Synthesis, Characterization Study of Schiff Base Complexes Derived from Ampicillin and 4 Hydroxy3-Methoxy Benzaldehyde

Introduction

Schiff bases are compounds that are derived by condensation reaction of primary amines with carbonyl groups (Abbas H Abdulasada et al., 2018). Schiff base ligand are ‘privileged ligands’ and are able to stabilize different metals in various oxidation states. It are extensively studied due to synthetic flexibility, selectivity and sensitivity towards variety of metal ions. It have application towards, degradation of organic compounds, radiopharmaceuticals and as corrosion inhibitors in especially acidic environments for various alloys and metals like steel, aluminium and copper Complexes of transition and non-transition metals with schiff base ligands are promising materials for opto electronic applications due to their outstanding photo and electroluminescent properties and the case of synthesis that readily allows structural modification for optimization of material properties. Various transition and inner transition metals complexes with bi, tri-and tetradentate schiff bases containing nitrogen and oxygen donor atoms play important role in biological systems and represent interesting models for metalloenzymes, which efficiently catalyze the reduction of dinitrogen and dioxygen (Mohammed Shakir, 2010). The schiff base derivatives are infer in the field of optical chemistry and biochemistry. It have been utilized as synthons in the preparation of a number of industrial and biologically active compounds like formazans, 4-thiazolidinines, benzoxazines and so forth, via ring closure, cycloaddition and replacement reaction (Anu Kajal et al., 2013), (Jarrahpur.A et al., 2007).

Literature Review

The articles related to the present study were reviewed for more clearance of the study

Materials And Methods

Synthesis Of Schiffbase Ligand (Ahmb)

The synthesis of ligand AHMB held as follows. To an ethanolic solution ofAmpicillin (0.05 mol) in alkali medium and 4-hydroxy3-methoxy benzaldehyde (0.05 mol) in 10 ml ethanolic solution was droped with constant mixing and heated under reflux for 2 hours on a heating mentle at 60°C(Isac Sobana Raj, et al., 2015). Then, the reaction mixture was cooled by pouring it into cool water Fine shinning yellow precipitate of (AHMB) formed was filtered off, washed thoroughly with ethanol-water and stored in a vacuum decicator to dry.

Synthesis of [M(AHMB)₂ (NO₃)₂] complexes

The Schiff basetransition metal complexes were synthesized as per the following literature procedure (Issac Sobana Raj et al., 2015). A 0.1 mol of ligand (AHMB) was dissolved in 10 ml of ethanol. To this a solution of 0.05 mol M(NO₃)₂.XH₂O (where M = Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) in 10 ml water, ratio of 2:1 was added drop by drop with constant stirring under relux for 10-12 hours in a heating mantle at 60-70°C. The product was cooled by pouring it into cool water.  A fine precipitate complexes formed was filtered off and dried.

Findings and Analysis

Molar conductivity of complexes

Molar conductivity of the transition metal complexes synthesised were measured using a systronic conductivity bridge type 305. Ethanol was the solvent, the observed values in the range 47-63 ohm^-1cm²mol^-1 are tabulated in the table given below.

Table 1: Molar conductance of AHMBL ligand and their metal complexes

S. No.	Denotion of compounds	Molar conductance (ohm-1 cm2mol-1)
1	AHMBL	–
2	Mn(AHMBL)2(NO­3)2	52
3	Co(AHMBL)2(NO­3)2	47
4	Ni(AHMBL)2(NO­3)2	61
5	Cu(AHMBL)2(NO­3)2	56
6	Zn(AHMBL)2(NO­3)2	63

Molar conductivity values suggests that those are non-electrolytes.

FT-IR spectra

FT-IR spectroscopy technique was utilized for find the bonding nature of AHMBL and their transition metal complexes. The FT-IR spectrum of (AHMBL) and their metal complexes are shown in figure.1 – 6. The stretching representation was given in the table 2.

The FT-IR range at 1666 cm^-1 schiffbase ligand indicates the presence of (C – N) group. In following metal complexes this value varies from 15 to 20 cm^-1 indicates a strong double bond character of the imine band and the azomethine nitrogen atom has coordination with transition metal ion. This is also confirmed by the intensity band around 462 cm^-1 assigned to (M – N) vibration.

The broad band at 3332 cm^-1 of FT-IR shows the stretching frequency of hydroxyl compound. The band ranges from 3340 cm^-1 – 3325 cm^-1 exhibit the non-coordination of –H₂O molecules in metal complexes to the central metal ion. This also proved by the M – O vibrational bands from 598 cm^-1 – 586 cm^-1.

Table 2 : FT-IR data for ligand (AHMBL) and their transition metal complexes.

Ligand / Complexes	VC–H	VC=C	VC=N	VS=O	VO–H VH2O	VN–H	VNO2	Vm–N	Vm–O
AHMBL	3062.96	1519.91	1666.50	1381	3332.99	3471	1519
Mn(AHMBL)2(NO3)2	3093.82	1504.48	1650.79	1357	3341.44	3595	1504	462	586
Co(AHMBL 2(NO3)2	3032.96	1509.81	1648.50	1364	3345.12	3524	1509	455	596
Ni(AHMBL)2(NO3)2	3011.42	1491.71	1652.50	1329	3330.70	3499	1521	431	594
Cu(AHMBL)2(NO3)2	3071.21	1456.91	1653.50	1391	3325.24	3506	1532	462	598
Zn(AHMBL)2(NO3)2	3044.01	1479.12	1647.27	1346	3339.70	3571	1501	432	586

 

Figure 1: FT-IR spectrum of the schiff base ligand (AHMBL). Click here to View figure

Figure 2: FT-IR spectrum of the [Mn(AHMBL)2 (NO3)2] complex. Click here to View figure

Figure 3: FT-IR spectrum of the [Co(AHMBL)2 (NO3)2] complex. Click here to View figure

Figure 4: FT-IR spectrum of the [Ni(AHMBL)2 (NO3)2] complex. Click here to View figure

Figure 5: FT-IR spectrum of the [Cu(AHMBL)2 (NO3)2] complex Click here to View figure

Figure 6: FT-IR spectrum of the [Zn(AHMBL)2 (NO3)2]complex Click here to View figure

Electronic spectra

To find  information regarding the coordination geometry, electronic spectra of the synthesised complex were determined with DMF at normal temperature notices and compared  with magnetic moment values and parameters. The observed data was given in table 3. Low intensity absorption bands and low molar extinction belongs to d-d-electron transition.

The colour of synthesised ligand (AHMBL) is yellow and the metal complexes synthesised from the schiff base ligand (AHMBL) are different and also it differ from the corresponding metal ions, it seems the properties of the metal complexes are different from its corresponding metal ions.

The schiff base ligand (AHMBL) showed two different absorption bands at 251nm and 330 nm assigned (p-p*) electronic transition and (n – p*) electronic transition.

In the observation ligand has two absorption bands assigned to p-p* and n-p* transitions. The spectra of metal complexes also has the same transitions, but they shifted lower and higher frequencies confirming the coordination of ligand with transition metal ions.

Metal complex [Mn(AHMBL)₂(NO₃)₂], showed four absorption bands. Two are of low wavelength shows the presence of (p-p*) and (n-p*) transition. The third and fourth are at low intensity and high wavelength region that is 414 nm and 502 nm are attributed to charge transfer which is (⁶A_1g – ⁴A_1g, ⁶A_1g®⁴E_g) electronic transitions assumed the complex is high spin octahedral geometry.

The metal complex [Co(AHMBL)₂ (NO₃)₂], showed five absorption bands. Two bands are low wavelength which are in UV-region that is 312 nm, 347 nm shows (p-p*), (n-p*) transitions. The other are in visible region are 417 nm, 556 nm, 639 nm can be assigned the charge transfer of ⁴T_1g®⁴T_2g(F), ⁴T_1g®⁴A_2g(F), ⁴T_1g®⁴T_1g(P). This showed it is octahedral geometry.

The electronic spectrum of [Ni(AHMBL)₂(NO₃)₂] also showed five bands. Two were in UV-region and the other three in visible region appeared at 417 nm, 584 nm, 761 nm) which showed the charge transfer ³A_2g(F) ®³T_2g(F), ³A_2g(F) ®³T_1g(F), ³A_2g(F) ®³T_1g(P) (d-d) electronic transition. These showed Ni(II) complex showed octahedral geometry.

The Cu(II) complex of synthesised ligand has  three electronic spectrum, one with low intensity at 771 nm to charge transfer ²E_g®²T_2g electronic transition, suggested octahedral geometry.

Electronic spectrum of Zn(II) complex produced only two bands in UV region and there is no absorption in visible region because of completely filled d-orbitals. The geometry of Zn(II) complex is octahedral.

Table 3: Electronic spectral data of ligand (AHMBL) and their complexes.

Ligand / complexes	lmax (nm)	Electronic transition	Charge transfer	Geometry
AHMBL	251 330	p-p* n-p*
Mn(AHMBL)2(NO3)2	272, 314 414. 502	p-p* n-p*	6A1g®4TAg 6A1g ®4Eg	Octahedral
Co(AHMBL)2(NO3)2	312, 347 471, 556, 639	p-p* n-p*	4T1g®4T2g(F) 4T1g®4A2g(F) 4T1g®4T1g(P)	Octahedral
Ni(AHMBL)2(NO3)2	269, 352 471, 584, 761	p-p* n-p*	3A2g(F) ®3T2g(F) 3A2g(F) ®3T1g(F) 3A2g(F) ®3T1g(P)	Octahedral
Cu(AHMBL)2(NO3)2	287, 366 771	p-p* n-p*	2Eg®2T2g	Octahedral
Zn(AHMBL)2(NO3)2	264 363	p-p* n-p*	No d-d transition	Octahedral

 

Magnetic Susceptibility Measurements

The magnetic susceptibility value of metal complexes synthesised from schiff base ligand (AHMBL) are given below.

Table 4: Magnetic susceptibility values of metal complexes.

Ligand / complexes	meff(BM) calculated	meff(BM) observed
Mn(AHMBL)2(NO3)2	5.41	5.33
Co(AHMBL)2(NO3)2	4.29	4.64
Ni(AHMBL)2(NO3)2	3.06	3.73
Cu(AHMBL)2(NO3)2	1.83	2.11
Zn(AHMBL)2(NO3)2	Diamagnetic	Diamagnetic

 

The magnetic moment of Mn(II), Co(II) and Ni(II) complexes of ligand shows high spin octahedral geometry. But Cu(II) complex shows low magnetic moment indicates low spin distorted octahedral geometry Zn(II) complex shows zero magnetic moment because of d¹⁰ system of electronic configuration.

¹H NMR spectra

¹H NMR spectrum of synthesised ligand (AHMBL) and its Zn(II) metal complex were recorded in chloroform solution (CDCl₃). Tetramethyl silane (TMS) calibrate the chemical shits of each analyte proton which act as internal standard.

The figure 4.8 and 4.9 showed the recorded signals of ¹H NMR spectrum of ligand and metal complexes. In ligand a singlet at d = 12.12 ppm was attributed to hydrogen of Ar(OH) group. A signal at d = 8.127 ppm showed azomethine proton (N = CH). A strong signal appeared between d(3-4 ppm, 2H) was due to excess phenyl amine group.

The Zn(II) complex was examined and compared with ligand showed Zn(II) complex was shifted downfield compared ligand.

Figure 7: 1H NMR spectrum of schiff base ligand (AHMBL). Click here to View figure

Figure 8: 1H NMR spectrum of [Zn(AHMBL)2 (NO3)2] complex. Click here to View figure

From the data, the structure of coordinated metal complex compounds prepared from ligand (AHMBL) is shown in figure.

Figure 9: Structure of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complex of schiff base ligand (AHMBL). Click here to View figure

XRD Analysis

X-ray diffraction gives information about crystallographic structure, chemical composition and physical properties of materials. Examined value of powder XRD for the ligand (AHMBL) and its metal complex [Cu(AHMBL)₂(NO₃)₂] data are listed in table 5 and 6. The graphical representation showed feeble peaks for ligand which explains the microcrystalline nature of the sample and also the strong peak indicates the complex formation. Scherrer’s equation is used to determine the size of crystals in the form of powder.

where t – particle size, K = 0.9 (shape factor), l – X-ray wavelength, b – line broadening at half the maximum intensity, q – Bragg angle.

Table 5: XRD data of ligand (AHMBL).

Angle	Net Intensity	d – value (Å)	Gross intensity	Rel. Intensity %
60.353	84.319	1.5324	876.31	7.2
40.952	153.554	2.202	1899.26	13.2
35.838	195.479	2.5036	2112.34	16.7
34.101	283.079	2.6271	2237.80	24.2
32.171	387.908	2.7801	2348.19	33.2
31.535	413.233	2.8348	2366.93	35.4
29.685	484.775	3.0071	2395.60	41.5
28.471	443.607	3.1325	2307.12	38
26.443	248.274	3.3679	1998.81	21.3
25.791	143.680	3.4516	1848.90	12.3
22.611	268.710	3.9293	1732.02	23
21.482	423.427	4.1332	1793.91	36.3
20.413	330.275	4.3472	1600.78	28.3
20.216	291.133	4.3890	1541.95	24.9
19.365	249.550	4.5799	1410.62	21.4
17.122	133.259	5.1745	1021.97	11.4
16.20	1167.51	5.4656	1929.72	100
15.532	141.180	5.7005	805.318	12.1
7.931	19.5284	11.1387	65.027	1.7

 

Table 6: XRD data of metal complex

Angle	Net Intensity	d – value (Å)	Gross intensity	Rel. Intensity %
42.410	116.485	2.1296	1545.00	23.4
28.335	496.990	3.1472	2074.92	100
19.010	209.704	4.6646	1093.29	42.2

 

Figure 10: Diffractogram of schiff base ligand (AHMBL). Click here to View figure

Figure 11: Diffractogram of [Cu(AHMB)2(NO3)2] complex Click here to View figure

SEM Analysis

SEM (Scanning Electron Microscopy) investigate a wide range of materials for surface fractures, flaws, corrosion or contaminants. It gives magnified images of the sample’s surface topography. The SEM images of ligand (AHMBL) and Ni(II) complex are shown in figure 12 and 13.

The figure showed the ligand look like cheese structure and metal complex looks graval like structure.

Figure 12: SEM pattern of ligand (AHMBL). Click here to View figure

Figure 13:  SEM pattern of metal complex Click here to View figure

Recommentations and Conclusions

The schiff base ligand AHMBsynthesised from  Ampicillin and 4-hydroxy,3-methoxy benzaldehyde. And Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal complexes were derived from AHMBL. They were characterized by following physic-chemical methods. FTIR, UV-Vis, H¹NMR spectroscopy, molar conductivity, magnetic moment data. The XRD and SEM analysis support to find the size and morphology of ligand and metal complexes. They were also recommended to study their biological activity for the pharmacological appliances.

Acknowledgement

We are grateful and thankful to the following organizations to carry out the analysis work. STIC Trivandram and SEM Instrumentation Centre, Alagappa University, Karaikudi.

Conflict to interest

The authors declare that they have no conflict of interest.

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