1H NMR, Diffused Reflectance, Thermal Studies, ESR and Anti Microbial Activities of Schiff Base Derived from 5-Nitro Salicylaldehyde and p-Anisidine

Transition metal complexes of the type ML1 [Where M= Co(II),Ni(II),Cu(II) and Zn(II), L= Schiff base of 5 nitro -salicylaldehyde and panisidine were characterized by using 1 H NMR ,TGA, Diffused reflectance and ESR spectroscopy. On the basis of above studies Co(II), Ni(II) shows tetrahedral structure, Cu(II) and Zn(II) shows square planar structure.


INTRODUCTION
The co-ordination behaviour and synthesis of Schiff base has received much attention in recent years 1-3 because of their enormous uses. Mononuclear complexes derived from Schiff proved to be valuable catalysts in various organic reactions, especially in enantio selective transformation. 4 .Different Schiff bases and their metal complexes find applications in tuberculosis 5 and as anticonvulsant 6 . Schiff base of 5-Nitro-Salicylaldehyde, P-Anisidine and its metal complexes of Co(II),Ni(II),Cu(II) and Zn(II) with their characterization by using elemental analysis , UV-Visible, IR, X-Ray diffraction were already reported by this lab 7 In this paper we are reporting further investigation of the Schiff base and its metal complexes by using 1 H NMR ,TGA, Diffused reflectance and ESR spectroscopy.

H NMR spectrum of the [Co(L ) 2 ] complex
In the 1 H NMR spectrum of the [Co(L 1 ) 2 ] complex the signals due to OH protons is absent, Suggesting the deprotonation -OH group attached to benzene ring in the Schiff base. This confirms the coordination of the ligand to the metal ion through phenolic oxygen atom [12][13] . The singlet due to azomethine proton at 9.20 ppm is deshielded and appears at 9.38 ppm indicates that azomethine group is coordinated to Co(II) ion through nitrogen atom. Multiple signals in the region of 7.00-8.60 ppm are assigned to aromatic protons [10][11] .

H NMR spectrum of the [Ni(L ) 2 ] complex
In the 1 H NMR spectrum of the [Ni(L 1 ) 2 ] complex the signals due to OH proton is absent. Suggesting the deprotonation -OH group attached to benzene ring in the Schiff base. This confirms the coordination of the ligand to the metal ion through phenolic oxygen atom [12][13][14] . The singlet due to azomethine proton at 9.20 ppm is deshielded and appears at 9.60 ppm indicates that azomethine group is coordinated to Ni(II) ion through nitrogen atom.Multiple signals in the region of 7.00-8.60 ppm are assigned to aromatic protons [10][11] .

H NMR spectrum of the [Cu(L ) 2 ] complex
In the 1 H NMR spectrum of the [Cu(L 1 ) 2 ] complex the signals due to OH protons is absent. Suggesting the deprotonation of-OH group attached to benzene ring in the Schiff base. This confirms the coordination of the ligand to the metal ion through phenolic oxygen atom International Letters of Chemistry, Physics and Astronomy Vol. 48 [14][15][16] . The singlet due to azomethine proton at 9.20 ppm is deshielded and appears at 9.40 ppm indicates that azomethine group is coordinated to Cu(II) ion through nitrogen atom [17][18] . Multiple signals in the region of 7.00-8.60 ppm are assigned to aromatic protons [10][11] .

H NMR spectrum of the [Zn(L ) 2 ] complex
In the 1 H NMR spectrum of the [Zn(L 1 ) 2 ] complex the signals due to OH protons is absent, Suggesting the deprotonation of -OH group attached to benzene ring in the Schiff base. This confirms the coordination of the ligand to the metal ion through phenolic oxygen atom [12][13] . The singlet due to azomethine proton at 9.20 ppm is deshielded and appears at 9.40 ppm indicates that azomethine group is coordinated to Zn(II) ion through nitrogen atom 19 . The representative 1 H NMR Spectra of the compound [Zn(L 1 ) 2 ] is as shown in the Fig.2.

Diffused Refluctance Spectra
Diffused reflectance spectrum of Schiff base L 1 Diffused reflectance spectrum is very important analytical tool for the diagnosis of various d-d transition and charge transfer spectra. The bands observed in the reflectance spectrum appears at 11481 cm -1 ,26525 cm -1 ,27472 cm -1 ,30303 cm -1 and 39215 cm -1 which may be assigned to n→π*, π→ π*and σ→ σ*. The position of these bands can be utilized for calculating shift in the corresponding position in the respective spectra of the metal complexes [20][21] .

Diffused reflectance spectrum of Schiff base [Co(L 1 ) 2 ]
The bands observed in the reflectance spectrum of the [Co(L 1 ) 2 ] complex of ligand shows absorption at 11723 cm -1 ,24154 cm -1 ,25906 cm -1 ,26525 cm -1 , 27932 cm -1 and 35587 cm -1 respectively which can be assigned to the transition 4 A 2 (F) → 4 T 1 (F), 4 A 2 (F) → 4 T 1 (P) and charge transfer bands. On the basis of paramagnetic nature and position of various d-d transition and charge transfer transition complex[Co(L 1 ) 2 ] may be assigned tetrahedral geometry 22,23,24,25 . The representative Diffused Reflectance Spectra of the compound [Co(L 1 ) 2 ]is as shown in the Fig.4.

Thermal decomposition studies of Cobalt(II) Complexes
The thermogram of [Co(L 1 ) 2 ] shows that the complex starts decomposing at the temperature corresponding to 400 0 C. Till this point there is no weight loss, horizontal nature of the curve up to 400 0 C indicate absence of coordinated water molecule. After this[Co(L 1 ) 2 ] complex shows sharp decrease in weight indicating decomposition of organic content of the metal complex, this loss and decomposition continue upto the temperature 600 0 C.The percentage weight loss of organic content from the Co(II) complex was found to be 87.53% which matches with the theoretical value (87.50%). After this the weight of the complex remains constant and the horizontal nature of the curve indicates the presence of thermally stable residual metal oxide [33][34].The percentage weight loss of the residual oxide was found to be 12.46% which is very close (12.50%). Thermal analysis further confirms our finding that coordinated water molecule is absent in [Co(L 1 ) 2 ] complex and Schiff base L 1 is bidentate ligand with O:N donar sequence and complex is having tetrahedral geometry.

Thermal decomposition studies of Nickel (II) Complexes
The thermogram of [Ni(L 1 ) 2 ] shows that the complex starts decomposing at the temperature corresponding to 300 0 C. Till this point there is no weight loss, horizontal nature of the curve upto 300 0 C indicate absence of coordinated water molecule. After this [Ni(L 1 ) 2 ] complex shows sharp decrease in weight indicating decomposition of organic content of the metal complex, this loss and decomposition continue up to the temperature 410 0 C. The

International Letters of Chemistry, Physics and Astronomy Vol. 48
percentage weight loss of organic content from the Ni(II) complex was found to be 87.53% which matches with the theoretical value(87.50%). After this the weight of the complex remains constant and the horizontal nature of the curve indicates the presence of thermally stable residual metal oxide [33][34].The percentage weight loss of the residual oxide was found to be 12.46% which is very close (12.50%).
Thermal analysis further confirms our finding that coordinated water molecule is absent in [Ni(L 1 ) 2 ] complex and Schiff base L 1 is bidentate ligand with O:N donar sequence and complex is having tetrahedral geometry. Fig.5 represents the TGA Curve of the compound [Ni(L 1 ) 2 ] .

Thermal decomposition studies of Copper (II) Complexes
The thermogram of [Cu(L 1 ) 2 ]shows that the complex shows decomposition at 300 0 C. After this Organic content of the metal complex is removed during this loss, decomposition continue up to the temperature 500 0 C. The percentage weight loss of organic content from the Cu (II) complex was found to be 86.86% which matches with theoretical value(86.73%). After this, weight of the complex remains constant and the horizontal nature of the curve indicates the presence of thermally stable residual metal oxide 35-36. (CuO). The percentage weight of the residual metal oxide was found to be 13.13% which matches with theoretical value (13.26%). Thermal analysis further confirms our finding that coordinated water molecule is absent in the of [Cu(L 1 ) 2 ] metal complex and Schiff base L 1 is bidentate ligand with O:N donar sequence and complex is having square planar geometry.

Thermal decomposition studies of Zinc (II) Complexes.
The thermogram of [Zn(L 1 ) 2 ]shows that the complex shows decomposition at 330 0 C. After this Organic content of the metal complex is removed during this loss, decomposition continue up to the temperature 800 0 C. The percentage weight loss of organic content from from the Zn(II) complex was found to be 86.86% which matches with theoretical value(86.73%). After this weight of the complex remains constant and the horizontal nature of the curve indicates the presence of thermally stable residual metal oxide 35-36. (ZnO). The percentage weight of the

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Volume 48 residual metal oxide was found to be 13.13% which matches with theoretical value(13.26%). Thermal analysis further confirms our finding that coordinated water molecule is absent in the [Zn(L 1 ) 2 ] metal complex and Schiff base L 1 is bidentate ligand with O:N donar sequence and complex is having square planar geometry

Esr spectral studies of copper (II) complex
This technique is used to detect the presence of unpaired electron in a metal cluster. The x-band ESR Specrum of [Cu(L 1 ) 2 ] complex exhibit a single line resulting the interaction of unpaired electron present in the Cu(II) complex. The table reveals that g ┴ factor is found to be 1.9350, while g║ factor is found to be 1.8549. The g║ value is less than 2.3 which suggest existence sufficient co-valency in the [2Cu(L) 2 ]. The solid state ESR spectrum of [2Cu(L) 2 ] complex at room temperature yielded a broad signal with g.avg.= 1.9083, indicating unpaired electron lie in d x2-y2 orbital of Cu(II) complex. 38,39,40 . Fig.6 represents the ESR Spectra of the compound [Cu(L 1 ) 2 ].

Biological Studies of Schiff Base L 1 And Co(Ii),Ni(II),Cu(II) and Zn(II) Metal Complexes
The concentration used for testing 5.0mg/ml, 2.5mg/ml and 1.25mg/ml in DMF. The results from the table reveals that the ligand is inactive towards all the fungi as well as bacterial strains. All the metal complexes were found to have excellent fungi toxic properties even after decreasing concentration of metal complex in the test sample, activity almost remains samewith slight decrease. Thus we can conclude that at low concentration metal complexes are most active against fungal and bacterial strains as desirable.In general metal complexes are more active than their parent ligand and hence may serve as vehicle for activation of the ligand as principle cytotoxic species. 12,41,42.

CONCLUSION
On the basis of 1 H NMR, Diffused reflectance data and Thermo gravimetric studies , Co(II),Ni(II shows tetrahedral structure where as Cu(II) and Zn(II) exhibits square planar structure.