Synthesis, Spectral and Biochemical Studies of New Complexes of Mixed Ligand Schiff Base and Anthranilic Acid

Introduction 

Schiff base stands for an imperative type of ligand in chemical coordinating to find comprehensive enforcement in diverse domains as biological, inorganic, analytical, and artificial chemistry branches.^1,2 Schiff bases are derived from aromatic-carbonyl compounds, and they have been more studied in linkage with metal ion.³ Tetra dentate schiff bases (L₁-L₃), which drevied from the reaction of  o-phthalaldehyde with 2-amino benzyl alcohol, 2-amino-2-methyl-1-propanol, and 2-aminobenzohydrazine,have been reacted with [RuCl₂(DMSO)₄]. The prepared ligand and their complexesare characterized by spctroscopic methods.⁴ Macrocyclic Schiff Basic metal complexes, derived from o-pathalaldehyde, have recently been reported by Shaker and et al., through Template  method.⁵ New three complexes are prepared from o-phthalaldrhde with coblt(II), nickel(II) acetate and perchlorate salts VO(II). The complexes are diagnosed by physiochemical instrument molar conductivity, FTIR, and elemantal analysis.⁶ Studies towards synthesis of new coordination compounds and their catalytic activities have been continued. Ponnusamy and co-works synthesized (N₄ and N₂O₂) tetradentate ligands of the o-pathalaldehyde (o-PA) by the non-mould method, and Co, pd and Ru complexes.⁷ Schiff base ligand is derived from the concentration of o-phthalaldehyde with the glycyl glycine amino acid. The data have been described using analytical, spectral, thermal, and magnetic data. Furthermore, these mineral complexes have also been applied as potential antibacterial agents.⁸ Synthesis and catalytic applications of the schiff base ligand with metal (II) transition are derived from o-pthalaldehyde.⁹ In this work, we have prepared and characterized new complexes with mixed ligand schiff base and anthranilicacid with some metal ions.

Materials and Devices 

All chemicals, used in laboratory work,are of highest purity that does not need any further purity, and they have been purchased from distigushed sources. Melting points are carried out via Stuart Melting Point Kit. Elemental micro analysis of the ligand is conducted by Euro (EA 3000) instrument. ¹H NMR spectra are obtained using Brucker DRX system (400 MHz). UV-Vis spectra are performed on a Shimadzu UV- 160A Ultra Violet-Visible Spectrophotometer in KBr discs on (4000-400) cm^-1 range. The IR-spectra are verifiedby FTIR- 8400S Spectrophotometer. Metal contents (A.A.S) of the complexes are carried out, using atomic absorption methodby means of AA 620G Shimadzu spectrophotometer. The Chloride substances of compounds are specifiedby testing all complexes and decomposed with Nitric acid, and diluted with water. Results of the magnetic measuresare found out by using Bruker BM6 instrument at room temperature and the Faraday’s method.

Synthesis of (N,N’E,N,N’E)-N,N’-(1,2-phenylenebis(methan-1-yl-1-ylidene))bis(4-nitroaniline) (L)

A solution of 4-nitroaniline (0.276g ,2mol) in 10 ml ethanol has beeninserted to a mixture solution of o-phthalaldehyde (0.134g, 1 mol) in 5ml ethanol and three drops of glacial acetic acid, and the product combination has been refluxed for 4h.¹⁰ The resulted brown  solid  is composed by filtration, recrystallisation from aceton absolute, and dried under m.p (189°C), yield 87% Schem-1.

Scheme 1: The synthesis route of the ligand L Click here to View figure

 

Synthesis of the Mixed Ligand Complexes

A solution of schiff base ligand (0.374g, 1mmol) in 5ml absolute ethanol, (anthranilic acid 0.274g and NaOH 0.08g) 2 mmol are added to stirred (1 mmol of metal chlorid) in 10 ml ethanol;0.126g Mn(II)chloride, 0.237g Co(II) chlorid.6H₂O,0.237g Ni(II) chloride.6H₂O, 0.17Cu(II) chlorid.2H₂O,0.201g Cd(II) chlorid.H₂O, and 0.272 g Hg(II) chlorid. The product mixture is stirred for sixty minutes and, then, the result is filtered and dried through anhydrous CaCl₂. The physical properties of schiff ligand and new compounds have been presented in table-1.

Biological Activity

The Schiff base and their metal compounds are investigated with four bacteria psuedomonas aruginosa, Escharia coli, Staphylococcus aureus and Streptococcus pyogenes by disc diffusion technique.The chemical solutions, used in the biological study, are prepared by using dimethyl sulfoxide (DMSO) as solvent, and they are  provided as a single concentration of  1×10^-3 M. The dishes are incubated at room temperature for 24 h. The inhibition zones (IZ) in  mm is formed after 24h as a criterion for the intensity of the synthetic chemical compound effect on the outgrowth of cultivated specific bacteria strains.

Figure 1: The synthesis route of [L1(M)(Anth)2] complexe Click here to View figure

 

Result and Discussion

Generally, all the complexes are soluble in DMSO and DMF but insoluble in water. The CHN analysis and the sensible features of the compounds are listed in table-1. The complexes can be symbolized as [M (L)(Anth)₂] when M=metal(II) ions, (L=Schiff base ligand), and (Anth= anthranilic acid).

Table 1: The details of Schiff ligand and new compounds

Complexes	code	M.wt	M.P oC	Color	Theoretical ( Calc.)
					C	H	N	O	M
C20H14N4O	L	347.35	187 – 189	Brown	64.17	3.77	14.97	17.10	—–
Mn (L)(Anth)2 C34H26MnN6O8	C1	701.54	250	Pail – brown	58.21	3.74	11.98	18.24	7.83 (7.03)
Co(L)(Anth)2 C34H26CoN6O8	C2	705.54	270	Brown	57.88	3.71	11.91	18.14	8.35 (7.32)
Ni (L)(Anth)2 C34H26NiN6O8	C3	705.30	250	Pail-brown	57.90	3.72	11.92	18.15	8.32 (7.03)
Cu(L)(Anth)2 C34H26CuN6O8	C4	710.15	230	Orange	57.50	3.69	11.83	18.12	8.95 (7.96)
Cd(L)(Anth)2 C34H26CdN6O8	C5	759.02	250	Pail-brown	53.80	3.45	11.07	16.86	14.81 (13.57)
Hg( L)(Anth)2 C34H26HgN6O8	C6	847.20	170 – 172	Dark brown	48.20	3.09	9.92	15.11	23.68 (22.23)

 

Mass Spectrum

Mass Spectrum of Schiff base ligand is carried out to determine its molecular weight and fragmentation pattern as explained in Figure-2 and table-2.^11,12

Figure 2: Mass spectrum of ligand Click here to View figure

 

Table 2: The fragmentation data for the (L)

L	Assignments	Peak m/z
	M= (C20H14N4O2)	373
	M- N2O4 = M1	281
	M1 – C6H4 = M2	206
	M2 – N=CH = M3	179
	M3 – C7H5N = M4	76

 

¹H-NMR Spectral Data of L

The ¹H-NMR spectrums of the synthesized Schiff base ligand (L) in DMSO-d₆are shown in Fig-3 and table -3. The singlet signal appeared at (δ= 2.45 ppm) can be assigned to the solvent DMSO. The multiple signals, ranged between (δ= 6.55-8.36), are assigned to the aromatic protons of the phenyl, and the doublet signal at (δ= 8.44) is attributed to the azomethine proton (HC=N) .^{13, 14}

Figure 3: 1H-NMR spctrum of ligand (L) Click here to View figure

 

Table 3: ¹H-NMR Spectral data for measured Land chemical shift in ppm

Ligand	Functional group	δ(ppm)
L	DMSO-d6	2.45
	Ar-H	6.55 – 8.36 (12H, m)
	N=C-H	8.44(2H, s)

 

FTIR Spectra

The FTIR spectrum of (L) is in KBr disc in range of  (4000-400) cm^-1. Figure-4 shows  the weak absorption band at 3111 cm^-1 which has been consigned for the (C-H) aromatic stretching vibration. The medium band at 1622 cm^-1 is assigned to the (HC=N) stretching vibration, and the band at 1577 cm^-1 is allocated for the (C=C) stretching vibration.¹⁵ The FTIR spectrum of Anthranilic acid shows bands of  υ(O-H),υ(NH₂), υ_as (COO), and υ_s (COO) at (3390) and (3324,3240), 1679, and 1486 cm^-1 respectively.¹⁶ In complexes, υ(O-H) is disappeared, and υ(NH₂) is shifted to higher frequencies for all complexes without C1 and C2, making NH₂ in an active location of coordinate. The bands of υ_as and υ_s(COO) in all these complexes shifted to higher frequencies for υ_asy (COO), and lower frequencies for υ_sym (COO).Therefore,the difference between Δ_as-s is equal to (235-247) cm^-1 that indicates the carboxlate ion coordination with the metal ions, and it is considered as mono dentatedonor.^17,18 New spectra have been appeared in the bands of all compounds in the regions (559-570) cm^-1 which refer to υ(M-O) mode.¹⁹ The bands at (486-489) cm^-1 refer to  υ(M-N) mode.^20,21

Figure 4: FTIR spectrum of ligand L Click here to View figure

 

Table 4: FTIR details of cm^-1 free ligands and its compounds

Comp.	υ(O-H)	υ(N-H)	υ(C-H) arom.	υ(COO) as & s	Δ as-s	υ(C=N)	υ(M-N)	υ(M-O)
L1	—-	—-	3111	—-	—-	1622	—-	—-
Anth	3390	3321 3210	2586	1679 1486	—–	——	—-	—-
C1	—	3305 3232	3143 3082	1693 1454	239	1654	559 536	489
C2	—-	3303 3224	3136 3086	1693 1458	235	1654	563	489
C3	—-	3363 3302	3120 3082	1693 1454	239	1654	567	489
C4	—-	3402 3275	3120 2924	1693 1458	235	1600	574	489
C5	—-	3360 3290	3136 3086	1693 1450	243	1654	574	489
C6	—-	3329 3263	3113 3078	1693 1446	247	1654	563	489

 

Electrnic Spectra, Molar Conductivity, and Magnetic Moments

The UV-Vis. band of ligand (L) is shown in Fig-5. The spectrum exhibits three peaks;  one of them is in (286 nm) due to (π→ π*) electronic shift while the others are in (345, and 358 nm) due to (n → π*) electronic shift.^22,23 The UV-Vis. spectrum of C1 complex shows five absorption peaks. The three absorption peaks at (264, 329 and 345) nm are due to intra ligand comparably with the spectrum of (L₁). The fourth absorption peak is at (380 nm ) assigned for charge transfer (C.T), and the last one has a weak intense peak at (448 nm), which indicates that there is a (d-d) electronic transition type⁶A₁g→⁴T₂g(G), and this proves an octahedral structure around Mn(II) complex.²⁴ The UV-Vis band of C2 compound has five absorption peaks; three absorption peaks are at (279, 327 and 347) nm assigned for  intra ligand, and two new absorption peaks, with weak intensity, are at (739 and 790 nm) due to (d-d) type⁴T₁g(F)→⁴A₂g(F) transition; this indicates that there is an octahedral structure around Co(II) complex.^25,26 The UV-Vis. band of C3 compound shows five absorption peaks,  the low absorption peaks are at (267 and 345) nm assigned for intra ligand. The absorption peak at (357 nm) is attributed to charge transfer (C.T). C3 has weak intensity (777 and 826) nm due to types ³A₂g(F)→³T₁g(F) and ³A₂g(F)→³T₂g(F)transitions, which support the existence of an octahedral structure around Ni(II) complex.²⁷ The UV-Vis. spectrum of C4 complex displays three absorption peaks; the highest absorption peaks at (345 nm )  is assigned to charge transfer (C.T), and the peak at (270 nm) is due to intra ligand. The third absorption peak with weak intensity at (800 nm ) is attributed  to²Eg→²T₂g. These peaks are congruencein location with the researches of octahedral Cu(II).²⁸ The UV-Vis. spectra of C5 and C6 complexes, show absorption peaks at (264 and 266) nm, respectively, and are assigned to intra ligand. The peaks at (342 and 345) nm are due to charge transfer (C.T) that shows diamagnetic as perspective from their electronic arranging. They support that there is an octahedral structure around Cd(II) and Hg(II) complexes.²⁹ The molar conductivities indicate that all complexes are non-electrolytes. Magnetic moment values show that there is an octahedral arrangement around the metal (II) ions [18] as revealed in table-4.

Table 4:  Spectral and magnetic moments (nm) of the complexes

Compounds	λmax.	ῡ cm-1	ϵ max. mol-1.L.cm-1	Assignments	Molar Cond.	µeff (BM)
L	286 345 358	34965 28986 27933	893 2019 1134	π    →     π* n    →      π* n     →     π*	—	—
C1	264 329 345 380 448	37879 30395 28986 26316 22321	1006 1783 1973 75 22	Intra-ligand Intra-ligand Intra-ligand C.T 6A1g → 4T2g(G)	0.95	5.72
C2	279 327 347 739 790	35842 30581 28818 13532 12658	1051 1228 1454 38 35	Intra-ligand Intra-ligand C.T. 4T1g(F) → 4A2g(f) 4T1g(F) → 4T2g(f)	1.09	4.72
C3	267 345 357 777 826	37435 28986 28011 12870 12107	1000 1635 1011 15 13	Intra-ligand Intra-ligand C.T. 3A2g(F)→ 3T1g(F)  3A2g(F)→ 3T2g(F)	1.83	4.61
C4	270 345 800	37037 28986 12500	1182 2023 49	Intra-ligand C.T. 2Eg → 2T2g	0.89	1.83
C5	264 342	37879 29239	1010 2312	Intra ligand C.T.	0.87	Dia.
C6	266 345	37594 28986	1143 2063	Intra ligand C.T.	1.57	Dia

 

Boiological Activity

The  schiff base ligand [L] and the corresponding metal compounds under study are tested against four antimicrobial activities; psuedomonas aruginosaand Escharia coli (G -), Staphylococcus aureus and Streptococcus pyogenes (G+) by plate well into agar nutrient method. Antimicrobial activity is expressed in millimeters (mm) by measuring the diameters of the inhibitory region and contrasting with the DMSO control; the values areexplained in Table -6,figure -5 and chart-1.^30,31

Table 5: Antibacterial performance of the ligand and their metal compounds

Comp.	Staphylococcus aureus	Streptococcus pyogenes	psuedomonas aruginosa	Escharia coli
DMSO	zero	zero	zero	Zero
L	zero	zero	zero	Zero
C1	zero	zero	zero	Zero
C2	16	14	20	17
C3	zero	zero	zero	Zero
C4	25	zero	zero	Zero
C5	30	21	17	20
C6	30	25	18	17

 

Figure 5: The zone of inhibition for all compounds Click here to View figure

 

Graph 1: The inhibition zones of the compounds Click here to View graph

 

Conclusion

The new Schiff base derived from o-phathalaldehyde with p-nitroaniline is synthesized and characterized. The results show the coordination of L format with metal ions through the N as a donor atom. The results of the electron spectra and the magnetic susceptibility of all complexes show that these complexes are of octagonal geometry. The composite compounds are studied as antimicrobial, and the results reveal that C2,C5 and C6 complexes have various activities against bacteria, while L, C1 and C2 are inactive against two types of bactria.

Acknowledgement                                                                                               

The authors express their sincere appreciation to Chemistry Department, College of Education for Pure Sciences in Ibn –Al Haitham, University in Baghdad, Iraq for the fiscalsupportof  this study.

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