Synthesis, spectral characterization, catalytic and antibacterial studies of new Ru(III) Schiff base complexes containing chloride/bromide and triphenylphosphine/arsine as co-ligands

Article abstract of DOI:10.1016/j.saa.2009.06.061

A new Ru(III) Schiff base complexes of the type [RuX(EPh₃)L] (X = Cl/Br; E = P/As; L = dianion of the Schiff bases were derived by the condensation of 1,4-diformylbenzene with o-aminobenzoic acid/o-aminophenol/o-aminothiophenol in the 1:2 stoic

Full text of DOI:10.1016/j.saa.2009.06.061

Spectrochimica Acta Part A 74 (2009) 591–596
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Short communication
Synthesis, spectral characterization, catalytic and antibacterial studies of new
Ru(III) Schiff base complexes containing chloride/bromide and
triphenylphosphine/arsine as co-ligands
∗
S. Arunachalam, N. Padma Priya, C. Jayabalakrishnan, V. Chinnusamy
Post Graduate and Research Department of Chemistry, Sri Ramakrishna Mission Vidyalaya College of Arts and Science, Coimbatore 641020, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new Ru(III) Schiff base complexes of the type [RuX(EPh )L] (X = Cl/Br; E = P/As; L = dianion of the
Schiff bases were derived by the condensation of 1,4-diformylbenzene with o-aminobenzoic acid/o-
aminophenol/o-aminothiophenol in the 1:2 stoichiometric ratio) have been synthesized from the
3
Received 6 September 2008
Received in revised form 22 June 2009
Accepted 30 June 2009
reactions of [RuX3(EPh3)3] with appropriate Schiff base ligands in benzene in the 2:1 stoichiometric ratio.
1
13
The new complexes have been characterized by analytical, spectral (IR, electronic, H, C NMR and ESR),
magnetic moment and electrochemical studies. An octahedral structure has been tentatively proposed for
all these new complexes. All the new complexes have been found to be better catalyst for the oxidation of
alcohols using molecular oxygen as co-oxidant at ambient temperature and aryl–aryl coupling reactions.
These complexes were also subjected to antibacterial activity studies against Escherichia coli, Aeromonas
hydrophilla and Salmonella typhi.
Keywords:
Schiff bases
1,4-Diformylbenzene
Electrochemical
Catalytic oxidation
Antibacterial
©
2009 Elsevier B.V. All rights reserved.
1
. Introduction
by the condensation of 1,4-diformylbenzene with o-aminobenzoic
acid/o-aminophenol/o-aminothiophenol in the 1:2 stoichiometric
ratio. The general structure of the Schiff base ligands are given in
Scheme 1.
Schiff base complexes of transition metals containing ligands
with N, S or N, S, O donors are known to exhibit interesting stere-
ochemical, electrochemical and electronic properties [1–3]. This
attention is still growing, so that a considerable research effort is
today devoted to the synthesis of new Schiff base complexes with
transition metal ions, to further develop applications in the area of
material and pharmaceutical chemistry [4–6]. In particular, triph-
enylphosphine/arsine complexes of ruthenium [7–9] have been
employed as catalysts for various organic transformations such as
oxidation [10], hydrogenation [11], C–C couplings [12], hydroformy-
lation [13], isomerization [14], polymerization [15], racemization
2. Experimental
2.1. Physical measurements
All the reagents used were of analar grade. RuCl ·3H O was
3
2
purchased from Loba Chemie and was used without further purifi-
cation. The starting complexes [RuCl (PPh ) ] [23], [RuCl (AsPh ) ]
3
3
3
3
3 3
[
24], [RuBr (PPh ) ], [RuBr (AsPh ) ] [25] were prepared by
3 3 3 3 3 3
[
16], etc. Among these, catalytic oxidation of alcohols to carbonyl
reported methods. Catalytic oxidation [26] and aryl–aryl cou-
pling [27] reactions have been carried out by reported literature
methods. The C, H, and N analysis were performed using Carlo-
Eraba 1106 instrument. IR spectra were recorded in KBr pellets
compounds is a pivotal reaction due to their utility in fine chemicals
and pharmaceutical industries. Ruthenium complexes are known
to mediate oxidation of alcohol using variety of co-oxidants such as
PhIO [17], NMO [18], BrO3–[19], 2SO8 [20], t-BuOOH [21], TEMPO
−
in the region 400–4000 cm using Shimadzu instrument. 1H and
−
1
[
9] and O2 or air [22]. In this paper, we discuss the synthesis,
13
C NMR spectra for the ligands were recorded in Indian Insti-
spectral characterization, redox behaviour, catalytic and antibac-
terial activities of new complexes of ruthenium(III) containing
tetradentate Schiff base ligands. The Schiff bases were derived
tute of Science, Bangalore. Electronic spectra were recorded in
CH Cl with a Systronics Double beam UV–Vis Spectrophotometer-
2
2
2
202 in the range 200–800 nm. The X-band EPR spectra of the
powdered samples were recorded on JEOL JESFA200 EPR spectrom-
eter using diphenylpicryl hydrazyl as reference. Electrochemical
studies were recorded in acetonitrile solution using a glassy car-
∗ Corresponding author. Tel.: +91 422 2692461.
E-mail addresses: drvcsrkv@gmail.com, vchinnusamy@yahoo.com
bon working electrode and [NBu ]ClO4 was used as supporting
4
(
V. Chinnusamy).
electrolyte. Catalytic and antimicrobial studies were carried out.
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.06.061

5
92
S. Arunachalam et al. / Spectrochimica Acta Part A 74 (2009) 591–596
(Scheme 2). All the complexes are soluble in most of the common
organic solvents. Their purity was checked by TLC on silica gel. The
analytical data obtained for the new complexes agree well with the
proposed molecular formulae (Table 1). In all of the above reactions,
the Schiff bases behave as binegative tetradentate ligands. Mag-
netic measurements show that all the complexes are paramagnetic
which confirms that ruthenium is in +3 oxidation state.
3.1. Spectroscopic studies
3.1.1. Infrared spectral analysis
The IR spectra of the ligands were compared with those of
the ruthenium complexes in order to confirm the binding mode
of the Schiff base ligands to the ruthenium ion in the com-
plexes. The free Schiff base ligands showed a strong band in
−
1
the region 1603–1627 cm , which is the characteristic frequency
Scheme 1. General structure of the new Schiff base ligands.
of the azomethine ꢀ(C N) group [28–30]. In all the complexes,
−
1
the ꢀ(C N) band is shifted to lower frequency 1595–1605 cm
,
Melting points were recorded on a Raaga apparatus and are uncor-
rected.
indicating coordination of the Schiff bases through the azome-
thine nitrogen atom. For the anthranilic acid moiety, the ꢀ(OH)
−
1
absorption observed at 3300 cm
in the free Schiff base lig-
and H2L1 and the ꢀ(C O) frequency of the carbonyl was seen as
2
2
.2. Recommended procedures
−
1
a band at 1680 cm
and also shows the absorption band at
−
1
−1
.2.1. Synthesis of new Schiff base ligands
1648 cm
and 1491 cm
for asymmetric (ꢀasyCOO− ) and sym-
The Schiff base ligands were derived by condensing 1,4-diform-
metric (ꢀsyCOO− ) stretching of the carboxylato group. In the
−
1
ylbenzene (0.1 mmol) with o-aminobenzoicacid (0.2 mmol)/o-
aminophenol (0.2 mmol)/o-aminothiophenol (0.2 mmol) in 1:2
molar ratio in ethanolic medium and refluxed for 6 h. The resul-
tant product was washed with ethanol and the purity of the ligands
were checked by TLC.
complexes the bands were observed in the 1615–1665 cm and
−
1
1409–1430 cm regions arising from asymmetric (ꢀasyCOO
symmetric (ꢀsyCOO ) stretching of the carboxylato group [29]. This
indicates the coordination of the carboxyl group to the ruthenium
−
) and
−
1
1
metal ion in the complexes [RuCl(PPh )(L )], [RuCl(AsPh )(L )],
3
3
1
1
[
RuBr(PPh )(L )] and [RuBr(AsPh )(L )]. The differences between
3
3
2
.2.2. Synthesis of new Ru(III) Schiff base complexes
All the new complexes were prepared by the following gen-
the asymmetric and symmetric stretching frequencies of the
−
1
coordinated carboxyl group lie in the 206–235 cm
range, a
eral procedure described below (Scheme 2). To a solution of
clear indication of the monodentate coordination of the car-
boxyl group with the free carbonyl group [29,31]. A medium
3
[
RuX (EPh ) ] (0.2 mmol) in benzene (20 cm ) the appropriate
3
3 3
−
1
Schiff base (0.1 mmol) was added in 1:1 molar ratio and heated
under reflux for 6 h. The resulting solution was then concentrated
to 3 cm3 and cooled. The complex was precipitated by the addition
intensity band which appeared at 3000 cm
due to ꢀ(OH) in
the free Schiff base ligand H2L2 disappeared upon complexation
showing deprotonation prior to coordination through the oxy-
◦
2
2
of small quantity of petroleum ether (60–80 C), recrystallized from
gen atom in the complexes [RuCl(PPh )(L )], [RuCl(AsPh )(L )],
3 3
2
2
CH Cl /petroleum ether and dried in vacuo.
[RuBr(PPh )(L )] and [RuBr(AsPh )(L )]. A band that appeared at
355 cm due to phenolic C–O stretching in the free Schiff base
ligand H2L has been shifted to higher frequency in the range
385–1430 cm indicating the coordination through the phenolic
2
2
3 3
1
−
1
2
3. Results and discussion
−
1
1
Stable ruthenium(III) Schiff base complexes of the general for-
oxygen atom in the complexes [32–34]. The band corresponding
to thiophenolic S–H also disappears in the complexes contain-
mula [RuX(EPh )(L)] (X = Cl/Br; E = P/As; L = dianion tetradentate
3
Schiffbase)havebeenpreparedbyreacting[RuX (EPh ) ](E = P/As)
ing H2L3 ligand. Moreover the absorption due to ꢀ
of H2L3
3
3
3
(C–S)
−
1
−1
is shifted to 1254–1269 cm in the these com-
with the respective Schiff bases in a 1:1 molar ratio in benzene
at 1240 cm
Scheme 2. Preparation of new Ru(III) Schiff base complexes.

S. Arunachalam et al. / Spectrochimica Acta Part A 74 (2009) 591–596
593
Table 1
Elemental, IR and UV–vis spectral data of ruthenium(III) tetradentate Schiff base complexes.
Complexes
Melting point
Found (calculated) (%)
FT-IR (cm−1)
ꢁmax (nm)
◦
(
C)
C
H
N
S
ꢀC
N
ꢀasyCOO
−
ꢀsyCOO
−
ꢀ
−
ꢀ
−
C–O
S–O
1
H2L
121
146
129
211
247
187
218
198
157
219
182
151
179
227
203
70.9 (69.8)
75.9 (74.8)
68.9 (68.7)
62.4 (62.3)
63.9 (62.7)
31.2 (60.9)
59.1 (58.9)
60.2 (59.7)
57.8 (57.0)
55.9 (55.2)
56.9 (56.1)
54.7 (53.9)
59.1 (58.8)
60.3 (59.2)
57.8 (57.2)
4.3 (4.1)
7.5 (7.2)
8.8 (8.6)
8.0 (7.9)
3.6 (3.4)
3.92 (3.9)
3.7 (3.6)
3.4 (3.1)
3.69 (3.61)
3.5 (3.5)
3.3 (3.1)
3.5 (3.3)
3.4 (3.1)
3.4 (3.1)
3.7 (3.5)
3.5 (3.4)
–
–
1603
1614
1627
1595
1598
1602
1605
1598
1595
1598
1595
1602
1605
1598
1595
1648
1491
–
1355
–
–
1240
–
–
1254
–
–
1259
–
–
1265
–
–
1269
291,358,476
275,379,559
287,352,473
333,602
288,554,466
351,336
2
H2L
5.1 (4.9)
4.6 (4.3)
3.7 (3.6)
4.1 (4.0)
3.9 (3.7)
3.59 (3.51)
3.8 (3.58)
3.7 (3.61)
3.4 (3.31)
3.6 (3.48)
3.5 (3.29)
3.6 (3.51)
3.9 (3.71)
3.7 (3.58)
–
–
1615
–
–
1640
–
–
1409
–
–
1415
3
H2L
18.4 (18.2)
–
–
8.6 (8.5)
–
–
8.13 (8.0)
–
–
7.6 (7.4)
–
–
–
1
[
[
[
[
[
[
[
[
[
[
[
[
RuCl(PPh3)(L )]
RuCl(PPh3)(L )]
RuCl(PPh3)(L )]
RuCl(AsPh3)(L )]
RuCl(AsPh3)(L )]
RuCl(AsPh3)(L )]
RuBr(AsPh3)(L )]
RuBr(AsPh3)(L )]
RuBr(AsPh3)(L )]
RuBr(PPh3)(L )]
RuBr(PPh3)(L )]
RuBr(PPh3)(L )]
–
1385
–
–
1397
–
–
1421
–
–
1430
–
2
3
1
248,333,436,614
288,549,462
332,452
2
–
–
3
–
1665
–
–
1650
–
–
1429
–
–
1430
–
1
312,472
300,468,574
333,366
338,426
332,461,572
330,346,368
2
3
1
2
3
8.1 (8.07)
–
–
3
3
3
plexes [RuCl(PPh )(L )], [RuCl(AsPh )(L )], [RuBr(PPh )(L )] and
region 572–614 nm can be attributed to d–d transitions involving
the metal orbitals [35].
3
3
3
3
[
RuBr(AsPh )(L )], indicating that the another coordination site is a
3
thiophenolic sulfur atom [3]. The characteristic bands due to triph-
enylphosphine/arsine were observed in the expected regions.
.1.3. 1H and 13C NMR spectra of the Schiff base ligands
3
The formation of Schiff base ligands were conveniently moni-
1
13
tored by peak ratios in the H and C NMR spectra of all the ligands
3
.1.2. Electronic spectral analysis
The electronic spectra of all the ligands and complexes in
were taken in DMSO·d solvent. The aromatic region is a set of mul-
6
tiplets in the range 6.8–8.2 ppm for all the Schiff base ligands. The
dichloromethane showed three bands in the 275–559 nm regions
Table 2). The electronic spectra of all the free ligands showed two
carboxylic OH proton of the H2L1 ligand appears as a singlet at
(
2
1
0 ppm while, the Ph-OH proton of the ligand H2L appears as a
types of transitions, the first one appeared at range 275–291 nm
which can be assigned to ␲–␲* transition due to transitions involv-
ing molecular orbitals located on the phenolic, thiophenolic and
carboxylic chromophore. These peaks have been shifted in the spec-
tra of the complexes. This shifting may be due to the donation of
a lone pair of electrons from the oxygen of the phenolic and car-
boxylic and thiophenolic sulfur group to the central metal atom,
respectively. This reveals that one of the coordination site is oxy-
gen of the phenolic and carboxylic and sulfur of the thiophenolic
groups, respectively. The second type of transitions appeared at
range 352–559 nm assigned to n → ␲* transition due to azomethine
groups and benzene ring of the ligands. These bands have also been
shifted in the spectra of the new complexes indicating the involve-
ment of imine group nitrogens in coordination with central metal
atom. The spectra of the all the complexes showed another types
of transitions which is different from the free ligands. All the com-
plexes showed absorption in the range 248–472 nm which can be
assigned to ligand to metal charge transfer followed by intra-ligand
transitions, respectively. The other type of bands in the visible
3
singlet at 9.1 ppm and the Ph-SH proton of the ligand H L appears
2
1
as a singlet at 3.4 ppm. The H NMR spectra of the CH proton appears
as a singlet in the region 8.1–8.31 ppm for all the Schiff base ligands
and a representative figure is depicted (Fig. 1). The 1 C NMR spec-
tra of the ligands have been recorded and the spectrum is shown in
Fig. 2. The chemical shifts for the carbon atoms of the phenyl rings
were recorded in the region 115–139 ppm. In all the ligands –CH
carbon appears in the range 154–155 ppm.
3
N
3.1.4. EPR spectral analysis
The solid-state EPR spectra of powdered samples of all the com-
plexes were recorded at room temperature and the ‘g’ values are
listed in Table 2 and depicted in Fig. 3. The EPR spectra of ruthe-
nium(III) complexes [RuCl(PPh )(L )] (Fig. 1), [RuCl(AsPh )(L )]
and [RuBr(AsPh )(L )] in room temperature exhibited three lines
with different ‘g’ values, indicating the presence of magnetic
anisotropy. The presence of three ‘g’ values is indicative of
a rhombic distortion in these complexes [36]. The complexes
2
2
3
3
3
3
Table 2
EPR, magnetic moment and electrochemical data of new ruthenium(III) Schiff base complexes.
RuIII/RuII
gx
gy
gz
ꢀgꢁ
a
ꢂeff (BM)
Complexes
Epa (V)
Epc (V)
ꢃEp (V)
E1/2 (V)
1
[
[
[
[
[
[
[
[
[
[
[
[
[
RuCl(PPh3)(L )]
−1091
–
−481
–
610
–
0.786
–
0.9
1.58
1.67
0.96
1.64
1.63
1.67
0.93
1.61
1.70
0.92
1.70
0.90
1.70
1.58
1.67
1.37
1.64
1.63
1.37
0.93
1.61
1.70
1.60
1.79
0.90
–
1.78
1.87
1.73
1.93
1.72
1.73
1.64
1.81
1.90
1.80
1.90
1.53
–
1.64
1.74
1.62
1.74
1.66
1.60
1.22
1.68
1.77
1.77
1.76
1.31
0.98
1.71
1
RuCl(PPh3)(L )] LNT
2
RuCl(PPh3)(L )]
−1255
−1326
−1292
−564
−1165
−1108
−387
−1182
−844
−1173
−1216
−546
−556
−581
−277
−539
−489
−167
−513
−522
−649
−522
709
770
711
287
626
619
220
669
322
524
694
–
–
1.76
–
–
1.74
–
–
1.72
–
–
3
RuCl(PPh3)(L )]
0.941
0.936
0.42
0.852
0.798
0.277
0.847
0.683
0.911
0.869
1
RuCl(AsPh3)(L )]
RuCl(AsPh3)(L )]
RuCl(AsPh3)(L )]
RuBr(AsPh3)(L )]
2
3
1
2
RuBr(AsPh3)(L )]
3
RuBr(AsPh3)(L )]
1
RuBr(PPh3)(L )]
2
RuBr(PPh3)(L )]
3
RuBr(PPh3)(L )]
a
2
2
2
1/2
Supporting electrolyte [NBu4]ClO4 (0.1 M); ꢃEp = Epa − Epc; ꢀgꢁ = [1/3gx + 1/3gy + 1/3g ]
.
z

5
94
S. Arunachalam et al. / Spectrochimica Acta Part A 74 (2009) 591–596
2
Fig. 4. Cyclic voltammogram of the complex [RuCl(PPh3)L ].
Fig. 1. 1H NMR spectrum of the Schiff base ligand H2L2.
1
3
3
[
RuCl(PPh )(L )], [RuCl(PPh )(L )], [RuCl(AsPh )(L )], [RuBr(As-
3 3 3
1
2
3
1
Ph )(L )], [RuBr(AsPh )(L )], [RuBr(AsPh )(L )], [RuBr(PPh )(L )]
3
3
3
3
2
and [RuBr(PPh )(L )] exhibited the spectra with gx = gy =/ gz. The
3
two different ‘g’ values (gx = gy =/ gz) are indicative of a tetragonal
distortion in these octahedral complexes [37]. Moreover, the com-
3
plex [RuBr(PPh )(L )], exhibit a single isotropic resonance with ‘g’
3
value at 0.98, indicating a very high symmetry around the ruthe-
nium ions. Such isotropic lines are usually observed either due
to the intermolecular spin exchange which can broaden the lines
or due to occupancy of the unpaired electrons in a degenerate
1
orbital. The spectrum of the complex [RuCl(PPh )(L )] at LNT show
3
improved resolution with the ‘g’ value and there is no much vari-
ation observed when compared with that observed that of RT. In
addition, the nature and position of the lines in the spectra of these
complexes are similar to those of the other octahedral complexes
[
38].
3
.1.5. Magnetic moments
The magnetic moments for a few complexes have been mea-
Fig. 2. 13 C NMR spectrum of the Schiff base ligand H2L2.
sured at room temperature using a vibration sample magnetometer.
The values obtained lie in the 1.71–1.79 BM range corresponding to
one unpaired electron, suggesting a low spin t5 configuration for
ruthenium(III) ion (Table 2).
3.1.6. Electrochemistry
Complexes were electrochemically examined at a glassy carbon
working electrode in acetonitrile solution. A representative voltam-
mogram has been depicted in Fig. 4 and the potential data are listed
in Table 2. All the complexes display irreversible oxidation potential
(IV)
(III)
(
Ru –Ru ). In all the complexes, the Ru(III)–Ru(II) redox couple
is quasi-reversible in nature, with a peak-to-peak separation (ꢃEp)
of 220–770 mV [39]. Coordination of the sulfur atom makes the
metal center more electron-rich and shifts the oxidation potential
towards more negative values [40].
3.2. Catalytic studies
3.2.1. Catalytic oxidation
The oxidation of benzyl alcohol, cyclohexanol, cinnamyl alco-
hol, isopropyl alcohol and butan-2-ol was carried out with the
different ruthenium complexes as catalysts using molecular oxy-
gen as co-oxidant at ambient temperature in dichloromethane. In
no case was there any detectable oxidation of alcohols in the pres-
ence of molecular oxygen alone without the ruthenium complexes.
The results of the catalytic oxidation by ruthenium(III) com-
1
Fig. 3. EPR specta of the complex [RuCl(PPh3)(L )] at (a) RT and (b) LNT.

S. Arunachalam et al. / Spectrochimica Acta Part A 74 (2009) 591–596
595
plexes are summarized in Table 3. Benzaldehyde was formed from
benzyl alcohol, cyclohexanol was converted into cyclohexanone,
cinnamyl alcohol was converted cinnamaldehyde and butan-2-ol
was converted to butan-2-al after 3 h of stirring at room tem-
perature. The aldehyde/ketone formed were quantified as their
is more acidic than that of cyclohexanol [39]. The relatively higher
product yield obtained for the oxidation of cinamyl alcohol than
benzyl alcohol is due to the presence of unsaturated aliphatic group
in the cinnamyl alcohol [5]. It has also been found that triph-
enylphosphine complexes possess higher catalytic activity than the
triphenylarsine complexes [3,40]. This may be due to the higher
donor ability of the arsine ligand compared with that of phosphine
[33].
2
,4-dinitrophenylhydrazone derivatives. All the synthesized ruthe-
nium complexes were found to catalyse the oxidation of alcohols to
aldehydes/ketones, but the yields and the turnover were found to
vary with different catalysts. The relatively higher product yield
obtained for the oxidation of benzyl alcohol than for cyclohex-
anol was due to the fact that the ␣-CH moiety of benzyl alcohol
3.2.2. Aryl–aryl coupling
Magnesium turnings (0.320 g) were placed in a two-necked
round-bottomed flask with a CaCl2 guard tube. A crystal of iodine
3
3
was added. PhBr [0.75 cm of total 1.88 cm ] in anhydrous Et O
2
Table 3
3
(
5 cm ) was added with stirring and the mixture was heated under
reflux. The remaining PhBr in Et O (5 cm ) was added drop wise
and the mixture was refluxed for 40 min. To this mixture, 1.03 cm
0.01 mol) of PhBr in anhydrous Et O (5 cm ) and the ruthenium
Catalytic oxidations of alcohols and aryl–aryl coupling of Ru(III) Schiff base
complexes.
3
2
3
Complexes
Oxidation of alcohols
Aryl–aryl coupling
3
(
2
Substrate Product Yielda Turnover Yield (g) Yield (%)
complex (0.05 mmol) chosen for investigation were added and
heated under reflux for 6 h. The reaction mixture was cooled and
1
[
[
[
[
[
[
[
[
[
[
[
[
RuCl(PPh3)(L )]
A
B
C
D
E
F
G
H
58
68
71
72
59
69
71
74
0.592
0.589
0.601
0.595
0.554
0.549
0.589
0.596
0.606
0.546
0.556
0.576
61.47
61.20
62.44
61.82
57.56
57.04
61.20
61.92
62.97
56.73
57.77
59.85
hydrolysed with a saturated solution of aqueous NH Cl and the pre-
4
cipitated biphenyl was chromatographed to get pure sample and
◦
compared well with an authentic sample (69–72 C) [41].
2
RuCl(PPh3)(L )]
A
B
C
D
E
F
G
H
56
67
74
77
57
67
75
77
3.3. Antibacterial activity studies
Three pathogenic microbials were used to test the biological
3
RuCl(PPh3)(L )]
A
B
C
D
E
F
G
H
54
67
75
79
56
67
75
79
potential of the Schiff bases and their ruthenium(III) complexes.
They were (i) Escherichia coli, (ii) Aeromonas hydrophilla and (iii)
Salmonella typhi. The antibacterial activity of the compound was
determined by disc diffusion method [42]. The results showed
(Table 4) that the ruthenium chelates are more toxic compared to
their parent ligands against the same microorganisms under iden-
tical conditions. The toxicity of ruthenium chelates increases on
increasing the concentration [6]. The increase in the antibacterial
activity of metal chelates may be due to the effect of the metal ion
on the normal cell process. A possible mode of the toxicity increase
may be considered in light of Tweedy’s chelation theory [43]. Chela-
tion considerably reduces the polarity of the metal ion because of
partial sharing of its positive charge with the donor groups and pos-
sible ␲-electron 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
1
RuCl(AsPh3)(L )]
A
B
C
D
E
F
G
H
50
61
66
70
51
63
67
72
2
RuCl(AsPh3)(L )]
A
B
C
D
E
F
G
H
54
62
68
74
54
63
68
76
3
RuCl(AsPh3)(L )]
A
B
C
D
E
F
G
H
53
64
67
74
54
65
67
76
1
RuBr(PPh3)(L )]
A
B
C
D
E
F
G
H
52
65
70
73
54
66
71
74
2
RuBr(PPh3)(L )]
A
B
C
D
E
F
G
H
52
63
73
76
53
65
75
76
Table 4
Antibacterial activity data of ligands and Ru(III) complexes.
Compound
Diameter of inhibition zone (mm)
3
Escherichia
coli
Aeromonas
hydrophilla
Salmonella
typhi
RuBr(PPh3)(L )]
A
B
C
D
E
F
G
H
54
66
75
79
56
67
77
80
0.25% 0.5% 1%
0.25% 0.5% 1%
0.25% 0.5% 1%
L1
7
7
12
11
12
12
9
12
11
12
14
8
10
12
11
11
9
12
11
11
13
11
10
13
12
13
9
13
13
11
13
10
14
14
11
13
10
13
14
11
14
1
1
[RuCl(PPh3)(L )]
11
10
10
RuBr(AsPh3)(L )]
A
B
C
D
E
F
G
H
50
61
66
70
50
63
68
70
1
[
[
[
RuCl(AsPh3)(L )]
RuBr(PPh3)(L )]
RuBr(AsPh3)(L )] 12
1
1
2
L2
8
11
12
10
9
10
11
11
14
9
11
11
11
14
8
10
10
11
12
9
12
12
11
13
8
13
12
12
13
10
12
11
12
14
11
11
13
12
14
11
13
12
14
14
RuBr(AsPh3)(L )]
A
B
C
D
E
F
G
H
54
62
68
74
54
64
69
75
2
[
[
[
[
RuCl(PPh3)(L )]
RuCl(AsPh3)(L )]
RuBr(PPh3)(L )]
RuBr(AsPh3)(L )] 13
2
2
2
3
RuBr(AsPh3)(L )]
A
B
C
D
E
F
G
H
53
64
67
74
55
66
69
75
L3
11
15
14
10
12
17
15
11
14
12
17
15
11
15
10
14
17
12
12
10
16
16
12
14
11
15
16
13
14
12
16
13
14
13
12
15
13
15
13
13
15
14
15
13
3
[
[
[
[
RuCl(PPh3)(L )]
RuCl(AsPh3)(L )]
RuBr(PPh3)(L )]
RuBr(AsPh3)(L )] 14
3
3
A: cyclohexanol; B: benzyl alcohol; C cinnamyl alcohol; D: butan-2-ol; E: cyclohex-
anone; F: benzaldehyde; G: cinnamaldehyde; H: butan-2-al.
3
a
Streptomycin
22
23
28
21
23
27
29
21
25
Moles oE product per mole oE catalyst.

5
96
S. Arunachalam et al. / Spectrochimica Acta Part A 74 (2009) 591–596
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90.
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The present study describes a simplistic synthesis of a new
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triphenylphosphine/triphenylarsine and chloride/bromide as co-
ligands. An octahedral geometry (Scheme 3) has been proposed
to all the complexes on the basis of analytical, IR, electronic,
EPR, magnetic moment and electrochemistry spectral data. All the
ruthenium(III) Schiff base complexes have been found as efficient
catalysts for the oxidation of alcohols to their corresponding car-
bonyl compounds by molecular oxygen at ambient temperature
and also for aryl–aryl coupling reactions. Further, the new com-
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explanations for the mode of actions of these complexes against
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[
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[
[
1
[