Accepted Manuscript Spectroscopic and structural studies of the Schiff base 3-methoxy-N-salicylidene-o-amino phenol complexes with some Transition metal ions and their antibacterial, antifungal activities M.M. Abo-Aly, A.M. Salem, M.A. Sayed, A.A. Abdel Aziz PII: DOI: Reference:

S1386-1425(14)01480-2 http://dx.doi.org/10.1016/j.saa.2014.09.122 SAA 12798

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

11 July 2014 8 September 2014 28 September 2014

Please cite this article as: M.M. Abo-Aly, A.M. Salem, M.A. Sayed, A.A. Abdel Aziz, Spectroscopic and structural studies of the Schiff base 3-methoxy-N-salicylidene-o-amino phenol complexes with some Transition metal ions and their antibacterial, antifungal activities, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.09.122

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Spectroscopic and structural studies of the Schiff base 3-methoxy-Nsalicylidene-o-amino phenol complexes with some Transition metal ions and their antibacterial, antifungal activities. M. M. Abo-Aly*, A. M. Salem, M. A. Sayed and A.A. Abdel Aziz Department of chemistry, Faculty of Science, Ain Shams University, Cairo, Egypt. Abstract Spectroscopic (IR, Raman, NMR, UV-visible, and ESR), and structural studies of the ligand 3-methoxy-N-salicylidene-o-amino phenol (H2L) and its

synthesized

complexes with some Transition metal ions (Mn(II), Co(II), Ni(II)), Cu(II) and Zn(II))

were recorded and analyzed. The magnetic properties and thermal

gravimetric analysis (TGA and DTA) were also measured for the complexes. The metal complexes were found to have The structural formula ML.H2O and the metal ions Mn(II), Co(II), Ni(II)) and Zn(II) were found to form tetrahedral complexes with the ligand whereas Cu(II) formed a square planar one. Antimicrobial activity of the ligand and its complexes were also investigated and discussed.

-----------------------------------------------------------------------------------------------Key words: IR, Raman, NMR, Salicylidene Schiff bases, complexes, assignment *For correspondence: E-mail:[email protected]

Introduction The Schiff bases are widely employed as ligands in complex formation. They coordinate with many transition metal ions producing metal complexes that display motivating physical, chemical, biological and catalytic properties [18]. Applications in analytical assessment require the presence of organic ligands as essential compounds of the measuring system. Schiff bases are also used as optical and electro sensors, as well as in various chromatographic methods, to enhance selectivity and sensitivity [9-11]. Schiff bases have likewise structural resemblance with natural biological systems [12, 13]. Many biologically vital Schiff bases exhibiting, antimicrobial, antibacterial, antifungal, anti-inflammatory and antitumor actions are reported in the literature [14-19]. Protonated Schiff bases is also involved in the chemistry of vision, where the reaction occurs between the aldehyde group of 11-cis-retinal and the amino group of the protein (Opsin) forming the rhodopsin visual pigment responsible for sending an impulse to the brain causing vision after light incidence [20]. The FTIR and Raman spectra of the ligand salicylidene-2-amino thiophenol (SATP) in the wave number 4000- 200 cm-1 are measured and assigned in terms of Cs- symmetry [21]. SATP complexes with Cu (II), Ni (II) are also synthesized and their structures are determined by elemental analysis, conductometric measurement, thermogravimetric analysis (TGA, DTA), UVVisible and FTIR spectra. The complexes are found to have the formula (ML.H2O) for Cu (II) and Ni (II) ions. The complexes of the ligand N-salicylidene-oaminophenol were prepared and their structures were found to be of the

formula (ML.H2O) in a tetrahedral or square planar environment where M= Zn, Cu, Ni, Co and Mn ions [22]. Recently, square planar complexes of Ni(II) with similar ligands as well as PPh3 were characterized [23]. In this study we consider the synthesis, characterization and the structure of the solid and solution state complexes formed between the transition metal acetate salts; Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) and the ligand 3-methoxy-Nsalicylidene-o-amino phenol which contain 3C-O groups available for coordination. In addition the Schiff base and its complexes were tested for antibacterial, antifungal activities. Experimental Materials 3-methoxy-salicylaldehyde (o-vanillin), 2-aminophenol, Eriochrome Black T (EBT), Muroxide, Co(CH3COO)2.4H2O, Zn(CH3 COO)2.2H2O, Cu(CH3COO)2.H2O, Ni(CH3COO)2.4H2O and Mn(CH3COO)2.4H2O were supplied from Aldrich. All solvents were of analytical grade. Instruments The IR measurements were carried out on a Unicam-Mattson 1000 FT-IR in KBr pellets (4000-400 cm-1). The Raman spectra were recorded on the dispersive Raman spectrometer of Santerra- Bruker, with a wavelength of 785 nm, laser power of 10 mW and a resolution of 9.18cm-1. Elemental analyses (CHN) were performed on a JEOL JMS-AX500 mass spectrometer. The 1HNMR measurements were done on a Spectrospin-Bruker AC 300 MHz spectrometer with DMSO-d 6 as a solvent and TMS as an internal reference. Molar conductivities of 1 x 10 −3 M DMSO complexes

in solution were measured on a Jenway 4010 conductometer. Electronic spectra were recorded in DMSO solution with a concentration (1.0×10−4 M) for the free ligand and its complexes using Shimadzu a UV-Vis 1800 spectrophotometer in the range 200800 nm. The thermal behavior of complexes under investigation was measured using thermogravimetric analysis (TGA) and differential thermal analysis (DTA) using a Shimadzu DT-50 thermal analyzer. The sample was analyzed in a platinum pan under N2 and the temperature was linearly increased by 10 oC min-1 over a temperature range 20–1000 oC. Magnetic moments of the paramagnetic complexes were determined on a Sherwood Scientific magnetic moment balance (Model No. MK1) at room temperature (25 oC) using Hg[Co(SCN)4] as a calibrant. Electron spin resonance (ESR) measurements of the solid complexes were recorded at room temperature on a Bruker EPR spectrometer at 9.706 GHz (X-band), the microwave power was 1.0 mW with 4.0 G modulation amplitude, using 2,2-diphenylpyridylhydrazone (DPPH) as a standard (g=2.0037). Antimicrobial Screening The in vitro antimicrobial activity of the ligand and its complexes toward two types of the bacteria: Staphylococcus aureus (gram +ve) and Escherichia coli (gram – ve) in Mueller Hinton-Agar medium and fungi: Aspergillus flavus and Candida albicans in Doxs medium was examined. The antibacterial and antifungal activities were tested at 20 mg/mL concentration in DMSO solvent. Antimicrobial activity of the tested samples was determined using a modified Kirby-Bauer disc diffusion method [24], 100 µL of the test bacteria or fungi were grown in 10 mL of fresh media

until their numbers reached approximately 108 cells/mL and 105 cells/mL for bacteria and fungi, respectively [25]. The microbial suspension was then spread on agar plates corresponding to the broth in which they were maintained. The bacterial strains; S. aureus and E. coli were incubated for 24 h at 37ºC and fungi strains; A. flavus and C. albicans were incubated at 25 °C and 30 °C for 48 h, respectively, then the diameters of the inhibition zones were measured in millimeters. Blank paper discs (Schleicher & Schuell, Spain) with a diameter of 8.0 mm were impregnated in 10 µL of tested concentration of the stock solutions. Standard antibacterial (tetracycline) and antifungal drug (amphotericin B) were used as references to estimate the effectiveness of the tested compounds under the same conditions. Activity was assessed by measuring the zone diameter indicating a complete inhibition (mm). 10 µL of solvent (DMSO) were used as a negative control. Finally the activity results are calculated as a mean of triplicates. Synthesis of the ligand The ligand H2L was synthesized as described in literature [26] according to the synthetic route shown in Scheme (2.1). To a hot ethanolic solution containing 100 mmol of the amine (o-amino phenol), 100 mmol of o-vanillin was added dropwise. The obtained yellow solution was refluxed for 2 h. After cooling, the orange precipitated schiff base was filtered, recrystallized from ethanol and then washed by diethyl ether. The schiff base was dried under vacuum over anhydrous CaCl2. The purity of the ligand was checked by TLC. Synthesis of the Complexes of the ligand H2L Cu(II), Co(II), Mn(II), Ni(II) and Zn(II) complexes were prepared by using the following general procedure: 10 mmol in 25 ml ethanol of metal salt was added to a

10 mmol in 25 ml ethanol hot solution of the ligand followed by refluxing for 6 hours. The volume of the obtained solution was reduced to one-half its original volume by evaporation. The precipitated product was then filtered, washed with hot ethanol and then hot 40-60 petroleum ether and finally dried under vacuum. The purity of the synthesized complexes was checked by TLC. Color, yield and melting point as given in Table 1 for each complex. The synthesis of complexes of H2 L ligand can be expressed by the equation. H2L+ M(CH3COO). xH2O = ML.H2O+2CH3COOH+(X-1)H2O

Determination of stoichiometry of complexes The metal to ligand ratio of the complexes was determined using Job’s continuous variation method [27]. A series of metal salt and ligand solutions with identical analytical concentrations (10-4 M) are mixed in such a way that the total volume and the total number of moles of reactants in each mixture are constant with changing the mole ratio of reactants. The absorbance of each solution was then measured at the maximum wavelength; the absorbance is plotted vs. the mole fraction of ligand (CL/ (CM+CL)). The resulting curve showed a maximum corresponding to the combining ratio of metal and ligand in the complex. Results and discussion In this work, new mononuclear complexes of Co(II), Cu(II), Ni(II), Mn(II) and Zn(II) ions with the neutral ONO donor tridentate Schiff base, 3-methoxy-Nsalicylidene-2-aminophenol (H2L) were synthesized. These complexes were

characterized by several analytical and spectroscopic techniques involving elemental analyses, FT-IR, Raman, 1 HNMR, ESR, UV–Vis spectra, magnetic moments and thermal studies. All the metal complexes are neutral, colored, air stable and insoluble in most solvents except DMF and DMSO. The molar conductivity (Λm) of 1×10-4 M solutions of the complexes in DMSO has been measured at 25 oC. The molar conductance values of the complexes had values in the range 0–32.5 µs.cm2.mol−1. These low values indicated that all complexes have none-electrolytic nature. The formation of 1:1 [M:L] ratio for all complexes was found using Job’s continuous variation method. Elemental analyses and some physical properties of the ligands and their complexes are listed in Table 1 Characterization of Ligands and their Complexes Spectroscopic Studies Infrared and Raman spectra The significant infrared bands of the Schiff base ligand and its metal complexes are listed in Table 2. Proposed assignment of the important IR and Raman bands has been made. The IR spectra of (H2L) and Zn(II) metal complex as an example are shown in Figs. 1 and 2, respectively. The IR spectra of the ligand showed a broad band of medium intensity at 3200 cm−1 for H2L ligand characteristic of H-bonded ν(O–H) of the phenolic groups. Comparison of the IR spectra of the metal complexes with those of the studied ligand showed that all complexes have a broad medium or strong band in the range 33843618 cm-1 attributable to ν(OH) of the coordinated water molecule in the complexes. In addition, the presence of one water molecule was proved by thermogravimetric analysis (vide infra). The involvement of the deprotonated phenolic-O groups in

chelation is confirmed by the observed shift of the two ν(C–O) expected for the ligand as coordination sites and its complexes as given in Table 2. The medium intense band observed at 1277 cm−1 for H2L was ascribed to the phenolic C–O stretching mode as in the case of salicylideneanilines containing one OH group [28]. This band is found at higher wave-numbers in the range 1284-1297 cm−1 in the IRspectra of the complexes showing the involvement of the phenolic oxygen in coordination. The other C-O group stretching is found at 1196 as a strong band and shifted also to higher wave-numbers, 1226-1267 cm−1, due to complex formation. These changes can be interpreted as proving the involvement of the phenolate oxygen atoms in coordination [21,22, 2 9]. The OH bending expected at about 1400 cm−1 is assigned to the IR band at 1357 cm−1 which disappeared by complexation. The free Schiff base displays a strong band at 1625 cm–1, corresponding to the C=N stretch of the free ligand [21,22, 29]. The νC=N of the ligand is shifted to 1605-1610 cm−1 region confirming the coordination of the C=N group to the metal ion for all the studied complexes [21,22, 29]. Moreover, the coordination of the azomethine nitrogen and phenolic oxygen's was supported by the appearance of two metal-ligand weak bands at 417-442 cm−1 and 511-532 cm−1 due to ν(M–N) and ν(M–O) [21,22, 29-31], respectively. The Raman spectra have also been measured for the ligand (Fig. 3) and its complexes, the Raman spectrum of the Zn(II) complex is given as an example, Fig. 4, its assignment is similar to that given for o-hydroxybenzylidene-o-hydroxyaniline [32]. The ν C=N was also shifted to lower wave-numbers at about 1600-1612 cm-1 from 1623 cm-1 as in the IR spectra. Also a new Raman line was found at about 600 cm-1 for all complexes which could be assigned a second ν M-O bond [32].

1

H NMR spectra Proof of the bonding type of the ligand is also confirmed by the 1 H NMR

spectra of the Schiff base in normal, deutrated solvent and its diamagnetic Zn(II) complex. The chemical shifts of the various types of protons in the 1H NMR spectra of the H2L ligand and its diamagnetic Zn(II) complex are given in Table 3 and displayed in Fig. 5. The 1HNMR spectrum of the parent schiff base H2 L showed two singlets at downfield values at δ 9.8 and 14.09 ppm which is attributed to two non Hbonded and the H-bonded phenolic -OH protons, respectively. The OH signals disappear with addition of the D2O confirming their assignment. The azomethine (CH=N) proton is observed as a singlet at δ 8.96 and the aromatic protons appear as multiplets of δ values in the range 6.82-7.39 ppm [33, 34]. One sharp singlet appeared at δ 3.8 ppm in the spectrum assigned to the protons of methoxy group [34]. For the Zn(II) complex the two OH protons of the ligand were absent displaying

the

chelation of the Schiff base via C–O groups of the deprotonated hydroxyl groups [33]. In case of Zn(II) complex of H2 L ligand, the protons signal of –OCH3 group at 3.8 ppm was unaffected by chelation indicating that it didn’t participate in coordination with the metal ion. The Mn(II), Co(II), Ni(II) and

Cu(II) complexes are

paramagnetic, so their 1HNMR spectra are Magnetic Studies and Electronic spectra In order to get information about the hyperidization and configuration of the complexes, the magnetic properties of the complexes were measured and the electronic spectra were obtained for the schiff base and its complexes and are given in Table 4.

The absorption spectra of the Schiff base ligand exhibited two high intensity bands around 226 nm and 346 nm assignable to π–π* transitions for the electrons on benzene rings and the C=N chromophore, respectively [21, 22]. These bands are red shifted due to the donation of a lone pair of electrons to the metal and hence the coordination of azomethine to the metal ions [21, 22]. All the complexes showed an intense broad band in the region 400-500 nm attributable to charge transfer transitions and d-d transitions were not observed [21, 22]. The magnetic moment values of complexes are in agreement with the proposed tetrahedral geometry for all studied metal ions except Cu(II) ion. The magnetic moment value of [CuL.H2O)] complex was 1.8 BM proving the presence of one unpaired electron per Cu(II) ion and suggesting a square-planar geometry [22]. The magnetic moments of the complexes [ML.H2 O)], M= Mn, Co, and Ni are listed in Table 4. The values found correspond to 5, 3 and 2 electrons, respectively indicating a tetrahedral configuration of the complexes. The Zn(II) complex is diamagnetic as expected for d10 configuration and, as expected, form a tetrahedral coordination in analogy with those described for Zn(II) complexes containing N–O Schiff bases [22, 33] and according to the molar ratio and all the above arguments a tetrahedral geometry was proposed for the Zn(II) complex. ESR spectra The ESR spectrum of Cu(II) complex, recorded in the solid state, is consistent with the square-planar geometry around each Cu(II) center in the complex [22, 35]. The ESR spectrum of CuL.H2O complex gives an anisotropic signal, Fig 6 with corresponding g-values as given in Table 5. The trend in the observed “g” values g || >

g⊥ > ge (2.0023) suggested that the unpaired electron lies mainly in the dx2−y2 orbital. For the reported Cu(II) complexes, g || < 2.3 value, confirming the covalent character of the metal-ligand bond. The axial symmetry parameter G value, which is a measure of exchange coupling interaction between two metal ions was calculated for Cu(II) ions via the equation, G = (g || -2)/ (g⊥-2) [36]. The calculated G value is higher than 4, suggestive a dx2–y2 ground state [37]. This result also indicates that the exchange coupling effects are not operative in the present complex [38]. The ESR spectra of the solid Mn(II), Co(II) and Ni(II) complexes at room temperature do not show ESR signal because a rapid spin lattice relaxation of the Co(II), Ni(II) and Mn(II) ions [22]. Thermogravimetric Studies Thermal analysis of the synthesized complexes indicated the presence of one coordinated water molecule. The decomposition mass losses were found in conformity with the formula weight of each proposed complex via the elemental analysis, Table 6. The elimination of one water molecule together with the ligand in a single step indicated that water molecules are strongly coordinated to the metal ions in all complexes due to the absence of strong steric effects. The above arguments and the elemental analyses indicated that H2L ligand behaves as a dibasic tridentate one coordinated tetrahedrally to the metal ions except Cu(II) ion which forms a square planar complex using two phenolic oxygen's and the nitrogen of the azomethine group and complete the coordination sites by one water molecule. Thus the proposed structures of the complexes are shown in Fig.7.

Biological applications of ligand H2L and its complexes

Antimicrobial activity of H2L ligand and its complexes The biological activity of the metal complexes is governed by the following factors (i) the chelate effect of the ligands, (ii) the nature of the donor atoms, (iii) the total charge on the complex ion, (iv) the nature of the metal ion, (v) the nature of the counter ions that neutralize the complex, and (vi) the geometrical structure of the complex [39]. Furthermore, chelation reduces the polarity of the metal ion because of partial sharing of its positive charge with the donor groups and possibly the p-electron delocalization within the whole chelate ring system that is formed during coordination [40]. These factors increase the lypophilic nature of the central metal atom and hence increasing the hydrophobic character and liposolubility of the molecule favoring its permeation through the lipid layer of the bacterial membrane. This enhances the rate of uptake/entrance and thus the antibacterial activity of the testing compounds. The schiff base H2L and its complexes (1-5) were tested for their inhibitory effects on the growth of bacteria: Staphylococcus aureus (G+) and Escherichia coli (G-) and fungi: Aspergillus flavus and Candida albicans because such organisms can achieve resistance to antibiotics through biochemical and morphological modification [41]. The antibacterial and antifungal activities of the new compounds are listed in Table 7. The results indicated that, Co(II), Cu(II) and Zn(II) complexes showed no activity whereas Mn(II) and Ni(II) complexes showed weak activity against A. flavus. With C. albicans only Cu(II) complex showed no activity and the other complexes had moderate activity. The different complexes exhibited weak to high activity against the bacterial strains when compared with standard tetracycline. The bactericidal activity of the complexes follow the order Co(II) > Ni(II) > Mn(II) > Cu(II) = Zn(II).

This would suggest that chelation could facilitate the ability of the complex to enter a cell membrane and can be explained by Tweedy’s chelation theory [42]. On chelation, the polarity of the metal ion will be reduced 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 p-electrons over the whole chelate ring and enhances the penetration of the complexes into lipid membranes with blocking of the metal binding sites inside 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 organisms [42]. The variation in the effectiveness of different compounds against different organisms depends on either the impermeability of the cells of the microbes or on differences in ribosome of microbial cells [40].

References

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[12] S. Patai (Ed.), the Chemistry of the Carbon-Nitrogen Double Bond, J. Wiley & Sons, London, 1970. [13] E. Jungreis, S. Thabet, Analytical Applications of Schiff bases, Marcell Dekker, New York, 1969. [14] S.N. Pandeya, D. Sriram, G. Nath, E. De Clercq, Pharm. Acta Helv. 74 (1999) 11. [15] S. N. Pandeya, D. Sriram, G. Nath, E. de Clercq, Arzneimittel Forsch. 50 (2000) 55. [16] W. M. Singh, B. C. Dash, Pesticides 22 (1988) 33. [17] J. L. Kelley, J. A. Linn, D. D. Bankston, C. J. Burchall, F. E. Soroko, B. R. Cooper, J. Med. Chem. 38 (1995) 3676. [18] G. Turan-Zitouni, Z. A. Kaplancikli, A. Özdemir and P. Chevallet, Arch. Pharm. Chem. Life Sci. 340 (2007) 586. [19] M. T. H. Tarafder, A. Kasbollah, N. Saravanan, K. A. Crouse, A. M. Ali, K. T. Oo, J. Biochem. Mol. BioI. Biophys. 6 (2002) 85. [20] F.A. Carry, Organic Chemistry. McGraw-Hill, 1992. [21] M. M. Aboaly, M. M. H. Khalil, Spectrosc. Lett. 34 (2001) 495. [22] A. A. Abdel-Aziz, A.N. Salem, M. A. Sayed and M. M. Abo-aly, J. Mol. Struct., 1010 (2012) 130. [23] M. MuthuTamizh, K. Mereiter , K. Kirchner, B. RamachandraBhat , R. Karvembu. Polyhedron 28 (2009) 2157.

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Figures

Fig. 1. FTIR spectrum of H2L schiff base ligand.

Fig. 2. FTIR spectrum of ZnL .H2 O complex.

Fig. 3. Raman spectrum of H2L Schiff base ligand.

Fig. 4. Raman spectrum of ZnL.H2 O complex. c

b

a

a

Fig. 5. 1 HNMR of a-H2L, b-H2L in D2O and c- ZnL.H2O complex.

400 300

Intensity

200 100 0 -1 0 0 -2 0 0 -3 0 0 -4 0 0 -5 0 0 20 0 0

25 0 0

3000

3500

4 00 0

4 50 0

50 0 0

(G )

Fig. 6. ESR spectrum of the CuL .H2 O complex.

OH2

OCH3

OH2

O M H3CO

M

O O

N

O

N

M= Cu(II)

M= Mn(II), Co(II), Ni(II), Zn(II)

Fig. 7. The proposed structures of the reported complexes of H2 L ligand.

Tables Table 1 Elemental analyses and some physical properties of H2L and its reported complexes. Compounds

M.P(o C)

Yield (%)

M.Wt

92

243.14

195-197

80

314.07

>300

88

318.07

>300

85

317.83

>300

[CuL (H2O)] (C14 H13NO4 )Cu

90

322.68

>300

[ZnL (H2O)] (C14 H13NO4)Zn

87

324.53

>300

(H2L) C14H13 NO3 [MnL (H2 O)] (C14H13NO4 )Mn [CoL (H2O)] (C14 H13NO4 )Co [NiL (H2 O)] (C14H13 NO4)Ni

Color C Orange

(Calculated) Found (%) H N

M

Λm (µs.cm2 .mol−1 )

69.51 (69.09) 54.22 (53.49) 50.79 (52.82) 50.92 (52.86)

5.80 (5.35) 3.48 (4.14) 3.17 (4.09) 4.69 (4.09)

6.25 (5.76) 4.59 (4.46) 3.55 (4.40) 4.37 (4.40)

-

-

18.33 (17.48) 18.75 (18.52) 19.05 (18.47)

9.3

Green

55.15 (52.06)

3.15 (4.03)

4.67 (4.34)

20.17 (19.68)

6.0

Yellow

52.70 (51.77)

3.26 (4.00)

4.49 (4.31)

21.20 (20.15)

5.1

Yellowish brown Deep brown Yellowish brown

32.5 8.5

Table 2 The infrared spectra (cm-1 , KBr) of H2 L and its reported complexes. Compound H2L [MnL(H2O)] [CoL(H2 O)] [NiL(H2O)] [CuL(H2 O)] [ZnL(H2 O)]

δOH

ν(C=N)

ν(C-O)

ν(M-O)

ν(M-N)

δ1357(m)

1625(s)

1277(m),1197s





3424(s, br.)b

-

1605(s)

1291(m),1232s

520(w)

427(w)

3384(s, br.)b

-

1607(s)

1297(m),1226s

532(w)

434 (w)

3618(w, br.)b

-

1607(s)

1284(m), 1227s

512(w)

435(w)

3431(s, br.)b

-

1607(s)

1291(m), 1267m

518(w)

442(w)

3432(m, br.)b

-

1610(s)

1290(m),1227 s

511(w)

417(w)

ν(OH) 3042(w, br.)

a

*s: strong, m: medium, w: weak, br.: broad. a: stretching frequency of phenolic-OH group of ligand. b: stretching frequency of OH of coordinated water molecule.

Table 3 The 1 H NMR spectral data (δ, ppm) of the ligand (H2L) and its reported Zn(II)complex.

Compound

OH (phenol )

CH=N

Aromatic protons

H3 C-attached

H2 L

14.09 (s), 9.80 (s)

8.96 (s)

6.82-7.39 (m)

to ring 3.8 (s)

[ZnL(H2 O)]

-

8.92 (s)

6.39-7.61 (m)

3.78 (s)

* s: singlet, m: multiplet.

Table 4 Characteristic electronic transition bands and magnetic moments of the H2 L ligand and its reported complexes. Compound

UV-Vis bands (nm, DMSO)

Assignments

µeff. (B.M)

H2L

226s, 346m

π→π∗, n→π∗

-

[CuL(H2 O)]

238m, 270vs, 440vs

π−π∗, n−π∗, CT

1.80

[NiL(H2 O)]

232m,264vs, 446vs

π−π∗, n−π∗, CT

3.94

[CoL(H2 O)]

242m, 268vs, 402s,br

π−π∗, n−π∗, CT

4.87

[MnL(H2O)]

268s, 298mbr, 442mbr

π−π∗, n−π∗, CT

5.85

[ZnL(H2 O)]

260s,304s, 434vs

π−π∗, n−π∗, CT

Dia

Table 5 ESR parameters of the Cu(II) complex of the H2 L ligand. Complexes

[CuL(H2 O)] gav. = 1/3(g⊥ +2 g||) b G = (g|| -2)/ (g⊥ -2) a

g||

g⊥

gav.a

Gb

2.09

2.02

2.07

4.5

Table 6 Thermogravimetric analysis of H2L complexes. Complex [Mn(L)(H2 O)] [Mn(C14 H13NO3 )(H2 O)] [Co(L)(H2O)] [Co(C14H13 NO3)(H2 O)] [Ni(L)(H2 O)] [Ni(C14 H13 NO3)(H2 O)] [Cu(L)(H2O)] [Cu(C14H13 NO3)(H2 O)] [Zn(L)(H2O)] [Zn(C14H13 NO3)(H2 O)]

Decomposition temp (oC)

Weight Loss (%)

Eliminated Species

Solid Residue

72.27

C14H11 NO + H2 O

MnO2

74.48

76.39

C14H11 NO2 + H2 O

CoO

209-684

72.66

76.45

C14H11 NO2 + H2 O

NiO

180-582

72.54

75.31

C14H11 NO2 + H2 O

CuO

347-806

74.39

74.87

C14H11 NO2 + H2 O

ZnO

Found

Calc.

220-733

71.65

253-668

Table 7 Antimicrobial activities of H2 L ligand and its reported complexes. Compounds

H2L2 [MnL2(H2 O)] (1) [CoL2 (H2O)] (2) [NiL2(H2 O)] (3) [CuL2 (H2O)] (4) [ZnL2 (H2 O)] (5) Tetracycline Amphotericin B DMSO

Diameter of inhibition zone (mm/mg sample) Antibacterial activity Antifungal activity S. aureus(G+) E.coli(G-) A. flavus C. albicans 12 11 10 11 15 15 10 12 16 17 0.0 13 17 15 10 14 13 13 0.0 0.0 13 13 0.0 12 28 30 20 21 0.0 0.0 0.0 0.0

Graphical abstract

Spectroscopic (IR, Raman, NMR, UV-visible, and ESR), and structural studies of the ligand 3-methoxyN-salicylidene-o-amino phenol (H2L) and its synthesized complexes with some Transition metal ions (Mn(II), Co(II), Ni(II)), Cu(II) and Zn(II)) were recorded and analyzed. OCH3

OH2

OH2

O M

M H3 CO

N

O O

O N

M= Cu(II)

M= Mn(II), Co(II), Ni(II), Zn(II)

Fig. (3.8): The proposed structures of the reported complexes of H2L ligand.

Highlight for review IR, Raman, NMR, UV-visible, and ESR of a Schiff base ligand and its complexes containing Two OH groups. Its biological importance.

Spectroscopic and structural studies of the Schiff base 3-methoxy-N-salicylidene-o-amino phenol complexes with some transition metal ions and their antibacterial, antifungal activities.

Spectroscopic (IR, Raman, NMR, UV-visible, and ESR), and structural studies of the ligand 3-methoxy-N-salicylidene-o-amino phenol (H2L) and its synthe...
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