Synthesis, spectral, and biocidal studies of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) mixed-ligand complexes

Article abstract of DOI:10.1081/SIM-120037513

Complexes of transition metals with salicylaldehyde (salH) or 5-bromosalicylaldehyde (Br-salH) in 1:2 molar ratio, have the compositions [M(H₂O)₂(sal)₂]·H₂O (1) or [M(H₂O)₂(Br-sal)₂

Full text of DOI:10.1081/SIM-120037513

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Synthesis, Spectral, and Biocidal Studies of Mn(II),
Co(II), Ni(II), Cu(II), and Zn(II) Mixed‐Ligand
Complexes
M. N. Patel a , N. H. Patel a , P. K. Panchal a & D. H. Patel b
a Department of Chemistry , Sardar Patel University , Vallabh Vidyanagar, Gujarat, 388
120, India
b Department of Biosciences , Sardar Patel University , Vallabh Vidyanagar, Gujarat,
India
Published online: 16 Nov 2010.
To cite this article: M. N. Patel , N. H. Patel , P. K. Panchal & D. H. Patel (2004) Synthesis, Spectral, and Biocidal Studies
of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) Mixed‐Ligand Complexes, Synthesis and Reactivity in Inorganic and Metal-Organic
Chemistry, 34:5, 873-882, DOI: 10.1081/SIM-120037513
To link to this article: http://dx.doi.org/10.1081/SIM-120037513
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 5, pp. 873–882, 2004
Synthesis, Spectral, and Biocidal Studies of
Mn(II), Co(II), Ni(II), Cu(II), and Zn(II)
Mixed-Ligand Complexes
1
1
M. N. Patel,1, N. H. Patel, P. K. Panchal, and
*
D. H. Patel2
2
1Department of Chemistry and Department of Biosciences,
Sardar Patel University, Vallabh Vidyanagar, Gujarat, India
ABSTRACT
Complexes of transition metals with salicylaldehyde (salH) or 5-bromo-
salicylaldehyde (Br-salH) in 1 : 2 molar ratio, have the compositions
.
.
[M(H2O)2(sal)2] H2O (1) or [M(H2O)2(Br-sal)2] H2O (2), respectively.
The Schiff base derived from ethylenediamine and acetophenone in 1 : 1
molar ratio in alcoholic solution yields bis(acetophenone)ethylenediamine
(acphen). Further reaction of (1) or (2) with acphen in alcohol yielded
mixed-ligand complexes of the type [M(sal)2acphen] or [M(Br-sal)2
acphen], respectively. All of these complexes are soluble in ethanol and
methanol. They were characterized on the basis of elemental analyses,
*
Correspondence: M. N. Patel, Department of Chemistry, Sardar Patel University,
Vallabh Vidyanagar, Gujarat 388 120, India; E-mail: jeenenpatel@yahoo.co.in.
873
DOI: 10.1081/SIM-120037513
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Patel et al.
magnetic measurements, infrared spectra, electronic spectra, and thermo-
gravimetric analyses. All of these complexes have been screened for
their antimicrobial activity against bacterial strands using the agar
diffusion method.
Key Words: Elemental analyses; Magnetic measurements; Schiff base;
Mixed-ligand complexes.
INTRODUCTION
Schiff bases and their metal complexes play a key role in our understand-
ing of transition metal ions. The complexes containing O,N donor atoms are
very important owing to their significant antibacterial and anticancer
activity.[1] It is well known that some drugs have increased activity when
administered as metal complexes than as free organic compounds.[2]
A large number of reports are available on the chemistry and the biocidal
activities of transition metal complexes containing O,N donor atoms. As a
continuation of our earlier work,[3] in this article, we describe the synthesis
and characterizations of bidentate Schiff base ligands and their metal
complexes. The structure of bis(acetophenone)ethylenediamine (acphen) is
shown in Fig. 1.
EXPERIMENTAL
Materials
The chemicals used in the synthesis were of A. R. grade. Stock solutions
of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) chlorides were prepared and stan-
dardized by complexometric titration.[4]
Figure 1. bis(Acetophenone)ethylenediamine (acphen).

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Preparation of Schiff Base
875
The acphen ligand was synthesized by mixing ethylenediamine (10 mmol,
0.06 g) and acetophenone (20 mmol, 0.528 g) in an ethanolic solution
(100 mL). The reaction mixture was heated in a water bath at 50 8C for
3–4 hr. The reaction mixture on ice-cooling overnight gave the Schiff base
in the form of yellow crystals. The product was filtered and dried in air. It
was recrystallized from ethanol to give 0.441 g (75%) of the ligand;
m.p. ¼ 260 8C.
Preparation of Complexes
bis(Salicylaldehydato)diaquonickel(II) and the an analogous complexes
of Mn(II), Co(II), Cu(II), and Zn(II) were synthesized by published pro-
cedures.[5] The preparation of [Ni(sal)2acphen] H2O was carried out by
.
refluxing an ethanolic solution (150 mL) of [Ni(sal)2(H2O)2] (20 mmol,
0.734 g) with the Schiff base (20 mmol, 0.528 g) for 1 hr. The solution was
then concentrated to 15 mL, and cooled in a refrigerator overnight at 6 8C.
The formed crystals were collected and recrystallized from chloroform and
dried in air. The mixed-ligand complexes of Mn(II), Co(II), Cu(II), and
Zn(II) were prepared similarly. The mixed-ligand complexes [M(Br-sal)2
.
acphen] H2O [M ¼ Mn(II), Co(II), Ni(II), Cu(II), and Zn(II)] were prepared
by the same method.
Analytical Procedures
Elemental analyses for carbon, hydrogen, and nitrogen were carried
out on a model 240 Perkin–Elmer elemental analyzer. Metal contents
were determined by EDTA titration. The infrared spectra were measured
on a FT-IR Nicolet 400 D spectrophotometer as KBr pellets. The elec-
tronic spectra of the complexes were recorded on a Beckman DK-2A
spectrophotometer using MgO as the reference in the solid state. The melt-
ing points of the ligands and complexes were recorded in open capillaries
in a capillary melting point apparatus (Tempo Instruments Co., Mumbai).
The magnetic moments were obtained by a model 7304 vibrating sample
magnetometer.

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RESULTS AND DISCUSSION
Characterization of the Complexes
The given formulas (Table 1) are based on analytical data. The formation
of the complexes may be represented by the following equations.
MCl2 ꢀ nH2O þ 2(salH) ꢁ! ½MðH2OÞ2ðsalÞ2ꢂ þ 2HCl
ð1Þ
ð2Þ
ð3Þ
ð4Þ
½MðH2OÞ2ðsalÞ2ꢂ þ acphen ꢁ! ½MðsalÞ2ðacphenÞꢂ þ 2H2O
MCl2 ꢀ nH2O þ 2ðBr-salHÞ ꢁ! ½MðH2OÞ2ðBr-salÞ2ꢂ þ 2HCl
½MðH2OÞ2ðBr-salÞ2ꢂ þ acphen ꢁ! ½M(Br-sal)2ðacphenÞꢂ þ 2H2O
Magnetic Measurements
The magnetic moment data of the complexes are presented in Table 1. The
magnetic moment values for the Cu(II) complexes are 1.71 and 1.84B.M.,
which is consistent[6] with an octahedral structure. The magnetic moment values
for the Co(II) complexes have been used as a criterion to determine the type of
coordination around the metal ion. Due to the intrinsic orbital angular momen-
tum in the ground state, there is consistently a considerable orbital contribution
and the effective magnetic moment lies between 4.7 and 5.2 B.M. at room
temperature. In the present case, the magnetic moment values of the Co(II)
complexes are 4.87 and 4.75B.M., suggesting[7] an octahedral geometry. This
deviation from the spin-only value (3.83 B.M.) maybe ascribed to spin–orbit
coupling. The magnetic moment values of the Ni(II) complexes are 2.67 and
2.72B.M., which are usual for the range expected for similar hexa-coordi-
nated[8] Ni(II) ions. The magnetic moment values of the Mn(II) complexes
are 5.74 and 5.75B.M., due to a high-spin d5-system with octahedral geometry.
The magnetic moment determinations show that the Zn(II) complexes are
diamagnetic.
Electronic Spectra
The electronic spectra of the complexes were recorded in the solid state.
The electronic spectra of the Mn(II) complexes exhibit 3 weak absorption
6
4
6
4
bands for the transitions A1g ! T1g(4G) (ꢀ15,000cm21), A1g ! T2g (4G)
(ꢀ20,000 cm21), and A1g ! Eg, A1g (4G) (ꢀ25,000 cm21), in accord with
6
4
4
an octahedral geometry.[9] The electronic spectra of the Co(II) complexes

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877
m

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Patel et al.
4
4
exhibit three bands. The assignments of the spectral bands are T1g(F) ! T2g
4
4
(n1 ꢀ 9500 cm21), 4T1g(F) ! A2g (n2 ꢀ 18,000 cm21), and 4T1g(F) ! T1g(P)
(n3 ꢀ 19,000 cm21). A strong charge transfer band is shown by the complex at
[10]
¨
was used to ascertain the correct position
of the bands. The Ni(II) complexes also exhibit three d–d transition bands at
ꢀ25,000 cm21. Konig’s method
3A2g(F) ! T2g(F)(n1 ꢀ 10,550 cm21),3A2g(F) ! T1g(F)(n2 ꢀ 17,400 cm21),
3
3
and A2g(F) ! T1g(P) (n3 ꢀ 25,000 cm21). The values of the electronic para-
meters such as the ligand field splitting energy (10 Dq), Racah interelectronic
repulsion parameter (B), nephelauxetic ratio (b), and the ratio n2/n1 are presented
in Table 2. All data are consistent with an octahedral geometry.[11] The electronic
spectra of the Cu(II) complexes[12] exhibit a band at ꢀ15,500 cm21 assigned to
3
3
2
2
the Eg ! T2g transition, which is in agreement with an octahedral geometry.
A strong charge transfer band is observed at 26,000 cm21. The 1 values of the
complexes were not determined.
Thermogravimetric Analyses
There are some remarkable features in the TGA curves. The decomposition
temperatures of the complexes are higher than those of acphen and salH or
Br-salH, indicating that the complexes are more stable than the ligands. Thermal
curves of the complexes clearly indicate that the weight loss between 35 and
105 8C corresponds to one water molecule for all complexes. Because of the
low temperatures, this water molecule may be considered as water of crystalli-
zation.[13] The TGA curve indicates that above 250 8C the compounds start to
loose mass with partial evaporation of the Schiff base (acphen) up to 320 8C.
In the temperature range 320–500 8C the remaining organic ligand molecules
are lost. In all cases the final products are metal oxides. These results are in
good agreement with the proposed composition of the complexes.
IR Spectra
The infrared spectra of the complexes have been studied to characterize
their structures. The infrared spectra of the complexes register the n(C55O)[14]
band at about 1600cm21 and n(C–O)[15] at about 1340 cm21. The Schiff
base (acphen) shows the n(C55N) stretching band at 1640cm21. This band shifts
to lower energy by 10–30cm21 in the chelates indicating coordination through
the azomethine nitrogen.[16] The sharp bands in the ranges 750–780 and
1525–1535 cm21 are due to aromatic n(C–H)[15] and n(C55C),[17] respectively.
The absorptions in the range 410–420 and 475–495 cm21 are attributed to
n(M–O)[18] and n(M–N),[19] respectively.

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b

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Patel et al.
Table 3. Antimicrobial activities of the complexes.a
S. typhi setatia spp.
Zone of
Zone of
Compound
Inhi (mm)
% Inhi
Inhi (mm)
% Inhi
Control (methanol)
SalH
acphen
10
11
12
12
12
11
11
12
11
13
13
14
13
13
13
14
14
13
13
—
10
20
20
22
15
11
22
10
30
50
30
40
40
30
40
40
30
30
11
12
12
13
13
13
12
12
12
14
16
14
14
14
14
16
16
15
14
—
09
09
18
18
18
09
09
09
27
45
27
27
27
27
45
45
36
27
BrsalH
MnCl2 4H2O
.
.
CoCl2 6H2O
.
NiCl2 6H2O
.
CuCl2 5H2O
ZnCl2
[Mn(sal)2acphen] H2O
.
.
[Co(sal)2acphen] H2O
.
[Ni(sal)2acphen] H2O
.
[Cu(sal)2acphen] H2O
.
[Zn(sal)2acphen] H2O
.
[Mn(Brsal)2acphen] H2O
.
[Co(Brsal)2acphen] H2O
.
[Ni(Brsal)2acphen] H2O
.
[Cu(Brsal)2acphen] H2O
.
[Zn(Brsal)2acphen] H2O
aacphen ¼ bis(acetophenone)ethylenediamine.
Figure 2. [M(sal)2acphen] or [M(Br-sal)2acphen] R ¼ H or Br, M ¼ Mn(II), Co(II),
Ni(II), Cu(II), and Zn(II).

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881
Antimicrobial Activity
In the present study, the ligands, metal salts, and complexes have been
tested for their effects on the growth of microbial cultures and were studied
for their interaction with S. typhi and Seratia spp. using the agar diffusion
method.[20,21] All compounds have significant antibacterial activity at
1 ꢃ 1024 g mL21 against bacteria. The growth was compared with a control
(blank) and is expressed as percentage inhibition vs. control. The percentage
inhibition of various compounds are recorded in Table 3. The data represent
the values of five replicates. From the data, it is observed that the complexes
show higher activity against bacteria as compared to the control, metal salts,
and ligands. Hence, complexation increased the antimicrobial activity.
The patterns of activity are complex and no clear trend can be ascertained. How-
ever, a suggested structure of the mixed-ligand complexes is shown in Fig. 2.
ACKNOWLEDGMENTS
The authors are thankful to Prof. R. M. Patel, Head, Department of Chemistry
and Prof. I. L. Kothari, Department of Biosciences, Sardar Patel University,
Vallabh Vidyanagar, India, for providing the necessary laboratory facilities.
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Received July 13, 2003
Accepted February 10, 2004
Referee I: J. Masnovi
Referee II: E. Voss

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