Synthesis, characterization, electro chemistry, catalytic and biological activities of ruthenium(III) complexes with bidentate N, O/S donor ligands

Article abstract of DOI:10.1016/j.saa.2005.12.029

New hexa-coordinated ruthenium(III) complexes of the type [RuX₂(EPh₃)₂(L)] (E = P or As; X = Cl or Br; L = monobasic bidentate Schiff base derived from the condensation of benzhydrazide with furfuraldehyde, 2-acetylfuran a

Full text of DOI:10.1016/j.saa.2005.12.029

Spectrochimica Acta Part A 65 (2006) 678–683
Synthesis, characterization, electro chemistry,
catalytic and biological activities of ruthenium(III)
complexes with bidentate N, O/S donor ligands
K.P. Balasubramaniana, K. Parameswaria, V. Chinnusamya,
R. Prabhakaranb, K. Natarajanb,∗
a Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore 641 020, India
b Department of Chemistry, Bharathiar University, Coimbatore 641 046, India
Received 3 August 2005; accepted 17 December 2005
Abstract
New hexa-coordinated ruthenium(III) complexes of the type [RuX2(EPh3)2(L)] (E = P or As; X = Cl or Br; L = monobasic bidentate Schiff
base derived from the condensation of benzhydrazide with furfuraldehyde, 2-acetylfuran and 2-acetylthiophene) have been synthesized from the
equimolar amounts of [RuX3(EPh3)3] or [RuBr3(PPh3)2(MeOH)] and Schiff bases in benzene. The new complexes have been characterized by
analytical, spectral (IR, electronic and EPR), magnetic moment, and cyclic voltammetry. An octahedral structure has been tentatively proposed.
All the complexes have exhibited catalytic activity for the oxidation of benzyl alcohol, cyclohexanol and cinnamylalcohol in the presence of
N-methylmorpholine-N-oxide as co-oxidant. All the new complexes were found to be active against the bacteria such as E. coli, Pseudomonas,
Salmonella typhi and Staphylococcus aureus. The activity was compared with standard Streptomycin.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Ruthenium(III) complexes; EPR; Cyclic voltammetry; Catalytic activity; Antibacterial studies
1. Introduction
activities of chemical and industrial versatility of metal-Schiff
base hydrazones of pyidoxal phosphate and its analogs have
been studied [26,27]. Having these all in our mind, we have inter-
ested to prepare a single complex having very good catalytic and
medicinal properties. Here, we disclose the synthesis, spectral
characterization, electrochemistry, catalyticactivityandbiologi-
cal activities of ruthenium(III) Schiff base complexes containing
triphenylphosphine/arsine. The general structure of Schiff base
ligands used in the present work is given in Fig. 1.
In the recent years, there has been considerable interest in
the chemistry of transition metal complexes containing Schiff
bases, mainly due to the fact that they offering opportunities for
inducing substrate chirality, turning metal centered electronic
factor, enhancing stability of either homogeneous or heteroge-
neous catalyst [1–9]. The interest in the study of compounds
containing sulphur and nitrogen donor atoms arises from their
significant antifungal [10], antibacterial, anticancer and catalytic
activities [11–15]. Moreover, it is well known that some drugs
have increased activity when administered as metal complexes
[16,17] and their interaction with DNA have been reported [18].
Several metal chelates have also been shown to inhibit tumor
growth [19]. The recent reports have been shown that the ruthe-
nium based complexes are not only having catalytic activity
and also very good medicinal properties [20–25]. The biological
2. Experimental
2.1. Materials and methods
All the reagents used were of analar or chemically pure grade.
Solventswerepurifiedanddriedaccordingtothestandardproce-
dures [28]. RuCl3·3H2O purchased from Loba chemie, was used
without further purification. The analyses of carbon, hydrogen
and nitrogen were performed at the Central Drug Research Insti-
tute, Lucknow, India. IR spectra of the complexes were recorded
in KBr pellets with a Shimadzu 8000 FT-IR spectrophotome-
∗
Corresponding author. Tel.: +91 422 2424655; fax: +91 422 2422387.
E-mail address: k natraj6@yahoo.com (K. Natarajan).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.12.029

K.P. Balasubramanian et al. / Spectrochimica Acta Part A 65 (2006) 678–683
679
2.2. Recommended procedures
2.2.1. Synthesis of new ruthenium(III) complexes
All the new complexes were prepared by following general
procedure. To a solution of [RuCl3(PPh3)3], [RuCl3(AsPh3)3],
[RuBr3(AsPh3)3] or [RuBr3(PPh3)2(MeOH)] (0.099–0.125 g,
0.1 mmol) in benzene (25 cm3) the appropriate Schiff base lig-
ands (0.1 mmol) were added. The mixture was then heated
under reflux for 6 h. The resulting solution was concentrated
to ca. 3 cm3 and cooled. Light petroleum (60–80 ◦C) was then
added, whereupon the product complex separated. The solid
was filtered off, washed and recrystalized from CH2Cl2/light
petroleum (60–80 ◦C) and dried in vacuo.
3. Results and discussion
The air and light stable complexes of general formula
[RuX2(EPh3)2(L)] (E = P or As; X = Cl or Br; L = monobasic
bidentate Schiff base anion) have been prepared by reacting
[RuX3(EPh3)3] or [RuBr3(PPh3)2(MeOH)] with the respective
Schiff bases in a 1:1 molar ratio in benzene.
Fig. 1. General structure of the ligands.
ter in the 4000–400 cm−1 range. The electronic spectra were
recorded in CH2C12 solution with Perkin-Elmer 20/200 spec-
trophotometer in the 800–200 nm range. EPR spectra of the
powdered samples were recorded on a Bruker E-112 Varian
model instrument in X-band frequencies at room temperature.
Magnetic susceptibilities were recorded on EG and G-PARC
vibrating sample magnetometer. The cyclic voltammetric stud-
ies were carried out with BAS CV-27 model electro chemical
analyzer in acetonitrile solution using a glassy carbon working
electrode and the potentials were referenced to saturated calomel
electrode.
[RuX3(EPh3)3]
or
+ HL
[RuBr3(PPh3)2(MeOH)]
B−en→zene [RuX2(EPh3) (L)] + HX + EPh3
2
Reflux, 6 h
All the complexes are green and soluble in common organic
solvents. The analytical data obtained for the new complexes
(Table 1) agree very well with proposed molecular formulae. In
all of the above reactions, the Schiff bases behave as mononeg-
ative bidentate ligands.
The starting complexes [RuCl3(PPh3)3] [29], [RuCl3
(AsPh3)3] [30], [RuBr3(AsPh3)3] [31], [RuBr3(PPh3)2
(MeOH)] [32], and the ligands [33–36] were prepared accord-
ing to the reported procedures. The procedure for catalytic
activity and antibacterial study are similar to that reported in
our earlier publication [37].
3.1. Infra red spectra
The IR spectra of the free ligands when compared with that
of the new complexes confirm the coordination of hydrazones to
the ruthenium metal (Table 1). The IR spectra of the free ligands
showed bands in the region 3250, 1660, 1640 and 1015 cm−1
Table 1
Analytical data of new ruthenium(III) complexes
Complexa
Melting point (◦C)
Found (calculated) (%)
C
H
N
(1) [RuCl2(PPh3)2(BFMH)]
(2) [RuCl2(PPh3)2(BFEH)]
(3) [RuCl2(PPh3)2(BTEH)]
(4) [RuBr2(PPh3)2(BFMH)]
(5) [RuBr2(PPh3)2(BFEH)]
(6) [RuBr2(PPh3)2(BTEH)]
(7) [RuCl2(AsPh3)2(BFMH)]
(8) [RuCl2(AsPh3)2(BFEH)]
(9) [RuCl2(AsPh3)2(BTEH)]
(10) [RuBr2(AsPh3)2(BFMH)]
(11) [RuBr2(AsPh3)2(BFEH)]
(12) [RuBr2(AsPh3)2(BTEH)]
163
167
181
175
187
190
169
171
176
178
172
176
62.15 (62.13)
62.73 (62.75)
61.68 (61.69)
57.00 (56.91)
56.12 (56.14)
55.23 (55.27)
57.00 (57.02)
57.40 (57.42)
56.52 (56.53)
57.56 (57.60)
57.95 (57.98)
57.03 (57.08)
4.18 (4.20)
4.25 (4.37)
4.28 (4.30)
3.83 (3.85)
4.06 (4.09)
4.50 (4.51)
3.92 (3.93)
4.0 (4.0)
3.96 (3.94)
3.68 (3.90)
4.03 (4.04)
3.89 (3.98)
4.52 (4.53)
4.48 (4.48)
4.38 (4.40)
4.17 (4.15)
4.10 (4.09)
4.02 (4.03)
4.10 (4.15)
4.08 (4.10)
4.01 (4.03)
4.19 (4.20)
4.10 (4.14)
4.02 (4.07)
a
Green.

680
K.P. Balasubramanian et al. / Spectrochimica Acta Part A 65 (2006) 678–683
Table 2
IR and electronic spectral data of new ruthenium(III) complexes
Complex
␯
␯
N–N
␯
C N–N C
PPh3/AsPh3
λmax
C
N
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
1587
1585
1581
1582
1535
1521
1587
1533
1517
1587
1515
1548
1002
1010
1010
1012
1001
1003
1005
1020
1004
1002
1002
1000
1649
1649
1649
1649
1649
1649
1646
1647
1649
1625
1640
1647
1434, 1085, 692 231, 263, 371
1433, 1085, 692 230, 260, 328
1433, 1078, 692 240, 258, 341
1433, 1078, 688 233, 266, 341
1433, 1085, 692 234, 263, 361
1434, 1093, 694 237, 263, 321
1433, 1078, 688 237, 274, 592
1433, 1080, 690 235, 371, 680
1433, 1078, 670 235, 372, 680
1434, 1085, 696 239, 371, 595
1433, 1078, 686 231, 257, 598
1436, 1074, 690 234, 253, 596
(9)
(10)
(11)
(12)
Fig. 2. Electronic spectra of (7).
ν, cm−1; λ, nm.
assigned to ␯NH, ␯C O, ␯
and ␯N N, respectively in view of
C N
earlier report [38]. The bands due to ␯ and ␯
stretching
C O
NH
3.4. EPR spectra
vibrations are not observed in the complexes. This indicates the
enolisation of >C O followed by deprotonation and complexa-
tion with metal. In the IR spectra of ruthenium(III) complexes,
All the ruthenium(III) complexes are paramagnetic, showing
a +3 oxidation state for ruthenium ion (Table 3). The solid state
of EPR spectra at X-band frequencies for several of the new
ruthenium(III) complexes have been recorded at room temper-
ature. All the complexes exhibit three lines with different ‘g’
values indicating the presence of magnetic anisotropy (Fig. 3).
The average ‘g’ values lies in the 2.15–2.35 range. These values
are in the range that are obtained for similar other ruthenium(III)
complexes [45,47,48]. The presence of three ‘g’ values is indica-
tive of a rhombic distortion in these complexes (Tables 4–6).
the absorption due to ␯
have been shifted to lower fre-
C N
quency [39] suggesting the presence of >C N–N C residues
of the stoichiometry and the destruction of keto group presum-
ably viz., enolisation and bonding of the ligand through the
resulting enolate oxygen. The two strong bands observed at
710–690 and 610–605 cm−1 regions in the complexes are due to
furan/thiophene modes [40,41]. There was no change in the posi-
tion of the furan/thiophene bands in the spectra of the ruthenium
complexes owing to non-coordination of the furan/thiophene
ring. In addition to the above absorptions, bands due to triph-
enyphosphine/arsine were also present in the spectra of all the
complexes.
3.5. Electrochemistry
Since, the ligands used in this study are not reversibly oxi-
dized or reduced in the applied potential range, it is assumed that
all redox processes are metal centered only. The cyclic voltam-
mograms of five complexes exhibit a reversible reduction peak
and a reversible oxidation peak at a scan rage of 100 mV s−1. The
oxidation and reduction of each complexes are characterized by
well-defined waves with Ef values in the range −0.06 to −1.95 V
and +0.86 to +7.0 V, respectively (Fig. 4). The redox pro-
cesses [Ru(IV)–Ru(III)/Ru(III)–Ru(II) couples] are reversible
(or quasi-reversible) with peak to peak separation (ꢀEp) values
ranging from 132 to 389 mV, suggestive of a single step one
electron transfer process [49–51]. Furthermore, a close exam-
3.2. Electronic spectra
The electronic spectra showed one to two bands in the
231–680 nm region (Fig. 2). The ground state of ruthenium(III)
2
is T2g and the first excited doublet levels, in the order of
increasing energy are A2g and T1g which arises from t42ge1g
configuration [42]. In the most of the ruthenium(III) complexes
the electronic spectra showed only charge transfer bands [43].
The band in the 680–592 nm region have been assigned to the
d–d transition, which is in conformity with assignments made
for the similar ruthenium(III) complexes [44,45]. Other bands in
the 371–231 nm region have been assigned to the charge transfer
transitions. In general the electronic spectra of all the complexes
are characteristic of an octahedral environment around ruthe-
nium(III) ions.
2
2
Table 3
EPR spectral data of new ruthenium(III) complexes
a
Complex
gx
gy
gz
ꢀgꢁ
(1)
(2)
(3)
(4)
(7)
(8)
(10)
(11)
(12)
2.31
2.31
2.13
2.32
2.22
2.15
2.21
2.17
2.22
2.36
2.32
2.16
2.36
2.25
2.18
2.16
2.14
2.26
2.38
2.29
2.17
2.38
2.27
2.20
2.20
2.20
2.29
2.35
2.31
2.15
2.34
2.22
2.17
2.18
2.16
2.25
3.3. Magnetic moments
The magnetic moments for some of the complexes have been
measured at room temperature using a vibration sample mag-
netometer. The values obtained lie in the 1.87–1.97 B.M. range
corresponding to one unpaired electron, suggesting a low spin
t52g configuration for ruthenium(III) ion in pseudo-octahedral
environment [46] (Table 2).
ꢀgꢁ = [1/3(g2x + gy2 + g2z)]2.
a

K.P. Balasubramanian et al. / Spectrochimica Acta Part A 65 (2006) 678–683
681
Table 4
Cyclic voltammetric dataa of some ruthenium(III) complexes
Complex
Ru(IV)–Ru(III)
Ru(III)–Ru(II)
Epa (V)
Epc (V)
Ef (V)
ꢀEp (mV)
Epa (V)
Epc (V)
Ef (V)
ꢀEp (mV)
(1)
(3)
(9)
(10)
(12)
−96
−213
−500
−213
−72
−0.029
−0.195
−0.144
−0.006
−0.150
250
389
289
132
300
797
–
117
758
129
547
–
55
645
85
0.672
–
0.086
0.701
0.107
250
–
62
113
44
−111
−76
−60
−400
−700
a
Working electrode, glassy carbon electrode; Reference electrode, silver/silver chloride electrode; Supporting electrode, [NBu4][CLO4] (0.05 m); Scan rate,
100 mV s−1; Ef, 0.5 (Epa + Epc), where Epa and Epc are anodic and cathodic potentials, respectively.
Table 5
Catalytic oxidation data of alcohols by Ru(III) complexes in the presence of
N-methylmorpholine–N-oxide
Complexes
Substrate
Product
Yield (%)a
Turnoverb
(2)
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
A
K
E
A
K
E
A
K
E
A
K
E
45.43
34.81
63.72
36.81
48.53
61.78
45.43
34.81
67.54
34.61
32.17
59.12
37.32
32.49
61.58
44.96
35.47
67.23
39.43
51.26
64.23
44.96
38.29
69.37
36.17
35.87
63.17
38.69
35.74
65.48
(3)
(4)
(8)
Cinnamyl alcohol
Benzyl alcohol
Cyclohexanol
(10)
A
K
E
Cinnamyl alcohol
A, benzaldehyde; K, cyclohexanone; E, cinnamaldehyde.
a
Yields based on substrate.
Moles of product per mole of catalyst
b
ination of the data reveals that there is no remarkable change
in redox potential of the complexes due to the replacement of
triphenylphosphine by triphenylarsine. From the electrochem-
ical data it is inferred that the present ligand system is highly
suitable for stabilizing higher oxidation states of ruthenium.
Based on the analytical, spectral and electrochemical data,
an octahedral structure (Fig. 5) has been proposed for all the
ruthenium(III) complexes.
Fig. 3. EPR spectrum of (3).
3.6. Catalytic activity
The ruthenium(III) complexes were found to exhibit catalytic
yield and turnovers comparable to those reported for similar
ruthenium(III) complexes [52]. The relatively higher product
Table 6
Antibacterial activity data for the ligand and their Ru(III) complexes
Complex
Diameter inhibition zone (mm)
E. coli (%)
Pseudomonous aeruginosa (%)
Salmonella typhi (%)
Staphylococcus aureus (%)
0.25
0.5
0.75
1
0.25
0.5
0.75
1
0.25
0.5
0.75
1
0.25
0.5
0.75
1
H-BFMH
(4)
(10)
H-BFEH
(5)
(8)
H-BTEH
(3)
(6)
8
10
9
10
12
11
10
12
11
11
12
12
12
13
13
11
13
12
13
14
14
13
15
14
12
15
14
14
16
15
8
10
9
9
11
11
10
12
10
11
12
12
10
13
12
12
14
12
14
15
15
12
16
14
13
15
14
15
17
17
9
11
10
10
12
11
8
10
12
11
11
13
13
9
12
13
13
13
15
14
11
13
12
14
16
15
14
17
16
12
15
14
7
8
8
9
10
11
12
13
13
12
13
13
13
14
14
13
14
14
13
14
14
14
15
17
15
16
16
14
17
16
9
9
9
10
10
9
10
10
10
10
8
10
9
11
10
8
10
9
10
9
12
11
Streptomycin
18
20
21
24
18
21
23
24
18
19
21
24
19
20
23
25

682
K.P. Balasubramanian et al. / Spectrochimica Acta Part A 65 (2006) 678–683
[58]. Though the complexes possess activity, it could not reach
the effectiveness of the standard drug Streptomycin. The vari-
ation in the effectiveness of the different compounds against
different organisms depends either on the impermeability of the
cells of the microbes or differences in ribosomes of microbial
cells [59,60].
4. Conclusion
Mononuclear complexes of the type [RuX2(EPh3)2(L)]
(E = P or As; X = Cl or Br; L = monobasic bidentate Schiff base
derivedfromthecondensationofbenzhydrazidewithfurfuralde-
hyde, 2-acetylfuran and 2-acetylthiophene) have been synthe-
sized. Based on the IR, electronic, EPR and electrochemical
studies, an octahedral geometry has been proposed for the new
complexes. The complexes exhibited considerable amount of
antibacterial activity at the time of screening.
Fig. 4. Cyclic voltammogram of (1).
Acknowledgement
One of the authors (VC) thanks the University Grants Com-
mission, SERO, Hyderabad, India for the award of minor
research project.
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Fig. 5. Structure of new Ru(III) complexes.
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3.7. Antibacterial activity studies
The results showed that the ruthenium chelates are more
toxic compared to their parent ligands against the same microor-
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increase in the antibacterial activity of metal chelates may be
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delocalization over the whole chelate ring. Such chelation could
enhance the lipophilic character of central metal atom, which
subsequently favours its permeation through the lipid layers of
cell membrane. Furthermore the mode of action of the com-
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azomethine (>C N) group with the active centers of cell con-
stituents, resulting in interference with the normal cell processes

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