Synthesis, characterization and antimicrobial activity of palladium(II) complexes with some alkyl derivates of thiosalicylic acids: Crystal structure of the bis(S-benzyl-thiosalicylate)-palladium(II) complex, [Pd(S-bz-thiosal) 2]

Article abstract of DOI:10.1016/j.poly.2011.08.042

S-Alkyl (R = benzyl, methyl, ethyl, propyl and butyl) derivatives of thiosalicylic acid and the corresponding palladium(II) complexes were prepared and their structures were proposed on the basis of infrared, ¹H and ¹³C NMR spectrosc

Full text of DOI:10.1016/j.poly.2011.08.042

Polyhedron 31 (2012) 69–76
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization and antimicrobial activity of palladium(II) complexes
with some alkyl derivates of thiosalicylic acids: Crystal structure of the
bis(S-benzyl-thiosalicylate)–palladium(II) complex, [Pd(S-bz-thiosal)2]
a
a
b
b
b
-
ˇ
´
´
´
´
´
´
Gordana P. Radic , Verica V. Glodovic , Ivana D. Radojevic , Olgica D. Stefanovic , Ljiljana R. Comic ,
a
c
c
a,
⇑
´
´
Zoran R. Ratkovic , Arto Valkonen , Kari Rissanen , Srecko R. Trifunovic
a
´
Department of Chemistry, Faculty of Science, University of Kragujevac, R. Domanovica 12, 34000 Kragujevac, Serbia
b Department of Biology and Ecology, Faculty of Science, University of Kragujevac, R. Domanovi´ca 12, 34000 Kragujevac, Serbia
c Nanoscience Center, Department of Chemistry, University of Jyväskylä, P.O. Box 35, 40014, Finland
a r t i c l e i n f o
a b s t r a c t
Article history:
S-Alkyl (R = benzyl, methyl, ethyl, propyl and butyl) derivatives of thiosalicylic acid and the correspond-
ing palladium(II) complexes were prepared and their structures were proposed on the basis of infrared,
1H and 13C NMR spectroscopy. The cis geometrical configurations of the isolated complexes were pro-
posed on the basis of an X-ray structural study of the bis(S-benzyl-thiosalicylate)–palladium(II), [Pd(S-
bz-thiosal)2] complex.
Antimicrobial activity of the tested compounds was evaluated by determining the minimum inhibitory
concentration (MIC) and minimum microbicidal concentration (MMC) in relation to 26 species of micro-
organisms. The tested ligands, with a few exceptions, show low antimicrobial activity. The palladium(II)
complexes, [Pd(S-R-thiosal)2], have statistically significant higher activity than the corresponding ligands.
The complexes [Pd(S-et-thiosal)2] and [Pd(S-pro-thiosal)2] displayed the strongest activity amongst the
all tested compounds. The palladium(II) complexes show selective and moderate antibacterial activity
and significant antifungal activity. The most sensitive were Aspergillus fumigatus and Aspergillus flavus.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 24 May 2011
Accepted 24 August 2011
Available online 21 September 2011
Keywords:
Palladium(II) complexes
Crystal structure
IR, 1H and 13C NMR spectroscopy
Antimicrobial activity
1. Introduction
other papers in the literature showing different intensities of palla-
dium complex activity on various species of bacteria and fungi
Thiosalicylic acid and its derivatives have many various applica-
tions: as reagents for metal determination [1,2], modificators for
graphite paste electrodes [3], as photoinitiators for free radical
polymerization [4] and in cosmetics in hair growth treatment [5].
They are useful in numerous disease treatments, in particular
inflammatory, allergic and respiratory diseases [6] as well as Ras-
tumor growth inhibitors [7]. Ketones derived from thiosalicylic
acids have application as bile acid transport inhibitors [8].
The synthesis and evaluation of the biological activity of new
metal-based compounds are fields of growing interest. Numerous
complexes based on the palladium(II) ion have been synthesized
and their different biological activities have been documented
[9–11]. The impact of different palladium complexes on the growth
and metabolism of various groups of microorganisms has been
studied. Garoufis et al. [12] reviewed numerous scientific papers
on anti-viral, antibacterial and antifungal activity of palladium(II)
complexes with different types of ligands (sulfur and nitrogen do-
nor ligands, Schiff base ligands and drugs as ligands). There are
[13–20].
S-Alkyl (alkyl = benzyl, methyl, ethyl, propyl and butyl)
derivatives of thiosalicylic acid have already been prepared and
characterized using IR and elemental microanalysis [21–24], and
the S-methyl derivate has also been characterized using NMR spec-
troscopy [22,23].
Thiosalicylic acid has been used for the synthesis of palla-
dium(II) complexes [25–28], but corresponding S-alkyl derivatives
have not. Our investigations are focused on the synthesis of the
corresponding Pd(II) complexes of S-alkyl derivatives as well as
the in vitro antimicrobial activity of the ligands and the complexes.
The structures of the isolated complexes are proposed on the basis
of their infrared, 1H and 13C NMR spectra. The structures as well as
the cis geometrical configurations of the isolated complexes are
proposed on the basis of an X-ray structural study of the cis-S-
cis-O bis(S-benzyl-thiosalicylate)–palladium(II) [Pd(S-bz-thiosal)2]
complex. Our investigations are focused on the impact of the newly
synthesized Pd(II) complexes on probiotics, since they are used as
supplements and they play a significant role in the protection and
maintenance of the balance of intestinal microflora during antibi-
otic therapy.
⇑
Corresponding author.
E-mail address: srecko@kg.ac.rs (S.R. Trifunovic´).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.08.042

´
G.P. Radic et al. / Polyhedron 31 (2012) 69–76
70
2.1.3. Preparation of the bis(S-benzyl-thiosalicylate)–palladium(II)
2. Experimental
2.1. Chemistry
complex, [Pd(S-bz-thiosal)2] (C1)
K2[PdCl4] (0.100 g, 0.3065 mmol) was dissolved in 10 cm3 of
water on
a steam bath and (S-benzyl)-2-thiosalicylic acid
(0.1497 g, 0.613 mmol) was added into the solution. The resulting
mixture was stirred for 2 h and during this time an aqueous solu-
tion of LiOH (0.0256 g, 0.613 mmol in 10 cm3 of water) was intro-
duced. The complex [Pd(S-bz-thiosal)2] (C1) as a yellow precipitate
was filtered, washed with water and air-dried. Yield: 0.11 g
(58.70%). Anal. Calc. for C28H22O4S2Pd (Mr = 592.98): C, 56.71; H,
3.74; S, 10.82. Found: C, 56.43; H, 3.85; S, 10.75%. IR (KBr, cmÀ1):
3420, 3057, 1634, 1616, 1562, 1327, 1146, 753, 708, 698. 1H
NMR (200 MHz, DMSO-d6, d ppm): 4.05 (s, 4H, CH2), 7.08–8.10
(m, 9H, Ar and bz). 13C NMR (50 MHz, DMSO-d6, d ppm): 25.9
(CH2), 124.1, 125.6, 125.7, 126.2, 126.3, 126.8, 127.3, 127.8,
129.5, 133.2, 136.2, 139.7 (Ar and bz), 171.5 (COOÀ).
2.1.1. Reagents and instruments
All chemicals were obtained commercially and used without
further purification. For the infrared spectra, a Perkin–Elmer Spec-
trum One FT-IR spectrometer was employed. Elemental microanal-
yses for C, H and S were performed by standard methods on a Vario
III CHNS Elemental Analyzer, Elemental Analysensysteme GmbH.
2.1.2. General procedure for the synthesis of S-alkyl thiosalicylic acids
(L1)–(L5)
The thioacid ligands L1–L5 were prepared by alkylation of thio-
salicylic acid by means of the corresponding alkyl halogenides in
alkaline water–ethanol solution.
Thiosalicylic acid (1 mmol) was added to a 100 cm3 round bot-
tom flask containing 50 cm3 of 3a 0% solution of ethanol in water
and stirred. A solution of NaOH (2 mmol in 5 cm3 of water) was
added to the acid suspension, whereupon the solution became
clear. The corresponding alkyl halogenide (2 mmol) was dissolved
in 5 cm3 of ethanol and transferred to the stirred solution. The
resulting mixture was kept overnight at 60 °C. The reaction mix-
ture was transferred into a beaker and ethanol was evaporated
off on a water bath. Diluted hydrochloric acid (2 mol/dm3) was
added to the resulting water solution and S-alkyl thiosalicylic acid
was precipitated as a white powder. The liberated acid was filtered
off and washed with plenty of distilled water. The product was
dried under vacuum overnight. Yield: 85–95%.
2.1.4. Preparation of the bis(S-methyl-thiosalicylate)–palladium(II)
complex, [Pd(S-met-thiosal)2] (C2)
The complex [Pd(S-met-thiosal)2] (C2) was prepared as de-
scribed in Section 2.1.3 using (S-methyl)-2-thiosalicylic acid
(0.103 g, 0.613 mmol) instead of (S-benzyl)-2-thiosalicylic acid.
Yield:
0.08 g
(59.80%).
Anal.
Calc.
for
C16H14O4S2Pd
(Mr = 440.672): C, 43.61; H, 3.20; S, 14.52. Found: C, 43.41; H,
3.39; S, 14.21%. IR (KBr, cmÀ1): 3419, 1619, 1597, 1399, 1385,
1332, 1306, 1142, 960, 865, 741, 693, 654. 1H NMR (200 MHz,
DMSO-d6, d ppm): 2.35 (s, 6H, CH3), 7.19–8.08 (m, 8H, Ar). 13C
NMR (50 MHz, DMSO-d6, d ppm): 14.6 (CH3), 123.6, 125.1, 125.2,
129.0, 132.7, 135.7, (Ar), 171.8 (COOÀ).
S-Benzyl-thiosalicylic acid (L1): M.p. 179–180 °C, white powder.
IR (KBr, cmÀ1): 3414, 3061, 2920, 2648, 2559, 1674, 1584, 1562,
1463, 1412, 1317, 1272, 1255, 1154, 1062, 1046, 897, 743, 711,
652, 551. 1H NMR (200 MHz, CDCl3, d ppm): 4.17 (s, 2H, CH2),
7.21–8.14 (m, 9H, Ar and bz). 13C NMR (50 MHz, DMSO-d6, d
ppm): 35.9 (CH2), 124.1, 125.9, 126.7, 127.3, 127.9, 128.3, 128.6,
129.3, 131.0, 132.4, 136.8, 141.3 (Ar and bz), 167.5 (COOH).
S-Methyl-thiosalicylic acid (L2): M.p. 165–166 °C, white powder.
IR (KBr, cmÀ1): 3446, 3068, 2916, 2652, 2560, 1674, 1586, 1561,
1466, 1412, 1308, 1291, 1270, 1255, 1151, 1062, 1048, 892, 743,
699, 652, 556. 1H NMR (200 MHz, CDCl3, d ppm): 2.48 (s, 3H,
CH3), 7.16–8.18 (m, 4H, Ar). 13C NMR (50 MHz, CDCl3, d ppm):
15.6 (CH3), 123.5, 124.4, 125.4, 132.5, 133.6, 144.4 (Ar), 171.6
(COOH).
S-Ethyl-thiosalicylic acid (L3): M.p. 133–134 °C, white powder. IR
(KBr, cmÀ1): 3435, 3066, 2972, 2652, 2562, 1682, 1588, 1563, 1466,
1414, 1315, 1275, 1252, 1152, 1063, 1049, 884, 740, 704, 690, 651,
550. 1H NMR (200 MHz, CDCl3, d ppm): 1.42 (t, 3H, CH3), 2.97 (q,
2H, CH2), 7.16–8.17 (m, 4H, Ar). 13C NMR (50 MHz, CDCl3, d
ppm): 13.1 (CH3), 26.2 (CH2), 124.0, 125.9, 126.4, 132.6, 133.2,
142.9 (Ar), 171.4 (COOH).
S-Propyl-thiosalicylic acid (L4): M.p. 104 °C, white powder. IR
(KBr, cmÀ1): 3414, 3056, 2979, 2641, 2555, 1678, 1588, 1562,
1462, 1405, 1310, 1271, 1257, 1150, 1062, 1053, 811, 740, 704,
691, 653, 554. 1H NMR (200 MHz, CDCl3, d ppm): 1.1 (t, 3H, CH3),
1.74 (m, 2H, CH2), 2.92 (t, 2H, CH2), 7.15–8.15 (m, 4H, Ar). 13C
NMR (50 MHz, CDCl3, d ppm): 13.8 (CH3), 21.6 (CH2), 34.1 (CH2),
123.8, 125.6, 126.2, 132.5, 133.1, 143.1 (Ar), 171.6 (COOH).
S-Butyl-thiosalicylic acid (L5): M.p. 82–83 °C, white powder. IR
(KBr, cmÀ1): 3420, 2955, 2869, 2641, 2556, 1674, 1586, 1560,
1462, 1408, 1320, 1270, 1250, 1153, 1060, 1048, 924, 810, 738,
704, 651, 553. 1H NMR (200 MHz, CDCl3, d ppm): 0.96 (t, 3H,
CH3), 1.46 (m, 2H, CH2), 1.78 (m, 2H, CH2), 2.94 (t, 2H, CH2),
7.15–8.16 (m, 4H, Ar). NMR (50 MHz, CDCl3, d ppm): 13.7 (CH3),
22.3 (CH2), 30.2 (CH2), 31.9 (CH2), 123.8, 125.7, 126.3, 132.5,
133.1, 143.1 (Ar), 171.4 (COOH).
2.1.5. Preparation of the bis(S-ethyl-2-thiosalicylate)–palladium(II)
complex, [Pd(S-et-thiosal)2] (C3)
The complex [Pd(S-et-thiosal)2] (C3) was prepared as described
in Section 2.1.3 using (S-ethyl)-2-thiosalicylic acid (0.1117 g,
0.613 mmol) instead of (S-benzyl)-2-thiosalicylic acid. Yield:
0.0832 g (57.90%). Anal. Calc. for C18H18O4S2Pd (Mr = 468.856): C,
46.11; H, 3.87; S, 13.68. Found: C, 45.97; H, 3.93; S, 13.54%. IR
(KBr, cmÀ1): 1436, 1587, 1518, 1393, 752. 1H NMR (200 MHz,
DMSO-d6, d ppm): 1.27 (t, 6H, CH3), 2.83 (q, 4H, CH2), 7.11–8.08
(m, 8H, Ar). 13C NMR (50 MHz, DMSO-d6, d ppm): 14.4 (CH3),
13.8 (CH2), 124.8, 125.3, 126.1, 128.7, 133.2, 135.9 (Ar), 172.0
(COOÀ).
2.1.6. Preparation of the bis(S-propyl-2-thiosalicylate)–palladium(II)
complex, [Pd(S-pro-thiosal)2] (C4)
The complex [Pd(S-pro-thiosal)2] (C4) was prepared as de-
scribed in Section 2.1.3 using (S-propyl)-2-thiosalicylic acid
(0.1203 g, 0.613 mmol) instead of (S-benzyl)-2-thiosalicylic acid.
Yield: 0.0889 g (58.40%). Anal. Calc. for
C20H22O4S2Pd
(Mr = 496.908): C, 48.34; H, 4.46; S, 12.91. Found: C, 48.52; H,
4.11; S, 12.73%. IR (KBr, cmÀ1): 1421, 1589, 1541, 1520, 1397,
752. 1H NMR (200 MHz, DMSO-d6, d ppm): 0.98 (t, 6H, CH3), 1.76
(m, 4H, CH2), 2.84 (t, 4H, CH2), 7.20–8.25 (m, 8H, Ar). 13C NMR
(50 MHz, DMSO-d6, d ppm): 13.2 (CH3), 22.0 (CH2), 27.6 (CH2),
125.1, 126.6, 126.7, 130.5, 134.2, 137.2 (Ar), 172.5 (COOÀ).
2.1.7. Preparation of the bis(S-butyl-2-thiosalicylate)–palladium(II)
complex, [Pd(S-bu-thiosal)2] (C5)
The complex [Pd(S-bu-thiosal)2] (C5) was prepared as described
in Section 2.1.3 using (S-butyl)-2-thiosalicylic acid, (0.1289 g,
0.613 mmol) instead of (S-benzyl)-2-thiosalicylic acid. Yield:
0.0941 g (58.43%). Anal. Calc. for C22H26O4S2Pd (Mr = 524.960): C,
50.33; H, 4.99; S, 12.22. Found: C, 50.52; H, 4.51; S, 12.56%. IR
(KBr, cmÀ1): 3420, 1634, 1616, 1561, 1327, 1146, 753, 698. 1H
NMR (200 MHz, DMSO-d6, d ppm): 0.95 (t, 6H, CH3), 1.33 (m, 4H,
CH2), 1.62 (m, 4H, CH2), 2.79 (t, 4H, CH2), 7.24–8.19 (m, 8H, Ar).

´
71
G.P. Radic et al. / Polyhedron 31 (2012) 69–76
Table 1
Crystal data and structure refinement for the [Pd(S-bz-thiosal)2] complex (C1).
2.3.2. Test microorganisms
The antimicrobial activity of the ligands L1–L5 and the corre-
sponding palladium(II) complexes C1–C5 was tested against 26
microorganisms. The experiment involved 14 strains of pathogenic
bacteria, including five standard strains (Escherichia coli ATCC
25922, Enterococcus faecalis ATCC 29212, Pseudomonas aeruginosa
ATCC 27853, Staphylococcus aureus ATCC 25923, Bacillus subtilis ATCC
6633) and nine clinical isolates (Escherichia coli, Enterococcus faecalis,
P. aeruginosa, S. aureus, Sarcina lutea, Bacillus subtilis, Proteus mirabilis,
Salmonella enterica, Salmonella typhimurium). Also, four species of
probiotic bacteria (Lactobacillus plantarum PMFKG-P31, Bacillus
subtilis IP 5832 PMFKG-P32, Bifidobacterium animalis subsp. lactis
PMFKG-P33, Lactobacillus rhamnosus PMFKG-P35), five species of
mould (Aspergillus niger ATCC 16404, Aspergillus fumigatus PMFKG-
F23, Aspergillus flavus PMFKG-F24, Aspergillus restrictus PMFKG-F25,
A. niger PMFKG-F26) and three yeast species (Candida albicans
(clinical isolate), Rhodotorula sp. PMFKG-F27, Saccharomyces boulardii
PMFKG-P34) were tested. All clinical isolates were a generous gift
fromthe Institute ofPublic Health, Kragujevac. Theothermicroorgan-
isms were provided from a collection held by the Microbiology
Laboratory Faculty of Science, University of Kragujevac.
Identification code
Empirical formula
Formula weight
T (K)
CCDC 824331
28H22O4S2Pd
592.98
C
123(2)
k (Å)
0.71073
monoclinic
P21/c
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
12.0280(5)
21.0330(8)
9.5049(4)
90
a
(°)
b (°)
92.578(2)
90
2402.16(17)
4
1.640
0.981
c
(°)
V (Å3)
Z
Dcalc (g/cm3)
Absorption coefficient (mmÀ1
F(000)
)
1200
Crystal size (mm3)
0.16 Â 0.04 Â 0.02
2.96–25.02°
À13 6 h 6 14, À23 6 k 6 25,
À11 6 l 6 11
13559
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to h = 25.02°
Absorption correction
Maximum and minimum
transmission
4212 [Rint = 0.1276]
99.3%
multi-scan
0.9807 and 0.8589
2.3.3. Suspension preparation
Bacterial and yeast suspensions were prepared by the direct
colony method. The colonies were taken directly from the plate
and were suspended in 5 cm3 of sterile 0.85% saline. The turbidity
of the initial suspension was adjusted by comparing it with 0.5
McFarland’s standard (0.5 cm3 1.17% w/v BaCl2 Â 2H2O + 99.5 cm3
1% w/v H2SO4) [35]. When adjusted to the turbidity of the 0.5
McFarland’s standard, the bacteria suspension contains about
108 colony forming units (CFU)/cm3 and a suspension of yeast con-
tains 106 CFU/cm3. Ten-fold dilutions of the initial suspension were
additionally prepared into sterile 0.85% saline. The suspensions of
fungal spores were prepared by gentle stripping of spore from
slopes with growing aspergilli. The resulting suspensions were
1:1000 diluted in sterile 0.85% saline.
Refinement method
full-matrix least-squares on F2
4212/78/316
0.981
R1 = 0.0624, wR2 = 0.1034
R1 = 0.1215, wR2 = 0.1179
0.587 and À0.637
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r(I)]
Largest difference in peak and hole
(e ÅÀ3
)
13C NMR (50 MHz, DMSO-d6, d ppm): 13.4 (CH3), 20.5 (CH2), 21.6
(CH2), 33.7 (CH2), 123.8, 124.4, 126.3, 130.2, 131.9, 135.9 (Ar),
171.9 (COOÀ).
2.3.4. Microdilution method
Antimicrobial activity was tested by determining the minimum
inhibitory concentrations (MIC) and minimum microbicidal
concentration (MMC) using the microdilution plate method with
resazurin [36]. The 96-well plates were prepared by dispensing
2.2. Crystal structure determination
Cystals of the [Pd(S-bz-thiosal)2] complex (C1) suitable for X-ray
determination were obtained by slow crystallization from a MSO-
water system. The structural data were collected by a Bruker-Nonius
Kappa CCD diffractometer equipped with an APEXII detector using
100
Sabouraud dextrose broth for fungi and yeasts, into each well. A
100 L aliquot from the stock solution of the tested compound
(with a concentration of 2000
g/cm3) was added into the first
lL of nutrient broth, Mueller–Hinton broth for bacteria and
l
graphite monochromatised MoKa radiation. The COLLECT [29] data
l
collection software was used and obtained data were processed with
DENZO-SMN [30]. The structures were solved by direct methods,
using SIR-2004 [31], and refined on F2, using SHELXL-97 [32]. The
reflections were corrected for Lorenz-polarization effects and
multi-scan absorption correction was applied [33]. The hydrogen
atoms were inserted at their calculated positions with isotropictem-
perature factors [Uiso(H) factors of 1.2 times Ueq(C)] and refined as
riding atoms. The figure was drawn with ORTEP-3 [34]. Other exper-
imental X-ray data are shown in Table 1.
row of the plate. Then, twofold, serial dilutions were performed
by using a multichannel pipette. The obtained concentration range
was from 1000 to 7.81 l lL aliquot of diluted bacterial
g/cm3. A 10
yeast suspension and suspension of spores were added to each well
to give a final concentration of 5 Â 105 CFU/cm3 for bacteria and
5 Â 103 CFU/cm3 for fungi and yeast. Finally, 10
lL resazurin solu-
tion was added to each well inoculated with bacteria and yeast.
Resazurin is an oxidation–reduction indicator used for the evalua-
tion of microbial growth. It is a blue non-fluorescent dye that be-
comes pink and fluorescent when reduced to resorufin by
oxidoreductases within viable cells [37]. The inoculated plates
were incubated at 37 °C for 24 h for bacteria, 28 °C for 48 h for
the yeast and 28 °C for 72 h for fungi. The MIC was defined as
the lowest concentration of the tested substance that prevented
the resazurin color change from blue to pink. For fungi, the MIC
values of the tested substances were determined as the lowest con-
centration that visibly inhibited mycelia growth.
2.3. In vitro antimicrobial assay
2.3.1. Test substances
The tested compounds were dissolved in DMSO and then di-
luted into nutrient liquid medium to achieve a concentration of
10%. An antibiotic, doxycycline (Galenika A.D., Belgrade), was dis-
solved in nutrient liquid medium, a Mueller–Hinton broth (Torlak,
Belgrade), while an antimycotic, fluconazole (Pfizer Inc., USA), was
dissolved in Sabouraud dextrose broth (Torlak, Belgrade).
Doxycycline and fluconazole were used as a positive control. A
solvent control test was performed to study the effect of 10% DMSO
on the growth of microorganisms. It was observed that 10% DMSO

´
G.P. Radic et al. / Polyhedron 31 (2012) 69–76
72
O
OH
O
ONa
O
OH
C
C
C
SH
S
S
Ethanol/H2O
H+
R
R
+
R-X
+
2NaOH
R= Benzyl, methyl, ethyl, propyl, butyl
Scheme 1. The preparation of the benzyl, methyl, ethyl, propyl and butyl esters of 2-thiosalicylic acid.
O
OH
O
O
C
C
O
S
C
O
S
S
Pd
R
2LiOH
K2PdCl4 + 2
R
R
R= Benzyl(C1), methyl(C2), ethyl(C3),
propyl(C4), butyl(C5)
Scheme 2. The preparation of the [Pd(S-R-thiosal)2].
did not inhibit the growth of microorganisms. Also, in the experi-
ment, the concentration of DMSO was additionally decreased be-
cause of the twofold serial dilution assay (the working
concentration was 5% and lower). Each test included growth con-
trol and sterility control. All tests were performed in duplicate
and the MICs were constant. Minimum bactericidal and fungicidal
and 1674 cmÀ1 for L5) are located at lower energies than expected
(1700–1750 cmÀ1) [38,39]. This could be explained by the pres-
ence of big R–S groups in the ortho position. The positions of these
bands in corresponding C1–C5 complexes are in the expected re-
gion (1600–1650 cmÀ1
)
[18] (1633 and 1616 cmÀ1 for C1,
1619 cmÀ1 for C2, 1587 cmÀ1 for C3, 1589 cmÀ1 for C4 and 1633
and 1615 cmÀ1 for C5), confirming their deprotonation and
coordination in the complexes. The presence of two bands for C1
and C5 suggests small energy differences. These differences could
be explained due to the presence of large benzyl and butyl groups
and their steric impact to the phenyl part of the thiosalicylic acid.
Chemical shifts arising from carbon and hydrogen atoms of this
type of thioether and the corresponding palladium(II) complexes
are found at the expected, and almost the same positions. Some
differences in the chemical shifts of the carbon atoms of the car-
boxylic groups of the S-benzyl, S-methyl, S-ethyl, S-propyl and S-
concentrations were determined by plating 10 lL of samples from
wells where no indicator color change was recorded, on nutrient
agar medium. At the end of the incubation period the lowest con-
centration with no growth (no colony) was defined as the mini-
mum microbicidal concentration.
2.3.5. Statistical analysis
All statistical analyses were performed using SPSS package.
Mean differences were established by the Student’s t-test. Data
were analyzed using one-way analysis of variance (ANOVA). In
all cases P values <0.05 were considered statistically significant.
3. Results and discussion
3.1. Synthesis and chemical characterization
S-Alkyl (R = benzyl, methyl, ethyl, propyl and butyl) derivatives
of thiosalicylic acid were prepared by the alkylation of thiosalicylic
acid using the corresponding alkyl halogenides in alkaline water–
ethanol solution (Scheme 1). The corresponding [Pd(S-R-thiosal)2]
complexes were obtained by the direct reaction of K2[PdCl4] with
the S-alkyl derivative of thiosalicylic acid (molar ratio 1:2) in water
solution with satisfactory yields (more than 50%) (Scheme 2).
A bidentate S–O coordination of the ligands L1–L5 to the Pd(II)
ion is expected. The lack of S–H stretching absorption bands in the
complexes C1–C5 in the range 2600–2550 cmÀ1 [38] (2559 cmÀ1
for L1, 2560 cmÀ1 for L2, 2562 cmÀ1 for L3, 2555 cmÀ1 for L4 and
2556 cmÀ1 for L5) suggests the deprotonation of the S–H groups
of the ligands and their coordination to the Pd(II) ion in the com-
plexes. The carboxylate asymmetric stretching bands of ligands
(1674 cmÀ1 for L1 and L2, 1682 cmÀ1 for L3, 1678 cmÀ1 for L4
Fig. 1. Molecular structure of the [Pd(S-benzyl)2] complex (C1) (heteroatoms are
shown with an octant shaded mode).

´
73
G.P. Radic et al. / Polyhedron 31 (2012) 69–76
Table 2
Selected bond lengths (Å) and angles (°) for the [Pd(S-benzyl)2] complex (C1).
Bond lengths
(Å)
Bond angles
(°)
Pd(1)–O(2)
Pd(1)–O(4)
Pd(1)–S(1)
Pd(1)–S(2)
S(1)–C(3)
2.024(4)
2.034(4)
2.246(2)
2.254(2)
1.778(7)
1.829(7)
1.787(7)
1.830(7)
1.278(8)
1.279(8)
1.229(8)
1.235(8)
1.516(10)
1.518(9)
1.493(9)
1.506(10)
O(2)–Pd(1)–O(4)
O(2)–Pd(1)–S(1)
O(4)–Pd(1)–S(1)
O(2)–Pd(1)–S(2)
O(4)–Pd(1)–S(2)
S(1)–Pd(1)–S(2)
C(3)–S(1)–C(8)
C(3)–S(1)–Pd(1)
C(8)–S(1)–Pd(1)
C(17)–S(2)–C(22)
C(17)–S(2)–Pd(1)
C(22)–S(2)–Pd(1)
C(1)–O(2)–Pd(1)
C(15)–O(4)–Pd(1)
88.4(2)
89.84(14)
172.52(15)
172.77(14)
89.70(14)
92.94(7)
105.9(3)
100.0(2)
104.4(2)
105.9(3)
99.1(2)
S(1)–C(8)
S(2)–C(17)
S(2)–C(22)
O(2)–C(1)
O(4)–C(15)
O(1)–C(1)
O(3)–C(15)
C(16)–C(15)
C(2)–C(1)
C(22)–C(23)
C(9)–C(8)
105.7(2)
128.5(4)
127.5(5)
Short contacts
HÁ Á ÁA (Å)
DÁ Á ÁA (Å)
(°)
Dihedral angles
(°)
C6–H6Á Á ÁO4a
3.318(9)
3.414(9)
3.293(9)
3.305(9)
3.380(9)
3.471(9)
3.388(9)
3.223(10)
3.653(10)
3.617(10)
3.778(10)
3.308(10)
125
155
156
127
134
144
168
127
174
159
153
Pd(1)–S(2)–C(22)–C(23)
Pd(1)–S(1)–C(8)–C(9)
Pd(1)–S(1)–C(3)–C(2)
Pd(1)–S(2)–C(17)–C(16)
C(3)–C(2)–C(1)–O(2)
C(17)–C(16)–C(15)–O(4)
À69.1(5)
À52.0(5)
À42.3(6)
À40.5(6)
29.2(11)
34.2(10)
C11–H11Á Á ÁO2b
C14–H14Á Á ÁO3c
C20–H20Á Á ÁO1b
C22–H22BÁ Á ÁO3d
C24–H24Á Á ÁO3d
C25–H25Á Á ÁO1e
C27–H27Á Á ÁO1a
C4–H4Á Á Ápd,g
2.71
2.71
2.87
C18–H18Á Á Ápd,g
C22–H22AÁ Á Ápf,h
p
Á Á Ápd,h
Symmetry operators:
a
Àx, Ày + 1, Àz.
b
Àx + 1, Ày + 1, Àz.
c
x, y, z + 1.
d
x, Ày + 1/2, z + 1/2.
e
Àx, yÀ1/2, Àz + 1/2.
f
x, Ày + 1/2, z À 1/2.
g
Distance to closest C atom.
h
Distance from C to closest C atom.
butyl derivatives of thiosalicylic acid (167.5, 171.6, 171.4, 171.6,
171.4 ppm) and the corresponding palladium(II) complexes
(171.5, 171.8, 172.0, 172.5, 171.9 ppm), respectively, can be ob-
served. These differences could be explained by the coordination
of the carboxylic group to the palladium(II) ion.
tation of benzyl groups, almost over the phenyl residues originat-
ing from another S-benzyl-thiosalicylic ligand. The non-parallel
positions of the phenyl and benzyl groups, and therefore non-sym-
metric structure of the [Pd(S-bz-thiosal)2] complex, can also be
It can be concluded from IR and NMR spectra of the ligands and
the corresponding complexes that the ligands are bidentately coor-
dinated to the palladium(II) ion, but nothing can be concluded
about geometry of complexes.
3.2. Description of the crystal structure
The [Pd(S-bz-thiosal)2] complex (C1) crystallizes in the P21/c
space group of the monoclinic crystal system. The molecular struc-
ture of the C1 complex is shown in Fig. 1 Selected geometric
parameters are listed in Table 2. The crystal structure analysis
shows the bidentate and a long cis-S–cis-O coordination (known
for Pd-complexes) [40] of the S-benzyl-thiosalicylic acid ligand
L1 to the Pd(II) ion (Fig. 1.) and the expected square-planar geom-
etry. All the bonds are in the expected region. But a small deforma-
tion of the geometry around Pd(II) [angles O(2)–Pd(1)–O(4)
88.37(19)° and S(1)–Pd(1)–S(2) 92.94(7)°] is expected and can be
explained as a consequence of the presence of large S atoms in
cis positions.
The two six-membered rings involving the Pd atom are in skew-
chair conformations in C1 (Fig. 1) and are practically equal, as ex-
pected due to restrictions of the coordination geometry around Pd
and the stiff thiosalicylic moieties. This is the reason for the orien-
Fig. 2. A pair of C1 complexes formed by intermolecular interactions: C–HÁ Á ÁO
(green, accepted by O3),
pÁ Á Áp (red, closest C25Á Á ÁC28) and C–HÁ Á Áp (blue, closest
accepted by C24 or C21). (Colour online.)

Table 3
In vitro antimicrobial activity of the tested ligands L1–L5 and the corresponding palladium(II) complexes C1–C5.
Species
L1
C1
L2
C2
L3
C3
L4
C4
L5
C5
Doxycycline/
fluconazole
MICa
MMCb MIC
MMC MIC
1000 500
MMC MIC
MMC MIC
MMC MIC MMC MIC
MMC MIC MMC MIC
MMC MIC
MMC MIC
1000 31.25
MMC
Bifidobacterium animalis subsp. lactis 500
500
500
1000
500
500
250
500
500
500
1000 1000 1000
500
500
1000
>1000 250 500
>1000 250 500
500 500
500
500
250
1000
500
>1000 250 500
250 500
250 250
1000
1000
1000
1000
500
62.5
15.63
7.81
31.25
3.75
62.5
Bacillus subtilis IP 5832
Lactobacillus plantarum
Lactobacillus rhamnosus
Sarcina lutea
Enterococcus faecalis
E. faecalis ATCC 29212
Bacillus subtilis
Bacillus subtilis ATCC 6633
Staphylococcus aureus
S. aureus ATCC 25923
Escherichia coli
Escherichia coli ATCC 25922
Pseudomonas aeruginosa
P. aeruginosa ATCC 27853
Proteus mirabilis
Salmonella enterica
Salmonella typhimurium
Candida albicans
Rhodotorula sp.
Saccharomyces boulardii
Aspergillus niger
Aspergillus niger ATCC 16404
Aspergillus restrictus
Aspergillus fumigatus
Aspergillus flavus
500
500
500
500
500
500
500
500
1000
500
>1000 250
>1000 500
500
500
1.953
0.448
>1000 >1000 1000 1000 1000
>1000 500
1000 500
>1000 500
1000 1000
1000
>1000 250 250
>1000 >1000 500 500
1000 250 500
>1000 250 250
>1000 >1000 250 250
1000 >1000 250 250
1000 500 500
>1000 500 500
>1000 >1000 500 500
500 500
1000 >1000 500 >1000 >1000 >1000 1000 1000 7.81
500 >1000 250 250 1000 >1000 250 500 <0.448
1000 >1000 500 500 >1000 >1000 1000 1000 7.81
500
1000
1000
500
500
250
500
1000
250
500
1000
500
500
1000 500
500
500
500
1000 1000
500
500
500
>1000 1000 1000 1000
1000
500
500
500
1000
500
250
250
250
500
500
500
500
500
1000
125
1000
500
1000
500
1000
500
500
500
500
500
1000
1000
250 500
250 250
1000
1000
1000
1000
1000
500
1000 7.81
62.5
1000
>1000 250
>1000 250
>1000 125
500
500
500
500
0.112
1.953
0.448
0.224
1.953
31.25
7.81
1000 >1000 250 250
250
500
1000 >1000 500 500
1000 >1000 500 500
>1000 500
1000 500
1000
1000
250 250
500 500
1000 1000
>1000 >1000 500
3.75
>1000 >1000 1000 1000 1000
>1000 500
>1000 500
>1000 500
>1000 250
>1000 500
>1000 500
>1000 500
1000
>1000 >1000 1000 1000 7.81
>1000 >1000 1000 1000 15.625
15.63
31.25
>250
125
>250
31.25
125
1000
1000
1000
1000
62.5
2000
1000
1000
1000
1000
500
1000
1000
1000
>1000 1000 1000 1000
>1000 1000 1000 500
>1000 500
>1000 500
>1000 1000 1000 1000
>1000 1000 1000 1000
1000 1000
500 500
1000 1000
500 1000
1000 1000
1000 1000 1000
500 1000 500
>1000 500 500
>1000 250 500
>1000 500 500
>1000 500 500
500
500
>1000 500 1000
>1000 500 1000
1000
500
>1000 1000 1000 250
>1000 500
1000 500
1000 1000
1000 62.5
1000 250
1000 >1000 500 1000
1000 >1000 500 1000
1000 >1000 500 1000
>1000 >1000 500
>1000 >1000 1000 1000 15.625
>1000 >1000 1000 1000 15.625
1000
1000
1000
1000
1000
500 500
>1000 >1000 500
>1000 >1000 500
1000
>1000 >1000 500
>1000 >1000 500
500
1000 1000
1000 500
1000 1000
1000 500
1000
1000
500 1000 1000 1000
250 500 1000 1000
500 1000 1000 1000
500 1000
250 500
500 1000
250 500
500 500
31.3 125
<7.8 <7.8
62.5 62.5
1000
500
500
1000
1000
250
62.5
125
1000
1000
1000
500
500
500
1000 62.5
1000 62.5
1000 31.25
>1000 500
>1000 1000 1000 1000
500 500 1000 500
500 1000 500
1000
1000
1000
>1000 250
500
1000 62.5
31.3 250 500
31.3 31.25 500
125 250 1000
500
1000 >1000 >1000 1000 1000 1000
>1000 500 1000 500
1000 125 250 500
<7.8 15.68 15.68 15.68 <7.8 <7.8
15.7 15.68 125 125 62.5 500
1000
250
62.5
1000
500
>1000 125
250
500
1000
250
1000
500
1000 500
62.5
31.25 250
62.5
62.5 62.5
<7.8 <7.8
62.5
1000
15.68 125
125 500
a
MIC values (
MMC values (
l
g/cm3) – means inhibitory activity.
l
g/cm3) – means microbicidal activity.
b

´
75
G.P. Radic et al. / Polyhedron 31 (2012) 69–76
explained by a skew-chair conformation of the six-membered rings
4. Conclusion
and, also, by the larger orientational freedom of the benzyl groups
bonded to the S(1) and S(2) atoms. The spatial orientations of the
benzyl groups are not similar, as can be seen from the values of
the Pd(1)–S(1)–C(8)–C(9) and Pd(1)–S(2)–C(22)–C(23) dihedral
angles (Table 2). Although the aromatic rings of the phenyl and
benzyl groups seem to be over each other, the distance between
The results of antimicrobial activity showed that the tested li-
gands and the corresponding palladium(II) complexes showed dif-
ferent degrees of antimicrobial activity in relation to the tested
species. The tested ligands, with few exceptions, showed low anti-
microbial activity. The palladium(II) complexes showed selective
and moderate activity. A difference in the antimicrobial activity
was observed between the ligands and the corresponding palla-
dium(II) complexes, with higher activities being displayed for the
palladium(II) complexes. Interesting results were obtained for
Aspergillus species, which are common in the environment and
which cause the infection known as aspergillosis. The tested com-
plexes reacted better than the positive control. The molecular
structure in the crystalline state was obtained for complex C1
and showed an unsymmetrical cis configuration around the Pd
atom. The crystal structure was found to be stabilized by C–
them is too long for any reasonable intramolecular
p p interac-
Á Á Á
tions to occur. The deprotonated carboxyl groups are also twisted
out of the adjacent aromatic plane, as can be seen from the C(3)–
C(2)–C(1)–O(2) and C(17)–C(16)–C(15)–O(4) dihedral angles from
Fig. 1.
The spatial orientation of the benzyl groups in the crystal struc-
ture is, of course, much more significantly defined by intermolecu-
lar interactions during the crystallization process, in which the
attractive and repulsive contacts compete with each other and a
stable balance between them must be achieved. The lack of strong
hydrogen bond donors gives space for much weaker C–HÁ Á ÁO inter-
actions to dominate as attractive ones in the crystallization process
of C1. Eight such interactions are found from the structure (Table
HÁ Á ÁO, C–HÁ Á Á
p-type and
pÁ Á Áp interactions.
Acknowledgements
2). Three potential C–HÁ Á Á
Two complexes seem to form a pair involving two C–HÁ Á ÁO, all
three C–HÁ Á Á and one additional Á Á Á contact in the x, Ày + ½,
z + ½ direction (Fig. 2).
Based on S,O-coordination of all the ligands and the crystal struc-
ture of the [Pd(S-bz-thiosal)2] complex, it can be assumed that the
other complexes occur in the form of a cis-S-cis-O geometric isomer.
p-type interactions were also found.
The authors are grateful for financial support from the Ministry
of Education and Science of Republic of Serbia (Projects Nos.
OI172016 and 41010) and the Academy of Finland (Project No.
122350).
p
p p
Appendix A. Supplementary data
3.3. Microbiology
CCDC 824331 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
The results of in vitro testing of antimicrobial activities for the
five new palladium complexes are shown in Table 3. The solvent
(10% DMSO) did not inhibit the growth of the tested
microorganisms.
The intensity of the antimicrobial action varied depending on
the species of microorganism and on the type of tested compound.
In general, the activity of the complexes was higher than the corre-
sponding ligands (p < 0.05). MICs and MMCs values for ligands
References
[1] A. Kumar Chhakkar, L. Rai Kakkar, Fresenius J. Anal. Chem. 347 (1993) 483.
[2] G.R.E.C. Gregory, P.G. Jeffery, Analyst 92 (1967) 293.
[3] M.J. Gismera, J.R. Procopio, M. Teresa-Sevilla, L. Hernandez, Electroanalysis 15
(2003) 126.
[4] M. Aydin, N. Arsu, Y. Yagci, Macromol. Rapid Commun. 24 (2003) 718.
[5] D. Shander, G. Ahluwalia, D. Grosso, US Patent 5411991.
[6] H. Jacobelli, US Patent 20050267095.
[7] J. Halaschek-Wiener, Y. Kloog, V. Wacheck, B. Jansen, J. Invest. Dermat. 120
(2003) 109.
[8] I. Sadao, S. Fujio, M. Eiichi, K. Keita, Kokai Tokkyo Koho (2000) 127.
[9] B.T. Khan, J. Bhatt, K. Najmoddin, S. Shamsuddin, K. Annapoorna, J. Inorg.
Biochem. 44 (1991) 55.
[10] C. Navarro-Eanninger, J.M. Peréz, F. Zamora, V.M. Gonzáles, J.M. Masaguer, C.
Alonso, J. Inorg. Biochem. 52 (1993) 37.
[11] I. Brudzinska, Y. Mikata, M. Obata, C. Ohtsuki, S. Yano, Bioorg. Med. Chem. Lett.
14 (2004) 2533.
[12] A. Garoufis, S.K. Hadjikakou, N. Hadjiliadis, Coord. Chem. Rev. 253 (2009) 1384.
[13] W. Guerra, E. de Andrade Azevedo, A.R. de Souza Monteiro, M. Bucciarellia-
Rodriguez, E. Chartone-Souza, A.M. Amaral Nascimento, A.P. Soares Fontes, L.
Le Moyec, E.C. Pereira-Maia, J. Inorg. Biochem. 99 (2005) 2348.
[14] L.M.M. Vieira, M.V. de Almeida, M.C.S. Lourenço, F.A.F.M. Bezerra, A.P.S. Fontes,
Eur. J. Med. Chem. 44 (2009) 4107.
[15] D. Kovala-Demertzi, M.A. Demertzis, J.R. Miller, C. Papadopoulou, C. Dodorou,
G. Filousis, J. Inorg. Biochem. 86 (2001) 555.
[16] R.R. Coombs, M.K. Ringer, J.M. Blacquiere, J.C. Smith, J.S. Neilsen, Y.-S. Uh, J.B.
Gilbert, L.J. Leger, H. Zhang, A.M. Irving, S.L. Wheaton, C.M. Vogels, S.A.
Westcott, Transition Met. Chem. 30 (2005) 411.
[17] M. Ali, M. Aminul, R. Butcher, C. Karen, Transition Met. Chem. 31 (2006) 79.
[18] I. Kizilcikli, Y.D. Kurt, B. Akkurt, A.Y. Genel, S. Birteksöz, G. Ötük, B. Ülküseven,
Folia Microbiol 52 (2007) 15.
[19] N.M. Aghatabay, M. Somer, M. Senel, B. Dulger, F. Gucin, Eur. J. Med. Chem. 42
(2007) 1069.
were in range 15.68 to >1000
l
g/cm3, and for complexes <7.8 to
1000
l
g/cm3. The best effect was observed for L3 and L4 for the li-
gands, and C3 and C4 for the complexes (p < 0.05).
The palladium(II) complexes showed significant antifungal activ-
ity. The most sensitive was A. fumigatus, A. flavus and A. restrictus.
The activity of the complexes was better than the positive control
fluconazole (p < 0.05). The obtained concentrations of palladium(II)
complexes which inhibit the growth of moulds were from <7.8 to
500 l
g/cm3. Antimicrobial testing of newly synthesized complexes
´
of palladium(II), done by Vasic et al., led to similar results [41]. The
standard and clinical strain of A. niger did not show sensitivity
similar to that mentioned, where the MIC went from 250 to
1000 l
g/cm3.
The tested compounds did not affect the growth of yeasts or
their activities were very low. The MIC and MMC values for yeasts
were from 500 to >1000
C4 against Rhodotorula sp., where the MIC was 250
l
g/cm3, except for the complexes C3 and
l
g/cm3.
All the tested compounds demonstrated weak and moderate
antibacterial activity. The Gram-positive bacteria were more sensi-
tive than the Gram-negative bacteria, especially for the activity of
the complexes. The most sensitive was S. aureus with a MIC value
of 125
bacteria were 500 and 1000
and C3 exhibited somewhat stronger antibacterial activity towards
P. aeruginosa ATCC 27853 (MIC = 250
g/cm3).
The probiotics showed sensitivity similar to the sensitivity of
the other bacteria. The MICs were from 250 to >1000
g/cm3 and
the MMCs were from 500 to >1000
g/cm3.
l
g/cm3 for the complex C5. The MICs for Gram-negative
l
g/cm3. The tested complexes C2
[20] M.K. Biyala, K. Sharma, M. Swami, N. Fahmi, R. Vir Singh, Transition Met. Chem.
33 (2008) 377.
[21] J.D. Smith, J. Org. Chem. 76 (6) (2011) 1513.
l
[22] H.V. Huynh, Organometallics 29 (6) (2010) 1479.
[23] J. Nakayama, T. Fujita, M. Hoshino, Chem. Lett. 11 (1982) 1777.
[24] J.J. Donleavy, J. English Jr., J. Am. Chem. Soc. 62 (1940) 220.
[25] I.M. Al-Daher, B.M. Al-Saadi, J. Iraq. Chem. Soc. 10 (1) (1985) 84.
l
l

´
G.P. Radic et al. / Polyhedron 31 (2012) 69–76
76
[26] Z. Koric´anac, B. Stankovic´, Arch. Pharm. 28 (1–2) (1978) 87.
[27] C. Nair, H.L. Nigam, Indian J. Chem. 12 (7) (1974) 769.
[28] I. Dema, V. Voicu, Acad. Rep. Populare Romine Studii cercetari chim. 23 (1960)
173.
[29] COLLECT, Bruker AXS, Delft, The Netherlands, 2008.
[30] Z. Otwinowski, W. Minor, in: C.W. Carter Jr., R.M. Sweet (Eds.), Methods
Enzymol., vol. 276: Macromolecular crystallography, part A, Academic Press,
New York, 1997, pp. 307–326.
[31] M.C. Burla, M. Camalli, B. Carrozzini, G.L. Cascarano, C. Giacovazzo, G. Polidori,
R. Spagna, J. Appl. Crystallogr. 38 (2005) 381.
[32] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[33] G.M. Sheldrick, SADABS, University of Göttingen, Germany, 1996.
[34] L.J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[35] J.M. Andrews, J. Antimicrob. Chemother. 56 (2005) 60.
[36] S.D. Sarker, L. Nahar, Y. Kumarasamy, Methods 42 (2007) 321.
[37] E. Banfi, G. Scialino, C. Monti-Bragadin, J. Antimicrob. Chemother. 52 (2003)
796.
[38] R.M. Silverstein, C.G. Bassler, T.C. Morril, Spectrometric Identification of
Organic Compounds, third ed., Wiley International Edition, 1974. p. 113.
[39] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds,
Wiley, New York, 1963. p. 206.
[40] D.A. Langs, C.R. Hare, R.G. Little, Chem. Commun. (London) (1967) 1080.
-
ˇ
[41] G.P. Vasic´, V.V. Glodovic´, I.D. Radojevic´, O.D. Stefanovic´, L.R. Comic´, V.M.
´
´
Ðinovic, S.R. Trifunovic, Inorg. Chim. Acta 363 (2010) 3606.