Synthesis and Pharmacological Activity of Metal Complexes having Hydrazinobenzimidazole Based Ligands

Anand Mohan Jha1*, Madhu Bala2, K. K. Jha 3 & L. K. Mishra4

1&* Department of Chemistry, K. S. R. College, Sarairanjan, Samastipur-848127, INDIA

2 Department of Chemistry, National Institute of Technology, Patna-800005, INDIA

3 P. G. Department of Chemistry, Lalit Narayan Mithila University, Darbhanga-846004, INDIA

4 Department of Chemistry, Patna Science College, Patna-800005, INDIA

* Correspondence: E-mail: amjha6182@gmail.com

(Received 22 June, 2018; Accepted 09 July, 2018; Published 17 July, 2018 )

ABSTRACT: The complexes of N1 -{(1E)-1Hbenzimidazol2yl) ethylidene 2hydrazinobenzimidazole} (BahbH) with some transition metal ions of composition, M(BahbH)2Cl2 (M=MnII, CoII, Ni II), [M (BahbH)X2] (M=CuII and X=Cl or Br, when M=ZnII, Cd II, X=Cl or I) Cu (BahbH)I, Ag (BahbH) NO3, [M(BahbH)2] SO4.nH2O (M=Mn II, CoII or NiII and n=1 or 2) have been prepared and characterized by elemental analysis, and studies of IR, UV, Magnetic susceptibility values and electrical conductance measurements at room temperature. The magnetic and spectral properties of MnII, CoII and Ni II complexes are consistent with octahedral structure. The complexes [M(BahbH)X2] have five coordinated pseudo trigonal bipyramidal structure. The ligand and its complexes with CuII, MnII, FeII, ZnII, CdII and AgI were screened for their antifungal and antibacterial activities. The complexes showed positive antifungal and two strains of Proteins mirabilis and Bacillus subtilis.

Keywords: Metal complexes; antifungal activity; antimicrobial activity; Magnetic susceptibility; Electrical Conductance; Benzimidazole and Schiff base.

INTRODUCTION: Imidazole nuclei of benzimida-zole and substituted benzimidazole are important pharmacophore and a privileged structure in medicinal chemistry and possesses wide spectrum of medicinal activity. 13 One of the important benzimidazole in nature is a-ribosyl 5,6-dimethyl benzimidazole which is a an axial ligand for cobalt (III) in vitamine-12. In which imidazole part provides an important binding sites in biological system displaying a vital role in metal protein interaction.45 The benzimidazole derivatives have trendy structure employed in various field of agriculture, material science, fuel cells and pharmaceutical industries. Nexium is effective proton pump inhibitor used to treat peptic ulcers and gastroesophageal reflux disease which is benzimidazole derivative. In 1872, when Hobrecker reported6 the first synthesis of 2, 5-and 2, 6-dimethyl benzimidazole, he had never suspected that benzimidazole scaffold would become such a preeminent structure. In recent two decades thousands of benzimidazole derivatives have been prepared and their complexing behaviour and pharmacological properties have been studied.78 Benzimidazole derivatives have wide spectrum of pharmacological activity. The complexes of benzimidazole and its derivatives have extensively been studied.916 The industrial utility, medicinal activity and prominent complexing ability of benzimidazole created immense interest for further studies on complexes. The schiff base of [(1H-benzimidazol-2-yl) ethanone with 2-hydrazinobenzimidazole (BahbH) potent nitrogen donor tridentate benzimidazole derivative (A).

img2

(A)

The perusal of literature shows that metal complexes of (BahbH) has not appeared in literature. Intrigued from medicinal and coordinative properties of benzimidazole derivatives I have synthesized and characterized the complexes of BahbH with Mn (II), Co(II), Cu(I), Ag(I), Cu(II), Zn(II) and Cd(II) in solid state. The complexes were prepared, analyzed and investigated and determined magnetic susceptibility and the electrical conductance value. The electronic absorption spectra and IR-spectra of some representative complexes have also been recorded and explained.

MATERIAL AND METHODS:

Preparation of ligand (BahbH): It was prepared by refluxing equimolar proportion of 2-acetyl benzimidazole and 2-hydrazino benzimidazole in ethanol containing a few drops of glacial acetic acid. The cream white precipitate separated was crystallized in ethanol + THF mixture. M. P. of BahbH was found 253C. Nitrogen found 28.84% required for BahbH(C16H14N 6) 28.96%.

Preparation of [Cu (BahbH) X2] (X = Cl or Br & M = Cu2+, Cd2+ Zn2+): About 10 millimole of Copper (II) halide was dissolved in 20 ml of dry methanol and treated with hot methanolic solution of ligand (10 millimole in 20 ml). The resulting solution was heated on steam bath at 60-65C with constant stirring when fine crystalline greenish yellow CuLCl2 and brownish yellow CuLBr2 separated on cooling and stretching the wall of the container. The products were collected on a filter and washed with ice cold methanol and dried in a desiccator over CaCl2.

Preparation of [ML2Cl2] (M = CoII, NiII and MnII): About 20 millimole of appropriate metal chloride was dissolved in 25 ml hot methanol and added with constant stirring to 40 millimole of (BahbH) dissolved in 30 ml of dry methanol. The mixed solutions were refluxed in R. B. flask for one hour and resulting solutions were concentrated when desired complex chloride separated as adding cold ether. The products were collected on a filter, then washed with ether and dried in a desiccator in vaccum. The dried products are fairly stable in dry air and dissolve in aqueous ethanol and aqueous methanol.

Preparation of Cu(I) complex [Cu(BahbH)I]: About 10 millimole of copper (II) sulphate was dissolved in 20 ml hot water and treated with excess of KI (potassium iodide) with stirring. The liberated I2 was removed by adding required amount of Na 2S2O3. The colourless solution containing white precipitate of Cu2I2 was filtered and washed with hot water and air free methanol. The separated Cu2I2 was suspended in 20 ml methanol and kept in CO2 atmosphere. The methanolic suspension of Cu2I 2 was treated with 10 millimole of ligand dissolved in 30 ml hot methanol. The resulting product was refluxed for one hour when Cu 2I2 went into solution to give yellow solution from which cream yellow product separated on concentration and cooling. The complex was collected on a filter washed with air free methanol and dried in vaccum desiccator over CaCl2. The dry product is fairly stable but get oxidised in moist air.

Preparation of Ag (BahbH) NO3: About 20 millimole of silver nitrate was dissolved in 10 ml hot water and added drop-wise with constant stirring to hot solution of 20 millimole of BahbH dissolved in 30 ml ethanol. The cream yellow product separated slowly. The product was digested on steam bath (60-70C) for fifteen minutes and collected on a filter. The product was washed with ethanol, ether and dried in a desiccator over CaCl2. The product is fairly stable and dissolves in DMF, DMSO and pyridine.

Preparation of ML2 SO4 nH2O (M = MnII, CoII, NiII and Cu II n = 2 or 1): About 10 millimole of hydrated metal sulphate was dissolved in 15 ml aqueous methanol and added slowly with constant stirring to 20 millimole of (BahbH) in 30 ml methanol. The resulting solution was heated when complex sulphate separated, gradually. The products were digested on steam bath at 60-65oC for half an hour and cooled in ice for one hour. The products separated were collected on filter, washed with methanol and ether and finally dried in a desiccator over CaCl2.

Preparation of MLX2 (M = ZnII or Cd II and X = Cl or I): The chloride and iodide of zinc(II) and Cd(II) are soluble in methanol. About 20 millimole of appropriate metal chloride was dissolved in 20 ml hot methanol and treated with 20 millimole of ligand dissolved in 30-40 ml hot methanol.

The resulting solutions were refluxed on a steam bath for 30 minutes and concentrated to half of its bulk when crystalline cream coloured precipitate started separating. The resulting products were cooled in ice and separated complexes were collected on buchner funnel. The products here washed with a few drops of methanol and excess of ether. The collected products were dried over CaCl2 in a vaccum desiccator. The yield of product was 80-85%.

The complexes were analysed for metal, nitrogen and sulphate or halide and recorded in Table-I. The prominent band positions of IR spectra and their probable assignments are shown in Table 2 and 3.

RESULTS AND DISCUSSION: The analytical results of complexes of Cu(II) and Cu(I) corresponds with composition Cu (BahbH) X2 (X = Cl or Br) and Cu (BahbH) I. In case of sulphate the composition of complex corresponds to Cu (BahbH)2.SO4.H2O. The analytical results of Co(II), Mn(II) and Ni(II) complexes corresponds to composition M(BahbH)2Cl2 (M = CoII or MnII) and M (BahbH)2 SO4H2 O (M = CoII, NiII or MnII). The zinc (II) and cadmium (II) halide complexes corresponds to composition M (BahbH)X2

(X = Cl or I). The complexes are fairly stable in air and hydrated complexes. [M (BahbH)2].SO4.2H2O, Cu (BahbH)2 SO4.H2O loss H2O on heating between 60-120C without change in morphology and lusture of the complexes indicating that H2O are not coordinated to metal atoms.

Table 1: Analytical result and Magnetic moment value of complexes at 304K in BM.

Compound

% elemental Results found (Cal)

Magnetic Moment

%M

Nitrogen

Anions

Values

CuLCl2

14.84 (14.83)

13.00 (13.06)

16.49 (16.56)

1.82

CuLBr2

12.10 (12.04)

10.59 (10.62)

30.29 (30.31)

1.83

CuLI

10.91 (10.88)

9.59 (9.60)

21.81 (21.75)

Diamagnetic

AgL(NO3)

22.50 (22.42)

15.19 (15.25)

Diamagnetic

MnL2Cl2

7.71 (7.69)

15.67 (15.69)

10.00 (9.95)

5.88

MnL2SO4.2H2O

7.25 (7.21)

14.55 (14.53)

12.51 (12.45)

5.91

CoL2Cl2

8.19 (8.21)

15.55 (15.60)

9.95 (9.89)

4.98

CoL2 SO4.2H2O

7.12 (7.06)

14.51 (14.45)

12.45 (12.39)

4.86

NiL2Cl2

8.22 (8.19)

15.71 (15.60)

9.95 (9.89)

3.25

NiL2 SO4.2H2O

7.61 (7.58)

14.51 (14.46)

12.43 (12.39)

3.16

CuL2 SO4.2H2O

8.26 (8.15)

14.41 (14.37)

12.29 (12.31)

1.89

ZnLCl2

15.23 (15.19)

12.98 (13.01)

16.62 (16.49)

Diamagnetic

CdLCl2

23.58 (23.54)

11.91 (11.73)

14.92 (14.87)

Diamagnetic

CdLI2

17.21 (17.02)

8.55 (8.48)

38.31 (38.44)

Diamagnetic

L=BahbH

The complexes of Cu(I) and Ag(I) correspond to composition [Cu(BahbH)I] and Ag(BahbH)NO3. The attempt to prepare Ag (BahbH)I was unsuccessful as AgI get separated on treatment with KI.

The complexes of Ag(I) and Cu(I) were diamagnetic where as the complexes of Cu(II), Mn(II), Ni(II) and Co(II) were paramagnetic and magnetic moment values of complexes occur in the range of high-spin octahedral complexes of respective metal ions.17 The magnetic moment values of Mn(II) complexes (Table 1) occurs in the range 5.885.91 BM and those of cobalt (II) in the range 4.864.98 BM similar to high spin octahedral cobalt (II) and Mn (II) complexes. 18 The magnetic moment of copper (II) complexes occur in the range 1.821.89 BM indicating that there magnetically dilute product. 19 The magnetic moment value of Nickel (II) complexes (3.16 and 3.25BM) are consistent with octahedral geometry.20 The electron absorption spectra of Ni(II) and Cu(II) complexes in ethyl alcohol show medium to weak band between 400-850 nm. Ag(I), Cu(I) and Mn(II) complexes did not show prominent band in visible region. Manganese (II) complexes always show spin forbidden transition hence its complexes seldom display prominent transition in visible region. The Nickel (II) complexes displayed two prominent band located at 420-430 and 580-590 nm assignable to 3A2g 3T1g(P) and 3A2g 3T1g (F) transition in weak octahedral field. [21a] The electronic absorption spectra of Co(BahbH)2Cl2 showed a medium band at 435 nm and a weak transition at 530 nm attributable to 4T1 4T1g (P) and 4T1g 4A2g transition consistent with octahedral structure of CoII complexes. The U.V spectra of Copper (II) complex Cu(BahbH)2SO4.H2O showed a broad band at 590-610 nm assignable to 2T2g? 2Eg transition in approximately octahedral field.20

Antifungal and antibacterial activity of ligand and its complexes: The ligand (BahbH) and its complexes M(BahbH)2 Cl 2 (M= MnII, CuII or FeII) and [M(BahbH) Cl2] (M= CuII, ZnII and CdII) and Ag(BahbH) NO3 were screened in vitro for their antimicrobial activity against two strains of bacteria proteus mirabilis and Bacillius subtilis as well as four strains of fungi. {Candila albicans (CA), Aspergillus niger (AN), Rizopus oryzal (RO) and Aspergillus fumigates (AF)}. The complexes were tested at 100g/ml concentration in DMSO by disc diffusion technique. 21b Commercial antibacterial (ciprofloxacin and antifungal Amphotericin B) were also screened under similar condition for comparision. The results have been reported in the form of inhibition zones and activity index Table 5 and Table 6. The results revealed that the ligand and all the complexes tested showed antifungal activities. The antifungal activity of CuII, ZnII, and CdII were moderated and higher than free ligand.

The antibacterial activity of Cu(II) complexes (Table-VI) are appreciable and encouraging. The activity of Zn(II) is slightly lower than ciprofloxacin.

Infrared Spectra: The IR spectrum of ligand (1H-benzimidazol-2-yl) ethanone hydrazinobenzimidazole shows NH stretches and CH3 stretches between 2880-3245 cm-1 located at 3147, 3070, 2927 and 2847 cm-1 (Table 2 and 3). These IR spectral bands are not affected appreciably in its complexes. However, the hydrated complex sulphate display a broad IR absorption in 3 region and show bands between 3400 to 3000 cm-1 attributed from hydrogen bonded n(OH) of water molecule. The ligand (BahbH) shows a medium n(C = N) stretching band at 1612 cm-1 is assigned to n(C = N) of benzimidazole ring. The N-H bending band of lignad was located at 1525 cm-1 and (CH3) bending band was located at 1468 and 1344 cm-1. These NH and (CH3) bending bands of ligand is retained in complexes and observed with slight change in intensity and their position. The change can be attributed to change in molecular weight of complex species on formation of complex with metal atoms. The phenyl and imidazole ring skeletal vibration of ligand is observed in finger print region at 1585, 1419, 1344, 1285, 1217, 1153, 1043, 971, 918, 857, 765, and 728 cm-1, the deformations vibrations are observed 695, 657, 577 and 462 cm1. In complexes these vibrations are slightly affected due to involvement of ligand molecule in bond formation. The IR band at 728 cm-1 in free ligand is assigned to phenyl ring out of plane (CH) vibration. In complexes the n(C=N) band is shifted to long frequency due to coordination. The n(C=N) vibration of free ligand is shifted to lower frequency in almost all complexes. The withdrawal of electron cloud of (C=N) nitrogen forwards metal atom causes the shift of (C=N) stretching frequency to lower frequency.2224 This indicated the coordination of imidazole ring tertiary nitrogen to metal atom. The NH stretches and N-H group of imidazole ring show (NH) at 1525 cm -1 and it is retained in complexes suggesting that N-H Hydrogen is not deprotonated in complexes and NH nitrogen is not involved in bonding.[2534] Thus the IR spectra result of ligand and metal complexes suggests the coordination of ligand through both benzimidazole ring pyridine nitrogen and hydrazino group (C=N) nitrogen and ligand behaves as tridentate donor molecule as shown below-

img2

(Tridentate donor)

From the studies of infrared spectra, magnetic susceptibility values, electronic absorption spectral results and molar electrical conductance value the following probable structures are suggested for the complexes of (BahbH = L).

The probable structures of complexes are shown below.

img2

Figure 1: Structure of CuLX2 (X=Cl or Br) and MLX 2 (M=Zn2+ or Cd2+ and X=Cl or I).

img2

Figure 2: Structure of [M(BahbH)2] X2nH 2O (M=Mn2+, Co2+, Ni2+, Cu 2+, X=Cl or SO4, n=1 or 2).

Table 2: IR spectral bands positions of Ligand (Bahbh = L) and its complexes in cm1.

Ligand

NiL2SO4

2H2O

CoL2SO4

2H2O

Assignment

3147

3420

3440

n(NH)+ n(OH)

3070

3050

3010

of H2O

2927

2930

2935

nas CH2

2847

2840

2836

ns CH2

1612

1595

1605

n(C=N)

1585

1575

1580

n(C=C)

1525

1521

1515

d(NH)

1468

1455

1458

d(CH2)

1419

1412

1420

Phenyl ring (C=C)

1344

1342

1336

d(CH2)

1285

1283

1281

Phenyl ring

1217

-

1210

n(CN)

1153

1150

1152

n(CC)

1043

1045

1045

CH2 Scissoring

971

972

970

CH2 rocking band

918

-

910

Substituted phenyl ring

765

758

762

-

728

712

710 (nCS)

Skeletal+CH out of plan

695

698

692

Bending band

651

650

641

ring deformation

577

-

-

Vibration

462

455

450

-

-

422

432

(MN) Stretch

Table 3: IR spectral bands positions of Ligand (Bahbh=L) and its complexes in cm1.

ZnLCl2

CdLI2

MnL2Cl2

Assignment

3152

3149

3159

n(NH) imidazole ring

3047

3040

3051

n(CH) Phenyl

2940

2935

2936

nas CH2

2947

2942

2941

ns CH2

1592

1595

1590

n(C=N)

1580

1581

1580

n(C=C)

1520

1522

1525

d(NH)

1462

1460

1462

d(CH2)

1419

1420

1420

Phenyl ring (C=N)

1342

1340

1345

d(CH2)

1280

1272

1286

Phenyl and imidazole ring

1215

1210

1212

n(CN)

1151

1150

1145

n(CC)

-

-

-

CH2 rocking

972

955

965

CH2 Scissoring

917

920

918

Bands

765

761

761

(CH) out of plane

710

712

708

n(CS)

690

695

695

Ring deform

641

650

652

Vibration

570

572

567

-

435

430

425

n(MN)

Table 4: IR bands of Ligand and its complexes in cm1.

Ligand(L)

CuLCl2

CoL2Cl2

Assignment

3147

3155

3145

n(NH) imidazole

3070

3060

3065

n(CH) Phenyl out

2927

2930

2925

nas (CH2)

2847

2840

2840

nS(CH2)

1612

1605

1601

n(C=N)

1585

1575

1580

n(C=C)

1525

1521

1508

d(NH) imidazole

1468

1465

1458

d(CH2)

1419

1420

1425

dC

1344

1344

1340

d(CH2)

1285

1281

1285

n(CN)

1217

1201

1207

n(CC)

1153

1150

1155

phenyl ring

1043

1043

1045

Skeletal

971

970

972

Vibration

918

920

920

-

857

855

850

-

765

765

760

phenyl ring (CH) out of plane

728

720

715

n(CSC)

695

699

-

-

651

651

650

ring deformation

577

570

Vibrations

462

450

453

-

Table 5: Antifungal activity of ligand and synthesized complexes, zone of Inhibition (mm) activity index.

S. No.

Complexes

Antifungal Activity

CA

AN

AF

RO

1

BahbH=L

13

12

9

13

2

CuL2Cl2

16

18

15

19

3

FeL2Cl2

14

14

12

16

4

MnL2Cl2

14

15

13

15

5

ZnLCl2

15

17

14

18

6

CdLCl2

14

16

13

13

7

CuLCl2

16

17

15

16

8

AgLNO3

13

14

11

14

9

Amphotericin

20

22

17

24

Candila albicans (CA), Aspergillus niger (AN), Rizopus oryzal (RO) and Aspergillus fumigates (AF)

Table 6: Antibacterial activity (zone of inhibition).

S. No.

Antibacterial

Compounds

Antibacterial Activity

Bacillus Subtilis

Proteus mirabilis

1

BahbH

11

12

2

CuL2Cl2

18

18

3

MnL2Cl2

14

13

4

ZnLCl2

19

20

5

CdLCl2

16

13

6

AgLNO3

17

16

7

Ciprofloxacin

25

24


CONCLUSION: In Summary we have demonstrated synthesis of some new transition metal complexes having MnII, CoII, CuII and Mn II with hydrazinobenzimidazole as ligand. We have also successfully screened their antifungal and antibacterial activity and few of them were found to be potent antibacterial and antifungal agents. Our research can open new doors in antimicrobial drug discovery research in near future.

ACKNOWLEDGEMENT: Authors acknowledge support from IIT Patna for recording IR and UV spectra.

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