Synthesis, characterization, and biocidal studies of some transition metal complexes containing bidentate monobasic hydroxyaldehydes and a neutral bidentate schiff base

Article abstract of DOI:10.1081/SIM-120016872

Complexes of the transition metals with salicylaldehyde (sa1H) or 5-bromosalicylaldehyde (Br-sa1H) 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 benzaldehyde in 1:1 molar ratio in alcoholic solution yields bis(benzylidene)ethylenediamine (benen). Further reaction of (1) or (2) with benen in alcohol yielded mixed-ligand complexes of the type[M(sal)₂benen] or [M(Br-sal)₂benen], respectively. All of these complexes are soluble in ethanol and methanol. They were characterized on the basis of elemental analyses, magnetic measurements, infrared spectra, electronic spectra and thermogravimetric analyses. All of these complexes have been screened for their antimicrobial activity against bacterial strands using the Agar Diffusion Method.

Full text of DOI:10.1081/SIM-120016872

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Synthesis, Characterization, and Biocidal Studies of
Some Transition Metal Complexes Containing Bidentate
Monobasic Hydroxyaldehydes and a Neutral Bidentate
Schiff Base
M. N. Patel a , N. H. Patel a , K. N. Patel a , P. P. Dholakiya a & D. H. Patel b
a Department of Chemistry , Sardar Patel University , Vallabh Vidyanagar, 388 120, Gujarat,
India
b Department of Biosciences , Sardar Patel University , Vallabh Vidyanagar, 388 120, Gujarat,
India
Published online: 15 Aug 2006.
To cite this article: M. N. Patel , N. H. Patel , K. N. Patel , P. P. Dholakiya & D. H. Patel (2003) Synthesis, Characterization,
and Biocidal Studies of Some Transition Metal Complexes Containing Bidentate Monobasic Hydroxyaldehydes and a Neutral
Bidentate Schiff Base, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 33:1, 51-62, DOI: 10.1081/
SIM-120016872
To link to this article: http://dx.doi.org/10.1081/SIM-120016872
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 33, No. 1, pp. 51–62, 2003
Synthesis, Characterization, and Biocidal Studies of
Some Transition Metal Complexes Containing
Bidentate Monobasic Hydroxyaldehydes
and a Neutral Bidentate Schiff Base
1
1
M. N. Patel,1, N. H. Patel, K. N. Patel,
*
P. P. Dholakiya,1 and D. H. Patel2
1Department of Chemistry and
2Department of Biosciences, Sardar Patel University,
Vallabh Vidyanagar, Gujarat, India
ABSTRACT
Complexes of the transition metals with salicylaldehyde (sa1H) or 5-
bromosalicylaldehyde (Br-sa1H) in 1:2 molar ratio, have the composi-
tions [M(H2O)2(sal)2]ꢀH2O (1) or [M(H2O)2(Br–sal)2]ꢀH2O (2), respect-
ively. The Schiff base derived from ethylenediamine and benzaldehyde in
1:1 molar ratio in alcoholic solution yields bis(benzylidene)ethylenedia-
mine (benen). Further reaction of (1) or (2) with benen in alcohol yielded
mixed-ligand complexes of the type[M(sal)2benen] or [M(Br-sal)2benen],
respectively. All of these complexes are soluble in ethanol and methanol.
*
Correspondence: M. N. Patel, Department of Chemistry, Sardar Patel University,
Vallabh Vidyanagar 388 120, Gujarat, India; E-mail: jeenen@rediffmail.com.
51
DOI: 10.1081/SIM-120016872
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

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52
Patel et al.
They were characterized on the basis of elemental analyses, magnetic
measurements, infrared spectra, electronic spectra and thermogravimetric
analyses. All of these complexes have been screened for their antimic-
robial activity against bacterial strands using the Agar Diffusion Method.
INTRODUCTION
An extensive amount of work on coordination compounds of transition
elements with Schiff bases has been done.[1] Generally, Schiff bases are
considered as a very important class of organic compounds. Mixed-ligand
complexes are well known to play an important role in biological sys-
tems.[2] In continuation of earlier work,[3] we prepared new mixed-ligand
complexes of the type[M(sal)2benen]ꢀH2O and [M(Br–sal)benen]ꢀH2O,
where, M =Co(II), Ni(II), Cu(II), Mn(II), Zn(II) and Fe(II), Sal =salicy-
laldehyde anion, Br-sal =5-bromosalicylaldehyde anion and benen =bis-
(benzylidene)ethylenediamine and their physical properties were determined
and discussed. The suggested structure of bis(benzylidene)ethylenediamine
is shown in Figure 1.
EXPERIMENTAL
Materials
The chemicals used in the synthesis were of A. R. grade. Stock solutions
of Co(II), Fe(II), Ni(II), Cu(II), Mn(II) and Zn(II) chlorides and ferrous
sulfate were prepared and standardized by the complexometric titration.[4]
Preparation of Schiff Base
The ligand benen was synthesized by a published procedure.[5]
Figure 1. Bis(Benzylidene)ethylenediamine (benen).

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Complexes of Hydroxyaldehydes
Preparation of Complexes
53
Bis(salicylaldehydato)diaquoNi(II) and the similar complexes of
Mn(II), Fe(II), Co(II), Cu(II), and Zn(II) were synthesized by published
procedures.[6] The preparation of [Ni(sal)2benen]ꢀH2O was carried out by
refluxing an ethanolic solution (150 mL) of [Ni(sal)2(H2O)2] (0.02 mol,
0.734 g) with the Schiff base (0.02 mol, 0.472 g) for an hour. The solution
was then concentrated to 15 mL, and cooled in a refrigerator overnight at
6 °C. The formed crystals were collected and recrystallized from chlo-
roform and dried in air. The mixed-ligand complexes of Co(II), Cu(II),
Mn(II), Zn(II) and Fe(II) were prepared similarly. The mixed-ligand com-
plexes [M(Br–sal)2benen]ꢀH2O [M =Co(II), Fe(II), Ni(II), Cu(II), Mn(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 electronic
spectra of the complexes were recorded on a Beckman DK-2A spec-
trophotometer using MgO as the reference in the solid state. The melting
points of the ligands and complexes were recorded in open capillaries in
a capillary melting point appratus (Tempo Instruments Co. Mumbai). The
magnetic moments have been obtained by a model 7300 vibrating sam-
ple magnetometer.
RESULTS AND DISCUSSION
Characterization of the Complexes
The given formulae (Table 1) are based on analytical data. The for-
mation of the complexes may be represented by the following equations.
H2O
MCl2 ꢀ nH2O þ 2ðsalHÞ À! ½MðH2OÞ2ðsalÞ2ꢁ þ 2HCl
ð1Þ
ð2Þ
EtOH; Reflux
½MðH2OÞ2ðsalÞ2ꢁ þ benen ÀÀÀÀÀÀ! ½MðsalÞ2benenꢁ þ 2H2O
1 hour

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54
Patel et al.

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Complexes of Hydroxyaldehydes
55

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56
Patel et al.
H2O
MCl2 ꢀ nH2O þ 2ðBrÀsalHÞ À! ½MðH2OÞ2ðBrÀsalÞ2ꢁ þ 2HCl
ð3Þ
EtOH; Reflux
½MðH2OÞ2ðBrÀsalÞ2ꢁþ benen ÀÀÀÀÀÀ! ½MðBrÀsalÞ2benenꢁþ 2H2O ð4Þ
1 hour
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 1.84
B.M., consistent[7] with an octahedral structure. The magnetic moment
values for 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 4.7–
5.2 B.M. at room temperature. In the present case the magnetic moment
values of the Co(II) complexes are 4.87 and 4.75 B.M., suggesting[8] an
octahedral geometry. This deviation from the spin-only value (3.83 B.M.)
may be ascribed to spin-orbit coupling. The magnetic moment values of the
Ni(II) complexes are 2.67 and 2.72 B.M., which are usual for the range
expected for similar hexa-coordinated[9] Ni(II) ions. The magnetic moment
values of the Fe(II) complexes are 5.25 and 5.24 B.M. This value identifies
it to be a high-spin complex in an octahedral geometry. The magnetic
moment values of the Mn(II) complexes are 5.74 and 5.75 B.M., due to a
high-spin d5-system with octahedral geometry. The magnetic moment de-
terminations shows 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 three weak
absorption bands for the transitions A1g ! T1g(4G) ( ꢂ 15,000 cm À 1),
6
4
4
6
4
4
6A1g ! T2g(4G) ( ꢂ 20,000 cm À 1) and A1g ! Eg, A1g(4G) ( ꢂ 25,000
cm À 1) in accord with an octahedral geometry.[10] The electronic spectra of
the Fe(II) complexes exhibit a band at about 11,500 cm À 1, assigned to the
5
5T2g ! Eg transition.[11] The electronic spectra of the Co(II) complexes
4
exhibit three bands. The assignments of the spectral bands are T1g-
(F) ! T2g (u1 ꢂ 9,500 cm À 1), T1g (F) ! T2g (u2 ꢂ 18,000 cm À 1) and
4
4
4
4T1g(F) ! T1g(P) (u3 ꢂ 19,000 cm À 1). A strong charge transfer band is
4
shown by the complex at ꢂ 25,000 cm À 1. Ko¨nig’s method was used to

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Complexes of Hydroxyaldehydes
57
Table 2. Electronic spectral data of the Co(II) and Ni(II) complexesa.
Observed band
(cm À 1
)
Complexes
u1
u2
u3
u2/u1
B
b
b0 10Dq
[Co(sal)2 benen]ꢀH2O
9,434 18,000 19,047 1.907 715.84 0.737 26.27 10,558
[Ni(Br-sal]2 benen]ꢀH2O 10,550 17,391 25,080 1.648 686.66 0.666 33.30 10,550
[Co(Br-sal)2 benen]ꢀH2O 9,392 18,181 19,047 1.954 721.96 0.746 25.38 10,466
[Ni(sal)2 benen]ꢀH2O
10,310 17,857 23,809 1.732 715.76 0.694 30.51 10,310
abenen = bis(benzylidene)ethylenediamine.
ascertain the correct position of the bands. The Ni(II) complexes also ex-
3
3
hibit three d–d transition bands at A2g(F) ! T2g (F) (u1 =10,550 cm À 1),
3
3
3
3A2g(F)! T1g(F) (u2 =17,391 cm À 1) and A2g(F) ! T1g (P) (u3 = 25,000
cm À 1). The values of the electronic parameters such as the ligand field
splitting energy (10 Dq), racah interelectronic repulsion parameter (B),
nephelauxetic ratio (b) and the ratio are u2/u1 are represented in Table 2.
All data are consistent with an octahedral geometry. The electronic spec-
tra of the Cu(II) complexes[12] exhibit a band at ꢂ 15,500 cm À 1 assigned
2
to the 2Eg ! T2g transition which is in agreement with an octahedral
Table 3. Infrared spectral data of the complexes (cm À 1)a.
Complexes
u(C = O) u(C–O) u(C = N) u(M–O) u(M–N)
benen
–
–
1640 s
1615 s
1610 s
1615 s
1610 s
1622 sh
1610 s
–
–
[Mn(sal)2 benen]ꢀH2O
[Fe(sal)2 benen]ꢀH2O
[Co(sal)2 benen]ꢀH2O
[Ni(sal)2 benen]ꢀH2O
[Cu(sal)2 benen]ꢀH2O
[Zn(sal)2 benen]ꢀH2O
1620 s
1610 sh
1615 s
1620 sh
1622 sh
1620 s
1330 w
1347 s
1340 s
1335 s
1347 s
1340 s
410 w
410 w
415 m
420 w
410 m
420 w
415 m
420 w
420 w
415 m
420 w
410 w
480 w
490 m
480 w
495 sh
490 w
485 w
480 w
475 m
480 w
475 w
480 w
485 m
[Mn(Br–sal)2 benen]ꢀH2O 1620 s
1330 sh 1620 s
[Fe(Br–sal)2 benen]ꢀH2O
[Co(Br–sal)2 benen]ꢀH2O
[Ni(Br–sal)2 benen]ꢀH2O
[Cu(Br–sal)2 benen]ꢀH2O
[Zn(Br–sal)2 benen]ꢀH2O
1620 s
1610 sh
1615 s
1620 sh
1620 s
1340 s
1330 w
1340 s
1335 s
1340 w
1610 s
1610 sh
1625 s
1620 sh
1610 s
ab = broad, m = medium, s = strong, w = weak.

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58
Patel et al.
geometry. A strong charge transfer band is observed at 26,000 cm À 1. The
e values of all the complexes can not be find out as the concentration are
not known.
Thermogravimetric Analyses
There are some remarkable features in the TGA curves. The de-
composition temperatures of the complexes are higher than those of benen
and sa1H or Br-sa1H, indicating that the complexes are more stable than
the ligands. Thermal curves of the complexes clearly indicate that the
weight loss between 35–105 °C corresponds to one water molecule for all
complexes. Because of the low temperatures, this water molecule may be
Table 4. Antimicrobial activities of the complexesa.
Percentage inhibition
Compound
S. typhi
Seratia spp.
salH
Br–salH
10
20
20
22
20
15
11
22
10
30
30
30
30
40
40
30
30
50
30
40
40
9
18
18
18
18
9
benen
MnCl2ꢀ4H2O
FeSO4ꢀ7H2O
CoCl2ꢀ6H2O
NiCl2ꢀ6H2O
9
CuCl2ꢀ5H2O
9
ZnCl2
9
[Mn(sal)2 benen]ꢀH2O
[Fe(sal)2 benen]ꢀH2O
[Co(sal)2 benen]ꢀH2O
[Ni(sal)2 benen]ꢀH2O
[Cu(sal)2 benen]ꢀH2O
[Zn(sal)2 benen]ꢀH2O
[Mn(Br–sal)2 benen]ꢀH2O
[Fe(Br–sal)2 benen]ꢀH2O
[Co(Br–sal)2 benen]ꢀH2O
[Ni(Br–sal)2 benen]ꢀH2O
[Cu(Br–sal)2 benen]ꢀH2O
[Zn(Br–sal)2 benen]ꢀH2O
27
27
45
27
36
45
27
27
36
27
45
45
abenen = bis(benzylidene)ethylenediamine.

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Complexes of Hydroxyaldehydes
59
considered as water of crystallization.[13] The TGA curve indicates that
above 250 °C the compounds start to loose mass with partial evaporation of
the Schiff base (benen) up to 320 °C. In the temperature range 320 to
500 °C the remaining organic ligand molecules are lost. In all cases the
final products are metal oxides. These results are in good agreement with
the composition of the complexes.
IR Spectra
The infrared spectra of the complexes have been studied to characterize
their structures. The important IR frequencies are given in Table 3. The
infrared spectra of the complexes register the u(C=O) band[14] at about
1600 cm À 1 and u(C–O)[15] at about 1340 cm À 1. The Schiff base (benen)
shows the C=N stretching band at 1640 cm À 1. This band shifts to lower
energy by 10–30 cm À 1 in the chelates indicating coordination through the
azomethine nitrogen.[16] The sharp bands in the ranges 750–780 and 1525–
1535 cm À 1 are due to aromatic u(C–H)[15] and u(C=C),[17] respectively.
The frequencies in the range 410–420 and 475–495 cm À 1 are attributed to
u(M–O)[18] and u(M–N),[19] respectively.
Figure 2. [M(sal)2benen] or [M(Br–sal)2benen], R = H or Br.

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60
Patel et al.
Antimicrobial Activity
In the present study, the ligands, the 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 ac-
tivity at 1 ꢃ 10À 4 g mL À 1 against bacteria. The growth was compared with
a control (blank) and is expressed as percentage inhibition versus controls.
The percentage inhibition of various compounds is recorded in Table 4. 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, the metal salts and ligands. Hence, complexation increases the
antimicrobial activity. The patterns of activity are complex and no clear
trend can be ascertained.
A suggested structure of the mixed-ligand complexes is shown in
Figure 2.
ACKNOWLEDGMENTS
The authors are thankful to Prof. R. M. Patel, Head, Department of
Chemistry and Prof. I. L. Kothari, Head, Department of Biosciences, Sardar
Patel University, Vallabh Vidyanagar, India, for providing the necessary
laboratory facilities.
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Complexes of Hydroxyaldehydes
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