Synthesis, spectral and thermal studies of the sodium salts of some Ru(III) complexes with quinolone antibiotics

Article abstract of DOI:10.1007/s10973-016-5902-z

Solubilisation by salt formation is an effective method to increase the solubility of slightly soluble drugs, applied especially for the development of liquid formulations for parenteral administration. In the present study, this strategy is applied for new Ru(III) complexes with quinolone antibiotics, valuable for biological application such as anticancer activity. The parent compounds, formulated as RuCl₃(HL)₂(DMSO)_m(H₂O)_n (HL: pipemidic acid, norfloxacin, ciprofloxacin, ofloxacin, levofloxacin, enrofloxacin, enoxacin), were transformed in their corresponding soluble sodium salts with general formula Na₂RuCl₃(L)₂(DMSO)_m(EtOH)_n(H₂O)_p. The sodium salts have been characterised by elemental analysis and some spectrometric methods (IR, UV–Vis, mass spectra). The thermal behaviour of these newly compounds was studied by simultaneous TG/DTG/DTA analysis, and it was evidenced a higher thermal stability compared to that of the parent compounds. The thermal transformations occur in two or three steps and comprise solvent (solvation or coordination) elimination as well as oxidative degradation of quinolone derivatives. A mixture of ruthenium and sodium chloride was identified as final residue.

Full text of DOI:10.1007/s10973-016-5902-z

J Therm Anal Calorim
DOI 10.1007/s10973-016-5902-z
Synthesis, spectral and thermal studies of the sodium salts of some
Ru(III) complexes with quinolone antibiotics
1
1
2
3
•
Mihaela Badea
Valentina Uivarosi
•
Rodica Olar
4
•
Luigi Silvestro
•
Martin Maurer
Received: 30 October 2015 / Accepted: 12 October 2016
Ó Akad e´ miai Kiad o´ , Budapest, Hungary 2016
Abstract Solubilisation by salt formation is an effective
method to increase the solubility of slightly soluble drugs,
applied especially for the development of liquid formula-
tions for parenteral administration. In the present study,
this strategy is applied for new Ru(III) complexes with
quinolone antibiotics, valuable for biological application
such as anticancer activity. The parent compounds, for-
mulated as RuCl (HL) (DMSO) (H O) (HL: pipemidic
of quinolone derivatives. A mixture of ruthenium and
sodium chloride was identified as final residue.
Keywords Quinolone derivative Á Ruthenium(III)
complex Á Sodium salt Á Thermal stability
Introduction
3
2
m
2
n
acid, norfloxacin, ciprofloxacin, ofloxacin, levofloxacin,
enrofloxacin, enoxacin), were transformed in their corre-
sponding soluble sodium salts with general formula Na2-
RuCl (L) (DMSO) (EtOH) (H O) . The sodium salts
The increase in solubility of poorly soluble biological
active compounds is a critical aspect related to the phar-
macological screening of new chemical entities as well as
in the design and development of pharmaceutical formu-
lations [1]. Salts formation is the most common and
effective method to increase the dissolution rate and solu-
bility of acidic and basic drugs [2]. The essential condition
for salt forming is the presence of ionisable groups in the
chemical structure. The advantages of using salts are rep-
resented by the enhanced stability and solubility in polar
solvents (mainly water). More than half of the solid-state
pharmaceutical active substances used nowadays are salts
2
3
2
m
n
2
p
have been characterised by elemental analysis and some
spectrometric methods (IR, UV–Vis, mass spectra). The
thermal behaviour of these newly compounds was studied
by simultaneous TG/DTG/DTA analysis, and it was evi-
denced a higher thermal stability compared to that of the
parent compounds. The thermal transformations occur in
two or three steps and comprise solvent (solvation or
coordination) elimination as well as oxidative degradation
(approx. 75 % are cationic salts and 25 % anionic salts).
The most used counterion for the anionic substances is
?
Na , followed by Ca , K and Mg [3].
2?
?
2?
&
Valentina Uivarosi
uivarosi.valentina@umf.ro
The synthetic strategy for obtaining soluble salts was
applied for some ruthenium (III) complexes with antitumor
or antimetastatic activity. The first type of complexes,
obtained by Keller and Keppler [4], is represented by
ruthenium (III) anionic complexes with N donors hetero-
cycles as unidentate ligands and most successful of its have
1
Department of Inorganic Chemistry, Faculty of Chemistry,
University of Bucharest, 90-92 Panduri St., Sector 5,
0
50663 Bucharest, Romania
2
3
4
Pharma Serv. International SRL, 52 Sabinelor St., Sector 5,
0
3
50853 Bucharest, Romania
-
the formula trans-[RuCl (L) ] , where L is imidazole
4
2
S-Pharmacological Consultation & Research GmbH, 1
(
KP418) or indazole (KP1019 and KP1339), and the
Koenigsbergerstrasse, 27243 Harpstedt, Germany
?
?
counterion is (LH) or Na .
Department of General Inorganic Chemistry, Carol Davila
University of Medicine and Pharmacy, 6 Traian Vuia St.,
KP1019 and KP1339 proved activity in the inhibition of
platinum resistant rat colorectal carcinomas [5]. The major
0
20956 Bucharest, Romania
123

M. Badea et al.
disadvantage of KP1019 in its development as anticancer
agent represented by the poor water solubility was solved
by transformation in sodium salt that results in an increase
of 35 times of the solubility compared to the parent com-
pound [6].
enrofloxacin, enoxacin, respectively) was suspended in
10 mL of distilled water and neutralised with 0.2 mL of
2 M sodium hydroxide aqueous solution in a 1:2 molar
ratio of complex to NaOH. The resulting solution was
concentrated on the water bath near dryness, cooled on ice,
and ethanol was added to yield a brown solid. The resulting
precipitate was collected by filtration, washed with ethanol
and air-dried.
The second class of ruthenium (III) compounds consists
in dimethyl sulfoxide-ruthenium (III) complexes with
metastatic activity [7]. The most active compounds of this
series are Na{trans-[Ru(III)Cl (dmso)(Him)]} (Him = im-
4
idazole) - NAMI, and [H im][trans-Ru(III)Cl (dmso)
2
4
Instruments
(Him)] - NAMI-A. NAMI, that belongs to a series of with
general formula Na[trans-RuC1 (R R SO)(L)], where R
1-
4
1
2
The chemical analyses were performed on a PerkinElmer
PE 2400 analyser (for C, H, N, S) and a Shimadzu AA
R SO = dimethyl sulfoxide (DMSO) or tetramethylene
2
sulfoxide (TMSO), L is a nitrogen donor ligand: imidazole
6300 spectrometer (for Ru and Na).
(
Im), oxazole (Ox), indazole (Ind), isoquinoline (Iq) [8], has
IR spectra were recorded in KBr pellets with a FT-IR
an intense action on lung metastases [9–11]. Although the
sodium salts of the anionic derivatives are slightly soluble in
water, the reproducibility of their formulation is sometimes
affected by the tendency to crystallise with DMSO and ace-
tone molecules in variable proportions. Reproducible results
VERTEX 70 (Bruker) spectrometer in the range
1
-
400–4000 cm
.
Electronic spectra by diffuse reflectance technique, with
MgO as standard, were recorded in the range 200–900 nm,
on a Jasco V 650 spectrophotometer.
?
?
4
are obtained with the LH and NEt salts, as it is NAMI-A.
Mass spectrometry measurements were performed with
THERMO PHINNIGAN MAT-900 mass spectrometer
with FAB (THERMO-FINNIGAN) ionisation source
operating in positive mode. Samples were dissolved in a
matrix on nitrobenzyl alcohol. Molecular ions scanning
range (m/z) was 0–1250.
This study is aimed to obtain soluble sodium salts of some
ruthenium (III) complexes with quinolone antibiotics. The
parent compounds, formulated as RuCl (HL) (DMSO)
m
3
2
(
H O) (HL: pipemidic acid, norfloxacin, ciprofloxacin,
2 n
ofloxacin, levofloxacin, enrofloxacin, enoxacin) [12, 13]
were transformed in their corresponding soluble sodium salts
withgeneralformula Na RuCl (L) (DMSO) (EtOH) (H O)
p
The thermoanalytical curves (TG and DTA) were
recorded using a Labsys 1200 SETARAM instrument, with
a sample mass of 13–22 mg over the temperature range of
2
3
2
m
n
2
by neutralisation with sodium hydroxide. The obtained
sodium salts were characterised by microanalytical, spectro-
metric methods (IR, UV–Vis, mass spectrometry) and thermal
analysis. Having in view a possible application as drugs, the
thermal analysis is required in order to develop proper drug
conditioning and storage methods. As a result, the thermal
analysis (TG, DTG and DTA) of the complexes was per-
formed in order to establish temperature range of compounds
thermal stability. This method also allowed us to confirm the
proposed formulas of complexes and to elucidate the number
and nature of the solvent molecules.
-
1
3
0–900 °C, using a heating rate of 10 K min . The
measurements were carried out in synthetic air atmosphere
3 -1
flow rate 17 cm min ) by using alumina crucibles. The
(
calibration of TG equipment was run both with gold (m.
p. 1064 ± 1 °C) and ultrapure CuSO Á5H O (99.9 %) with
4
2
a measurement error of 0.1 %.
The X-ray powder diffraction patterns were collected on
a DRON-3 diffractometer with a nickel-filtered Cu Ka
˚
radiation (k = 1.5418 A) in 2h range of 5°–70°, a step
width of 0.05° and an acquisition time of 2 s per step.
Na [RuCl (pip) (DMSO)]ÁEtOH
(Hpip = pipemidic
acid) (1) Analysis found: C, 39.54; H, 4.87; N, 13.96; S,
.66; Ru, 10.15; Na, 4.28 %; calculated for C H Cl
2 44 3-
2
3
2
Experimental
Materials
3
3
N Na O RuS: C, 39.12; H, 4.52; N, 14.26; S 3.26; Ru,
1
0
2 8
1
0.29; Na, 4.68 %. Reaction yield: 94 %.
Na [RuCl (enx) (DMSO)]ÁEtOHÁ3H O (Henx = enox-
2
3
2
2
All chemicals were purchased from Sigma-Aldrich, reagent
grade and were used without further purification.
acin) (2) Analysis found: C, 38.18; H, 4.37; N, 9.98; S,
2.80; Ru, 9.12; Na 3.99 %; calculated for C H Cl F
34 50 3 2-
N Na O RuS: C, 38.15; H, 4.72; N, 10.47; S 2.94; Ru,
8 2 11
Synthesis of complexes
9.44; Na 4.29 %. Reaction yield: 79 %.
Na [RuCl (nf) (DMSO)]ÁEtOHÁH O (Hnf = norfloxacin)
2
3
2
2
0
.2 mmol of each parent neutral complex of general for-
(
3) Analysis found: C, 41.95; H, 4.14; N, 7.89; S, 3.48; Ru,
mula RuCl (HL) (DMSO) (H O) (HL: pipemidic acid,
3
2
m
2
n
9
.29; Na, 4.11 %; calculated for C H Cl F N Na O RuS:
36 48 3 2 6 2 9
norfloxacin, ciprofloxacin, ofloxacin, levofloxacin,
1
23

Synthesis, spectral and thermal studies of the sodium salts of some Ru(III) complexes with…
C, 41.65; H, 4.69; N, 8.14; S, 3.10; Ru, 9.79; Na, 4.45 %.
Reaction yield: 82 %.
IR spectra
Na [RuCl (cp) (DMSO)]ÁDMSOÁ2EtOH (Hcp = cipro-
An important information concerning the coordination
mode of quinolone ligands in the parent Ru(III) complexes
and their corresponding salts can be obtained in a first
approach by comparative analysis of IR spectra of nor-
floxacin, its Ru(III) neutral complex and the corresponding
sodium salt (Fig. 1), data presented in Table 2. IR spec-
trum of norfloxacin is characteristic for the zwitterionic
form, having in view the very week stretching vibration of
2
3
2
floxacin) (4) Analysis found: C, 43.81; H, 4.51; N, 7.22; S,
.43; Ru, 8.31; Na, 3.42 %; calculated for C H Cl F
42 58 3 2-
5
N Na O RuS : C, 43.39; H, 5.04; N, 7.23; S 5.52; Ru,
6
2
10
2
8
.69; Na, 3.96 %. Reaction yield: 85 %.
Na [RuCl (enro) (DMSO)]Á1.5EtOH
(Henro = en-
2
3
2
rofloxacin) (5) Analysis found: C, 46.58; H, 4.82; N, 8.11;
S; 2.87; Ru, 8.75; Na, 3.81 %; calculated for C H Cl
3 57 3-
4
-
1
F N Na O8.5RuS: C, 46.26; H, 5.15; N, 7.52; S 2.87; Ru,
2
m(C=O) carboxylic at 1731 cm due to moving of car-
boxylic hydrogen to the terminal piperazinyl nitrogen atom
6
2
9
.05; Na, 4.11 %. Reaction yield: 81 %.
-
1
Na [RuCl (of) (DMSO)] (Hof = ofloxacin) (6) Analy-
2
[14]. The two bands at 1580 and 1380 cm are assigned to
asymmetric and the symmetric stretching of the deproto-
nated carboxylato group, respectively [15], while the very
3
2
sis found: C, 43.76; H, 3.86; N, 7.50; S, 3.00; Ru, 9.31; Na,
3
4
.97 %; calculated for C H Cl F N Na O RuS: C,
38 44 3 2 6 2 9
-
1
3.37; H, 4.22; N, 7.98; S 3.04; Ru, 9.60; Na, 4.37 %.
strong band at 1621 cm is due to the stretching vibration
of the m(C=O) pyridone. In the neutral complex [RuCl (-
Hnf) O norfloxacin acts as unidentate ligand
Reaction yield: 92 %.
3
Na [RuCl (levof) (DMSO)]Á2EtOH
(Hlevof = levo-
2
(DMSO)]ÁH
2
2
3
2
4
floxacin) (7) Analysis found: C, 44.28; H, 5.27; N, 7.71; S,
3
[12] coordinated through N (piperazyl) atom. As conse-
quence, the vibration of m(C=O) carboxylic from proto-
nated carboxyl group gives a very strong band in the IR
spectrum. The stretching vibration of the m(C=O) pyridine
.31; Ru, 8.44; Na, 3.64 %; calculated for C H Cl F
42 56 3 2-
N Na O RuS: C, 44.08; H, 4.94; N, 7.34; S 2.80; Ru,
6 2 11
8
.83; Na, 4.02 %. Reaction yield: 95 %.
-
1
is very slightly shifted from 1621 to 1626 cm and with
unchanged intensity, suggesting that this group is not
involved in coordination. The IR spectrum of the sodium
salt of this complex, Na [RuCl (nf) (DMSO)]ÁEtOHÁH O,
Results and discussion
2
3
2
2
In this paper, we report the preparation and physico-chemical
characterisation of the sodium salts of some Ru(III) com-
plexes with quinolone antibiotics. Synthesis of these deriva-
tives was carried out according to a simple procedure as
described in Scheme 1. The obtained salts have been for-
mulated on the basis of chemical analysis, IR, electronic and
mass spectra as well as thermal analysis as Na RuCl (L) (-
has a pattern very similar to that of norfloxacin in the
zwitterionic form, proving both the carboxyl group
deprotonation, and that the carboxyl and carbonyl (pyri-
done) groups are not involved in coordination.
In the IR spectra of the sodium salt of Ru(III) com-
plexes, the carboxyl group deprotonation is clearly evi-
denced through the presence of the two characteristic
2
3
2
-
DMSO) (EtOH) (H O) , their formulation being described
m
vibration bands of carboxylate group: mas(COO ) around
n
2
p
-
1
-
-1
in Scheme 1 and Table 1. All these sodium salts are brown
powders very soluble in water and slightly soluble or very
slightly soluble in organic solvents as dimethylformamide,
dimethyl sulfoxide, methanol and ethanol.
1585 cm and m (COO ) around 1390 cm (Table 3).
s
The values of Dm are the criteria that can be used to dis-
tinguish between the binding states of the carboxylate
-
1
group: (i) Dm [ 200 cm was found in case of unidentate
O
O
R2
N
COOH
X2
2Na
+
R2
N
COO
X2
X1
N
X1
N
N
Ru
N
R1
R3
Cl
N
Ru
N
R1
Cl
R3
Cl
Cl
Cl
DMSO
R3
+
-
2NaOH
2H O
Cl
DMSO
R3
R1
N
R1
N
X1
N
2
X1
N
X2
HCOO
R2
X2
OOC
O
R2
O
Scheme 1 General scheme for synthesis
123

M. Badea et al.
Table 1 Proposed formulae of complexes (1)–(7)
Compound
X1
X2
R1
R2
R3
m
n
p
Na
Na
Na
Na
2
2
2
2
[RuCl
[RuCl
[RuCl
[RuCl
3
3
3
3
(pip)
(enx)
(nf)
(DMSO)]ÁEtOHÁH
(cp)
(DMSO)]ÁDMSOÁ2EtOH (Hcp = ciprofloxacin) (4)
(enro)
(DMSO)]Á1.5EtOH (Henro = enrofloxacin) (5)
(DMSO)] (Hof = ofloxacin) (6)
2
(DMSO)]ÁEtOH (Hpip = pipemidic acid) (1)
(DMSO)]ÁEtOHÁ3H O (Henx = enoxacin) (2)
O (Hnf = norfloxacin) (3)
N
N
C
C
C
H
2 5
H
2 5
H
2 5
–
F
F
F
H
H
H
H
1
1
1
2
1
1
1
2
0
3
1
0
2
2
N
CH
C
2
2
CH
CH
2
C
Na
2
[RuCl
[RuCl
3
2
CH
CH
C
C
F
F
C
2
H
5
1
1
1.5
0
0
0
Na
2
3
(of)
2
CH
CH
3
3
O
O
CH3
CH3
Na [RuCl
2
3
(levof)
2
(DMSO)]Á2EtOH (Hlevof = levofloxacin) (7)
CH
C
F
1
2
0
spectra of norfloxacin, its Ru(III) neutral and anionic
complexes (Fig. 2; Table 3); it can be observed that free
norfloxacin has two distinct absorption bands. The first one
at 280 nm may be attributed to p ? p* transition of the
heterocyclic moiety and benzene ring, respectively. The
second band observed at 330 nm is attributed to n ? p*
intraligand transition. In the spectra of Ru(III) neutral
complex and the corresponding sodium salt, the first band
is unchanged, and this reflects that aromatic group is not
involved in the coordination. The second band is slightly
shifted (5 nm) in the spectra of Ru(III) neutral complex,
suggesting either a minor modification of electronic density
of the ligand upon coordination or an overlapping with a
charge transfer transition. This band is strongly shifted
Na Ru-nf
2
Ru-Hnf
Hnf
3
500
3000
2500
2000
1500
1000
500
Wavenumber/cm–1
Fig. 1 Infrared spectra of norfloxacin (Hnf), [RuCl
DMSO)]ÁH O (Ru-Hnf) and Na [RuCl (nf) (DMSO)]ÁEtOHÁH
Na Ru-nf)
3 2
(Hnf) (-
2
2
3
2
2
O
(
*16 nm) in the spectra of the sodium complex, and this
(
2
can be assigned both to carboxyl group deprotonation and
to overlapping with the charge transfer transition. In the
visible region of spectrum, both for Ru(III) neutral com-
plex and its sodium salt, the broadband with the absorption
maxima around 530 nm can be assigned to the spin-al-
-
1
carboxylato complexes, (ii) Dm \ 100 cm is character-
istic for bidentate or chelating carboxylato complexes, and
-
1
finally, (iii) Dm * 150 cm indicates bridging complexes
that show Dm comparable to ionic values [16]. As a result,
2
2
2
lowed transition T
? A , T for Ru(III) in an octahe-
2 1
2
-
-
the Dm values [m (COO ) - m (COO )] ranging between
dral distorted stereochemistry [17].
as
s
-
90 and 205 cm suggest in this case the presence of
1
1
In the electronic spectra of the other sodium salts, three
bands are also observed (Table 4): Two of these are placed
in the UV region of electronic spectrum, between 270–290
and 336–348 nm, respectively. The third band, a broad
one, with absorption maxima ranging between 450 and
540 nm is observed in the visible region of the electronic
spectrum.
uncoordinated carboxylate group.
UV–Vis spectra
The formation of the sodium salts was also confirmed by
UV–Vis spectra. By comparative analysis of the electronic
-
1
)
Table 2 Selected infrared bands of norfloxacin, its Ru(III) neutral complex and the corresponding sodium salt (cm
Compound
m(C=O)
m(C=O) (carbonyl)
m
as(COO)
s
m (COO)
s
Dm = [mas(COO) - m (COO)]
Norfloxacin (Hnf)
1731w
1721s
–
1621vs
1626vs
1622vs
1580s
–
1380s
–
200
–
[
RuCl (Hnf)
3
2
(DMSO)]ÁH
2
O
Na [RuCl
2
3
(nf)
2
(DMSO)]ÁEtOHÁH
2
O (3)
1584s
1380m
204
1
23

Synthesis, spectral and thermal studies of the sodium salts of some Ru(III) complexes with…
-1
)
Table 3 Selected infrared bands of complexes (1)–(7) (cm
-
-
(COO )
-
-
(COO )]
Compound
m(C=O)
m(C=O) (carbonyl)
m
as(COO )
m
s
Dm = [mas(COO ) - m
s
(1)
(2)
(3)
(4)
(5)
(6)
(7)
–
1633vs
1630vs
1621vs
1623vs
1621vs
1621vs
1621vs
1577s
1382m
1390w
1380m
1391m
1392m
1395m
1387m
195
191
204
195
193
196
203
1709sh
1581m
1584s
–
–
–
1586m
1585m
1591s
–
1590vs
Mass spectrometry measurements
The ESI–MS spectra performed in the positive mode ioni-
sation confirmed the complexes formulation. Thus, the
complexes spectra contain either a peak corresponding to
Ru-Hnf
Na Ru-nf
2
?
protonated coordination sphere [RuCl (L) (DMSO) ?3H] ,
3
2
m/z: 1005 and 1008 for complexes (5) and (6), respectively,
Á
or their adduct with DMSO: [RuCl (L) (DMSO) ?3H ?-
3
2
?
DMSO] , m/z: 971, 1005, 1003, 1027 and 1087 for com-
plexes (1)–(4) and (7), respectively. Also, for some
complexes were detected sodiated adducts [RuCl (L) (-
3
2
?
DMSO) ?3Na] , m/z: 959, 1015, 1075 and 1075 for com-
plexes (1), (4), (6) and (7), respectively.
Hnf
Thermal analysis
Thermal analysis techniques are frequently used in order to
obtain useful information concerning the composition and
stability of complexes. In this way, the thermal behaviour
of complexes was investigated by simultaneous TG/DTG/
DTA analysis, and the final residue was identified by
powder X-ray diffraction. The data are summarised in
Table 5. The corresponding thermal decomposition curves
for some of these complexes are represented in Figs. 3–6.
2
10
400
600
Wavelength/nm
800
Fig. 2 Electronic spectra of norfloxacin (Hnf), [RuCl
DMSO)]ÁH O (Ru-Hnf) and Na [RuCl (nf) (DMSO)]ÁC
Na Ru-nf)
3
(Hnf)
2
(-
2
2
3
2
2
5
H OHÁH
2
O
(
2
Thermal decomposition of complexes
Table 4 Absorption maxima from UV–Vis spectra of complexes
1)–(7)
Na [RuCl (pip) (DMSO)]ÁEtOH (1)
2
3
2
(
and Na [RuCl (enro) (DMSO)]Á1.5EtOH (5)
2
3
2
Compound
k/nm
The complexes (1) and (5) lose both coordinated and
uncoordinated solvent molecules in a first step which
seems to be not a single one according to DTG curve
(
(
(
(
(
(
(
1)
2)
3)
4)
5)
6)
7)
*494 (br)
*536 (br)
*536 (br)
*524 (br)
*465 (br)
*449 (br)
*476 (br)
346
336
346
339
343.5
348
348
273
279
270
(
Fig. 3). This endothermic step undergoes in 71–240 °C/
7–215 °C temperature ranges due the very low volatility
278
6
277
of DMSO (boiling point 189 °C). This behaviour was also
evidenced for another species which contain DMSO
molecules [18]. The remaining product undergoes a few
oxidative degradation steps (as TG, DTG and DTA curves
290 (sh)*
291.5 (sh)
*
br broad
123

M. Badea et al.
1
23

Synthesis, spectral and thermal studies of the sodium salts of some Ru(III) complexes with…
3
3
2
5
0
5
0.4
.2
0
0
0
0
.3
.2
.1
.0
TG
40
30
20
TG
0
–20
–40
0
20
40
60
80
0
DTG
20
–
–
–
–
0.0
1
1
5
0
–
–
5
0
10
–0.1
–0.2
–0.3
–0.2
–0.4
0
DTA
–
–
60
80
–10
–20
5
–0.4
–
–
0.6
0.8
10
–0.5
–0.6
–15
20
1000
–30
–
0
200
400
600
800
1000
0
200
400
600
800
Temperature/°C
Temperature/°C
Fig. 4 TG, DTG and DTA curves of complex (2)
Fig. 3 TG, DTG and DTA curves of complex (1)
5
0
show) leading to the final residue which, according to
powder X-ray diffraction, is a mixture of metallic ruthe-
nium and sodium chloride (Fig. 7).
TG
0
0.2
40
0
0
.1
.0
3
2
1
0
0
0
–
–
20
40
DTG
Thermal decomposition of complexes
–0.1
–0.2
Na [RuCl (enx) (DMSO)]ÁEtOHÁ3H O (2)
2
3
2
2
DTA
and Na [RuCl (nf) (DMSO)]ÁEtOHÁH O (3)
–60
2
3
2
2
0
–
0.3
–
–
10
–0.4
–0.5
–
80
Thermal decomposition of complexes (2) and (3) occurs
quite similar, sustaining their related formulation. The first
two endothermic steps, well delimited, correspond to the
ethanol molecules release in the 70–125 °C temperature
range followed by the water molecules loss. This behaviour
can be explained by the higher volatility of ethanol toge-
ther with the lack of hydrogen bonds interaction with the
complex [19]. On the other hand, it is known that the water
molecules are easily involved in hydrogen bonds which
explain the higher temperature needed to be released
20
0
200
400
600
800
1000
Temperature/°C
Fig. 5 TG, DTG and DTA curves of complex (3)
Over 295 °C, the remaining compound undergoes
oxidative degradation leading to the same residue as pre-
vious complexes.
[
20–22]. The intermediates without solvent molecules
Thermal decomposition of complex
decompose in several overlapped steps according to TG,
DTG and DTA curves (Figs. 4, 5). The final residue is also
a mixture of metallic ruthenium and sodium chloride.
Na [RuCl (of) (DMSO)] (6)
2
3
2
The Na [RuCl (of) (DMSO)] complex decomposes in two
2
3
2
steps. The first one corresponds to the DMSO loss. This is
an endothermic process which occurs in 70–215 °C tem-
perature range. The remaining product decomposes in
several overlapped processes, the residue at 900 °C being
the same as previous complexes.
Thermal decomposition of complex
Na [RuCl (cp) (DMSO)]ÁDMSOÁ2EtOH (4)
2
3
2
According to TG, DTG and DTA curves, complex (4)
decomposes in three well-defined steps. First, the uncoor-
dinated solvents are released in the 55–195 °C temperature
range. The next step corresponds to the coordinated DMSO
molecules loss in 195–295 °C temperature range [18, 23].
Taking into account the high temperature and the miscel-
laneous thermal effects observed on DTA curve, we can
conclude that several processes occur in this step, such as
volatilisation and partial/total oxidation. The successive
and well-defined release steps of DMSO molecules can be
associated with the different interaction strengths involving
these molecules (hydrogen interactions or coordinative
bonds).
Thermal decomposition of complex
Na [RuCl (levof) (DMSO)]Á2EtOH (7)
2
3
2
The thermal decomposition of complex (7) starts with the
release of ethanol molecules, an endothermic process
which occurs in 76–140 °C temperature range [19]
(
Fig. 6). The IR spectrum of isolated residue at 140 °C is
almost identical with that of parent compound except the
-
1
disappearance of band at 1055 cm assigned to m(C–O)
characteristic to primary alcohols. The next steps corre-
spond to DMSO loss in the 140–245 °C temperature range
123

M. Badea et al.
6
5
4
3
0
0
0
0
A higher thermal stability for sodium salts was observed
compared to the parent compounds as thermal analysis
revealed. The decomposition of complexes occurs in two or
three steps corresponding to solvent molecules (lattice or
coordinated) followed by oxidative degradation of quino-
lone derivative. The final product of degradation consists in
a mixture of metallic ruthenium and sodium chloride for all
complexes.
TG
0
20
40
60
80
0
0
–
.2
–
–
–
–
DTG
.0
20
0.2
1
0
–
–
0
DTA
–0.4
–0.6
10
20
Acknowledgements This work was supported by a grant of the
Romanian National Authority for Scientific Research, CNDI—
UEFISCDI, Project Number 136/2012.
0
200
400
600
800
1000
Temperature/°C
Fig. 6 TG, DTG and DTA curves of complex (7)
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123