Novel Mn2+, Fe3+, Co2+, Ni2+ and Cu2+complexes of potential OS donor thiosemicarbazide: Design, structural elucidation, anticorrosion potential study and antibacterial activity

Article abstract of DOI:10.1016/j.molstruc.2019.127495

Novel series of Co²⁺, Ni²⁺, Cu²⁺, Mn²⁺ and Fe³⁺complexes derived from 4,4-dimethyl-2,6-dioxo-N-phenylcyclohexanecarbothioamide (HDDPT) were prepared and characterized by conventional techniques. The c

Full text of DOI:10.1016/j.molstruc.2019.127495

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2+
3+
2+ 2+
2+
Novel Mn , Fe , Co , Ni and Cu complexes of potential OS donor
thiosemicarbazide: Design, structural elucidation, anticorrosion potential study and
antibacterial activity
Ola A. El-Gammal, Abd El-Aziz S. Fouda, Doha M. Nabih
PII:
S0022-2860(19)31604-7
DOI:
https://doi.org/10.1016/j.molstruc.2019.127495
MOLSTR 127495
Reference:
To appear in: Journal of Molecular Structure
Received Date: 28 August 2019
Revised Date: 21 November 2019
Accepted Date: 27 November 2019
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Please cite this article as: O.A. El-Gammal, A.E.-A.S. Fouda, D.M. Nabih, Novel Mn , Fe , Co
,
2+ 2+
Ni and Cu complexes of potential OS donor thiosemicarbazide: Design, structural elucidation,
anticorrosion potential study and antibacterial activity, Journal of Molecular Structure (2019), doi: https://
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Graphical Abstract
Electron density for HDDPT

Novel Mn2+, Fe3+, Co2+, Ni2+ and Cu2+complexes of potential OS donor thiosemicarbazide: Design,
structural elucidation, anticorrosion potential study and antibacterial activity
Ola A. El-Gammal*, Abd El-Aziz S. Fouda and Doha M.Nabih
Chemistry Department; Faculty of Science; Mansoura University- Mansoura, P.O; 70, Mansoura;
Egypt
Abstract
Novel series of Co2+, Ni2+, Cu2+, Mn2+ and Fe3+complexes derived from 4,4-dimethyl-2,6-dioxo-N-
phenylcyclohexanecarbothioamide (HDDPT) were prepared and characterized by conventional
techniques. The complexes have adopted the formulae; {[Mn(DDPT)Cl( H2O)3].3H2O, [Ni(DDPT-
H)(H2O)(OH)], [Cu (HDDPT) Cl2(H2O)2].2H2O, [Co(HDDPT)2Cl2] and [Fe (DDPT)Cl2] ,
respectively. Spectral data revealed that HDDPT coordinates as OS donor in a neutral or
mononegative manner. Electronic and magnetic measurements suggested a square planar geometry
for Ni2+ complex and an octahedral one for the other complexes. X-ray powder diffraction data
suggested monoclinic and orthorhombic structures for Fe3+ and Ni2+complexes, respectively. DFT
method was utilized to prove the geometry and evaluate the bond lengths, bond angles as well as
different energetic parameters. The thermal stability of the compounds was examined and the
corresponding thermodynamic parameters were determined using Coats-Redfern and Horowitz-
Metzger methods. Also, the corrosion hindrance of carbon steel (CS) in 0.5M HCl by HDDPT was
carried out using potentiodynamic polarization (PP) measurement. The data proved the
thiosemicarbazide to be a powerful inhibitor and it is demonstrated that the protection efficiency and
surface converge (Ɵ) increase with increasing the inhibitor concentration and decrease with
increasing temperature. Finally, the adsorption procedure obeys Langmuir's adsorption isotherm.
Moreover, all compounds were screened against the growth of four pathogenic bacterial strains.
Keywords: OS bidentate, thermodynamic parameters, orthorhombic, corrosion of carbon steel.
*Corresponding author: e-mail: olaelgammal@yahoo.com
Tel: 002-01018199550
1. Introduction
Over decades, thiosemicarbazides are proved to be potent intermediates for the synthesis of
numerous pharmaceutical and bioactive materials and thus, they are utilized extensively in medicinal
chemistry. The diversity of heterocycles generated from thiosemicarbazides is associated primarily
with the fact that these compounds can exhibit properties of N(1)-; N(2)-; N(1);N(4)-; N(2);N(4)-;

N(1);S-, N(2);S- and N(4),S-nucleophiles [1].Also, thiosemicarbazides have been extensively
utilized commercially as dyes, photographic films, plastic and in textile industry[2]. Transition metal
complexes derived from thiosemicarbazides become of valuable importance in industry and
biology[3].Such metal complexes have revealed obviously the role played by sulfur coordination in
these compounds and consequently their “soft by acid-soft base” preference is [4].The real impetus
toward developing the coordination chemistry of these potential ligands was probably provided by
the remarkable antitumor [5], antiviral [6], and antimalarial [7,8] activity observed for some of these
derivatives, which has since been shown to be related to their metal-complexing ability [9].
Obviously, the molecular features essential for such activities must be ascertained by designing
synthetic routes to modify, replace, or substitute the derived thiosemicarbazide. Thus, as part of a
research programme aimed at the synthesis of compounds with antibacterial, antioxidant and
antitumor properties,[10-14] we prepared and characterized new Co2+, Ni2+, Cu2+, Mn2+ and
Fe3+complexes of 4,4-dimethyl-2,6-dioxo-N-phenylcyclohexanecarbothioamide (HDDPT).The word
extended to include the test of the inhibition power of the thiosemicarbazide towards corrosion
hindrance of carbon steel in 0.5M HCl as well as the antibacterial activity of all title compounds.
2. Experimental
2.1. Materials
All reagents used were purchased from Fluka, Aldrich-Sigma companies. For corrosion study,
pipeline carbon steel (CS) according to the American Petroleum Institute (API) grade N80 (weight
%; C=0.23, Mn=1.35, Cr=0.05, Mo=0.01, Si=0.22, P=0.017, S=0.01, Ni=0.02 & Fe=98.093) was
utilized for corrosion study.
2.2. Instrumentation
Thermo-Nicolet IS10 FTIR spectrometer was used for IR spectral measurements (as KBr disc).
1
Unicam UV-VIS UV2 spectrometer was used to measure the electronic spectra. H-NMR spectra in
d6-DMSO was recorded on a Varian Gemini WM-200 MHz spectrometer. XRD patterns were
recorded using Bruker aXS-D8 Advance Cu-Kα diffractometer (wavelength, λ = 1.504 Å).
Thermogravimetric analysis performed using an automatic recording Thermo balance, type 951
DuPont; heating rate of 10 °C/min (25-800 °C) in N2. Mass spectrum recorded on Varian Mat 311.
Molar conductance (10-3 mol/l in DMF) was measured on a Tacussel conductivity bridge model
CD6NG. The C, H, N and S contents, were determined using a Perkin-Elmer 2400 series II analyzer
while M and Cl contents were determines according to standard method [15].

2.3 Preparation of HDDPT
0.7 g of 5,5-dimethyl 1,3-cyclohexandione (5mmol) were added to 0.6 ml of phenylisothiocyanate
(5mmol) in presence of 0.28g solid KOH (5 mmol ) and 15 ml DMF. The reaction mixture was
heated under reflux with stirring overnight. Then poured in ice, two drops of concentrated
hydrochloric acid were added and the pale yellow precipitate that formed was filtered off, washed
several times with cold water and allowed to dry in a vacuum desiccator over anhydrousCaCl2. The
1
product was tested by TLC, IR and HNMR and the yield was %80 (0.277 g); m.p.:1300C.
2.4. Preparation of metal complexes
The metal chloride (1.0 mmol) in ethanol was added to ethanolic solution of HDDPT (0.2751 g,1
mmol) and heated under reflux for 2–3 h and the precipitates formed were filtered, washed with
ethanol, diethyl ether and finally dried in a vacuum desiccator over anhydrousCaCl2 and checked by
TLC, partial elemental analysis (C, H, N and S) as well as spectral tools (IR, UV-Vis.,). The
analytical data are listed in table 1 and the complexes are stable in air, soluble in
dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) and non-electrolytes (1-18 ohm-1 cm2
mol-1) [16]. Many trials were performed to isolate a single crystal but failed.
2.5. Corrosion study
2.5.1. Solutions
1 M solution of HCl (analytical Grade, 37%) was prepared by diluting it with bidistilled water in
1:2 acid to water ratio. A series of solutions of the inhibitor, namely HDDPT were prepared.
2.5.2. Corrosion measurements
The corrosion inhibition of CS in 1 M HCl in absence and presence of different doses of HDDPT has
been investigated using potentiodynamic polarization (PP) measurement.
2.6. Antibacterial activity
The antibacterial activity of 200 mg/ml of HDDPT and its corresponding metal complexes in DMSO
were carried out against Streptococcus pyogenes ATCC 19615 and Bacillus ATCC 6051 (Becton
Dickinson and Company. Becton Dickinson Company, USA) as Gram-positive bacteria and
Klebsiella spp. 155095A (Carolina trademark, USA ) and Escherichia Coli ATCC11775 as Gram-
negative bacteria by agar well diffusion method [17].The positive control was ampicillin,
ciprofloxacin and gentamicin drugs and DMSO was the negative one. The experiments were
triplicate and the inhibition zone diameter was measured.

2.7. Molecular modeling
DMOL3 module calculations were used to examine the cluster estimations [18] and double numerical
basis sets plus polarization functional (DNP) implemented in Materials Studio bundle [19]. It is
designed for the realization of large scale density functional theory (DFT) calculations [20-23]. The
geometric optimization is performed without any symmetry restriction.
3. Results and discussion
3.1. IR spectra
The most important IR bands of the ligand viz HDDPT and its metal complexes are listed in Table
2.The spectrum of the ligand shows strong bands at 1735 and 1661cm-1 assignable to stretching
vibrations of hydrogen bonded and free carbonyl groups (Structure 1a) as revealed by a band at 3447
cm-1 (ν(OH)) and weak bands in the region 1800-1900 cm-1. In complexes the ν (C=O) suffers
weakness and shift to lower wavenumber suggesting, one of carbonyl groups converts to C-OH as
supported by the new band 3447-3474 cm-1 [24] being not involved in chelation while the other
participates in coordination. The bands due to thioamide I-IV vibrations observed at 1502, 1330 and
914 cm-1 which have substantial contributions from ν(C-N), δ(C-H) and δ (N-H) and vibrations
[25].The band assigned to ν (NH) mode appeared at 3250 cm-1. The stretching and bending
vibrations (υ/ δ) of C=S group are observed as strong bands at 1277 and 785 cm-1, respectively
[26].The possibility of thione/thiol tautomerism in the solid state (Structure 1)is obscure as there are
no bands characteristic for ν (SH) mode. On comparing the spectrum of and its metal complexes
indicated that coordinates as OS neutral or monobasic chelate. Firstly, as neutral as in [Cu (HDDPT)
Cl2].4H2O and [Co (HDDPT)2Cl2] (Structure 2a, 2c) via free (C=O) and C=S groups which
confirmed by the shift of their bands to lower wavenumber. Secondly, HDDPT binds as
monnegative bidentate in [Mn(DDPT)Cl( H2O)3].3H2O , [Fe (HDDPT) (DDPT)Cl2] and [Ni(DDPT -
H)(H2O)2]complexes in thiol-enol form (Structures 2b, 2d and 2e) through C-S and the free C=O
group as indicated by:
(i) The disappearance of bands due to υ/ δ( C=S) vibrations with simultaneous appearance of new
bands at 1551 and 623 cm-1 assignable to new (C=N)*, resulting due to thiolization of (C=S)
followed by deprotonation [27].
(ii) Shift of the band assigned to free (C=O) to lower wavenumber while the other one is converted
into C-OH and does not participate in coordination as evidenced by the existence of the broad
band at 3447 cm-1 [27], respectively (Structure 2).

(iii) The new bands at 524-504 cm-1 were observed and assigned to ν(M-O) vibration [27].
Structure 1:4,4-dimethyl-2,6-dioxo-N-phenylcyclohexanecarbothioamide (HDDPT).
(a)
(b)
H3C CH3
OH
Cl
O
H
S
N
Co
H3C
H3C
O
Cl
S
N
OH
H
(c )
H3C CH3
(d)
OH
O
H
Cl
2HO
S
N
Cu
2H2O
Cl
2HO
(e)
H3C CH3
OH
O
Cl
S
N
Fe
H3C
O
Cl
H3C
S
N
OH
H
Structure 2:(a) [Co (HDDPT)2Cl2], (b) [Ni(DDPT)(OH)(H2O)],(C) [Cu (HDDPT) Cl2(H2O)2].2H2O,
(d) [Mn(DDPT)Cl( H2O)3].3H2O and (e) [Fe (HDDPT) (DDPT)Cl2] .

3.2. 1H, 13C- NMR, spectra
The 1H NMR spectrum of the ligand displayed ind6-DMSO (Fig. 1a) exhibits no signal in the region
8.00-11.00 ppm attributed to NH proton but instead two new signals at δ: 13.79 and 16.70 ppm
appeared that may be referred to OH and SH protons resulting from rearrangement (Structure 1c)
that disappeared upon adding D2O confirming the possibility of thiol- enol form in solution. The
signals attributable to phenyl protons appear as two multiplets at δ: 7.28-7.31 & 7.40-7.46 ppm. The
peaks at 3.36 ppm (dd, J=7, 4H) and 1.01 ppm are due to the protons of two equivalent CH2 groups
(C2-C6) and 2CH3 protons. The13C NMR spectrum of the ligand in d6-DMSO (Fig.1b) reveals
signals at δ: 198.00, 188.30 and 137.30 ppm assignable to C-OH, C=O and (C-S), respectively [28].
The phenyl carbons appear as two multiplets at δ: 129.01-127.21 & 125.89-122.90 ppm. Moreover,
the peaks for (C16-C17) and (C17-C18) appear as multiplet at 39.50 while that attributed to two C-C
of unequivalent CH2 groups appeared at 27.80 &27.30 ppm.
3.3. UV-visible spectra
The electronic absorption spectra were displayed in DMF and the data are represented in table 3.
The bands that observed at 35530-32580.08 and 28370 cm-1 in the spectrum of HDDPT are due to
(π→π*) and n → π*transitions [29] that suffer a noticeable great change upon complexation and
appeared at 32980-30629 and 29841-26089 cm-1 indicating the chelation of central metal ion
through the carbonyl and thione groups, respectively [30]. A new n→π* band at 19020-19626 cm-1
that overlap with Cl→M2+ transition was observed in the electronic spectra of the complexes
confirming the coordination of S atom of C-S group to central metal ion.
The spectrum of Mn2+ complex showed bands at 26240, 19511 and 17552 assignable to
6
6
6A1g→4Eg(4D), A1g→4T2g(4G) and A1g→4T1g(4G) transitions, respectively in an octahedral
environment. The magnetic moment values (5.64 B.M.) is lower than the spin only value may be
attributed to strong M-M interaction [31].
6
The spectrum of Fe3+ complex shows bands at 15608 and 24690 cm-1 assignable to A1g→
4T1g(G)and 6A1g→ 4T2g (G) transitions in an Oh configuration. The ν3 corresponding to 6A1g→4Eg (G)
not observed because it is covered by the broad ligand bands. Also, the band at 11764 cm-1 is
referred to a low-energy thiolate→Fe (III) charge transfer band which causes a noticeable stability to
iron in the +3 oxidation state [32]. In addition, the magnetic moment (4.26 B.M.) which is smaller

than the calculated value for two Fe (III) ions in octahedral geometries and this may be due to
antiferromagnetism between the two ion-centers [33].
The electronic spectrum of Co2+ complex shows two bands at 15241 and 17136 cm-1 due to
4
4
4T1g(F)→4A2g(F) (υ2) and T1g(F) → T1g(P) (υ3) transitions, respectively, in an octahedral
configuration [34]. The calculated values of Dq, B and β and as well as the magnetic moment value
µeff = 5.61 B.M. of the aforementioned complex lie in the range reported for octahedral Co (II)
complexes [35].
1
The broad bands at 19626 (ν2) and 23362 (ν3) cm-1 are assignable to A1g→1A2g transition and
to spin-forbidden transition 1A1g →1B2g in [Ni (DDPT) (H2O) (OH)] complex [36] (fig.2) as well as
the magnetic moment value (ꢀeff. = zero) suggesting a square planar geometry.
Finally, the bands at 17376 and 18954 cm−1 assignable to 2B1g→2Eg and 2B1g→2A1g transitions
in the spectrum of Cu2+ complex support an octahedral geometry. The band at 21186 cm-1 is referred
to S→Cu transition [37]. Also, the magnetic moment value (ꢀeff. =2.04 B.M.) is consistent with one
unpaired electron [37].
3.4. Electron paramagnetic resonance
The EPR spectrum of powdered [Cu (HDDPT) Cl2].4H2O complex (Fig.3) was recorded at room
temperature. The spectrum is unique in that it can be directly correlated to the equatorial ligand types
and is typical spectrum similar to those reported for mononuclear copper [38]. It exhibits a broad
single line focused at g = 2.08 with well resolved hyperfine structure suggesting that the
thiosemicarbazide (ONS) chelating system seems to be coplanar with the two chelate rings, thus
adopting the nearly planar octahedral structure (g
Cu(II) ion and neighbors, expressed by G( 2.07 < 4.0) indicates an appreciable exchange coupling
present in solid complexes. The hyperfine splitting for parallel orientation value (A =0.007) is
larger than those for the perpendicular one (A =0.006) revealing that the single d electron is in a
(2.180)˃ g (2.088)). The interaction between
-
nonbonding orbital away from the equatorial plane ligands and consistent with the literature [39].The
molecular orbital coefficient (α2) for in-plane σ-bonding and β 2 (π-bonding ) was calculated and
found to be 0.44 and 0.97, respectively indicating that in-plane σ-bonding is more covalent and in a
good agreement the literature [40].
3.5. Mass spectral studies

The mass spectra of all compounds were recorded and represented in figure 1S (Supplementary
material). The spectrum of HDDPT showed the fragmentation patterns which is corresponding to
degradation of the molecule the parent peak at m/z = 75.21(Calcd.275.10) corresponding to
C15H17O2NS. The spectrum shows peaks with different intensities at m/z values as illustrated in
Scheme 1.
3.6. X ray powder diffraction
The XRD pattern of [Ni(DDPT)(H2O)(OH)] complex is reported in figure 4 and table 4. All of the
diffraction peaks were perfectly indexed into the monoclinic C11H32N4NiO10S2 structures with
lattice constants a=17.0640, b=16.5370, c= 15.3720 Å and α= γ=90 & β= 111.770 º and C 1 2/c
space group[41].This is in accordance with the Joint Committee for Powder Diffraction Studies
(JCPDS) File No. 26-1342 [41]. Finally, many sharp peaks (at 2θ 12.44, 13.21, 15.48, 26.73 29.16,
30.80 and, 36.78º) are appeared in the XRD spectrum attributed to the structural nature of HDDPT
ligand meaning that the free ligand of that Ni(II)2+ complex presented as semi crystalline form. On
the other hand the spectrum of the [Fe (HDDPT) (DDPT)Cl2]complex (figure 4 & table 5) indexed
into an orthorhombic C47 Fe2 N19 O2 S4 structure with a lattice constants; a=17.1342 Å; b= 17.7157
Å; c= 17.9936 Å and α= γ=90 & β= 111.770 º and P 21 21 21 space group that is in good
accordance with the Joint Committee for Powder Diffraction Studies (JCPDS) File No 96-450-9921
[42].
3.7. Thermogravimetric studies
An insight on the data represented (table 6) (figure 5) revealed higher stability on chelation. Thermal
degradation takes place through three, two and four steps, respectively. The thermogram of the
[Ni(DDPT)(H2O)(OH)] complex showed first decomposition step at 113-228 °C corresponding to
loss of one water molecule (Found: 4.73 %; Calcd.:4. 66 %) which confirmed the existence of water
molecules inside the coordination sphere (Figure 5). On the other hand, for example, the TG curve of
[Cu (HDDPT) Cl2(H2O)2].2H2O complex exhibited the first decomposition stage at 35-170°C
attributed to loss of two water molecules (Found: 8.30%; Calcd.: 7.50%) which evidenced the
presence of these molecules as water of crystallization (outside coordination sphere) (Figure 5).The
residual part that being left after complete degradation was {MnS, NiS} and CuO+S+3C for present
complexes.

3.8. Kinetic data
The kinetic and thermodynamic parameters of thermal degradation process using Coats-Redfern and
Horowitz-Metzger models (Supplementary material) (figs. 2S & 3S) [43, 44] have been evaluated. A
number of pyrolysis processes can be represented as a first order reaction. The enthalpy of activation,
ꢁH*, entropy of activation, ꢁS* and free energy of activation, ꢁG* were calculated by Eyring equation
[45].The data obtained are recorded in tables 7 & 8 and represented graphically in. The high values of
activation energy, Ea indicates the high stability of chelates because of their covalent bond character
[46] and the positive sign of ꢁG* indicates all the decomposition steps are non-spontaneous processes
and ꢁG* increase significantly for the subsequent decomposition stages of a given complex which may
be due to increasing the values of TꢁS* from one step to another which overrides the values of ꢁH*
[46]. The values of enthalpy of activation, ꢁH* are positive revealing the degradation process is an
endothermic one. On the other hand, ꢁS* has negative values indicating more ordered activated
complex than the reactants or the reaction is slow [47].
3.9. Computational studies
The DFT molecular modeling structure of HDDPT and its Ni (II) complex are shown in table 9
contains bond lengths and bond angles of DFT optimized structures that are in accordance with
analogue compounds with differences { 0.01-0.10 Å} [48,49] that may arise due to the absence of
intermolecular interactions between neighboring molecules in gaseous state on applying theoretical
calculations for isolated molecules which in contrast the situation is the opposite in solid crystal
lattice [49].Table 9 summarizes the variability in the in bond lengths in the five membered chelate
ring around Ni(II) species clarifying the significant distortion in the bond angle from optimal square
planar environment, i.e., O8-Ni-S10 = 91.43 while O21-Ni-S10 = 96.05 and O22-Ni-O21=83.88°.
Also, there is a planarity of the ring system that is maintained on protonation with an apparent bond
distance changes occurring mostly in C-S bonds concomitant with smaller changes in C-N bonds.
Finally, it is obvious that Ni-O ˂ Ni-S reflecting the high strength of Ni-O bond [50].
The Frontier molecular orbitals (FMO’s){ (HOMO and LUMO) }i.e..the highest occupied and
lowest unoccupied molecular orbitals that evaluated using B3LYP/6-3111G method are recorded in
table 10. For a molecule, the gap between HOMO and LUMO describes the charge transfer and
clarifies its chemical stability [51]. Some concepts like chemical reactivity, conjugation, aromaticity
and electron lone pair could be obtained molecular orbitals qualitative graphical representation in

which positive is in red and negative is green color [52]. Figure 6 reveals the 3D HOMO and LUMO
plots for HDDPT indicating the localization of HOMO;EHOMO=-5.16eV on the thiosemicarbazide
arm and the spreading of LUMO; ELUMO = -2.49 eV over the cyclohexane ring as well as
thiosemicarbazide moiety with energy gap ꢁE = 2.67 eV. For Ni 2+ complex, FMO’s plots (figure 7)
indicates the localization of HOMO (-4.06 eV) on phenyl rings and that of LUMO (-2.39 eV) are
spreading over the coordinated thiosemicarbazide arm. It is clear that the energy gap ꢁE, -1.13 eV of
the complex is lower than that of the ligand itself which in turn proves that the present complex
could be considered as potential material for harvesting solar radiation in solar cell applications as it
can absorb the photons of light beam powerfully increasing the obtained circuit current resulting in
more efficient power conversion [53]. The electronegativity (χ) that measure the ability of the
molecule to attract electrons and calculated as in literature [45] and that of the ligand (3.82 eV)
supporting it behaves as a Lewis acid and that of Ni2+ complex (3.50 eV) is extremely low value
indicating Lewis base character. Other energetic parameters such as global hardness (η) and global
softness (δ) that measure the resistance of a molecule to charge-transfer , and the capability to
receive electrons, respectively are recorded in table 10. From the data, one can conclude that Ni2+
complex with η = 1.33 and δ = 0.56eV values will be less soft than the thiosemicarbazide, HDDPT
[54].
3.10.Corrosion Data
3.10.1.Potentiodynamic polarization (PP) measurements
PP is a useful method because they give more information about the corrosion mechanism and the
factors affecting the corrosion process and inhibition behavior of the thiosemicarbazide, HDDPT.
The PP has been performed using PCI4-G750 Potentiostat/Galvanostat and a personal computer with
Gamry PCI4-G750 software for calculations. In PP measurements, electrode potential from –1000 to
1000 mV was applied at scanning rate 1 mVs-1. %IE and θ from PP measurements from equation:
% IE = θ x 100 = [(icorr (free) - icorr(inh))/ icorr (free)] x 100
(1)
where icorr(inh) is the corrosion current density with compound HDDPT and icorr (free) is the current
without compound HDDPT. PP curves without and with different concentrations for carbon steel
dissolution in 1M HCl solution were showed in Figure 8. The difference of corrosion potential
(Ecorr), icorr, βa, βc, CR, θ and % IE with compound HDDPT concentration were given in Table11.
Experimental results indicate that icorr is significantly decreases with increasing HDDPT

concentration [54]. Both the anodic and cathodic curves were affected by the existence of compound
HDDPT, i.e. compound HDDPT limited both the anodic and cathodic reactions (mixed type
inhibitor).
.
3.10.2.Electrochemical Impedance Spectroscopy (EIS) Measurements
EIS tests were utilized to study the mechanism of corrosion. The results of Nyquist and Bode
diagrams are demonstrated in Figure 9a, 9b, respectively. These figures indicate a gradual increase
in the semicircle diameter of the Nyquist diagrams by raising the concentration of compound
HDDPT. So the compound HDDPT retard the corrosion rate by adsorption [55]. From Figure 8a one
noticed that the deviation from an ideal semicircle as a result of frequency dispersion because of the
inhomogeneity of the surface. Table 12 gives different parameters of impedance as, (Rct), (ꢀdl),
(%IE) and electrolyte resistance (ꢁs). The data of table 10 demonstrated that, the ꢀdl data lowered by
raising the concentration of compound HDDPT, this behavior as a result of molecules adsorbed on
the surface of carbon steel. Figure 8b shows the equivalent circuit (fig.4S) (Supplementary material)
which used in our study [56]. In electrochemical impedance spectroscopy (EIS) procedures, the
frequency scope is between 100 kHz and 0.1 Hz and AC signal is 10 mV peak to peak. % IE and θ
were obtained by employing the following relation:
%IE = θ x 100 = [(Rct(free) - Rct(inh)) / Rct(free)] x 100
(2)
where Rct(inh) is the charge transfer resistance with Compound HDDPT and Rct(free) is the charge
transfer resistance without compound HDDPT.
3.11. Antibacterial activity
All compounds under study were screened for inhibition of growth of four bacterial strains, namely
Bacillus and Streptococcus pyogenes (Strp. py.) as Gram’s positive and Escherichia coli (E.coli) and
klebsiella spp. (kleb. spp.) as Gram’s negative using antibiotics, ampicillin, and ciprofloxacin and
gentamicin drugs. The data represented in table1S (Supplementary material) and figure 9 revealed
that HDDPT exhibited potent activity against Strp.py.) exceeding that of antibiotic itself followed by
Co(II), Cu (II) and Ni(II) complexes. HDDPT exhibited potent activity toward Bacillus has the
higher activity followed by Cu (II), Co (II) and Ni (II), respectively represented in table 3S
(supplementary material) and figure 10. Only Cu (II) has activity against (kleb. spp.) while Cu (II)
and Co (II) inhibits the growth of E. coli. The inability to inhibit the growth of bacterial strain can be
referred to the difficulty of diffusion of the compound through the cell membrane or the possibility

of diffusion through the membrane but being deactivated by unknown cellular mechanism. On the
other hand, Cu(II) complex exhibited a higher activity due to the moderate hydrophobicity when
compared with HDDPT and other metal complexes resulting in an enhancement of ability to diffuse
through the cell membrane and consequently inhibiting the growth of the micro-organisms [57].
3.12. Structure activity relationship (SAR) studies
The potent activity of HDDPT is referred to as its nature as a soft ligand as confirmed by confirmed
by the difference between EHOMO and ELUMO (-2.41) in addition to the fact that it contains many free
sides, C=O, C=S OH and NH groups free. Also, the reasonable moderate activity of some complexes
such as Cu (II) is attributed to the presence of 2Cl- and the smaller size of the metal ion that
facilitate the diffusion through the organism membrane.
Conclusion
HDDPT thiosemicarbazide derivative forms new complexes with Mn2+, Fe3+, Co2+, Ni 2+ and Cu2+
ions. Spectral and elemental analyses data suggested an octahedral for all complexes except the
diamagnetic Ni2+ that adopted a square planar geometry. Also, the ESR data of Cu (II) complex data
are consistent with the proposed structure. The higher values ofα2 and β2 in case of the complex
revealed appreciable covalence in the metal-ligand bonding, presumably arising out of M-thione-
coordination. X-ray powder diffraction indicated a monoclinic structure for Ni2+ complex and
orthorhombic for Fe3+ complexes. The TG analysis for the title complexes displayed high residual
part indicating high stability of the formed chelates. Moreover, all compounds were screened for
antibacterial and antifungal activities. The assay showed a potent activity of the thiosemicarbazide
and variable inhibition power for the complexes under study. It was remarked that induction of some
moieties, such as an azomethine linkage or a thioketone into a compound causing an extensive
biological activities that may be responsible for the increase in the hydrophobic character and
liposolubility of the molecules in crossing the cell membrane of the microorganism, thereby
enhancing the biological utilization ratio and activity of such complexes.
Acknowledgments
First author gratefully acknowledges the Microbiology Unit at Faculty of Pharmacy, Mansoura
University, and Mansoura for carrying out the diabetes experimental work.

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.

Table 1: Analytical and physical data of HDDPT and its metal complexes.
Yield
(%)
% Found (Calcd.)
Compound
F.wt.
M.p.
(°C)
Colour
Empirical formula
(Calcd.)
M
Cl
C
H
N
S
HDDPT
C15H17NO2S
275.21
(275.37)
65.21
6.52
5.23
11.06
White 130
-
-
85
80
(64.21) (6.1) (5.08) (11.64)
[Co(HDDPT)2Cl2]
C30H34Cl2CoN2O4S2
680.38
pale
240
8.61
10.35
52.89 5.25 4.90 8.92
(680.57) green
(7.90) (10.80) (52.50) (5.00) (4.10) (9.42)
[Ni(HDDPT)(OH)(H2O)]
C15H21CLNNiO4S
366.99
orange
15.98
48.72
5.91
4.45
8.32
_
(368.09)
270 (16.30)
(48.30) (5.80) (3.78) (8.66)
85
80
481.04 reddish
(481.87) brown
13.15
280
14.69
37.34
5.32
3.53
6.89
[Cu(HDDPT)Cl2(H2O)2].2H2O
C15H25Cl2CuNO6S
(14.5) (14.20) (37.80) (5.01) (2.90) (6.65)
[Mn(DDPT)Cl( H2O)3].3H2O
C15H28ClMnNO8S
11.50
7.26
38.03
6.14
3.21 7.22
473.21 brown
(472.06)
80
82
200 (10.9) (7.40) (37.8) (5.90) (2.97) (6.79)
[Fe(HDDPT)(DDPT)Cl2]
C30H35Cl2FeN2O4S2
675.42
dark
8.25
10.4
53.1
5.19
4.67
9.12
180
(676.48) brown
(8.10) (11.20) (53.02) (5.10) (4.12) (9.44)
Molecular weight values obtained from mass spectra.
Table 2: Principle infrared bands of HDDPT and its metal complexes.
ν(C=O) ν(O-H) ν(N-H) ν(C=S) δ(C=S) ν(C=N)* ν(M-O) ν(M-S)
Compound
HDDPT
1615
1625
1607
1624
1608
1620
3447
3432
3447
3473
3438
3250
3150
3061
3160
3064
1277
1347
1270
1275
1271
785
750
761
758
754
-
-
-
-
[Co(HDDPT)2Cl2]
524
518
513
504
485
490
484
495
[Ni(HDDPT)(OH)(H2O)]
[Cu(HDDPT)Cl2(H2O)2].2H2O
[Mn(DDPT)Cl( H2O)3].3H2O
[Fe(HDDPT) (DDPT)Cl2]
1551
-
1550
3448
3060
1271
757
1553
504
489

Table 3.Magnetic moments and electronic spectral data of HDDPT and its complexes.
Ligand field
parameters
Band
ꢀeff
(B.M.)
Compound
HDDPT
Assignment
position,cm-1
B
-
β
∆
q
32580
28370
π→π*
n→π*
-
-
-
15241
20790
4T1g(F)→4A2g(F)
4T1g(F)→4T1g(P)
814
8
[Co(HDDPT)2Cl2]
[Ni(HDDPT)(OH)(H2O)]
[Cu(HDDPT)Cl2(H2O)2].2H2O
964.28 0.993
5.61
Dia.
2.04
19626
26875
1A1g →1A2g
1A1g →1B2g
-
-
-
-
-
-
19432
21186
2B1g→2Eg
2B1g→2B2g
6A1g→4Eg(4D)
6A1g→4T2g(4G)
6A1g→4T1g(4G)
26240
19511
17552
[Mn(DDPT)Cl( H2O)3].3H2O
-
-
-
-
-
-
5.64
4.26
15608
24690
20687
6A1g→ 4T1g(G)
6A1g→ 4T2g (G)
LMCT
[Fe(HDDPT) (DDPT)Cl2]
Dia=diamagnetic
Table 4: Powder XRD data: area, FWHM, intensity, crystallite (grain)size D, d-spacing, ε microstrain and dislocation
density of [Ni(HDDPT)(OH)(H2O)]complex.
No.
Grain
Lattice
Dislocation
denisty (A)
x10-3
Average inner
crystal
separation (S)
FWH
M
2theta [º] d [Å] h,k,l
11.45
(Cystallite) strain ε x10-
3
size D (nm)
1
2
29.1
7.71
12.44
13.21
15.48
26.73
29.16
30.8
1,1,0
0,0,2
2,0,-2
2,2,0
5,1,-2
2,4,2
5,3,-2
2,2,4
-116
7,1,0
4,2,4
2,0,6
-
0.45
0.27
0.65
0.15
1.15
0.45
0.91
1.02
0.19
0.21
0.53
1.23
0.60
18.48
2.93
1.05
6.06
3.21
18.2
2.75
11.2
14.0
0.47
0.56
3.57
19.0
6.67
14.32
8.88
8.37
7.15
4.16
3.82
3.62
3.53
3.05
2.80
2.73
2.60
5.42
7.11
6.70
5.72
3.33
3.06
2.90
2.83
2.44
2.24
2.19
2.08
4.34
10.8
30.91
3
24.5
12.85
4
4.82
55.82
5
21.1
7.42
6
7.55
19.05
7
14.4
9.46
8
15.7
8.45
31.62
36.78
40.15
41.26
43.54
-
9
2.49
46.02
10
11
12
2.51
42.07
6.14
16.73
13.4
7.26
29.1
Average
22.88

Table 5: Powder XRD data: area, FWHM, intensity, crystallite (grain)size D, d-spacing, ε microstrain and
dislocation density of [Fe (HDDPT) (DDPT)Cl2] complex.
Grain
(Cystallite)
size D
(nm)
Average
Lattice
strain ε
x10-3
Dislocation
denisty δ
(nm-1) x10-3
inner crystal
separation
(S)
No.
2theta [º]
d [Å]
hkl
FWHM
1
7.06
9.72
12.51
9.09
8.03
4.44
4.36
3.78
3.16
2.74
2.48
2.12
2.10
4.98
1,0,1
0,0,2
0,1,2
0,4,0
0,1,4
4,1,2
0,4,4
4,4,3
1,7,1
3,5,6
0,3,8
-
0.61
0.48
0.43
0.43
0.40
0.49
0.47
0.49
0.48
0.29
0.30
0.44
13.71
17.35
19.39
19.59
21.08
17.30
18.20
17.64
18.19
30.71
29.73
20.26
29.1
10.8
24.5
4.82
21.1
7.55
1.44
1.57
2.49
2.51
6.14
12.7
2.93
1.05
6.06
0.321
18.2
2.75
11.2
14.0
0.472
0.565
3.57
6.67
15.63
11.36
10.04
5.54
2
3
11.00
20.00
20.37
23.52
28.24
32.62
36.20
42.56
43.01
4
5
5.44
6
4.72
7
3.95
8
3.43
9
10
3.10
2.65
11
2.63
Average
6.23
Table 6. Decomposition steps with the temperature range and weight loss for HDDPT and its complexes.
Complex
HDDPT
Temp.
Removed species
Wt. Loss
Found%
Range,°C
Calcd.%
72.83
14.90
13.07
4.66
223-307
308-378
379-800
113-228
229-326
327-507
508-800
35-170
-C4H6N +C5H7O2 + H2S
- C3H6
73.93
13.35
12.72
4.73
3C
-H2O
-H2O +C7H8+ CO2
-C7H5N
40.86
28.88
25.53
8.30
41.88
28.83
24.63
7.50
[Ni(DDPT)(H2O)(OH)]
[Cu (HDDPT) Cl2(H2O)2].2H2O
[Mn(DDPT)Cl( H2O)3].3H2O
NiS
-2 H2O
171-356
356-556
557-800
25-86
-2HCL+C4H9NO3
-C8H5
40.05
22.29
29.36
10.46
20.28
49.82
40.42
21.98
30.10
11.43
19.14
50.38
CuO+S+3C
3 H2O
87-266
3 H2O +HCL
CO2+C9H12N+5C
MnS
267-465
465- 800
19.41
19.05

Table 7: Kinetic Parameters evaluated by Coats-Redfern equation for HDDPT complexes.
Ea
A
∆H*
∆S*
∆G*
KJ/mo
l
Mid
Temp(K)
Complex
peak
KJ/mol
25.27
48.25
(S-1)
5.03
95.3
KJ/mol KJ/mol.K
1st
2nd
3rd
1st
2nd
3rd
1st
416.55
599.40
21.81
43.26
-0.2343 119.40
-0.2128 170.83
[Ni(HDDPT)(OH)(H2O)]
[Cu(HDDPT)Cl2(H2O)2].2H2O
779.64 134.62 7.14x106 128.13 -0.1217 223.02
375.99
558.04
759.93
328.56
539.02
737.84
24.50
14.9
19.90
-0.2276 145.83
-0.2175 160.32
-0.1659 216.49
43.58
50.50
38.94
96.73 3.42x104 90.42
41.07 3.76x104 38.34
65.72 1.58x104 61.24
74.66 5.08x103 68.52
-0.1581
90.29
[Mn(DDPT)Cl( H2O)3].3H2O
2nd
3rd
-0.1695 152.59
-0.1815 202.44
Table8: Kinetic Parameters evaluated by Horowitz-Metzger equation for HDDPT complexes.
Ea
A
(S-1)
∆H*
∆S*
KJ/mol.
K
∆G*
Mid
Temp(K)
Complex
peak
KJ/mol
KJ/mol
KJ/mol
1st
2nd
3rd
1st
2nd
3rd
1st
416.55
599.40
779.64
375.99
558.04
759.93
328.56
539.02
32.34
48.70
28.88 -0.2154 118.60
53.24 -0.1949 170.04
58.22 8.26x102
142.08 2.27x107 135.60 -0.1121 222.98
31.07 1.48x102
52.78 4.24x102
108.64 2.42x105 102.31 -0.1496 216.19
47.07 3.78x105
44.33 -0.1390 89.99
[Ni(HDDPT)(OH)(H2O)]
[Cu(HDDPT)Cl2(H2O)2].2H2O
27.95 -0.2053 105.14
48.14 -0.1998 159.64
2nd
75.46 1.54x105 70.98 -0.1505 152.12
88.62 1.10x104 82.49 -0.1751 211.67
[Mn(DDPT)Cl( H2O)3].3H2O
3rd
737.84
Table 9: Selected bond lengths (Å) and bond angles (°) of HDDPT and [Ni(HDDPT)(OH)(H2O)] complex using
DFT-method from DMOL3 calculations.
[Ni(HDDPT)(OH)(H2O)] complex
HDDPT
Length
(Å)
Length
Angle
(Å)
Bond
Angle
Degree(°)
Bond
Degree (°)
N(13)-H(20)
N(13)-C(14)
1.019
1.425
H(20)-N(13)-C(14)
H(20)-N(13)-C(11)
114.653
114.792
O(22)-H(41)
O(22)-H(42)
Ni(20)-O(21)
O(22)-Ni(20)
O(8)-Ni(20)
S(10)-Ni(20)
S(10)-C(7)
C(7)-N(11)
C(4)-C(7)
C(3)-O(8)
C(4)-C(5)
C(3)-C(4)
O(9)-H(28)
C(7)-N(11)
C(5)-O(9)
0.991
0.986
1.860
2.064
1.990
2.206
1.800
1.300
1.507
1.411
1.402
1.402
0.983
1.300
1.370
H(42)-O(22)-H(41)
H(42)-O(22)-Ni(20)
H(41)-O(22)-Ni(20)
O(21)-Ni(20)-O(22)
O(21)-Ni(20)-O(8)
O(21)-Ni(20)-S(10)
O(22)-Ni(20)-O(8)
O(22)-Ni(20)-S(10)
O(8)-Ni(20)-S(10)
Ni(20)-S(10)-C(7)
Ni(20)-O(8)-C(3)
S(10)-C(7)-N(11)
S(10)-C(7)-C(4)
103.106
109.792
93.114
83.889
171.782
96.057
88.609
179.869
91.438
107.532
112.251
126.683
116.462
116.360
121.731
C(11)-N(13)
C(11)-S(12)
C(4)-C(11)
C(3)-C(4)
C(3)-O(10)
C(5)-O(9)
1.364
1.682
1.496
1.473
1.245
1.360
1.380
1.410
1.019
1.425
0.977
1.360
1.380
C(14)-N(13)-C(11)
N(13)-C(11)-S(12)
N(13)-C(11)-C(4)
S(12)-C(11)-C(4)
O(9)-C(5)-C(4)
C(11)-C(4)-C(3)
C(11)-C(4)-C(5)
C(3)-C(4)-C(5)
C(4)-C(3)-O(10)
C(19)-C(14)
129.502
126.941
116.032
116.954
119.042
118.824
121.311
119.157
122.061
1.410
C(4)-C(5)
C(19)-C(14)
N(13)-H(20)
N(13)-C(14)
O(9)-H(31)
C(5)-O(9)
N(13)-H(20)
N(13)-C(14)
O(9)-H(31)
1.019
1.425
0.977
N(11)-C(7)-C(4)
C(7)-C(4)-C(5)
C(4)-C(5)

C(2)-H(21)
C(2)-C(3)
1.105
1.530
C(5)-O(9)
C(4)-C(5)
1.360
1.380
C(4)-C(7)
N(11)-C(12)
1.507
1.409
C(7)-C(4)-C(3)
C(5)-C(4)-C(3)
121.623
116.468
Table 10: Calculated EHOMO, ELUMO, energy band gap (EH – EL), chemical potential (ꢀ), electronegativity (χ), global
hardness (η), global softness (S), global electrophilicity index (ω) and softness (ϭ) for HDDPT and its complexes.
Compound
EH /
eV
EL / eV
(EH-EL)
/eV
χ / eV
µ / eV
η / eV
S / eV-1
ω / eV
ϭ / eV-1
0.374111 5.4806420
HDDPT
C15H17NO2S
-5.164
-2.491
-2.673
3.8275
-3.8275
1.3365
0.748
485
69
[Co(HDDPT)2Cl2]
-3.142
-4.069
-2.65
-2.931
-3.325
-0.492
-1.138
-0.498
2.896
3.5
-2.896
-3.5
0.246
0.569
0.249
2.032
0.879
2.008
17.046
10.764
25.649
4.065
1.758
4.016
[Ni(HDDPT)(OH)(H2O)]
[Cu(HDDPT)Cl2(H2O)2].2H2O -3.823
3.574
-3.574
[Mn(DDPT)Cl( H2O)3].3H2O
-3.14
-2.185
-3.400
-0.955
-0.337
2.662
3.568
-2.662
-3.568
0.477
1.047
2.967
7.423
2.094
5.934
[Fe(HDDPT) (DDPT)Cl2]
-3.737
0.1685
37.786
H=HOMO, L=LUMO.
Table 11. The effect of compound (HDDPT) concentrations on the free corrosion
potential (Ecorr), corrosion current density (jcorr),,Tafel slopes(βc ,βa), degree of surface
coverage (θ) ,inhibition efficiency(%IE) and corrosion rate(CR) of 1 M HCl at 25oC.
Cinh, -Ecorr, mV
icorr,
βc,
βa,
CR,
% IE
M
vs SCE
ꢀA cm-2 mV dec-1 mV dec-1 mmy-1
Blank
1x10-6
5x10-6
10x10-6
15x10-6
399
128.0
69.80
48.90
30.60
15.60
109
107
110
108
86
94
86
79
76
62
85.2
32.6
28.6
13.9
7.5
ــــــ
ـــــ
394
0.457
0.623
0.768
0.881
45.7
62.3
76.8
88.01
393
397
400
Table 12. EIS results without and with different compound (HDDPT) concentrations for
carbon steel in corrosive solution.
Compounds
Concentration
M
Cdlx10-3,
Rct,
θ
% IE
ꢀF cm-2
Ω cm2
Blank
0.0
5.60
4.30
2.80
2.10
1.80
5.68
7.40
----
----
HDDPT
1x10-6
5x10-6
10x10-6
15x10-6
0.233
0.565
0.616
0.705
23.3
56.5
61.6
70.5
13.07
14.80
19.24

CH3
CH3
H3C
H3C
CH3
H3C
CHNS•
58.983
•
C6H5
77.0391
O
OH
O
OH
O
OH
C
C
S
NH
S
N
H
•
C9H12NO2S•
198.059
C8H11O2
139.076
20.4 %
C15H17NO2S
275.1
6.5 %
9.60 %
•
2CH3
30.0235
O
OH
••
C6H6O2
110.037
52.5 %
Scheme 1: fragmentation pattern of HDDPT.

(a)
(b)
Figure 1: (a) 1HNMR and (b) 13CNMR spectra of HDDPT in d6DMSO.

Figure 2. Electronic spectrum of [Ni(DDPT)(OH)(H2O)] complex.
Figure 3, ESR spectrum of [Cu(HDDPT)Cl2].4H2O complex

Figure 4.x-ray powder diffraction spectrum of [Fe(HDDPT)(DDPT)Cl2] and
[Ni(DDPT)(OH)(H2O)] complexes.

(a)
(b)
(c )
Figure 5.TGA curves of: (a) [Mn(DDPT)Cl( H2O)3].3H2O (b) [Ni(DDPT)(OH)(H2O)] and
(c) [Cu(HDDPT)Cl2(H2O)2].2H2O and complexes.