Synthesis, characterization and antimicrobial activity of mixed schiff base ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II)

Article abstract of DOI:10.1155/2011/598171

The mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) with Schiff bases N-(2-hydroxy-1-naphthylidene)-4-methylaniline (L¹H) and N-(2-hydroxybenzylidene)-2,3-dimethylaniline (L²H) have been synthesized and characterized. The

Full text of DOI:10.1155/2011/598171

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(3), 1258-1263
http://www.e-journals.net
Synthesis, Characterization and Antimicrobial
Activity of Mixed Schiff Base Ligand Complexes of
Co(II), Ni(II), Cu(II) and Zn(II)
A. K. MAPARI*, M. S. HATE and K. V. MANGAONKAR#
*Ramnarain Ruia College, Matunga (E)
Mumbai: - 400019, Maharashtra, India
#Mithibai College, Vile-Parle (W)
Mumbai: - 400056, Maharashtra, India
akmapari@gmail.com
Received 13 September 2010; Accepted 22 November 2010
Abstract: The mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II)
with Schiff bases N-(2-hydroxy-1-naphthylidene)-4-methylaniline (L1H) and
N-(2-hydroxybenzylidene)-2,3-dimethylaniline (L2H) have been synthesized
and characterized. The resulting complexes were characterized by elemental
analysis, thermogravimetric analysis, magnetic moment measurements,
conductivity measurements, 1H NMR, IR, UV-visible and ESR spectral
studies. The Schiff bases acts as bidentate monobasic ligands, coordinating
through deprotonated phenolic oxygen and azomethine nitrogen atoms. The
complexes are non-electrolytic in DMSO. The presence of the two coordinated
water molecules in these complexes was indicated by IR spectra and
thermogravimetric analysis of the complexes. From the analytical and spectral
data the stoichiometry of these complexes have been found to be
[M(L1)(L2)(H2O)2] {where M = Co(II) , Ni(II), Cu(II) and Zn(II)}. It is found
that Co(II), Ni(II), Cu(II) and Zn(II) complexes exhibited octahedral geometry.
The antimicrobial activities of ligands and their mixed ligand complexes were
screened by disc diffusion method. It is found that the metal complexes have
higher antimicrobial activity than the free ligand.
Keywords: Schiff bases, Mixed ligand, Metal complexes, Antimicrobial activity.
Introduction
In the field of coordination chemistry, Schiff base metal complexes have a curious history1,2.
Metal ions play vital roles in a vast number of biological processes. The ions with
biologically active ligands are a subject of considerable interest. Some of these compounds
act via chelation3. The present work is the study of mixed ligand complexes of Co(II), Ni(II),
Cu(II) and Zn(II) with Schiff bases N-(2-hydroxy-1-naphthylidene)-4-methylaniline (L1H)
and N-(2-hydroxybenzylidene)-2,3-dimethylaniline (L2H).

1259
A. K. MAPARI et al.
Experimental
All the chemicals used in the present work were of analytical grade. The metal salts used
were in their hydrated form.
Synthesis of ligands
The ligands (L1H and L2H) were prepared by the condensation of the corresponding
aldehyde and amine in 1:1 molar ratio by refluxing in distilled methanol4.
Preparation of complexes
A metal(II) chloride (1.0 mmol) dissolved in water (2 mL) was added slowly with constant
stirring to a solution of N-(2-hydroxy-1-naphthylidene)-4-methylaniline (L1H) (1.0 mmol)
and N-(2-hydroxybenzylidene)-2,3-dimethylaniline (L2H) (1.0 mmol) in ethanol (100 mL).
The pH of the solution was slowly raised to obtain the appropriate pH for the formation of
the complex by the drop wise addition of 0.1 N sodium hydroxide solution. The resulting
mixture was stirred for 2-3 h. The product was digested on a hot water bath for half an hour.
The complex thus formed was filtered out, washed with aqueous alcohol followed by
distilled water and dried in vacuum over fused CaCl2. Similarly all the complexes were
prepared. The metal estimations were carried out by standard Methods5. Elemental analysis
was performed at SAIF, IIT Bombay, Mumbai. The conductance was measured in DMSO
solvent on an Equiptronic EQ-660 conductivity meter. The magnetic susceptibility
measurements at room temperature were made on Gouy balance using HgCo(NCS)4 as
calibrant. The 1H NMR spectrum of the ligands and Zn(II) complex was recorded on varian
mercury plus 400 MHz spectrometer using TMS as internal standard and (D6) DMSO as a
solvent. The IR spectra of ligands and their complexes were recorded on a Shimadzu FTIR –
8400 S spectrometer in KBr pellets in the range of 4000-350 cm-1. UV-visible spectra were
recorded on a Jasco V-530 UV-visible spectrometer in the range 200-1100 nm. Electron spin
resonance spectra of powdered Cu(II) complex was recorded on varian E-112x-band ESR
spectrometer using TCNE as ‘g’ marker (g=2.0027) at room temperature. Thermal analysis
of the metal complexes was carried out using Mettler Toledo stare SW 7.01 thermal analyzer
in an inert atmosphere of nitrogen. The antimicrobial activities of ligands and their mixed
ligand complexes were screened by disc diffusion method.
Results and Discussion
The elemental analysis shown in the Table 1 indicates that, all the metal complexes have
1:1:1 stoichiometry with respect to L1H: L2H: M {where M = Co(II), Ni(II), Cu(II) and
Zn(II)} and are dark colored amorphous substances, soluble in DMF and DMSO. The molar
conductance values (0.010 - 0.020 ohm-1 mol-1 cm2) of 10-3 M solution in DMSO indicate
that the metal complexes are non-electrolytic in nature.
Electronic spectra and magnetic moment
The electronic spectral studies of mixed ligand complexes of Co(II), Ni(II), Cu(II) and
Zn(II) with Schiff basses L1H and L2H were carried out in DMSO solution. The absorption
spectrum of the Co(II) complex shows bands at ~ 10010 cm-1 (ε ~ 15) and ~ 19608 cm-1
4
4
4
4
(ε ~ 47) attributed to T1g(F) → T2g(F) (ν1) and T1g(F) → T1g(P) (ν3) transitions
respectively in an octahedral field6. The spectral parameters of Co(II) complex are as
follows7: Dq = 1113.27, Bꢀ = 718.24, β = 0.740 and β0 = 26%. The reduction of Racah
parameter from the free ion value 971 cm-1 and β0 value of 26% testify the presence of
considerable covalence in the complex8.

Synthesis, Characterization and Antimicrobial Activity
1260
Table 1. Physical, analytical, magnetic susceptibility and molar conductance data of the
ligands and their mixed ligand complexes
M.P /
decomp.
temp.°C
Analysis % found (calculated) Magnetic
λ
Ligand / complex, Mol.
molecular formula Wt.
Ohm-1
cm2 mol-
Moment
1
C
H
N
M
-
µeff B.M.
L1H,
261.32
82.92
5.61
5.48
132
91
-
-
C18H15NO
(82.73) (5.79) (5.36)
79.75 6.63 6.12
(79.97) (6.71) (6.21)
68.51 5.32 4.71
L2H,
225.29
-
-
-
C15H15NO
[Co(L1)(L2)(H2O)2],
579.55
10.33
>250
209
5.18
3.40
1.83
-
0.020
0.014
0.010
0.012
C33H32N2O4Co
[Ni(L1)(L2)(H2O)2],
579.31
(68.39) (5.57) (4.83) (10.17)
68.33 5.29 4.72 10.02
(68.42) (5.57) (4.84) (10.13)
67.73 5.31 4.65 10.73
(67.85) (5.52) (4.80) (10.88)
67.47 5.68 4.63 11.27
(67.63) (5.50) (4.78) (11.16)
C33H32N2O4Ni
[Cu(L1)(L2)(H2O)2],
584.16
>250
>250
C33H32N2O4Cu
[Zn(L1)(L2)(H2O)2]
586.03
C33H32N2O4Zn
The Co(II) complex has magnetic moment 5.18 B M also suggest an octahedral
geometry. Ni(II) complex exhibits two electronic spectral bands at ~ 10616 cm-1 (ε ~ 20)
3
3
3
and ~ 16556 cm-1 (ε ~ 60) which can be assigned to A2g(F) → T2g(F) (ν1) and A2g(F) →
3T1g(F) (ν2) transitions in an octahedral field9. The transition due to A2g (F) → T1g (P) (ν3)
was completely obscured by the intense intra ligand transition band. The ν 2: ν 1 ratio is 1.56
is in the usual range reported for the octahedral Ni(II) complexes10. The spectral parameters
of the Ni(II) complex are as follows7: Dq = 1061.4, Bꢀ =732, β = 0.711 and β0 = 28.9% . The
reduction of Racah parameter from the free ion value 1030 cm-1 and β0 value of 28.9%
confirms the presence of considerable covalence in the complex8. The Ni(II) complex has
magnetic moment 3.40 B M also suggest an octahedral geometry. The Cu(II) complex
exhibit broad band centered at ~ 14706 cm-1 (ε ~ 77) mainly due to Eg → T2g transition
suggesting the distorted octahedral geometry11. The observed magnetic moment value for
Cu(II) complex is 1.83 B M suggestive of distorted octahedral nature for the complex12.
Zn(II) complex does not exhibit any characteristic d-d transitions and is also found to be
diamagnetic in nature.
3
3
2
2
Infrared spectra
The important infrared frequencies exhibited by the ligands L1H and L2H and their mixed
ligand complexes are given in the Table 2. Infrared spectra of the Schiff bases L1H and L2H
show a broad band centered at around 3445 and 3447 cm-1 due to the phenolic hydroxyl
group respectively in free ligands which disappeared in spectra of their complexes indicating
probably the coordination through phenolic oxygen moiety. The Schiff bases L1H and L2H
show a medium intensity band at around 1327 and 1279 cm-1 due to phenolic ν(C-O) group
is shifted to higher region at around 1383-1391 and 1361-1362 respectively indicating the
coordination through the phenolic oxygen atoms13, 14. The IR spectra of the Schiff bases L1H
and L2H exhibit a strong band at 1613 and 1619 cm-1 due to ν(C=N) (azomethine) which has
been seen shifted towards lower region at around 1614-1616 and 1600-1603 respectively in
the spectra of complexes indicating the participation of the azomethine groups in the
complex formation15. The spectra of the complexes show a broad diffused bands in the
region at around 3100-3650 cm-1, strong bands at 1532-1537 cm-1 and week intensity bands

1261
A. K. MAPARI et al.
at 818-829 cm-1 due to ν(OH), δ(OH) and ρr(OH) respectively of the coordinated water
molecules6,16. The coordination through nitrogen of azomethine and oxygen of (C-O) group of
ligands are further evidenced by the appearance in the complexes of non-ligand bands around
500-552 cm-1and 417-464 cm-1 are due to ν(M-O) and ν(M-N) vibrations respectively16.
Table 2. Characteristic IR bands of the ligands L1H, L2H and their mixed ligand complexes
IR bands, cm-1
δOH νC-O
(H2O) (phenolic) (H2O)
Schiff base /
complex
νOH
(phenolic) H2O
νOH
νC=N
ρrOH
νM-N
νM-O
L1H
L2H
3445
3447
-
-
1619
1613
-
-
1327
1279
1386,
1362
1383,
1361
1385,
1361
1391,
1362
-
-
-
-
-
-
3150 – 1615,
3650 1600
3200 – 1616,
3650 1603
3150 – 1614,
3650 1601
3100 – 1616,
3650 1600
552, 463,
500 418
548, 461,
503 417
547, 461,
502 419
549, 464,
505 418
[Co(L1)(L2)(H2O)2]
[Ni(L1)(L2)(H2O)2]
[Cu(L1)(L2)(H2O)2]
[Zn(L1)(L2)(H2O)2]
-
-
-
-
1533
1537
1532
1536
821
818
821
829
1H NMR spectra
1
The H NMR spectrum of the ligand (L1H) showed singlet at 15.412 δ (s, 1H, OH) due to
proton of phenolic –OH group. The azomethine proton have resonated as singlet at 9.593 δ
(s, 1H, CH=N). The ten aromatic protons have resonated in the region 6.946 – 8.434 δ
(m, 10H, Ar-H) as multiplet. The three protons of methyl group resonated as singlet at 2.312
δ (s, 3H, Ar-CH3). The 1H MR spectrum of the ligand (L2H) showed singlet at 13.291 δ (s,
1H, OH) due to proton of phenolic -OH group. The azomethine proton have resonated as
singlet at 8.77 δ (s, 1H, CH=N). The seven aromatic protons have resonated in the region
6.956 – 7.622 δ (m, 7H, Ar-H) as multiplet. The six protons of two methyl groups resonated
as two singlets at 2.198 δ (s, 3H, Ar-CH3) and 2.251 δ (s, 3H, Ar-CH3).
1
The H NMR spectrum of the Zn(II) complex showed two singlet at 9.427 δ (s, 1H,
CH=N) and 8.425 δ (s, 1H, CH=N) due to protons two azomethine group. The seventeen
aromatic protons have resonated in the region 6.681 - 8.240 δ (m, 17H, Ar-H) as multiplet.
The nine protons of three methyl groups resonated as three singlets at 2.191 δ (s, 3H, Ar-
CH3) and 2.078 δ (s, 3H, Ar-CH3), 1.861 δ (s, 3H, Ar-CH3). The proton of phenolic -OH
group which was observed at 15.412 δ (s, 1H, OH) and 13.291 δ (s, 1H, OH) for Schiff
bases L1H and L2H respectively has disappeared in Zn(II) complex, indicating coordination
through phenolic oxygen moiety to the metal ion via deprotonation17.
Thermogravimetric analysis
The dynamic TGA with the percentage mass loss at different steps have been recorded. The
elimination of lattice and coordinated water molecules take place in the first step. The
Co(II), Ni(II), Cu(II) and Zn(II) complexes lose their weight in the temperature range ~ 130-
270 °C, 125-250 °C, 120-260 °C and 135-275 °C respectively corresponding to two
coordinated water molecules with an endothermic peak in DTA curve. After the total loss of
water, the organic moiety decomposes on further increment of temperature. The complete
decomposition of ligands occurs at ~ 450-650 oC and the observed residue corresponds to the

Synthesis, Characterization and Antimicrobial Activity
1262
respective metal oxide18. The occurrence of endothermic peak and elimination of the two
water molecules at comparatively higher temperature unambiguously confirm our earlier
observation based upon the IR spectrum that the water molecules are coordinated in the
metal complexes.
ESR spectra
The ESR spectrum of the powdered sample of the Cu(II) complex was recorded at room
temperature. The observed value for the [Cu(L1)(L2)(H2O)2] complex are g|| = 2.134, g┴ = 2.086
and G = 1.571. The observed g|| value is less than 2.3 in agreement with the covalent character
of the metal – ligand bond8. The trend g|| > g┴ > ge (2.0023) observed for this complex shows
that the unpaired electron is localized in dx2–y2 orbital of Cu(II) ion and the spectral features are
characteristic of axial symmetry; tetragonal elongated structure may be assumed for this Cu(II)
complex8,19. The anisotropic G values have been calculated by using the equation
G = (g||-2.002) / (g┴-2.002). If the G value is less than 4.0, the ligand forming the copper(II)
complex is regarded as strong field ligand while a value of G greater than 4.0 indicates weak
field ligand. As G = 1.571 for the present complex indicates that the ligands L1H and L2H are
strong field ligands and the metal-ligand bonding in this complex is covalent8.
Antimicrobial activity
Synthesized Schiff bases and their corresponding mixed ligand metal complexes were
screened against E. coli, S. aurious, B. subtilis and S. typhi to assess their potential as
antimicrobial agent by disc diffusion method. The zones of inhibition based upon zone size
around the discs were measured. The measured zone of inhibition against the growth of
various microorganisms is listed in Table 3. It is found that the metal complexes have higher
antimicrobial activity than the free ligand. Hence complexation increases the antimicrobial
activity20. Such increased activity of the metal complexes can also be explained on the basis
of chelation theory’21.
Table 3. Antimicrobial activity data of the ligands L1H, L2H and their mixed ligand
complexes
Zone of inhibition, mm
Schiff base / complex
S.aureus
B.subtilis
E.coli
S.typhi
0.0
L1H
2.5
2.6
2.7
L6H
0.0
2.5
2.8
2.6
[Co(L1)(L2)(H2O)2]
[Ni(L1)(L2)(H2O)2]
[Cu(L1)(L2)(H2O)2]
[Zn(L1)(L2)(H2O)2]
7.5
6.5
4.5
6.8
4.5
8.5
7.0
8.2
3.3
4.5
5.7
6.2
4.3
8.3
10.3
8.3
Conclusion
1
The elemental analysis, magnetic susceptibility, electronic, H NMR, IR and ESR spectral
observations suggest the octahedral geometry for the Co(II), Ni(II), Cu(II) and Zn(II)
complexes and exhibit coordination number six. The general structure of the complexes is
shown in Figure 1. The Schiff’s bases do show some antimicrobial activity to certain extent
but their complexes exhibit comparatively greater amount of activity against the
microorganisms.

1263
A. K. MAPARI et al.
M = Co(II), Ni(II), Cu(II) and Zn(II).
Figure 1. Proposed structure for the complexes
Acknowledgment
One of the authors (A. K. M.) is grateful to UGC.WRO, Pune for the award of teacher
fellowship.
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