International Journal of Inorganic Chemistry

International Journal of Inorganic Chemistry / 2014 / Article

Research Article | Open Access

Volume 2014 |Article ID 902575 | https://doi.org/10.1155/2014/902575

Madhu Bala, L. K. Mishra, "Complexing Behaviour and Antifungal Activity of N-[(1E)-1-(1H-Benzimidazol-2-yl)ethylidene]morpholine-4-carbothiohydrazide and Related Ligand with Metal Ions", International Journal of Inorganic Chemistry, vol. 2014, Article ID 902575, 10 pages, 2014. https://doi.org/10.1155/2014/902575

Complexing Behaviour and Antifungal Activity of N-[(1E)-1-(1H-Benzimidazol-2-yl)ethylidene]morpholine-4-carbothiohydrazide and Related Ligand with Metal Ions

Academic Editor: Alfonso Castiñeiras
Received06 Sep 2013
Revised11 Dec 2013
Accepted17 Dec 2013
Published22 Apr 2014

Abstract

The coordination complexes of bivalent metal ions with N-[(1E)-1-(1H-Benzimidazol-2-yl)ethylidene]morpholine-4-carbothiohydrazide (H2bmctz, H2L-1) and N-[(1E)-1-(1H-Benzimidazol-2-yl)(phenyl)methylidene] morpholine-4-carbothiohydrazide (H2bpmctz, H2L-2) were prepared and their neutral, monoanionic, and dianionic forms of ligands of compositions [M(H2L)X2] (M=, , , , , or , X=Cl or Br, and H2L=H2L-1 or H2L-2), [M(HL)2]nH2O where (M=, , , , or , H2L=H2L-1 or H2L-2, and n = 0 or 2), and [MLB]nB (M=, , , , or , B=H2O, Py, or -pic, n = 0 and n = 1 if B=H2O for Ni(II) and H2L=H2L-1 or H2L-2) have been characterised by magnetic susceptibility measurements, electrical conductance values, and spectral properties. The magnetic moment value of [M(HL2)] (M=, , or ) type complexes is consistent with high spin octahedral structure while those of [M(H2L)X2] (M=, , , , or , X=Cl or Br) possess five coordinated trigonal bipyramidal geometry. The adduct complexes [MLB]·nB (M=, or , B=H2O, Py, or -pic) are four coordinated planar and those of and complexes [MLB], (H2L=H2L-1 or H2L-2, B=H2O, Py or -pic) are tetrahedral. These ligands have been suggested to coordinate as tridentate (N N S) donor molecule in complexes of type [M(H2L)X2], [M(HL)2], and [MLB]. The antifungal activity of ligands and some of their metal complexes were studied and it was observed that metal complexes show higher activity than free ligand.

1. Introduction

Preparation and structural aspects of various metal ions with a number of benzimidazole derivatives have been reported by one of us and a number of chemists [110]. Medicinal properties of benzimidazole derivatives have established that benzimidazoles have privileged substructures for drug design [11, 12]. The most vital benzimidazole derivatives is N-ribosyl-5,6-dimethylbenzimidazole which is axial ligand in vitamin B12 possessing selective neuropeptide YY1 receptor antagonists [13], 5-lipo xyginase inhibitor [14] and poly (ADP-ribose) polymerase inhibitors [14]. Benzimidazole derivatives are of immense interest because of their wide spectrum of biological activity such as anticancer [15], antiviral [16, 17], antihistaminic [18], antifungal [19], anti-HBV [20], antibacterial [21], antitumoral [22], antiparasitic [22], antihelminitic [23], anti-inflammatory, local analgesic, hypotensive [24], antiulcer [25], and neuro leptic cardiotonic [26]. Extensive biochemical and pharmacological studies have confirmed that various benzimidazole derivatives are effective against various strains of microorganisms [25]. The wide ranging biological and industrial interest intrigued chemists to explore new benzimidazole derivatives and their metal complexes which might have novel mechanisms of action and drug activity [1525]. The metal ions selected for present studies Mn(II), Co(II), Cu(II), Fe(II), Ni(II), Zn(II), and Cd(II) are versatile essential micronutritents in biological systems [2732]. Copper is crucial for biological function of several enzymes and proteins, in energy metabolism, antioxidant, and mitochondrial respiration [27]. Zinc(II) is essential for nucleic acid synthesis, cell growth division, and differentiation and its deficiency causes abnormalities in function of cell carboxypeptidase, amino peptidase, carbonic anhydrase, DNA and RNA polymerase. Zinc is also essential for life and it regulates the function of genes in the nuclei of thecell (Lipsocomb and Starter, 1996). Iron is the most vital element for life and iron-sulphur proteins formation (Richardson, 2002). Manganese is a component of nucleic acid and it accelerates the synthesis of cholesterol. Manganese enzymes are involved in metabolic pathway of DNA synthesis, sugar metabolism and protein modification. Cobalt is a component of vitamin B12 and enzyme nutritional cofactor necessary for the formation of red blood cell [31]. Nickel is remarkably useful metal in biological chemistry. It modifies antioxidant system and is associated with chromosomal aberrations and mutation [31]. In continuation of our work on coordinating behaviour of benzimidazole and imidazole derivatives with various metal ions [26], and biological significance of above metal ions, we report in present communication, the preparation, characterization, and antifungal activity of complexes of these metals with of N-[(1E)-1-(1H-benzimidazol-2-yl)ethylidene]morpholine-4-carbothiohydrazide (H2L-1) and N-[(1E)-1-(1H-benzimidazol-2-yl)(phenyl)methylidene]morpholine-4-carbothiohydrazide (H2L-2).

2. Material and Methods

The metal salts used were usually BDH Anal-R chemicals or E. Merk Extra pure reagent. Palladium(II) chloride was obtained from Johnson Matthey London. Solvents and organic reagent, hydrazine, morpholine, carbon disulphide, Chloroacetic acid were obtained from E. Merk, Nice, Sd. Fine and Ranbaxy. The metal contents of complexes were estimated by standard method sulphur content was determined as sulphate, and nitrogen content was estimated by Nitrometer (Duma,s method) in the laboratory. The infrared spectra of complexes were recorded on Shimadzu-FTIR spectrometer at IIT patna. The results of C, H, and N were obtained from CDRI Lucknow. The results of mass spectrum and U-V absorption spectrum of ligand and some complexes were obtained from IIT patna. The 1HNMR spectrums were recorded at CDRI Lucknow. The magnetic susceptibilities of complexes were determined by Gouy method at room temperature. The electrical conductance values of complexes were determined in DMF on Systonic conductivity Meter Bridge at 30–31°C. The results of measurements are given in Tables 1 and 2.


CompoundColour % analysis found (Calc)  B.M (305°K)  mol−1 ohm−1 cm2, 30°C
MNHalogen

Cu(H2L-1)Cl2Green ash14.31 (14.52) 15.73 (16.00)16.01 (16.25)1.8112
Cu(H2L-1)Br2Brown11.91 (12.07)13.31 (13.48)30.11 (30.44)1.848
Zn(H2L-1)Cl2White14.61 (14.88)15.91 (16.18)15.01 (15.12)Dia10
Zn(H2L-1)Br2White12.31 (12.52)13.01 (13.25)30.11 (30.25)Dia8
Cd(H2L-1)Cl2Cream22.86 (23.13)14.11 (14.29)14.36 (14.53)Dia11
Cd(H2L-1)Br2Cream19.46 (19.54)12.11 (12.32)27.38 (27.67)Dia10
Ni(H2L-1)Cl2Greenish yellow 13.32 (13.54)16.31 (16.48)16.57 (16.70)3.1810
Co(H2L-1)Cl2Brown13.41 (13.58)16.28 (16.49)16.51 (16.71)3.2511
Ni(H2L-1)Br2Bottle green11.10 (11.21)13.50 (13.61)30.17 (30.64)3.218
Cu(H2L-2)Cl2Ash green12.53 (12.71)14.21 (14.02)13.87 (14.19)1.8111
Cu(H2L-2)Br2Brown10.61 (10.79)11.63 (11.81)26.93 (27.13)1.838
Cd(H2L-2)Cl2Cream20.49 (21.67)12.76 (13.54)12.69 (12.93)Dia11
Zn(H2L-2)Cl2Cream13.31 (13.45)13.21 (13.96)14.00 (14.15)Dia10
Cd(H2L-2)Br2Cream17.38 (17.64)10.71 (10.98)23.01 (23.30)Dia9
Zn(H2L-2)Br2Cream10.91 (11.08)11.61 (11.84)26.81 (27.06)Dia11
Ni(H2L-2)Cl2Greenish yellow11.61 (11.86)13.96 (14.15)14.16 (14.35)3.2012
Co(H2L-2)Cl2Brown11.68 (11.89)13.89 (14.16)14.23 (14.36)3.3213
Ni(H2L-2)Br2Bottle green9.92 (10.05)11.71 (11.99)27.01 (27.38)3.1814

(H2L-1)=H2bmctz and (H2L-2)=H2bpmctz.

Compound H2L=H2bmctz H2L′= 
H2bpmctz
Colour % analysis found/(Calc)  B.M 305°K  mol−1 Ohm−1 cm2, 30°C
MN Sulphur

Co(HL-1)2 2H2OBrown8.61 (8.88)21.01 (21.12)9.50 (9.65)3.268
Cu(HL-1)2 Ash colour9.31 (9.52)20.87 (21.09)9.31 (9.59)1.867
Mn(HL-1)2 Dull cream8.14 (8.33)21.22 (21.24)9.41 (9.78)5.888
Fe(HL-1)2 Light brown8.31 (8.47)21.01 (21.20)9.48 (9.64)4.916
Cu(HL-2)2 Ash green7.91 (8.01)17.61 (17.79)8.00 (8.08)1.888
Mn(HL-2)2 Dull cream6.88 (7.01)17.61 (17.88)9.11 (9.26)5.928
Fe(HL-2)2 Light brown7.01 (7.12)17.15 (17.86)9.11 (9.24)4.866
Co(HL-2)2 2H2OBrown7.02 (7.16)17.00 (17.01)7.61 (7.77)3.6810
Ni(HL-1)2 2H2OReddish brown8.37 (8.40)19.81 (20.02)9.00 (9.22)3.138
Ni(HL-2)2 2H2OReddish brown7.10 (7.13)16.81 (17.01)7.57 (7.78)2.987
Zn(HL-1)2 Yellow9.82 (9.76)20.73 (20.90)9.09 (9.10)Dia10
Zn(HL-2)2 Yellow8.01 (8.29)17.51 (17.65)8.01 (8.06)Dia8
Pd(HL-1)2 Reddish brown14.61 (14.98)19.56 (19.71)8.90 (9.01)Dia9
Pd(HL-2)2 Reddish brown12.61 (12.75)16.66 (16.87)7.51 (7.67)Dia7
Pd(L-1)Py Orange21.63 (21.75)17.01 (17.27)6.51 (6.58)Dia6
Pd(L-2)Py Orange19.31 (19.40)15.01 (15.32)5.69 (5.83)Dia8
Pd(L-1)(Y-pic) Orange21.11 (21.27)16.68 (16.86)6.30 (6.39)Dia8
Pd(L-2)(Y-pic) Orange18.68 (18.98)14.91 (15.01)5.68 (5.73)Dia7
Ni(L-1)Py Yellowish red13.31 (13.38)19.11 (19.21)7.10 (7.29)Dia8
Ni(L-1)(Y-pic) Yellowish red12.78 (12.99)18.48 (18.59)6.87 (7.08)Dia7
Ni(L-1)(H2O) H2OYellowish orange14.63 (14.83)17.51 (17.69)8.11 (8.06)Dia9
Ni(L-2)Py Orange yellow11.43 (11.72)16.71 (16.77)6.11 (6.39)Dia10
Ni(L-2)(Y-pic) Orange yellow11.14 (11.42)16.21 (16.32)6.01 (6.23)Dia8
Ni(L-2)(H2O) H2OOrange yellow12.78 (12.82)15.11 (15.29)6.81 (6.99)Dia7
Cd(L-1)(Y-pic) Orange yellow22.01 (22.22)16.51 (16.62)6.11 (6.33)Dia10
Cd(L-1)(H2O) Orange yellow26.15 (26.05)16.02 (16.23)7.31 (7.42)Dia8
Cd(L-1)Py Orange yellow22.61 (22.81)17.34 (17.51)6.41 (6.49)Dia9
Cd(L-2)Py Orange yellow20.11 (20.21)15.01 (15.15)5.70 (5.77)Dia11
Cd(L-2)(Y-pic) Orange yellow19.61 (19.88)14.92 (14.88)5.41 (5.64)Dia10
Cd(L-2)(H2O) Yellow22.48 (22.78)14.21 (14.19)6.51 (6.48)Dia9
Zn(L-2)Py Orange yellow14.51 (14.62)18.76 (18.86)7.00 (7.18)Dia10
Zn(L-1)(H2O) Yellow17.14 (17.01)18.41 (18.23)8.10 (8.32)Dia8
Zn(L-2)Py Yellow12.81 (12.88)16.47 (16.55)6.03 (6.36)Dia 6
Zn(L-2)(Y-pic) Orange yellow12.41 (12.54)15.91 (16.11)5.91 (6.14)Dia9
Zn(L-2)(H2O) Yellow14.61 (14.72)15.58 (15.78)6.91 (7.17)Dia8
Zn(L-1)(Y-pic) Yellow14.21 (14.23)18.41 (18.59)6.91 (7.08)Dia11
Cu(L-1)Py Bottle green14.01 (14.32)18.32 (18.54)7.03 (7.21)1.868
Cu(L-2)Py Bottle green13.81 (13.95)18.71 (18.93)7.11 (7.21)1.849
Cu(L-1)(Y-pic) Ash colour13.61 (13.88)18.17 (18.36)6.81 (6.99)1.896
Cu(L-2)(Y-pic) Ash colour12.31 (12.25)16.01 (16.20)6.01 (6.16)1.845
Cu(L-2)(H2O) Brown13.61 (13.73)15.00 (15.14)6.71 (6.91)1.798
Cu(L-1)(H2O) Brown15.48 (15.74)17.13 (17.35)7.76 (7.93)1.7810

Ligand molecules (H2bmctz, H2L-1 or H2bpmctz, H2L-2) were prepared by condensing 2-acetylbenzimidazole or 2-benzoylbenzimidazole [33] with morpholine-N-thiohydrazide [34] in aqueous ethanol containing a little amount of acetic acid. 2-Acetylbenzimidazole or 2- benzoylbenzimidazole in situ was prepared by oxidation of 1-(1H-benzimidazol-2-yl)ethanol and 1-(1H-benzimidazol-2-yl)phenylmethanol [35] with chromic acid [33]. The 0.1 mole of 2-acetylbenzimidazole in 100 mL aqueous ethanol containing 2 mL acetic acetic acid was refluxed with 0.12 mole of aqueous ethanolic solution of morpholine-N-thiohydrazide(morpholine-4-carbothiohydrazide) on a steam bath for two hours. The ligand separated as cream of yellow product. The ligands were analysed. For H2bmctz (H2L-1) (C14H17N5SO) nitrogen was found 23.06% calculated value is 23.11%. M.pt recorded, 197°C (uncorrected). The value of nitrogen found for H2bpmctz (H2L-2) is 19.01%, and that calculated for H2L-2 (C19H19N5SO) is 19.18%, M.pt recorded 242°C (uncorrected).

2.1. Preparation of Complexes [M(H2L)X2] (M=CuII, CoII, NiII, ZnII or CdII X=Cl or Br and H2L=L-1 or L-2)

About 0.01 mole of metal halide was dissolved in 40–50 mL ethanol and treated with 0.01 mole of appropriate ligand in dry ethanol (30–40 mL) slowly with constant stirring. The resulting solution was refluxed on a steam bath for half an hour and concentrated to 20–30 mL. The concentrated solution was chilled when crystalline precipitate separated. In case of Cu (II) the product were obtained immediately. The product was filtered, washed with cold dry ethanol, and dried over CaCl2. Yield 80–85%.

2.2. Preparation of Bis Ligated Complexes [M(HL)2], nH2O (M=MnII, FeII, CoII, NiII, CuII, ZnII, CdII or PdII, H2L=H2L-1 or H2L-2 and but 2 for NiII or CoII)

About 20 millimoles of ligand was dissolved in 80–90 mL hot methanol and treated slowly with aqueous methanolic solution of 10 millimoles of appropriate metal acetate {chloride in case of Pd(II) and sulphate in case of Fe(II)} and refluxed on steam bath for half an hour. In some cases a little aqueous solution of sodium acetate was added to adjust the pH 6–8. In most of the cases complexes were obtained immediately on diluting them with water. The products were digested on a steam bath and collected on a filter, washed with aqueous methanol, and dried over CaCl2. Yield is 95–98%.

2.3. Preparation of [MLB]·nB (M=CuII, PdII, NiII, ZnII or CdII B=H2O, py or  -pic and , H2L=H2L-1 or H2L-2, if B=H2O, for NiII and H2L-1 or H2L-2)

About 5 or 10 millimole of metal chloride was dissolved in 30–40 mL aqueous methanol and treated with 5-6 mL pyridine or -pic. The resulting solution was treated with 5 or 10 millimole of ligand dissolved in hot methanol (20–25 mL).The pH of the solution was raised by adding dilute ammonia when appropriate complexes separated. The aqua complexes were obtained on refluxing [MLPy] in hot water in presence of a little ammonia. The products were collected on a filter, washed with cold aqueous methanol, and dried over CaCl2. The results of elemental analysis and physical data of complexes are presented in Tables 1 and 2.

3. Results and Discussion

The ligands N-[(1E)-1-(1H-benzimidazol-2-yl)ethylidene]morpholine-4-carbothiohydrazide (H2L-1) and N-[(1E)-1-(1H-benzimidazol-2-yl)phenyl(methylidene)]morpholine-4-carbothiohydrazide (H2L-2) are potential N N S donor coordinating molecule capable of forming five membered strong chelates with The elemental analysis of complexes of , , , , and halide formed in dry ethanol corresponds to compositions [M(H2L)X2 ], and (H2L=H2L-1 or H2L-2, X=Cl or Br) metal ions. Depending on pH of medium, these ligands coordinate as neutral, monoanionic, and dianionic donor molecules. The elemental analysis of complexes of , , , , , , , and corresponds to compositions [M(H2L)X2] (=, , or and X= or ) [M(HL)2]H2O (=, , , , , , or , H2L=H2L-1 or H2L-2, but 2 for and ) and [MLB]B (=, , , or and = or H2L-2, B=Py, -pic or H2O and or 1). These complexes are quite stable at room temperature and do not lose texture in desiccator. On heating the complexes [M(HL)2·H2O (=, or , and HL=HL-1 or HL-2) in air oven between 60 and 80°C for one hour, is loss H2O and loss in weight incurred in complexes correspond to loss of required for 2H2O, and no change in colour of the complexes that was noticed which indicated that H2O molecules are not coordinated to metal atom rather they are held up in crystal lattices. The weight loss incurred in complexes Ni(L-1)2H2O and Ni(L-2)2H2O at 120°C corresponds to loss of only one H2O, indicating that one H2O is coordinated to nickel (II) in complex [NiL(H2O)]H2O and the second H2O is held up in crystal lattices. The dihalo complexes are formed in dry ethanol by interacting solutions of ligand with metal halides. The bis ligated complexes [M(HL)2]H2O were formed in neutral or weakly basic medium (pH 6–8) by interacting aqueous methanolic or ethanolic solutions of metal acetate or metal chloride and appropriate ligand in 1 : 2 molar proportion. The ligands coordinate as dianionic tridentate molecule in much basic medium (pH 9–12) and form complexes of stoichiometry, [MLB]·nB (=, , , or and H2L=H2L-1 or H2L-2, B=H2O, py or -pic and or 1). The complexes are all insoluble in water but aqueous ethanolic suspension of [M(H2L)X2] gradually dissociates into M(HL)2 and MX2 giving conducting solution. Freshly prepared DMF solution of complexes, however shows negligible electric conductance value indicating them to be nonionic and even halogens are coordinated to metal atom [36]. Zinc(II), cadmium(II), and nickel(II) complexes [NiLB]·nB are diamagnetic. At room temperature all copper(II) complexes show normal magnetic moment value (1.81–1.89 B.M) and magnetic moment value of Mn(II) complexes [Mn(HL)2] (5.88–5.92 B.M), Ni(II) complexes [Ni(HL)2] (2.93–3.01 B.M), and Fe(II) complexes Fe(HL)2 (4.89–4.91 B.M) corresponds to spin free octahedral geometry of metal ions [37]. The moment value of cobalt(II) complexes [Co(HL)2] (3.26–3.68 B.M) is lower than spin free octahedral geometry and anomalous probably due to spin-exchange interactions [38]. The dihalo complexes [Co(HL)X2] show magnetic moment value (4.54–4.71 B.M) similar to five coordinated TBP structure [37, 38]. As expected zinc(II) or Cd(II) complexes M(HL)2 and [M(H2L)X2] (X=  or ) are diamagnetic. The electronic absorption spectra of ligand (H2L-1 or H2L-2) and their complexes were determined in ethanol or ethanol DMF (50%) mixed solvent in the range 200–850 nm. The ligand H2L-1 displays strong bands at 214, 252, and 268 and a medium band at 295 nm attributed from , , , and transitions of ligand molecule [39]. The electronic absorption bands of H2L-2 are observed as strong band at 212, 245, 270, and 290 nm attributed from , , , and (C=S) of ligand. In complexes these transition are mostly enveloped by strong charge transfer from and electronic transitions. The metal complexes form very deep coloured solutions in DMF-ethanol mixture and distinct d–d electronic transitions could not be located below 380–390 nm. The Zn(II) and Cd(II) complexes as expected do not have d–d electronic transition but due to charge transfer band show strong absorption near 420–400 nm. The medium band at 460–480 nm for [NiLB]·nB (H2L=H2L-1 or H2L-2, B=py or -pic) is attributed to transition in planar field [39]. In DMF-ethanol mixture the complexes [Ni(HL)2] as well as [Ni(H2L)Cl2] have same colour and similar electronic absorption band near 460–480 nm. The complexes probably acquire planar structure in basic DMF medium. The cobalt (II) complexes display weak electronic absorption near 430–440 nm and 560–580 nm assignable to and , transitions in octahedral field [39]. The Cu(II) complexes [Cu(HL)2] show strong absorption below 420 assignable to charge transfer transition. The complexes display d–d transitions at 450 nm (medium) and 650–680 nm as broad weak band assignable to , , and transition in distorted octahedral field [39]. In case of Mn(II) no distinct d–d transitions could be located definitely, since all d–d transitions of Mn(II) complexes are of spin forbidden type. Iron (II) complexes display a shoulder near 440 and 450 nm attributable to transitions in octahedral field [3739] (See Figures 1 and 2).

The IR spectra of ligands and their complexes were recorded as KBr optics in range 4000–400 cm−1. The diagnostic I.R. bands of ligands and some of their complexes are recorded in Table 3. The ligand H2L-1 displays medium I.R. bands at 3350, 3240, 3120, 3040, 2949, 2860, and 2840 cm−1 attributed from ν(NH), phenyl (C–H) stretches, and morpholine ring ν(CH2) vibrations and most of them are retained in complexes. The ν(C=N), ν(N–N) of imidazole ring and azomethene part of ligand were observed at 1653, 1610 and 1585 cm−1. The  (NH) of ligand was located at 1515 and 1485 cm−1. The IR spectrum of Cu(H2L-1)Cl2 displays azomethene ν(C=N) at 1622 cm−1 and imidazole ring ν(C=N) at 1590 which is lower than free ligand molecule that indicated the coordination of both (C=N) nitrogen to metal atom. The thione ν(C=S) of ligand shifted from 912 cm−1 to 892 cm−1 in complex [Cu(H2L-1)Cl2] indicated the involvement of thiol sulphur in coordination. Thus the ligand is bonded as tridentate N, N, S donor molecule in complexes. The (NH) at 1515 and ν(N–H) at 3240 cm−1 of ligand were absent in complexes with dianionic ligand [M(L-1)B]. The complexes containing pyridine or -picoline molecule display a prominent band at 1590–1595 and 1015–1025 cm−1 due to ν(C=N) of coordinated pyridine ring and pyridine ring breathing mode of vibration [40]. The imidazole part ν(C=N) and azomethene part ν(C=N) stretches of ligand shift to lower frequency in complexes by 10–15 cm−1 that suggested the coordination of both (CN) nitrogen. The thioamide ν(C=S) of ligand was observed at 912 cm−1, which is shifted by 20–25 cm−1 in complexes of type [M(H2L-1)X2] indicating that (C=S) is bonded through thione sulphur. The ν(C=S) of ligand shifts to 760–780 cm−1 in complexes [M(HL-1)2] and [M(L-1)B] type of complexes indicating the coordination of thioamide (C=S) through deprotonated thiol sulphur. The ligand H2L-2 shows ν(N–H), ν(C–H) phenyl ring and (CH2) ring vibration morpholine at 3238, 3190, 3060, 2950, and 2832 cm−1. These are retained with some change in intensity and band position in complexes. The complexes [M(HL)2]2H2O,(HL=HL-2 or HL-1) show broad IR band near 3180–3450 cm−1 attributed to hydrogen bonded ν(OH) of H2O. The ν(C=N) of azomethene part and benzimidazole located at 1628, 1605, and 1585 of (H2L-1) shift to lower frequencies that indicated their bonding to metal atom. The thioamide ν(C=S) of H2L-2 located at 938 cm−1 shifted by 20–30 cm−1 in complexes of types [M(H2L-2)X2] indicating bonding of thione sulphur (Table 3). The ν(C=S) shifts to 770–790 cm−1 in complexes of types [M(HL-2)2] and [M(L-2)B] supporting bonding through deprotonated thiol sulphur of thioamide group [40, 41]. The I.R. spectral band of both H2L-1 and H2L-2 shows similar trend of bonding of donor atoms. Infar I.R. range, the I.R. spectra of complexes were recorded above 400 cm−1, therefore ν(M–S) and ν(M–N) stretches could not be located definitely. However, the new I.R. bands in complexes at 420–435 cm−1 are tentatively suggested to ν(M–N) and ν(M–S) vibrations (Table 3). In Finger print region H2L-1, H2L-2, and their complexes display a number of I.R. bands due to phenyl ring skeletal vibrations and (CH2), (CH3), ν(N–N), ν(C–N), and ν(C–C) vibrations as well as ring deformation vibrations [40, 41]. In general, almost all complexes display very strong band near 735–745 cm−1 attributed to phenyl ring out of plane bending of substituted phenyl ring. The Finger print region, I.R. stretches of H2L-1 are located at 1545, 1515, 1480, 1441, 1363, 1271, 1235, 1155, 1110, 1004, and 744 cm−1. These are retained in complexes with slight change in intensity and slight change in position [4042]. The I.R. bands of H2L-2 were observed at 1540, 1505, 1482, 1442, 1336, 1280, 1240, 1150, 1105, 1030, 845 and 742 cm−1. From the I.R. studies, it is concluded that the ligands are tridentate and dianionic in [MLB] type of complexes.


Compound (NH), (OH), (CH2), + (C–H) (C=N)imidazole, (C=N)azometheneRing breathing mode (C=S) (M–N)
(M–S)

H2L-13350, 3240, 3120, 3040, 2949, 28601653, 1610, 15851040912435, 415
H2L-23238, 3190, 3060, 2950, 28321628, 1605, 15851035938431, 418
Cu(H2L-1)Cl2 3280, 3235, 3125, 3040, 2950, 28501622, 1590, 15801055892427
Zn(H2L-1)Cl2 3320, 3235, 3140, 3035, 2960, 2845 1615, 1595, 15801024896429
Cu(H2L-2)Cl2 3340, 3230, 3145, 3045, 2960, 28401621, 1610, 15901025908436, 413
Ni(H2L-2)Cl2 3340, 3240, 3140, 3045, 2950, 28401618, 1595, 15841040912428, 410
Co(HL-1)2 2H2O3320, 3245, 3140, 3050, 2960, 28401618, 1602, 15951035768441, 418
Zn(HL-2)2 3340–3140, 3050, 2960, 28501622, 1605, 15921030772438, 416
Ni(HL-2)2 2H2O 3380–3100br, 2960, 28401615, 1600, 15951040782435, 418
Cd(HL-2)2 3320, 3240, 3130, 2960, 28501612, 1595, 15801038788436, 417
Co(HL-2)2 2H2O 3400–3120br, 2960, 28401618, 1605, 15851028792438, 422
Ni(L-1)Py 3320–3180, 3040, 2980, 28451612, 1595, 15751024760443, 418
Cu(L-2) Y-pic3340, 3260, 3140, 3050, 28401620, 1590, 15801025772434, 415
Cu(L-2) 2H2O3350–3060, 2950, 28401620, 1600, 15801025781438, 410
Zn(L-1)Py 3320, 3270, 3130, 3040, 2955, 28451615, 1600 15901030776436, 413

1H NMR spectra of ligands H2L-1 and H2L-2 were recorded in DMSO at field strength 300 MHz. The ligand H2L-1 shows (CH2) proton. Signals of morpholine ring as two triplets for 8H at = 4.016, 4.030, 4.047and 4.154, 4.170, 4.184 ppm, the CH3, proton signals at = 1.787 ppm (Singlet), the phenyl ring signal at =  ppm as multiplet (4H). The benzimidazole ring N–H and hydrazide part NH signals are located at = 7.262 and = 8.6 ppm. The ligand H2L-2 displays (CH2) proton signal of morpholine ring at 3.781–4.145 ppm as two triplets (8H, t) and phenyl ring (C–H) proton signal at = as multiplet (9H). The benzimidazole ring (NH) and hydrazide (N-H) proton signals were located at = 7.415 and 8.215 ppm. The mass spectrum of H2L-1 gave at 303(3%), 288(3.8%), 217(40%), 117(100%), and 86(30%). The calculated value of mass was 303. The mass spectral results of H2L-2 indicated values 365(5%), 288(3%), 279(8%), 86(30%), and 117(100%) as base peak. The mass calculated for H2L-2 was 365. The 1HNMR spectra of complexes could not be recorded due to their poor solubility (See Figure 3).

3.1. Antifungal Studies

The antifungal activity of ligands and some of their complexes have been evaluated by radial growth method [43, 44]. Czapek agar medium was prepared by dissolving 20 g starch, 20 g agar agar and 20 g glucose in one litre distilled water. The resulting medium was added requisite amount of test compound to get 100 and 200 ppm of solution. The resulting medium was then poured into Petri plates and the spores of fungi were placed on medium with the help of inoculum needle. The petri plates were wrapped in polythene bags containing two to three drops of ethanol and then placed in incubator at °C. The linear growth of fungus was evaluated by measuring the fungal zone diameter after five days. The percentage inhibition was calculated from the relation where and are the diameter of the fungus colony and control test plate, respectively. The fungi used in present investigation for screening against the fungi, Aspergillus niger, Aspergillus flavus, F. oxysporum, Rhizoctonia bataticola, and R. phaseoli. The control solution was mycostatin. The result of activity is shown in Table 4. It has been found that the ligand containing phenyl substituent is more active than methyl substituent. The Cu(II) and Zn(II) complexes in general show larger activity than Mn(II) and Fe(II) complexes. The bromo complexes show larger activity than that of chloro or pydridine or -picoline adduct. The chemical Mancozeb fungicides were used as standard for this process. In general the antifungal activities observed for Cu(II) and Zn(II) halo complexes were much larger than other metal complexes and ligand. The antifungal activity observed for R. phaseoli is larger compared to other fungi, indicating selectivity of complexes for particular fungi. The enlarged activity of complexes may be attributed to increased delocalisation of π-electrons of ligand over the whole chelate ring which enhances the lipophilicity of the complexes. The increase lipophilicity enhances the penetration of complexes into fungi membrane and blocking the active binding sites in the microorganism. In addition the complexes disturb the respiration process of the fungi cell thus blocking the synthesis of proteins essential for fungi growth and restrict the further growth of the organism. The activity of complexes of phenyl substituted ligand is larger than methyl derivatives due to larger π-delocalised electron in phenyl substituted ligand than that of methyl derivatives and free ligand as well.


CompoundConc. in ppmA. niger A. flavus F. oxisporum R. bataticola R. phaseoli

H2bmctz = H2L-11004035304550
2005550526875
H2bpmctz = H2L-21004636404855
2006852657280
Cu(H2L-1)Cl21004855325055
2006570557585
Cu(H2L-2)Cl21005060425256
2007078707886
Cu(H2L-1)Br2100 5056425257
200687268 7687
Cu(HL-1)21004850355054
2006265607080
Zn(H2L-1)2 Cl21004842404854
2006460607080
Zn(H2L-2)2 Br21005045425055
2006862657482
Zn(H2L-2)Br21005242455260
2007260707685
Mn(HL-1)21004240354650
2005853557075
Fe(HL-2)21004142364852
2005755557478
Pd(L-1)Py1005245405052
2006868627278
Ni(H2L-1)Cl21004842454854
2005656557280
Ni(L-1)Py1004640324552
2005652557076
Cd(HL-1)21004643354854
2006058607280
Cd(HL-2)21004842435060
2006660657485
Ref. Mancozeb1007580788182
20099989799100

In addition to above facts, the chelate formation reduces the polarity of metal ions, increases the lipophilic character of the chelate, and increases the interaction between metal ion and fungi cell membrane. Consequently it blocks the cell growth of microorganism. According to overtone’s concept the lipophilicity of complexes is major factor which favours antimicrobial activity [45, 46]. The hydrogen bond formation between fungi and complex molecule through azomethene (C=N) and heteroatoms S and O and halogens of complexes interacts with cell constituents resulting in interference with the normal cell process. These factors are tentatively suggested for enhanced antimicrobial activities of metal chelates complexes of N and S donor.

From the results of I.R. and physical data, the probable structures of complexes are shown in Figures 4, 5, 6, and 7.

4. Conclusion

The physicochemical data suggested octahedral structure for [M(HL)2] type of complexes of Ni(II), Co(II), and Cu(II) while four coordinated planar to Pd(II) complexes. The monoligated Ni(II) and Pd(II) complexes [M(L-1)/(l-2)B] show characteristics of planar geometry. The complexes of [M(H2L)Cl2], (=, , , or ) have been suggested to possess trigonal bipyramidal structures. The ligand H2L-1 and H2L-2 coordinate as neutral, monoanionics or dianionic tridentate (N, N, S) donor molecules. The biological activity of phenyl substituted ligand and its complexes are larger than those of methyl substituted products probably due to excessive delocalized π-electron system present in phenyl ring.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

Thanks are due to authority of IIT Patna for recording IR, U-V, and mass spectra, BIT Mesra Ranchi for C, H, or N analysis, and CDRI Lucknow for 1H NMR spectra, and the Head of the Chemistry Department, Patna for magnetic susceptibility measurements. The authority of NIT Patna is thankful for providing necessary laboratory facilities. We thankfully acknowledge the help of Biotechnology Department, Science College Patna, for screening antifungal activity.

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