Synthesis, characterization and antimicrobial activity of copper(II) complexes with some S-alkyl derivatives of thiosalicylic acid. Crystal structure of the binuclear copper(II) complex with S-methyl derivative of thiosalicylic acid

Article abstract of DOI:10.1016/j.poly.2014.04.053

The five new copper(II) complexes with some S-alkyl derivatives of thiosalicylic acid (alkyl = benzyl (L1), methyl (L2), ethyl (L3), propyl (L4), butyl (L5)) have been synthesized and characterized by microanalysis and infrared spectra. The spectroscopica

Full text of DOI:10.1016/j.poly.2014.04.053

Accepted Manuscript
Synthesis, characterization and antimicrobial activity of copper(II) complexes
with some S-alkyl derivatives of thiosalicylic acid. Crystal structure of the bi-
nuclear copper(II) complex with S-methyl derivative of thiosalicylic acid
Miloš V. Nikolić, Marina Ž. Mijajlović, Verica V. Jevtić, Zoran R. Ratković,
Ivana D. Radojević, Ljiljana R. Čomić, Slađana B. Novaković, Goran A.
Bogdanović, Srećko R. Trifunović, Gordana P. Radić
PII:
S0277-5387(14)00273-3
DOI:
http://dx.doi.org/10.1016/j.poly.2014.04.053
POLY 10697
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
12 December 2013
26 April 2014
Please cite this article as: M.V. Nikolić, M. Mijajlović, V.V. Jevtić, Z.R. Ratković, I.D. Radojević, L.R. Čomić,
S.B. Novaković, G.A. Bogdanović, S.R. Trifunović, G.P. Radić, Synthesis, characterization and antimicrobial
activity of copper(II) complexes with some S-alkyl derivatives of thiosalicylic acid. Crystal structure of the binuclear
copper(II) complex with S-methyl derivative of thiosalicylic acid, Polyhedron (2014), doi: http://dx.doi.org/
10.1016/j.poly.2014.04.053
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Synthesis, characterization and antimicrobial activity of copper(II)
complexes with some S-alkyl derivatives of thiosalicylic acid. Crystal
structure of the binuclear copper(II) complex with
S-methyl derivative of thiosalicylic acid
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Miloš V. Nikolića, Marina Ž. Mijajlovića, Verica V. Jevtićb, Zoran R. Ratkovićb, Ivana D.
Radojevićc, Ljiljana R. Čomićc, Slađana B. Novakovićd, Goran A. Bogdanovićd, Srećko R.
Trifunovićb, Gordana P. Radića*
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aFaculty of Medical Sciences, University of Kragujevac, Svetozara Markovića 69, 34000 Kragujevac, Republic of Serbia;
bDepartment of Chemistry, Faculty of Science, University of Kragujevac, Radoja Domanovića 12, 34000 Kragujevac,
Republic of Serbia;
cDepartment of Biology and Ecology, Faculty of Science, University of Kragujevac, Radoja Domanovića 12, 34000
Kragujevac, Republic of Serbia;
dVinča Institute of Nuclear Sciences, Laboratory of Theoretical Physics and Condensed Matter Physics, University of
Belgrade, PO Box 522, 11001 Belgrade, Republic of Serbia;
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Abstract
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The five new copper(II) complexes with some S-alkyl derivatives of thiosalicylic acid (alkyl =
= benzyl (L1), methyl (L2), ethyl (L3), propyl (L4), butyl (L5)) have been synthesized and
characterized by microanalysis and infrared spectra. The spectroscopically predicted structure of the
obtained binuclear copper(II) complex with S-methyl derivative of thiosalicylic acid was confirmed by
X-ray analysis. Single crystals suitable for X-ray measurements were obtained by slow crystallization
from a water solution. The compound crystallizes with two binuclear Cu(II) complex molecules in the
* Corresponding author, Tel.: +38134306800; +38134306800
e-mail address: vasic_gordana@yahoo.com (G.P. Radić)
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asymmetric unit. Both molecules have typical paddle-wheel structure with apical positions occupied
by water molecules. The independent molecules showed slight difference in configuration mainly
reflected in the different orientation of the phenyl rings relating to their carboxylate groups.
Antimicrobial activity of these complexes was tested by microdilution method and both minimal
inhibitory and microbicidal concentration were determined. The intensity of the antimicrobial activity
varied depending on the species of microorganism and the compound type. In general, the activity of
the complexes was higher than or similar to the corresponding ligands. All the tested complexes
demonstrated moderate or selective antibacterial activity and low antifungal activity.
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Keywords: S-alkyl derivatives of thiosalicylic acid; copper(II) complexes; infrared spectra; crystal structure;
antimicrobial activity
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1. Introduction
The complex forming ability of thiosalicylic acid with many metal ions has been the
subject of several investigations [1-6]. Also, detailed studies on the complexation equilibria of
copper(II) with thiosalicylic acid have been previously published [7]. The synthesis and
characterization of copper(II) complexes with thiosalicylic acid proceeded the studies on the
interaction of metals with ligands containing biological and pharmacological activities. The
antimicrobial activity of dinuclear and mononuclear copper(II) complexes with the COO
group coordinated to Cu for some bacteria, yeast and mold was demonstrated
[8-16]. The previous work reported the formation of a light blue complex containing
copper(II) with thiosalicylic acid in which the metal ion occupied only one of two potential
sites of the ligand: the –SH group [17]. Then, Ferrer et. al. reported synthesis and
characterization of a new green dimeric complex copper(II) with thiosalicylic acid and
pyridine [18].
Our investigations presented in this paper are focused on the synthesis of the
corresponding copper(II) complexes of S-alkyl derivatives as well as in vitro antimicrobial
activity of the ligands and the complexes. The preparation and spectral characterization of
S-alkyl derivatives of thiosalicylic acid were published earlier [19-23]. The structures of the
isolated complexes are proposed on the basis of elemental microanalysis and infrared spectra.
The dimeric structures of isolated copper(II) complexes are confirmed on the basis of an
X-ray structural study of copper(II) complex with S-methyl derivative of thiosalicylic acid,
[Cu2(S-met-thiosal)4(H2O)2]. Our research is are related to the impact of the newly
synthesized copper(II) complexes on some pathogenic bacteria and fungi, in particular on
probiotics, since being used as supplements they play a significant role in protection and
maintenance of the balance of intestinal microflora during antibiotic therapy.
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2. Experimental
2.1. Materials and measurements
The reagents were obtained commercially and used without further purification.
Elemental analyses were done on a Vario III CHNOS Elemental Analyzer, Elemental
Analysensysteme GmbH. For infrared spectra
a
Perkin-Elmer FTIR 31725-X
spectrophotometer and KBr pellet technique were employed. The magnetic measurements of
synthesized complexes were performed at 294 K by the Evans’ method using a MSB-MK1
balance (Sherwood Scientific Ltd.) with Hg[Co(SCN)4] as calibrant; diamagnetic corrections
were calculated from Pascal’s constants.
2.2. Syntheses
2.2.1. General procedure for the synthesis of S-alkyl derivatives of thiosalicylic acid
(L1)–(L5)
The S-alkyl derivatives of thiosalicylic acid ligands (alkyl = benzyl (L1), methyl (L2),
ethyl (L3), propyl (L4), butyl (L5)) were prepared [19] by alkylation of thiosalicylic acid by
means of the corresponding alkyl halides in alkaline water-ethanol solution.
2.2.2. Preparation of copper(II) complex with S-benzyl derivative of thiosalicylic acid,
[Cu2(S-bz-thiosal)4(H2O)2] (C1)
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Copper(II)-nitrate trihydrate (0.1000 g, 0.4139 mmol) was dissolved in 10.0 mL of
water on a steam bath and S-benzyl thiosalicylate (0.2022 g, 0.8278 mmol) was added. The
reaction mixture was heated for 3 h and during this period 10.0 mL of LiOH water solution
(0.0348 g, 0.8278 mmol) was added in small portions and the solution was filtered and
evaporated to small volume. The blue precipitate of copper(II) complex was separated by
filtration, washed with cold water and air-dried. Yield: 0.1910 g (81.21 %). Anal. Calc. for
[Cu2(S-bz-thiosal)4(H2O)2] = Cu2C56H48O10S4 (Mr = 1136.308): C, 59.19; H, 4.26; S, 11.29.
Found: C, 59.01; H, 4.18; S, 11.14. µ(294 K) = 1.56 µB
2.2.3. Preparation of copper(II) complex with S-methyl derivative of thiosalicylic acid,
[Cu2(S-met-thiosal)4(H2O)2] (C2)
Copper(II)-nitrate trihydrate (0.1000 g, 0.4139 mmol) was dissolved in 10.0 mL of
water on a steam bath and S-methyl derivative of thiosalicylic acid (0.1392 g, 0.8278 mmol)
was added. The reaction mixture was heated for 3 h and during this period 10.0 mL of LiOH
water solution (0.0347 g, 0.8278 mmol) was added in small portions and the solution was
filtered. Single crystals of [Cu2(S-met-thiosal)4(H2O)2], (C2) suitable for X-ray measurements
were obtained by slow crystallization from a water solution by evaporation. Yield: 0.1970 g
(81.74 %). Anal. Calc. for [Cu2(S-met-thiosal)4(H2O)2] = Cu2C32H32O10S4 (Mr = 831.932):
C, 46.20; H, 3.88; S, 15.42. Found: C, 46.17; H, 3.69; S, 15.39. µ(294 K) = 2.30 µB.
2.2.4. Preparation of copper(II) complex with S-ethyl derivative of thiosalicylic acid,
[Cu2(S-et-thiosal)4(H2O)2] (C3)
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Copper(II)-nitrate trihydrate (0.1000 g, 0.4139 mmol) was dissolved in 10.0 mL of
water on a steam bath and S-ethyl derivative of thiosalicylic acid (0.1509 g, 0.8278 mmol)
was added. The reaction mixture was heated for 3 h and during this period 10.0 mL of LiOH
water solution (0.0347 g, 0.8278 mmol) was added in small portions and the solution was
filtered and evaporated to small volume. The blue precipitate of copper(II) complex was
separated by filtration, washed with cold water and air-dried. Yield: 0.1490 g (81.07 %). Anal.
Calc. for [Cu2(S-et-thiosal)4(H2O)2] = Cu2C36H40O10S4 (Mr = 888.036): C, 48.69; H, 4.54;
S, 14.44. Found: C, 48.55; H, 4.39; S, 14.28. µ(294 K) = 1.99 µB.
2.2.5. Preparation of copper(II) complex with S-propyl derivative of thiosalicylic acid,
[Cu2(S-pr-thiosal)4(H2O)2] (C4)
Copper(II)-nitrate trihydrate (0.1000 g, 0.4139 mmol) was dissolved in 10.0 mL of
water on a steam bath and S-propyl derivative of thiosalicylic acid (0.1625 g, 0.8278 mmol)
was added. The reaction mixture was heated for 3 h and during this period 10.0 mL of LiOH
water solution (0.0347 g, 0.8278 mmol) was added in small portions and the solution was
filtered and evaporated to small volume. The blue precipitate of copper(II) complex was
separated by filtration, washed with cold water and air-dried. Yield: 0.1590 g (81.37 %). Anal.
Calc. for [Cu2(S-pr-thiosal)4(H2O)2] = Cu2C40H48O10S4 (Mr = 944.140): C, 50.88; H, 5.12; S,
13.58. Found: C, 50.71; H, 5.04; S, 13.48. µ(294 K) = 1.85 µB
2.2.6. Preparation of copper(II) complex with S-butyl derivative of thiosalicylic acid,
[Cu2(S-bu-thiosal)4(H2O)2] (C5)
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Copper(II)-nitrate trihydrate (0.1000 g, 0.4139 mmol) was dissolved in 10.0 mL of
water on a steam bath and S-butyl derivative of thiosalicylic acid (0.1741 g, 0.8278 mmol)
was added. The reaction mixture was heated for 3 h and during this period 10.0 mL of LiOH
water solution (0.0347 g, 0.8278 mmol) was added in small portions and the solution was
filtered and evaporated to small volume. The blue precipitate of copper(II) complex was
separated by filtration, washed with cold water and air-dried. Yield: 0.1680 g (81.20 %). Anal.
Calc. for [Cu2(S-bu-thiosal)4(H2O)2] = Cu2C44H56O10S4 (Mr = 1000.244): C, 52.83; H, 5.64; S,
12.82. Found: C, 52.75; H, 5.58; S, 12.71. µ(294 K) = 1.80 µB
2.3. Single crystal X-ray crystallography
Single crystals of [Cu2(S-met-thiosal)4(H2O)2], (C2) suitable for X-ray measurements
were obtained by slow crystallization from a water solution. Single-crystal diffraction data for
C2 were collected at room temperature on an Agilent Gemini S diffractometer equipped with
CuKα radiation (λ = 1.5418 Å). Data reduction and empirical absorption corrections were
accomplished using CrysAlisPro [24]. Crystal structure was solved by direct methods, using
SIR2002 [25] and refined using SHELXL program [26]. The hydrogen atoms attached to C
atoms were placed at geometrically idealized positions with C–H distances fixed to 0.93 and
0.96 Å from phenyl and methyl C atoms, respectively. Their isotropic displacement
parameters were set equal to 1.2Ueq and 1.5Ueq of the parent phenyl and methyl C atoms. The
hydrogen atoms of the apical water ligands were located in difference Fourier map and
refined isotropically. The crystallographic data are listed in Table 1. The PARST [27] and
PLATON [28] programs were used to perform geometrical calculation and the programs
ORTEP [29] and Mercury [30] were employed for molecular graphics.
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2.4. In vitro antimicrobial assay
2.4.1. Test substances
The tested compounds were dissolved in DMSO and then diluted into nutrient liquid
medium to achieve a concentration of 10 %. An antibiotic, doxycycline (Galenika A.D.,
Belgrade), was dissolved 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).
2.4.2. Test microorganisms
The antimicrobial activity of the copper(II) complexes C1–C5 was tested against 18
microorganisms. The experiment involved 8 strains of pathogenic bacteria, including two
standard strains (Escherichia coli ATCC 25922 and Bacillus subtilis ATCC 6633) and six
clinical isolates (Escherichia coli, Enterococcus faecalis, Bacillus subtilis, Proteus mirabilis,
Salmonella enterica, Salmonella typhimurium). Also, three species of probiotic bacteria
(Lactobacillus plantarum PMFKG-P31, Bacillus subtilis IP 5832 PMFKG-P32,
Bifidobacterium animalis subsp. lactis PMFKG-P33), three mould species (Aspergillus niger
ATCC 16404, Aspergillus flavus PMFKG-F24, Botrytis cinerea PMFKG-F33) and three yeast
species (Candida albicans ATCC 10231, Candida albicans, clinical isolate, Rhodotorula sp.
PMFKG-F27, Saccharomyces boulardii PMFKG-P34) were tested. All clinical isolates were
a generous gift from the Institute of Public Health, Kragujevac. The other microorganisms
were provided from the collection held by the Microbiology Laboratory Faculty of Science,
University of Kragujevac.
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2.4.3. Suspension preparation
Bacterial and yeast suspensions were prepared by the direct colony method. The
colonies were taken directly from the plate and suspended in 5 mL of sterile 0.85 % saline.
The turbidity of the initial suspension was adjusted by comparing it with
0.5 McFarland’s [31]. When adjusted to the turbidity of the 0.5 McFarland’s standard, the
bacterium suspension contains about 108 colony forming units (CFU)/mL and the suspension
of yeast contains 106 CFU/mL. 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.
2.4.4. 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 [32]. The 96-well plates were prepared by
dispensing 100 µL of nutrient broth, Mueller–Hinton broth for bacteria and Sabouraud
dextrose broth for fungi and yeasts, into each well. A 100 µL aliquot from the stock solution
of the tested compound (with a concentration of 2000 µg/mL) was added into the first row of
the plate. Then, twofold serial dilutions were performed by using a multichannel pipette. The
obtained concentration range was from 1000 to 7.8 µg/mL. The method is described in detail
in the reported paper [19].
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. 10 %
DMSO was recorded not to inhibit the growth of microorganisms. Also, the concentration of
DMSO in the experiment was additionally decreased because of the twofold serial dilution
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assay (the working concentration was 5 % and lower). Each test included growth control and
sterility control. All the tests were performed in duplicate and the MICs were constant.
Minimum bactericidal and fungicidal concentrations were determined by plating 10 µL of
samples from wells where no indicator color change was recorded, on nutrient agar medium.
At the end of the incubation period the lowest concentration with no growth (no colony) was
defined as the minimum microbicidal concentration.
3. Results and discussion
3.1. Synthesis and chemical characterization
S-alkyl (R = benzyl (L1), methyl (L2), ethyl (L3), propyl (L4) and butyl (L5))
derivatives of thiosalicylic acid were prepared [19] by alkylation of thiosalicylic acid by
means of the corresponding alkyl halogenides in alkaline water-ethanol solution (Scheme 1).
The corresponding [Cu2(S-R-thiosal)4(H2O)2] complexes were obtained by direct reaction of
Cu(NO3)2 with S-alkyl derivatives of thiosalicylic acid (molar ratio 1:2) in water solution with
satisfactory yields (more then 80 %) (Scheme 2).
Infrared spectra of the isolated complexes were measured in order to find coordination
mode of the S-alkyl derivatives of thiosalicylic acid. The asymmetric stretching frequencies
of carboxylic group were specially used to determine whether this carboxylic group was
coordinated (the absorption bands are located in the region 1600-1650 cm-1) or uncoordinated
(the absorption bands are located in the region 1700-1750 cm-1) to the metal ion [33-35].
The isolated [Cu2(S-R-thiosal)4(H2O)2] complexes show double sharp and strong
asymmetric stretching frequencies of the carboxylic groups of the coordinated S-alkyl
derivatives of thiosalicylic acid to Cu(II) ion at about 1565-1620 cm-1 (Table 2). The observed
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clear double bands for isolated complexes suggest the small differences in the coordination of
carboxylic groups of the ligands to the Cu(II) ion. Based on the content of the complexes and
the shape of thier IR spectra it can not be concluded with certainty how S-alkyl derivatives of
thiosalicylic acid are coordinated to Cu(II) ion. Although we expected the same coordination
type of S-alkyl derivatives of thiosalicylic to the Cu(II) as to Pd(II) ion [19], the proper
molecular structure was obtained on the basis of X-ray analysis of
[Cu2(S-met-thiosal)4(H2O)2] complex. Also the strong sharp single symmetric stretching
bands of the coordinated carboxylic groups of the S-alkyl derivatives of thiosalicylic acid lie
in the expected region (about 1400 cm-1) [34,35].
3.2. Magnetic measurements
Dinuclear cupper(II) carboxylates complexes (18, 36) are stable in dimeric form. The low
value of µeff at room temperature (1.20-2.30 BM) is indicative of an antiferromagnetic
interaction between the two metal centers typical of binuclear carboxylates of copper(II) of
the type: [Cu(R~COO)2L]2 (37-39). The main factor determining the magnitude of the
antiferromagnetic interaction in the dimeric copper(II) carboxylates is the electronic structure
of the bridging OCO moiety as published earlier (18, 36-39).
3.3. Structural description of the complex [Cu2(S-met-thiosal)4(H2O)2], (C2)
The crystal structure of [Cu2(S-met-thiosal)4(H2O)2] complex consists of two
crystallographically independent dinuclear Cu(II) complex molecules (A and B), each with
inversion center located between the metal ions. In both molecules the pairs of Cu(II) are
bridged by four S-methyl-thiosalicylate ligands forming a so-called “paddle-wheel” type
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structure. Fig. 1 shows the molecular structure and atom numbering scheme of molecule A.
The structure of molecule B and equivalent numbering scheme are given in Fig. S1
(Supplementary Material file). The distances between the Cu atoms in A and B are 2.6220(6)
and 2.6180(6) Å, respectively which is closely comparable to the Cu…Cu distance found in
dimeric copper(II) acetate (2.614 Å) [40]. Both Cu centers (Cu1 and Cu2) display a square-
pyramidal coordination geometry with the four oxygen atoms from symmetry related
carboxylate ligands placed at the corners of the basal plane. In both molecules the apical
positions of the copper coordination polyhedron are occupied by the water O atoms. The Cu1
and Cu2 atoms deviate from the basal plane towards the apical ligand for 0.2011(8) and
0.1964(8) Å, respectively.
The geometrical parameters listed in Table 3 show slight differences in conformation
of the A and B molecules. The different distortion in the square-pyramidal environment of
each Cu(II) is evidenced from the range of coordination angles [86.80(7)-101.87(7)° in A and
−O and Cu2−O
88.03(8)-99.71(8)° in B] as well as from variation in lengths for the basal Cu1
bonds [1.952(2)-1.984(2) Å in A and 1.948(2)-1.975(2) Å in B]. The bonds to the axial water
molecules have nearly the same lengths (Table 3); these ligands however, show slightly
different bending with regard to Cu…Cu direction, resulting in O1w−Cu1−Cu1i and
O2w−Cu2−Cu2ii angles of 172.39(6) and 168.15(5)° (symmetry codes: (i) −x+1, −y, −z+1;
(ii) −x+1, −y+1, −z ). The geometrical parameters in both molecules are within those found in
corresponding O-methyl derivative [41].
The most evident structural difference between two independent molecules of C2
includes their S-methyl-thiosalicylate ligands with phenyl rings displaying different rotation
with respect to the corresponding carboxylate groups (Fig. S2). Thus, in molecule A the
rotation angles of the C2a/C7a and C2b/C7b rings with regard to their COO moieties are
7.9(3) and 17.1(4)°, while in molecule B the corresponding rotation angles of the C2c/C7c
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and C2d/C7d rings are 24.3(2) and 5.8(2)°. Another noticeable difference between the A and
B molecules regards their paddle wheel cores, Cu2C4O8, which seems to present a different
degree distortion. Bearing in mind the fine differences in coordination environment of Cu1
and Cu2 this is not unexpected. One should however point to the pronounced dissimilarity in
−O−C angles formed by bridging coordination of ca
the pairs of Cu
rboxylate ligand to the pair
of Cu atoms. Thus, in A molecule the coordination of one S-methyl-thiosalicylate ligand (ring
C2a/C7a) gives the pair of angles, Cu1−O1a−C1a and Cu1i−O2a−C1a, with the very
dissimilar values of 116.6(1) and 130.1(1)°, respectively whereas the coordination of the
second ligand (ring C2b/C7b) results in Cu1−O1b−C1b and Cu1i−O2b−C1b angles with
values of 126.2(1) and 120.1(1)°. For B molecule these differences are less visible, and the
−O1c−C1c and Cu2ii
angles Cu2
−O2c−C1c have the values of 127.4(2) and 119.3(2)°, while
−O1d−C1d and Cu2ii
the angles Cu2
−O2d−C1d are equal to 124.9(1) and 122.2(1)°,
−O−C angles (from 2.7 to 14.4°)
respectively. These noticeable variations in the pairs of Cu
formed by the same type of ligand indicate a considerable influence of the crystal packing on
the shape and deformation of two paddle wheel cores of A and B.
The examination of the crystal packing of C2, as expected, shows the dominance of
O−H…O hydrogen bonds which involve the axial ligands as donors and the carboxilic
oxygens as acceptors. Three interactions, O1w−H11…O1c, O1w−H12…O1d and
O2w−H21…O1b (Table 4), interconnect the independent molecules to form an infinite
ABAB chain (Fig. 2). The connection between the A and B molecules within the chain is
−H…S interactions,
reinforced by two significant O
engaging the S acceptors to form the
phenyl substituents (Table 4). The formed ABAB chain (Fig. 2) could be considered as the
−H…O interactions do n
main structural motif of C2. It can be noted that the O
ot involve O1a
and O2a atoms suggesting that the distortion in the peddle wheel of A (especially visible in
angles involving O1a and O2a) could not be directly related to the strong hydrogen bonds. In
13

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order to search for other potential causes of peddle wheel deformation in C2 the similar
crystal structures found in Cambridge Structural Databank (CSD) have also been analyzed
[42].
A CSD search for Cu(II) paddle wheel complexes comprising aromatic carboxylate
(ArCOO) and water ligands, [Cu2(ArCOO)4(H2O)2], resulted in 26 examples. The geometrical
properties of the C2 compound are in good agreement with those observed for the Cu(II)
complexes extracted from CSD. One can suggest several common features in the crystal
structures of [Cu2(ArCOO)4(H2O)2] complexes: (i) as in C2 the substituted phenyl rings of the
different carboxylate ligands in 26 crystal structures display a free rotation with respect to
their COO moiety resulting in a wide range of corresponding dihedral angles. In accordance
with the previous findings [43] the rotation of phenyl ring increases in the case of the
structures with ortho-substituted aromatic ligands compared to those with meta- and para-
substituted ligands (Fig. S3); (ii) the paddle wheel cores, Cu2C4O8, permit a considerable
−O−C angles
degree of distortion. This is mostly reflected in visible differences of two Cu
formed
by
a
bridging
carboxylate
ligand.
Thus
the
intetrakis(µ2-2-
Hydroxycarbamoylbenzoato-O,O')-diaqua-di-copper(II) complex [44] (CSD refcode
VEYCUY) the Cu1−O1−C1 and Cu1−O2−C1angles differ for 2.5°, whereas in the
tetrakis(µ2-4-Hydroxy-3-methoxybenzoato-O,O')-diaqua-di-copper(II) complex [45] (CSD
refcode GUSCAY01) these two angles differ for 12°. At the same time the corresponding
pairs of Cu−O bonds have nearly the same length; (iii) among the 26 extracted
[Cu2(ArCOO)4(H2O)2] peddle wheel complexes 15 display the chain-like structural motif
similar to that observed in C2 (Fig. 2). The axial water ligands take place in the region of
−H…O
carboxyl O atoms of the neighboring molecule and form at least one pair of O
hydrogen bonds eventually producing a chain of molecules (Fig. S3). This arrangement can
be found even in structures containing solvents or additional acceptors on phenyl substituents.
14

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One can also observe that the connection of complex molecules into the chain requires
successive rotation of their closely adjacent substituted rings in order to reduce the potential
steric hindrance (Fig. S3). In contrast to other examples, the chain formed in C2 (Fig. 2)
includes two types of symmetrically independent molecules. While in molecule B the ring
C2c/C7c shows the largest twisting with respect to its COO group [24.3(2)°], the rotation of
the adjacent C2a/C7a ring in molecule A [7.9(3)°] is partly prevented by the relatively strong
O−H…S hydrogen bond. Therefore the visible distortion of the paddle wheel core observed in
A molecule could serve in additionally separating the adjacent phenyl rings (C2a/C7a and
C2c/C7c in Fig. 2 denoted as a and c) and decreasing their potential repulsion.
Apart from the hydrogen bonding arranging the molecules into ABAB chain there are
no further significant interactions between A and B molecules. The three-dimensional crystal
packing of C2 viewed down the b axis shows the separate blocks of A and B molecules
parallel to (001), (Fig. 3a). Inside the corresponding blocks the A molecules mutually interact
by means of C–H…π interactions, while B molecules employ their least rotated C2d/C7d
rings [5.8(2)°] to interconnect by weak π…π interaction (Fig. 3b,c).
3.4. Microbiology
The results of in vitro testing of antimicrobial activities for the five new copper(II)
complexes are shown in Tables 5 and 6. For comparison, MIC and MMC values of the
corresponding ligands [19] and doxycycline and fluconazole are also listed in the same tables.
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 the tested compound type. MIC and MMC values for complexes were in
range 31.3 to >1000 µg/mL. In general, the activity of the complexes was higher than or
15

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400
similar to the corresponding ligands. The exceptions are filamentous fungi, particularly
Aspergillus flavus, where the ligands have higher activity.
Overall the copper(II) complexes showed low antifungal activity. 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 µg/mL, except for the complexes C2 and C3
against Rhodotorula sp., where the MIC was 250 µg/mL.
All the tested complexes demonstrated moderate or selective antibacterial activity. The
probiotics showed sensitivity similar to the sensitivity of the other Gram-positive bacteria.
Lactobacillus plantarum showed somewhat higher resistance to the tested complexes. The
Gram-positive bacteria Bacillus subtilis and probiotics Bif. animalis subsp. lactis, Bacillus
subtilis IP 5832, were more sensitive than the other Gram-positive and Gram-negative
bacteria. The most sensitive was Bif. animalis subsp. lactis with a MIC value of 31.3 µg/mL
for the complexes C2 and C4. The MICs for Gram-negative bacteria were in range 250 to
> 1000 µg/mL. The tested complex C2 exhibited somewhat stronger antibacterial activity to
Escherichia coli, E. coli ATCC 25922 and Salmonella enterica (MIC = 250 µg/mL).
The previous research of antimicrobial activity of dinuclear and mononuclear
copper(II) complexes with the COO group coordinated to Cu provides diverse conclusions.
Basically, in most studies, as in ours weak antifungal activity is observed.
In some studies [8] the lack of specificity (and of activity) of the Cu(II) complex
against all the tested Gram(_) and Gram(+) bacteria suggests that the sensitivity of test
organisms to test compounds is not associated to the different cell wall structures.
Some research suggests that the Cu(II) complexes exhibit mild antimicrobial activities.
The result revealed that copper complexes displayed inhibition still significantly lower than
the standard drugs [10]. The results of the antibacterial activity of the tested Cu(II) complexes
showed moderate activity against E. coli and S. aureus when compared to the standard drug,
16

401
tetracycline [11]. The same Cu(II) complexes either demonstrate the limited activity against
402
403
404
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407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
A. flavus and C. albican or not [11]. The water-insoluble Cu(II) dicarboxylate complex and
the water–soluble Cu(II) simple salts were inactive against all of the microorganisms. These
data indicate that the decrease of the ligand solubility (via complex formation) lowers the
bioavailablility of the dicarboxylates. Some Cu(II) complexes demonstrated no significant
activity whilst the phen adducts were active against S. aureus MRSA, E. coli and Patonea
agglumerans. Against C. albicans the phen-containing Cu(II) complexes had significantly
lower antifungal activity comparable to those of the commercial antifungal agent
ketoconazole. Thus, unlike the antibacterial studies, whereby formation of a Cu(II) phen
complex enhances the antibacterial activity of the phen ligand, the anti-Candida activity is
reduced upon complex formation [12]. The Cu(sparfloxacinato)(N-donor)Cl complexes are
among the most active ones against Escherichia coli, Pseudomonas aeruginosa and
Staphylococcus aureus, when compared to other corresponding copper–quinolone complexes
and their antimicrobial activity is increased in the order bipyam < bipy = phen [13].
While some binary Cu(II) complexes have a low effect on A. flavus and C. albicans,
ternary do not have it at all. The same binary and ternary Cu(II) complexes act on bacteria
better than tetracycline [14].
Some studies show the good antimicrobial activity of Cu(II) complexes in range of
standard drugs (ciprofloksacin/griseofulvin) [9,15]. Some Cu(II) complexes are good
antimicrobial agents (in the range of standard drugs such as ciprofloxacin/griseofulvin) [16]
compared to those reported for analogous ternary complexes [9,46].
4. Conclusion
17

425
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427
428
429
430
431
432
433
The five new copper(II) complexes with some S-alkyl derivatives of thiosalicylic acid
(alkyl = benzyl, methyl, ethyl, propyl, butyl) have been synthesized and characterized by
microanalysis and infrared spectra. Both independent paddle-wheel complex molecules (A
−H…O
and B) in the crystal structure of [Cu2(S-met-thiosal)4(H2O)2] interact by means of O
−H…S interactions and form A
and O
BAB chain. In crystal packing, A molecules develop
extensive C−H…π interconnections, while B molecules form the distinct chain by π…π
stacking interactions. The intensity of the antimicrobial activity varied depending on the
species of microorganism and the tested compound type. All the tested complexes
demonstrated moderate or selective antibacterial activity and low antifungal activity.
434
435
436
437
Appendix A. Supplementary data
CCDC 974908 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.
438
439
440
441
442
443
444
445
446
Acknowledgment
This work was financially supported by the Ministry of Education, Science and
Technological Development of the Republic of Serbia (Projects 172016, 172034, 172035,
173032). The authors are grateful to assistant professor Tamara Todorović, Faculty of
Chemistry University of Belgrade, for the magnetic measurements.
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21

Fig. 1. Crystal structure and the atom numbering scheme of A molecule. Structure of
B molecule and equivalent numbering scheme are given in Fig. S1

Fig. 2. A view of a chain consisting of hydrogen bonded A and B molecules

Fig. 3. (a) Blocks of A (red) and B (blue) molecules viewed done b axis; (b) C−H…π
interactions between the A molecules; (c) π…π interaction between the B molecules

O
OH
O
ONa
O
OH
C
C
C
SH
S
S
Ethanol/H2O
R
R
+
H+
R-X
+
2 NaOH
L1 L5
L2
L3
L4
R= Benzyl ( ), methyl ( ), ethyl ( ), propyl ( ), butyl ( )
Scheme 1. The preparation of the benzyl (L1), methyl (L2), ethyl (L3), propyl (L4) and butyl
(L5) derivatives of thiosalicylic acid

Scheme 2. The preparation of the binuclear copper(II) complex with S-alky derivatives of
thiosalicylic acid

525
Table 1. Crystallographic data for C2.
Empirical formula
Formula weight
Color, crystal shape
Crystal size (mm3)
Temperature (K)
Wavelength (Å)
Crystal system
C32H32O10Cu2S4
831.90
Green, prism
0.14 x 0.09 x 0.05
293(2)
1.5418
Triclinic
P-1
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
11.3834(5)
11.8107(4)
13.9707(7)
69.317(4)
77.826(4)
88.925(3)
V (Å3)
1714.54(13)
2,1
1.611
Z,Z’
Dcalc (Mg/m3)
µ (mm-1)
4.288
θ range for data collection (°)
Reflections collected
3.47 to 72.30
12035
Independent reflections, Rint
Completeness (%) to θ = 67°
Refinement method
6612, 0.0218
99.9
Full-matrix least-squares on F2
6612 / 0 / 453
1.041
Data / restraints / parameters
Goodness-of-fit on F2
Final R1/wR2 indices [I >2σ(I)]
Final R1/wR2 indices (all data)
0.0328/ 0.0894
0.0384/ 0.0935
Largest diff. peak and hole (e Å-3)
0.492/−0.276
526
527
528
529
22

530
Table 2. The most important infrared bands (cm-1) of the investigated compounds.
Compound
-S-R
-COO- (as) -COO- (sim)
S-met-thiosal
[Cu2(S-met-thiosal)4(H2O)2]
699(m)
697(m)
1672(s)
1596(s)
1581(s)
1682(s)
1619(s)
1592(s)
1678(s)
1614(s)
1594(s)
1678(s)
1590(s)
1570(s)
1675(s)
1589(s)
1567(s)
1412(s)
1411(s)
S-et-thiosal
[Cu2(S-et-thiosal)4(H2O)2]
704(m)
697(m)
1414(s)
1399(s)
S-pr-thiosal
[Cu2(S-pr-thiosal)4(H2O)2]
702(m)
704(m)
1410(s)
1401(s)
S-bu-thiosal
[Cu2(S-bu-thiosal)4(H2O)2]
703(m)
696(m)
1414(s)
1403(s)
S-bz-thiosal
[Cu2(S-bz-thiosal)4(H2O)2]
710(m)
696(m)
1412(s)
1403(s)
531
532
s-strong, m-medium
533
534
535
536
23

537
538
Table 3. Selected bond lengths (Å) and angles (°) for two independent molecules of C2.
A
B
−Cu1i
Cu1
−Cu2ii
Cu2
2.6220(6)
1.952(16)
1.9641(16)
1.9817(15)
1.9845(15)
2.1463(18)
1.253(3)
2.6180(6)
1.9475(16)
1.9603(16)
1.9664(16)
1.9751(16)
2.1453(18)
1.256(3)
1.256(3)
1.258(3)
1.259(3)
Cu1−O2ai
−O1b
Cu2−O2dii
−O1d
Cu2
Cu1
Cu1−O1a
Cu2−O1c
−O2bi
−O2cii
Cu1
Cu2
Cu1−O1w
−C1b
O1b
Cu2−O2w
−C1c
O1c
O2a−C1a
−C1a
O2c−C1c
−C1d
1.257(3)
1.259(3)
1.268(3)
O1a
O2b−C1b
O2d
O1d−C1d
−Cu1−O2bi
−Cu2−O2cii
O1a
O1d
86.80(7)
89.61(8)
89.81(7)
89.85(7)
91.39(8)
93.79(8)
98.10(7)
101.87(7)
168.06(7)
168.28(7)
88.03(8)
88.88(8)
90.27(8)
90.52(8)
99.71(8)
91.79(8)
97.26(7)
99.71(8)
168.39(7)
168.45(7)
O2ai−Cu1−O1b
O1d−Cu2−O1c
O2dii−Cu2−O2cii
O2dii−Cu2−O1c
O2cii−Cu2−O2w
O2dii−Cu2−O2w
−Cu1−O1a
O1b
O2ai−Cu1−O1w
O2ai−Cu1−O2bi
O1b−Cu1−O1w
O2bi−Cu1−O1w
O1a−Cu1−O1w
−Cu2−O2w
O1d
O1c−Cu2−O2w
−Cu1−O2bi
O1b
−Cu2−O2cii
O1c
O2ai−Cu1−O1a
O2dii−Cu2−O1d
539
540
541
Symmetry codes: (i) −x+1, −y, −z+1; (ii) −x+1, −y+1, −z
542
543
24