,p) [17,18] with Gaussian 03 program package [19]. X-ray
Crystal structure used as starting point for Calculations. The opti-
mized structures were characterized by frequency calculations as
true minima. The density functional theory has been used to
Experimental
Materials and instrumentation
calculate the dipole moment (l), mean polarizability (a) and the
total first static hyperpolarizability (b) for [HL] and [CuL(phen)]
in terms of x, y, z components and are given by following equations
[20].
All chemicals were analytical grade and were used as received.
Elemental analyses of C, H and N were performed on a Heracuse
CHN rapid analyzer. The FT-IR spectrum was recorded on a Nico-
let-Impact 400D spectrometer (4000–400 cmꢁ1) in KBr pellets.
Conductance measurements were made by means of a Metrohm
712 Conductometer in DMSO. 1H NMR spectrum was recorded
at 25 °C with a Bruker BRX 100 AVANCE spectrometer. The elec-
tronic spectra were recorded in DMSO on a Cary 50 UV–Vis spec-
trophotometer. Melting point was determined on a Gallenkamp
melting point apparatus. Crystal was mounted on loop and all
geometric and intensity data were taken from a single crystal.
ꢀ
ꢁ
1=2
l
a
¼
¼
lx2
þ
ly2
þ
lz2
1
3
ð
axx
þ
ayy
þ
azz
Þ
1=2
2
2
2
btot ¼½ðbxxx þbxyy þbxzzÞ þðbyyy þbyzz þbyxxÞ þðbzzz þbzyy þbzxxÞ ꢃ
Data collection using Mo Ka radiation (k = 0.71073 Å) was per-
The polarizability and hyperpolarizability tensors (axx axy, ayy, axz,
,
formed at 200 K with a Stoe IPDS II diffractometer, equipped with
an oxford cryostat. The SHG efficiency of [CuL(phen)] was mea-
sured with respect to urea by the powder technique developed
by Kurtz and Perry using a Q switched Nd-YAG laser (1064 nm,
10 ns, 10 Hz). The homogeneous powder was mounted in the
path of a laser beam of pulse energy 2.2 mJ obtained by the split
beam technique.
ayz
,
azz and bxxx, bxxy, bxyy, byyy, bxxz, bxyz, byyz,bxzz, byzz, bzzz) can be
obtained by a frequency job output file of Gaussian. However,
and b values of Gaussian output are in atomic units (a.u.) so they
have been converted into electrostatic units (esu) ( ; 1 a.u. =
a
a
0.1482 ꢄ 10ꢁ24 esu, b; 1 a.u. = 8.6393 ꢄ 10ꢁ33 esu). Furthermore,
determination of the origin of structural behaviors had been done
with Natural Band Orbital (NBO) and Wiber index analysis (WBI)
at the same level [21]. UV–Vis spectra, electronic transitions, absor-
bance and oscillator strengths were computed with the time-
dependent DFT (TD-DFT) method at the B3LYP/6-31+G(d,p) level.
Solvent (DMSO) was considered as a uniform dielectric constant
46.7 and Polarized Continuum Model (PCM). GAUSSSUM 3.0 with
FWHM 0.3 eV have been used for analyzing the contribution per-
centage of groups and atoms to the molecular orbitals [22].
Synthesis of (E)-N0-(2-hydroxybenzylidene)acetohydrazide [HL]
In typical procedure [16], an ethanolic solution (4 ml) of 2-
hydroxybenzaldehyde (0.025 g, 0.2 mmol) was added to 3 ml eth-
anolic solution of acetohydrazide (0.015 g, 0.2 mmol). The mixture
was stirred for 10 min. the resulting white precipitate was sepa-
rated by filtration, washed with cold ethanol and dried in a desic-
cator over anhydrous CaCl2.
Crystal structure determination
Yield: 0.028 g, 78%. m.p.: 199 °C. Anal. Calc. for C10H11N2O2
(178.19 g molꢁ1): C, 60.66; H, 5.66; N, 15.72. Found: C, 60.14; H,
Absorption correction was partially integrated in the data
reduction procedure [23]. The structure was solved refined using
full-matrix least-squares on F2 with the SHELX-97 package [24].
5.43; N, 15.78%. FT-IR (KBr), cmꢁ1
:
m
(OH) 3186,
m
(NAH) 3074,
(C@Cring
m(C@H)aro 2869–2947,
m
(C@O) 1678,
m
(C@N) 1616,
m
)
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S. Yousef Ebrahimipour et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
3
Table 1
inoculum was prepared using a 4–6 h broth culture of each bacte-
ria and 24 culture of yeast strains adjusted to a turbidity equivalent
to a 0.5 McFarland standard [27]. Petriplates containing 20 ml Agar
test plates were seeded with 24 h culture of microorganism strains.
Crystal data and structure refinement for [CuL(phen)].
Empirical formula
Formula weight
Temperature
C21 H16 Cu N4 O2
419.92
200(2) K
Wells were cut and 100 ll of the compounds (5000 lg/ml; DMSO
Wavelength
0.71073 Å
was used as solvent) were added. The plates were then incubated
at 37 °C for 24 h. The antibacterial activity was assayed by measur-
ing the diameter of the inhibition zone formed around the well.
DMSO as solvent was used as a negative control whereas media
with ciprofloxacin (standard antibiotic) and fluconazole (standard
antifungal drug) were used as the positive controls. The experi-
ments were performed in triplicate. Serial dilutions ranging from
Crystal system
Space group
Unit cell dimensions
Monoclinic
P 21/c
a = 10.9518(5) Å
b = 11.7188(7) Å
c = 13.7990(7) Å
1758.33(16) Å3
4
a
= 90°
b = 96.856(4)°
= 90°
c
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
1.586 Mg/m3
1.268 mmꢁ1
5000 lg/mL to 4.9 lg/mL were prepared in medium.
860
Crystal size
Theta range for data collection
Index ranges
0.240 ꢄ 0.143 ꢄ 0.080 mm3
Results and discussion
1.87–25.00°
ꢁ13 6 h 6 13,
ꢁ13 6 k 6 13, ꢁ16 6 l 6 16
21,995
3096 [R(int) = 0.0448]
100.0%
The [HL] ligand (Scheme 1) can exist in two main tautomeric
forms. Spectroscopic analysis shows that enolic form is preferred
in complexation with Cu(OAc)2.4H2O. [HL] and [CuL(phen)] are
stable in air and soluble in most solvents except water and n-
hexane. Molar conductivity values of Cu(II) complex equal to
17 ohmꢁ1 cm2 molꢁ1 in DMSO, indicating non-electrolyte behav-
iors of it.
Reflections collected
Independent reflections
Completeness to theta = 25.00°
Absorption correction
Max. and min. transmission
Refinement method
Integration
0.8329 and 0.6782
Full-matrix least-squares
on F2
3096/0/254
0.973
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole
R1 = 0.0297, wR2 = 0.0745
R1 = 0.0447, wR2 = 0.0786
0.240 and ꢁ0.384 e.Åꢁ3
X-ray crystal structure
An ORTEP view of Cu is presented in Fig. 1. Also a unit cell of
[CuL(phen)] by 50% thermal ellipsoid is shown in Fig. 2. Selected
bond distance and interatomic angles are listed in Table 2. In this
structure Cu(II) has a five coordination sphere in which central
atom is surrounded by donor atoms of tridentate ONO Schiff base
and two nitrogen atoms from bidentate heterocyclic ligand. X-ray
analysis data shows that Cu complex has a distorted square pyra-
midal with trigonality index of 5% that square plane is made up
of donor atoms of [HL] and one nitrogen atom of 1,10-phenanthro-
A summary of the crystal data and refinement details for the
[CuL(phen)] are given in Table 1.
Determination of antimicrobial activity
The four bacterial strains and Candida albicans used in the pres-
ent study were the clinical isolates obtained from Afzalipour Hos-
pital in Kerman, Iran. The used bacteria were Escherichia coli,
Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria mono-
cytogenes. The antimicrobial effect of [HL] and [CuL(phen)] on the
microorganisms were assayed by Agar well diffusion method
[25]. Mueller–Hinton medium (Merck) for bacteria and YGC med-
ium (Merck) for yeast strain was used as the test medium. Also,
the minimum concentrations of the compounds to inhibit the
microorganisms (MIC) were determined by the micro broth dilu-
tions technique strictly following the National Committee for Clin-
ical Laboratory Standards (NCCLS) recommendations [26]. The
Scheme 1. The main tautomeric forms of the free ligand [HL].
Fig. 1. Perspective view of complex with displacement ellipsoids drawn at the 50% level.
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4
S. Yousef Ebrahimipour et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
line, also another nitrogen of heterocyclic ligand occupies the axial
position.
Trigonality indexed is defined by b–
a/60 that beta and alpha are
the two largest bond angles around the metal center in five coordi-
nated environment. An ideal square pyramid have b = 180° and
a
= 180° and therefore s = 0%, but an ideal trigonal-bipyramidal
structure will have b = 180° and
a = 120° and s is equal to 100%
[28].
As can be seen in packing diagram (Fig. 3) there are pi–pi inter-
action in lattice which stabilize crystal structure of compound.
These interactions occurs between two 1,10-phenanthroline of
neighbors molecules, the distances are reported in Table 3. The
two central centroid, Cg(6), are distant of 3.6119(16) Å with a per-
pendicular distance of 3.4144(11) Å and a slippage of 1.178 Å. The
overlap of phenanthroline ligand is, for the best of our knowledge,
the most important for this type of compound (copper phenan-
throline and 2-hydroxybenzylidene) hydrazide type [29–31].
Fig. 2. ORTEP drawing of unit cell of the complex [CuL(phen)].
Table 2
Selected calculated and experimental bond lengths (Å) and bond angles (°) for
[CuL(phen)].
Geometry optimization
Type
Exp
Calc.
Type
Exp
Calc.
The geometry of the compounds was optimized using DFT
method with the B3LYP function. In order to get more stable struc-
ture for the ligand, all the proposed tautomers were optimized at
B3LYP/6-31+G(d,p) level of theory and result is shown in Fig. 4.
According to this, a owns a more stable structure that is accor-
dance with X-ray data of ligand, so that we performed other calcu-
lations on the basis of a.
Geometrical calculated parameters are listed in Table 2. Accord-
ing to it, there is a good agreement between structural parameters
from DFT calculation and X-ray crystallography result. Maximum
deviations are 0.102 Å and 2.7° for the Cu1-N1 bond and the
O1ACu1AO2 angle, respectively. A little difference between theo-
retical and experimental values may origin from this fact that the
experimental data was obtained in the solid state, while the calcu-
lated values are concerned to single molecules in the gaseous state
without considering lattice interactions.
Cu1AN3
Cu1AO1
Cu1AN2
Cu1AO2
Cu1AN1
N3AN4
N3AC19
O1AC13
O2AC20
C13AC18
N4AC20
C19AC18
1.935(2)
1.919(2)
2.049(2)
1.949(2)
2.309(2)
1.404(3)
1.280(3)
1.308(3)
1.282(3)
1.417(3)
1.306(3)
1.440(4)
1.947
1.912
2.108
1.964
2.411
1.385
1.296
1.309
1.298
1.439
1.318
1.439
N3ACu1AO1
N3ACu1AN2
N3ACu1AO2
N3ACu1AN1
O1ACu1AN2
O1ACu1AO2
N2ACu1AO2
N2ACu1AN1
Cu1AN3AN4
Cu1AN3AC19
N4AN3AC19
Cu1AO1AC13
Cu1AO2AC20
O1AC13AC18
N3AN4AC20
N3AC19AC18
O2AC20AN4
93.01(8)
168.91(8)
80.21(8)
113.86(8)
90.20(8)
165.92(8)
94.29(8)
76.50(8)
115.3(1)
126.7(2)
117.9(2)
125.7(2)
110.9(2)
124.3(2)
108.2(2)
124.0(2)
125.2(2)
93.9
170.3
80.9
112.9
91.1
168.7
92.6
74.3
114.9
126.2
118.9
126.6
109.5
124.7
109.3
124.8
125.2
Fig. 3. Illustration of p-stacking interaction in [CuL(phen)] with hydrogen omitted for clarity.
Table 3
Analysis of short ring-interactions with Cg–Cg distances.
Cg(i)
Cg(j)
Cg(i)–Cg(j) (Å)
Cg(i)–Perp(j) (Å)
Cg(j)–Perp(i) (Å)
Slippage (Å)
3.591
Cg(4)
Cg(4)
Cg(5)
Cg(6)
4.7612(17)
3.8553(16)
4.5046(17)
3.1262(11)
3.3877(11)
3.3748(11)
3.1262(11)
3.4340(11)
3.4422(11)
Cg(5)
Cg(6)
Cg(4)
Cg(5)
Cg(6)
3.8554(16)
4.9900(15)
3.6315(15)
3.4340(11)
3.4460(11)
3.4028(11)
3.3878(11)
3.4460(11)
3.4191(11)
3.609
1.178
Cg(4)
Cg(5)
Cg(6)
4.5047(17)
3.6316(15)
3.6119(16)
3.4422(11)
3.4192(11)
3.4144(11)
3.3749(11)
3.4028(11)
3.4143(11)
Cg(4): C1 C2 C3 C4 C12 N1; Cg(5): C7 C8 C9 C10 N2 C11; Cg(6): C4 C5 C6 C7 C11 C12; Cg(i)–Cg(j): Distance between ring Centroids (Å); Cg(i)–Perp(j): Perpendicular distance
of Cg(i) on ring j (Å); Cg(j)–Perp(i): Perpendicular distance of Cg(j) on ring i (Å); Slippage: Distance between Cg(i) and Perpendicular Projection of Cg(j) on ring i (Å).
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S. Yousef Ebrahimipour et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
5
Vibrational analysis
in the Experimental section. The observed and calculated FT-IR
spectra of [CuL(phen)] are also shown in Fig. 5. For more investiga-
tion, selected experimental and scaled calculated vibrational fre-
quencies of title complex are compared in Table 4. In the FT-IR
Assignments of selected prominent IR bands in the
400–4000 cmꢁ1 region for [HL] and its Cu(II) complex are listed
(a) (0)
(b) (8.37)
(c) (33.47)
(d) (33.47)
(e) (0.1)
(f) (58.58)
(g) (75.31)
(h) (33.47)
Fig. 4. The optimized geometries of the possible tautomeric forms of [HL].
Fig. 5. Calculated (a) and Experimental (b) FT-IR spectra of [CuL(phen)].
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6
S. Yousef Ebrahimipour et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
Table 4
values of electronic potential. The red colors are correlated with
electron rich area while the blue is used for representation of
electronpositive sites. According to Fig. 6 oxygens are electron rich
area and suitable for nucleophilic attacks while in complex, this
tendency of oxygen donor atoms have been decreased. In contrast,
the configuration of the ligand while connecting to the central
atom in complexation makes electrostatic potential of nitrogen
shift to more negative values.
Vibrational assignments of FT-IR peak along with the theoretically computed
wavenumber.
Experimental
Calculated
B3LYP/6-31+G(d,p)
Assignment
FT-IR, cmꢁ1
Unscaled
Scaledꢅ
3124.90
3050.83
3004.03
3000.68
2922.44
1612.41
1596.83
1512.14
1445.53
1423.56
1338.86
1321.23
1303.81
1252.67
1195.34
1103.21
759.90
3224.23
3171.44
3119.01
3110.08
3051.05
1668.83
1659.98
1578.96
1494.23
1489.53
1399.88
1376.89
1347.55
1297.45
1243.49
1152.86
781.42
3104.933
3054.097
3003.597
2995.007
2938.161
1607.083
1598.561
1520.538
1438.943
1434.417
1348.084
1325.945
1297.691
1249.444
1197.481
1110.204
752.5075
733.0356
585.2344
472.0819
m
m
m
CH II
CH I
CH
azm
masy CH3
msy CH3
Frontier molecular orbitals
m
m
m
m
CN
CN II,
CC I
CC I,
CH3
azm
m
CC II
Frontier molecular orbitals, i.e. the highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)
play an important role in the electric properties as well as,
UV–Vis spectra and determination of chemical reactivity [36].
Figs. S1 and 7 shows the molecular energies orbitals with isoden-
sity surface plots of HOMO and LUMO for [HL] and [CuL(phen)]
respectively. As can be seen, The electron population of HOMO
and LUMO are localized on the whole skeleton of [HL] while In
[CuL(phen)], the electron density of HOMO is mainly located on
the deprotonated Schiff base ligand and LUMO electron density is
localized on the aromatic rings of heterocyclic moiety. Details of
the frontier molecular orbitals in the complex are presented in
Tables S1 and S2. HOMO–LUMO energy gap correlates with the
stability of compounds. Results show that the band gaps between
HOMO and LUMO equal 4.33 and 2.4 eV for [HL] and [CuL(phen)]
respectively Hence, Cu(II) complex has more chemical activity than
parent tridentate ligand [HL].
m
asy
C18C19
r
dsy CH3, d C19
H
m
m
C20O2
CO I
dipb CH II
dipb CH I
m
d
NN
CH II
opb
729.83
582.81
475.35
761.2
607.72
490.22
dopb CH I
m
m
CuO
CuN
Abbreviation:
m; stretching, d; bending, asy; asymmetric, sy; symmetric, ipb; in
plane bending, opb; out of plane bending, I; aldehyde ring, II; 1,10-phenanthroline
rings, azm; azomethine.
spectrum of the ligand, a sharp band with high intensity at
1678 cmꢁ1 is assigned to C@O vibrations [32]. The OH and NH
vibrations are located at 3186 and 3074 cmꢁ1 respectively [33].
The absence of these frequencies and the red shift of the CAO band
from (1315 cmꢁ1) to (1303 cmꢁ1) in [CuL(phen)] indicate ligand in
the enolic form coordinates to the metal center through deproto-
nated phenolic and aliphatic oxygen atoms [34]. This band is
observed at 1297.7 cmꢁ1 in the calculation.
Electronic spectra
In the electronic spectrum of [HL], three bands at 284 nm,
293 nm and 326 nm have been observed in the ligand. They can
be attributed to
p ? p ?
p⁄ transitions of the phenyl ring and p⁄
Also in the [HL], strong band at 1616 cmꢁ1 is assigned to vibra-
tions of the azomethine moiety while on complexation, it appear-
ing at 1612 cmꢁ1 shows that the azomethine nitrogen atom of
ligand coordinates to central atom [15], the DFT calculation gives
and n ? p⁄ of the azomethine moiety and carbonyl group respec-
tively. The spectra of the Cu(II) complex (Fig. 8) has similar features
[37,38]. The band at approximately 389 nm reveals coordination of
the ligand to metal center. The high epsilon value of log e = 4.01
confirms that this band is due to MLCT (metal to ligand) and LMCT
(ligand to metal) charge transfer transitions. In five coordinated
Cu(II) complexes Visible spectrum can be used for predicting pre-
ferred geometry. SP or distorted SP geometries exhibit a band in
this band at 1607 cmꢁ1
.
Molecular electrostatic potential
Molecular electrostatic potential (MEP) is used for identifying
chemical reactivities as well as presence of intra and intermolecu-
lar interactions on the skeleton of compound [35]. Molecular
electrostatic potential of ligand and complex is shown in Fig. 6.
In these figures, different colors are used to distinguish different
the 550–660 nm range that is assigned to dxz; dyz ! dx2
while
ꢁy2
TBP structures have a characteristic band around >800 nm is
related to dxz; d
! dz2 . Spectrum of [CuL(phen)] shows a band
x2ꢁy2
at 652 nm, Thus Cu central atom in this complex is closer to SP
[39].
Fig. 6. Molecular electrostatic potential map of [HL] (left) and [CuL(phen)](right).
Please cite this article in press as: S. Yousef Ebrahimipour et al., J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.05.024

S. Yousef Ebrahimipour et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
7
HOMO
HOMO-1
HOMO-2
LUMO
LUMO+1
LUMO+2
Fig. 7. Contour plots of some selected MOs (b-spin) of [CuL(phen)].
Fig. 8. Experimental absorption spectra of Cu(II) complex in DMSO. The d–d transition is shown in inset for title complex (a).
To investigate the electronic transition corresponding to these
bands, TDDFT calculations have been performed at 6-31G+(d,p)
level in DMSO. Summary of the results is gathered in Table 5.
According to it, low energy weak transitions belonged to d-d tran-
sitions. Other intense bands attributed to ILCT, LMCT and MLCT.
For investigation of photostability of [CuL(phen)], UV–Vis spec-
trum of the complex after irradiation (3 h) is shown in Fig. S3.
According to it, main characteristic bands of this compound are
not shifted upon irradiation of light (Xe lamp-70 W) and only small
changes in band intensity was appeared.
Natural bond orbital analysis
NBO results show that electronic configuration of Cu(II) in com-
plex is [core]4S0.373d9.354p0.414d0.015p0.01. This arrangement con-
tains 18 core electrons, 10.13 valance electrons and 0.03 rydberg
electrons. These amount is consistent with calculated charge
(0.8496) of Cu(II) central ion and also all coordination sites in
ligands have a calculated atomic charge and electron configuration
lower than expected these observations confirm significant elec-
tron donation from the donor atoms to the center metal ion. The
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8
S. Yousef Ebrahimipour et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
Table 5
Main calculated optical transition with composition in terms of molecular orbital contribution of the transition, vertical excitation energies and oscillator strength for
[CuL(phen)].
Composition
Weight (%)
E (eV)
Oscillatory strength (f)
kmax (Calc.)
kmax (Exp)
Assignment
H-6(b)ꢁ > L + 2(b)
H-8(b)ꢁ > L + 2(b)
H-9(b)ꢁ > L(b)
76
14
44
25
48
53
27
67
29
36
19
95
98
16
77
98
1.5072
0.0008
(675.82)
652(2.32)
d–d
1.9609
0.0005
442.596
MLCT, ILCT
H-1(b)ꢁ > L(b)
H-10(b)ꢁ > L(b)
H-16 (b)ꢁ > L + 2(b)
H-14(b)ꢁ > L + 2(b)
H(b)ꢁ > L + 3(b)
H-7(b)ꢁ > L(b)
2.1560
2.2899
0.0004
0.0038
402.542
379.015
MLCT
LMCT, MLCT
389(4.01)
2.4330
2.5620
0.0000
0.0003
356.713
338.758
ILCT
ILCT
H(b)ꢁ > L(b)
H(b)ꢁ > L + 1(b)
H(b)ꢁ > L + 1(b)
2.5825
2.6317
2.7569
0.0001
0.0031
0.0006
336.063
329.784
314.804
ILCT
ILCT
ILCT
H(
a
)ꢁ > L + 3(
a
)
319(4.23)
282(4.56)
H(b)ꢁ > L + 1(b)
H(b)ꢁ > L + 3(b)
H(
a
)>L + 3(
a
)
2.8211
0.0018
307.643
ILCT
NLO properties
Table 6
Charges and electron configurations for [CuL(phen)].
Nonlinear optics properties of metal complexes have been the
subject of extensive investigations during recent decades because
of its potential in optical electronic application such as electro-
optical (EO) switches [40,41] Zhang and coworkers showed that
[HL] is a good candidate for NLO material [15]. For investigation
of NLO properties of [CuL(phen)], it was screened for this com-
pound by the quasi-Kurtz powder technique. A comparison of the
area of second harmonic generation (SHG) signal emitted by the
Atom
Charge
Electron configuration
Cu
N3
O1
N1
O2
N2
0.84960
ꢁ0.34040
ꢁ0.69636
ꢁ0.44266
ꢁ0.71056
ꢁ0.42597
[core]4S(0.37)3d(9.35)4p(0.41)4d(0.01)5p(0.01)
[core]2S(1.31)2p(4.00)3S(0.01)3p(0.02)3d(0.01)
[core]2S(1.65)2p(5.03)3p(0.01)
[core]2S(1.31)2p(4.11)3p(0.02)
[core]2S(1.68)2p(5.02)3p(0.01)
[core]2S(1.33)2p(4.08)3p(0.01)3d(0.01)
calculated atomic charges from the natural population analysis
(NPA) are summarized in Table 6.
Table 8
The calculated electric dipole moments (Debye), static polarizability components
(a.u.), first hyperpolarizability components (a.u.) of [HL] and [CuL(phen)].
Thermodynamic properties
Parameters
[HL]
[CuL(phen)]
Title complex was studied for the purpose of the standard ther-
modynamic functions ;enthalpy ðH0mÞ, entropy ðSm0 Þ, and capacity
ðC0p;mÞ at different temperatures, used by B3LYP/6-31+G(d,p) level
of theory, and the details shown in Table 7 are based on this study.
Its concluded from the table that, these thermodynamic values are
increased with the increase of temperature from 200 K to 800 K.
The fact of increasing vibrational intensities with the temperature
can be the explanation for this phenomenon.
lx
ly
lz
axx
ayy
azz
bxxx
bxxy
bxyy
byyy
bxxz
byyz
bxzz
byzz
bzzz
ꢁ1.024
ꢁ0.477
0
3.278
ꢁ0.926
0.423
223.280
117.528
46.585
ꢁ155.196
11.240
ꢁ12.409
ꢁ108.716
1.736
ꢁ2.018
ꢁ18.845
16.905
ꢁ0.274
354.131
272.042
271.984
ꢁ60.982
ꢁ202.661
ꢁ74.544
ꢁ227.067
95.474
14.908
47.698
24.320
ꢁ140.129
Hꢆm ¼ 1 ꢄ 10ꢁ4T2 þ 0:0347T þ 203:74ðR2 ¼ 0:9998Þ
Cpꢆ;m ꢁ 2 ꢄ 10ꢁ4T2 þ 0:3837T ꢁ 7:1356ðR2 ¼ 0:9999Þ
Sꢆm ¼ ꢁ8 ꢄ 10ꢁ5T2 þ 0:3591T þ 66:3ðR2 ¼ 1Þ
Table 9
Selected Wiberg bond index (WBI) of title complex.
Table 7
Wiberg
Bond index Wiberg
Bond index Wiberg
Bond index
Thermodynamic properties of [CuL(phen)] at different temperatures.
WCuAN1
WCuAN2
WCuAN3
WCuAO1
WCuAO2
0.2339
0.1598
0.3552
0.3967
0.3494
WC20AO2
WC20AN4
WN3AC19
WC19AC18 1.1845
WC18AC17 1.3211
WC17AC16 1.4954
WC16AC15 1.3495
WC2AC3
WC3AC4
WC4AC5
1.2731
1.5168
1.5852
WC15AC14 1.5080
WC14AC13 1.2868
Temperature
(K)
Enthalpy
Heat capacity
(cal molꢁ1 Kꢁ1
Entropy
(Kcal molꢁ1
)
)
(cal molꢁ1 Kꢁ1
)
WC13AO1
WN2AC10
WN2AC11
1.2205
1.4730
1.3074
200
298.15
300
400
500
600
700
800
215.18
222.7
62.69
90.528
91.044
117.373
139.466
157.221
171.429
182.929
135.233
166.251
166.825
197.28
226.373
253.793
279.442
303.375
222.868
233.319
246.199
261.067
277.525
295.262
WC21AC20 1.0097
WC18AC13 1.2200
WN4AN3
WC12AN1
WC1AN1
WC1AC2
WC7AC11
1.0917
1.2871
1.4455
1.3487
1.2761
WC5AC6
WC9AC10
WC8AC9
WC7AC8
1.6461
1.3401
1.5180
1.3039
1.5118
1.3064
1.2784
WC11AC12 1.1416
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S. Yousef Ebrahimipour et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
9
Table 10
In vitro antimicrobial activity of the compounds, 5000
l
g/ml (IZ).
Microorganism
[HL] dia. of
clear zone (mm)
[CuL(phen)] dia. of
clear zone (mm)
Ciprofloxacin. dia. of
clear zone (mm)
Fluconazol, dia. of
clear zone (mm)
E. coli
S. aureus
P. aeruginosa
L. monocytogenes
C. albicans
15
20
8
0
33
23
40
11
32
45
31
24
19
20
0
0
0
0
0
33
Table 11
In vitro antimicrobial activity of the compounds, (MIC,
l
g/ml).
Compound
Microorganisms
E. coli
S. aureus
P. aeruginosa
L. monocytogenes
C. albicans
[HL]
[CuL(phen)]
225
78.0
125
62.5
625
125
–
62.5
62.5
39.0
sample with the standard urea under the same experimental con-
ditions, showed that it is 1.4 times more than that for urea.
The calculated nonlinear optical parameters of title compounds
are listed in Table 8. According to equations of [1–3], the calculated
[CuL(phen)] have antibacterial and antifungal activity. The more
activity of complex against bacteria and fungus is due to the posi-
tive charge of central atom shared with donor atoms of [HL] and p-
electron delocalization in over the whole chelate moiety hence the
lipophilic nature of complex will be increased so this makes it
stronger in penetrating through the lipid layers of microbial mem-
branes, that means it will be a better anti-microbial agent.
total static dipole moment (
are equal to 1.13 and 3.43 Debye respectively. The magnitude of
mean polarizability ( 0) of ligand and Cu(II) complex are 19.14
l0) of [HL] and [CuL(phen)] complex
a
and 44.32 Å3 respectivley and finally calculated values of first-
order hyperpolarizability (b0) were found to be 17.53 and
35.93 cm5/esu, respectively for [HL] and [CuL(phen)] respectively
The higher values of these parameters and lower energy gap
between HOMO and LUMO in case of [CuL(phen)] indicate the
increase of NLO properties of Cu(II) complex in comparison with
the free ligand.
Conclusions
The tridentate ONO Schiff base ligand (E)-N0-(2-hydroxybenzy-
lidene) acetohydrazide [HL] and its mixed ligand Cu(II) complex
were synthesized and characterized by spectroscopic methods
such as FT-IR, CHN and UV–Vis. X-ray diffraction was also per-
formed on Cu(II) complex. From spectral characterization, it was
included that the metal complex has square pyramidal geometry.
DFT calculations were performed to predict the structural geome-
try and interpret the NLO properties as well as experimental data.
Wiberg bond index analysis
Wiberg bond index (WBI) is a useful method for analyzing the
type of bands in molecule. Selected bond index for [CuL(phen)]
are listed in Table 9. According to it, all bonds between donor
atoms and central atom in this complex have a covalent nature.
In this case CuAO bonds have larger bond order in compared with
CuAN. Also the interaction between the central metal and the N
atom of the 1,10-phenanthroline moiety is remarkably weaker
than that with the other atoms atoms, as proved by the wiberg
bond indexes (WBI) less value of CuAN bond order, causes the
grater bond length the bond order of C20AN4 and C19AN3 are
1.5168 and 1.5852 respectively which is larger than 1.5 and is
due to double bond attributed of them. All aromatic ring bonds
The higher first hyper-polarizability (b), polarizability (
dipole moment ( ) as well as the lower HOMO–LUMO gap of the
a) and
l
[CuL(phen)] compared to the [HL], indicate the high NLO properties
of the Cu(II) complex. The SHG efficiency of the complex was mea-
sured by the Kurtz-powder technique, and the results indicate that
[CuL(phen)] possesses promising potential for the application as
useful NLO material. In addition, experimental investigation shows
that these compounds have antibacterial activity against E. coli, S.
aureus, P. aeruginosa, and L. monocytogenes. They act as antifungal
agents against C. albicans Results showed that [CuL(phen)] has a
stronger antibacterial effect against all bacterial varieties in com-
parison with [HL] Schiff base ligand.
order are smaller than 1.5 which indicates the presence of p–p con-
jugation among contributed atoms.
Antimicrobial activity
Acknowledgements
The antibacterial activity of [HL] and [CuL(phen)] ligands
against Escherichia coli, Staphylococcus aureus, Pseudomonas aeru-
ginosa, Listeria monocytogenes and Candida albicans was assessed
by evaluating the presence of inhibition zone (IZ) and MIC values.
Results (Table 10), showed that the [HL] and [CuL(phen)] have
great potential of antibacterial and antifungal activity. It seems
that the antibacterial effect of [HL] is not more on Gram negative
bacteria. However, [CuL(phen)] are very effective both Gram nega-
tive and Gram positive bacteria. The MIC values for the ligands
Authors gratefully acknowledge the financial support provided
for this work by the Shahid Bahonar University of Kerman as well
the University of Fribourg. We thank optic laboratory in valie asr
University (Rafsanjan) for the provision of Nd:YAG laser.
Appendix A. Supplementary material
were in the range of 4.9–5000
showed that the ligands were effective on bacteria and C. albicans
(Table 11). According to the results we found that the [HL] and
l
g/ml. The results of our study
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.2014.
05.024.
Please cite this article in press as: S. Yousef Ebrahimipour et al., J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.05.024

10
S. Yousef Ebrahimipour et al. / Journal of Molecular Structure xxx (2014) xxx–xxx
Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.
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Please cite this article in press as: S. Yousef Ebrahimipour et al., J. Mol. Struct. (2014), http://dx.doi.org/10.1016/j.molstruc.2014.05.024