Synthesis, characterization of binary and ternary copper(II)-semicarbazone complexes: Solvatochromic shift, dipole moments and TD-DFT calculations

Article abstract of DOI:10.1016/j.molstruc.2019.02.103

A novel semicarbazone O₂N donor ligand, HL, was synthesized by condensation of 2-aminochromone-3-carboxaldehyde with semicarbazide hydrochloride. The HL ligand is allowed to react with several copper(II) salts namely: AcO^–, NO₃ ^–, SO₄ ^2– and Cl^–, in absence and presence of secondary ligand (SCN^-, 8-HQ and 1,10-phen), forming binary and ternary copper complexes. Characterization of the compounds has been done using various techniques like elemental analyses, magnetic moments, conductance measurement, thermogravimetry and FT-IR, UV-Vis, ¹H and ¹³C NMR, EPR and mass spectroscopy. The HL ligand acts as monoanionic O₂N tridentate in most complexes, forming Cu(II) complexes with an octahedral and square planar geometrical arrangements. The compounds exhibit luminescence property; promising interesting potential applications as photoactive materials. The ground state (μ_g) and excited state (μ_e) dipole moments are estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (?) and refractive index (n) by using Bilot–Kawski, Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet and Reichardt correlation methods. Excited state dipole moment is observed as larger than the ground state dipole moment. The molecular structural parameters of the ligand and its Cu(II)- complexes have been calculated on the basis of DFT level implemented in the Gaussian 09 program at the B3LYP/6-31G(d,p) level and the theoretical data are correlated with the experimental data. The antibacterial properties of the ligand and its complexes have been screened against selected kinds of bacteria and fungi.

Full text of DOI:10.1016/j.molstruc.2019.02.103

Accepted Manuscript
Synthesis, characterization of binary and ternary copper(II)-semicarbazone
complexes: Solvatochromic shift, dipole moments and TD-DFT calculations
Omima M.I. Adly, Ali Taha, Shery A. Fahmy
PII:
S0022-2860(19)30243-1
10.1016/j.molstruc.2019.02.103
MOLSTR 26260
DOI:
Reference:
To appear in:
Journal of Molecular Structure
Received Date:
Accepted Date:
02 December 2018
25 February 2019
Please cite this article as: Omima M.I. Adly, Ali Taha, Shery A. Fahmy, Synthesis, characterization
of binary and ternary copper(II)-semicarbazone complexes: Solvatochromic shift, dipole moments
and TD-DFT calculations, Journal of Molecular Structure (2019), doi: 10.1016/j.molstruc.
2019.02.103
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ACCEPTED MANUSCRIPT
Synthesis, characterization of binary and ternary copper(II)-semicarbazone complexes:
Solvatochromic shift, dipole moments and TD-DFT calculations
*
Omima M.I. Adly , Ali Taha, Shery A. Fahmy
Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo 11711,
Egypt
Graphical abstract
The optimized structure of the hydrazone, HL, ligand

ACCEPTED MANUSCRIPT
Synthesis, characterization of binary and ternary copper(II)-semicarbazone complexes:
Solvatochromic shift, dipole moments and TD-DFT calculations
*
Omima M.I. Adly , Ali Taha, Shery A. Fahmy
*
Corresponding author: Omima_adly@yahoo.com
Tel: 20 1008693220
Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt
Abstract
A novel semicarbazone O N donor ligand, HL, was synthesized by condensation of 2-
2
aminochromone-3-carboxaldehyde with semicarbazide hydrochloride. The HL ligand is
–
–
2–
–
allowed to react with several copper(II) salts namely: AcO , NO , SO and Cl , in absence
3
4
-
and presence of secondary ligand (SCN , 8-HQ and 1,10-phen), forming binary and ternary
copper complexes. Characterization of the compounds has been done using various
techniques like elemental analyses, magnetic moments, conductance measurement,
1
13
thermogravimetry and FT-IR, UV-Vis, H and C NMR, EPR and mass spectroscopy. The
HL ligand acts as monoanionic O N tridentate in most complexes, forming Cu(II) complexes
2
with an octahedral and square planar geometrical arrangements. The compounds exhibit
luminescence property; promising interesting potential applications as photoactive materials.
The ground state (µ ) and excited state (µ ) dipole moments are estimated from
g
e
solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric
constant (Ɛ) and refractive index (n) by using Bilot–Kawski, Lippert–Mataga, Bakhshiev,
Kawski–Chamma–Viallet and Reichardt correlation methods. Excited state dipole moment is
observed as larger than the ground state dipole moment. The molecular structural parameters
of the ligand and its Cu(II)- complexes have been calculated on the basis of DFT level
implemented in the Gaussian 09 program at the B3LYP/6-31G(d,p) level and the theoretical
data are correlated with the experimental data. The antibacterial properties of the ligand and
its complexes have been screened against selected kinds of bacteria and fungi.
Keywords: 2-Aminochromone-3-carboxaldehyde; Binary and Ternary Complex;
Fluorescence, Solvatochromic, Ground- Excited states dipole moments, DFT level.
1

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1
. Introduction
Chromones are naturally occurring compounds and widely known to have antitumor,
anticancer, antioxidant, anti-inflammatory, antimalarial [1-5], α-amylase and α-glucosidase
inhibitory activity as well as treatment of Alzheimer’s disease [6-8]. Coordination chemistry
of chromone derivatives is able to form stable and colored complexes with various metal ions
[7-9]. Hydrazones of 3-formylchromone and their metal complexes have various applications
in biological and pharmacological fields [10-14]. However, semicarbazones are also reported
to possess versatile structural features [15, 16]. Metal complexes, especially those containing
copper(II) and iron(II) are more active than uncoordinated semicarbazones and this enhanced
biological activity [17]. On the other-hand, solvent effect on the absorption and fluorescence
spectra has been a topic of interesting investigation [18]. The cognition of dipole moments of
electronically excited species is frequently helpful in the design of non-linear optical
materials and elucidation of the nature of excited states [19].
Encouraged by above-mentioned finding, the chelating behavior of a new
semicarbazone ligand, obtained from the condensation of 2-aminochromone-3-
carboxaldehyde and semicarbazide hydrochloride, towards different copper(II) salts.
–
–
2–
–
including AcO , NO , SO and Cl , is investigated to explore the effect of anions on the
3
4
structure of the binary complex formation. Additionally a series of ternary complexes in
presence of secondary ligand L′ namely: thiocyanate, 8-hydroxyquinoline and 1,10-
phenanthroline has been synthesized and characterized using various physicochemical
studies. The ground (µ ) and excited (µ ) states dipole moments have been calculated by
g
e
using solvatochromic shift methods. Antimicrobial studies of the ligand and its binary and
ternary complexes are screened against selected kinds of two pathogenic gram negative
bacteria (Escherichia coli and Salmonella typhimurium), two gram positive pathogenic
bacteria (Staphylococcus aureus and Bacillus subtilis) a and Candida albicans as fungus
strain. DFT calculation at the B3LYP/6-31G(d,p) level by means Gaussian 09 program was
carried out for the ligand and its copper(II) complexes to assign the experimental
observations.
2

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2
. Experimental
2
.1. Materials
2
-Aminochromone-3-carboxaldehyde was prepared according to literature [20]. 8-
Hydroxyquinoline, 1,10-phenanthroline, KSCN, copper(II)-salts and semicarbaziede
hydrochloride were either BDH or Merck products. Organic solvents were reagent grade
chemicals and used without further purification.
2
.2. Analyses and Instrumentation
Elemental analyses of (C, H, and N) were carried out at the Ministry of Defense,
Chemical War Department, Cairo, Egypt. The metal ion contents were determined
complexometrically according to literature procedure [21]. IR spectra of neat samples as a
-1
KBr discs were performed in the range 4000-400 cm on FTIR Nicolet IS10 Spectrometer.
1
13
H NMR (300 MHz) and C NMR (75 MHz) spectra were recorded using a Mercury-300BB.
Dimethylsulphoxide, DMSO-d , was used as a solvent and tetramethylsilane (TMS) as an
6
internal reference. The electronic spectra of the ligand and its metal complexes were
measured with a JASCO model V-550 UV-VIS spectrophotometer (200-900 nm) using
dimethylformamide as solvent and reflactance or Nujol mulls. EPR spectra were recorded on
X-Band of a Bruker, Model: EMX, spectrometer. Mass spectra were obtained using GC-2010
Shimadzu Gas chromatography instrument mass spectrometer (70 eV). The fluorescence
studies were recorded on perkin-Elmer650-10S spectro-fluorimeter, equipment with 1-cm
quartz cell and 150W Xenon Arc lamp at room temperature. Magnetic susceptibility data
were collected on powdered samples using a Johnson Matthey, Alfa product, Model No.
(MKI) by the Gouy's method. All data were corrected for diamagnetism estimated from
Pascal's constants for all atoms in the compounds [22]. The Shimadzu TGA-50H instrument
was used to carry out thermal analysis of metal complexes from room temperature up to 800
−
1

C at a heating rate of 10 °C min . Melting points were measured in open capillaries on a
Stuart SMP3 melting point apparatus.
3

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2
.3. Computational method
The molecular structure of the current compounds were optimized without constraints
of any sort, by the DFT functional at the B3LYP/6-31G(d,p) level of theory [23,24], using
Gaussian 09 program and Gauss View 5.0 package was used to obtain various graphic views
[25]. Atomic charges are important parameters in structure-property and structure-activity
relationships, affecting many molecular properties [26]. Among the existing atomic charge
models, we choose Mulliken’s population analysis (MPA) [27] for atomic charge calculations
on ligand and its metal complexes. The MPA method was chosen because it has been the
most widely used population analysis method for determining atomic charges, although its
results tend to vary with basis set size and yields unnatural values in some cases [28-30]. To
minimize these errors related to the use of variation basis sets, same basis set has been applied
for investigating compounds.
The frontier molecular orbitals play a vital role in the electrical and optical properties,
as well as in UV–Vis spectra and chemical reactions [31]. One can determine the way the
molecule interacts with other species. The gap between HOMO and LUMO characterizes the
molecular chemical stability [32]. The energy of the frontier molecular orbitals in terms of
ionization energy (IE) and electron affinity (EA) of the current complexes are related using
Koopmans’s theorem [33]. The absolute electronegativity (χabs) and absolute hardness (η)
are related to IE and EA [34]. Hard molecules have a large gap and soft molecules have a
small gap between HOMO-LUMO [35]. Another important property related to the dipole
moment and hardness is electrophilicity index (ω), global softness (S) [36].
2
.4. Antimicrobial screening
The antimicrobial activities of the ligand (HL) and its binary and ternary copper(II)
complexes have been studied by the agar disc diffusion method [37], at 100 and 50 μg/mL
concentrations of different compounds in DMSO solvent which has no inhibition activity.
Two pathogenic gram negative bacteria (Escherichia coli and Salmonella typhimurium), two
gram positive pathogenic bacteria (Staphylococcus aureus and Bacillus subtilis) and Candida
albicans as fungus strain were used in the current study. The solution of ligand and its
copper(II) complexes were added to the agar (PDA) plates which contain infusion of 200 g
potatoes, 6 g dextrose and 15 g agar and incubated at 27 °C for 36 h; and diameter of the
inhibition zones was measured in millimeters [38].
4

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2
.5. Synthesis of the semicarbazone ligand, HL
Synthetic of semicarbazone ligand, HL occurs by preparation of 2-aminochromone-3-
carboxaldehyde [27], which condensed with semicarbazide hydrochloride afforded the target
semicarbazone (HL); as summarized in Scheme 1.
2
.6. Synthesis of the copper(II)- complexes
The methanolic solutions of the respective copper(II) salt and the HL ligand were
mixed in the molar ratio 1:1 for binary complexes and refluxed for 3 h, except for nitrato
complexes, the molar ratio 1:1 and 2:1 (L:M) were attempted. However, in ternary complexes
-
the methanolic solution of auxiliary ligand (L′: 8-HQ, 1,10 phen or SCN ) was added to the
binary mixture of the nitrato complex 2 in a ratio 1:1:1 (M:HL:L′). The resulting precipitates
were filtered off, washed with methanol then ether and finally air-dried. The complexes were
kept in a desicator over anhydrous calcium chloride. The following detailed procedures are
given as examples for binary and ternary complexes and the other complexes were similarly
obtained.
2
.6.1. Synthesis of binary [(L)Cu(NO )].H O complex (2)
3 2
Cu(NO ) .2.5H O (0.70 g, 3.0 mmol) dissolved in methanol (30 mL) was added
3
2
2
gradually to the ligand (HL) (0.74 g, 3.0 mmol) dissolved in methanol (30 mL). The reaction
mixture was refluxed for 3 h; the green precipitate so formed was filtered off, washed several
times with methanol, diethylether and finally air-dried. The yield was (0.51 g, 65%).
2
.6.2. Synthesis of ternary [(L)Cu(8-HQ)(CH OH)](NO ), complex (7)
3 3
Cu(NO ) .2.5H O (0.70 g, 3.0 mmol) dissolved in methanol (30 mL) was added
3
2
2
gradually to the HL ligand (0.74g, 3.0 mmol), dissolved in methanol (30 mL). The reaction
mixture was refluxed for 30 min. and then 8-hydroxyquinoline (8-HQ) (0.44 g, 3.0 mmol)
dissolved in methanol was added to the above mixture. The resulting mixture was refluxed for
3
h, the green precipitate so formed was filtered off, washed several times with methanol,
diethylether and finally air-dried; the yield was (0.46 g, 62%).
5

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3
. Results and discussion
The structure semicarbazone HL ligand (Scheme 2), which synthesized by the direct
condensation of semicarbazide hydrochloride with 2-aminochromone-3-carboxaldehyde, was
1
13
elucidated by elemental analyses, electronic, IR, H and C NMR and mass spectra. The
results of the elemental analyses (Table 1) are in good agreement with the proposed formula
1
13
(
C H O N ). H- and C-NMR spectra of the current ligand (HL) was recorded in DMSO-
11 10 3 4
d6 and the data are summarized in Tables 2 and 3. The singlet resonances at δ 8.38 ppm and
1
7
.36-7.98 ppm regions in the H-NMR spectrum might attributed to the protons of the
azomethine and phenyl ring, respectively. Whereas, three D O-exchangeable signals observed
2
at δ 6.38, 8.64 and 9.80 ppm (Table 2) were assigned to NHamidic, NH at chromone moiety
2
and NH proton, respectively. However, the eleven signals of 13C-NMR spectrum are
ascertained to the number of carbon atoms in HL ligand. Moreover, the characteristic signals
appeared in the spectrum at δ 92.6 and 173.4 ppm (Table 3) was alienable to C-3 and C-4,
respectively. Further support for the structure of HL, was deduced from its mass spectrum
that shows a well-defined parent ion peak at m/z = 246 (15%) amu (calc. 246.22), and can
coordinate with metal ions through keto or enol forms.
–
–
The present HL ligand was allowed to react with various copper(II) salts (AcO , NO ,
3
SO42– or Cl ) to prepare binary complexes to explore the effect of the counter-anions on the
products. Also, the ligand was allowed to react with copper(II) nitrate in the presence of
secondary ligands (L′) namely: 8-hydroxyquinoline, 1,10-phenanthroline and KSCN to
prepare ternary complexes. The prepared complexes are stable at room temperature and
limited soluble in most common organic solvents. The obtained complexes are characterized
by elemental, thermal analyses and spectral (IR, UV-Vis, NMR, ESR and mass spectra) as
well as molar conductance and magnetic measurements. Attempts to isolate a single crystals
suitable for X-ray studies were unsuccessful. Elemental analysis proposed the formation 1:1,
–
1
:2 and 1:1:1 for binary and ternary copper(II)- complexes; respectively.
3
.1. Infrared spectra
The IR spectra of the current compounds were recorded with KBr disc in the range
-1
4
000-400 cm . The significant IR bands with their tentative assignments of the free ligand
and its copper(II) complexes are presented in Table 4. The characteristic IR absorption bands
of the complexes differ from their semicarbazone, HL, and provide significant indications
6

ACCEPTED MANUSCRIPT
regarding the coordination and bonding sites of semicarbazone. The presence of strong
-1
absorption bands at 1712 and 1659 cm of HL are assigned to (C=Oamide) and (C=Oγ-pyrone).
The appeareance of (C=Oamide) absorption band, suggests the existence of HL in the solid
-1
state as ketoamine form (Scheme 2) [39]. Disappearing of the band at 1712 cm and shift of
-1
the other band at 1659 cm in all complexes, exclude sulphato complex 3, to a lower
-1
frequency in the range 2-29 cm , refers to the presence of HL in the enolate form during
coordination process. However, in complex 3, the v(C=O) has undergone a shift to a higher
-1
frequency from 1659 to 1671 cm suggesting a coordination through keto oxygen atom [40].
The coordination through keto/enol oxygen atom is further substantiated from the appearance
-1
of new bands at 528-540 cm region due to v(Cu–O) stretching in the spectra of the
complexes [40,41]. Furthermore, the negative slope of the linear relationship of the stretching
frequencies of v(Cu–O) versus v(C=O), indicates elongation (weakness) of C=O as the bond
-1
-1
strength of Cu–O increases (shortness); v(Cu–O) /cm = 1675.4 – 0.698 v /cm , r = 0.94 ,
C=O
n = 5, except complexes: 3, 4 and 5.
-1
Vanishing or red shifts of the band observed for free HL ligand at 3279 cm , that
assigned to va (NH) vibrations of the imino group, in the spectra of the complexes provides a
further evidence for the keto-enol tautomerism of the ligand via enolate form with copper(II)
-1
ion [41,42]. The intense band at 1612 cm in the spectrum of HL has been assigned to
-1
v(C=N) of the semicarbazone moiety. This band sustains red shifted by 3-53 cm in the
spectra of the complexes, inform involvement of azomethine nitrogen in the coordination
sphere [42]. Coordination of azomethine nitrogen is consistent with the presence of a new
-1
band at ca. 449-477 cm , assignable to v(Cu–N ) for these complexes [39]. But, another
azo
strong band observed in the region 1537-1578 cm-1 revealing enolization of the
semicarbazone in the current complexes except 1 and 4, confirms again the coordination via
enolate oxygen. However, the positive slope of vM-N verus the azomethine stretching
-1
-1
frequency, vM-N/cm = -2740 + 2.0 vC=N/cm , r = 0.94, n = 5, except 3, 5 and 7 proposing
dynamic conjugation which enhances the double bond character through chelation, thus
offsetting the loss of electron density via donation to the metal ion, and supportive of
azomethine coordination.
Coordination modes of the secondary ligand and anions could be considered from the
IR spectra. The asymmetric and symmetric stretching vibrations of the acetato complex 1
-1
-1
look at 1442 and 1336 cm respectively,  = ( - ) = 106 cm , which is comparable to the
as
s
7

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values cited for the bidentate character of the acetato group [39]. However, nitrato complexes
-1
2
and 8 display two strong bands at (1384, 1136) and (1384, 1138) cm , respectively, related
to v and v of the nitrato group indicating the presence of a terminal monodentate
2
4
coordination of the nitrato group, while, in complex 7 the NO group acts as ionic and
3
showed two absorption bands at (1384,825) [39]. Whereas, the sulphato complex 3 shows
-1
two bands at 1115 and 1035 cm corresponding to  (S-O) bands which are characteristic for
3
the monodentate of the high symmetry T (tetrahedral) point group [41]. But, the thiocyanato
d
-1
-1
ternary complex 6 has a characteristic band at 2095 cm , medium band at 775 cm and weak
-1
band at 493 cm corresponding to v(CN), v(CS) and δ(NCS); respectively, points to the
unidentate coordination through nitrogen atom.[41]. The linear relationship of vC=O/cm-1
-1
-1
2
-1
versus the molar conductance (vide infra), vC=O/cm =1628.7 + 0.28 Ω cm mol , r = 0.99, n
3, except, nitrato- and chloro-complexes, 2 and 4, reveals increase of molar conductance
=
with the increase of stretching frequency of vC=O (weak coordinating) which intensify the
coordinating ability of anion towards Cu(II) ion and consequently high molar conductance.
-1
The mixed-ligand complexes 7 and 8 showed new bands in the range 1492 and 1519 cm ,
supporting the coordination of the C=N group of the secondary ligands to the metal ion [39].
-1
The present complexes showed a broad band in the range 3361-3486 cm assignable to
(OH) of the coordinated/uncoordinated water or methanol molecules associated with the

complexes that, resolved by elemental and thermal analyses. Reinforcement the above
interpretation is the appearance of the non-ligand bands at 528-540 and 449-477 cm-1
assigned to (M-O) and (M-N), respectively [41,43].
3
.2. Conductivity measurements
The conductivity measurements carried out in DMF solutions at room temperature are
collected in Table 5. All complexes, except 2 and 7, were found to be in the range 5.45- 37.25
-1
2
-1
Ω cm mol , revealing non-electrolytes [44]. The relative high values of the molar
conductance data of complexes 6 and 8 may be due to the partial dissociation in their DMF
solutions [44]. However, complexes 2 and 7 display molar conductance values: 70 and 98 Ω-1
2
-1
cm mol , suggesting 1:1 electrolytic nature, this is compliant with the infrared data.
Furthermore, the negative slope of the linear correlation of molar conductance versus the
-1
2
-1
Lewis basicity of anion, DNx [45], Ʌ/Ω cm mol = 148.92 – 3.65 DN , r = 0.987, n = 3,
X
8

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except acetate complex, refers to decreasing the molar conductance of complexes with the
increasing of Lewis acid base interaction of the Cu(II) with anion.
3
.3. Electronic spectra and magnetic measurements
The electronic spectral data of semicarbazone ligand, HL and its copper(II) complexes
recorded in DMF solution, Nujol mulls and/or reflectance are presented in Table 5. The free
-1
-1
semicarbazone has three absorption bands at 259 nm (38610 cm ) and 286 nm (34965 cm )
-1
due to π-π* transitions of the chromone ring and imine group, and 316 nm (31646 cm ) that
corresponds to n-π* transitions of the amide group of HL ligand [46].
-1
The intraligand transitions observed in the range 259- 316 nm (34965-31646 cm )
undergoes shift upon complexation which might attributed to the donation of electron pairs of
coordinating centers to Cu(II) on complexation. The high intense bands observed in the
-1
region 21377-25640 cm reflects ligand-to-metal charge transfer (LMCT) transitions which
might originate from O→ Cu and N→ Cu, transitions. The LMCT transitions are linearly
-1
correlated with the IR data (Table 4); νCu-O/cm = -2687.8 + 5.77 λMLCT/nm, r = 0.942, n =
, except 3, 5 and 8 complexes, the positive slope indicates a higher red shift of LMCT as the
coordinating ability of HL towards Cu(II) increased. Furthermore, the negative slope of νC=O
5
-1
versus λLMCT; νC=O/cm = 1755.4 – 0.31027λLMCT/nm, r = 0.983, n = 5, except 2, 3, 4 and 8
complexes, revealing again a hypsochromic shift of LMCT as the coordinating extent of
carbonyl group decreases (less shift to the lower frequency).
2
2
2
2
For a tetragonal field three spin allowed transitions: A ← B , B ← B and
1
g
1g
2g
1g
2
2
2
2
2
2
2
E ← B are possible and tetragonal complexes have the dyz, dxz← dx -y and dz ←dx -y
g
1g
transitions. But it is difficult to resolve them into separate bands due to the little energy
difference between these bands. All copper(II) complexes have very broad d-d combination
--1
bands in the range 15197 - 16666 cm [47,48]. The magnetic moment values of the current
copper(II) complexes were in the range of 1.63–2.15 B.M., which are close to spin only value
9
1
.73 B.M. corresponding to single unpaired electron of copper(II)-d complexes [40].
9

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3
.4. Electron paramagnetic resonance spectra (EPR)
Since the UV-Vis spectral data were unable to distinguish between the geometries of
the current Cu(II)-complexes. Thus, the EPR spectra recorded in polycrystalline state at room
temperature for the present complexes can provides information about the coordination
environment around Cu(II) -center. Complexes 3, 5, 6 and 7 were selected as examples and
their EPR data collected in Table 6. The results are in good agreement with earlier reported
values of Cu(II)-semicarbazones [49]. The EPR spectra of complex 3 shows only one broad
signal at g = 2.05, (Fig .1), such isotropic spectra arises from extensive exchange coupling
iso
through misalignment of the local molecular axes between different molecules in the unit cell
(dipolar broadening) and enhanced spin lattice relaxation. This type of spectra unfortunately
give no information about the electronic ground state of the Cu(II) ion present in the complex,
which is similar to that found for the square planar geometry around Cu(II) ion in the
complex [50].
However, complexes 5-7 display axial spectra with well defined: G, g and g features,
||
⊥
indicate the geometry of the complexes in the solid state that affected by the nature of the
coordinating anions. The geometric parameter G for axial spectra measures exchange
interaction between copper centers in the polycrystalline compound. The geometric parameter
G for the complexes 5, 6 and 7 are 1.29, 1.24 and 1.17; respectively (Table 6), indicating a
considerable exchange interaction in the solid complex, i.e., the unit cells of the complexes
contains magnetically equivalent sites [51-53]. For the complexes 5, 6 and 7, g > g > 2 and
||
⊥
2
2
G- values falling in the range 1–2 are consistent with a dx -y ground state. As g > g , the
||
⊥
distorted octahedral geometry around the Cu(II) center is suggested, which is confirmed by
the shapes of the spectra that consistent with octahedral geometry of similar complexes [41].
For all the present complexes g is also calculated using the equation, g =1/3 (g +2g ) and
av
av
||
⊥
found in the range 2.063-2.077. According to Kivelson and Neiman considerable covalent
character is suggested for M–L bond for the complexes when the g < 2.3 [54]. The g values
||
||
in the current complexes are > 2.3 is an indication of covalent bonding in these complexes.
The g values are nearly the same for the reported complexes indicating that the bonding is
||
dominated by the semicarbazone moiety. The EPR bonding parameters were estimated as
described previously [55,56], the data are given in Table 6. The EPR parameters, g , g A
⊥, ||
||
2
(
Cu) and the energies of d-d transitions were used to evaluate the bonding parameters α , and
1
0

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β2 which may be regarded as measures of covalency of the in-plane σ bonds, in-plane π-bonds
and out-of plane π-bonds respectively.
The orbital reduction factors, K and K were calculated using the expressions
||
⊥
reported elsewhere [57]. According to Hathaway [53], for pure σ bonding K ≈ K ≈ 0.77, and
||
⊥
for in-plane π-bonding, K < K ; while for out-of-plane π-bonding, K < K . As seen in Table
||
⊥
⊥
||
6
, K > K which indicates the presence of significant out-of-plane π-bonding. Furthermore,
||
⊥
2
2
α and β have values less than unity (< 1) that expected for 100% ionic character of bonds;
suggest the covalency of the bonds in the current complexes. The empirical factor f = g /A
||
||
-1
(
cm ) is an index of tetragonal distortion and depends on the nature of the coordinated atom.
-1
In the investigated complexes, f falls in the range 95-99.5 cm corresponding to a Cu(II)
center with medium distortion [58].
3
.5. Thermal analysis
Thermogravimetric (TGA) and differential thermogravimetric (DTG) analyses were
carried out within the temperature range from room temperature up to 800 ºC for the
isolated solid complexes 1, 2, 5 and 7 as representative examples, to get information about the
thermal stability and ascertain the nature of associated water molecules of the present
complexes. Table 7 summarized the maximum temperature values for decomposition stages
of complexes along with their assignments. The thermal decomposition of the binary
complexes, [(L)Cu(OAc)(H O)].0.5H O (1), [(L)Cu( NO )].H O (2) and [(L )Cu].3H O (5)
2
2
3
2
2
2
exhibit two main degradation steps as shown in Figs 2 and 3. The first stage of decomposition
occurs within the temperature ranges 46–130, 38-121 and 48-174 °C with maximum
temperatures at 83 and 99 and 113 °C, accompanied by a weight loss of 2.27, 4.69 and 8.51
%
corresponding to the loss of 0.5H O, H O and 3H O lattice water parallel to the theoretical
2 2 2
values of 2.83 and 4.63, and 8.88%, for complexes 1, 2 and 5, respectively. The second
decomposition stage is associated with the remaining molecular unit. This step occurs at three
maxima for complex 1: 193, 344 and 393 °C, accompanied by a weight loss of 77.29 %,
analogous to coordinated H O, -CH COOH + C H N O, and C H O species, leaving CuO as
2
3
2
4
4
9
4
residue. Whereas, the second decomposition stage of complex 2 and 5 occurs at two maxima:
45, 485 and 269, 399 °C with a weight loss 75.1 and 72% corresponding to the decompose
of -C H N O , C H +HNO and -C H N O -C H N species leaving residue as a final
2
5
5
4
2
6
4
3
11
9
4
3,
11
5
4
1
1

ACCEPTED MANUSCRIPT
products proportionate to the rest percentages for complexes 2 and 5; respectively.
Notwithstanding, the TGA of ternary complex, [(L)Cu(8-HQ)(CH OH)](NO ) 7, shows four
3
3
steps in the ranges: 42-302, 302-365, 365-532 and 532-800 ºC. The first stage due to loss of
one coordinated methanol and CH N O molecules (calcd. 16.45%, found 16.50%). The
2
2
2
second step displays loss of HCN molecule (calcd. 4.94 %, found 4.99%); and the third step
shows loss of HNO and C H N O molecules (calcd.41.68%, found 42.96%). The fourth
3
10
8
2
stage related to the loss of C H molecule (calcd.16.82%, found 16.19%), leaving at the back
7
4
the residue related to mass loss (found:19.66%).
Calculation of activation thermodynamic parameters for the decomposed complexes
was adopted by Costs-Redfern equations [59] of the various decomposition stages and
collected in Table 8.
The kinetic parameters, particularly the energy of activation (E ) values, are helpful in
a
assigning the strength of complexes [60]. The calculated E values of the investigated
a
-1
complexes of the first dehydration step were at 48.31, 144.68 and 26.32 kJ mol as shown in
Table 8 for complexes 1, 2 and 5; respectively. Based on the E values, the thermal stability
a
of complexes follows the order: 2 >> 1> 5. Moreover, Ea of the second stage of
decomposition of complexes 5 and 7 are lower than the first stage, indicating that the rate of
decomposition for this stage is higher than the first stage, which is opposite to that found for
complex 1 [61]. The other kinetic parameters listed in Table 8, views the following remarks:
(
1) The positive values of ΔH*, means that the decomposition processes are endothermic.
2) The values of ΔG* are relatively low and positive sign inform the autocatalytic effect of
(
metal ions on thermal decomposition of the complexes and non–spontaneous processes [43].
3) There was no definite trend in the values of the entropy of activation (ΔS*). However, the
(
negative values of the entropy changes proposed that the activated complex has a more
ordered structure than the reactants, and the reactions are slower than expected [62]
3
.6. Mass spectra
Mass spectra being an excellent tool for getting molar mass and from the mode of
fragmentation, the exact structure of the compounds could be deduced; and the
characteristic fragments can be given as m/z (% abundance) [63]. The fragmentation
pattern of free ligand, HL was depicted in Scheme 3. The first hand fragmentation of HL
takes place due to either loss of -NH and -CO from the molecular ion species (A) to give
1
2

ACCEPTED MANUSCRIPT
species (B) with peak at m/z 203 (6%), or loss of NH to yield species (B`) with peak at
3
m/z 229 (5%). The species (B) further degrades with the loss of –NH species forming the
2
base peak species (C) at m/z 187 (100%). The species (C) loss H radical forming species (D)
with peak at m/z 186 (17%). The species (D) degrades with removal of NC-C H -NH then
2
2
2
accept H radical forming stable species (E) at m/z 121(75% abundance). The species (E)
further degrades and loss -CO forming species (F) with peak at m/z 93 (16%). The species
(
F) further degrades with loss either 0.5 O forming species (G) or -CO forming (G`) with
2
peaks at m/z 77 (11%) and 65 (17%), respectively. The mass spectra of complexes 2, 5, 6
and 8 were taken as representative complexes and provide good evidence for the molecular
formulas of these complexes. The mass spectra of these complexes displayed the first peak
as molecular ion peaks at m/z: 368, 553, 402 and 550, which refer to M.wt. with the
abundance of 9, 4, 5 and 6%; respectively. Therefore, mass spectral data without solvated
molecules agree well with the formula weights deduced from the elemental analysis of the
complexes [(L)Cu(NO )].H O (F.Wt = 388.77), [(HL)Cu(SO )] (F.Wt = 404.82)
3
2
4
[(L )Cu].3H O (F.Wt = 608.01), [(L)Cu(SCN)(H O) ] (F.Wt = 402.86), and
2 2 2 2
[
(L)Cu(NO )(Phen)] (F.Wt = 550.96). Analysis of the mass spectrum of complex 2 depicted
3
in Scheme 4 was introduced in details as a typical example for fragmentation pattern that
pretense the first peak at m/z 369 which represents the molecular ion peak of the complex.
The primary fragmentation of the complex takes place due to the loss of CO from the
species (A) to give species (B) with peak at m/z 342 (7%). The species (A) degrades with
the subsequent loss of –NH NCO species forming species (C) with peak at m/z 312 (5%).
2
The species (C) also degrades with the subsequent loss of either –HCN +H species forming
species (D) with its peak observed at m/z 286 (4%) or loss of CuNO + H radical forming
3
2
-amino-3-cyanochromone as species (D`). The species (D) further degrades with the
subsequent loss of –CuNO species forming species (E) with its peak at m/z 161 (6%).
3
Species (E`) was also degrades by giving fragment (2-aminooxirane) as the base peak at
m/z 57 (100%) species (E). The species (D) further degrades with the subsequent loss of
either–CO species forming species (F) with peak at m/z 133 (6%) or loss of C HNH
2
2
forming (F`) with peak at m/z 121 (23% abundance). The species (F`) further degrades with
the subsequent loss of –CO species forming species (G) with peak at m/z 93 (15%) and
species (G) further degrades with the subsequent loss of other –CO species forming species
(
H) with peak at m/e 64 (15%). Moreover, species (F`) loss 0.5 O forming species (G`)
2
1
3

ACCEPTED MANUSCRIPT
with peak at m/z 105 (15%) further degrades with the subsequent loss of –CO species
forming species (H`) with peak at m/z 77(16%) (similar to that found for free HL ligand).
4
. Fluorescence spectra
In order to study the emission photo luminescence properties of the studied compounds,
the adiabatic emission spectra were measured at room temperature by passing UV radiation of
appropriate wavelength either in DMF solution or in solid state and the data is collected in
Table 9. The excitation wavelength is selected in between 333-400 nm, the ligand HL
exhibits an emission band maxima at 444 nm which is changed to the range 447 - 586 nm in
complexes The emission data are linearly correlated with their LUMO energies calculated
using DFT (vide infra), λem/nm = 446.2 + 4.63 ELUMO/eV, r =0.91, n = 6, except: 3, 4 and 6
complexes, the positive slope reveals that the increasing of ELUMO enhanced the red shift of
the emission spectra. Emission occurs to a manifold of vibrational states in the ground state,
causing a red shift emission. This red shift due to vibrational relaxation of the initial excited
state to the lowest vibrational state of the first electronic excited state.
The fundamental parameters commonly used in describing and comparing
fluorophores are the: extinction coefficient (), quantum yield (), fluorescence lifetime ()
and stokes shift (SS). The emission spectra arising from S state which assigned to π* →π
1
might analogous to LUMO→HOMO transition character for all molecules. Through
analyzing the transition configuration of the fluorescence, was found to be just the reverse
process of the lowest lying absorption. Extinction coefficient () is a direct measure of the
ability of a fluorophore to absorb light, and those chromophores having a high extinction
coefficient i.e., high probability of fluorescence emission. The extinction coefficients
-1
-1
(
Ɛ/mol.L cm ) of the current compounds in DMF solution recorded in Table 10, follows the
order: 6< 1< 3< 7< 5< 8< 2< HL <4, which evident that the fluorescence emission intensity
of the ligand quenched by complex formation with the metal ions (except chloro complex 4),
this explained by the processes such as electronic energy transfer, magnetic perturbation,
redox activity [63,64]. These copper(II) complexes make the energy transfer from the excited
state of the ligand to the metal ion causing decreases of the fluorescence intensity.
Furthermore, the dramatic decreases in intensity of the thiocyanato complex 6 and acetato
complex 1 may attributed to the presence of quenching groups like thiocyanato and acetato in
these complexes [65]. On the other hand, the fluorescence lifetime () follows the opposite
1
4

ACCEPTED MANUSCRIPT
order of extinction coefficients, because the intrinsic lifetime of a fluorophore is inversely
proportional to the extinction coefficient, molecules exhibiting a high extinction coefficient
have an excited state with a short intrinsic lifetime.
The Stokes shift phenomenon is a large part of the reason that fluorescence
spectroscopy is more sensitive to the environment around the chromophore. The primary
origin of the Stokes shift is the rapid decay of excited electrons to the lowest vibrational
energy level of the S excited state. Additionally, fluorescence emission is usually
1
supplemented by transitions to higher vibrational energy levels of the ground state, resulting
in further loss of excitation energy to thermal equilibration of the excess vibrational energy.
Other events, such as solvent orientation effects, excited-state reactions, complex formation,
and resonance energy transfer can also contribute to longer emission wavelengths.
The data in Table 9 refers in general to a higher stokes shifts in DMF solution than in
solid phase, correlating of stokes shifts in solution versus solid state, Stokes shift (solid)/cm-1
-1
=
3426 + 0.245 Stokes shift (soln)/cm , r =0.93, n = 6, except: HL, complexes, 5 and 6,
indicates that Stokes shift value in solid state ≈ 0.245 Stokes shift in DMF solution; i.e,
intimating, excited state reactions with the environment in solution is more probable than in
solid state. This object proposed higher difference in dipole moments between the ground and
excited states in solution compared with the solid state. This interpretation emphasized by
the linear relationships of the Stokes shift (SS) values of the current compounds with the
-
quantum chemical calculations (vide -infra): µ /D = 21.82 - 0.0025ν Stokes in DMF soln/cm
g
1,
r = 0.96, n = 5, except: HL and complexes: 2, 3 and 4; Stokes in DMFsoln/cm =17208 -
-1
6
1.56 ELUMO/eV., r = 0.92, n = 7, except, HL and acetato complex 1; and ν Stokes in soln/cm-
1
=
17115 - 3264.83 E /eV., r = 0.92, n = 5, except: 2, 5, 6, 7 and 8 complexes. The negative
gap
slopes suggest that compounds have less µ , E
or Egap are accompanied with higher
LUMO
g
Stokes shift.
The Stokes shift of the current compounds given in Table 9 follows the order: 6 <
HL < 7< 1< 8 < 4 < 5 < 3 < 2. Thus, the displacement in potential surface between the ground
and excited states, and loss of vibrational energy in the excited state go in the same order.
The lowest Stoke shift found for complex 6 is 56 nm, but the highest Stoke shift (245 nm) for
nitrato complex 2. Consequently, the free ligand and thiocyanato complex 6 with the highest
stokes shifts promising optical properties and good candidates in the solar cell devices. The
-1
Stokes shifts values for complexes 2, 3 and 5 as shown in (Table 9) >10000 cm indicative a
1
5

ACCEPTED MANUSCRIPT
remarkably excited state reactions, which often excited state proton transfer. However, Stokes
-1
shifts of the rest compounds were found in the range 3070 -7273 cm that might assigned to
changes in dipole moment between ground and excited states in polar environments.
Interactions between the solute and solvent can occur in either the ground state or the
excited state. This fact stimulated us to investigate the effect of solvent on the spectroscopic
properties of the current compounds. Complex 5, [(L )Cu].3H O, was chosen as a
2
2
representative example and its spectroscopic properties collected in Table 11 was correlated
with their relevant of polarity scales. Effect of solvent polarity on the Stokes shift of complex
-1
5
follows this order: THF (9588 cm ) > DCM (8453) > CHCl (7639) > EtAc (7413) > DMF
3
-1
(
7253 cm ), referring to decrease of Stokes shift value with the increasing of solvent polarity.
This finding emphasized by the negative slopes of the linear relationship of Stokes shift/cm-1
N
-1
versus the relative polarity (normalized E ) and polar index of solvent [65]: Stokes/cm
T
N
=
12075 -12683 E , r = 0.99, n =3, except: CHCl and ethylacetate (EtAc) solutions; and
T
3
-1
Stokes/cm =10942 - 803.53 polar index, r = 0.99, n = 3, except: DMF and THF solutions.
For chromophores that have a large difference in dipole moment between the ground and
excited state, the fluorescence emission maximum often depends strongly on solvent polarity
in simple fluid solvents and the emission is detected to shift to longer wavelengths during the
excited-state life time. Such dynamic Stokes shifts have been extensively studied as a probe
of solvent polarity [66,67].
4
.1. Estimation of ground state and excited state dipole moments
By employing the simplest quantum–mechanical second order perturbation theory and
taking into account Onsager’s model [68]. Solvent effect on the Stokes shifts (ν −ν ) of the
a
f
current compound based on a linear correlation between the wavenumbers of the absorption
and fluorescence maxima and a solvent polarity function which involves both dielectric
permittivity(ε) and refractive index (n) of the medium Bilot–Kawski, Lippert–Mataga,
Bakhshiev, Kawski–Chamma–Viallet and Reichardt have obtained expressions based on the
various solvatochromic shift methods [69-74]. The Onsager radius “a” of the solute complex
1
/3
5
was evaluated by using atomic increment method, a (radius) = (3M/4πδN) , M = molar
mass,δ = density, N = Avogadro’s number [68] and found to be 6.468 Å.
The results of the statistical treatment of the Bilot–Kawski, Lippert–Mataga,
Bakhshiev, Kawski–Chamma–Viallet and Reichardt correlations, namely the slopes and
1
6

ACCEPTED MANUSCRIPT
number of data are summarized in Table 10. Dipole moments of ground state (µ ) and
g
excited state (µ ) are determined from the slopes m(1) and m(2) of the Bilot–Kawski
e
correlation [69]. However, the excited state dipole moments (µe) are determined from the
slopes (m , m , m and m ) of Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet and
1
2
3
4
Reichardt correlations [69-74]. All of the results are presented in Table 11.
As can be noted in Table 12, excited state dipole moment (9.55D) is found to be
higher than the ground state dipole moment (3.01D) by 6.54D indicating that, the studied
complex molecule is significantly higher polar in its excited state than ground state. Hence,
the extent of solvent– solute interactions higher in the excited than in the ground state,
demonstrating an important redistribution of charge densities between both electronic states.
Moreover, Reichardt method based on the empirical polarity scale ETN [18] was used for
estimating dipole variation (Δµ = 9.77 D) from solvatochromic shift. The spectral data
correlation with microscopic solvent polarity generally provides superior results as compared
to traditionally used bulk solvent polarity functions. These differences between the values of
μe may be in part, due to the various assumptions and simplifications made in the use of
Lippert’s, Bakshiev’s and Chamma Viallet’s correlations [70, 72,73].
It is clear from Table 9 that the magnitude of Stokes shift varies between 7253 cm-1
-1
(
in DMF solution) and 9588 cm (in THF solution). The absorption spectra show the bands in
the regions of 313–343 nm do not show solvent sensitive shift. Unchanged absorption
spectrum with solvent polarity implies that the ground state energy distribution is not affected
possibly due to less polar nature of the molecule in the ground state. On the other hand, blue
shift of the emission maximum with the solvent changes indicates greater stabilization of
excited state in less polar solvents [70].
Ground and excited states dipole moments calculated by using theoretical methods at
the TDDFT/B3LYP/6-311++G(d,p) level of theory are found as 4.911 Debye and 5.691
Debye in vacuum. Discrepancies between experimental and theoretically obtained results can
be attributed to the fact that theoretical calculations exist in gaseous phase of isolated
molecule and the experimental results belong to solution of solid-state of the complex 5.
1
7

ACCEPTED MANUSCRIPT
5
. Antimicrobial studies
The antimicrobial activity of the ligand, HL and its copper(II)-complexes was
investigated against the sensitive organisms Staphylococcus aureus and Bacillus subtilis as
Gram–positive bacteria; Escherichia coli, and Salmonella typhimurium as Gram–negative
bacteria; yeast: Candida albicans and fungus: Aspergillus fumigatus. (Table 13). From the
results depicted in Table 13, we can conclude that: The hydrazone, HL, ligand showed lower
activity towards Gram-positive bacteria, Gram-negative bacteria, Candida albicans and
Aspergillus fumigates as the fungi. The prepared complexes revealed moderate activity
towards most the tested strains. Complex 2 showed high activity towards Bacillus subtilis as
Gram-positive bacteria, while complex 3 and 4 showed high activity toward Staphylococcus
aureus as Gram-positive bacteria. Such increased activity of the present copper complexes
can be explained on the basis of the oxidation state of the metal ion, overtone concept and
chelation theory. According to the overtone concept of cell permeability, the lipid membrane
that surrounds the cell favors the passage of only lipid-soluble materials in which
liposolubility is an important factor that controls the antimicrobial activity. On chelation, the
polarity of the metal ion will be reduced to a greater extent due to overlap of ligand orbital
and partial sharing of the positive charge of the metal ion with donor groups. Further, it
increases the delocalization of π-electrons over the whole chelate ring and enhances the
lipophilicity of the complexes [42]. This increased of lipophilicity enhances the penetration of
complexes into the lipid membranes and blocks the metal binding sites in enzymes of
microorganisms.
Finally, from the interpretation of elemental, thermal analyses and spectral data
(infrared, electronic, ESR and mass) as well as molar conductance and magnetic susceptibility
measurements at room temperature and in absence of x-ray single crystal, it is possible to
draw up the plausible structures of the current Cu(II)- complexes (Scheme 6).
6
. Molecular modeling
Full geometry optimization, of the proposed structures of keto-enol of HL tautomers
and its copper(II) complexes based on the measurements mentioned above, was carried out
using density functional theory (DFT) at the B3LYP/6-311G (pd) level implemented on the
1
8

ACCEPTED MANUSCRIPT
Gaussian 09 [23-25] (Figs 4-6). The structural parameters of the ligand and its copper(II)-
complexes were computed to analyze the energetic behaviour and stability of the current
compounds [25].
6
.1. Frontier Molecular Orbital Analysis (FMO)
To gain a deeper insight into the nature of the electronic transitions in a molecular species, a
detailed examination of its FMOs, highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO), is conclusive owing to their close relationship
with electronic excitation properties [29]. One can predict the host‐guset interaction between
the current ligand, HL and Cu(II) ion. Another important property was calculated by using
HOMO and LUMO energy values for complexes at the same level (Table 14). The energy
gap can be calculated as follows Egap : Egap = -A + I, the electronegativity χ = (I + A)/2,
2
chemical hardness η = (I-A)/2, electrophilicity ω = μ / 2 and global softness S = 1/2 ɳ where I
and A are ionization potential and electron affinity, and I = −EHOMO and A = −ELUMO
,
2
2
2 1/2
respectively. Also, the total static dipole moment (μ) was calculated by μ = (μ + μ + μ )
x
y
z
[36,75,76]
The electronic transition occurred from ground state to the excited state (HOMO→LUMO),
which denotes the ability of the orbitals to donate and accept electrons, respectively. Figs. (7-
9
) illustrate the contours of HOMO and LUMO orbitals, the red color of the orbital represents
the positive and green refers to negative phases accordingly. In the current ligand, the HOMO
contour (Fig. 7) showed that the electron density is collected at chromone moiety and side
chain. Whereas, the LUMO is spread over the entire molecule except the amino group
attached with chromone ring and enolate group. Thus, the HOMO→LUMO electron
transition potentially occurs from chromone moiety and side chain (π) to the vacant orbitals
(
π*) with 4.295 for keto form and 4.139 eV for enol form [77]. This interpretation emphasized
from the matching between the wavelength calculated of the keto form in Table 14 for
HOMO → LUMO (288.7 nm) with the experimental value of 286 nm, that arised from imine
function of the semicarbazone moiety as described in section 3.2.3. But Egap of enol form =
1
9

ACCEPTED MANUSCRIPT
3
00 nm supporting that the keto tautomer is the common for free ligand, HL. The chemical
reactivity and stability of each nominated molecule depend on the eigen values of HOMO-
LUMO and energy gaps given in Table 14. The energy gap (E ) of the studied complexes
gap
varied between 0.771 eV for Cu(II) complex 8 refers to more reactive and 3.505 eV for
acetato complex 1 which is least reactive. The negative slope of Egap versus νC=O, E /eV=
gap
-1
7
986.82 – 4.843 νC=O/cm , r = 0.93, n = 5, except: HL and 3, 4 and 5 complexes, refers to
increase the stability (higher E ) of complex that is correlated with the hypsochromic shift
gap
of the νC=O group (shift to lower frequency). The maximum open circuit voltage (Voc) of
the bulk heterojunction (BHJ) solar cell has been calculated as described in our previous work
[78]. As shown in Table 14, the theoretical values of the open circuit voltage Voc of the
studied molecules range from 0.139 to 3.229 eV relative to TiO . These values are smaller
2
than that obtained for similar compounds [77]. Subsequently, the current compounds can be
used in solar cells with the presence of acceptor sites.
The copper ion in the complexes studied is formally in the second oxidation state, but
the computed natural charges for this ion found in the range: +0.215 to +0.865 which is
considerably lower than +2, signifying that they preserve most of the electrons withdrawn
from the ligands. Therefore, ligand-to-metal electron donations are advantageous over metal-
to-ligand back donations in these complexes. This charge transfer pattern is corroborated by
the changes undergone by the atomic charges on the ligand donor atoms, upon coordination to
the central metal ions. The magnitude of the negative charge on the N19 donor atom of
uncomplexed HL (natural charge is −0.545) reduces in all complexes (natural charges range
from −0.151 to −0.521, but the magnitude on the O15 donor atom of uncomplexed HL
(natural charge is −0.457) increases in all complexes (natural charges range from -0.478 to -
0
.736. This shows that HL-to-metal donation of electrons might occur via atom N19, whereas
metal-to-HL back donation of electrons happens through O15. However, N18 donor atom of
ligand HL, suffers a modest reduction natural charge from −0.332 in all complexes to the
range -0.207 to -0.277, except complexes 1, 7 and 8 which has increment of the negative
charge on N18 (metal-to-HL back donation of electrons through N18). Nevertheless, O27
donor atom in uncomplexed ligand (natural charge is −0.464) accumulates the negative
charges ranges from -0.482 to - 0.567 in all complexes, except complexes 3, 5 and 7 which
have been reduced (-0.437, -0.094 and -0.357, respectively). The natural charges on the Cl of
2
0

ACCEPTED MANUSCRIPT
the chloro complex 4 is drastically reduced from the formal −1 charge on a free chloride ion
to an average charge −0.456 following its coordination to the central copper (II) ion. This is
an indicative of significant electron donation from Cl to the copper(II) ion.
Finally, the selected bond lengths from the optimized structures are reported in Table
1
5. The bond lengths of free lgand HL in the vicinity of coordinating centers are generally
more or less elongated in most complexes in the ranges: C-O15 (0.028 -0.142), C-O27 (0.03 -
.13), C-N18 ( 0.037 - 0.086) and C-N19 (0.04 -0.11) Å, this suggests that modest overlap
with copper ion; but other bond lengths are comparable with that of free HL ligand.
0
7
. Conclusion
The present work describes the synthesis of a series of binary and ternary copper(II)-
complexes of tridentate semicarbazone (HL) derived from the condensation reaction of 2-
aminochromone-3-carboxaldehyde with semicarbazide hydrochloride. The physical
1
3
1
(
magnetic measurements, molar conductance, TGA), spectral (UV-Vis, IR, C and H NMR,
fluorescence, ESR), and analytical data for these complexes clearly suggest that the primary
ligand (HL) is coordinated to various copper(II) salts through its azomethine nitrogen, γ-
pyrone oxygen and enolate oxgyen forming binary mononuclear complexes. Also, ternary
complexes were obtained in molar ratios: 1:1:1 M:L:Lʹ by using secondary ligands (Lʹ) such
as 8-hydroxyquinoline, 1,10-phenanthroline as well as potassium thiocyanate. The presence
of coordinated water in metal complexes was confirmed by IR and TGA studies. The
semicarbazone ligand exhibits a strong fluorescence emission contrast to this partial
fluorescence quenching phenomena is observed in its copper(II)- complexes. The calculated
dipole moment of the excited state found to be higher than that of the ground state. This
reveals that molecule is more polar in the excited state than in the ground state and therefore,
is more sensitive to solvent effects. The proposed structures of complexes were geometrically
optimized and their structural parameters were calculated on the basis of B3LYB/6-311G(p,d)
using DFT level that is implemented in Gaussian09 program and the data were correlated
with the current experimental data. The different MO’s show a different extent of localization
on the different fragments of the complex, and the above rationalization is valid for MO
analysis of all the studied complexes. The antimicrobial studies suggested that the ligand was
found to be biologically active and their metal complexes show significantly enhanced
2
1

ACCEPTED MANUSCRIPT
antibacterial and antifungal activity against microbial strains in comparison to the free ligand,
thus, exhibiting their broad spectrum nature and can become a new antimicrobial agent.
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(D)
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[G ]
Fig.1. ESR spectra of [(HL)Cu(SO )] 3(A), [(L )Cu].3H O 5(B),
4
2
2
[
(L)Cu(SCN)(H O) ] 6 (C) and [(L)Cu(8-HQ)(CH OH)](NO ) 7 (D)
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TGA(mg)
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Temprature (C)
Fig. 2. TGA /DrTGA of [(L)Cu(OAc)(H O)].0.5H O.
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2