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1 ISSN: X CODEN: IJPTFI Available Online through Research Article SYNTHESIS, CHARACTERIZATION AND ANTIMICROBIAL STUDIES OF Cu(II), Ni(II), Mn(II) and Zn(II) SCHIFF BASE COMPLEXES DERIVED FROM 2-HYDROXY NAPHTHALDEHYDE AND 1,8-DIAMINONAPHTHALENE 1 M. Sakunthala and 2 P. Subramanian* 1 Department of Chemistry, Government Arts College for Women, Salem-8, Tamil Nadu. 2 Department of Chemistry, Government Arts College, Salem-7, Tamil Nadu. subraslm@gmail.com Received on Accepted on Abstract The symmetrical tetra-dentate Schiff base complexes were prepared by the reaction of 2-hydroxy naphthaldehyde and 1,8-diaminonaphthalene in 2:1 molar ratio. The ligand and its complexes with Cu(II), Ni(II), Mn(II) and Zn(II) ions were characterized by elemental analysis, molar conductance, infrared, electronic spectra, cyclic voltammetry, thermal, Magnetic and EPR studies. Furthermore, antibacterial activity of representative complexes was also investigated. The molar conductance value of all metal complexes in DMF solvent indicates the non-electrolytic nature. In IR spectra, the comparison of shift in frequency of the complexes with the ligand reveals the coordination of donor atom to the metal atom. The electronic, magnetic and EPR spectra of the metal complexes provides information about the geometry of the complexes and are in good agreement for the proposed square planar geometry for Cu(II), Ni(II), Mn(II) and Zn(II) complexes. The free ligands and their metal complexes were screened for their antimicrobial activities against pathogenic bacteria like staphylococcus aureus, Escherichia coli and Klebsilla pneumonia. The activity data show that the Cu(II), Ni(II), Mn(II) and Zn(II) complexes are more potent antimicrobials than the parent Schiff base ligands against microorganisms. Keywords: Schiff base, 1,8-diaminonaphthalene, 2-hydroxy1-naphthaldehyde, Antimicrobial activity. 1. Introduction Schiff bases complexes have remained an important and popular area of research due to their simple synthesis, versatility, and diverse range of applications [1,2]. Thus, Schiff bases have played a marvelous role in the development IJPT Oct-2012 Vol. 4 Issue No Page 4630

2 of coordination chemistry. Schiff base metal complexes had been a widely studied subject due to their industrial and biological applications [3]. Because of new interesting applications found in the field of pesticides and medicine, the metal complexes with tetra-dentate N 2 O 2 types had attracted the attention of chemists [4, 5]. The Cu(II) and Ni(II) complexes are well known to accelerate drug action and the efficiency of a therapeutic agent can often be enhanced upon coordination with a metal ion. The pharmacological activity has been found to be highly dependent on the nature of the metal ion and the donor sequence of the ligands, with different ligands showing widely dissimilar biological properties. The copper (II) complexes have aroused extensive interest due to their importance in biological processes and in inorganic material science [6]. The coordination geometry around the Cu(II) ion plays a major role as well in the redox-mediated formation of reactive oxygen species. The activation of molecular oxygen by a mononuclear Cu(II) complex in the presence of DNA is expected to lead to the abstraction of a proton/hydrogen from the sugar backbone or from the bulk solvent. The coordination chemistry of manganese in the +2, +3 and +4 oxidation states is receiving considerable attention due to the biological importance of these ions [7]. The synthesis and characterization of manganese coordination complexes to model the structure, reactivity and spectroscopy of manganese in its various oxidation states, with various ligand types and nuclearities, has contributed substantially to our understanding of the role and mechanism of manganese enzyme. This study presents the synthesis and characterization of some new Cu(II), Ni(II), Mn(II) & Zn(II) complexes with tetra-dentate Schiff bases derived from 2-hydroxy naphthaldehyde and 1,8-diaminonaphthalene. The synthesised complexes have been characterized by elemental analysis, molar conductance, infrared, electronic spectra, cyclic voltammetry, thermal, Magnetic and EPR studies. 2. Experimental Materials and physical measurements Metal salts, 2-hydroxy naphthaldehyde and 1, 8-diaminonaphthalene were purchased from Aldrich. Ethanol, DMSO and DMF were used as solvents purchased from Loba chemicals. The solvents and reagents with analytical grade were obtained commercially and used without further purification. The Elemental analysis was performed using Carlo-Eraba 1106 instrument. Molar conductances of the complexes in DMF solution were measured with ELICO CM 185 conductivity Bridge. The Infrared spectra were recorded on the SHIMADZU model spectrometer using KBr disc. IJPT Oct-2012 Vol. 4 Issue No Page 4631

3 Electronic absorption spectra in the UV-Visible range were recorded on Perkin Elmer Lambda-25 between nm by using DMF as the solvent. ESR spectra were recorded on a Varian JEOL-JES-TE100 ESR spectrophotometer at X- band microwave frequencies for powdered samples at room temperature. Magnetic susceptibility data were collected on powdered sample of the compounds at room temperature with PAR155 vibrating sample magnetometer. Thermal studies were carried out in the C range using an SDT Q600 V20.9 Build 20 model thermal analyzer. Synthesis of Ligand The symmetrical tetra-dentate Schiff base ligand was prepared according to the literature method. To an ethanolic solution of 2-hydroxy naphthaldehyde and ethanolic solution of 1,8-diaminonaphthalene was added in dropwise. The reaction mixture was kept on water bath for refluxtion. It was refluxed for 2 hours. Yellowish brown colour solid was separated and was filtered off, washed with 5 ml of cold ethanol and then dried in air. Synthesis of Metal Complexes All the new Schiff base complexes were prepared by the same general procedure with stoichiometric amount of ligand and metal salts in a 1:1 mole ratio. To an ethanolic solution of Schiff base ligand metal salt was added. The reaction mixture was refluxed for about 2 hrs on hot water bath. The reaction mixture was cooled, filtered and left in a petridish to allow the solvent to evaporate slowly. The complex was separated out. Cyclic voltammetry All voltammetric experiments were performed with a CHI 760 electrochemical analyzer, in single compartmental cells using tetrabutylammonium perchlorate as a supporting electrolyte. The redox behavior of the complexes has been examined in a scan rate of 0.1 Vs 1 in the potential range +1.2 to 2.0 V. A three-electrode configuration was used, comprising a glassy carbon electrode as the working electrode, a Pt-wire as the auxiliary electrode, and an calomel electrode as the reference electrode. The electrochemical data such as cathodic peak potential (Epc) and anodic peak potential (Epa) were measured. Antimicrobial activity The antibacterial activity of the complexes of Cu(II), Ni(II), Mn(II) and Zn(II) were checked by the disc diffusion technique [8]. This was done on Gram negative bacteria like Klebsiella pneumoniae, Escherichia coli and Gram IJPT Oct-2012 Vol. 4 Issue No Page 4632

4 positive bacteria Staphylococcus aureus at 37 C. The disc of Whatmann no.4 filter paper having the diameter 8.00 mm were soaked in the solution of compounds in DMSO (1.0 mg cm -1 ). After drying it was placed on nutrient agar plates. The inhibition areas were observed after 36 hours. DMSO was used as a control and Streptomycin as a standard. 3. Result and discussion Elemental composition The elemental analysis data were compared with that of the formulation, which gives good agreement with the proposed formula. The elemental analysis data of the complexes were produced by Table 1. Table-1: Analytical and physical data of the Schiff base metal complexes. Compounds Calculated (Found) (%) C H N Metal ΛM (Ohm 1 cm 2 mol 1 ) (C 32 H 22 N 2 O 2 ) (82.35) 4.72 (4.70) 6.00 (5.54) [Cu(C 32 H 20 N 2 O 2 )] (72.78) (3.75) (5.32) (12.13) [Ni(C 32 H 20 N 2 O 2 )] (73.53) (3.80) (5.32) (11.14) [Mn(C 32 H 20 N 2 O 2 )] (74.11) (3.82) (5.41) (10.40) [Zn(C 32 H 20 N 2 O 2 )] (72.51) (3.74) (5.27) (12.26) Conductivity studies The molar conductance of the complexes was an aid for proposing their formulas. Conductivity measurements were carried out in 10 3 mol dm 3, DMF at 30 C. The molar conductance values of the Cu(II), Ni(II) and Mn(II) and IJPT Oct-2012 Vol. 4 Issue No Page 4633

5 Zn(II) complexes in the range of Ohm 1 cm 2 mol 1 (Table 2) which indicates the non-ionic nature of these complexes and they are considered as non-electrolytes [9]. Table-1: Infrared spectral data for Schiff base metal complexes. Compounds (C=N) C=C (M N) (M O) (cm 1 ) (cm 1 ) (cm 1 ) (cm 1 ) (C 32 H 22 N 2 O 2 ) [Cu(C 32 H 20 N 2 O 2 )] [Ni(C 32 H 20 N 2 O 2 )] [Mn(C 32 H 20 N 2 O 2 )] [Zn(C 32 H 20 N 2 O 2 )] IR spectra A strong band is observed in the free ligands around 1622 cm -1, characteristic of azomethine (C=N) group [10]. Coordination of the Schiff base to the metal through azomethine nitrogen atom is expected to reduce the electron density in the azomethine link and lower the (C=N) absorption frequency. In the spectra of all new complexes, the band due to (C=N) showed a negative shift to cm 1, indicating coordination of the azomethine nitrogen to metal atom [11]. Another medium intensity band around 3385 cm 1 cm in the free ligands due to the (OH) was absent in the complexes, indicating deprotonation of the Schiff bases prior to the coordination. The various absorption bands in the region cm 1 may be assigned due to υ(c=c) aromatic stretching vibrations of the 2-hydroxynaphthaldehyde and 1, 8-diaminonaphthalene ring. The infrared spectra show bands in the region cm 1 corresponding to υ(m-n) vibrations [12]. The presence of bands in all the complexes in the region cm 1 orginates from the (M-N) azomethine vibration IJPT Oct-2012 Vol. 4 Issue No Page 4634

6 modes and identifies coordination of azomethine nitrogen and also presence of bands at cm 1 indicates that υ(m-o) vibrations. Electronic spectra The geometry of the metal complexes has been deduced from the electronic spectra of the complexes. Electronic spectra of all the complexes were recorded in DMF medium in Table 3. The peaks obtained in the range of nm was assigned to the intra ligand charge transfer transition (π π*). An intense peak in the range of nm was due to ligand-to-metal charge transfer transitions. The bands are indicative of benzene and other chromophore moieties present in the complexes. Table-3: UV Visible data of Schiff base metal complexes. Absorption nm (cm -1 ) Complexes π π* n π* L M CT d-d (C 32 H 22 N 2 O 2 ) [Cu(C 32 H 20 N 2 O 2 )] [Ni(C 32 H 20 N 2 O 2 )] , 644 [Mn(C 32 H 20 N 2 O 2 )] , 626, 691 [Zn(C 32 H 20 N 2 O 2 )] The copper(ii) complex shows a broad absorption peak at 550 nm arises due to the d-d transition 2 B 1g 2 A 1g suggest that the copper ion exhibits a square planar geometry [13]. According to the literature data, the principal feature of square planar nickel(ii) complexes is the presence of three well-defined bands [14]. We have also observed two weak intensity bands of the mononuclear Ni(II) complex at 536, 644 nm corresponding to 1 A 1g 1 A 2g, 1 A 1g IJPT Oct-2012 Vol. 4 Issue No Page 4635

7 1 B 1g transitions, respectively. The electronic spectra of mononuclear Mn(II) complexes exhibit three weak intensity absorption bands at 519, 626, 691 nm. These bands may be assigned to the transitions 6 A 1g 4 T 1g (4G), 6 A 1g 4 E g (4G), 6 A 1g 4 E g (4D). Which may be expected to arise from the Mn(II) ions [15] in Square planar geometry. No transitions were observed in the visible region for the Zn(II) complex consistent with the d 10 configuration of the Zn 2+ ion. This complex is also found to be diamagnetic as expected for the d 10 configuration. Cyclic Voltammetry The electrochemical behaviour was studied by cyclic voltammetry in DMSO containing 10 1 M tetra(n-butyl) ammonium perchlorate over the range of 1.2 to 2.0 V. The electrochemical data of the complexes are summarized in Tables 4. (reduction) and 5(oxidation). [Cu(C 32 H 20 N 2 O 2 )] complex shows quasireversible reduction waves. Controlled potential electrolysis was carried out at 100 mvs 1 and the experiment reports that each couple correspond to one electron transfer process. So, the processes are assigned as follows. Cu II Cu I The [Cu(C 32 H 20 N 2 O 2 )] complex show a quasireversible oxidation waves, which is assigned as a Cu(III)/Cu(II) couple. The Ep values are suggest the each couple was quasireversible. The E 1/2 values indicate that each couple corresponds to one electron transfer process. A typical cyclic voltammograms of the complex [Ni(C 32 H 20 N 2 O 2 )] shows quasireversible reduction waves. The Ep values suggest the existence of a quasireversible couple. The E 1/2 values indicate that each couple corresponds to one electron transfer process. Tables 4 and 5 represent the electrochemical data of [Ni(C 32 H 20 N 2 O 2 )] complex in cathodic and anodic potential, respectively. Controlled potential electrolysis was also carried out and the experimental reports that each couple correspond to one electron transfer process, as follows: Ni II Ni I The cyclic voltammograms of nickel (II) complexes obtained at positive potential region show one electron transfer waves. The oxidation process is also quasireversible in nature. The oxidation process can be assigned as follows: IJPT Oct-2012 Vol. 4 Issue No Page 4636

8 Ni II Ni III The [Mn(C 32 H 20 N 2 O 2 )] complex shows reduction waves. The Ep values suggest the existence of a quasireversible couple. The E1/2 values indicate that each couple corresponds to one electron transfer process. Controlled potential electrolysis was also carried out and the experimental reports that each couple correspond to one electron transfer process, as follows: Mn III Mn II The obtained oxidation peak at the positive potential side indicated that the processes take place on the metal center of the complex Mn(II). This peak describes a one-electron oxidation of Mn(II)/Mn(III). Table-4: Thermoanalytical data of the Schiff base metal complexes. Complexes TG rang ( o C) L Estimated (Calculated) (%) Mass Total mass loss loss (43.28) (99.06) (55.78) (47.15) Assignment Loss of naphthalene groups Loss of aromatic ligand groups. Loss of naphthalene groups and aromatic ligand groups. Metallic residue -- Decomposition is in progress Loss of naphthalene groups and (52.98) -- aromatic ligand groups. Decomposition is in progress (65.70) -- Loss of naphthalene groups and aromatic ligand groups. MnO residue (45.55) Loss of naphthalene groups and aromatic ligand groups. Decomposition is in progress IJPT Oct-2012 Vol. 4 Issue No Page 4637

9 Table-5: Electrochemical data Schiff base metal complexes in DMF medium (reduction). Complexes E pc (V) E pa (V) E 1/2 (V) E (mv) [Cu(C 32 H 20 N 2 O 2 )] [Ni(C 32 H 20 N 2 O 2 )] [Mn(C 32 H 20 N 2 O 2 )] [Zn(C 32 H 20 N 2 O 2 )] Thermal analysis The thermogram of ligand with the molecular formula (C 32 H 22 N 2 O 2 ) shows two decomposition steps within the temperature range from C. The first step occurs within the temperature range C with an estimated mass loss 44.00% (calculated mass loss = 43.28) which is reasonably accounted for the loss of naphthalene groups. The second step occurs within the temperature range C with an estimated mass loss of 56.00% (calculated mass loss = 55.72%), which is reasonably accounted for the loss of aromatic ligand groups. The TG curves of the copper(ii) complex with the molecular formula [Cu(C 32 H 20 N 2 O 2 )] is thermally decomposed in single step in the temperature range from C with an estimated mass loss 47.12% (calculated mass loss = 47.15%), which is attributed to the loss of naphthalene groups and aromatic ligand groups. The last step did not finish completely. Therefore, last decomposition residue was not determined. The TG curves of the nickel(ii) complex with the molecular formula [Ni(C 32 H 20 N 2 O 2 )] is thermally decomposed in single step in the temperature range from C with an estimated mass loss 53.94% (calculated mass loss = 52.78%), which is attributed to the loss of naphthalene groups and aromatic ligand groups. The last step did not finish completely. Therefore, last decomposition residue was not determined. The TG curves of the manganese(ii) complex with the molecular formula [Mn(C 32 H 20 N 2 O 2 )] is thermally decomposed in single step in the temperature range from C with an estimated mass loss 65.13% (calculated mass loss = 65.70%), which is attributed to the loss of naphthalene groups and aromatic ligand groups. The last step is MnO residue. IJPT Oct-2012 Vol. 4 Issue No Page 4638

10 The TG curves of the Zinc(II) complex with the molecular formula [Zn(C 32 H 20 N 2 O 2 )] is thermally decomposed in single step in the temperature range from C with an estimated mass loss 45.26% (calculated mass loss = 45.55%), which is attributed to the loss of naphthalene groups and aromatic ligand groups. The last step did not finish completely. Therefore, last decomposition residue was not determined. Magnetic moment studies The magnetic susceptibility measurements provide information regarding the structure of the metal complexes. Magnetic susceptibility was determined using a magnetic susceptibility balance. The magnetic moment data of the solid-state complexes were recorded at room temperature. The magnetic susceptibility measurements show that the complexes are paramagnetic at ambient temperature. The magnetic moment values of copper(ii) complex is 1.70 B.M. indicates square planar geomentry and Manganese(II) complex is 5.87 indicates square planar geometry [16]. EPR spectra The EPR spectra of complexes provide information of importance in studying the metal ion environment. The EPR spectra of the [Cu(C 32 H 20 N 2 O 2 )] and [Mn(C 32 H 20 N 2 O 2 )] Schiff base complexes recorded on powder samples with room temperature, on X-band at frequency 9.3 GHz under the magnetic field strength 4000G. The EPR spectrum of the [Cu(C 32 H 20 N 2 O 2 )] complex shows a broad signal with g iso at , which is consistent with an square planar geometry. The broadening of this signal might be due to dipolar interactions, indicating lowered site symmetry suggesting that the unpaired electron resides mainly in the dx 2 -dy 2 orbital. This indicates a considerable exchange interaction in the complex [17]. In a similar fashion, a single unresolved signal observed in the [Mn(C 32 H 20 N 2 O 2 )]. In the present case, the g iso value is found to be , which can be corroborated with a square planar environment. Antimicrobial activity The synthesized schiff base ligand and its metal complexes were tested against the bacteria species like Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus. The comparison of biological activities of the ligand is complexes show the following results. The free ligand having some biological activity because of nitrogen present in the ligand molecule. The free ligand and metal complexes show moderate activity because of chelation [18]. The IJPT Oct-2012 Vol. 4 Issue No Page 4639

11 minimum inhibitory concentration (MIC) values of the investigated compounds are summarized in tables 7. The values indicate that most complexes have higher antimicrobial activity than the free ligand. Such increased activity of the metal chelates can be explained on the basis of chelation theory. 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 the positive charge of the metal ion with donor groups. Further, it increases the delocalization of π-electrons over the whole chelate ring and enhances the penetration of the complexes into lipid membranes and blocking of the metal binding sites in the enzymes of microorganisms. These complexes also disturb the respiration process of the cell and thus block the synthesis of proteins, which restricts further growth of the organism [19]. Table-6: Electrochemical data of Schiff base metal complexes in DMF medium (oxidation). Complexes E pc (V) E pa (V) E 1/2 (V) E (mv) [Cu(C 32 H 20 N 2 O 2 )] [Ni(C 32 H 20 N 2 O 2 )] [Mn(C 32 H 20 N 2 O 2 )] [Zn(C 32 H 20 N 2 O 2 )] Table-7: Antibacterial activity of the Schiff base metal complexes. IJPT Oct-2012 Vol. 4 Issue No Page 4640

12 Figure-1: Synthesis of Schiff base ligand. Figure-2: Synthesis of Schiff base metal complexes. IJPT Oct-2012 Vol. 4 Issue No Page 4641

13 Figure 3: The EPR spectrum of the [Cu(CC 32 H 20 N 2 O 2 )] complex at room temperature, Frequency = GHz. Figure 4: The EPR spectrum of the [Mn(C 32 H 20 N 2 O 2 )] complex at room temperature, Frequency = GHz. Klebsiella pneumoniae Zone of Inhibition (mm) Compounds μl 75 μl 25 μl 50 μl 75 μl 100 μl IJPT Oct-2012 Vol. 4 Issue No Page 4642

14 P. Subramanian* et al. /International Journal Of Pharmacy&Technology Zone of Inhibition (mm) Escherichia coli μl μl μl μl 75 μl μl 4 5 Compounds Zone of Inhibition (mm) Staphylococcus aureus μl μl μl μl 75 μl μl 4 5 Compounds Figure 5: Difference between the antimicrobial activities of the trinuclear Schiff base metal complexes.1. complexes Ligand, 2. [Cu(C32H20N2O2)], 3. [Ni(C32H20N2O2)], 4. [Mn [Mn(C32H20N2O2)], 5. [Zn(C32H20N2O2)]. Conclusion In this report, coordination chemistry of a Schiff base ligand, obtained from the he reaction of 2-hydroxy1naphthaldehyde and 1, 8-diaminonaphthalene diaminonaphthalene is described. Cu(II), Ni(II), Mn(II) and Zn(II) complexes have been synthesized using the Schiff base ligand and characterized by spectral and analytical data. Based on these data, a square planar geometry has been assigned to the complexes complexes. The metal complexes have higher antimicrobial activity than the ligand. IJPT Oct-2012 Vol. 4 Issue No Page 4643

15 References P. Subramanian* et al. /International Journal Of Pharmacy&Technology 1. M.K. Taylor, J. Reglinski, D. Wallace, Polyheron 23 (2004) S. Yamada, Coordin. Chem. Rev. 192 (1999) Z. M. Zaki, S. S. Haggag and A. A. Soayed, Spectroscopy Letters, 31 (1998) C. K. Bhaskare and P. P. Hankare, J. Ind. Chem. Soc., 72 (1995) W. S. Sawodny and M. Riederer, Angew. Chem., Int. Edn. Engl., 16 (1977) E. L. Hegg, S. H. Mortimore, C. L. Cheung, J. E. Huyett, D. R. Powell and J. N. Burstyn, Inorg. Chem., 38 (1999) V. L. Pecoraro, M. J. Baldwin and A. Gelaso, Chem. Rev. 94 (1994) S. Chandra, L.K. Gupta, Spectrochim. Acta Part A, 2004, Vol 60, pp G. G. Mohamed, M. M. Omar, A. A. Ibrahim, Spectrochim. Acta Part A., 75, 678 (2010). 10. R. Ramesh, K. Natarajan, Synth. React. Inorg. Met-Org. Chem. 26(1996) R. Ramesh, N. Dharmaraj, R. Karvembu, K. Natarajan, Ind. J.Chem. 39A (2000) S. Chandra, R. Kumar, Transition. Met. Chem., 29, 269 (2004). 13. F. Akagi, Y. Michihiro, Y. Nakao, K. Matsumoto, T. Sato, W. Mori, Inorg. Chim. Acta., 357, 684 (2004). 14. L. V. Ababei, A. Kriza, A. M. Musuc, C. Andronescu, E. A. Rogozea, J. Therm. Anal. Calorim, doi /s z (2009). 15. S. Chandra, S. D. Sharma, Transition. Met. Chem., 27, 732 (2002). 16. S. Djebbar-Sid, O. Benali-Baitich, J. P. Deloume, Transition. Met. Chem., 23, 443 (1998). 17. S. Khan, S. A. A. Nami and K. S. Siddiqi, Spectrochim. Acta A., 68 (2007) N. Raman, J. Dhaveethu Raja and A. Sakthivel, J. Chem. Sci., 119 (2007) N. Dharmaraj, P. Viswanathamurthi, K. Natarajan, Trans. Met. Chem., 26 (2001) 105. Corresponding Author: P. Subramanian* IJPT Oct-2012 Vol. 4 Issue No Page 4644