Studies on some transition metal complexes with bidentate Schiff bases

Article abstract of DOI:10.1081/SIM-120028307

Metal complexes of the types [M(HSB-Cl)₂benen] and [M(HSB-Br)₂benen] where M = Mn(II), Co(II), Ni(II), Cu(II), and Cd(II); HSB-Cl = 5-chlorosalicylidene-p-anisidine, HSB-Br = 5-bromosalicylidene- p-anisidine and benen = bis(benzylide

Full text of DOI:10.1081/SIM-120028307

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Synthesis and Reactivity in Inorganic and Metal-
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Studies on Some Transition Metal Complexes with
Bidentate Schiff Bases
Prakash P. Dholakiya a & M. N. Patel a
a Department of Chemistry , Sardar Patel University , Vallabh Vidyanagar, Gujarat, 388
120, India
Published online: 16 Nov 2010.
To cite this article: Prakash P. Dholakiya & M. N. Patel (2004) Studies on Some Transition Metal Complexes with
Bidentate Schiff Bases, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 34:2, 371-382, DOI: 10.1081/
SIM-120028307
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 2, pp. 371–382, 2004
Studies on Some Transition Metal
Complexes with Bidentate Schiff Bases
*
Prakash P. Dholakiya and M. N. Patel
Department of Chemistry, Sardar Patel University,
Vallabh Vidyanagar, Gujarat, India
ABSTRACT
Metal complexes of the types [M(HSB-Cl)2benen] and [M(HSB-Br)2benen]
where M ¼ Mn(II), Co(II), Ni(II), Cu(II), and Cd(II); HSB-Cl ¼ 5-chloro-
salicylidene-p-anisidine, HSB-Br ¼ 5-bromosalicylidene-p-anisidine and
benen ¼ bis(benzylidene)ethylenediamine have been prepared and charac-
terized on the basis of elemental analyses, magnetic susceptibility measure-
ments, electronic and infrared spectra. An octahedral structure has been
assigned to all of the prepared complexes. The complexes show higher
antimicrobial activity against the Fasarium oxysporum (fungi), Salmonella
typhi (bacteria), Saccharomyces cerevisiae (yeast), Lasiodiplodia theo-
bromae (fungi) as compared to the ligands, metal salt, and control.
Key Words: Metal complexes; Mixed-ligand complexes; Schiff base;
Antimicrobial activity.
*
Correspondence: M. N. Patel, Department of Chemistry, Sardar Patel University,
Vallabh Vidyanagar, Gujarat 388 120, India; E-mail: jeenenpatel@yahoo.co.in.
371
DOI: 10.1081/SIM-120028307
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Dholakiya and Patel
INTRODUCTION
Mixed-ligand complexes are well known to play an important role in
biological systems.[1] In continuation of our earlier work,[2] we report here the
preparation, spectroscopic, and biocidal studies of Mn(II), Co(II), Ni(II),
Cu(II), and Cd(II) complexes with 5-chlorosalicylidene-p-anisidine (HSB-Cl)
or 5-bromosalicylidne-p-anisidine (HSB-Br) and bis(benzylidene)ethylene-
diamine (benen) as a secondary ligand (Fig. 1).
EXPERIMENTAL
Materials and Measurements
The IR spectra were recorded on a FT-IR Nicolet 400 D spectropho-
tometer in KBr pellets. The elemental analyses were carried out using a model
240 Perkin–Elmer elemental analyzer. Metal contents were determined
Figure 1. Structure of the ligands.

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Complexes with Bidentate Schiff Bases
373
by EDTA titration. Magnetic susceptibility measurements were done on a
model 7300 vibrating sample magnetometer. The electronic spectra were
recorded on a Beckman DK-2A spectrophotometer using MgO as a reference.
The melting points of the ligands and complexes were recorded in open
capillaries in a capillary melting point apparatus (Tempo Instruments Co.
Mumbai).
Preparation of the Schiff Bases
The preparation of HSB-Cl or HSB-Br was carried out by refluxing a
solution of 10 mmol (1.23 g) of p-anisidene in 100 mL ethanol with a solution
of 10 mmol of 5-chlorosalicylaldehyde (1.56 g) or 5-bromosalicylaldehyde
(2.00 g) in 100 mL ethanol for 2–3 hr. The reaction mixture was then allowed
to cool to room temperature. The yellow crystals that formed were collected
and dried in air.
The preparation of benen was carried out by refluxing a solution
of 2 mmol (0.212 g) of benzaldehyde in 100 mL ethanol and a solution of
2 mmol (0.06 g) of ethylenediamine in 100 mL ethanol for 2–3 hr. The
reaction mixture gave the Schiff base in the form of yellow crystals.
The product was filtered and washed with ether and dried in air. Yield,
0.15 g (75.0%).
Preparation of the Complexes
Bis(5-chlorosalicylidene-p-anisidine)diaquoM(II) or bis(5-bromosalicy-
lidene-p-anisidene)diaquoM(II), [M ¼ Mn(II), Co(II), Ni(II), Cu(II), and
Cd(II)] were synthesized by a published procedure.[3] The preparation of the
mixed-ligand complexes of bis(5-chlorosalicylidene-p-anisidine)benenNi(II) or
bis(5-bromosalicylidene-p-anisidine)benenNi(II) was carried out by refluxing
a solution of 2 mmol of bis(5-chlorosalicylidene-p-anisidine)diaquoNi(II)
(1.22 g) or bis(5-bromosalicylidene-p-anisidine)diaquaNi(II) (1.42 g) in 100 mL
dimethylformamide with a solution of 2 mmol of bis(benzylidene)ethylene-
diamine (0.47 g) in 100 mL dimethylformamide for an hour. The solution was
then concentrated to 15mL, scratched in the flask and cooled in a refrigerator
overnight. The obtained crystals were collected and recrystallized from
chloroform. Finally, the crystals were dried in air. The complexes of Mn(II),
Co(II), Cu(II), and Cd(II) were prepared similarly.

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Dholakiya and Patel
RESULTS AND DISCUSSION
Elemental analysis data, formula weights, colors, percentage yields,
melting points, and magnetic moment data are given in Table 1. The
compounds in this work were synthesized following the general procedures
outlined in the following equations.
H2O
![M(SB)2(H2O)2] þ 2HCl þ (n ꢁ 2)H2O
ErOH, Reflux
MCI2 ꢀ nH2O þ 2HSB
[M(SB)2(H2O)2] þ benen ꢁ![M(SB)2benen] þ 2H2O
1 hr
Here HSB ¼ HSB-Cl or HSB-Br.
The magnetic moment values of the Mn(II) complexes are 6.00 and
6.01 B.M., respectively, and are within the limits of the spin-free value
for five-unpaired electrons, due to a high-spin d5 system.[4] The electronic
spectra of the Mn(II) complexes exhibit three weak absorption bands at
6
4
ꢀ14,500, ꢀ18,000, and ꢀ25,000 cm21 assigned to A1g ! T1g(4G) (n1),
4
6
4
4
6A1g ! T2g(4G) (n2), and A1g ! A1g, Eg(4G) (n3) transitions.[5]
The magnetic moment values of the Co(II) complexes have been used as
criterion to determine the type of coordination around the metal ion. Due to the
intrinsic orbital angular momentum in the ground state, there is consistently a
considerable orbital contribution and the effective magnetic moment lies
between 4.70 and 5.20 B.M. In the present case, the magnetic moment values
(4.50 and 4.14 B.M.) suggest[6] an octahedral geometry for the Co(II) complex
in the high-spin state. The complexes exhibit three bands at ꢀ9,200,
4
ꢀ18,500, and ꢀ19,500 cm21. These bands are assigned to 4T1g(F) ! T2g(F)
4
4
4
4
(n1), T1g(F) ! A2g (n2), and T1g(F) ! T1g(P) (n3) transitions, respect-
ively, consistent with an octahedral geometry.[7] The magnetic moment values
of the Ni(II) complexes are 2.71 and 2.67 B.M., which are in the range usually
expected for similar hexa-coordianted Ni(II) metal ions.[8] The bands
observed at ꢀ10,500, ꢀ18,500, and ꢀ24,000 cm21, are assigned to
3
3
3
3
3
3A2g(F) ! T2g(F) (n1), A2g(F) ! T1g(F) (n2), and A2g(F) ! T1g(P) (n3)
transitions, respectively, which suggest an octahedral geometry.[9]
The observed magnetic moment values of the Cu(II) complexes are 1.89
and 1.99 B.M., which are very close to the spin-only value (1.83 B.M.)
expected for one unpaired electron,[10] and the band observed at
2
ꢀ14,000 cm21 is assignable to the 2Eg ! T2g(F) transition, which also
suggests an octahedral geometry.[11] The magnetic moment determination
shows that the Cd(II) complexes are diamagnetic. The value of the ligand field
splitting energy (Dq), nephelauxetic ratio (b), and ratio n2/n1 for the Ni(II) and
Co(II) complexes are presented in Table 2.

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375
m

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Dholakiya and Patel
m

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377
b

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Dholakiya and Patel
The infrared spectra of the HSB-Cl and HSB-Br exhibit a medium-intense
band at ꢀ2700cm21, which may be assigned to the intramolecularly hydrogen
bonded n(OH).[12] The absence of this band in the complexes indicates the
deprotonation of the phenolic groups and coordination of the oxygen atom to
the metal ion. In the free ligand, a strong band at ꢀ1525cm21 which may be
assigned to n(C–O) (phenolic), shifts to higher energy by 5–15cm21 in the
complexes indicating the coordination of the phenolic oxygen atom to the metal
ion.[13] This band shift to higher energy is expected due to the maintenance of
ring currents arising from the electron delocalization in the chelate ring. The
infrared spectra of benen, HSB-Cl, and HSB-Br exhibit the C55N stretching
band at ꢀ1645cm21. This band shifts to lower energy by 10–20cm21 in the
mixed-ligand complexes indicating coordination through the azomethine
nitrogen.[14]
The complexes of HSB-Cl exhibit a band at ꢀ750 cm21, which may be
due to n(C–Cl).[15] The complexes of HSB-Br exhibit a band at ꢀ685 cm21
which may be due to n(C–Br).[16] The frequencies in the range ꢀ2815–2830
and ꢀ1375–1385 cm21 may be due to n(C–OCH3)[17] and n(C–CH3),[18]
respectively. The bands observed in the range 455–465 and 420–430 cm21
may be attributed to n(M–N)[19] and n(M–O),[20] respectively.
The suggested structure of the complexes is shown in Fig. 2.
Antimicrobial Activity Study
The medicinal potency of many coordination compounds has been
established by their antitumor, antiviral,[21] and antimalarial[22] activities. These
Figure 2. Suggested structure of the complexes [M(SB-Cl)2benen] [X ¼ Cl] or
[M(SB-Br)2benen] [X ¼ Br].

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379
characteristic properties have been related to the ability of the metal ion to form
complexes[23] with ligands containing nitrogen and oxygen donor atoms. It has
been observed[24] that chelation in compounds is to a large extent responsible
for the antimicrobial activity. In view of the medicinal potency of the ligands,
the metal salts and the metal complexes, we evaluated the antimicrobial activity
of the compounds against bacteria and yeast using the “Agar Diffusion
Method.” [25] The antifungal activity of the compounds has been screened
against Lasiodiplodia theobromae and Fusarium oxysporum using the “Potato
Dextrose Method.” [26] All of the compounds have significant antimicrobial activity
at 5 ꢂ 1024 g mL21 against Salmonella typhi, Saccharamyces cerevisiae,
L. theobromae, and F. oxysporum. The compounds are soluble in dime-
thylformamide. Therefore, the growth was compared with dimethylformamide
as the control and is expressed as percentage inhibition vs. controls.
The percentage inhibition of various compounds are recorded in Table 3. The
Table 3. Antimicrobial activities of the complexes.a
% Inhibition
Fungi
Yeast
S. cerevisiae L. theobromae F. oxysporum
Bacteria
S. typhi
Compounds
.
MnCl2 4H2O
22.22
15.16
11.11
22.22
16.66
22.20
27.77
38.33
55.50
55.00
68.66
66.66
72.22
66.66
52.50
66.66
55.00
56.00
21.05
10.52
8.26
20.00
6.60
15.30
7.70
.
CoCl2 6H2O
.
NiCl2 6H2O
10.30
20.00
6.60
10.30
15.30
7.70
.
CuCl2 2H2O
15.78
8.26
.
CdCl2 2H2O
HSB-Cl
HSB-Br
Benen
15.78
26.31
5.00
6.60
23.00
37.00
36.00
61.30
80.00
62.00
69.00
80.00
62.00
53.00
69.00
61.30
61.30
13.30
20.00
46.60
53.30
40.00
54.00
46.00
47.00
33.30
46.00
40.00
47.60
[Mn(SB-Cl)2benen]
[Co(SB-Cl)2benen]
[Ni(SB-Cl)2benen]
[Cu(SB-Cl)2benen]
[Cd(SB-Cl)2benen]
[Mn(SB-Br)2benen]
[Co(SB-Br)2benen]
[Ni(SB-Br)2benen]
[Cu(SB-Br)2benen]
[Cd(SB-Br)2benen]
50.00
53.63
68.40
57.89
52.63
53.00
42.10
52.63
42.10
53.00
aHSB-Cl ¼ 5-chlorosalicylidene-p-anisidene;
HSB-Br ¼ 5-bromosalicylidene-p-
anisidene.

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Dholakiya and Patel
data represent the average values of five replicates. From the data it is observed
that the complexes show higher activity against S. typhi, S. cerevisiae, L. theo-
bromae, and F. oxysporum compared to the control, metal salts, and ligands.
The results suggest that changes in structure due to coordination in the
complexes decreases the growth of microorganisms relative to the metal ions
and ligands. Hence, complexation increases the antimicrobial activity due to
the presence of two halogen and four azomethine (C55N) groups. The
complexes are more active against S. typhi and F. oxysporum compared to
S. cerevisiae and L. theobromae. The complexes are also more active against
S. cerevisiae compared to L. theobromae. The pattern of activity is complex
and no clear trend can be ascertained.
ACKNOWLEDGMENTS
The authors are thankful to the Head, Department of Chemistry, and
Head, Department of Bio-Sciences, Sardar Patel University, Vallabh
Vidyanagar, India, for providing the necessary laboratory facilities.
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Received July 13, 2002
Accepted October 23, 2003
Referee I: S. M. Socol
Referee II: A. G. Sykes

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