Synthesis, characterization and antibacterial activity of Pd(II), Pt(II) and Ag(I) complexes of 4-ethyl and 4-(p-tolyl)-1-(pyridin-2-yl)thiosemicarbazides

Article abstract of DOI:10.1080/17415990903569569

Pd(II), Pt(II) and Ag(I) ions were found to form stable complexes with 4-(p-tolyl)- or 4-ethyl-1-(pyridin-2-yl)thiosemicarbazides (Hp-TPTS or HEPTS). The complex structure was elucidated by analysis (elemental and thermal), spectroscopy (electronic, IR and ¹H NMR spectra) and physical measurements (magnetic susceptibility and molar conductance). The ligands coordinate to the metal ions as monobasic bidentate through nitrogen and sulfur atoms. The electronic spectra of the Pt(II) complexes in DMF showed a metal to ligand charge transfer transition at 11,935-13,260 cm^-1. The structural, electronic and vibrational features of HEPTS and Hp-TPTS were discussed on the basis of semi-empirical quantum mechanic calculations [ZINDO/S and semi-empirical parameterization (PM3)]. The simulated IR and electronic spectra are found reasonable in accordance with the experimental data. Finally, the antibacterial activities of the ligands and their complexes were investigated and some were found promising.

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Synthesis, characterization and
antibacterial activity of Pd(II),
Pt(II) and Ag(I) complexes of 4-
ethyl and 4-(p-tolyl)-1-(pyridin-2-
yl)thiosemicarbazides
Ahmed A. El-Asmy a , Mohammad M. Hassanian b & Mohammad H.
Abdel-Rhman a
a Chemistry Department, Faculty of Science , Mansoura
University , Egypt
b Chemistry Department , Industrial Education College, Beni-Suef
University , Egypt
Published online: 07 Apr 2010.
To cite this article: Ahmed A. El-Asmy , Mohammad M. Hassanian & Mohammad H. Abdel-Rhman
(2010) Synthesis, characterization and antibacterial activity of Pd(II), Pt(II) and Ag(I) complexes
of 4-ethyl and 4-(p-tolyl)-1-(pyridin-2-yl)thiosemicarbazides, Journal of Sulfur Chemistry, 31:2,
141-151, DOI: 10.1080/17415990903569569
To link to this article: http://dx.doi.org/10.1080/17415990903569569
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Journal of Sulfur Chemistry
Vol. 31, No. 2, April 2010, 141–151
Synthesis, characterization and antibacterial activity
of Pd(II), Pt(II) and Ag(I) complexes of 4-ethyl and
4-(p-tolyl)-1-(pyridin-2-yl)thiosemicarbazides
Ahmed A. El-Asmya*, Mohammad M. Hassanianb and Mohammad H. Abdel-Rhmana
aChemistry Department, Faculty of Science, Mansoura University, Egypt; bChemistry Department,
Industrial Education College, Beni-Suef University, Egypt
(Received 12 October 2009; final version received 13 December 2009)
Pd(II), Pt(II) andAg(I) ions were found to form stable complexes with 4-(p-tolyl)- or 4-ethyl-1-(pyridin-2-
yl)thiosemicarbazides (Hp-TPTS or HEPTS). The complex structure was elucidated by analysis (elemental
and thermal), spectroscopy (electronic, IR and 1H NMR spectra) and physical measurements (magnetic
susceptibility and molar conductance). The ligands coordinate to the metal ions as monobasic bidentate
through nitrogen and sulfur atoms. The electronic spectra of the Pt(II) complexes in DMF showed a metal to
ligand charge transfer transition at 11,935–13,260 cm−1. The structural, electronic and vibrational features
of HEPTS and Hp−TPTS were discussed on the basis of semi-empirical quantum mechanic calculations
[ZINDO/S and semi-empirical parameterization (PM3)]. The simulated IR and electronic spectra are found
reasonable in accordance with the experimental data. Finally, the antibacterial activities of the ligands and
their complexes were investigated and some were found promising.
Keywords: thiosemicarbazide; Pd(II) complexes; Pt(II) complexes; Ag(I) complexes; antibacterial
activity
1. Introduction
Thiosemicarbazides constitute an important class of NS donors. The chemistry of these com-
poundswasearlyexplored(1)fortheirvariabledonorproperties, structuraldiversityandbiological
applications. The coordination chemistry of a number of metal ions and a wide variety of com-
plexes had been reported (2–9). Thiosemicarbazide complexes have anticancer and antimicrobial
activity owing to their ability to diffuse through the semipermeable membrane of the cell lines.
The enhanced effect may be due to the increase of lipophilicity of the complexes compared to
the ligand (5, 10–12). Thiosemicarbazides have been used for extraction and determination
of some metal ions in biological and pharmacological samples (13, 14). Following the discovery
of the antitumor activity of cis-platin and related complexes, much interest has been focussed on
the synthesis of more complexes. Pd(II) complexes, the analogs to cis-platin, are found efficient
for clinical trials against tumors. However, cis-palladium complexes have high toxicity and lower
*Corresponding author. Email: aelasmy@yahoo.com
ISSN 1741-5993 print/ISSN 1741-6000 online
© 2010 Taylor & Francis
DOI: 10.1080/17415990903569569
http://www.informaworld.com

142 A.A. El-Asmy et al.
H
2
H
N
4
1
N
N
N
H
S
CH3
HEPTS
Figure 1. 4-Ethyl and 4-(p-tolyl)-1-(pyridin-2-yl)thiosemicarbazide.
Hp-TPTS
antitumor activity than Pt(II) complexes. Pd(II) chelates with NS donors were suggested as effec-
tive antitumor agents (15, 16) due to their higher ability to bring the metal into DNA. In this
respect, Pt(II) chelates are kinetically inert, while those of Ni(II), Zn(II), Cu(II), etc., do not
have sufficient thermodynamic stability (15). 2-Hydrazinopyridine complexes were used in the
delivery of cytotoxin for therapy or radionuclide for imaging (17, 18). Rhenium complexes of
4-t-butyl- and 4-phenyl-1-(pyridin-2-yl)thiosemicarbazides were used for radiopharmaceutical
applications. The crystal structure showed that the ligand containing phenyl derivative behaves
as SN1 donor where t-butyl behaves as SN3N (19).
Cu(II) complexes of 4-ethyl-1-(pyridin-2-yl)thiosemicarbazide (HEPTS) were synthesized and
characterized (20). This ligand was used for separation, preconcentration and determination of
Cu(II) ions (21, 22).
The present work aims to synthesize and characterize Pd(II), Pt(II) and Ag(I) complexes of 4-
ethyl- and 4-(p-tolyl)-1-(pyridin-2-yl)thiosemicarbazide (HEPTS and Hp-TPTS) and examining
their antibacterial activities (Figure 1).
2. Results and discussion
The elemental analysis indicated the stoichiometry of the isolated complexes (Table 1). All have
high melting points (>300 ◦C) and are insoluble in most common organic solvents but soluble in
DMF and DMSO; Ag(I) complexes are partially soluble. The molar conductance values, in DMF,
indicate non-electrolytes (ꢀm = 5–10 ꢁ−1 cm2 mol−1).
Table 1. Elemental analysis of the ligands and their isolated complexes.
Found %
H
Calcd. %
Compound, formula (F. wt)
Color
M.p. (◦C)
C
M
–
C
H
M
HEPTS, C8H12N4S (196.27)
[Pd(EPTS)2].4H2O, C16H30N8O4S2Pd
(569.01)
[Pt(EPTS)2].5H2O, C16H32N8O5S2Pt
(675.68)
Yellowish white
Green
177
>300
49.02 6.34
48.96 6.16
–
33.73 5.02 18.52 33.77 5.31 18.70
28.01 4.18 28.95 28.44 4.77 28.87
34.42 5.29 30.44 34.40 4.91 30.89
Reddish brown
Brown
>300
>300
[Ag(EPTS)].EtOH, C10H17N4OSAg
(349.20)
Hp-TPTS C13H14N4S (258.34)
[Pd(p-TPTS)2].4H2O, C26H34N8O4S2Pd
(693.15)
White
Green
167
>300
59.82 5.11
–
60.44 5.46
44.64 5.51 14.98 45.05 4.94 15.35
39.62 4.12 24.52 39.94 4.38 24.95
43.37 4.86 25.98 43.81 4.66 26.23
[Pt(p-TPTS)2]·4H2O, C26H34N8O4S2Pt
Reddish brown
Brown
>300
>300
(781.81)
[Ag(p-TPTS)]·EtOH, C15H19N4OSAg
(411.27)

Journal of Sulfur Chemistry 143
2.1. IR spectra
The IR spectrum of Hp-TPTS showed bands at 3267, 3170, 3135 and 725 cm−1 attributed to ν
(N4H), ν(N1H), ν(N2H) and ρ(NH), respectively (4, 23). Also, the bands at 1595 (1522, 1449
and 782) cm−1 are assigned to ν(C N)Py (24) and thioamide (I, III and IV) (4), respectively,
=
2
=
indicating that the ligands exist in the thione form. The ν(N H), and ν(C N)Py bands were
found at lower wave numbers than those of HEPTS due to the involvement of these groups in
intramolecularH-bonding(25).ThemostimportantspectraldataoftheligandsarelistedinTable 2.
Careful comparison of the IR spectra of the ligands with their Pd(II), Pt(II) andAg(I) complexes
reveals the shift of ν(N1H) to higher wavenumbers supporting its coordination (26). The new band
at ∼1635 cm−1, assigned to ν(C N ), and the disappearance of ν(N H) and ν(C S) indicate the
2
2
=
=
−
=
thioenolization of the ligands (C SH) and their coordination via sulfur atoms. The ν(C N)py
appears more or less at the same position indicating its non-involvement in coordination. Thus,
the ligands behave as a monobasic bidentate (NS donors) (20). A new band at 500–520 cm−1
−
is assigned to ν(M N) (26, 27). The nitrate bands in the Ag(I) complexes are absent (28). An
angular structure is proposed for Ag(I) complexes.
2.2. 1H NMR spectra
The 1H NMR spectrum of Hp-TPTS in DMSO-d6 (Figure 2) showed the signals of the phenyl
and pyridyl protons (Table 3) (25, 29). The three singlet signals at 8.50, 9.61 and 9.76 ppm are
attributed to the N2H, N1H and N4H protons, respectively. It is observed that the N2H signal
appears in the aromatic region which confirms its involvement in intramolecular H-bond with the
Npyridyl. The other NH protons are shifted upfield due to the inductive effect of pyridyl and phenyl
−
rings as electron donor groups (25). The CH3 protons appear as a singlet at 3.40 ppm.
The spectrum of [Pd(p-TPTS)2].4H2O in DMSO-d6 (Figure 3) showed the disappearance of
the N2H signal and the downfield shift of N1H indicating that the ligand exists in the thiol form
with the involvement of N1H in coordination. The pyridyl and phenyl protons appear more or less
at the same position indicating that they are not involved in coordination to the metal ion (30).
Comparison of the spectrum of HEPTS in CD3Cl (20) with its Pd(II) complex in DMSO reveals
that the N1H signal is shifted downfield while the N2H disappeared confirming its thioenolization
and involvement in coordination (30). The spectra indicate the presence of ethyl and pyridyl
signals at the same position (Table 3).
Table 2. Infra-red spectral date of ligands and isolated solid complexes in KBr as well as calculated frequencies in the
gaseous state.
HEPTS
Hp-TPTS
Assignment Exp. PM3 Pd–EPTS Pt–EPTS Ag–EPTS Exp. PM3 Pd–p-TPTS Pt–p-TPTS Ag–p-TPTS
ν(OH)solv
ν(N4H)
–
–
3433
3286
3233
1637
1607
1531
1437
–
3432
3282
3260
1636
1598
1489
1448
–
3395
3324
3265
1635
1595
1461
1436
–
–
3439
3343
3215
1634
1604
1515
1440
–
3407
3348
3220
1636
1598
1515
1444
–
3377
3240
3200
1635
1608
1500
1440
–
3239 3350
3154 3255
–
3267 3351
3170 3290
–
1595 1746
1522 1510
1449 1431
782 798
725 763
ν(N1H)
2
=
ν(C N )
–
=
ν(C N)Py
NHCS(I, III) 1519 1525
1604 1745
1446 1496
=
ν(C S)
ρ(NH)
798 842
773 772
736
752
750
776
750
748
760
Note: Hp-TPTS: N2H 3135 cm−1
.

144 A.A. El-Asmy et al.
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
12.0 11.0 10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0
–1.0 –2.0
X: parts per Million : 1H
Figure 2. 1H NMR spectrum of Hp-TPTS in DMSO-d6.
Table 3. 1H NMR spectral data of HEPTS and Hp-TPTS and their Pd(II) complexes (ppm).
N1H
N2H
N4H
H3
H4
H5
H6
Py
CH2–
CH3
−
−
Compound
Py
Py
Py
HEPTS
6.87
8.49
N1H
7.62
–
N2H
–
7.76
N4H
6.87
6.71
7.62
7.17
6.87
7.56
8.09
8.17
3.63
3.46
1.75
1.46
[Pd(EPTS)2]·4H2O
Compound
H3
H4
H5
H6
H2
H3
Py
Py
Py
Py
Bz
Bz
Hp-TPTS
[Pd(p-TPTS)2]·4H2O
9.61
10.14
8.50
–
9.76
9.77
6.60
6.79
7.60
7.81
7.04
7.15
8.10
8.32
7.32
7.33
7.59
7.60
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
11.0
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0
X: parts per Million : 1H
Figure 3. 1H NMR spectrum of [Pd(p-TPTS)2]. 4H2O in DMSO-d6.

Journal of Sulfur Chemistry 145
2.3. Electronic spectra
The electronic spectra of HEPTS and Hp-TPTS, in DMF, showed bands at 35,460–36,765,
31,950–32,260, 30,305–31,950 and 23,200–24,940 cm−1 attributed to (π → π*)Py, (π → π*)CS
(24, 25), (n → π*)Py and (n → π∗)CS (24, 31), respectively. Moreover, the spectrum of Hp-TPTS
in DMF showed another band at 33,780 cm−1 assigned to (π → π*)Ph (Table 4). The appearance
of two bands at 32,575–33,670 and 28,655–29,411 cm−1 attributed to (π → π*) and (n → π∗)
2
=
of the newly formed (C N ) supports the thiol form of the ligand (24, 31).
In the spectra of square planar Pd(II) and Pt(II) complexes, three spin-allowed singlet–singlet
1
d–d transitions were predicted. The ground state is A1g and the excited states corresponding
1
1
1
to the three transitions are A2g, B1g and Eg. Strong charge transfer transitions interfere and
prevent the observation of all the expected bands (32). The spectra of Pd(II) complexes in DMF
showed two bands at 24,875–25,250 and 18,450–18,520 cm−1 attributed to ligand-metal charge
transfer (LMCT) (overlapped with 1A1g → Eg) and 1A1g → A2g (32, 33). In Nujol, the spectra
showed the three bands assignable to LMCT with d–d transitions (Table 4). The spectra of Pt(II)
complexes in DMF showed two bands at 24,040–24,450 and 11,930–13,260 cm−1 attributed to
1
1
LMCT (overlapped with 1A1g → Eg) and MLCT (30), respectively. In Nujol, the spectra showed
1
Table 4. The electronic spectral bands of ligands and its complexes observed in DMF, Nujol and the gas state (ZINDO/S
calculations).
Compound
HEPTS
Solvent
DMF
Bands [ZINDO/S estimated] (assignment)
ν2/ν1
35,460 [35,971] (π−π∗)Py; 31,950 [31,949] (π−π∗)CS; 30,865
[27,027] (n–π*)Py; 24,940 [25,010] (n–π*)CS
–
[Pd(EPTS)2]·4H2O
[Pt(EPTS)2]·5H2O
DMF
Nujol
36,765 (π−π∗)Py; 32,575 (π−π∗)2 ; 30,770 (n–π*)Py; 24,875
1.28
1.13
CN
(1A1g → Eg + LMCT); 18,450 (1A1g → A2g + LMCT)
1
1
1
1
25,640 (1A1g → Eg + LMCT); 23,475 (1A1g → B1g + LMCT);
18,315 (1A1g → A2g + LMCT)
1
DMF
36,765 (π−π∗)Py; 33,115 (π−π∗)2 ; 30,305 (n–π*)Py; 24,450
CN
(1A1g → Eg + LMCT);
1
1
17,185 (1A1g → A2g + LMCT); 13,260 (MLCT)
1
1
Nujol
DMF
24,270 (1A1g → Eg + LMCT); 21,645 (1A1g → B1g + LMCT);
19,230 (1A1g → A2g + LMCT)
1
[Ag(EPTS)]·EtOH
36,500 (π−π∗)Py; 33,670 (π−π∗)2 ; 30,395 (n–π∗)Py; 29,760
–
CN
(n−π∗)2CN; 26,110 (LMCT)
Nujol
DMF
24,875 (LMCT); 21,100 (LMCT)
Hp-TPTS
36,500 [35,335] (π−π∗)Py; 33,785 [33,557] (π−π∗)Ph; 32,260
[31,546] (π−π∗)CS; 30,490 [28,818] (n–π*)Py; 23,200 [23,474]
(n–π*)CS
–
[Pd(p-TPTS)2]·4H2O
DMF
Nujol
35,970 (π−π∗)Py; 33,900 (π−π∗)Ph; 31,150 (n–π*)Py; 29,585
1.15
(n−π∗)2
;
CN
1
1
25,250 (1A1g → Eg + LMCT); 18,520 (1A1g → A2g + LMCT)
23,925 (1A1g → Eg + LMCT); 21,645 (1A1g → B1g + LMCT);
1
1
18,870 (1A1g → A2g + LMCT)
1
[Pt(p-TPTS)2]·4H2O
[Ag(p-TPTS)]·EtOH
DMF
Nujol
36,230 (π−π∗)Py; 33,900 (π−π∗)Ph; 31,950 (n–π*)Py; 29,675
1.26
–
(n−π∗)2 ; 24,040 (1A1g → Eg + LMCT); 11,935 (MLCT)
1
CN
25,000 (1A1g → Eg + LMCT); 21,550 (1A1g → B1g + LMCT);
1
1
17,065 (1A1g → A2g + LMCT)
1
DMF
Nujol
36,500 (π−π∗)Py; 34,245 (π−π∗)Ph; 31,545 (n–π*)Py; 28,655
(n−π∗)2CN; 26,385 (LMCT)
26,595 (LMCT); 23,585 (LMCT)

146 A.A. El-Asmy et al.
HN
S
R
N
N
HN
xH2O
M
S
NH
N
N
R
NH
M = Pd(II), R = Et and p-tolyl, x = 4
M = Pt(II), R = Et,
M = Pt(II), R = p-tolyl,
x = 5
x = 4
Figure 4. Proposed structure of Pd(II) and Pt(II) complexes.
the bands at 25,000–24,270, 21,645–21,550 and 19,230–17,065 cm−1 assignable to the LMCT
1
1
1
(overlapped with 1A1g → Eg, 1A1g → B1g and 1A1g → A2g) transitions, respectively. The ν2/ν1
values lie in the 1.13–1.28 range, comparable with the values reported for the square-planar Pd(II)
and Pt(II) complexes (33) (Figure 4).
The spectra of Ag(I) complexes in DMF showed a charge transfer band at 26,110–
26,385 cm−1 (32).
2.4. Thermal analysis
The thermogravimetry (TG) curve of Hp-TPTS indicates a thermal stability till 170 ◦C (its melting
point is 178 ◦C). The curve showed three decomposition steps at 191 ◦C, 257 ◦C and 501 ◦C
corresponding to the loss of PyNHNHC (Found 44.94; Calcd. 46.89%), PhNHS+3H (Found
50.75, Calcd. 49.60%) and complete decomposition of the ligand.
The TG thermograms of the isolated complexes were taken as a proof for the water molecules
to be outside the coordination sphere which was lost at 70–248 ◦C with mid-point at ∼110 ◦C
(Table 5). Generally, the complexes showed a higher thermal stability than the ligands where the
beginning of decomposition was observed at 190–266 ◦C. Complete data of all decomposition
steps are shown in Table 5.
2.5. Kinetic and thermodynamic data
To evaluate the kinetic and thermodynamic parameters for the different thermal decomposition
steps, the Coats–Redfern (34) and Horowitz–Metzger (35) equations are employed. The data
of activation enthalpy (ꢂH*), the activation entropy (ꢂS*) and the free energy of activation
(ꢂG*) are determined and presented in Table 5. From the results, one can point out the following
remarks:
The ꢂE* values reveal high stability of the chelates due to their covalent bond character.
The positive sign of ꢂH* indicates that the decomposition stages are endothermic processes.
The positive sign of ꢂG* reveals that all the decomposition steps are non-spontaneous
processes.
The negative values of ꢂS* suggest the residue after decomposition is more ordered than the
starting ones.

Table 5. Thermal analysis data and thermodynamic parameters of ligands and complexes.
Thermal analysis
Kinetic parameters
Compound
Temp.
Wt%
Assignment
ꢂE*
ꢂS*
ꢂH*
ꢂG*
A
R
SD
Hp-TPTS
168–214
214–300
300–702
44.94
50.75
4.31
PyNHNHC (46.89)
3H + PhNHS (49.60)
C (4.65)
–
–
–
139.52
–
–
106.98
–
–
–
–
143.94 (152.78)
–
61.20
–
1.74E16
–
0.9835 (0.9818)
–
0.2918 (0.3243)
–
[Pd(p-TPTS)2]·4H2O
[Pt(p-TPTS)2]·4H2O
[Pd(EPTS)2]·4H2O
[Pt(EPTS)2]·5H2O
28–200
200–500
500–750
Res.
9.99
30.09
23.21
36.71
4H2O (10.40)
2(NHPhCH3) (30.63)
2Py (22.53)
22.72 (28.24)
46.64 (52.66)
44.93 (65.77)
–
−94.93
−217.64
−196.01
–
19.49
41.46
37.50
–
56.33
177.09
212.54
–
8.89E7
55.57
1073.49
0.9822 (0.9817)
0.9863 (0.9819)
0.9854 (0.9900)
–
0.1266 (0.1587)
0.2092 (0.2458)
0.0655 (0.0778)
–
Pd(CHN2S)2 (36.44)
–
28–190
190–490
490–740
Res.
10.10
27.89
19.08
42.94
4H2O (9.22)
2(NHPhCH3) (27.16)
2Py (19.98)
33.47 (28.24)
46.64 (51.47)
−235.83
30.37
41.46
–
118.45
177.09
–
–
3.74
55.57
–
0.9822 (0.9817)
0.9863 (0.9864)
0.2498 (0.1587)
0.2092 (0.1769)
−217.64
–
–
–
–
–
–
–
–
Pt(CHN2S)2 (43.64)
–
–
28–248
266–344
344–744
Res.
12.81
16.12
26.11
44.80
4H2O (12.67)
2(NHEt) (15.49)
2Py (27.45)
24.47 (23.16)
124.53 (130.91)
−214.26
21.33
119.67
–
–
102.32
197.29
–
–
50.64
1.41E6
–
–
0.9787 (0.9875)
0.9844 (0.9837)
0.2562 (0.1979)
0.1224 (0.1345)
−132.80
–
–
–
–
–
–
–
–
Pd(CHN2S)2 (44.37)
28–230
240–450
450–750
Res.
12.58
12.84
31.66
42.92
5H2O (13.12)
37.06 (33.57)
40.61 (50.29)
−236.90
33.79
35.51
–
126.96
166.36
–
–
3.46
92.35
–
0.9819 (0.9861)
0.9866 (0.9843)
0.2615 (0.1658)
0.1182 (0.1583)
2(NHEt) (13.05)
2(Py + CN) (30.19)
Pt(NS)2 (42.48)
−213.29
–
–
–
–
–
–
–
–
–
–
Note: Values between brackets were calculated by Horowitz–Metzger equation.

148 A.A. El-Asmy et al.
2.6. Molecular modeling and spectral analysis data
The geometric optimization structure of HEPTS was discussed in the previous work (22). The
Hp-TPTS modeling indicates a non-planar structure (Figure 5). On comparison with HEPTS, it
is observed that the pyridyl nitrogen atom is involved in intramolecular H-bond [HN2 . . .. H(24)];
the phenyl ring is perpendicular to the pyridyl ring and S(11) is in the same direction with the
pyridyl nitrogen.
Also, the molecular modeling of [Pd(p-TPTS)2].4H2O and [Pd(EPTS)2]·4H2O is drawn in
Figures 1S and 2S (supplementary material, online only). The data of their bond lengths (Table 1S)
1
4
revealed that: (i) the bond lengths of N4 H, N H, CEt N and (C N)Py of the two Pd(II)
−
−
−
=
complexes are quite close to those of the corresponding ligand which clearly indicates that they
are not affected by the complex formation. (ii) The CPy N bond lengths are found long which
attributed to its involvement in coordination. (iii) The Pd S and Pd N bond lengths are similar
to those reported earlier from X-ray crystallography (9).
1
−
−
−
The electrostatic potential calculations of the ligands showed that N and S atoms have negative
potentials that support their involvement in coordination (Figure 6). The Mulliken charge density
distributions in the ligands and their complexes are listed in Table 2S. The selected angles and the
molecular parameters are displayed in Tables 3S–6S.
2.7. Antibacterial activity
The ligands and their complexes were tested to show their antibacterial and antifungal activ-
ities; the obtained values (mm) were compared with gentamicin. The experiments showed no
antifungal activity towards Asperigallus ochraceus, Staphylococcus aureus and Bacillus subtilis
as Gram positive and Escherichia coli and Pseudomonas aeruginosa as Gram negative are the
tested bacteria. HEPTS has activity against S. aureus, whereas Hp-TPTS has no activity. The
Pd(II) and Pt(II) complexes of Hp-TPTS showed higher activity than HEPTS complexes and
Figure 5. The PM3-optimized structure of Hp-TPTS.

Journal of Sulfur Chemistry 149
Figure 6. Electrostatic potential diagram of PM3-optimized Hp-TPTS (colour online).
Table 6. Antibacterial activity of ligands and its complexes.
Gram -ve
Gram +ve
P. aeruginosa
Complexes
S. aureus
B. subtilis
E. coli
Gentamicin
HEPTS
25.9
15.8
16.3
16.0
15.2
–
17.5
18.8
–
19.8
19.4
20.1
20.5
18.8
13.7
27.1
28.5
14.9
20.0
–
23.6
–
–
[Pd(EPTS)2]·4H2O
[Pt(EPTS)2]·5H2O
[Ag(EPTS)]·EtOH
Hp-TPTS
[Pd(p-TPTS)2]·4H2O
[Pt(p-TPTS)2]·4H2O
[Ag(p-TPTS)]·EtOH
12.0
12.4
13.9
12.5
26.0
25.7
16.8
–
11.8
11.4
30.4
29.5
14.8
gentamicin against all bacteria except S. aureus. The complexes have activity more than the lig-
ands againstB.subtilis bacteria, andtheHp-TPTScomplexeshavenearlydoubleactivity(Table 6).
On the other hand, HEPTS and its complexes showed no activity against P. aeruginosa except
[Ag(EPTS)]EtOH while the complexes of Hp-TPTS showed more activity. Generally, the data
reveal the higher activity of Hp-TPTS complexes than HEPTS complexes (Table 6). Compar-
ing the data with previous data (20) indicates that Pd(II), Pt(II) and Ag(I) complexes derived
from HEPTS showed more activity against Gram-negative bacteria than the ligand and its Cu(II)
complexes.
3. Conclusion
4-Ethyl- or 4-p-tolyl-1-(pyridin-2-yl)thiosemicarbazides have been introduced as chelating
agents for the formation of Ag(I), Pd(II) and Pt(II) complexes. The complexes have the
formulae: [Pd(EPTS)2]·4H2O, [Pd(p-TPTS)2]·4H2O, [Pt(EPTS)2]·5H2O, [Pt(p-TPTS)2]·4H2O,
[Ag(EPTS)]·EtOH and [Ag(p-TPTS)]·EtOH. The Pd(II) and Pt(II) complexes have a square-
planar geometry while Ag(I) complexes have angular geometry. All compounds were found

150 A.A. El-Asmy et al.
promising for antibacterial activity especially [Pd(p-TPTS)2].4H2O and [Pt(p-TPTS)2].4H2O.
The in vitro activity of Pd(II) complexes of steroidal thiosemicarbazone have values against E.
coli less than our values.
4. Experimental
4.1. Apparatus and reagents
The IR spectra were recorded on a Mattson 5000 FT–IR spectrophotometer. The electronic spec-
1
tra were measured on a Unicam UV–VIS spectrophotometer UV2. The H NMR spectra of
HEPTS (in CDCl3); HpTPTS and its Pd(II) complexes, in DMSO-d6, were recorded on EM-390
(200 MHz) and Jeol Delta2 (500 MHz) spectrometers, respectively. Thermogravimetric analysis
was performed using an automatic recording thermo balance, type 951 DuPont; samples were
subjected to heat on a rate of 10 ◦C min−1 (25–750 ◦C) in N2. Carbon and hydrogen content of the
ligands and their complexes was determined at the Microanalytical Unit, Mansoura University,
Egypt. Pd(II), Pt(II) and Ag(I) contents were determined using the Perkin Elmer 2380 flame
atomic absorption spectrometer (Vernon Hills) with a conventional 10 cm slit burner head for air
acetylene flame and Pye Unicam (England) hollow cathode lamps for the investigated elements
were used as spectral radiation sources (where λ = 244.8, 266 and 328.1 nm and current = 15, 15
and 4 mA for Pd(II), Pt(II) and Ag(I), respectively). All salts and reagents used were purchased
from Fluka, Aldrich or Merck.
4.2. Synthesis of the ligands
HEPTS was prepared as previously reported (20). Hp-TPTS was prepared by heating under reflux
of a mixture of 2-hydrazinopyridine (0.1 mol) and p-tolylisothiocyanate (0.1 mol) in absolute
ethanol for 2 h. On cooling, the yellowish white crystals were formed, filtered off, washed with
ethanol and diethyl ether and recrystallized from ethanol (m.p. 167 ◦C; yield 95%). The purity of
the compound (Figure 1) was checked by thin layer chromatography.
4.3. Synthesis of complexes
On mixing HEPTS or Hp-TPTS (0.01 mol) in ethanol (20 mL) with 0.01 mol of K2PdCl4, K2PtCl4
orAgNO3, in water (5 mL), dark green, red break or brown precipitates were immediately formed.
The reaction mixture was heated under reflux for 1 h on a water bath. The precipitates were filtered
off after cooling, washed successfully with ethanol then diethyl ether, dried and preserved in a
vacuum desiccator over anhydrous calcium chloride.
4.4. Computational details
All theoretical calculations of the quantum chemistry were performed using HyperChem 7.51
program system. First, molecular geometries of the ligand and its Pd(II) complexes were
optimized by PM3 using the Polak-Ribiere algorithm in restricted RHF-SCF, set to terminate
at a root mean square (RMS) gradient of 0.01 kcalÅ−1 mol−1 and convergence limit was fixed to
1 × 10−8 kcal mol−1. Secondly, the vibrational analysis and electronic spectra of ligands were per-
formed by PM3 and RHF-SCF ZINDO/S calculations, respectively. The configuration interaction
was limited to 10 occupied and 10 unoccupied orbitals.

Journal of Sulfur Chemistry 151
4.5. Antibacterial activity
The ligands and their complexes have been tested as antibacterial agents at the Department of
Microbiology, Faculty of Pharmacy, Mansoura University. The seeded agar plates were prepared
by putting 50 mL portion of inoculated agar into 15 cm Petri dishes and allowed to solidify. Cups
were made to receive 25 μL of the reagent solution and allowed to diffuse and incubated at
37 ◦C for 24 h. The inhibition zone was measured (36) and compared with that of gentamicin
solution (commercial antibiotic, Memphis Co., Egypt, 1000 μg mL−1). The experimental control
was DMF.
References
(1) Gingras, B.A.; Somorjai, R.L.; Bayley, C.H. Can. J. Chem. 1961, 39, 973–985.
(2) Al-Gammal, O.A.; El-Asmy, A.A. J. Coord. Chem. 2008, 61, 2296–2306.
(3) Campbell, M.J.M. Coord. Chem. Rev. 1975, 15, 279–319.
(4) El-Metwally, N.M.; El-Shazly, R.M.; Gabr, E.; El-Asmy, A.A. Spectrochim. Acta: A 2005, 61, 1113–1119.
(5) West, D.X.; Padhye, S.; Sonawane, P.B. Struct. Bond. (Berlin, Ger.) 1991, 76, 4–50.
(6) Abou-Hussen, A.A.; Saad, I.M.; El-Metwally, N.M.; El-Asmy, A.A. J. Coord. Chem. 2005, 58, 1735–1749.
(7) Casas, J.S.; Garcia-Tasende, M.S.; Sordo, J. J. Coord. Chem. Rev. 2000, 209, 197–261.
(8) El-Metwally, N.M.; Al-Hazmi, G.A.; El-Asmy, A.A. Transition Met. Chem. 2006, 31, 673–680.
(9) Lobana, T.S.; Sharma, R.; Bawa, G.; Khanna, S. Coord. Chem. Rev. 2009, 253, 977–1055.
(10) Beraldo, H.; Gambino, D. Min. Rev. Med. Chem. 2004, 4, 31–39.
(11) Ferrari, M.B.; Bisceglie, F.; Fava, G.G.; Pelosi, G.; Tarasconi, P.; Albertini, R.; Pinelli, S. J. Inorg. Biochem. 2002,
89, 36–44.
(12) Seleem, H.S.; El-Shetary, B.A.; Khalil, S.M.E.; Mostafa, M.; Shebl, M. J. Coord. Chem. 2005, 58, 479–493.
(13) Akl, M.A.; Ismael, D.S.; El-Asmy, A.A. Microchem. J. 2006, 83, 61–69.
(14) Saad, E.M.; El-Shahwai, M.S.; Saleh, H.; El-Asmy, A.A. Transition Met. Chem. 2007, 32, 155–162.
(15) Blower, P.J.; Dilworth, J.R.; Maurer, R.I.; Mullen, G.D.; Reynolds, C.A.; Zheng, Y. J. Inorg. Biochem. 2001, 85,
15–22.
(16) Garoufis, A.; Hadjikakou, S.K.; Hadjiliadis, N. Coord. Chem. Rev. 2009, 253, 1384–1397.
(17) Das, M.; Livingstone, S.E. Br. J. Cancer 1978, 37, 466–470.
(18) Banerjee, S.R.; Maresca, K.P.; Francesconi, L.; Valliant, J.; Bbich, J.W.; Zubieta, J. J. Nucl. Med. Biol. 2005, 32,
1–20.
(19) Clarke, C.; Cowley, A.R.; Dilworth, J.R.; Donnelly, P.S. J. Chem. Soc. Dalton Trans. 2004, 2402–2403.
(20) Hassanian, M.M.; Abdel-Rhman, M.H.; Gabr, I.M.; El-Asmy, A.A. Spectrochim. Acta: A 2008, 71, 73–79.
(21) Hassanian, M.M.; Abdel-Rhman, M.H.; Gabr, I.M.; El-Asmy, A.A. Transition Met. Chem. 2007, 32, 1025–1029.
(22) Hassanian, M.M.; Abdel-Rhman, M.H.; Gabr, I.M.; El-Asmy, A.A. J. Chem. Eng. Data 2009, 54, 1277–1283.
(23) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds, 5th ed.; John Wiley and
Sons: New York, 1997; Part III.
(24) Silverston, R.M.; Bassler, C.G.; Morrill, T.C. Spectrometric Identification of Organic Compound; John Wiley: New
York, 1974; Chapters 3 and 4.
(25) Valdés-Martínez, J.; Hernàndez-Ortega, S.; West, D.X.; Ackerman, L.J.; Swearingen, J.K.; Hermetet, A.K. J. Mol.
Struct. 1999, 478, 219–226.
(26) Mortel, E. Coordination Chemistry; Van Nostrand Reinhold: New York, 1971; Vol. 1, Chapter 3.
(27) Mendes, I.C.; Teixeira, L.R.; Lima, R.; Carneiro, T.G.; Beraldo, H. Transition Met. Chem. 1999, 24, 655–658.
(28) Ramos, J.M.; Viana, R.M.; Tellez, C.A.; Pereira, W.C.; Izolani, A.O.; da Silva, M.I.P. Spectrochim. Acta: A 2006,
65, 433–438.
(29) Perera, S.D.; Fernandez-Sanchez, J.J., Shaw, B.L. Inorg. Chim. Acta 2001, 325, 175–178.
(30) Bhowmik, S.R.; Gangopadhyay, S.; Gangopadhyay, P.K. J. Coord. Chem. 2005, 58, 795–801.
(31) Seena, E.B.; Kurup, M.R.P. Polyhederon 2007, 26, 829–836.
(32) Lever, A.B.P. Inorganic Electronic Spectroscopy, 2nd ed.; Elsevier: Amsterdam, 1984; Chapter 9.
(33) Offiong, O.E.; Martelli, S. Transition Met. Chem. 1997, 22, 263–269.
(34) Coats, A.W.; Redfern, J.P. Nature 1964, 201, 68–69.
(35) Horowitz, H.H.; Metzger, G. Anal. Chem. 1963, 35, 1464–1468.
(36) Collee, J.G.; Fraser, A.G.; Marmion, B.P.; Simmons, A. Mackie and McCartney; Practical Medical Microbiology,
14th ed.; Churchill: New York, 1996; Chapter 7.