Synthesis, spectroscopic characterization, electrochemical behaviour and antibacterial activity of Ru(III) complexes of 2-[(4-N,N′-dimethylaminophenylimino)-methyl]-4-halophenol

Article abstract of DOI:10.1016/j.saa.2008.11.019

The reaction of the chelating Schiff base ligands 2-[(4-N,N′-dimethylaminophenylimino)-methyl]-4-X-phenol with [Ru(Cl)₃(EPh₃)₃]; (E = P or As); (X = Cl, Br or I) in the benzene afforded new stable ruthenium complexes of th

Full text of DOI:10.1016/j.saa.2008.11.019

Spectrochimica Acta Part A 72 (2009) 796–800
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectroscopic characterization, electrochemical behaviour and
antibacterial activity of Ru(III) complexes of
2-[(4-N,Nꢀ-dimethylaminophenylimino)-methyl]-4-halophenol
G. Puthilibaib, S. Vasudhevanc, S. Kutti Ranid, G. Rajagopala,∗
a Department of Chemistry, Government Arts College (Men), Nandanam, Chennai 600 035, Tamilnadu, India
b Department of Chemistry, Sri Sairam Engineering College, Chennai 600 073, India
c Department of Chemistry, KV, CLRI, Chennai 600 020, India
d Department of Chemistry, B.S.A. Crescent Engineering College, Chennai 600 048, India
a r t i c l e i n f o
a b s t r a c t
The reaction of the chelating Schiff base ligands 2-[(4-N,Nꢀ-dimethylaminophenylimino)-methyl]-4-X-
phenol with [Ru(Cl)3(EPh3)3]; (E = P or As); (X = Cl, Br or I) in the benzene afforded new stable ruthenium
complexes of the general formula [Ru(Cl)2(EPh3)2(L)] (L = anion of bidentate Schiff bases). The newly
synthesized complexes were characterized using molar conductivity, spectral (UV–vis, FT-IR and EPR)
and electrochemical studies. The molar conductance measurements proved that all these complexes are
non-electrolytes. All complexes show strong d–d transition in the visible region. The coordination of
imine nitrogen and phenolic oxygen of ligands to ruthenium metal was confirmed with the change in
the IR stretching frequency values. The EPR spectral data showed that the complexes are paramagnetic
with one unpaired electrons. The redox behaviour of the complexes have been investigated by the cyclic
voltammetric technique. All the complexes display an irreversible reduction (RuIII/RuII) in the range of
−0.826 to −0.971 V. In view of the biological activity, the ligands and the complexes were observed that
all the complexes showed moderate activity. Also the antibacterial activity of the ligand increased on
Article history:
Received 22 August 2008
Received in revised form 9 November 2008
Accepted 15 November 2008
Keywords:
Ru(III) complexes
Schiff bases
Spectral
Cyclic voltammetry
Antibacterial screening
chelation with metal ion.
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
of hexacoordinated ruthenium complexes of Schiff bases contain-
ing O and N donor atoms and PPh3/AsPh3. The Schiff bases used to
There has been considerable interest in the ruthenium Schiff
base complexes now-a-days because of their redox stability, excited
state life time and excited state reactivities [1,2], effective catalysts
[3–8], their ability to act as probes in investigating the structure of
DNA [9,10] and its antibacterial activity [11–14].
prepare the new ruthenium(III) complexes were shown in Fig. 1.
2. Experimental
2.1. Materials
Schiff bases a class of chelators capable of forming coordinate
bonds with many of metal ions through both azomethine group and
phenolic group or via its azomethine or phenolic groups [12–15].
Chemotherapeutic Schiff bases and their complexes receives sig-
nificant interest and attention of inorganic biochemists because of
their biological activity including anti-tumor, antibacterial, fungi-
cidal and anticarcenogenic properties [16,17]. However, literature
survey reveals that little work has been done on biological studies
of Schiff base complexes of Ru(III) [5,18,19].
All the reagents used were chemically pure and AR grade.
Solvents were purified and dried according to standard proce-
dure [20]. RuCl3·3H2O was purchased from Loba Chemie Pvt. Ltd.,
Bombay, India and was used without further purification. 5-Halo-2-
hydroxy benzaldehyde and 4-N,Nꢀ-dimethylaniline were purchased
from Aldrich. [Ru(Cl)3(EPh3)3] (where E = P or As) was prepared by
reported literature method [21].
In the present investigation, we describe the synthesis, charac-
terization, redox behaviour and antibacterial screening of new class
2.2. Physical measurements
The electronic spectra in MeCN were obtained on a JASCO V-
550 UV–Vis spectrophotometer. The IR spectra (KBr disc) were
recorded on a JASCO FT-IR 410 spectrophotometer in the range of
4000–400 cm−1 1H NMR spectra were recorded in CDCl3 with TMS
∗
Corresponding author. Tel.: +91 44 22751347; fax: +91 44 22750520.
E-mail address: rajagopal18@yahoo.com (G. Rajagopal).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.11.019

G. Puthilibai et al. / Spectrochimica Acta Part A 72 (2009) 796–800
797
Fig. 1. Schiff base.
as an internal standard on a Joel GSX-400 MHz, FT NMR spectropho-
tometer. The ESR spectra in MeCN were obtained at 77 K on a E-112
varian ESR spectrometer. Cyclic voltammetric measurements were
made in MeCN using a Bio Analytical System (BAS) model CV-50 W
electrochemical analyser, with a glassy carbon working electrode,
Pt auxiliary electrode and Ag/AgCl reference electrode: [Bu4N]ClO4
(TBAP) (0.1 M) was used as supporting electrolyte.
2.3. Synthesis of the ligands
The ligand was prepared by condensing 4-N,Nꢀ-dimethylamino-
aniline in hot ethanolic solution of 4-halo-2-hydroxybenzaldehyde
in 1:1 molar ratio. The purity of the compound was checked with
TLC. The 1H NMR spectra of all the Schiff bases provide compelling
evidence of the presence of azomethine group.
2.3.1.
Fig. 2. Synthesis of ruthenium(III) complexes.
2-[(4-N,Nꢀ-dimethylaminophenylimino)-methyl]-4-chlorophenol
(DMAPIMP-Cl)
Yield: 76%; m.p.: 142 ◦C. 1H NMR (CDCl3, 400 MHz): ı = 13.759
(O–H, s, 1H); 8.541(–CH N, s, 1H); 7.229–7.321(Ar, m, 4H); 6.732–
6.754(Ar, d, 2H); 6.924–6.945(Ar, d, 1H); 3.009(N(CH3)2, s, 6H).
2.5. Antibacterial screening
The in vitro antibacterial screening effects of the investigated
compounds were tested against the Gram +ve bacteria Staphylo-
coccus aureus and Gram −ve bacteria Proteus mirabilis by the well
diffusion method using agar nutrient as the medium at 37 ◦C for
18 h. The stock solutions of the Schiff bases and the complexes
were prepared in 10% MeCN in methanol and were stored dry at
room temperature. In a typical procedure [22] a well was made
on the agar medium inoculated with microorganisms. The well
was then filled with the test solution using a micropipette and the
plates were incubated at 35 ◦C for 24 h for bacteria. During this
period, the test solution diffused and the growth of the inoculated
microorganisms was affected. The inhibition zone developed on
the plate was measured and the data is summarized in Table 5.
Ampicillin was used as the control.
2.3.2.
2-[(4-N,Nꢀ-dimethylaminophenylimino)-methyl]-4-bromophenol
(DMAPIMP-Br)
Yield: 74%; m.p.: 145 ◦C. 1H NMR (CDCl3, 400 MHz): ı = 13.805
(O–H, s, 1H); 8.561(–CH N, s, 1H); 7.280–7.489(Ar, m, 4H); 6.888–
6.932(Ar, d, 2H); 6.744–6.786(Ar, d, 1H); 3.031 (N(CH3)2, s, 6H).
2.3.3.
2-[(4-N,Nꢀ-dimethylaminophenylimino)-methyl]-4-iodophenol
(DMAPIMP-I)
Yield: 78%; m.p.: 159 ◦C. 1H NMR (CDCl3, 400 MHz): ı = 13.854
(O–H, s, 1H); 8.525(–CH N, s, 1H); 7.262–7.634(Ar, m, 4H); 6.73–
6.752(Ar, d, 2H); 6.774–6.796(Ar, d, 1H); 3.011(N(CH3)2, s, 6H).
3. Results and discussion
2.4. Synthesis of ruthenium(III) complexes
All the complexes are amorphous powder, insoluble in water and
ether, but soluble in solvents such as CHCl3, CH2Cl2, MeCN, DMF and
DMSO. The molar conductance datas (Table 1) indicate that all the
complexes are non-electrolytes [23].
A
solution of [Ru(Cl)3(PPh3)3] (0.1 mmol, 99.342 mg) or
[Ru(Cl)3(AsPh3)3] (0.1 mmol, 112.542 mg) in C6H6 (20 cm3) and a
solution of the appropriate Schiff base (0.1 mmol, 27.4–36.6 mg) in
CHCl3(10 cm3) was added, colour change was noticed on the addi-
tion of the ligand due to the formation of complexes (Fig. 2). The
contents were refluxed for 4–5 h. The resulting solution was con-
centrated to small volume (3 cm3) on a rotary evaporator and the
product was separated by the addition of small amount of pet-ether
(60–80 ◦C). The compound that separated was filtered, washed with
benzene followed by ether, dried in vacuo over anhydrous CaCl2,
then recrystallised from 1:2 (v:v) chloroform-pet ether (60–80 ◦C)
mixture.
3.1. Electronic absorption spectra
The electronic absorption spectral bands of the complexes were
recorded over the range of 200–1100 nm in MeCN together with
tentative assignments [24] (Table 1) are discussed in detail.
The low spin paramagnetic ruthenium(III), a d5 system with 2T2g
as the ground term and the first excited doublet levels in the order
1
of increasing energy are 2A2g and 2T1g, which arise from 4T2g → Eg
configuration. All complexes exhibit three bands in the range of

798
G. Puthilibai et al. / Spectrochimica Acta Part A 72 (2009) 796–800
Table 1
Electronic spectral and molar conductance data.
Complex
ꢀmax (nm) (ε) (dm3/mol/cm)a
Molar conductance (×10−3
ꢁ
−1 cm2 mol−1
)
CH3CN
CH3OH
(1) [Ru(Cl)2(DMAPIMP-Cl)(PPh3)2]
(2) [Ru(Cl)2(DMAPIMP-Br)(PPh3)2]
(3) [Ru(Cl)2(DMAPIMP-I)(PPh3)2]
(4) [Ru(Cl)2(DMAPIMP-Cl)(AsPh3)2]
(5) [Ru(Cl)2(DMAPIMP-Br)(AsPh3)2]
(6) [Ru(Cl)2(DMAPIMP-I)(AsPh3)2]
212 (20,320),b 369 (12,400),c 630 (510)d
213 (20,700),b 374 (11,750),c 621 (530)d
203 (21,700),b 369 (12,600),c 618 (490)d
214 (20,450),b 406 (12,380),c 616 (495)d
223 (19,400),b 365 (11,600),c 619 (550)d
211 (19,800),b 355 (12,100),c 618 (520)d
27.6
26.9
27.1
23.4
22.1
20.8
44.8
42.1
44.4
44.2
43.0
44.6
a
In acetonitrile.
␲–␲* transition.
n–␲* transition.
d–d transition.
b
c
d
Table 2
FT-IR spectral data (cm−1) of the ligands and RuIII complexes.
Compound
ꢂ(C
ꢂ(C–O)
ꢂ(O–H)
ꢂ(Ru–O)
ꢂ(Ru–N)
Bands for PPh3/AsPh3
N)
DMAPIMP-Cl
DMAPIMP-Br
DMAPIMP-I
[Ru(Cl)2(DMAPIMP-Cl)(PPh3)2]
[Ru(Cl)2(DMAPIMP-Br)(PPh3)2]
[Ru(Cl)2(DMAPIMP-I)(PPh3)2]
[Ru(Cl)2(DMAPIMP-Cl)(AsPh3)2]
[Ru(Cl)2(DMAPIMP-Br)(AsPh3)2]
[Ru(Cl)2(DMAPIMP-I)(AsPh3)2]
1619
1619
1619
1611
1611
1611
1611
1611
1611
1369
1370
1355
1386
1361
1394
1440
1453
1440
3464
3454
3430
–
–
–
–
–
–
–
–
–
423
425
425
411
424
407
–
–
–
472
469
467
453
457
474
–
–
–
1428,1021,692
1434,1078,695
1434,1077,694
1433,1071,697
1435,1067,692
1434,1077,694
Table 3
203–630 nm. The spectral profiles below 400 nm are very similar
and are ligand centered transitions. The intense bands appeared in
the range of 203–223 nm (ε = 19,400–21,700 dm3/mol/cm) which
can be assigned to ␲–␲* transition was due to transitions involv-
ing molecular orbitals located on the phenolic chromophore
[25,26]. Another band appeared in the region 355–400 nm
(ε = 11,600–12,400 dm3/mol/cm) can be assigned to n–␲* transition
was due to transitions involving molecular orbitals of the C N chro-
mophore and the benzene ring [26,27]. The other broad appeared
in the range of 616–630 nm (ε = 490–530 dm3/mol/cm) which can
be attributed to d–d transitions in the metal orbitals [5,26].
ESR spectral and magnetic moment data of ruthenium(III) complexes.
a
b
Complex
gx
gy
gz
ꢁgꢂ
ꢃeff
[Ru(Cl)2(DMAPIMP-Cl)(AsPh3)2]
[Ru(Cl)2(DMAPIMP-Br)(AsPh3)2]
[Ru(Cl)2(DMAPIMP-I)(AsPh3)2]
2.415
2.385
2.335
2.243
2.248
2.354
1.979
2.03
2.146
2.219
2.226
2.2803
1.916
1.923
1.975
[1/3 gx2 + 1/3 gy2 + 1/3 gz
]
.
a
2 1/2
ꢀ
b
gav
s(s + 1).
obtained for other similar octahedral ruthenium(III) complexes
[32–34].
The effective magnetic moments ꢃeff (Table 3) lie in the range
of 1.916–1.923BM also suggesting that these complexes are one
electron paramagnetic low spin t2g (s = 1/2) configuration of the
ruthenium(III) ion in an octahedral environment which is similar
to reported O,N–coordinated Ru(III) complexes [5].
3.2. Infrared spectra
5
The IR spectra (Table 2) of the free Schiff bases were compared
with their respective ruthenium complexes in order to determine
the coordination mode of the ligands [28]. The free ligands show a
broad band of medium intensity observed at ca. 3430–3464 cm−1
is assigned to ꢂ(O–H) of the phenolic group. In complexes the two
intense bands centered at ca. 1611 and 1361–1453 cm−1 assigned
3.4. Electro chemical study
The redox properties of the mixed ligand complexes of ruthe-
nium in MeCN were studied by cyclic voltammetry under nitrogen
to ꢂ(C
and ꢂ(C–O), respectively [13,25]. The bands observed
N)
in the region of 407–425 cm−1 has been assigned to ꢂ(Ru–O) and
ꢂ(Ru–N) [25,29]. The disappearance of ꢂ(O–H), the downward shift
of ꢂ(C–O) and the lower frequency of ꢂ(C
[30] on complexation
Table 4
N)
Electrochemical redox data of ruthenium(III) complexes.a.
proves the bonding of ligands through imine nitrogen [31] and
deprotonated phenolic oxygen [23]. Also the characteristic bands
due to triphenylphosphine or triphenylarsine were observed in the
expected regions [13].
Complex
RuII/RuIII
Potential (V)
Current (A)
E Ipa/Ipc
½
Epa
Epc
ꢄEp
[Ru(Cl)2(DMAPIMP-Cl)(PPh3)2]
[Ru(Cl)2(DMAPIMP-Br)(PPh3)2]
[Ru(Cl)2(DMAPIMP-I)(PPh3)2]
[Ru(Cl)2(DMAPIMP-Cl)(AsPh3)2]
[Ru(Cl)2(DMAPIMP-Br)(AsPh3)2]
[Ru(Cl)2(DMAPIMP-I)(AsPh3)2]
−0.591
−0.667
−0.576
−0.567
−0.646
−0.596
−1.147
−1.183
−1.076
−1.122
−1.296
−1.288
0.556
0.516
0.505
0.555
0.65
−0.869
−0.925
−0.826
−0.844
−0.971
−0.942
−0.2
3.3. Magnetic moment and EPR studies
−0.32
−0.98
−0.64
−0.2
The solid state EPR spectra of ruthenium(III) complexes [5,11]
recorded at liquid nitrogen temperature (77 K) shows a simple three
line spectra indicating magnetic anisotropy [13] in these systems
and the complexes are in a low spin octahedral geometry. The aver-
age ‘g’ values (gx, gy, gz) with gx =/ gy =/ gz lie in the 2.219–2.226BM
range (Table 3) and these values fit very well with the values
0.619
−0.14
a
Solvent—acetonitrile; supporting electrolyte—[Bu4N]ClO4 (TBAP) 0.1 M; refer-
ence electrode—SCE; E1/2 = 0.5(Epa + Epc) where Epa and Epc are anodic and cathodic
peak potential, respectively; ꢄEp = Epa − Epc; scan rate = 100 mV s−1
.

G. Puthilibai et al. / Spectrochimica Acta Part A 72 (2009) 796–800
799
Table 5
Antibacterial activities of Schiff base ligands and ruthenium(III) complexes.
Compound
Diameter of inhibition zone (mm)
Staphylococcus aureus
Proteus mirabilis
0.15%
0.2%
0.25%
0.15%
0.2%
0.25%
DMAPIMP-Cl
DMAPIMP-Br
–
–
–
–
–
–
–
–
–
–
–
–
DMAPIMP-I
–
–
–
–
–
–
[Ru(Cl)2(DMAPIMP-Cl)(PPh3)2]
[Ru(Cl)2(DMAPIMP-Br)(PPh3)2]
[Ru(Cl)2(DMAPIMP-I)(PPh3)2]
[Ru(Cl)2(DMAPIMP-Cl)(AsPh3)2]
[Ru(Cl)2(DMAPIMP-Br)(AsPh3)2]
[Ru(Cl)2(DMAPIMP-I)(AsPh3)2]
Control (acetonitrile)
10
9
10
9
8
10
–
12
10
11
12
9
13
13
12
12
10
12
–
15
14
13
16
14
16
–
15
15
14
16
15
17
–
16
16
16
17
17
18
–
12
–
Standard (ampicillin)
30
32
34
22
23
24
Symbol “–” denotes no activity.
atmosphere and the relevant electrochemical data are given in
Table 4. All Ru(III) complexes (Fig. 2) exhibit redox peak (E1/2 values)
in the range of −0.826 to −0.971 V has been assigned to metal-
based reduction Ru(III)/Ru(II) [11] with peak-to-peak separation
value (ꢄEp) ranging from 505 to 650 mV suggesting that an irre-
versible one electron transfer process [35]. Representative cyclic
voltammogram of [Ru(Cl)2(PDMAAS-Cl)(PPh3)2] is shown in Fig. 3.
The presence of such redox waves seems to be typical for ruthe-
nium salicyliminato complexes [5,13,36]. The Schiff bases, when
co-ordinated through N and O, stabilise ruthenium(III) rather than
ruthenium(II). That is, the hard oxygen atom stabilises the higher
oxidation state of ruthenium and lower valencies are stabilised by
␲-acid ligands like triphenyl phosphine and triphenyl arsine.
increased activity for the metal chelates as compared to the free
ligands can be explained on the basis of Tweedy’s chelation theory
[39]. The activity increases with increase in concentration of test
solution containing the new complexes. The different compounds
exhibit microbial activity with small variations against the bacte-
rial species and this difference in activity could be attributed to the
impermeability of the cell of the microbes or differences in the ribo-
somes of the microbial cells [40]. Although the complexes are active,
they did not reach the effectiveness of the conventional bacteriocide
ampicillin.
Acknowledgements
Authors thank SAIF, IIT, Madras for providing ESR and NMR facili-
ties. Also, we express our sincere thanks to Prof. PR Athappan, Head,
Department of Inorganic Chemistry, School of Chemistry, Madu-
rai Kamaraj University, Madurai for providing cyclic voltammetric
facility.
3.5. Antibacterial investigation
The Schiff base ligands and ruthenium(III) complexes were
screened in vitro for their microbial activity against two pathogenic
bacterial species S. aureus and P. mirabilis using the well diffusion
method. The test solutions were prepared in MeCN and the results
are summarized in Table 5. Blank experiments with RuCl3·3H2O
and the Ru(III) precursors were carried out under identical exper-
imental conditions and show the inability of these complexes to
inhibit the bacterial growth. The effectiveness of an antimicrobial
agent in sensitivity is based on the zones of inhibition. The diame-
ter of the zone is measured to the nearest millimeter (mm). These
compounds were found to exhibit moderate activity against both
the organisms. The complexes are more active than their parent
ligands, which is consistent with earlier reports [37,38]. Such an
References
[1] J. Chakravarty, S. Bhattacharya, Polyhedron 13 (1994) 2671.
[2] V. Balzani, A. Juris, M. Venturi, S. Compagna, S. Serroni, Chem. Rev. 96 (1996)
759.
[3] R.I. Kureshy, N.H. Khan, S.H.R. Abdi, S.T. Patel, P. Iyer, J. Mol. Catal. A 150 (1999)
175.
[4] R. Karvembu, S. Hemalatha, R. Prabhakaran, K. Natarajan, Inorg. Chem. Com-
mun. 6 (2003) 486.
[5] S. Kannan, R. Ramesh, Polyhedron 25 (2006) 3095.
[6] Y. Aoyama, J.T. Kujisawa, T. Walanawe, A. Toi, H. Ogashi, J. Am. Chem. Soc. 108
(1986) 943.
[7] R.S. Sdrawn, M. Zamakani, J.L. Coho, J. Am. Chem. Soc. 108 (1986) 3510.
[8] T.D. Thangadurai, K. Natarajan, Indian J. Chem. 41A (2002) 741.
[9] H. Deng, J. Cai, H. Xu, H. Zhang, L.-N. Ji, J. Chem. Soc., Dalton Trans. (2003) 325.
[10] V. Murali, C.V. Sastri, B.G. Maiya, Proc. Indian Acad. Sci. (Chem. Sci.) 114 (2002)
403.
[11] R. Ramesh, S. Maheswaran, J. Inorg. Biochem. 96 (2003) 457.
[12] C. Jayabalakrishnan, R. Karvembu, K. Natarajan, Trans. Met. Chem. 27 (2002)
790.
[13] R. Prabhakaran, A. Geetha, M. Thilagavathi, R. Karvembu, Venkatakrishnan, Hel-
mut Bertagnolli, K. Natarajan, J. Inorg. Biochem. 98 (2004) 2131.
[14] K.P. Balasubramanian, R. Karvembu, R. Prabhakaran, V. Chinnusamy, K. Natara-
jan, Spectrochim. Acta A 68 (2007) 50.
[15] S.A. Sadeek, M.S. Refat, J. Korean Chem. Soc. 50 (2) (2006) 107.
[16] R.J. Cozens, K.S. Murray, B.O. West, Organomet. Chem. 27 (1971) 399.
[17] A. Bigotto, V. Galasso, G. Dealti, Spectrochim. Acta 28A (1972) 1581.
[18] R. Prabhakaran, R. Huang, K. Natarajan, Inorg. Chim. Acta 359 (2006) 3359.
[19] N. Chitrapriya, V. Mahalingam, M. Zeller, R. Jayabalan, K. Swaminathan, K.
Natarajan, Polyhedron 27 (2008) 939.
[20] A.I. Vogel, Textbook of Practical Organic Chemistry, 5th ed., Longman, London,
1989.
[21] N. Ahmed, J.J. Levision, S.D. Robinson, M.F. Uttley, Inorg. Synth. 15 (1974) 48.
[22] M.J. Relezar, E.C.S. Chan, N.R. Krieg, Microbiology, 5th ed., McGraw Hill, New
York, 1998.
[23] M.S. Refat, J. Mol. Struct. 742 (2007) 24.
[24] A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, New York, 1984.
Fig. 3. Cyclic voltammogram of [Ru(Cl)2(PDMAAS-Cl)(PPh3)2].

800
G. Puthilibai et al. / Spectrochimica Acta Part A 72 (2009) 796–800
[25] R.K. Sharma, R.V. Singh, J.P. Tandon, J. Inorg. Nucl. Chem. 42 (1980) 1382.
[26] M.S. Refat, S.A. EI-Korashy, D.N. Kumar, A.S. Ahmed, Spectrochim. Acta A 70
(2008) 898.
[27] M.J.M. Cambell, Coord. Chem. Rev. 15 (1975) 279.
[28] L.J. Bellamy, The Infrared Spectra of Complex Molecules, 3rd ed., Chapman &
Hall, London, 1975.
[29] M. Turner, C. CeliK, H. Koksal, S. Serin, Trans. Met. Chem. 24 (1999) 525.
[30] W.J. Evans, CyH. Fujimoto, J.W. Ziller, Polyhedron 21 (2002) 1683.
[31] M. Sivagamasundari, R. Ramesh, Spectrochim. Acta A 67 (2007) 256.
[32] D. Bhattacharya, S. Chakraborthy, P. Munshi, G.K. Lahiri, Polyhedron 18 (1999)
2559.
[33] R. Ramesh, N. Dharmaraj, R. Karvembu, K. Natarajan, Indian J. Chem. 39A (2000)
1079.
[34] R.S. Drago, Physical Methods in Inorganic Chemistry, Reinhold, New York,
1968.
[35] L. Mishra, R. Prajapati, K.K. Pandey, Spectrochim. Acta A 70 (2008) 79.
[36] H. Doine, F.F. Stephens, R.D. Cannon, Bull. Chem. Soc. Jpn. 58 (1985) 1327.
[37] K.N. Kumar, R. Ramesh, Spectrochim. Acta A 60 (2004) 2913.
[38] R.S. Srivastava, J. Inorg. Nucl. Chem. 42 (1990) 1526.
[39] B.G. Tweedy, Phytopathalogy 55 (1964) 910.
[40] P.G. Lawrence, P.L. Harold, O.G. Francis, Antibiot. Chemother. (1957) 1980.