Ruthenium(III) tetradentate Schiff-base complexes: Spectral, catalytic, and its biocidal efficacy

Article abstract of DOI:10.1080/00958972.2010.487937

New six-coordinate ruthenium(III) Schiff-base complexes of general formula [Ru(X)(PPh₃)(L)] (where X = Cl/Br and L = mononucleating bibasic tetradentate ligand derived by condensing actetoacetanilide/acetoacetotoludide with o-aminophenol/o-amin

Full text of DOI:10.1080/00958972.2010.487937

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Ruthenium(III) tetradentate Schiff-base
complexes: spectral, catalytic, and its
biocidal efficacy
S. Arunachalam a , N. Padma Priya a , C. Saravanakumar a , C.
Jayabalakrishnan a & V. Chinnusamy a
a Post Graduate and Research Department of Chemistry , Sri
Ramakrishna Mission Vidyalaya College of Arts and Science ,
Coimbatore–641020, Tamil Nadu, India
Published online: 11 Jun 2010.
To cite this article: S. Arunachalam , N. Padma Priya , C. Saravanakumar , C. Jayabalakrishnan
& V. Chinnusamy (2010) Ruthenium(III) tetradentate Schiff-base complexes: spectral,
catalytic, and its biocidal efficacy, Journal of Coordination Chemistry, 63:10, 1795-1806, DOI:
10.1080/00958972.2010.487937
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Journal of Coordination Chemistry
Vol. 63, No. 10, 20 May 2010, 1795–1806
Ruthenium(III) tetradentate Schiff-base complexes: spectral,
catalytic, and its biocidal efficacy
S. ARUNACHALAM, N. PADMA PRIYA, C. SARAVANAKUMAR,
C. JAYABALAKRISHNAN and V. CHINNUSAMY*
Post Graduate and Research Department of Chemistry, Sri Ramakrishna Mission Vidyalaya
College of Arts and Science, Coimbatore – 641020, Tamil Nadu, India
(Received 10 August 2009; in final form 3 February 2010)
New six-coordinate ruthenium(III) Schiff-base complexes of general formula [Ru(X)(PPh3)(L)]
(where X ¼ Cl/Br and L ¼ mononucleating bibasic tetradentate ligand derived by condensing
actetoacetanilide/acetoacetotoludide with o-aminophenol/o-aminothiophenol/o-aminobenzoic
acid in 1 : 2 molar ratio in ethanol) have been synthesized and characterized by physico-
chemical and spectroscopic methods. The new ruthenium(III) complexes possess 2NO/2NS
metal binding sites and are catalysts for the oxidation of alcohols using molecular oxygen as
co-oxidant and in C–C coupling reactions. These complexes possess good biocidal
(antibacterial and antifungal) activity.
Keywords: Schiff base; Tetradentate ligands; Electrochemical; Molecular oxygen; Biocidal
1. Introduction
Design, synthesis, and structural characterization of Schiff-base complexes are of
interest due to their structural, magnetic, spectral, catalytic, and redox properties [1–9].
Much research has been published concerning the use of Schiff-base ligands, which
incorporate nitrogen imine, phenolate, thiophenolate, and carboxylato donors for
synthesizing ruthenium complexes capable of oxidizing organic substrates [9–13].
Activation of molecular oxygen by transition metals for the catalytic oxidation of
organic substrates has been of continued interest [14–16]. Particularly, the use of
ruthenium complexes to catalyze oxidation of alcohols by oxygen donors has been well-
documented [17, 18]. Mechanism of oxidation using hydrogen peroxide in the presence
of Mo, V, W, and Ti and peracids is also studied [19]. Further, primary oxidants, such
as iodobenzene [20], alkylhydroperoxides [21], p-cyano-N-N-dimethylaniline-N-oxide
[22], and molecular oxygen [23] and C–C coupling [24] have been reported. It has been
reported that high-valent metal-oxo species are responsible for Cytochrome P-450
catalyzed epoxidation and hydroxylation. Sharpless et al. [25] carried out an oriented
study of oxidation of cholesterol, geraniol, etc., catalyzed by ruthenium complexes in
the presence of N-methylmorpholine-N-oxide and N-N-dimethylaniline-N-oxide.
*Corresponding author. Email: drvcsrkmv@gmail.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958972.2010.487937

1796
S. Arunachalam et al.
Here, we report the synthesis, spectral, catalytic, and biocidal efficacies of
six-coordinate ruthenium(III) complexes incorporated with Schiff-base ligands.
The Schiff bases were derived by condensation of actetoacetanilide/acetoacetotoludide
with o-aminophenol/o-aminothiophenol/o-aminobenzoic acid in the 1 : 2 ratio.
The preparation of the Schiff bases are given in scheme 1.
2. Experimental
2.1. Materials and methods
All reagents were of AnalaR grade. RuCl3 ꢀ 3H2O was purchased from Loba Chemie
and used without purification. The starting ruthenium(III) complexes [RuCl3(PPh3)3]
[26], [RuBr3(PPh3)3] [27], and the Schiff bases [28] were prepared by the methods
reported in the literature. Microanalyses were performed using a Vario EL III CHNS
analyzer at Cochin University, Kerala, India. Infrared (IR) spectra were recorded in
KBr pellets from 400 to 4000 cmꢁ1 using a Shimadzu instrument. 1H-NMR spectra for
the ligands were recorded with a Bruker-NRC 500 MHz in the Indian Institute of
Science, Bangalore. Electronic spectra were recorded in CH2Cl2 with a Systronics
Double beam UV-Vis Spectrophotometer-2202 from 200 to 800 nm. X-band electron
paramagnetic resonance (EPR) spectra of the powdered samples were recorded on a
JEOL JESFA200 EPR spectrometer at room temperature (RT) and liquid nitrogen
temperature (LNT) using diphenylpicrylhydrazyl as reference. Electrochemical studies
were recorded in dichloromethane using a glassy carbon working electrode and
[NBu4]ClO4 as the supporting electrolyte. Catalytic and biocidal studies were carried
out in the Gene-Pool Biotech Research Center. Melting points were recorded on a
Veego VMP-DS melting point apparatus and are uncorrected.
R
NH
N
N
YH
YH
Abbreviation
H2L1
R
Y
O
S
H
H
H2L2
H2L3
H2L4
H2L5
H2L6
H
COO
O
CH3
CH3
CH3
S
COO
Scheme 1. Preparation of mononucleating tetradentate Schiff-base ligands.

Ruthenium(III) tetradentate Schiff base complexes
2.2. Preparation of Schiff-base ligands
1797
To an ethanolic solution of actetoacetanilide (0.17 g; 1 mmol)/acetoacetotoludide
(0.19 g; 0.1 mmol), o-aminophenol(0.2 g; 2 mmol)/o-aminothiophenol (0.24 mL;
2 mmol)/o-aminobenzoic acid (0.27 g; 2 mmol) was added and the mixture was stirred
for 30 min and then refluxed for 6 h (scheme 2). The resulting solution was concentrated
and the product obtained was washed with ethanol and purity was checked by thin layer
chromatography (TLC).
2.3. Synthesis of new ruthenium(III) Schiff-base complexes
All the new complexes were prepared by the following general procedure (scheme 3).
To a solution of [RuX3(PPh3)3] (where X ¼ Cl/Br) (1 mmol) in benzene (20 cm3)
the appropriate Schiff base (1 mmol) was added (1 : 1 molar ratio) and refluxed for 6 h.
The solution was then concentrated to 3 cm3 and cooled. The complexes were
precipitated by the addition of a small quantity of petroleum ether (60–80ꢂC),
recrystallized from CH2Cl2/petroleum ether mixture, and dried in vacuo).
2.4. Catalytic oxidation of alcohols
Catalytic oxidation of alcohols (scheme 4) by the Schiff bases, ruthenium(III) starting
complexes, and new ruthenium(III) Schiff-base complexes were carried and the results
are given in table 1. Benzaldehyde and cyclohexanone were formed from benzyl alcohol
and cyclohexanol, respectively, after stirring for 6 h in the presence of molecular
R
R
NH2
NH
NH
YH
N
N
YH
YH
Reflux for 6h
Ethanol
O
O
+
2
R = H/CH and Y=O/S/COO
3
Scheme 2. Preparation of new tetradentate Schiff bases.
R
R
NH
NH
N
N
N
YH
Y
Y
Reflux for 6h
X
N
+
Ru
[RuX (PPh ) ]
PPh3
3
3 3
Benzene
YH
R = H/CH ; X = Cl/Br and Y = O/S/COO
3
Scheme 3. Formation of new mononuclear Ru(III) Schiff-base complexes.

1798
S. Arunachalam et al.
III
OH
[Ru -Catalyst], Stir 6h
O
CH Cl , O at RT
2
2
2
OH
O
III
[Ru -Catalyst], Stir 6h
CH Cl , O at RT
2
2
2
Scheme 4. Oxidation of alcohols in the presence of Ru(III) Schiff-base complexes.
Br
Mg/I
+ MgBr
2
2
MgBr
Br
Diethyl ether
III
[Ru -Catalyst]
Scheme 5. Phenyl–phenyl coupling in the presence of Ru(III) complexes.
oxygen; the resulting carbonyl compounds were quantified as 2,4-dinitrophenyl-
hydrazone derivatives [29].
2.5. Catalytic activity of ruthenium(III) Schiff-base complexes in 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 was added. PhBr (0.75 cm3 of total 1.88 cm3)
in anhydrous Et2O (5 cm3) was added with stirring and the mixture was heated under
reflux for 30 min. The remaining PhBr in Et2O (5 cm3) was added dropwise and the
mixture was refluxed for 40 min. To this mixture, 1.03 cm3 (0.01 mol) of PhBr in
anhydrous Et2O (5 cm3) and the ruthenium complex (0.05 mmol) chosen for
investigation were added and heated under reflux for 6 h. The reaction mixture was
cooled and hydrolyzed with a saturated solution of aqueous NH4Cl; the precipitated
biphenyl was chromatographed to get pure sample and compared well with an authentic
sample (69–72ꢂC) [30]. The results are given in table 1 (scheme 5).
2.6. Biocidal activity of ruthenium(III) Schiff-base complexes
The ligands and their ruthenium complexes have been tested in vitro to assess their
growth inhibitory activity against Staphylococcus epidermidis, Escherichia coli, Botrytis
cinerea, and Aspergillus niger by the disc diffusion method [31]. Streptomycin and
co-trimoxazole were used as standards. The ligands, ruthenium(III) starting complexes,
and new ruthenium(III) complexes were stored at RT and dissolved in
dichloromethane. Both the S. epidermidis and E. coli bacteria were grown in nutrient
agar medium and incubated at 37ꢂC for 24 h followed by frequent subculture to fresh
medium and were used as test bacteria. The bacteria were cultured in nutrient agar
medium in Petri plates and used as inoculum for the study. Both the B. cinerea and
A. niger grown in Sabouraud dextrose agar medium were incubated at 27ꢂC for 72 h

Ruthenium(III) tetradentate Schiff base complexes
1799
Table 1. Catalytic activity of ruthenium(III) Schiff-base complexes.
Oxidation of alcohols
Substrate Product Yield Turnovera Yield (g) Yield (%)
C–C coupling
Complex
H2L1
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
A
B
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
C
D
03
02
03
03
04
02
04
05
02
04
06
05
29
31
31
35
75
81
74
85
76
82
73
86
78
86
78
81
76
81
75
87
74
83
76
87
77
89
79
81
5
05
02
03
05
05
03
06
05
04
04
06
07
29
33
33
36
77
83
74
87
77
85
75
88
79
86
80
82
76
83
77
87
75
84
78
88
77
90
80
82
7
0.01
0.03
0.02
0.01
0.03
0.05
0.03
0.37
0.59
0.65
0.68
0.62
0.67
0.57
0.66
0.68
0.58
0.64
0.69
0.67
3
5
H2L2
H2L3
4
H2L4
3
H2L5
5
H2L6
7
[RuCl3(PPh3)3]
[RuBr3(PPh3)3]
[RuCl(PPh3)(L1)]
[RuCl(PPh3)(L2)]
[RuCl(PPh3)(L3)]
RuCl(PPh3)(L1)]
[RuCl(PPh3)(L2)]
[RuCl(PPh3)(L3)]
[RuBr(PPh3)(L1)]
[RuBr(PPh3)(L2)]
[RuBr(PPh3)(L3)]
[RuBr(PPh3)(L1)]
[RuBr(PPh3)(L2)]
[RuBr(PPh3)(L3)]
O2
05
39
61
67
70
64
69
59
68
70
60
66
71
69
–
9
9
Error limit, 0.2–0.3% for oxidation of alcohols; 0.2–0.5% for aryl–aryl coupling. A, cyclohexanol;
B, benzylalcohol; C, cyclohexanone; and D, benzaldehyde.
aMoles per catalyst.
followed by periodic subculturing to fresh medium and were used as test fungi.
The compounds to be tested were dissolved in dichloromethane to final concentrations
of 0.25%, 0.5%, and 1% and soaked in filter paper discs of 5 mm diameter
and 1 mm thickness. These discs were placed on the previously seeded plates
and incubated at 35ꢂC ꢃ 2ꢂC for 24 h. The diameter (mm) of the inhibitory zone
around each disc was measured after 24 h. Ciprofloxacin and co-trimoxazole were

1800
S. Arunachalam et al.
used as standards. Inhibition was recorded by measuring the diameter of the inhibitory
zone after incubation.
3. Results and discussion
Stable ruthenium(III) Schiff-base complexes [RuX(PPh3)(L)] (X ¼ Cl/Br; L ¼ dianion
of the tetradentate Schiff base) have been prepared by reacting [RuX3(PPh3)3]
(X ¼ Cl or Br) with the respective Schiff bases in a 1 : 1 molar ratio in benzene.
All the complexes are soluble in common organic solvents. The analytical data
(Supplementary material) obtained for the new complexes agree well with the proposed
molecular formula. In all of the above reactions, the Schiff bases are bibasic
tetradentate ligands.
3.1. Spectroscopic studies
3.1.1. FT-IR spectra. IR spectra of the free Schiff bases were compared with those
of the ruthenium complexes to ascertain the binding of the Schiff base to ruthenium and
the results are given in table 2. The free Schiff-base ligands showed a strong band at
1603–1667 cmꢁ1, characteristic of the azomethine ꢀ(C¼N) group. Coordination of
the Schiff bases to metal through nitrogen is expected to reduce the electron density
in the azomethine link and lower the ꢀ(C¼N) absorption frequency. The band due to
ꢀ(C¼N) shifts to lower frequencies 1578–1657 cmꢁ1 in the complexes, indicating
coordination of the azomethine nitrogen to ruthenium [12, 13, 32–34]. A strong band
at 1310–1330 cmꢁ1 in the free Schiff bases H2L1 and H2L4 has been assigned to the
phenolic C–O stretch. On complexation, this band is shifted to higher frequency, 1437–
1439 cmꢁ1, indicating coordination through phenolic oxygen [32–35]. This has been
further supported by disappearance of the broad ꢀ(OH) band around 3000 cmꢁ1 in
[RuCl(PPh3)(L1)], [RuCl(PPh3)(L4)], [RuBr(PPh3)(L1)], and [RuBr(PPh3)(L4)], indicat-
ing deprotonation of the phenolic proton prior to coordination. A very weak
absorption at 2600 cmꢁ1 corresponding to ꢀ(S–H) in the free Schiff base disappears in
spectra of the complexes due to coordination through sulfur after deprotonation.
Moreover, the absorption due to ꢀ(C–S) of the ligand at 1212–1245 cmꢁ1 shifts to higher
frequency (1246–1266 cmꢁ1) in [RuCl(PPh3)(L2)], [RuCl(PPh3)(L5)], [RuBr(PPh3)(L2)],
and [RuBr(PPh3)(L5)] indicating that coordination is through the phenolic sulfur [11].
For the anthranilic acid moiety, the free Schiff bases H2L3 and H2L6 show ꢀ(O–H)
at 3300 cmꢁ1 and ꢀ(C¼O) of the carbonyl at 1680 cmꢁ1, and also shows the absorption
bands at 1668–1671 cmꢁ1 and 1419–1420 cmꢁ1 for asymmetric ꢀ
and symmetric
ðCOOꢁÞ
ꢀ
, respectively. In [RuCl(PPh )(L3)], [RuCl(PPh )(L6)], [RuBr(PPh )(L3)], and
ꢁ
ðCOO
Þ
3 3 3
[RuBr(PPh3)(L6)], the bands were observed at 1654–1657 cmꢁ1 and 1409–1438 cmꢁ1
ðCOOꢁÞ
ðCOOꢁÞ
and symmetric ꢀ
arising from asymmetric ꢀ
stretching of carboxylate [13].
This indicates coordination of carboxyl to ruthenium in the complexes. The differences
between the asymmetric and symmetric stretching frequencies of the coordinated
carboxyl lie in the 219–245 cmꢁ1 range, a clear indication of monodentate coordination
[12, 35]. Characteristic bands due to triphenylphosphine were observed in the
expected region.

Ruthenium(III) tetradentate Schiff base complexes
1801

1802
S. Arunachalam et al.
3.1.2. Electronic spectra. The electronic spectra of all the ligands and complexes in
dichloromethane showed 4–6 bands in the 254–644 nm regions (table 2). The electronic
spectra of free ligands showed two types of transitions, the first at 255–298 nm which
can be assigned to ꢂ–ꢂ* transition due to transitions involving molecular orbitals
located on the oxygen of the phenolic/carboxylic or thiophenolic sulfur chromophore.
These peaks shift in spectra of the complexes due to donation of a lone pair of electrons
from the oxygen of the phenolic/carboxylic or thiophenolic sulfur group to ruthenium.
This reveals that one coordination site is oxygen of the phenolic and carboxylic and
sulfur of the thiophenolic groups. The second type of transitions at 342–426 nm are
assigned to n ! ꢂ* transition due to azomethine and benzene of the ligands.
These bands also shift in spectra of the new complexes indicating involvement of
imine nitrogens in coordination. Spectra of all the complexes showed another transition
in the range 254–473 nm which can be assigned to ligand-to-metal charge transfer
followed by intra-ligand transitions, respectively, based on the extinction coefficients
(" ¼ 271–15,992 dm3 molꢁ1) which are characteristic of ruthenium(III) octahedral
complexes [36, 37]. The other types of bands in the visible region 503–644 nm can be
attributed to d–d transitions involving the metal orbitals [38].
3.1.3. 1H-NMR spectra of the Schiff-base ligands. 1H-NMR spectra of the ligands in
CDCl3 (Supplementary material) show multiplets at 6.3–8.1 ppm for aromatic protons.
The –NH proton, –CH2 proton, and methyl protons appear as singlets in the regions
8.6–10.1 ppm, 2.4–3.5 ppm, and 1.8–2.2 ppm for all the ligands. In H2L1 and H2L4,
the phenolic OH appears as a singlet at 10.8–10.9 ppm. In H2L2 and H2L5, the
thiophenolic SH appears as a singlet at 3.6–3.7 ppm. In H2L3 and H2L6, the COOH
proton appears as a singlet at 9.6–10.8 ppm.
3.1.4. EPR spectra. EPR parameters observed for the complexes at RT and LNT
(table 2) were recorded at X-band frequencies. Three of the complexes
[RuCl(PPh3)(L4)], [RuBr(PPh3)(L3)], and [RuBr(PPh3)(L4)] have isotropic spectra
with ‘‘g’’ of 1.9–2.2. Such isotropic lines are usually observed either due to
intermolecular spin exchange which can broaden the lines or due to occupancy of the
unpaired electrons in degenerate orbitals. In addition, the nature and position of the
lines in the spectra of these complexes are similar to those of the other octahedral
complexes [34]. [RuCl(PPh3)(L2)], [RuCl(PPh3)(L3)], and [RuBr(PPh3)(L5)] exhibited
spectra with gx ¼ gy ¼ gz, indicative of a tetragonal distortion in octahedral complexes
[16]. [RuCl(PPh3)(L1)], [RuCl(PPh3)(L5)], [RuCl(PPh3)(L6)], [RuBr(PPh3)(L1)],
[RuBr(PPh3)(L2)], and [RuBr(PPh3)(L6)] at RT exhibited three lines with different
‘‘g’’ values, indicating magnetic anisotropy. The presence of three ‘‘g’’ values is
indicative of a rhombic distortion [39]. The spectra of [RuBr(PPh3)(L1)] (figure 1) at RT
and LNT shows no variation.
3.2. Cyclic voltammetry
Complexes were electrochemically examined at a glassy carbon working electrode in
dichloromethane using cyclic voltammetry (Supplementary material). The oxidation
and reduction of each complex were characterized by well-defined waves with Ef values

Ruthenium(III) tetradentate Schiff base complexes
1803
Figure 1. EPR spectra of [RuBr(PPh3)(L1)] at (a) RT and (b) LNT.
in the range from 0.3 to 1.25 mV (oxidation) and from ꢁ3.4 to ꢁ1.45 mV (reduction)
against Ag/AgCl electrode. [RuCl(PPh3)(L4)], [RuBr(PPh3)(L3)], [RuBr(PPh3)(L5)], and
[RuBr(PPh3)(L1)] show reversible oxidations in the range 80–100 mV. [RuBr(PPh3)(L2)]
shows reversible reduction at 90 mV and [RuCl(PPh3)(L2)] showed reduction only.
Other complexes showed redox couples with peak-to-peak separation values (DEp)
ranging from 120 to 790 mV revealing that this process is at best quasi-reversible [40],
attributed to slow electron transfer and adsorption of the complex on to the electrode
surface; a representative picture is provided in ‘‘Supplementary material.’’
3.3. Catalytic activity
3.3.1. Oxidation of alcohols. Catalytic oxidations of alcohols (scheme 4) by the new
ruthenium(III) Schiff-base complexes are given in table 1. Benzaldehyde and
cyclohexanone were formed from benzyl alcohol and cyclohexanol, respectively, after
stirring for 6 h. Only a very little amount of carbonyl compound is formed when the
reaction is carried out in the presence of Schiff bases under oxygen atmosphere at
ambient temperature without the catalyst. The relatively higher product obtained for
oxidation of benzyl alcohol compared with cyclohexanol due to ꢃ-CH of benzyl alcohol
is more acidic than cyclohexanol [41]. The catalytic activity of the ruthenium(III)
starting complexes is higher than that of the Schiff bases but lower than that of the
chelate complexes. The reaction was repeated four times and the corresponding
carbonyl compound was produced at the same rate as in the first run. The error limit
was found to be 0.2–0.3%.
3.3.2. Aryl–aryl coupling. The new ruthenium(III) complexes have been used as
catalysts for phenyl–phenyl coupling reactions (scheme 5) and the results are given in
table 1. The system chosen for the study is the coupling of phenyl magnesium bromide
with bromobenzene to give biphenyl. Bromobenzene was first converted into the
Grignard reagent, followed by the addition of the complex chosen for investigation,

1804
S. Arunachalam et al.
Table 3. Antimicrobial activity of ruthenium(III) Schiff-base complexes.
Antibacterial activity
Antifungal activity
B. cinerea A. niger
0.25% 0.5% 1% 0.25% 0.5% 1% 0.25% 0.5% 1% 0.25% 0.5% 1%
S. epidermidis
E. coli
Complex
[RuCl3(PPh3)3]
[RuBr3(PPh3)3]
H2L1
21
20
4
7
3
3
6
3
21
23
5
7
3
5
5
3
23
23
5
8
4
5
5
3
24
23
3
6
5
4
7
5
24
23
3
5
5
5
8
5
26
25
5
5
5
5
8
6
22
21
4
7
6
2
5
6
23
22
4
7
6
2
5
6
23
22
4
7
7
3
5
7
20
23
2
5
2
4
6
5
21
23
3
5
2
5
7
5
21
23
3
6
2
4
7
6
H2L2
H2L3
H2L4
H2L5
H2L6
[RuCl(PPh3)(L1)]
[RuCl(PPh3)(L2)]
[RuCl(PPh3)(L3)]
[RuBr(PPh3)(L4)]
[RuBr(PPh3)(L5)]
[RuBr(PPh3)(L6)]
Standard
27
29
30
27
27
26
27
29
30
29
27
26
27
29
30
29
29
26
29
26
29
27
26
28
29
27
29
28
27
28
30
27
30
29
27
30
31
28
28
30
29
28
31
29
28
28
29
29
32
29
29
28
30
29
35
26
27
26
26
28
35
26
27
26
25
29
35
26
27
26
26
28
Streptomycin (22)
Co-trimoxazole (21)
Dichloromethane
No activity
Error limit, 0.2–0.5 mm.
and the mixture was heated under reflux for 6 h. Only little biphenyl was isolated when
the reaction was carried out without the catalyst; an insignificant amount compared
to biphenyl was obtained from the reaction catalyzed by ruthenium(III) complexes [42].
The catalytic activity of the ruthenium(III) starting complexes is higher than that of
the Schiff bases but lower than that of the chelate complexes. The experiment was
repeated thrice and the error limit was found to be 0.2–0.5%.
3.4. Biocidal activity of ruthenium(III) Schiff-base complexes
The in vitro cytotoxicity of ligands and complexes were screened in order to evaluate the
activity against S. epidermidis, E. coli, B. cinerea, and A. niger at 0.25%, 0.50%, and 1%
concentrations (table 3). The ruthenium(III) Schiff-base complexes are more active than
the parent ligands, ruthenium(III) precursors, and standard reference against the same
microbes under identical experimental conditions [43, 44]. The microbial screening
was repeated twice and the error limit was found to be 0.2–0.5 mm.
Based on the physico-chemical and spectroscopic data, an octahedral structure has
been proposed for the mononuclear ruthenium(III) complexes (scheme 6).
4. Conclusion
New six-coordinate ruthenium(III) complexes have been synthesized using Schiff
bases formed by condensing actetoacetanilide/acetoacetotoludide with o-aminophenol/
o-aminothiophenol/o-aminobenzoic acid in 1 : 2 stoichiometric ratio. The new

Ruthenium(III) tetradentate Schiff base complexes
1805
R
NH
N
Y
X
Ru
PPh
3
Y
N
R=H/CH ; X=Cl/Br and Y=O/S/COO
3
Scheme 6. Proposed structure for the new mononuclear ruthenium(III) complexes.
complexes have been characterized by analytical and spectral (IR, electronic, and EPR)
studies. An octahedral structure has been proposed for all the complexes. All complexes
show good catalytic and antimicrobial activities. Our Schiff-base complexes show better
activity in catalysis and biocidal studies [11, 34, 36]. In these articles, oxidation
of alcohols was carried out using N-methylmorpholine-N-oxide as oxidant.
But N-methylmorpholine-N-oxide releases oxides of nitrogen which leads to pollution.
In our study, we prefer molecular oxygen as the oxidant, which is a greener technique.
Synthesis, characterization, and crystal data have been reported [45, 46], but we have
carried out application studies. Ruthenium(III) Schiff-base complexes in the literature
[47] have poor antibacterial activities, but our complexes have better inhibitory activity
against bacteria and fungi than the standard compounds.
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