Synthesis, structural characterization, oxygen sensitivity, and antimicrobial activity of ruthenium(II) carbonyl complexes with thiosemicarbazones

Article abstract of DOI:10.1080/00958972.2014.948433

[Ru(CO)(PPh₃)₂(η³-O,N³,S-TSC¹)] (1), [Ru(Cl)(CO)(PPh₃)₂(η²-N³,S-TSC²)] (2), and [Ru(Cl)(CO)(PPh₃)₂(η²-N³

Full text of DOI:10.1080/00958972.2014.948433

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Synthesis, structural characterization,
oxygen sensitivity, and antimicrobial
activity of ruthenium(II) carbonyl
complexes with thiosemicarbazones
a
b
cd
b
Nurdan Öztürk , Pelin Köse Yaman , Murat Yavuz , Özlem Öter ,
c
b
Suna Timur & Elif Subaşi
a
The Graduate School of Natural and Applied Sciences, Dokuz
Eylül University, İzmir, Turkey
b
Faculty of Science, Department of Chemistry, Dokuz Eylül
University, İzmir, Turkey
c
Faculty of Science, Department of Biochemistry, Ege University,
Click for updates
İzmir, Turkey
d
Faculty of Science, Department of Chemistry, Dicle University,
Diyarbakir, Turkey
Accepted author version posted online: 28 Jul 2014.Published
online: 20 Aug 2014.
To cite this article: Nurdan Öztürk, Pelin Köse Yaman, Murat Yavuz, Özlem Öter, Suna Timur & Elif
Subaşi (2014): Synthesis, structural characterization, oxygen sensitivity, and antimicrobial activity
of ruthenium(II) carbonyl complexes with thiosemicarbazones, Journal of Coordination Chemistry,
DOI: 10.1080/00958972.2014.948433
To link to this article: http://dx.doi.org/10.1080/00958972.2014.948433
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Journal of Coordination Chemistry, 2014
http://dx.doi.org/10.1080/00958972.2014.948433
Synthesis, structural characterization, oxygen sensitivity, and
antimicrobial activity of ruthenium(II) carbonyl complexes
with thiosemicarbazones
NURDAN ÖZTÜRK†, PELIN KÖSE YAMAN‡, MURAT YAVUZ§¶, ÖZLEM ÖTER‡,
SUNA TIMUR§ and ELIF SUBAŞI*‡
†
The Graduate School of Natural and Applied Sciences, Dokuz Eylül University, İzmir, Turkey
Faculty of Science, Department of Chemistry, Dokuz Eylül University, İzmir, Turkey
Faculty of Science, Department of Biochemistry, Ege University, İzmir, Turkey
Faculty of Science, Department of Chemistry, Dicle University, Diyarbakir, Turkey
‡
§
¶
(
Received 25 March 2014; accepted 26 June 2014)
Ru(II) carbonyl complexes were prepared by reacting [Ru(H)(Cl)(CO)(PPh
thiosemicarbazone ligands and the complexes were characterized by UV–vis, FT-IR, and H and
3 3
) ] with the respective
1 31
P
NMR spectroscopy. Oxygen sensitivities and antimicrobial activities of the complexes were
determined.
3
3
1
2
3
2
[
(
Ru(CO)(PPh
3
)
2
(η -O,N ,S-TSC )] (1), [Ru(Cl)(CO)(PPh
3
)
2
(η -N ,S-TSC )] (2), and [Ru(Cl)(CO)
2
3
3
PPh
3
)
2
(η -N ,S-TSC )] (3) have been prepared by reacting [Ru(H)(Cl)(CO)(PPh ] with the respec-
tive thiosemicarbazones TSC (2-hydroxy-3-methoxybenzaldehyde thiosemicarbazone), TSC
3-hydroxybenzaldehyde thiosemicarbazone), and TSC (3,4-dihydroxybenzaldehyde thiosemicarba-
3 3
)
1
2
3
(
zone) in a 1 : 1 M ratio in toluene and all of the complexes have been characterized by UV–vis, FT-IR,
1
31
1
and H and P NMR spectroscopy. The spectroscopic studies showed that TSC is coordinated to the
central metal as a tridendate ligand coordinating via the azomethine nitrogen (C=N), phenolic oxygen,
2
3
and sulfur to ruthenium in 1, whereas TSC and TSC are coordinated to ruthenium as a bidentate
ligand through azomethine nitrogen (C=N) and sulfur in 2 and 3. Oxygen sensitivities of 1–3 and [Ru
Cl)(CO)(PPh ) (η -N ,S-TSC )] (4), and antimicrobial activities of 1–3 have been determined.
3 2
2
3
4
(
Keywords: Ruthenium(II) carbonyl complexes; Thiosemicarbazones; Oxygen sensitivity; Antimicrobial
activities
1. Introduction
Complexes of transition metals containing ligands with N, S or N, S, O donors exhibit inter-
esting stereochemical, electrochemical, and electronic properties [1, 2]. Derivatives of semi-
carbazones and thiosemicarbazones (TSCs) are widely studied nitrogen and oxygen/sulfur
*
Corresponding author. Email: elif.subasi@deu.edu.tr
2014 Taylor & Francis
©

2
N. Öztürk et al.
donors [3, 4]. Particularly, TSCs are an important class of sulfur donor ligands because of
their mixed hard–soft donor character and versatile coordination behavior [5]. TSCs exist as
thione–thiol tautomers and can bind to a metal in neutral or anionic forms. The anionic form
2
is produced after loss of –N H or –SH hydrogen ions. A number of bonding modes have been
observed for TSCs in their neutral or anionic forms as shown in figure 1.
TSCs usually react as chelating ligands with transition metal ions by bonding through
sulfur and azomethine nitrogen and in some cases they behave as tridentate ligands and
bond through sulfur and two nitrogens [6]. TSCs and their metal complexes have become
the subjects of severe study because of their wide-ranging biological activities (antitumor,
antibacterial, antiviral, antiamoebic, and antimalarial activities), analytical applications, and
interesting chemical and structural properties [7–9].
Medicinal chemistry has focused on TSCs due to their biological activities demonstrated
by various derivatives incorporating the heterocyclic moiety [10–12]. Owing to their
chemistry, versatile activity, and prospective use as drugs, they have ample interest
[
13, 14]. For transition metal complexes, decreased or increased biological activities are
reported [15–17]. Complexes of ruthenium with TSCs, which can coordinate either in
neutral thione form or in the anionic thiolate form, have received attention for varied
coordination modes [18].
Use of ruthenium complexes as chemotherapeutic agents for treatment of cancer is well
established [19]. Recently, an oligomer of thiophene-2-carboxaldehyde thiosemicarbazone
was electrochemically deposited on graphite surfaces as the matrix for enzyme immobiliza-
6
tion [20]. The biosensing applicability and evaluation as antimicrobial agents of [(η -p-cym-
N-S
N-S
ene)RuClTSC ]Cl and [Ru(CO)Cl(PPh ) TSC ] (4) were investigated using glucose
3
2
oxidase as a model enzyme [21]. Ruthenium complexes are widely used for oxygen-sensing
purposes due to the fact that they produce metal-to-ligand charge-transfer excited states
which are readily quenched by oxygen. They are preferred for their high quantum yields,
fast response times, strong visible absorptions, large Stoke’s shifts, and high photophysical
and photochemical stabilities [22–24]. In this study, we have also investigated the applica-
bility of the complexes for oxygen-sensing purposes.
As ligands, TSCs have more than one potential donor. Therefore, we tried to observe
the sites of substitution of these ligands to the metal center. Our continued interest in
the synthesis and structural aspects of ruthenium(II) led us to launch an exploratory
1
–3
investigation into the behavior of [Ru(H)(Cl)(CO)(PPh ) ] with TSC . As an extension
3
3
of our previous studies, herein, we describe the synthesis and full characterization of
3
3 2 3 2
3
1
2
3
2
[
(
(
Ru(CO)(PPh ) (η -O,N ,S-TSC )] (1), [Ru(Cl)(CO)(PPh ) (η -N ,S-TSC )] (2), and [Ru
2
3
3
Cl)(CO)(PPh ) (η -N ,S-TSC )] (3) which have been prepared by reacting [Ru(H)(Cl)
3
2
1
CO)(PPh ) ] with the respective thiosemicarbazone ligands TSC (2-hydroxy-3-methoxy-
3
3
2
benzaldehyde thiosemicarbazone), TSC (3-hydroxybenzaldehyde thiosemicarbazone), and
3
TSC (3,4-dihydroxybenzaldehyde thiosemicarbazone). The complexes were elucidated by
Figure 1. Thione and thiol forms of TSCs.

Ruthenium(II) carbonyl thiosemicarbazones
3
elemental analysis, FT-IR, UV–vis spectroscopy, and a combination of multinuclear
NMR spectroscopy. Oxygen sensitivities and antimicrobial effects of these complexes are
also investigated.
2
2
. Experimental
.1. Chemicals and physical measurements
Toluene, ethanol, petroleum ether, dichloromethane, and silica gel were purchased from
Merck and RuCl ·3H O was purchased from Aldrich. These reagents were used as sup-
3
2
plied. The solvents used were purified and distilled according to routine procedures [25].
Ethyl cellulose was from Organics with an ethoxy content of 48%. The plasticizer dioctyl
phthalate (DOP) was from Aldrich. The ionic liquid (IL) 1-ethyl-3-methylimidazolium tetra-
+
−
fluoroborate ([EMIM ][BF ]) was from Fluka. Oxygen and nitrogen gas cylinders were of
4
9
9.9% purity and obtained from Linde Company, Izmir, Turkey.
Reactions were carried out under dry nitrogen using Schlenk techniques. All solvents
were dried and degassed prior to use. Elemental analyses were carried out using a LECO-
CHNS-O-9320 by Technical and Scientific Research Council of Turkey, TUBITAK. IR
spectra on a Varian 1000 FT spectrophotometer and UV–vis Spectra Shimadzu Model 1800
1
31
spectrophotometer were recorded on samples at the Dokuz Eylül University. H and
P
NMR spectra were recorded in DMSO-d on 500 MHz High Performance Digital FT NMR
6
at Ege University.
2
2
.2. Synthesis of the compounds
.2.1. Synthesis of the ligands. The preparative methods for TSCs were well described by
Klayman et al. [26] and Scovill [27]. In general, a thiosemicarbazide was dissolved in
methanol by refluxing for half an hour; however, sometimes, a few milliliters of distilled
water are added to completely dissolve it. After addition of a given aldehyde or ketone, the
reaction mixture is refluxed for 8–10 h and evaporation gave crude sample which was
recrystallized from methanol.
2
.2.2. Synthesis of the complexes. Complexes 1–4 were prepared by reacting [Ru(H)(Cl)
1
–4
(CO)(PPh ) ] with the respective thiosemicarbazone ligands TSC
and were obtained in
3
3
7
5–80% yields. The methods employed for the preparation of 1–3 are very similar, so that
3
3
1
the preparation of [Ru(CO)(PPh ) (η -O,N ,S-TSC )], 1 is given in detail as a representa-
tive example. [Ru(Cl)(CO)(PPh ) (η -N ,S-TSC )], 4, was prepared according to the pub-
3
2
2
3
4
3
2
lished results [21].
.2.2.1. [Ru(CO)(PPh ) (η -O,N ,S-TSC )] (1). To a solution of [Ru(H)(Cl)(CO)(PPh ) ]
3
3
1
2
(
3
2
3 3
1
950 mg, 1 mM) in toluene (25 mL) TSC (225 mg) was added. The mixture was refluxed
for 5 h under nitrogen. The resulting solution was concentrated to 5 mL and the product
was separated by addition of a small amount of petroleum ether. It was filtered and dried in
vacuo. The composition of the compounds is confirmed by elemental analysis. Yield (80%).
Found: C, 62.75; H, 4.75; N, 4.71; S, 3.59. Calcd for C H N O P RuS: C, 62.79; H,
4
6 42 3 3 2
4
.81; N, 4.78; S, 3.64. FT-IR (ν, KBr): 3148 (s, N–H), 1586 (m, C=N), 719 (w, C–S), 1093

4
N. Öztürk et al.
−
1
1
(
w CN, NCN), 1944 (s, C≡O) cm . H NMR (500 MHz, δ, DMSO-d ): 8.54 (1H, s,
,
6
3
1
N–H), 8.38 (1H, s, HC=N), 6.74–8.08 (3H, m, Ar–H) ppm. P NMR: 27.61. UV–vis
(
THF) (nm) (A): λ : 281.0 (0.212).
1
2
3
2
2
.2.2.2. [Ru(Cl)(CO)(PPh ) (η -N ,S-TSC )] (2). A similar synthetic procedure as that
3 2
1
2
used for 1 was used except that TSC was replaced by TSC (195 mg), giving orange crys-
tals. The composition of the compound is confirmed by elemental analysis. Yield (75%).
Found: C, 61.02; H, 4.26; N, 4.70; S, 3.60. Calcd for C H ClN O P RuS: C, 61.12; H,
4
5
39
3 2 2
4
.45; N, 4.75; S, 3.63. FT-IR (ν, KBr): 1587 (m, C=N), 744 (m, C–S), 1092 (w, CN,
−
1 1
NCN), 1955 (s, C≡O) cm . H NMR (500 MHz, δ, DMSO-d ): 8.37 (1H, s, HC=N),
6
6
3
1
.79–7.96 (3H, m, Ar–H) ppm. P NMR: 55.01, 43.52. UV–vis (THF) (nm) (A): λ : 284.0
1
(0.138).
2
3
3
2
.2.2.3. [Ru(Cl)(CO)(PPh ) (η -N ,S-TSC )] (3). A similar synthetic procedure as that
3
2
1
3
used for 1 was used except that TSC was replaced by TSC (211 mg), giving orange crys-
tals. The composition is confirmed by elemental analysis. Yield (79%). Found: C, 60.01; H,
4
.35; N, 4.60; S, 3.51. Calcd for C H ClN O P RuS: C, 60.03; H, 4.37; N, 4.67; S, 3.56.
45 39 3 3 2
−
1
FT-IR (ν, KBr): 1592 (m, C=N), 742 (w, C–S), 1113 (w, CN, NCN), 1935 (s, C≡O) cm .
1
H NMR (500 MHz, δ, DMSO-d ): 8.30 (1H, s, HC=N), 6.74–7.17(3H, m, Ar–H) ppm.
6
31
P NMR: 36.73 ppm. UV–vis (THF) (nm) (A): λ : 267.0 (0.299).
1
2
.3. Preparation of thin films
The sensing cocktail was prepared by mixing 240 mg of ethyl cellulose (ethoxy content of
4
3
8%) polymer, 192 mg of plasticizer (DOP), 10 mg of dye, 48 mg of ionic liquid, 1-ethyl-
-methylimidazolium tetrafluoroborate, in tetrahydrofuran (THF). After homogenation of
the cocktail under magnetic stirring, the cocktail was spread onto a 125 μm polyester sup-
port (Mylar TM type) by knife coating technique and located in a THF-saturated desiccator.
Thicknesses of the films were measured using a Tencor Alpha Step 500 Prophylometer and
were found to be 5.43 μm. This result was an average of eight measurements and exhibited
a standard deviation of ±0.12. Each sensing film was cut to 1.2 cm diameter, fixed in the
cell, and the emission and excitation spectra were recorded.
2
.4. Fluorescence-based studies
Steady-state fluorescence emission and excitation spectra were measured using a Varian
Cary Eclipse Spectrofluorometer with a Xenon flash lamp as the light source. The excitation
and emission slits were set to 20 nm and the detector voltage was set to 600 V.
2
.5. Gas-sensing studies
The gases O and N were mixed in the concentration range of 0.0–100.0% in a Sonimix
2
2
7
5
000A gas blending system. The output flow rate of the gas mixture was maintained at
50 mL min . The gases were introduced on the sensing slides in a covered cuvette via a
−1
diffuser needle under ambient conditions. Excitation and emission spectra of the sensing
materials were recorded after exposure to certain concentrations of oxygen.

Ruthenium(II) carbonyl thiosemicarbazones
5
2.6. Test for antimicrobial activity
3
3
1
The antimicrobial activity of [Ru(CO)(PPh ) (η -O,N ,S-TSC )] (1), [Ru(Cl)(CO)
(
3
2
2
3 2 3 2
3
2
2
3
3
PPh ) (η -N ,S-TSC )] (2), and [Ru(Cl)(CO)(PPh ) (η -N ,S-TSC )] (3) was evaluated
using the disk diffusion test method according to the National Committee for Clinical Labo-
ratory Standards [28] against the laboratory control strains belonging to the American Type
Culture Collection (Escherichia coli ATCC 25,922, Enterobacter cloacae ATCC 23355,
Pseudomonas aeruginosa ATCC 27853, Bacillus subtilis ATCC 11774, Staphylococcus
aureus ATCC 25923, Streptococcus pyogenes ATCC 19615, and one fungus Candida albi-
cans ATCC 10231) (LGC Standards GmbH, Wesel, Germany) and clinical isolate (P. aeru-
ginosa, S. aureus, and Streptococcus agalactiae were kindly supplied from the
Microbiology Department, Faculty of Medicine at the Dicle University).
The inocula of the test organisms were prepared by transferring three to five freshly
grown colonies of the cultures into 25 mL of sterile Nutrient Broth (NB, Oxoid) and incu-
bated at 37 °C for 4–5 h. The bacterial cultures were adjusted with 0.5 McFarand turbidity
8
−1
standards (1 × 10 CFU mL ) and streaked evenly onto the Nutrient Agar (NA, Oxoid)
plate with a sterile cotton swab. Three to five colonies of C. albicans ATCC 10231 were
inoculated into 25 mL of Sabouraud Dextrose Broth (SDB, Oxoid) and incubated at 37 °C
for 8–10 h. C. albicans ATCC 10231 cultures were adjusted with 0.5 McFarand turbidity
8
−1
standards (1 × 10 CFU mL ) and streaked evenly onto the Sabouraud Dextrose Agar
SDA, Oxoid) plate with sterile cotton swabs [29]. Six–millimeter-diameter sterile filter
(
−
1
paper disks (Oxoid, England) were impregnated with 10, 15, and 20 μL (at 5 mg mL ) of
ruthenium complexes 1–3 solutions in dichloromethane/methanol (8 : 2) and were then dried
4
h on a clean Petri dish. The seeded plates were left for drying for 3–5 min, and the disks
were placed on the agar using sterile forceps and were gently pressed down to ensure con-
tact. Then the plates were incubated in an upright position at 37 °C for 24 h for bacteria
and 48 h for fungi. Positive control (ofloxacin, 5 μg/disk (OFX); amoxycillin/clavulanic
acid (2 : 1), 30 μg/disk (AMC); imipenem, 10 μg/disk (IMP); erythromycin, 15 μg/disk (E)
(all from Oxoid) and nystatin, 60 μg/disk (N) (Sigma)) and negative control (disks imbued
with 20 μL of DCM/MeOH (8 : 2) solvent system) were also included for each experiment.
The diameters of zones of inhibition were determined in millimeters using an inhibition
zone ruler and the results were recorded.
3
3
. Results and discussion
.1. Synthesis
3
3
1
2
3
Ruthenium(II) complexes [Ru(CO)(PPh ) (η -O,N ,S-TSC )] (1), [Ru(Cl)(CO)(PPh ) (η -N ,
3
2
2
3 2
2
3
3
S-TSC )] (2), and [Ru(Cl)(CO)(PPh ) (η -N ,S-TSC )] (3) have been prepared by reacting
3
2
1
2
3
[
Ru(H)(Cl)(CO)(PPh ) ] with the respective thiosemicarbazone ligands TSC , TSC , and TSC
3 3
in a 1 : 1 M ratio in toluene and benzene (figure 2). The analytical data for 1–3 are summarized
in the experimental section. The stoichiometry of the ligands and their complexes have been
n
confirmed by elemental analyses. The spectroscopic data confirm that TSC (n = 1–3)
n
coordinate thiosemicarbazone derivatives. For the structural characterization of TSC (n = 1–3)
1
31
with their Ru(II) complexes 1–3, FT-IR spectra, UV–vis spectra, and H and P NMR spectra
were used and the corresponding data are given in the experimental section.

6
N. Öztürk et al.
1
TSC
1
2
TSC
2
3
TSC
3
4
TSC
4
Figure 2. Structures of 1–4.
Source: Taken from Ref. [21].
All the complexes were isolated in moderate yields and are quite stable in air and light.
The analytical data for the complexes are in agreement with the formula proposed. The
complexes are soluble in common organic solvents such as dimethyl sulphoxide, dichloro-
methane, and chloroform. Various attempts have been made to obtain single crystals of the
complexes but were unsuccessful.

Ruthenium(II) carbonyl thiosemicarbazones
7
Based on elemental analysis and spectroscopic data, the complexes are best formulated
3
3
1
2
3
2
as [Ru(CO)(PPh ) (η -O,N ,S-TSC )] (1), [Ru(Cl)(CO)(PPh ) (η -N ,S-TSC )] (2), and [Ru
3
2
2
3 2
3
3
(
Cl)(CO)(PPh ) (η -N ,S-TSC )] (3). The spectroscopic data reasonably support the formu-
3 2
las of the compounds.
3
3
.2. Spectroscopic characterization
.2.1. Infrared spectra. TSCs can coordinate in a number of different manners. Most
commonly they bind as either of two tautomeric forms, a neutral thione form or the anion
from the thiol form. Infrared spectroscopy was used to confirm coordination as the thiol
form in 1–3. FT-IR spectra of the free ligands were compared with the complexes to
confirm the coordination of the ligand to ruthenium. The main stretching frequencies of the
1
–3
FT-IR spectra of ligands TSC
section.
and Ru(II) complexes 1–3 are given in the experimental
−
1
The highest frequency bands at 3337 cm in spectra of the ligands are assigned to υasym
and υsym of terminal NH . These bands are present in the spectra of the complexes as well,
2
indicating non-involvement of this group in coordination.
Coordination via the azomethine nitrogen is inferred by the following observations. The
−
1
1
−1
2
absorption due to C=N of the free ligand at 1591 cm (TSC ), 1593 cm (TSC ), and
1
−
1
3
595 cm (TSC ) in spectra of the complexes indicates coordination of azomethine nitro-
gen. Coordination of the thiosemicarbazone ligands to ruthenium ion through azomethine
nitrogen is expected to change the electron density in the azomethine and thus alters υ
to 1596 cm , 1; 1589 cm , 2; and 1596 cm , 3 after complexation, indicating coordina-
(
C=N)
−
1
−1
−1
tion of azomethine nitrogen to ruthenium ion.
−
1
1
−1
2
The υ(
bands of the ligands are at 1053 cm (TSC ), 1062 cm (TSC ), and
N–N)
1
−
3
−1
−1
1
111 cm (TSC ). The change in frequency of these bands 1093 cm , 1; 1093 cm , 2;
and 1090 cm , 3 in spectra of the complexes provides evidence for coordination via azo-
−
1
−
1
−1
−1
methine nitrogen [30]. A strong band at 3151 cm , 1; 3155 cm , 2; and 3181 cm , 3
attributed to υ(N–H) of –NH–N=C in spectra of free ligands is not present in spectra of metal
complexes [31].
−
1
1
−1
2
The free ligands display υ
38 cm (TSC ). This band is also not present in spectra of the complexes. However, new
absorption at 819 cm (TSC ), 831 cm (TSC ) and
C=S)
(
−
1
3
8
−
1
−1
−1
−1
bands are present at 1541 cm , 1; 1542 cm , 2; 1548 cm , 3; 1020–1036 cm , 1 and
−
1
−1
−1
7
–
27 cm , 1; 750 cm , 2; and 742 cm , 3 which are assigned to the new azomethine group
C=N–, –C–O and–C–S, respectively. The disappearance of υ(C=S) and υ(N–H) in 1–3 confirm
that TSC ligands coordinate in the thiol form. Bands due to –SH are not present in spectra of
–3. These observations indicate the thiolization of –NH–C=S and subsequent deprotonation
1
−
1
1
before coordination. A strong band was obtained at 1254 cm in free TSC , assigned to phe-
nolic –C–O absorption. On complexation, this band shifted to higher frequency at
−
1
1
1
286 cm , indicating coordination of TSC through the phenolic oxygen [32]. This is fur-
−
1
ther confirmed by disappearance of the υ(ph–C–OH) broad band υ(OH) at 2967 cm in 1, indi-
cating deprotonation of the phenol prior to coordination through the deprotonated oxygen;
υ(OH) of the phenolic group in ligand spectra disappears in the spectrum of 1 and an increase
in frequency of phenolic C–O vibration from ligand (1261–1278 cm ) to metal complex
1313–1319 cm ) is observed. These results suggest coordinating phenolic oxygen.
−
1
−1
(
−
1
−1
−1
In all of the complexes, a strong band at 1944 cm , 1; 1955 cm , 2; and 1935 cm , 3
is due to terminally coordinated carbonyl and is observed at higher frequency than in the

8
N. Öztürk et al.
−
1
precursor complexes [RuHCl(CO)(PPh ) ] (1928 cm ). Characteristic absorptions due to
3
3
triphenylphosphine were also observed for the complexes in their expected regions, 1433–
−
1
−1
−1
−1
1
438 cm , 1090–1093 cm , 750–794 cm , and 518–526 cm . Replacement of hydride
in the starting complexes by TSC has been confirmed by the absence of a band at
−1
2
020 cm in all the complexes [33].
Spectra of the complexes show that TSC is coordinated tridentate to ruthenium via azo-
1
2
3
methine nitrogen (C=N), phenolic oxygen, and sulfur; TSC and TSC coordinate bidentate
to ruthenium via azomethine nitrogen (C=N) and sulfur. C=N/SH vibrations have different
wavenumbers in the FT-IR spectra of 1–3, respectively.
Bands are assigned to υ(M–N), further supporting coordination of the azomethine nitrogen.
−
1
In the complexes the medium intensity band at 518–526 cm is attributed to Ru–N [34].
−
1
In the low frequency region 439 cm is attributed to Ru–O [35].
1
31
1
3
.2.2. H and P NMR spectra. The ligand-to-metal bonding is further supported by H
3
1
and P NMR spectra. The TSC ligands and the complexes are very soluble in DMSO and
so their NMR spectra were obtained in DMSO-d . The H NMR spectral results obtained
for TSC and 1–3 in DMSO-d with their assignments are given in the experimental section.
Signals of phenolic proton appear at 11.38 ppm (TSC ) and NH protons at 9.16 ppm
1
6
n
6
1
1
2
3
1
(
TSC ), 9.51 ppm (TSC ), and 9.28 ppm (TSC ) in H NMR spectra of the ligands. These
signals are not present in spectra of the complexes, indicating deprotonation of these
1
groups. The proton resonance as a singlet at δ = 11.38 ppm in the spectra (TSC ) due to the
–
OH proton disappeared in the spectra of 1. The absence of OH resonance in 1 indicates
deprotonation of the phenolic group of the thiosemicarbazone on complexation and
coordination to ruthenium through phenolic oxygen. In spectra of 1–3, a sharp singlet at
8
.38 ppm, 1; 8.37 ppm, 2; and 8.30 ppm, 3 has been assigned to azomethine proton
(
–HC=N). The positions of azomethine signal in the complexes are shifted to a lower field
1
2
3
compared to free ligands at 8.18 ppm (TSC ), 8.16 ppm (TSC ), and 8.04 ppm (TSC ),
indicating coordination through the azomethine nitrogen. In spectra of 1–3, a multiplet
observed at 6.74–8.08 ppm, 1; 6.79–7.96 ppm, 2; and 6.74–7.17 ppm, 3 is assigned to
aromatic protons and the phenyl group of triphenylphosphine.
Resonances of terminal NH in 1–3 are seen in the same positions as in ligand spectra
2
3
.29–3.34, confirming the non-involvement of this group in coordination. The resonances
1
for the methoxy protons are singlet at 3.8 ppm in TSC and 1 with no significant change.
1
In the H NMR spectra of 1–3 all indications are that the TSC ligands are anionic (evi-
denced by the absence of the –NH– protons). Enolization of thiocarbonyl group is indicated
by the singlet present at 10.4 ppm in spectra of the ligand, attributed to –C–SH protons of
thioamide group of TSC. The absence of thionyl group in the complexes indicates deproto-
nation of this group on coordination through thionyl sulfur. The absence of signals ascribed
to –SH is consistent with the idea that in solution, as in the solid state, the ligand exists as
the deprotonated thiol tautomer [36].
3
1
The P NMR spectra showed one peak in 1 and 3 at 27.61 and 36.73 ppm, respectively,
indicating that the triphenylphoshine groups are trans in these complexes [37]. In 2, it is
observed as peaks at 55.01 and 43.52 ppm, indicating that the triphenylphosphine groups
are cis.
3
.2.3. Electronic spectra. Electronic spectral assignments of 1–3, given in the experimen-
tal section, showed two and three bands at 333–324 nm. The ground state of ruthenium(II)

Ruthenium(II) carbonyl thiosemicarbazones
9
1
6
is A , arising from the t configuration in an octahedral environment. Excited state cor-
1
g
2g
5
1
3
3
1
1
responding to the t 2ge configuration are T , T , T , and T . Hence, four bands
corresponding to the transitions A → T , A → T , A → T , and A → T are
g
1g
2g
3
1g
1
2g
1
3
1
1
1
1
1
g
1g
1g
2g
1g
1g
1g
2g
possible, in order of increasing energy. The electronic spectra of the complexes show sev-
eral absorptions in the ultraviolet region.
Bands at 281–284 nm in all the complexes may be assigned to Ru (4dπ)→π* (imine)
MLCT) transition. The other bands below 275 nm are due to intraligand transitions occur-
(
ring within ligand orbitals. These bands are seen in the spectra of the ligands also but at a
slightly lower wavelength, indicating the coordination of the ligands to ruthenium. The pat-
tern of the electronic spectra of all the complexes indicates the presence of an octahedral
geometry around ruthenium(II) [33].
3
.2.4. Fluorescence-based spectra. The photoluminescence properties were studied at
room temperature for 1–3 either doped in DMSO or solid matrix of ethyl cellulose.
The fluorescence data are given in table 1. All of the complexes in the solution phase
were excited in the range 235–341 nm. The emissions were observed as a broad and
intense band from 340 to 550 nm, attributed to the spin-allowed ligand-centered π→π*
bands in the UV region of the excitation spectra [38, 39]. Intense emission maxima
were observed at 382, 358, 387, and 389 nm for 1, 2, 3, and 4, respectively. The
emission maximum of 2 which had only one phenolic group in its thiosemicarbazone
ligand was the lowest at 358 nm. The emission maximum of 4 which had a thiophene
was the highest at 389 nm. Mishra et al. reported that the attachment of the 2-thienyl
2
+
group in [Ru(tpy-th)2] (th = thiophene) causes a red shift in the absorption maximum
which consequently will cause a red shift in the emission maximum [38]. This red
shift indicates that the thiophene has very strong electronic interactions with
Ru-to-ligand charge transfer states and strongly stabilizes these MLCT states. The thio-
semicarbazone binds the metal center via the nitrogen and oxygen forming five- and
six-membered chelate rings in the case of 1. The relatively higher emission maximum
of 1 when compared with 2 can be attributed to these rings and the hindered rotational
movements. Thus, by doping of 1 in solid ethyl cellulose membrane for oxygen
sensing, no significant red shift in the excitation and emission maxima was observed.
However, in the case of 4, by the doping of the complex into the solid matrix, the
structure became more rigid, preventing rotational movements and causing a red shift
of 60 nm from 280 to 340 nm in its excitation maximum (figure 3).
Table 1. Fluorescence-based data in solution of DMSO and in solid matrix of EC.
Fluorescence Fluorescence
λ
max for
λ
max for
Stokes
shift
intensity
intensity
Relative signal
change, %
Complexes excitation, nm emission, nm
(100% N
2
)
(100% O
2
)
Matrix
1
2
3
4
1
4
282, 341
235, 280
305
309
320, 340(s)
330, 345(s)
382
358
387
100
74
120
80
67
65
575
410
350
480
890
815
280
360
300
420
710
760
51
13
14
13
20
7
DMSO
DMSO
DMSO
DMSO
EC
389
375(s), 387
380(s), 395
EC

1
0
N. Öztürk et al.
Figure 3. Emission and excitation spectra for 4 and in solid matrix of ethyl cellulose (a and a′) and in solution of
DMSO (b and b′).
The Stoke’s shift values of the complexes were also calculated (table 1). All of the com-
plexes exhibited relatively high Stoke’s shifts ranging from 65 to 120 nm, allowing the
emitted fluorescence photons to be easily distinguished from the excitation photons, and is
of great importance for future sensor studies.
3
.2.5. Oxygen-sensing studies. Triplet oxygen is able to quench fluorescence of ruthenium
complexes via collisions with the fluorophore in its excited state leading to a non-radiative
energy transfer. This is called “dynamic fluorescence quenching.” The degree of quenching
relates to the frequency of collisions, and therefore to the concentration, pressure, tempera-
ture, and matrix material of the sensor. In our case, the oxygen-sensing properties were
examined both for the solution phase (DMSO) and for the ethyl cellulose matrix. In the
solution phase, 1 exhibited the highest quenching efficiency for oxygen with a relative sig-
nal change of 51% after exposure to 100% N (g) and 100% O (g). However, in the solid
2
2
ethyl cellulose matrix the relative signal change was only 22% (figure 4). This can be attrib-
uted to the diffusion-controlled mechanism of quenching where the microstructure and
porosity of the sensing films influence the oxygen permeability. Complex 1 is promising for
future oxygen sensor designs and the relative signal change can be enhanced by utilization
of different matrices or by modification of the current matrix.
3
.3. Antimicrobiological activities
Complexes 1–3 were tested for their in vitro antibacterial and antifungal activity by disk dif-
fusion method [28, 29] with five Gram-positive bacteria B. subtilis ATCC 11774, S. aureus
ATCC 25923, S. pyogenes ATCC 19615, S. aureus (clinical isolate), and S. agalactiae
(clinical isolate), four Gram-negative bacteria E. coli ATCC 25922, E. cloacae ATCC
2
3355, P. aeruginosa ATCC 27853, and P. aeruginosa (clinical isolate), and one fungal
strain C. albicans ATCC 10231. Ofloxacin, amoxycillin/clavulanic acid (2 : 1), imipenem,
erythromycin, and nystatin were used as standard drugs. Table 2 shows the antimicrobial
activity of standard antibiotics against the test micro-organisms. The ruthenium complexes
did not show any inhibition zone against micro-organisms at the concentration (50, 75, and
1
00 μg/6 mm paper disk) evaluated in this work. Some Ru(II) thiosemicarbazone com-
plexes do not exhibit antimicrobial activity against medically important bacterial and fungal
strains, and therefore research results are obtained by Beckford et al. [40, 41] that shows
parallels with the results of this study.

Ruthenium(II) carbonyl thiosemicarbazones
11
Figure 4. Emission spectra for 4 in solid matrix of ethyl cellulose (a) 0.0%, (b) 10%, (c) 20%, (d) 40%, (e) 60%,
f)100%, and O (g).
(
2
Table 2. Antimicrobial activities of standard antibiotics.
a
Inhibition zone diameter (mm)
Tested organisms
E (15)
AMC (30)
OFX (5)
IPM (10)
N (60)
Bacillus subtilis ATCC 11774
>30
20
24
18
28
12
r
r
r
nt
28
30
24
16
>30
18
19
r
27
22
16
22
22
28
28
13
23
nt
>30
>30
28
>30
>30
20
23
22
24
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
22
Staphylococcus aureus ATCC 25923
Streptococcus pyogenes ATCC 19615
b
Staphylococcus aureus
b
Streptococcus agalactiae
Escherichia coli ATCC 25922
Enterobacter cloacae ATCC 23355
Pseudomonas aeruginosa ATCC 27853
b
Pseudomonas aeruginosa
r
nt
Candida albicans ATCC 10231
Notes: E: erythromycin; AMC: amoxycillin/clavulanic acid (2 : 1); OFX: ofloxacin; IPM: imipenem; N: nystatin; nt: not tested; and
r: resistance.
a
μg/6 mm paper disk.
Clinical isolates.
b
4. Conclusion
This paper describes the synthesis, structural, and spectral characterization of four TSCs of
-hydroxy-3-methoxybenzaldehyde, 3-hydroxybenzaldehyde, 3,4-dihydroxybenzaldehyde,
2
thiophene-2-carbaldehyde and their ruthenium complexes and some reactivities of these
complexes.
The spectroscopic studies showed one ligand is coordinated to ruthenium as a tridendate
ligand coordinating via the azomethine nitrogen (C=N), phenolic oxygen, and sulfur in 1,
whereas second, third, and fourth ligands are coordinated to the central metal as a bidentate
ligand, coordinating via azomethine nitrogen (C=N) and sulfur in 2 and 3. The new ruthe-
nium complexes were not found to have any toxic activity against the Gram-negative and
Gram-positive bacteria and also fungus. When compared with other complexes, 1 exhibited
higher sensitivity to gaseous oxygen and can be employed as optical chemical sensor for
further studies. The relative signal change when exposed to oxygen gas was promising and
5
1% in solution phase. By the utilization of different matrices or by applying modification
procedures, the diffusion of oxygen to the relative signal change in the solid matrix can be
enhanced.

1
2
N. Öztürk et al.
Acknowledgements
This study was supported by project number 2011.KB. FEN.047 and 2012.KB. FEN.047
from Dokuz Eylul University Rectorship, Scientific Research Project Coordination Center.
We also thank the Graduate School of Natural and Applied Sciences, Dokuz Eylul
University, EBILTEM, Ege University for NMR analysis, and TUBITAK, for elemental
analysis.
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