New nano-complexes of Zn(II), Cu(II), Ni(II) and Co(II) ions; spectroscopy, thermal, structural analysis, DFT calculations and antimicrobial activity application

Article abstract of DOI:10.1016/j.molstruc.2017.06.121

This work presents synthesis, characterization, and application of several metal (II) complexes with (E)-2-hydroxy-N^/-((thiophen-2-yl)methylene)benzohydrazide (H₂L). Prepared complexes were identified by elemental, thermal, FT-IR, UV–Vis, ¹H NMR, and XRD analysis, as well as molar conductivity and magnetic moment measurements. Changes in FT-IR and ¹H NMR spectra of hydrazone ligand upon coordination indicated that the ligand behaves the same way as a monoanonic ligand with ONS donor sites. Kinetic parameters were determined for each thermal degradation stage of the ligand and its complexes using ‘Coats–Redfern’ method. All results confirm that all prepared compounds have 1:2 metal-to-ligand stoichiometry except Zn(II) complex, which has 1:1 metal-to-ligand stoichiometry. The antimicrobial activity for complexes was investigated. The antimicrobial activity results revealed that Zn(II) complex (1) has a good potency against gram positive bacteria (E. coli) and gram negative bacteria (P. vulgaris) in comparision with doxymycin standard, AT B3LYP/6-311G (d,p) level, Density Functional Theory (DFT) calculations were carried out to investigate the optimized structure of both, the ligand and the complexes. Total energy, energy of HOMO, and LUMO as well as Mullikan atomic charges were calculated. Dipole moment, orientation, and structure activity relationship were performed and discussed.DFT calculations, moreover, confirmed practical antimicrobial results.

Full text of DOI:10.1016/j.molstruc.2017.06.121

Accepted Manuscript
New Nano-complexes of Zn(II), Cu(II), Ni(II) and Co(II) ions; spectroscopy, thermal,
structural analysis, DFT calculations and antimicrobial activity application
Hoda F. El-Shafiy, M. Saif, Mahmoud M. Mashaly, Shimaa Abdel Halim, Mohamed F.
Eid, A.I. Nabeel, R. Fouad
PII:
S0022-2860(17)30901-8
10.1016/j.molstruc.2017.06.121
MOLSTR 24007
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 22 July 2016
Revised Date: 29 May 2017
Accepted Date: 26 June 2017
Please cite this article as: H.F. El-Shafiy, M. Saif, M.M. Mashaly, S.A. Halim, M.F. Eid, A.I. Nabeel, R.
Fouad, New Nano-complexes of Zn(II), Cu(II), Ni(II) and Co(II) ions; spectroscopy, thermal, structural
analysis, DFT calculations and antimicrobial activity application, Journal of Molecular Structure (2017),
doi: 10.1016/j.molstruc.2017.06.121.
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Graphical abstract
New Nano-complexes of Zn(II), Cu(II), Ni(II) and Co(II) ions;
Spectroscopy, Thermal, Structural Analysis, DFT Calculations and
Antimicrobial Activity Application
Hoda F. El-Shafiy1, M. Saif1*, Mahmoud M. Mashaly1, Shimaa Abdel Halim1, Mohamed
F. Eid1, A.I. Nabeel2, R. Fouad1
1Department of Chemistry, Faculty of Education, Ain Shams University,
Roxy 11711, Cairo, Egypt
2Biochemistry Laboratory, Faculty of Education, Ain Shams University,
Roxy, Cairo, Egypt
*Corresponding author: email: mona_saif1@yahoo.com; Phone No.
0201009542296; Fax. (02) 22581243
Novel thiophene-2-carbaldehyde nano-complexes of Zn(II) (1), Cu(II) (2), Ni(II)
(3), and Co(II) (4) were successfully prepared in nano-scale domain. The antimicrobial
results and DFT calculations confirm that the prepared Zn(II) nano-complex (1) are a
promising nano-material for antibacterial application.

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New Nano-complexes of Zn(II), Cu(II), Ni(II), and Co(II) ions; Spectroscopy,
Thermal, Structural Analysis, DFT Calculations, and Antimicrobial Activity
Application
Hoda F. El-Shafiy1, M. Saif1*, Mahmoud M. Mashaly1, Shimaa Abdel Halim1, Mohamed F.
Eid1, A. I. Nabeel2, R. Fouad1
1Department of Chemistry, Faculty of Education, Ain Shams University, Roxy
11711, Cairo, Egypt
2Biochemistry Laboratory, Faculty of Education, Ain Shams University, Roxy,
Cairo, Egypt
*Corresponding author: email: mona_saif1@yahoo.com; Phone No.
0201009542296; Fax. (02) 22581243
Abstract
This work presents synthesis, characterization, and application of several metal (II)
complexes with (E)-2-hydroxy-N/-((thiophen-2-yl)methylene)benzohydrazide (H2L). Prepared
1
complexes were identified by elemental, thermal, FT-IR, UV-Vis, H-NMR, and XRD analysis,
1
as well as molar conductivity and magnetic moment measurements. Changes in FT-IR and H-
NMR spectra of hydrazone ligand upon coordination indicated that the ligand behaves the same
way as a monoanonic ligand with ONS donor sites. Kinetic parameters were determined for each
thermal degradation stage of the ligand and its complexes using ‘Coats–Redfern’ method. All
results confirm that all prepared compounds have 1:2 metal-to-ligand stoichiometry except
Zn(II) complex,which has 1:1 metal-to-ligand stoichiometry. The antimicrobial activity for
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complexes was investigated. The antimicrobial activity results revealed that Zn(II) complex (1)
has a good potency against gram positive bacteria (E. coli) and gram negative bacteria (P.
vulgaris) in comparision with doxymycin standard. AT B3LYP/6-311G (d,p) level, Density
Functional Theory (DFT) calculations were carried out to investigate the optimized structure of
both, the ligand and the complexes. Total energy, energy of HOMO, and LUMO as well as
Mullikan atomic charges were calculated. Dipole moment, orientation, and structure activity
relationship were performed and discussed.DFT calculations, moreover, confirmed practical
antimicrobial results.
Keywards: inorganic compounds; Nano-complex; antimicrobial, DFT, Thermal analysis
1. Introduction
Sulphur containing heterocycles and their complexes are, nowadays, of the most
promising classes of substances utilized in drug development. Benzothiophene derivatives, in
combination with other ring systems and their metal complexes, have been used in
pharmaceutical applications such as antiallergic, analgesic, anti-inflammatory, and ocular
hypotensive activities [1-4]. Raloxifene, a drug based on benzo[b]-thiophene, has been approved
by the U.S Food and Drug Administration for the prevention and treatment of osteoporosis
associated with woman postmenopausal [5].
The preparation of metal complexes, based on benzothiophene derivatives in Nano-
domain, creates new materials with unique physical, chemical, and biological properties. Most
reports on transition metal complexes with benzothiophene derivatives-based ligand and their
antimicrobial applications are in bulk scale [6]. Reports on Nano-scale transition metal
complexes with benzothiophene derivatives-based ligand are still unexplored.
In this paper, we are, therefore, concerned with the synthesis and characterization of the
new ligand, (E)-2-hydroxy-N/-((thiophen-2-yl)methylene)benzohydrazide, H2L and its metal
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Nano-complexes for antimicrobial application. The DFT calculations for model systems
perfectly correlate with experimentally-determined metrical parameters. Besides, thermal
stability of the reported metal complexes was studied.
2. Experimental
2.1. Materials
The starting materials used in these studies are analytical grade. They include methyl
salicylate (Chemical Laboratory) and hydrazine hydrate (PanreacQuimica). Metal salts, Lithium
hydroxide, and 2- thiophenecarbaldehyde from BDH, Analar or Merck chemicals were also used.
All solvents used are of spectroscopic grade. Gram-negative bacteria: Klebsiella pneumoniae,
Proteus vulgaris, and Escherichia coli (ATCC 28737); a Gram-positive bacterium:
Staphylococcus aureus (AT 6538), and a pathogenic fungus: Candida albicans (ATCC10231)
were used.
2.2. Characterization
Electronic spectra were carried out as DMF (10-3M) solutions and recorded on a ‘JASCO
model V-550 UV-Vis’ spectrophotometer. FT-IR spectra (4000-400 cm-1) for metal complexes
were recorded using ‘FT-IR Nicolet IS10’ spectrometer. Magnetic susceptibilities of complexes
were measured by the ‘Gouy’ method at room temperature using shelwood scientific, Cambridge
Science Park, magnetic susceptibility balance (England). Effective magnetic moments were
calculated using the relation µeff = 2.828(χm.T)1/2B.M., where χm is the molar susceptibility
1
corrected using Pascal’s constants for the diamagnetism of all atoms in compounds. H-NMR
spectra (DMSO-d6) were recorded at room temperature on a ‘Varian FT-290.90 MHZ’
spectrometer. The XRD patterns were recorded using ‘PHILIPS’ diffractometer with CuKα1
radiation (k = 1.54056 Å). An accelerating voltage of 40 kV and an emission current of 30 mA
were used. ‘TGA-DTG’ measurements were carried out on a ‘Shimadzu’ thermo gravimetric
analyzer using ‘TA-50 WSI’ program. Microanalyses of carbon, hydrogen, nitrogen and sulfur
were carried out at the Ministry of Defense, Chemical War Department. Melting or
decomposition points were determined on a melting point apparatus (stuart), England. Molar
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conductivities of 10-3 M solutions of solid complexes in DMF were measured using Corning
conductivity meter NY 14831 model 441.
2.3. Synthesis of ligand, (E)-2-hydroxy-N/-((thiophen-2-yl)methylene)benzohydrazide, H2L
The ligand H2L was prepared on two steps (scheme 1).First step: Synthesis of salicylic
acid hydrazide according to literature method [7,8]. Second step: preparation of hydrazone
ligand through condensation of salicylic acid hydrazide stiochiometrically in molar ratio (1:1)
with 2-thiophene carbaldehyde in absolute ethanol. The reaction mixture was refluxed for 2
hours. Drops of glacial acetic acid were added at the onset of reflux. After cooling, the obtained
pale yellow crystals were filtered off, washed with ethanol, and recrystallized with 1:1 (v:v)
DMF/H2O to give pure crystals with m.p. of 260 oC.
2.4. Synthesis of transition metal complexes (1-4)
A 0.125 g (3 mmol) mixture of LiOH.H2O and 0.738 g (3 mmol) of H2L in 30 mL
methanol were added to the metal salt (3 mmol); namely Zn(NO3)2.6H2O, Cu(NO3)2.3H2O,
Ni(NO3)2.6H2O, and Co(NO3)2.6H2O dissolved in the least amount of bi-distilled water. The
reaction mixture was stirred for 12 hours to ensure complete formation of metal complexes.
LiOH.H2O was added as a deprotonating agent. The precipitate was filtered and washed several
times with 50 % (v/v) methanol-water to remove any traces of unreacted starting materials.
Finally, the precipitate was dried in vacuum desiccators over anhydrous CaCl2.
Complexes obtained by this method are [Zn(HL)(OH2)2(NO3)]ꢀH2O (1), [Cu(HL)2] (2),
[Ni(HL)2] (3), and [Co(HL)2]ꢀH2O (4). The chemical structure of transition metal Nano-
complexes was collected in Scheme 2.
2.5. Antimicrobial study
Biological activities of synthesized hydrazone ligand, H2L, and their metal complexes
were studied for antibacterial and antifungal properties using agar diffusion method [9] in DMF
solvent against different types of bacteria; Gram-positive- S. aureus, and E. coli (Escherichia
coil) and Gram-negative- K. pneumonia and P. vulgaris, and C. albicans for fungus. S.aureus,
C. albicans, E. coil, K. pneumonia, and P. vulgaris were originated from ATCC6538,
ATCC10231, ATCC 28737, ATCC 547732 and ATCC 253674, respectively.
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2.6. Computational method
Calculations were been performed using ‘Khon-Sham’s DFT’ method subjected to the
gradient-corrected hybrid density functional B3LYP [10]. This function is a combination of
Becke’s three parameters; non-local exchange potential with the non-local correlation functional
of Lee et al. For each structure, a full geometry optimization was performed using this function
[11] and the 6-311G (d,p) bases set [12] as implemented by Gaussian 09 package [13]. All
geometries were visualized using either ‘GaussView 5.0.9’ [14] or ‘chemcraft 1.6’ 15] software
packages. No symmetry constrains were applied during geometry optimization.
3. Results and discussion
3.1 Characterization of H2L and its metal Nano-complexes
All complexes are stable under normal conditions. Upon heating, decomposition occurs.
Complexes are soluble in both, DMF and DMSO, but insoluble in methanol and ethanol.
Physical and analytical data of prepared compounds are listed in Table 1. Elemental analysis
confirms the proposed chemical structure of H2L and its metal Nano-complexes. All complexes
of Cu(II), Ni(II), and Co(II) ions (2, 3 and 4) have 1:2 metal-to-ligand stoichiometry, as shown
from Scheme 2, whilst Zn(II) complex (1) has 1:1 metal-to-ligand stoichiometry. Molar
conductance values of 10-3 M solution for all prepared Nano-complexes were measured at room
temperature in DMF when in the range characteristic of non-electrolytic nature [16-19].
Supplement 1 shows the FT-IR spectra of H2L and its Cu complex. FT-IR data of H2L
and its metal Nano-complexes are listed in Table 2. The ligand (H2L) can exhibit keto-enol
tautomerism –N(H)-C(=O)↔N=C(-OH)-, since it contains an azomethine–NH-C=O functional
group. The presence of ν(N-H) band at 3250 cm-1 and ν(C=O) band at 1654 cm-1 [20-24] in FT-
IR data of the ligand indicates that, in solid state, it remains as thione tautomer. Furthermore, the
strong band due to υ(C-S-C), stretching vibration of thiophene, appeared at 855 cm-1 in the free
ligand [24-28]. The disappearance of characteristic spectral bands of N-H and C=O of hydrazone
ligand and the appearance of new bands of (C=N)enolic in the region of 1510-1524 cm-1[21,23,27]
in all complexes suggest the coordination via enol form instead of keto form by deprotonation of
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N-H proton during the tautomerisation process. Stretching vibrations of azomethine group C=N
shifted to lower frequencies (10-13 cm-1) due to coordination of nitrogen atom of azomethine
group with the central metal atom[29]. The presence of a new band in the region of 417–479 cm-
1 due to ν(M–N) is another indication of the involvement of nitrogen of azomethine group in the
coordination [18]. FT-IR spectra of all Nano-complexes showed new band in the range of 515-
580 cm-1due to ν(M–O) [18].υ(C-S) stretching vibration of thiophene underwent a downward
shift to 775, 783, 793, and 788 cm-1 in Zn(II), Cu(II), Ni(II), and Co(II) Nano-complexes,
respectively, indicating the participation of Sulphur of this entity in bonding with metals. FT-IR
results of complex (1) showed new bands at 1290 and 1045 cm-1 due to asymmetric and
symmetric stretches ν1, and ν2, respectively, of coordinated nitrate group [18,30]. It is concluded
that the ligand behaves as a monoanionic tridentate ligand coordinated to metal ions via
azomethine N, carbonyl O, and thiophene S.
1H-NMR data of H2L and its diamagnetic Nano-complex (1) in DMSO-d6, with and
without D2O,are listed in Table 3. The free ligand (H2L) spectrum showed three signals at δ
12.44, δ 11.77, and δ 8.66 ppm due to –OH proton, -NH proton, and azomethine proton
1
(-CH=N-), respectively [23,31]. The presence of –NH proton in H-NMR spectrum of H2L
proved the thione nature (Supplement 2). Upon complexation, the signal for NH proton
disappeared in diamagnetic complex (1) indicating that the ligand behaves as monoanionic.
Signals due to azomethine proton shifted upon complexation (Supplement 2). This is due to the
donation of the lone pair of electrons by nitrogen atom to the central metal ion, resulting in the
formation of coordination linkage (M←N).The slightly down field shift of this signal is due to
the existence of strong hydrogen bond in the free ligand. Moreover, the presence of the signal of
–OH proton in the spectra of diamagnetic complex enhances the hypothesis which suggests that
1
–OH protons are not participating in the coordination groups. H-NMR spectra of H2L and their
complex (1) showed aromatic protons as a number of complex multiplets in the region of δ 6.84-
7.93 ppm [22,23,25,31]. Signals due to protons of OH and NH groups completely disappeared on
adding D2O while other signals persisted at the same positions.
The electronic spectrum of H2L is characterized by its absorption bands at 233 and 303 nm
(Fig. 1a). The highest energy bands are assigned to π–π* transitions within C=O and C=N
groups, whilst the lowest energy bands can be assigned to n–π*transitions within C=O and C=N
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groups [25,32]. The electronic absorption spectrum of complex (2) shows a maximum broad
2
band at 597 nm (Fig. 1b). This band is assigned to B1g→2B2g transition in the octahedral Cu(II)
Nano-complex [33]. The magnetic moment of Cu(II) Nano-complex is in agreement with the
value of the octahedral geometry (1.8 B.M) [18,34]. Absorption spectrum of Ni(II) Nano-
complex (3) is characterized by broad structural bands at 522 and 702 nm (Fig. 1b). These bands
3
3
are attributed to A2g (F) →3T1g(p), A2g(F) →3T1g(P) transitions, respectively, in favor of the
octahedral geometry [30,35]. Magnetic moment value of Ni(II) Nano-complex (2.9 B.M.)
confirms the presence of two unpaired electrons in the octahedral geometry [36]. Co(II) Nano-
complex (4) shows a broad absorption spectrum with humps at 661 and 819 nm [30] (Fig. 1b).
Magnetic moment value of Co(II) Nano-complex equals 4.3 B.M., which is in agreement with
the values of Co(II) octahedral geometry [37]. The spectra of Zn(II) Nano-complex is dominated
only by ligand bands.
TGA results of synthesized Nano-complexes are shown in Table 4. Fig. 2(a-b) represents
TG-DTG curves for [Ni(HL2] (3) and [Co(HL)2]ꢀH2O (4) Nano-complexes as representative
examples. Results show a good agreement with the theoretical formula as suggested by the
analytical data (Table 1). Nano-complexes (1) and (4) become anhydrous at 70 and 76oC,
respectively by losing lattice H2O. Nano-complex (1) loses two coordinated water molecules in
addition to one HNO3 molecule in one step at 250 ºC. The removal of C4H4S molecules in a
separate step was observed for Nano-complexes (3) and (4) in the range of 350-379 ºC. For
Nano-complex (2), the removal of C4H4S molecules is accompanied by the elimination of one
C6H6O molecule. The removal of HNO3 molecule from Nano-complex (1) is accompanied by
elimination of one HCN molecule.
In order to access the influence of structural properties of the ligand and the type of metal
on thermal behavior of complexes, the order n, and the heat of activation E of various
decomposition stages were determined through TG and DTG thermograms using Coats–Redfern
equations in the following forms:
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where M=−E/R and B = ln AR/ΦE; E, R, A, and Φ are the heat of activation, the universal gas
constant, pre-exponential factor, and heating rate, respectively. The correlation coefficient, r,
was computed using the least square method for different values of n by plotting the left-hand
side of Eqs. versus 1000/T. The n value which gives the best fit (ꢀ ≅ 1) was chosen as the order
parameter for the decomposition stage of interest. Fromboth, intercept and linear slope of such
stage, A and E values were determined. Other kinetic parameters, ꢀH, ꢀS, and ꢀG were
computed using the relationships; ꢀH= E−RT, ꢀS = R[ln(Ah/kT)−1], and ꢀG=ꢀH−TꢀS, where k
is Boltzmann’s constant and h is Planck’s constant. Kinetic parameters are listed in Table 5.The
following remarks can be pointed out: (1) all Nano-complexes decomposition stages show the
best fit for (n = 1), indicating a first order decomposition in all cases. Other n values (e.g. 0.00,
0.33 and 0.66) did not lead to better correlations. (2)The positive sign of ꢁG for the investigated
complexes reveals that the free energy of the final residue is higher than that of the initial
compound, and all the decomposition stages are non-spontaneous processes [38].(3) Negative
values of activation entropies ꢀS indicate either a more orderly activated complex than reactants
or slow reactions [39]. (4) Positive values of ꢀH mean that decomposition processes are
endothermic. In general, there are no obvious trends in values of ꢁH and ꢁS for the studied
Nano-complexes. This is attributed to the fact that thermal decomposition of complexes is
controlled, not only by structure of the ligand, but also by configuration of the coordination
sphere [39].
Figs. 3 and 4 show XRD patterns of H2L and its Nano-complexes. Patterns and results of
XRD suggest that crystals of complexes are not perfect but lying between amorphous and
crystalline character in comparison with free ligand. Due to this, complexes were not found
suitable for single crystal XRD. From studying patterns, it can be noted that the diffraction angle
and intensity of prepared complexes are different from those of the ligand. This result suggests
that metal ions were bonded with the ligand to form new complexes. Broadening of peaks
indicates that the particles were of Nano-meter scale [40].
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The crystallite size of the complexes can be determined from the broadening of
corresponding X-ray spectral peaks by Scherrer formula L = K
λ/β cos θ [41]. Where L is the
crystallite size, is the wavelength of the X-ray radiation (Cu Kα1 = 1.54056A˚), K is usually
λ
taken as 0.9, and β is the line width at half-maximum height. Values obtained for H2L, Zn(II),
Cu(II),and Ni(II) complexes are 36,11, 22, and 22 nm, respectively. Crystal size of Co(II)
complex couldn’t be determined due to the highly amorphous pattern. Small crystal size was
observed in case of Zn(II) complex (1). Obtained data confirm that sizes of prepared complexes
are in the Nano-domain.
3.2 Antimicrobial activity
Antimicrobial activities of synthesized H2L and its metal Nano-complexes were studied
for antibacterial and antifungal properties by agar diffusion method [9] in DMF solvent against
different types of bacteria; Gram-positive- S. aureus and E. coli and Gram-negative- K.
pnemonia and P. vulgaris. Besides, C. albicans for fungus. Results were recorded by measuring
the growth inhibition (zone of inhibition) surrounding the disc of material. Results of MIC are
summarized in Table 6. Some antibiotics were evaluated for their antibacterial activities and their
results were compared with free ligands and their binary metal Nano-complexes. Ligand (H2L) is
found ineffective to all bactria and fungus. Nano-complexes of H2L show weak activity except
for both, Zn(II) (1) and Co(II) complexes (4). Co(II) complex (4) is quite effective against E.
coli, P. vulgaris, and C. albicans. Antimicrobial activity results revealed that Zn(II) complex
(1) has a good potency against all Gram-positive bacteria specially E. coli and all Gram-negative
bacteria specially P. vulgaris in comparisonwith doxymycin standard. A comparative study of
H2L and its Nano-complexes indicates that most complexes exhibited higher antimicrobial
activity than the free ligand. Higher inhibition zone of metal Nano-complexes than those of
ligands can be explained on basis of overton´s concept and chelation theory. According to
overton´s concept of cell permeability, the lipid membrance surrounding the cell favours the
passage of only lipid soluble materials due to which liposolubility is an important factor which
controls the antifungal activity. On chelation, when metal ion chelates with ligand, its polarity
will be reduced to a greater extent due to the overlap of the ligand orbital and the partail sharing
of positive charge of the metal ion with donor groups. Futhermore, it increases the delocalization
of π-electrons over the whole chelate ring, which results in an increase in the lipophilicity of
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metal complexes. This increased lipophilicity enhances the pentration of complexes into lipid
membrance and restricts further multiplicity of microorganisms. These metal complexes also
affect the respiration process of the cell, hence, they block the synthesis of protiens which restrict
further growth of the organism [42].
One other important factor; they increase penetration of complexes into lipid membrane,
and, consequently, increase antimicrobial activity in the complex crystal size [43]. As shown
from XRD analysis, Zn(II) complex (1) is characterized with very low crystal size with respect to
its parent molecule (H2L) and other complexes. Those complexes give more explanation of the
high antimicrobial activity against all tested bacteria and fungi in which the small size of Zn(II)
complex (1) increases its absorption ability on the surface of the cell wall of microorganisms and
the respiration process of the cell. Hence,it blocks the synthesis of protiens that restrictfurther
growth of the organism[44]. Zn(II) complex (1), therefore, is essential for the growth-inhibitor
effect.
3.3Ground state properties
The optimized structures of the ligand and the studied complexes are obtained using
B3LYB/6-311G (p,d) level, numbering system, net charge, and the vector of dipole moment – all
presented in Figs (5 and 6). The total energy (ET), energy of highest occupied molecular orbital
(EHOMO), energy of lowest unoccupied molecular orbital (ELUMO), energy gap (Eg), and dipole
moment (ꢂ) of the ligand and complexes are collected in Table 7. From calculations of energy
gap, (Eg), which measures the chemical reactivity, Zn Nano-complex (1) was found to be more
reactive than the ligand. Accordingly, one can put the order of decreasing the energy gap (Eg)
asH2L>Cu (2)>Co (4)>Zn (1)>Ni(3). The polarity or charge separation over the molecule, which
is measured by the dipole moment (ꢂ), shows that (ꢂ) of Zn Nano-complex (1)> (ꢂ)of other
complexes and the ligand. Also, the vector of dipole moment of Zn Nano-complex (1) is in
opposite direction of the vector (ꢂ) of other complexes and the ligand. The general trend of
dipole moment (ꢂ) for studied complexes and the ligand, consequently, follows the order Zn
(1)>H2L>Co (4)>Cu (2)>Ni(3). Finally, the theoretically computed ionization energy (I.E.) of
Zn Nano-complex (1), which measures the donating property (oxidation power), is 5.80 eV
(Table 7). Accordingly, one can put the order of decreasing the donating power as Ni(3)>Co
(4)>Cu (2)>Zn (1)>H2L. However, the electron affinity (E.A) of Zn Nano-complex (1), which
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measures the accepting property (reducing power), is 2.39 eV. The order of accepting properties
of studied complexes and the ligand follows H2L<Cu (2)<Co (4)<Ni(3)<Zn (1).
3.4Charge distribution analysis
Table 8 presents the net charge on active centers of studied metal complexes and the
amount of charge transferred from ligands to central metal ions; i.e. H2L → M (Zn), H2L → M
(Cu), H2L → M (Ni) and H2L → M (Co). The results of Table 8 show that Zn (1) metal ion
received 1.077 e, Cu (2) metal ion received 0.855 e, Ni(3) metal ion received 1.020 e, and Co (4)
metal ion received 0.968 e from its surrounding ligand. From the results of Table 8, there is a
large electron back-donation from the metal ion to the donating sites O23, O24, N11, N12, S5,
O26, O50, N27, N38, and S36 in Cu (2), Ni(3),and Co (4) complexes. While it is O23, O24,
N11, N12, S5, O26, O50, N27, O34, O35, and O36 in Zn (1) complex. These results were further
confirmed by comparing values of calculated charge on the liganding atoms in complexes and on
the same atoms in the free ligand. In all studied complexes, the charge density increases on the
donating atoms after complexation.
3.5Structure activity relationship
The biological activity of prepared complexes can be correlated to the calculated ground
state properties. The higher reactivity of Zn (1) and Co (4) complexes over Cu (2) and Ni(3) can
be explained in terms of energy gap which measure the reactivity; as the energy gap decreases
the reactivity increases and the amount of electronic charge transferring from the ligand to the
central metal ion increases (Table 7).
Theoretically, reactivity of prepared complexes follows the order: Ni(3) ˃ Zn (1) ˃Co
(4)˃Cu (2) which is the same order of reactivity towards G- , G+, and fungus (Table 7).
Mullikan electronic charge from the ligand to the central metal ion of studied complexes
follows the order: Zn (1) ˃ Ni(3) ˃ Co (4)˃Cu (2) which is the same order of reactivity towards
G- , G+, and fungus (Table 8).
4. Conclusion
Novel thiophene-2-carbaldehyde Nano-complexes of Zn(II) (1), Cu(II) (2), Ni(II) (3), and
Co(II) (4) were successfully prepared and characterized with different techniques. Obtained
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Nano-complexes were tested as antimicrobial agents. Experimental results indicate that Zn(II)
complex (1) is a useful antimicrobial agent for different bacteria and fungus. Zn Nano-complex
(1) was found to be more reactive and more polar than other complexes and the ligand.
Theoretically, reactivity of the prepared complexes follows the order: Ni(3) ˃ Zn (1) ˃Co (4)˃Cu
(2) which is the same order of reactivity towards G- , G+, and fungus.
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Table captions
Table 1: Physical data, elemental analysis and molar conductance values of H2L and its metal
Nano-complexes.
Table 2: Characteristic FT-IR bands (cm-1) of H2L and its metal Nano-complexes.
1
Table 3: H-NMR chemical shift (ppm) at 25oC, internal reference TMS, of H2L and its
diamagnetic Zn(II) Nano-complex (1).
Table 4: Thermal analysis of the prepared Nano-complexes.
Table 5: Temperature of decomposition, and the kinetic parameters of H2L and its Nano-
complexes
16

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Table 6: The antimicrobial activity of H2L and its metal Nano-complexes.
Table 7: Total energy,"au",energy of HOMO," eV ", of LUMO," eV ", energy gap," eV ", and
dipole moment," Debye", for the ligand and the studied complexes using B3LYP/6-311G(d,p).
Table 8: Net charges on metals and active centers of the studied complexes using B3LYP/6-
311G (d,p).
Figure Captions
Fig. 1: The electronic spectra of a) H2L and b) its metal Nano-complexes ([Cu(HL)2] (2),
[Ni(HL)2] (3) and [Co(HL)2]ꢀH2O (4)).
Fig. 2: TGA-DTG curves of a) [Ni(HL)2] (3) and b) [Co(HL)2]ꢀH2O (4)
Fig. 3: XRD pattern of free ligand, H2L.
Fig. 4: XRD pattern of [Zn(HL)(OH2)2(NO3)]ꢀH2O (1), [Cu(HL)2] (2), [Ni(HL)2] (3) and
[Co(HL)2]ꢀH2O (4) Nano-complexes.
Fig. 5: The optimized structure, numbering system, net charge and the vector of the dipole
moment of the ligand using B3LYP/6-311G (d,p).
Fig. 6: The optimized structure, numbering system and the vector of the dipole moment of the
studied complexes using B3LYP/6-311G (d,p).
Scheme captions
Scheme 1: Synthesis of the ligand, H2L.
Scheme 2: Chemical structure of the prepared Nano-complexes.
Supplementary materials:
Supplement 1: FT-IR spectra of a)H2L and b) [Cu(HL)2] (2).
Supplement 2: 1H-NMR of a) H2L and b) [Zn(HL)(OH2)2(NO3)]ꢀH2O (1).
17

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Table 1
Elemental analysis, Found (Calc.)%
M.F
(F.WT)
M.P.
Co
Yield
%
Compound
Color
Λm
C
H
N
S
Metal
Ohm-1cm2mol-1
12.99
(13.01)
-
-
-
-
C12 H10 N2 O2S
(246.28)
Pale
yellow
58.80
4.18
11.60
H2L
246
90
(58.52) (4.09) (11.37)
Prepared metal complexes
(1)
7.60
(7.51)
C12 H15 N3 O8S Zn
(426.700)
33.49
3.28
9.30
15.00
(15.31)
Yellow ˃300
Green ˃300
71
83
[Zn(HL)(OH2)2(NO3)]
ꢀH2O
20
15
(33.71) (3.54) (9.84)
C24 H18 N4 O4
51.61
3.29
9.88
11.00
(11.46)
10.78
(11.57)
S2Cu
(554.10)
(2) [ Cu(HL)2]
(3) [Ni(HL)2]
(52.02) (3.27) (10.11)
C24 H18 N4 O4S2
Ni
52.29
3.60
10.16
10.52
(10.68)
11.62
(11.67)
11
19
Orange ˃300
brown ˃300
806
78
(52.48) (3.30) (10.19)
(549.27)
C24 H20 N4 O5S2
Co
50.41
3.93
9.65
10.00
(10.38)
10.75
(11.29)
(4) [Co(HL)2]ꢀH2O
(50.79) (3.55) (9.87)
(567.50)

ACCEPTED MANUSCRIPT
Table 2.
ν(OH)
(phenolic/H2O)
Additonal
bands
Compound
ν (NH)
ν (C=O)
ν (C=N)
ν (C=N)enolic
ν (C-S)
ν (M-O)
ν (M-N)
H2L
1
3450 br
3442 br
3441 br
3441 br
3250 br
1654 s
1630 s
1618s
1619 s
1620 s
-
855
-
-
-
1290, 1045
(coordinate
d nitrate)
515m,
580 m
419 m,
441m
-
-
-
-
-
-
1524 s
1518 s
1510 s
775
783
535m,
560 m
418 m,
478m
-
-
2
536 m,
560 m
419 m,
479 w
793
788
3
533 m
558 w ,
417m,
473 m
3455 br
-
-
1617 s
1510 s
-
4
S=(strong), br=(broad), m=(medium), w=(weak)

ACCEPTED MANUSCRIPT
Table 3
Compound
δ(NH)
δ (OH)
δ (CH=N)
Additional bands
7.93 – 7.16 (4H) aromatic Protons , 6.92 – 6.82 (3H)
aromatic Protons
11.77 (1H)
_
12.44(1H)
12.45(1H)
8.85(1H)
8.95(1H)
H2L
1
7. 36 – 7.15 (4H) aromatic Protons , 6.92- 6.84 (3H)
aromatic Protons

ACCEPTED MANUSCRIPT
Table 4
Compound
Temp
% Loss in weight Composition of the Probable Composition of the
Range oC
Found ( Calc.)
Residue
Expelled Groups
30.0-70.0
71.0-250
251-330
331-465
4.00 (4.22)
12.4 (12.6)
27.0 (27.4)
53.1 (53.4)
[Zn(HL)(OH2)2(NO3)] One molecule of Lattice water
1
2
[Zn(HL)(NO3)]
[Zn(L)]
Two molecule of coordinated water
One molecule HNO3
C7H3NZn
One molecule of HCN and C4H4S
30.0-363
364-450
62.9 (64.3)
69.0 (69.2)
C10H4N4O3Cu
C9H3N3O3Cu
One molecule of C6H6O and two
molecule of C4H4S
One molecule of HCN
30.0-379
380-438
30.1 (30.6)
47.1 (47.7)
C16H10N4O4Ni
C10H4N4O3Ni
Two molecule of C4H4S
One molecule of C6H6O
3
4
30.0.-76.0 3.00 (3.17)
77.0-350 32.4 (32.8)
[Co(HL)2]
C16H10N4O4Co
One molecule of lattice water
Two molecules of C4H4S

ACCEPTED MANUSCRIPT
Table 5
Compound
Step
first
T
(K)
A
E
H
S
G
(S−1)
(kJ
(kJ
(kJ mol−1
K−1)
(kJmol−1)
mol−1)
mol−1)
137.57
H2L
451.00 38.19x 108 141.32
-0.07
170.69
751.00 16.49x10-7 24.77
323.00 80.70 x107 75.09
18.53
72.41
-0.25
-0.08
211.28
99.22
sec
first
[Zn(HL)(OH2)2(NO3)]·H2O
sec
third
fourth
434.00 37.20
564.00 34.94 x107 100.98
671.00 28.34x104
82.41
21.94
18.33
96.29
76.83
-0.22
-0.09
-0.15
116.48
149.83
181.00
first
sec
Cu(HL)2]
[Ni(HL)2]
470.00 12.54x10-7 13.86
9.96
48.49
-0.31
-0.29
159.42
250.52
680.00 11.46x10-8 54.14
478.00 74.41x10-2 196.59
192.63
116.61
-0.02
-0.14
206.92
215.09
first
sec
682.00 10.92x105
326.00 42.82x104
122.27
first
sec
[Co(HL)2]·H2O
40.00
37.29
10.35
-0.15
-0.26
86.92
139.16
487.00 40.99x10-7 14.40

ACCEPTED MANUSCRIPT
Table 6
Diameter of inhibition zone (mm) at conc. of (µg/ml)
Compound
Grame + Ve
Grame –Ve
fungus
S. aureus
E. Coil
K. Pneumoniae P. Vulgaris C. albicans
- (>50)
- (>50)
- (>50)
- (>50)
- (>50)
H2L
(1)
15 (~10)
15(~1.5) 10 (~25)
7 (~1.5)
12 (~50)
- (>50)
- (>50)
- (>50)
- (>50)
- (>50)
- (>50)
- (>50)
- (>50)
- (>50)
10 (~50)
- (>50)
- (>50)
6 (~50)
(2)
(3)
(4)
10 (~50) - (>50)
10 (~10) 10 (~10)
Doxymycina
Fluconazoleb
15 (~10)
-
15 (~10)
-
-
-
-
16 (~10)
b
a Antibacterial standard
Antifungal standard.

ACCEPTED MANUSCRIPT
Table 7
Parameter
ET,au
1
2
H2L
-1121.623
-6.126
-2.042
4.083
3
4
-3333.212
-5.800
-2.393
3.406
-3882.392
-5.792
-2.223
3.569
-3750.215
-5.687
-2.304
3.382
-3624.679
-5.781
-2.267
3.513
EHOMO,(eV)*
E
LUMO,(eV)**
Egap,(eV)
8.041
2.696
µ, D
5.455
2.622
2.849
* I.E = -EHom
** E.A = -ELumo

ACCEPTED MANUSCRIPT
Table 8
Center
1
2
3
4
Zn
Cu
Ni
Co
M
0.923
-0.523
-0.692
-0.352
-0.407
0.307
1.145
-0.352
-0.525
-0.216
-0.549
0.268
0.980
-0.348
-0.498
-0.212
-0.497
0.267
1.032
-0.349
-0.498
-0.213
-0.524
0.268
O23
O24
N11
N12
S5
O26
O50
N27
N38
S36
-0.659
-0.657
-0.700
--------
---------
-0.612
-0.349
-0.155
-0.597
0.462
-0.582
-0.348
-0.158
-0.542
0.462
-0.609
-0.348
-0.153
-0.545
0.464
O34
O35
-0.559
-0.433
-0.416
1.077
-------
-------
-------
0.855
------
------
------
1.020
-------
-------
-------
0.968
O36
H2L→M

ACCEPTED MANUSCRIPT
Fig. 1
a
200
250
300
350
400
Wavelength (nm)
b
Complex (2)
Complex (3)
Complex (4)
400
500
600
700
800
Wavelength (nm)

ACCEPTED MANUSCRIPT
Fig. 2
DTG
mg/min
TGA
%
100
a
Complex (3)
0.000
-0.002
-0.004
80
60
40
20
0
0
100 200 300 400 500 600 700 800
Temp oC
DTG
TGA
mg/min
%
100
b
Complex (4)
0.000
-0.002
-0.004
80
60
40
20
0
0
100 200 300 400 500 600 700 800
Temp oC