Synthesis, structural characterization, and antibacterial studies of some mixed-ligand first row d-transition metal complexes

Article abstract of DOI:10.1081/SIM-120039271

Some mixed-ligand complexes of the transition metal ions Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) with the potassium salt of salicylidene-glycine and 2,2′-bipyridylamine or di(benzylidene)-1,8- diaminonaphthalene have been prepared. The coordination behavior of the mixed-ligand complexes was characterized on the basis of elemental analyses, IR, and electronic spectra. The magnetic measurements have been obtained by a vibrating sample magnetometer. It is observed that the mixed-ligand complexes of Mn(II), Co(II), Ni(II), Cu(II) are paramagnetic, while the Zn(II) and Cd(II) complexes are diamagnetic. All of these mixed-ligand complexes are colored crystalline solids. Octahedral geometries have been assigned to all of the prepared mixed-ligand complexes. The antibacterial activities of the ligands, the metal chlorides, the mixed-ligand complexes, the standard drug (tetracycline), and control (dimethyl sulfoxide) were tested on the pathogenic bacteria S. typhi, E. coli, and Serratia marcescens using the disc diffusion method, and the results are discussed.

Full text of DOI:10.1081/SIM-120039271

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Synthesis and Reactivity in Inorganic and Metal-
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Synthesis, Structural Characterization, and
Antibacterial Studies of Some Mixed‐Ligand First Row
d‐Transition Metal Complexes
Pragnesh K. Panchal a & M. N. Patel a
a Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar, 388 120,
Gujarat, India
Published online: 16 Nov 2010.
To cite this article: Pragnesh K. Panchal & M. N. Patel (2004) Synthesis, Structural Characterization, and Antibacterial
Studies of Some Mixed‐Ligand First Row d‐Transition Metal Complexes, Synthesis and Reactivity in Inorganic and Metal-
Organic Chemistry, 34:7, 1277-1289, DOI: 10.1081/SIM-120039271
To link to this article: http://dx.doi.org/10.1081/SIM-120039271
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 7, pp. 1277–1289, 2004
Synthesis, Structural Characterization, and
Antibacterial Studies of Some Mixed-Ligand
First Row d-Transition Metal Complexes
*
Pragnesh K. Panchal and M. N. Patel
Department of Chemistry, Sardar Patel University,
Vallabh Vidyanagar, Gujarat, India
ABSTRACT
Some mixed-ligand complexes of the transition metal ions Mn(II), Co(II),
Ni(II), Cu(II), Zn(II), and Cd(II) with the potassium salt of salicylidene-
glycine and 2,20-bipyridylamine or di(benzylidene)-1,8-diaminonaphtha-
lene have been prepared. The coordination behavior of the mixed-ligand
complexes was characterized on the basis of elemental analyses, IR, and
electronic spectra. The magnetic measurements have been obtained by a
vibrating sample magnetometer. It is observed that the mixed-ligand com-
plexes of Mn(II), Co(II), Ni(II), Cu(II) are paramagnetic, while the Zn(II)
and Cd(II) complexes are diamagnetic. All of these mixed-ligand com-
plexes are colored crystalline solids. Octahedral geometries have been
assigned to all of the prepared mixed-ligand complexes. The antibacterial
activities of the ligands, the metal chlorides, the mixed-ligand complexes,
*
Correspondence: M. N. Patel, Department of Chemistry, Sardar Patel University,
Vallabh Vidyanagar 388 120, Gujarat, India; E-mail: jeenenpatel@yahoo.co.in.
1277
DOI: 10.1081/SIM-120039271
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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Panchal and Patel
the standard drug (tetracycline), and control (dimethyl sulfoxide) were
tested on the pathogenic bacteria S. typhi, E. coli, and Serratia marces-
cens using the “disc diffusion method,” and the results are discussed.
Key Words: Mixed-ligand; Disc diffusion method; Schiff bases;
2,20-Bipyridylamine.
INTRODUCTION
Schiff bases and their metal complexes have shown biological activity as
carcinogenic[1] and antitumor[2] because of their specific structures. Amino
acid Schiff base complexes derived from aldehydes are involved in a variety
of biological processes such as catalysis of transamination, racemization, and
carboxylation reactions.[3,4] In continuation of earlier work,[5] we prepared
some new mixed-ligand complexes of the type [M(L)(bipy-amine)(H2O)] or
[M(L)(bendan)(H2O)], where, M ¼ Mn(II), Co(II), Ni(II), Cu(II), Zn(II),
and Cd(II), KHL ¼ potassium salt of salicylideneglycine and bipy-
amine ¼ 2,20-bipyridylamine and bendan ¼ di(benzylidene)-1,8-diamino-
naphthalene. The physical properties were determined and are discussed
herein. The suggested structure of the ligands are shown in Fig. 1.
Figure 1. Structures of the organic ligands used in this study.

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Mixed Ligand Transition Metal Complexes
EXPERIMENTAL
Reagent and Solvents
1279
All the chemicals used were of analytical grade. 2,20-Bipyridylamine
and 1,8-diaminonaphthalene were purchased from the Eastgate, White Lund,
Morecambe, Lancaster, England. Salicylaldehyde, glycine, benzaldehyde, and
metal chlorides were purchased from E. Merck (India) Limited, Mumbai.
The organic solvents were purified by standard methods.[6]
Preparation of Schiff Bases
Potassium Salt of Salicylideneglycine (KHL)
A solution of potassium hydroxide (10 mmol, 0.56 g) in 30 mL absolute
alcohol was added to glycine (10 mmol, 0.75 g). The mixture was stirred
until all dissolved in the ethanol–KOH solution. Then an ethanolic solution
(100 mL) of salicylaldehyde (10 mmol, 1.22 g) was quickly added. The reac-
tion was allowed to complete by stirring at 50 8C for an hour. The product
was crystallized by diffusion of excess absolute diethyl ether into the solution.
The product was filtered, and dried in a vacuum desiccator. Yield: 1.59 g
(63%), m.p.: 207 8C.
Di(benzylidene)-1,8-diaminonaphthalene (Bendan)
An ethanolic solution (100 mL) of 1,8-diaminonaphthalene (10 mmol,
1.58 g) and an ethanolic solution (100 mL) of benzaldehyde (20 mmol,
2.12 g) in the mole ratio 1 : 2 were mixed with constant stirring. Refluxing
was carried out for 5 hr and then the solution was cooled in a refrigerator
to 0–2 8C overnight. A fine-crystalline yellow product was obtained. The
product was filtered and dried in air. Yield: 2.51 g (68%), m.p.: 235 8C.
Synthesis of the Mixed-Ligand Complexes
The preparation of the mixed-ligand complexes was carried out by mixing
an aqueous (100 mL) solution of metal chloride (10 mmol) with a hot metha-
nolic (100 mL) solution of the potassium salt of salicylideneglycine (10 mmol,
2.17 g) and 2,20-bipyridylamine (10 mmol, 1.71 g) or di(benzylidene)-1,8-dia-
minonaphthalene (10 mmol, 3.34 g) in 1 : 1 : 1 mole ratio. The mixed-ligand
complexes were formed upon heating the mixtures in a water bath for 2 hr

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Panchal and Patel
at 50 8C. The mixtures were kept overnight at room temperature. The obtained
crystals were removed by filtration, washed with water, ethanol, and dried in
air. Elemental analyses, formula weight, colors, melting points and percentage
yields data are presented in Table 1.
Physical Measurements
The magnetic moments have been obtained by a model 7304, vibrating
sample magnetometer,[7] Lake Shore, USA. The vibrating sample magneto-
meter reports the total magnetic moment, m, of a sample in emu. However,
the end goal of the magnetic measurement is not the moment in emu, but to
get the effective magnetic moment. Therefore, the magnetic moment can be
converted to susceptibility units by realizing that 1 emu ¼ 1 gauss cm3. The
susceptibility of a sample has units of volume and is defined for paramagnetic
material by the equation:
m ðemuÞ
x ðcm3Þ ¼
H ðoerstedÞ
The gram susceptibility xg, was calculated using the expression. Gram
susceptibility:
x ðcm3Þ
xg ¼
mass
The gram susceptibility was multiplied by the molecular weight of the sample
to obtain the molar susceptibility, xM. A correction was applied for the
diamagnetism of the ligands to obtain the corrected molar susceptibility xM0 .
The effective magnetic moment was calculated from the expression.
1=2
meff ¼ 2:84 ðxM0 ꢀ TÞ
;
where T ¼ absolute temperature ðKÞ
Infrared spectra were recorded on a FT–IR Nicolet 400D spectrophotometer
in KBr pellets. Carbon, hydrogen, and nitrogen were analyzed with a model
240 Perkin–Elmer elemental analyzer. The metal contents of the mixed-
ligand complexes were analyzed by EDTA titration[8] after decomposing
the organic matter with a mixture of perchloric, sulfuric, and nitric acids
(1 : 1.5 : 2.5). Themogravimetric analyses have been obtained by a model
5000\2960 SDTA, TA Instruments, USA. The TGA curves were obtained at
a heating rate of 10 8C/min in N2 atmosphere over the temperature range of
50–800 8C. The reflectance spectra of the mixed-ligand complexes were
recorded in the range 1700–350 nm (as MgO discs) on a Beckman DK-2A
spectrophotometer.

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Mixed Ligand Transition Metal Complexes
1281
m

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Panchal and Patel
m

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Mixed Ligand Transition Metal Complexes
RESULTS AND DISCUSSION
1283
The formation of mixed-ligand complexes having 1 : 1 : 1 metal-ligand
mole ratio is facilitated by loss of two protons from the salicylideneglycinate
ligand. All the mixed-ligand complexes are insoluble in water, methanol, and
dimethyl formamide, but are soluble in dimethyl sulfoxide. They possess
high melting points, are colored, and are stable in air. The general equations
for the formation of the mixed-ligand complexes are shown below.
MCl2 ꢁ nH2O þ KHL þ bipy-amine ꢂ! ½MðLÞðbipy-amineÞðH2OÞꢃ
þ KCl þ HCl þ ðn ꢂ 1ÞH2O
ð1Þ
MCl2 ꢁ nH2O þ KHL þ bendan ꢂ! ½MðLÞðbendanÞðH2OÞꢃ þ KCl
þ HCl þ ðn ꢂ 1ÞH2O
ð2Þ
IR Spectra
The spectra of the mixed-ligand complexes exhibit a broad band in the
region 3200–3300 cm21 due to n(O–H) and other bands at ꢀ850 cm21 and
ꢀ715 cm21 due to the rocking and wagging mode of the OH group. The
presence of the latter band indicates the coordination nature of the water
molecule.[9] The n(C55N) frequency of 2,20-bipyridylamine occurs at
1585 cm21. This band shifts to higher energy by ꢀ35–45 cm21 in the
mixed-ligand complexes indicating the bidentate (N,N-pyridyl nitrogen)
coordination of this heterocyclic ligand.[10] In the Schiff base the strong-
intensity band due to n(C55N) at 1645 cm21 is shifted to lower frequency
by about 10–20 cm21 in the case of the mixed-ligand complexes indicating
the coordination of the azomethine[11] group through its nitrogen. The mode
of coordination is further supported by the presence of a new band in the
ꢀ530 cm21 region due to n(M–N) vibrations.[12] The mixed-ligand
complexes exhibit two characteristic strong and broad bands in the
1400–1600 cm21 region, attributed to the nas(COO2) (ꢀ1585 cm21) and
ns(COO2) (ꢀ1390 cm21) stretching vibrations of the coordinated carboxylate
groups.[13] The mode of coordination is further supported by the presence of
a new band in the ꢀ420 cm21 region due to the n(M–O)carbo vibration.[12]
The n(O–H) band identified in the free ligand was absent in the IR spectra
of all the mixed-ligand complexes. This is attributed to the deprotonation
of the phenolic group on complexation.[14] Further, a shift in the n(C–O)
band by 10–20 cm21 to higher frequency confirms coordination through the
phenolic oxygen in the ligand.[15] In the mixed-ligand complexes a new band

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Panchal and Patel
observed in the ꢀ470 cm21 region is due to the n(M–O)phenolic vibration.[12]
The sharp bands in the range 750–780 cm21 and 1525–1535 cm21 are due
to aromatic n(C–H) and n(C55C), respectively. The absorption in the
1160–1170 cm21 range is attributed to n(C–N).
Magnetic Moments and Electronic Spectra
The information regarding geometry of the mixed-ligand complexes is
obtained from their electronic spectral data and magnetic moments.
The Co(II) mixed-ligand complexes show magnetic moment values of
4.03 and 4.01 B.M., respectively, at room temperature. These high values of
the magnetic moments and the stoichiometries suggest a coordination number
of six for the central Co(II) ion and an octahedral geometry. The electronic
spectra of the mixed-ligand complexes are also consistent with their
octahedral environment around the Co(II) ion. The Co(II) mixed-ligand
complexes exhibit three bands at ꢀ9,200 (n1), ꢀ18,000 (n2), and ꢀ19,000
4
4
(n3) cm21, which may be assigned to the transitions T1g(F) ! T2g(F),
4
4
4
4T1g(F) ! A2g(F), and T1g(F) ! T1g(P) expected for an octahedral struc-
ture.[16] The electronic spectra of the Ni(II) mixed-ligand complexes exhibit
absorption bands at ꢀ10,500 (n1), ꢀ17,500 (n2), and ꢀ24,200 (n3) cm21
3
3
3
3
3
3
attributed to A2g(F) ! T2g(F), A2g(F) ! T1g(F), and A2g(F) ! T1g(P)
transitions, respectively, in an octahedral geometry. The values of the ligand
field parameters for the Co(II) and Ni(II) complexes are in the range reported
for an octahedral structure[17] and are presented in Table 2. The values of the
magnetic moment (2.98 and 3.01 B.M.) may be taken as additional evidence
for their octahedral structure.[18] The Cu(II) mixed-ligand complexes exhibit
magnetic moments of 1.84 and 1.82 B.M., respectively. These values are
close to the spin-allowed values expected for a S ¼ 1/2 system (1.73 B.M.)
and may be indicative of an octahedral geometry around the Cu(II) ions.
The Cu(II) mixed-ligand complexes display a broad band at ꢀ15,000 cm21
2
2
due to the Eg ! T2g transition.[19] The electronic spectra of the Mn(II)
mixed-ligand complexes exhibit three weak absorption bands for the tran-
6
4
6
4
sitions A1g ! T1g (ꢀ15,000 cm21) (n1), A1g ! T2g (ꢀ20,000 cm21
)
(n2), and A1g ! Eg, A1g (ꢀ25,000 cm21) (n3). These absorptions are
consistent with an octahedral geometry around Mn(II) in all of the mixed-
ligand complexes. The magnetic moment values of the Mn(II) mixed-ligand
complexes are 6.01 and 6.03 B.M., suggesting an octahedral geometry.[20]
The Zn(II) and Cd(II) mixed-ligand complexes are diamagnetic as expected
for d10 systems. The electronic spectra of the mixed-ligand complexes were
recorded in the solid state. Therefore, the 1 values of all the mixed-ligand
complexes were not determined.
6
4
4

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Mixed Ligand Transition Metal Complexes
1285
b
b
b
b
b
b
b
b

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Panchal and Patel
Thermogravimetric Analyses
Thermogravimetric analyses studies were carried out on the mixed-ligand
complexes in the temperature range of 50–800 8C. All of the mixed-ligand
complexes show a loss in weight corresponding to one water molecule in
the range ꢀ150–180 8C indicating that these water molecules are coordinated
to the metal ion.[21] In the temperature range 180–800 8C, the ligand mol-
ecules are lost. In all cases, the final products are metal oxides. These results
are in good accordance with the proposed mixed-ligand complex compo-
sitions. From the above discussion, suggested structures for the mixed-ligand
complexes are shown in Fig. 2.
Antibacterial Activity
The ligands, the metal chlorides, and the mixed-ligand complexes have
been tested for their effects on the growth of the microbial cultures of
S. typhi, E. coli, Serratia marcescens using the disc diffusion method.[22,23]
A stock solution of 250 mg/mL was made by dissolving 25 mg of each com-
pound in dimethyl sulfoxide (100 mL). Filter paper, Whatmann No. 4 discs of
6 mm diameter, were soaked in solutions (20 mL) of the test compounds and
after drying off the solvent were placed on a nutrient agar plate containing
lawn cultures of different bacteria. The plates were incubated at an optimum
growth temperature of 37 8C. The zone of inhibition (in mm) around the discs
was measured after 24 hr. All experiments were performed in triplicate and the
average of the three trials was considered as the zone of inhibition. Tetra-
cycline was used as a standard drug. The mixed-ligand complexes are soluble
in dimethyl sulfoxide. Therefore, the growth was compared with dimethyl
Figure 2. Proposed structures of the mixed-ligand complexes.

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Mixed Ligand Transition Metal Complexes
1287
sulfoxide as the control. For the control experiments equivalent volumes of
solvents without added test compounds were applied to the paper discs and
the zone of inhibition (in mm) measured. Results are expressed as zone of
inhibition and percentage inhibition vs. control. The results are presented in
Table 3. From this data it is observed that the mixed-ligand complexes
show higher activities against bacteria compared to the control (blank),
the ligands, and metal salts. The mixed-ligand complexes show moderate
activities as compared to the standard drug (tetracycline). The results suggest
that the changes in structure due to the coordination in the mixed-ligand
complexes decrease the growth of microorganisms relative to the metal ion,
Table 3. Antibacterial activities of the mixed-ligand complexes.a
Zone of inhibition in mm (% inhibition)
Serratia
marcesens
Compounds
S. typhi
E. coli
DMSO (control)
Tetracycline
KHL
9
12
15
18 (100)
10 (11)
10 (11)
11 (22)
10 (11)
10 (11)
11 (22)
11 (22)
10 (11)
11 (22)
12 (33)
12 (33)
13 (44)
13 (44)
12 (33)
13 (44)
13 (44)
12 (33)
12 (33)
13 (44)
13 (44)
12 (33)
21 (75)
13 (08)
15 (25)
14 (17)
13 (08)
13 (08)
14 (17)
13 (08)
14 (17)
14 (17)
16 (33)
16 (33)
17 (42)
18 (50)
17 (42)
17 (42)
17 (42)
17 (42)
16 (33)
18 (50)
18 (50)
16 (33)
26 (73)
17 (13)
16 (06)
17 (13)
16 (06)
17 (13)
16 (06)
17 (13)
17 (13)
17 (13)
19 (27)
23 (53)
21 (40)
23 (53)
22 (47)
21 (40)
20 (33)
22 (47)
23 (53)
21 (40)
21 (40)
23 (53)
bipy-amine
bendan
.
MnCl2 4H2O
.
CoCl2 6H2O
.
NiCl2 6H2O
.
CuCl2 2H2O
ZnCl2
CdCl2 2H2O
.
[Mn(L)(bipy-amine)(H2O)]
[Co(L)(bipy-amine)(H2O)]
[Ni (L)(bipy-amine)(H2O)]
[Cu(L)(bipy-amine)(H2O)]
[Zn(L)(bipy-amine)(H2O)]
[Cd(L)(bipy-amine)(H2O)]
[Mn(L)(bendan)(H2O)]
[Co(L)(bendan)(H2O)]
[Ni(L)(bendan)(H2O)]
[Cu(L)(bendan)(H2O)]
[Zn(L)(bendan)(H2O)]
[Cd(L)(bendan)(H2O)]
aKHL, potassium salt of salicylideneglycine; bipy-amine, 2,20-bipyridylamine; bendan,
bis(benzylidene)-1,8-diaminonaphthalene.

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Panchal and Patel
the ligands, and control. Hence, the complexation increases the antibacterial
activity. The patterns of activity are complex, and no clear trend can be
ascertained.
ACKNOWLEDGMENTS
We wish to express our sincere thanks to Prof. R. M. Patel, Head, Depart-
ment of Chemistry and Prof. M. Dutta, Head, Department of Biosciences,
Sardar Patel University, Vallabh Vidyanagar, India, for providing the necess-
ary laboratory facilities.
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Received December 15, 2003
Accepted March 23, 2004
Referee I: S. M. Socol
Referee II: M. L. Illingsworth

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