International Journal of the Physical Sciences Vol. 5(14), pp. 2203-2211, 4 November, 2010 Available online at http://www.academicjournals.org/IJPS ISSN 1992 - 1950 ©2010 Academic Journals
Full Length Research Paper
Preparation and characterization of Cr(III), Mn(II), Co(III), Ni(II), Cu(II), Zn(II) and Cd(II) chelates of schiffs base derived from vanillin and 4-amino antipyrine M. S. Suresh and V. Prakash* Department of Chemistry, Government Arts College, Ooty, The Nilgiris, Tamil Nadu, India, 643 002. Accepted 21 October, 2010
A novel bidentate Schiff base, synthesized from 1-phenyl 2, 3-dimethyl-4-aminopyrazol-5-one (4aminoantipyrene) and vanillin forms stable complexes with transition metal ions such as Cr (III), Mn (II), Co (II), Ni (II), Cu (II), Zn (II) and Cd (II). Their structures were investigated by elemental analysis, infrared spectroscopy, electronic spectroscopy, NMR spectroscopy; thermo gravimetric analysis and electron spin resonance spectroscopy. On the basis of the studies the coordination sites were proven to be through oxygen of the ring C = O and Nitrogen of the azomethine CH = N group. The microbiological studies revealed the anti bacterial nature of the complexes. Key words: Schiff bases, metal complexes, 4-aminoantipyrine, vanillin, 1-phenyl 2, 3-dimethyl-4-aminopyrazol5-one. INTRODUCTION Schiff bases and their metal complexes are of growing importance in co-ordination chemistry, attributable to recent observations in antibacterial, antifungal and oxygen carrier properties. The investigations of structure and bonding of Schiff base complexes help understand the complexes .Most of the biological systems possesses metal ions in unsymmetrical environments. These structures can be modified through condensation with aldehydes, ketones etc., Schiff bases of 4-amino antipyrine and its complexes have a variety of application in biological, clinical, analytical and pharmacological areas (Raman et al., 2008; Hitoshi et al., 1997; Raman et al., 2007). Studies of new chemotherapeutic Schiff bases attract much attention (Vogel, 1997; Argarago and Perin, 1942). Earlier work reported that some drugs showed increased activity when administered as metal complexes rather than organic compounds (Choi et al., 1995; Katia et al., 1996; Dharmaraj et al., 2001; Agarwal et al., 1997; Singh et al., 1999). Properties of 4-amino antipyrine to coordinate with metal is varied by condensing it with aldehydes, ketones, thiosemicarbazides and carbazides
*Corresponding author. E-mail:
[email protected].
etc., Metal complexes of 4-amino antipyrine and biological behavior involving the amino group of 4-aminoantipyrine has been studied exhaustively, when compared to the work carried out on the chemistry of transition metal complexes and biological behavior involving the amino group of 4-amino antipyrine (Raman et al., 2008). It is found that less work has been done on the synthesis of Schiff base and transition metal complexes involving carbonyl group of 4-amino antipyrine. In this paper we have described the synthesis, characterization and antibacterial property of transition metal complexes containing bidentate Schiff bases derived from vanillin and 4-aminoantipyrine. The structure of the similar complexes is reported to be octahedral (Raman et al., 2002). MATERIALS AND METHODS All the chemicals and solvents were of AR grade. Metal salts were purchased from Merck and Loba chemie Mumbai, India. Vanillin and anthranilic acid were purchases from Loba chemie, Mumbai, India. Ethanol, methanol and the solvents were dried by the standard procedures (Argarago and Perin, 1942; Choi et al., 1995). The elemental analyses were performed at Central Electrochemical Research Institute (CECRI) India using vario EL elemental
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O N H3C
N
O
NH2
+
CH3
H
OH O
N O CH3
H3C
N
N CH3
OH O CH3
Figure 1. Structure and preparation of Schiff base Ligand.
analyzer. IR spectroscopy analyses were recorded on Schimadzu FTIR 8400S spectrometer in 4000 – 200 cm-1 range using KBr pellet. The UV-Visible spectra were recorded on a Schimadzu UV spectrometer in the wave length range 200 - 800 nm. The NMR spectrum was recorded on a Joel NMR Spectrometer-G × 270. The thermal analyses were recorded on Universal V4.3A TA Instrument from CECRI, India. The ESR spectral analyses were recorded on Bruker instrument at 300 and 77 K from CECRI. The 1H-NMR and 13 C-NMR were recorded on a Bruker DPX-300 spectrometer using EtOD as solvent and TMS as internal standard (Hayvali and Fen Bil, 2005). The molar conductance was measured on ELICOCM180 using DMSO as the solvent at room temperature. The antibacterial activity was determined with the Disc Diffusion method. Stock solutions were prepared by dissolving the compounds DMSO and serial dilutions of the compounds were prepared in sterile distilled water to determine the Minimum Inhibition Concentration (MIC). Synthesis of Schiff base (Kriza et al., 2000; El-ajaily et al., 2007) An ethanolic solution (20 ml) of 1-phenyl-2, 3-dimethyl-4aminopyrazol-5-one (2.03 gm, 0.01 mol) (4-aminoantipyrine) was added to an ethanolic solution of vanillin (1.52 gm, 0.01 mol). The solution was stirred vigorously when a yellow colored solid was obtained. The mixture was refluxed for calculated 5 h, the reaction was followed using TLC and allowed to cool. The mixture was poured in crushed ice when crystals were formed. The Schiff base was prepared according to the equation given below. It was filtered and recrystallized from ethanol (Figure 1). Yield; 85%: m.p: 205°C.
over the solid nutrient agar plates with the help of a spreader. Fifty microlitres of the stock solutions was applied on the 10 mm diameter sterile disc. After evaporating the solvent, the discs were placed on the inoculated plates. The Petri plates were placed at low temperature for 2 h to allow the diffusion of the chemical and then incubated at a suitable optimum temperature (29+/-2°C) for 30 - 36 h. The diameter of the inhibition zones was measured in millimeters.
RESULTS The analytical data for the complexes together with their physical properties are summarized in (Table 1). The conductance values of the chelates support the +3 +2 +2 +2 +2 +2 electrolytic nature for Cr , Mn , Co , Ni , Cu , Zn +2 and Cd complexes. The primary valencies are neutralized by the presence of anions outside the coordination sphere. Infrared spectra and mode of bonding The diagnostic IR frequencies of the ligand and its complexes are compiled in Table 2. The infrared spectrum of the free ligand is compared with that of the complexes to determine the coordination sites that may have involved in the chelation.
Synthesis of metal complexes The metal complexes of Cr (III), Mn (II), Co (II), Ni (II), Cu (II), Zn (II) and Cd (II) were prepared by refluxing 1:2 molar mixtures of the metal salt with the ligand for 5 h. The contents were cooled and allowed to crystallize. The complexes were collected by filtration and then washed several times with hot ethanol until the mother liquor becomes colorless. The resultant products were dried in air and stored in a desiccator over anhydrous calcium chloride under vacuum. Antibacterial activity The antibacterial activity was determined with the Disc Diffusion method. Stock solutions were prepared by dissolving the compounds DMSO and serial dilutions of the compounds were prepared (Chandra et al., 2009; Maurya et al., 2006; Rosu et al., 2006), in sterile distilled water to determine the Minimum Inhibition Concentration (MIC). The nutrient agar medium was poured into Petri plates. A suspension of the tested microorganism (0.5 ml) was spread
Electronic spectral analyses The electronic spectrum gives information on the electronic environment of the metal. The splitting of d orbital and in turn the structure expected for the complexes. The Table 3 gives information on the various electronic excitations obtained for the complexes. Thermal analyses Thermo gravimetric analyses of the complex is used to get the; (i) Information on water of hydration if present in the coordination sphere of the central metal ion. (ii) Scheme of thermal decomposition of the complexes
Suresh and Prakash
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Table 1. Physical characterization, analytical and molar conductance data of the complexes.
Comp. (color)
M.wt, m.p (°C)
Yield (%)
C19H19N3O3= L
337.5, 167 (Yellow)
86
797.95,213 (Green)
+2
+2
Found (Calc.) (%) N 12.642 (12.45)
C 66.422 (67.66)
H 5.8 (5.6)
60
66.42 (67.66)
5.8 (5.6)
861.44,184 (Cream)
55
52.44 (52.93)
887.43,180 (Pink)
62
865.19,158 (Green)
+2
m(
-1
M -
12.642 (12.45)
0 (0)
6.420 (5.984)
220
4.82 (4.876)
9.886 (9.751)
4.640 (3.715)
6.215 (6.377)
127
53.782 (54.29)
5.042 (5.001)
9.823 (10.002)
0 (0)
6.082 (7.01)
210
56
52.706 (52.736)
4.864 (4.857)
9.689 (9.714)
3.483 (3.701)
6.64 (6.78)
98
870.05,186 (Green)
66
52.248 (52.411)
4.891 (4.872)
9.665 (9.655)
3.986 (3.678)
7.48 (7.304)
118
+2
871.89,166 (Cream)
54
51.892 (52.33)
4.642 (4.819)
9.581 (9.639)
3.586 (3.672)
7.461 (7.504)
96
+2
893.81,170 (Pink)
54
51.02 (49.968)
4.699 (4.583)
9.938 (9.986)
0 (0)
12.576 (11.948)
108
+3
[Cr (L)2(H2O)2]Cl3 +3 C38H42N6O8Cl3Cr [Mn (L)2(H2O)2]SO4 +2 C38H42N6O12SMn [Co (L)2(H2O)2]Cl2 +2 C38H42N6O8 Cl2Co +2
[Ni (L)2(H2O)2]SO4 +2 C38H42N6O8 SNi [Cu (L)2(H2O)2]SO4 +2 C38H42N6O12S Cu [Zn (L)2(H2O)2]SO4 +2 C38H42N6O12S Zn [Cd (L)2(H2O)2]Cl2 +2 C38H42N6O8 Cl2 Cd
-1
mol )
S 0 0
Table 2. Characteristic infrared absorption frequencies in (cm-1) of ligand (L) and complexes.
Compound C19H19N3O3 +3 [Cr (L)2(H2O)2]Cl3 +2 [Mn (L)2(H2O)2]SO4 +2 [Co (L)2(H2O)2]Cl2 +2 [Ni (L)2(H2O)2]SO4 +2 [Cu (L)2(H2O)2]Cl2 +2 [Zn (L)2(H2O)2]SO4 +2 [Cd (L)2(H2O)2]Cl2
-1
(OH)cm water 3117 3117 3103 3117 3117 3130 3117
-1
(OH) cm Phenolic 3064 3064 3065 2993 3064 3122 2993 3064
cm
-1
(C = O) 1624 1610 1607 1606 1607 1607 1607 1610
-1
cm (C = N) 1579 1569 1559 1549 1559 1559 1559 1569
M-O and
-1
M-N cm
702 and 500-450 702 and 500-450 702 and 500-450 714 and 500-450 702 and 500-450 716 and 500-450 702 and 500-450
Table 3. Electronic absorption spectral data for the ligand and their metal complexes. -1
Compound
Absorption (cm )
Band assignment
Geometry
C19H19N3O3 +3 [Cr (L)2(H2O)2]Cl3 +2 [Mn (L)2(H2O)2]SO4 +2 [Co (L)2(H2O)2]Cl2 +2 [Ni (L)2(H2O)2]SO4 +2 [Cu (L)2(H2O)2]Cl2 +2 [Zn (L)2(H2O)2]SO4 +2 [Cd (L)2(H2O)2]Cl2
38461 and 31746 15948, 20833 and 35354 17717, 23310 and 26882 13513, 17123 and 24038 12820, 25123 and 26042 12650 27777 28571
* , n- * transitions. 4A2g 3T2g, 4A2g 3T1g (F)4A2g 3T1g (P) 6 4 6 4 6 4 A1g T1g(S), A1g T2g (G), A1g A1g 4 4 4 4 4 4 T2g T2g 1, T1 g A2g 2, T1 g T1g (P) 3 3 3 3 3 3 A2g T2g, A2g T1g(F) A2g T1g(P) 2 Eg 2T2g LMCT LMCT
Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral
and (iii) To find thermal stability of the complex. Table 4
3
gives the information on the thermal analyses of the
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Table 4. Thermo gravimetric analyses of complexes.
S/No
Compound
130-220 220-590 Above 590
I II III
Weight loss (%) Found Calculated 5.016 4.5 84.75 85.91 9.842 9.523
112-182.97 182.97-547.56 Above 547.56
I II -
5.02 83.86 11.11
4.82 87.73 10.09
208.72-359.56 359.56-711.09 Above 711.09
I II -
3.76 87.78 8.46
4.164 88.35 7.48
234.86 234.86-555.57 Above 555.57
I II IV
3.04 83.14 12.79
2.81 84.5 11.26
127.21 238.09-658.63 Above 658.63
I II IV
2.13 88.76 9.10
2.06 88.605 9.33
Temp. range (ºC)
+3
1
[Cr (L)2(H2O)2]Cl3
2
[Mn (L)2(H2O)2]SO4
3
[Ni (L)2(H2O)2]SO4
4
[Cu L2(H2O)2] SO4
5
[Zn L2(H2O)2] SO4
+2
+2
+2
+2
Stage
NMR analyses
complexes. +2
Stage 1. [Mn (C19H19N3O3)2(H2O)2]SO4 +2 [Mn (C19H19N3O3)2] SO4 + 2 H2O +2
Stage 2. [Mn (C19H19N3O3)2]SO4
MnO2 (Residue) (2)
+2
Stage 1. [Ni (C15H12NO4)2(H2O)2] +2 [Ni (C15H12NO4)2] + 2H2O +2
Stage 2. [Ni (C15H12NO4)2] SO4 +2
(1)
SO4
NiO (Residue)
Stage 1. [Cu (C19H19N3O3)2(H2O)2] +2 [Cu (C19H19N3O3)2] SO4+ 2H2O (1)
(2)
SO4
+2
Stage 2. [Cu (C19H19N3O3)2] SO4 CuS (Residue) (2) +2 Stage 1 [Zn (C19H19N3O3)2(H2O)2] SO4 +2 [Zn (C19H19N3O3)2] SO4 + H2O (1) +2
Stage 2. [Zn (C19H19N3O3)2] SO4 (Residue)
(2)
CuO
ESR analyses The ESR spectra of copper complex provide information of importance in studying the metal ion. The ESR spectra of the Cu (II) complex recorded at liquid nitrogen temperature (77 K) and room temperature (300 K) .The spectrum of copper complex has a single intense absorption band in the high field region. The molecule is isotropic due to the tumbling motion of the molecule. When the complex is frozen to liquid nitrogen temperature, four well resolved peaks with low field region are obtained. This shows the presence of an octahedral geometry for the copper complex.
The NMR spectrum of the ligand and Zn complex were recorded in DMSO at room temperature (Raman et al., 2005). The proton NMR spectrum shows peaks at 2.44, 3.10, 3.85, 5.35, 6.93, 7.37, 7.51, 9.49 ppm respectively, shown in Figure 2. The C-13 NMR spectrum of the ligand shows peaks at 12.92, 34.83, 56.36, 110.37, 112.83, 117.03, 122.90, 123.68, 129.16, 133.86, 149.51, 150.29, 151.08, 160.86, 163.21 ppm respectively, shown in Figure 3. The proton NMR of Zn complex showed peaks at 2.44, 3.10, 3.85, 5.35, 6.90, 6.95, 7.37, 7.42, 7.68, 9.79 ppm respectively, shown in Figure 4. The proton NMR is already reported (Raman et al., 2005) for the ligand, whereas the proton NMR spectrum for the Zn complex and C-13 NMR recorded shows the peaks mentioned. Antibacterial activity The antibacterial activity was determined with the Disc Diffusion method (Kriza et al., 2000). Stock solutions were prepared by dissolving the compounds DMSO and serial dilutions of the compounds were prepared (Sulekh et al., 2009; Tudor et al., 2006) in sterile distilled water to determine the Minimum Inhibition Concentration (MIC). The nutrient agar medium was poured into Petri plates. A suspension of the tested microorganism (0.5 ml) was spread over the solid nutrient agar plates with the help of a spreader. Fifty microlitres of the stock solutions was applied on the 10 mm diameter sterile disc. After evaporating the solvent, the discs were placed on the inoculated plates. The Petri plates were placed at low
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2.44
10
3.10
3.85
Suresh and Prakash
9
7.37
8 7 9.49
6 5 4
1
5.35
7.51
2
6.93
3
0
129.16 127.00 123.68
Figure 2. NMR spectrum of the ligand.
10 9 8
5 4 3 2 1 0
Figure 3. C13 spectrum of the ligand.
12.92
34.83
56.36
122.90 117.03 112.83 110.37
133.86
151.08
160.86
6
163.21
7
1.0
2.44
3.10
Int. J. Phys. Sci.
3.85
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0.9
7.37
0.8 0.7 9.79
0.6 0.5 0.4
0.1
5.35
7.37
0.2
6.95 6.90
7.42
0.3
0
Figure 4. Proton NMR spectrum of Zn complex.
Table 5. Antibacterial activity data for the ligand and their metal complexes.
S. no 1 2 3 4 5 6 7 8.
Compound C19H19N3O3 +3 [Cr (L)2(H2O)2]Cl3 +2 [Mn (L)2(H2O)2]SO4 +2 [Co (L)2(H2O)2]Cl2 +2 [Ni (L)2(H2O)2]SO4 +2 [Cu (L)2(H2O)2]Cl2 +2 [Zn (L)2(H2O)2]SO4 +2 [Cd (L)2(H2O)2]Cl2
Staphylococcus aureus 4 6 7 8 4 16 18
temperature for two hours to allow the diffusion of the chemical and then incubated at a suitable optimum + temperature (29 /-2°C) for 30 - 36 h. The diameter of the inhibition zones was measured in millimeters. The synthesized ligand and complexes were tested for their antibacterial activity against Staphylococcus aureus and +2 +2 Escherichia coli. Table 5 shows that Zn and Cd complexes shows good antibacterial activity against the strain of bacteria taken under study. The rest of the complexes have a minimum activity towards the strain of bacteria taken under study.
Escherichia coli 3 5 6 9 3 15 17
Inference anti bacterial activity + + + ++ No effect + ++++ +++++
DISCUSSION Infrared spectra and mode of bonding The O-H water is absent in the spectrum of the ligand, -1 but is present in the complex at 3117.07 cm . This is supported by the presence of the M-O peak noticed in -1 the complex at 702.11 cm . The phenolic O-H stretching does not undergo any change in the spectrum. -1 The phenolic O-H stretching appears at 3064.99 cm . Hence the phenolic O-H group does not participate in the
Suresh and Prakash
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Table 6. UV-visible spectral data of the compounds.
Complex +3 [Cr (L)2(H2O)2]Cl3 +2 [Co (L)2(H2O)2]Cl2 +2 [Ni (L)2(H2O)2]Cl2
-1
max cm 15948, 20833 and 35354 13513, 24038 and 27932 12820 ,25123 and 26042
bond formation with the metal. The frequency corresponding to the C=O for the five member ring -1 stretching in the region 1624.79 cm in the ligand is -1 shifted to lower frequency at 1610.07 cm in the complexes. The frequency corresponding to C=N at -1 -1 1579.79 cm shifts to lower frequency at 1569.75 cm in -1 the complexes. New bands in the region 500 to 450 cm typical for the presence of M-O and M-N are present in the complex as new bands. This is not present in the ligand. Thus it is concluded from the IR spectrum for metals, that the metal is participating in the bond formation through the azomethine C=N group and the C=O carbonyl of the five member ring (Lever, 1984). The primary valencies of the metals are satisfied by the presence of ions present outside the coordination sphere. Electronic spectral analyses The UV-spectrum of Chromium (III) complex shows three -1 -1 peaks at 627 nm (15948 cm ), 480 nm (20833 cm ) and -1 282 nm (35354 cm ) respectively (Table 6). The peak at -1 627 nm (15948 cm ) corresponds to the 4A2g 4T2g -1 transitions. The peak at 480 nm (20833 cm ) correspond to 4A2g 4T1g (F) transition. The peak at 282 nm (35354 -1 cm ) corresponds to the 4A2g 4T1g (P) electronic transition respectively. The electronic transitions observed for the Cr III complexes suggest the octahedral 3 geometry for the complex. Chromium III is a d complex 3 5 with the d configuration. The orgel diagram for the d +2 configuration for Mn shows the three bands at 587.50, 6 4 6 4 317 and 340 nm assigned for A1g T1g(S), A1g T2g 6 4 (G), A1g A1g. These show the octahedral geometry +2 Mn complexes. Three peaks are predicted in their 4 4 4 electronic spectra, namely, T2g T2g 1, T1 g 4 4 4 A2g 2, T1 g T1g (P) 3 found at 604, 352 and 342 nm respectively for the cobalt complex. This shows the presence of an octahedral structure in cobalt complex. 8 Nickel (II) has a (d ) configuration having the following -1 orgel diagram, found at 780 nm (12820 cm ), 398 nm -1 -1 (25123 cm ) and 384 nm (26042 cm ) respectively for the nickel complex. Based on the orgel diagram the first 3 3 peak at 648 nm is assigned for the A2g T2g, the 3 3 second at 349 nm for the A2g T1g (F) and the third at 3 3 338 nm due to the A2g T1g (P) transition respectively. This confirms the presence of an octahedral geometry for 9 the Nickel complex. Copper (II) has a (d ) configuration having the following absorption found at 748 nm (13368 2 2 2 -1 2 2 dx -y ) 1, 537 nm cm ) for the A1g B1g (dz 2 2 -1 2 2 (18621cm ) for the B2g B1g (dxy dx -y ) 2 and 418
-1
-1
10Dq cm 15948 14517 12820
B cm 598.4 762 847
-1
0.58 0.68 0.784
2
2
Geometry Octahedral Octahedral Octahedral
2
2
nm (23923 cm ) for the Eg B1g (dxz, dyz dx -y ) 3, respectively for the copper complex. The spectra are typical of Cu (II) complexes with an elongated 22 -1 tetragonal . Zinc (II) shows absorption at 360.00 cm for the ligand metal charge transfer transition. This confirms the presence of an octahedral geometry for the zinc complex. Cadmium (II) shows absorption at 342 nm -1 (29239 cm ) for the ligand metal charge transfer transition. This confirms the presence of an octahedral geometry for the cadmium complex. The value of Racah parameter (B) can be evaluated by the equation of underhill and Billing, (Dubey et al., 2006; Dubey et al., 2005; Krishnapillai et al., 2005; Lever, 1984) B= ( 3 + 2 – 30 Dq)/15. The observed value of 598.4 of the Racah interelectronic repulsion parameter (B’) was +3 -1 compared to the free Cr ion (1030 cm ), which indicates considerable covalent character of the metalligand bonds with covalence factor = 0.58. Similarly the ligand parameters for the other metals were calculated. Thus based on the UV-Visible spectroscopy it is found that metals form complexes with the prepared Schiff base ligand with octahedral geometry. Thermal analyses The TGA analyses show the presence of octahedral geometry for the complexes. Two molecules of water is present in the coordination sphere which is lost in stage I, in stage II the complex decomposes and the residue is formed. The calculated and observed values are nearly the same. NMR analyses The NMR spectrum is used to find the structure of the ligand and Zn complex (Raman et al., 2005; Zeliha and Bau, 2005). The peak at 5.35 ppm due to the –OH group is not changed in the Zn complex this shows that the –OH group does not participate in the complexation. The azomethine proton signal in the spectrum of the Zn complex is shifted downfield compared to the free coordination with metal ion. There is no appreciable change in the rest of the signals of this complex (Raman et al., 2008). ESR analyses The four well resolved peaks in the low field region
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H3C
CH3
N
O
N
H2O
M
OH2 O
H HO
OH H
O
N O
H 3C
N CH 3
(Raman and Raja, 2007; Suresh and Prakash, 2010; Hathaway and Tomlinson, 1968; Tharmaraj et al., 2009; Thangadurai and Natarajan, 2002; Suresh and Prakash, 2010) correspond to g (2.302) and g (2.048). The trend g (2.302) > g (2.048) > ge (2.0023) observed for the copper complex suggests that the unpaired electron is 2 2 localized in the dx -y orbital of the copper ion. The fact 2 2 that the unpaired electron lies predominantly in the dx -y orbital is also supported by the value of the exchange interaction G estimated from expression -
2.0023)
(1)
If G > 4.0, the local axes are aligned parallel or slightly misaligned. If G < 4.0, significant exchange coupling is present and the misalignment is appreciable. The observed value for the exchange interaction parameter for the Cu (II) complex (G = 6.445) suggests that the 2 2 unpaired electron is present in the dx -y orbital. The spin -1 orbit coupling constant, (value : -25525 cm ) was calculated using the relation, gav =1/3 (g + 2 g ) and gav = 2 ( 1- 2
/ 10 Dq)
(2) -1
is less than that for the free Cu (II) ion, - 12019 cm , which also supports the covalent character of the M-L 2 bond in the complex. The covalence parameter, , was calculated using the following equation: 2
(Cu) = A / P + ( g - 2.0023) + 3/7 (g - 2.0023) + 0.004
2
(Cu) = (A / 0.036) + ( g - 2.0023) + 3/7 (g - 2.0023) + 0.004 (3) 2
– bonding K > K
0.77 and for in-
- bonding K < K , while for the out-of-plane
bonding K
K (0.4627) relation indicates the absence of significant in- plane - bonding. The molar conductance of the complexes reveals the presence of chloride ions outside the coordination sphere +2 +2 in chromium complexes. In the complexes of Mn , Co , +2 +2 +2 +2 Ni , Cu , Zn and Cd the primary valency of the metals are satisfied within the coordination sphere due to the coordination with the carboxyl ate groups of the ligand (Figure 5).
N
Figure 5. (M= Cr+3, Mn+2, Co+2, Ni+2, Cu+2, Zn+2 and Cd+2).
G= (g - 2.0023) / (g
that for the pure plane
N
H 3C
CH3
The (0.7547) value for the complex supports its 23 covalent nature of the bonding. Hathway pointed out
Antibacterial activity
The antibacterial property of the ligands was compared to +2 +2 the complexes. The Zn and Cd complexes show good antibacterial activity against the strain of bacteria taken under study when compared to the ligand and other metal complexes taken for study. Conclusion
In this paper we have reported the co-ordination chemistry of complexes derived Schiff base ligand, obtained from the reaction of vanillin and anthranilic acid +3 +2 +2 +2 +2 +2 with metals such as Cr , Mn , Co , Ni , Cu , Zn and +2 Cd . The structures of the ligand (Raman et al., 2008) the structures of the complexes were confirmed by elemental analyses, IR, molar conductance, UV-Visible spectroscopy, thermo gravimetric analyses and ESR spectroscopic analyses. The Schiff base coordinates through its azomethine nitrogen and the carbonyl group of the five member ring, to the central metal atom. The Schiff base behaves as a bidentate ligand. The molar conductance measurements suggest the presence of +3 +2 anion outside the coordination sphere for Cr , Mn , +2 +2 +2 +2 +2 Co , Ni , Cu , Zn and Cd as shown in Figure 2. The metals, forms 1:2 complexes with the Schiff base ligand. The antibacterial study shows that the complexes are more toxic to the strain of bacteria taken under study than the ligand. The complexes of zinc and cadmium are found to have a good antibacterial property when compared to the other metal complexes. It has been observed from the results that the metal complexes have higher activity than the free ligands (Paulmony et al., 2009). This is probably due to the greater lipophilic nature of the complexes. Such increased activity of the metal
Suresh and Prakash
chelates can be explained on the basis of Overtone’s concept and chelation theory. According to Overtone’s concept of cell permeability the lipid membrane that surrounds the cell favours the passage of lipid soluble materials due to which liposolubility is and important factor which controls the antimicrobial activity. On chelation, the polarity of the metal ion will be reduced to a greater extent due to the overlap of the ligand orbital and partial sharing of positive charge of the metal ion with donor groups. Further, it increases the delocalization of -electrons over the whole chelate ring and enhances the lipophilicity of the complex. This increased lipophilicity enhances the penetration of the complexes into lipid membrane and blocks the metal binding sites on enzymes of microorganisms. REFERENCES
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