Accepted Manuscript Bivalent transition metal complexes of ONO donor hydrazone ligand: synthesis, structural characterization and antimicrobial activity Ravindra Bhaskar, Nilesh Salunkhe, Amit Yaul, Anand Aswar PII: DOI: Reference:
S1386-1425(15)30047-0 http://dx.doi.org/10.1016/j.saa.2015.06.121 SAA 13891
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
1 December 2014 28 June 2015 29 June 2015
Please cite this article as: R. Bhaskar, N. Salunkhe, A. Yaul, A. Aswar, Bivalent transition metal complexes of ONO donor hydrazone ligand: synthesis, structural characterization and antimicrobial activity, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.06.121
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Bivalent transition metal complexes of ONO donor hydrazone ligand: synthesis, structural characterization and antimicrobial activity Ravindra Bhaskar, Nilesh Salunkhe, Amit Yaul and Anand Aswar* Department of chemistry, Sant Gadge Baba Amravati University, Amravati, 444602, (MS), India. *[email protected]
ABSTRACT Mononuclear transition metal complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with a new hydrazone ligand derived from pyrazine-2-carbohydrazide and 2-hydroxyacetophenone have been synthesized. The isolated complexes were characterized by elemental analysis, spectral and analytical methods including elemental analyses, IR, diffuse reflectance,
1
H-NMR, mass spectra, molar
conductance, magnetic moment, ESR, XRD, TG and SEM analysis. From the elemental analyses data, the stoichiometry of the complexes was found to be 1:1 (metal: ligand) having the general formulae [M(L)(Cl)(H2O)2], [M = Mn(II), Co(II), Ni(II) and Cu(II)] and [M(L)(H2O)], [M = Zn(II) and Cd(II)]. The molar conductance values indicate the nonelectrolytic nature of metal complexes. The IR spectral data suggest that the ligand behaves as tridentate moiety with ONO donor atoms sequence towards central metal ion. The Mn(II), Co(II), Ni(II) and Cu(II) complexes have been assigned a monomeric octahedral geometry whereas tetrahedral to Zn(II) and Cd(II) complexes. The antibacterial and antifungal activities of the ligand and its metal complexes were studied against bacterial species E. coli, P. aeruginosa, S. aureus, B. subtilis, E. faecalis and S. pyogenes and fungi C. albicans, A. niger and A. clavatus. The activity data show that the metal complexes have a promising biological activity comparable with the parent ligand against all bacterial and fungal species. Keywords: Hydrazone ligand, complexes, spectroscopy, biological activity
Introduction Hydrazone ligands attracted special attention of researchers due to their well-known chelating capability, structural flexibility and diverse range of applications. The metal complexes
of hydrazones including heterocyclic moieties containing nitrogen, oxygen and sulphur as a hetro atoms have been studied extensively in order to establish a probable relationship between the chemical structure and biological activity [1–4]. Among them, Schiff base hydrazones bearing nitrogen containing moiety have attracted considerable attention due to their impressive, chemical and physical properties [5–8], biological activities [9–12] and also their analytical applications [13]. Literature survey reveals that though some work reported on hydrazone complexes but no attention has given to pyrazinoic acid hydrazones. In view of the enormous importance of pyrazinoic acid hydrazones, here we report the synthesis of a new hydrazone ligand, 2-hydroxyacetophenone pyrazine-2-carbohydrazone (H2L) (Fig. 1) and its Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes. The complexes were characterized by elemental analyses, IR, UV-VIS, 1H-NMR, mass, SEM, XRD, ESR spectral analysis, TG and molar conductance studies. All the synthesized compounds were screened antibacterial and antifungal activity. Fig. 1. Synthesis of ligand (H2L) Experimental Materials and physical measurements All chemicals used were of either AR or chemically pure grade. The solvents obtained from commercial sources were dried using standard methods [14] as and when required. All the metal salts were obtained from SD fine chemicals and were used without further purification. The IR spectra were recorded as KBr pellets using a Shimadzu 8201 spectrophotometer in the range 400−4000 cm-1. Carbon, hydrogen and nitrogen contents were determined on a Carlo Erba 1108 elemental analyzer. 1H and
13
C NMR spectra were recorded on Bruker Advance II,
400MHz, NMR spectrophotometer in d6-DMSO with TMS as an internal standard. Magnetic
measurements were carried out by the Sherwood magnetic susceptibility balance MK 1 at room temperature. The solid-state reflectance spectra of the complexes were recorded in the 200−1000 nm range (as MgO) disc on a Cary 60 UV−Vis spectrophotometer. The X−band ESR spectrum of Cu(II) complex was recorded on Varian E−112 spectrophotometer using TCNE (tetracyanoethylene) as the g-marker. Thermogravimetric analyses were performed on a Perkin Elmer, Diamond TG thermal analyzer in the temperature range 40−750oC with a heating rate of 10oC min-1. Metal contents of the complexes were analyzed gravimetrically after decomposing the organic matter with a mixture of HClO4, H2SO4 and HNO3 (1:1.5:2.5) and then igniting to metal oxide. X-ray diffraction patterns were obtained with a Bruker AXS, D8 advance equipped with Si(Li) PDS. Mass spectra were recorded on a Waters, Q-TOF micromass (LC-MS) spectrometer. The surface morphology was observed using a JEOL Model JSM - 6390LV scanning electron microscope. The molar conductance was recorded using 10-3 molar solutions in DMSO with an Elico conductivity bridge and dip type cell calibrated with KCl solution. Synthesis Synthesis of the ligand (H2L) Ethanolic solution of pyrazine-2-carbohydrazide (1g, 0.0072 mmol) was added drop wise to the magnetically stirred ethanol solution (10 ml) of 2-hydroxyacetophenone (0.9862g, 0.0072 mmol) and reaction mixture was refluxed for 3 h on water bath. The progress of reaction was monitored by TLC. The resulting Schiff base that separated out on cooling the reaction mixture was filtered, washed with ethanol and recrystallized with DMF. Yeild: 63%. Microanalytical data for C13H12N4O2. Anal. Calc.: C, 60.93; H, 4.72; N, 21.86. Found: C, 61.12; H, 4.70; N, 21.83%. IR (KBr disc, cm-1): 3346(OH), 3182 (NH), 1691 m(C=O), 1630 m(C=N), 1301 (C−O). 1H- NMR (DMSO-d6, 400 MHz): δ 12.99 (s,1H, OH), 11.44 (s,1H, NH),
9.31 (s, 1H, C3-H), 8.94 (J=2.4Hz, d, 1H, C5-H), 8.77 (J= 2.4Hz, d, 1H, C6-H), 7.71 (J= 1.4 & 6.7Hz, dd, 1H, C11-H), 7.59 (J= 1.4 & 6.7Hz, dd, 1H, C8-H), 7.28 (m, 2H, C10-H), 2,54 (s, 3H, CH3).
13
C NMR (DMSO-d6, 100 MHz): 167.80(C=N), 158.78(C=O), 159.74(C12), 147.85(C6),
144.04(C2), 143.85(C3), 143.12(C5), 132.48(C10), 131.39(C8), 128.34(C9), 118.71(C7), 117.29(C11), 14.66(CH3). Mass spectrum (ESI) [M]+1 = 257.2. Synthesis of the Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of ligand Equimolar quantities (0.01 mol) of Schiff base and appropriate metal salt were dissolved separately in DMF (25ml) and ethanol respectively. The solutions were filtered and mixed them in hot conditions under continuous stirring. The resulting reaction mixture was refluxed for 6−8 h on an oil bath. On cooling to room temperature, the colored complexes precipitated out was filtered, washed with DMF, ethanol and petroleum ether and finally dried under vacuum at room temperature. Yield: 60-65 %. Antimicrobial activity The bacterial strains, E. coli MTCC 443, P. aeruginosa MTCC 424, S. aureus MTCC 96, B. subtilis MTCC 8979, E. faecalis MTCC 439 and S. pyogenes MTCC 442 and fungal strains, C. albicans MTCC 227, A. niger MTCC 282 and A. clavatus MTCC 1323 were used in the study. The solutions of ciprofloxacin (antibacterial drug) and ketoconazole (antifungal drug) were used as standard. The disc agar diffusion method [15] was employed for the determination of antimicrobial activities. MICs (minimum inhibitory concentration) of the compounds against test organisms were determined by the broth micro dilution method. All the tests were performed in duplicate and repeated twice. Model values were selected. Results and discussion
Condensation of pyrazine-2-carbohydrazide with 2-hydroxyacetophenone in ethanol yields the Schiff base (H2L). The analytical and molar conductance data of the metal complexes are given in (Table 1). Table 1 Analytical and molar conductance data of the metal complexes The complexes obtained are coloured solids, air stable and insoluble in common organic solvents viz. ethanol, methanol, chloroform, benzene, cyclohexane, acetone, diethyl ether and but soluble in DMF and DMSO. The elemental analysis show 1:1 metal: ligand stoichiometry for all the complexes and it is in good agreement with the proposed structures and geometries of the ligand and complexes respectively. All the complexes are non-electrolytes as indicated by their low molar conductance values of 10-3M solutions of the complexes in DMSO at room temperature. IR spectra The IR spectra of the metal complexes are compared with the free ligand in order to determine the coordination sites that may be involved in coordination complexes (Fig. X). The important IR bands with their tentative assignments are depicted in Table 2. Fig. 2. IR spectra of ligand and its metal complexes Table 2 Infrared spectral bands for ligand and its metal complexes IR spectrum of the ligand shows a medium intensity band at 3346 cm-1 due to intramolecular hydrogen bonding vibrations (O–H⋯N) [16]. The absence of this band in the spectra of the complexes indicates the deprotonation of the phenolic oxygen and subsequent coordination to the metal ions. This is further supported by the upward shifting of ν(C–O) phenolic band by 39−16 cm-1 from 1301 cm-1, suggesting the coordination of phenolic oxygen to the metal ion [17]. The ligand exhibits strong band at 1630 cm-1, due to azomethine group (C=N). In all the complexes this band shifted to lower frequency (33−25 cm-1), indicating the participation of azomethine
nitrogen in coordination [18]. A ligand spectrum exhibits band at 977 cm-1 due to the ν(N−N) stretch. This band is shifted to higher wave number by 8−52 cm-1 in the complexes also supports the coordination of the azomethine nitrogen atom. The high frequency shift of the ν(N−N) band is expected because of diminished repulsion between the lone pairs of adjacent nitrogen atoms. The IR spectrum of ligand shows a strong band at 3182 and 1691 cm-1 due to N−H and C=O groups respectively. The IR spectra of Mn(II), Co(II), Ni(II) and Cu(II) complexes display ν(N– H) band almost at the same frequency as in the spectrum of the ligand suggesting that non involvement (NH) in coordination whereas ν(C=O) shows decrease in frequency by 52−8 cm-1 suggesting that involvement of the carbonyl oxygen atom in the coordination with the metal ion [19]. However, the absence of both the bands in the Zn(II) and Cd(II) complexes indicate the destruction of carbonyl moiety as a result of the enolization and subsequent coordination of the enolic oxygen after the dissociation of proton and the formation of the –C=N–N=C– group. In the spectra of complexes the appearance of low intensity broad band in the range 3390−3447 cm1
which may be assigned to stretching vibrations of ν(OH) group of water molecules. Besides
this, complexes also show bands in the range 1547−1554 and 836−867 cm-1 assignable to δγ(H2O) and δw(H2O) respectively for coordinated water molecules [20]. Conclusive evidence for metal binding is given by new bands in the IR spectra of the complexes at 516–599 and 459– 496 cm-1, assigned to ν(M–O) and ν(M–N) vibrations respectively [21]. Electronic spectra and magnetic moments The electronic spectrum of Mn(II) complex is in consistent with an octahedral geometry showing three weak d–d bands at 10212, 14342 and 25272 cm-1, assignable to the 6A1g → 4
T1g(4G), 6A1g→ 4Eg, 4 A1g (4G) and 6A1g→ 4Eg (4D), transitions, respectively. This evidenced by
the magnetic moment 5.82 B.M. suggesting a high spin octahedral configuration for the
complex. The electronic spectrum of Co(II) complex exhibits bands at 9095, 14421 and 16783 cm-1 corresponding to 4T1g → 4T2g(F), 4T1g → 4A2g(F) and 4T1g → 4T2g(P), transitions, respectively. These bands are characteristics of high spin octahedral Co(II) complexes. The ligand field parameters Dq, B and β also further supports the presence of octahedral geometry around the metal ion (Table 3). Table 3 Magnetic moments, electronic spectral data and ligand fied parameters of metal complexes Also, the room temperature magnetic moment value of Co(II) complex was found to be 4.71 BM suggest spin free octahedral geometry around the Co(II) ion [22]. The Ni(II) complex show three bands at 10256, 16431 and 26357 cm-1, which may be assigned to the transitions 3A2g → 3
T2g(F), 3A2g → 3T1g(F), and 3A2g(F) → 3T1g(P), respectively, of a typical octahedral structure.
The observed ν2/ν1 ratio (1.60) is as expected for an octahedral Ni(II) complexes. The observed B0 value (801 cm-1) compared to the free-ion value (1041 cm-1) indicates a considerable covalent character in the metal−ligand bond. The magnetic moment value is found to be 2.86 B.M., which is good agreement with an octahedral geometry [23]. The electronic spectrum of Cu(II) complex shows two bands at 13869 and 15407 cm-1 which are assigned to 2B1g → 2A1g and 2B1g → 2Eg, transition, respectively. The additional band appears at 24147 cm-1 assigned to ligand to metal charge transfer transition. This complex has magnetic moment 1.84 BM, which is higher than the spin-only value (1.73 BM) expected for one unpaired electron and offers possibility of distorted octahedral geometry [24]. Zn(II) and Cd(II) complexes are found to be diamagnetic as expected for d0 configurations and do not show any d-d transitions. ESR
The ESR spectrum of Cu(II) complex was recorded at 25oC and did not show any hyperfine splitting, it give only single signal for which gll and g⊥ have been calculated. The calculated gll and g⊥ values are found to be 2.13 and 1.96 respectively, which support the presence of unpaired electron in the dx2-y2 orbital [25]. 1
H NMR spectra The essential features of the 1H NMR spectrum of the Zn(II) complex as a representative
case is similar to that of ligand (H2L). The
1
H NMR spectrum of ligand shows a signal at δ
12.99 ppm due to −OH proton , which is absent in the spectrum of Zn(II) complex, indicating the deprotonation of the −OH group and confirming that the ligand coordinate to zinc metal ion via deprotonation. The signal for NH proton of the ligand was observed at δ 11.44 ppm which gets disappeared in case of Zn(II) complex supports the coordination through enolic form of ligand to the Zn(II) ion. 1H NMR of [Zn(L)(H2O)], (DMSO-d6, 400MHz): δ 9.31 (s, 1H, C3H), 8.91 (d, 1H, C5-H), 8.77 (1H, C6-H), 7.40(dd,1H, C11-H), 7.44 (dd, 1H, C8-H), 6.96(m, 2H, C9 & C10), 2.52(s, 3H, CH3). Mass spectra Mass spectrum of the ligand shows the molecular ion peak at m/z = 257.2, which correspond to the molecular mass of the ligand. The mass spectra of the Cu(II), Ni(II) and Zn(II) complexes show a molecular ion peak (M+) at m/z = 389.01, 384.01 and 337.34 respectively is indicative of monomeric nature of the complex. Powder XRD The x-ray diffraction study of ligand H2L and its Ni(II), Cu(II) and Zn(II) complexes was carried out using CuKα radiation with λ = 1.5406Å. The XRD patterns of the compounds were recorded at 2θ values between 5o and 55oand. The diffraction patterns reveal the crystalline
nature of complexes. X-ray crystal system has been worked out by trial and error method for finding the best fit between observed and calculated values. The unit cell parameters of all complexes are as follows; H2L: system = triclinic, a = 10.3769 Å, b = 16.9788 Å, c = 6.7953 Å, α = 92.225o, β = 99.964o, γ = 93.369o, V = 1175.69 Å3; [Ni(HL)(Cl)(H2O)2]: system = monoclinic, a = 17.6352 Å, b = 6.0608 Å, c = 12.9937 Å, β = 94.607o, V = 1384.32 Å3; [Cu(HL)(Cl)(H2O)2]: system = triclinic, a = 12.4216 Å, b = 17.6561 Å, c = 11.4830 Å, α = 131.903o, β = 119.614o, γ = 90.577o, V = 1386.32 Å3; [Zn(L)(H2O)]: system = triclinic, a = 9.6332 Å,
b = 13.8571 Å, c = 7.1572 Å, α = 94.519o, β = 118.051o, γ = 111.834o, V =
744.20 Å3. The average crystallite size of the H2L, Ni(II), Cu(II) and Zn(II) compounds was calculated from Scherer’s formula [26, 27]. Using the full width at half maximum intensity of the patterns, the average sizes of the crystals are around 16, 24, 32, and 31 nm for H2L, Ni(II), Cu(II) and Zn(II) respectively, indicating that the compounds are in nanocrystalline phase. SEM The SEM-EDS micrographs of the Ni(II), Cu(II) and Zn(II) complexes (Figs. 3−5) show that the Ni(II) and Zn(II) complexes have platelet-like structure, while Cu(II) complex exhibits cauliflower-like structure. Fig. 3. SEM-EDS graph of [Co(HL)(Cl)(H2O)2] complex Fig. 4. SEM-EDS graph of [Ni(HL)(Cl)(H2O)2] complex Fig. 5. SEM-EDS graph of [Cu(HL)(Cl)(H2O)2] complex The surface morphology of the complexes shows that the particles are agglomerated. The smaller average crystallite size found from XRD also shows that the particles are agglomerated. Thermogravimetric analysis
TG analysis was used to explore associated water or solvent molecules in the coordination sphere or crystalline form. Table 4 shows TG analysis data of the ligand and its complexes that recorded in the temperature range from 40 up to 750 ºC. Table 4 Thermogravimetric data of metal complexes The results are in good agreement with the proposed formulae. The ligand (H2L) decompose in a single stage, whereas Zn(II) and Cd(II) complexes decomposed in two stages while Mn(II), Co(II), Ni(II) and Cu(II) complexes decomposed in three stages. The first stage is due to the loss of coordinated water molecules in the temperature range 90–205 oC [28]. In case of Mn(II), Co(II), Ni(II) and Cu(II) complexes second stage is corresponds to the loss of coordinated chloride ions in the temperature range 185–255 oC. After the loss of coordinated water/chloride ion, all the complexes shows rapid degradation in the temperature range 255–750oC [29]. This may be due to the decomposition of organic part of the complex, indicated by the rapid fall in the percentage mass loss. The decomposition continues above 260 oC in each complex as indicated by the consistency in weight in the plateau of the thermogram and formed stable respective metal oxide. Antimicribial activity The ligand (H2L) and its metal complexes were screened against the bacterial stains S. aureus MTCC 96, S. pyogenes MTCC 442, B. subtilis MTCC 8979, E. coli MTCC 443, P. aeruginosa MTCC 424 & E. faecalis MTCC 439 and fungal stains A. niger MTCC 282, A. clavatus MTCC 1323, C. albicans MTCC 227. The results of inhibition are compared with standard antibacterial drug ciprofloxacin and antifungal drug clotrimazole. The antimicrobial activity of H2L ligand and its complexes bacteria and fungi is summarized in Table 5. Table 5 Antimicrobial activity of the H2L ligand and its metal complexes
It is clear that the Mn(II), Co(II), Ni(II) and Cu(II) complexes exhibit significant activity against all bacterial and fungal stains, this may be due to the presence of NH group on the ligand playing an important role in the activity. In addition, these complexes also contain chloride ion inside the structure which may also be responsible for higher activity. These groups are believed to impart the transformation reaction in biological systems. Generally, all of the metal complexes show higher antimicrobial properties compared to the free H2L ligand. Coordination reduces the polarity [30] of the metal ion, mainly because of the partial sharing of its positive charge with the donor groups within the chelate ring system formed during coordination. This process, in turn, increases the lipophilic nature of the central metal atom, which favors its permeation more efficiently through the lipid layer of the microorganism [31, 32], thus destroying them more aggressively. Some important factors, such as the nature of the metal ion, nature of the ligand, coordinating sites, geometry of the complex, concentration, hydrophilicity, lipophilicity and presence of co-ligands, have considerable influence on the antibacterial activity. From the antimicrobial assay, thus it is found that, the tested compounds possess better antimicrobial activities but less as compared to standards used. Conclusions The analytical and physico-chemical analysis confirmed the composition and structure of the newly synthesized complexes. The IR, electronic spectra and magnetic moment data led to the conclusion that the metal ions take different geometries. An octahedral geometry was assigned to Mn(II), Co(II), Ni(II) and Cu(II) complexes while tetrahedral to Zn(II) and Cd(II) complexes. Antimicrobial screening of the free ligand and its complexes showed high activity for Mn(II), Co(II), Ni(II), Cu(II) complexes; however Zn(II) and Cd(II) complexes exhibit moderate activities.
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Figure cations Fig. 1. Synthesis of ligand (H2L) Fig. 2. IR spectra of ligand and its metal complexes Fig. 3. SEM-EDS graph of [Ni(HL)(Cl)(H2O)2] complex Fig. 4. SEM-EDS graph of [Cu(HL)(Cl)(H2O)2] complex Fig. 5. SEM-EDS graph of [Zn(L)(H2O)] complex
O
O
CH3
O 1
N NH
NH2
N
HO
6
N 2
Ethanol
+
3
5
N
N
CH3
NH 7
HO
8
12
4 11
9 10
Fig. 1. Synthesis of ligand (H2L)
Fig. 2. IR spectra of ligand and its metal complexes
Fig. 3. SEM-EDS graph of [Ni(HL)(Cl)(H2O)2] complex
Fig. 4. SEM-EDS graph of [CuHL)(Cl)(H2O)2] complex
Fig. 5. SEM-EDS graph of [Zn(L)(H2O)] complex Cation for tables Table 1
Analytical and molar conductance data of the metal complexes Table 2 Infrared spectral bands for ligand and its metal complexes Table 3 Magnetic oments, electronic spectral data and ligand fied parameters of metal complexes Table 4 Thermogravimetric data of metal complexes Table 5 Antimicrobial activity of the H2L ligand and its metal complexes
Table 1 Analytical and molar conductance data of the metal complexes
Compound
Formula
Formula weight
Elemental analysis found (calcd)
Molar conductance
C
H
N
M
(-1 cm2 mol-1)
[Mn(HL)(Cl)(H2O)2]
C13H15ClN4O4Mn
381.61
41.32 (40.91)
3.52 (3.96)
14.92 (14.68)
14.73 (14.39)
13.4
[Co(HL)(Cl)(H2O)2]
C13H15ClN4O4Co
385.63
40.72 (40.49)
3.61 (3.92)
14.04 (14.53)
15.14 (15.28)
7.6
[Ni(HL)(Cl)(H2O)2]
C13H15ClN4O4Ni
384.59
40.03 (40.51)
3.17 (3.92)
14.21 (14.54)
15.97 (15.24)
9.2
[Cu(HL)(Cl)(H2O)2]
C13H15ClN4O4Cu
390.01
40.62 (40.00)
3.43 (3.87)
14.34 (14.36)
15.74 (16.28)
5.1
[Zn(L)(H2O)]
C13H12N4O3Zn
337.72
45.83 (46.24)
3.94 (3.58)
17.07 (16.60)
19.79 (19.36)
7.9
[Cd(L)(H2O)]
C13H12N4O3Cd
384.60
40.43 (40.60)
3.19 (3.13)
14.985 (14.55)
29.66 (29.22)
12.9
Table 2 Important IR spectral bands (cm-1) of the ligand and its metal complexes
3346
3182
1691
1630
(CO) phenolic 1301
[Mn(HL)(Cl)(H2O)2]
-
3187
1676
1599
1325
-
1029
582
461
[Co(HL)(Cl)(H2O)2]
-
3182
1649
1605
1318
-
985
516
488
[Ni(HL)(Cl)(H2O)2]
-
3180
1683
1603
1317
-
992
517
491
[Cu(HL)(Cl)(H2O)2]
-
3184
1672
1602
1318
-
989
583
496
[Zn(L)(H2O)]
-
-
-
1600
1321
1232
983
599
459
[Cd(L)(H2O)]
-
-
-
1597
1340
1237
1015
581
461
Compound H2L
(OHN) (NH)
(C=O)
(C=N )
(CO) enolic -
(NN)
(MO)
(MN)
977
-
-
Table 3 Magnetic moments, electronic spectral data and ligand field parameters of metal complexes Complex
eff (B.M.)
Band position (cm-1)
Assignments
Dq (cm-1)
B0 (cm-1)
2/1
[Mn(HL)(Cl)(H2O)2]
5.82
6
-
-
-
4.71
7687
734
0.75
1.58
[Ni(HL)(Cl)(H2O)2]
2.76
1026
801
0.78
1.60
[Cu(HL)(Cl)(H2O)2]
1.64
A1g 4T1g(4G) 6 A1g 4Eg, 4A1g(4G) 6 A1g 4Eg(4D) 4 T1g 4T2g(F) 4 T1g 4A2g(F) 4 T1g 4T2g(P) 3 A2g 3T2g(F) 3 A2g 3T1g(F) 3 A2g 3T1g(P) 2 B1g 2A1g 2 B1g 2Eg LMCT
-
[Co(HL)(Cl)(H2O)2]
10212 14342 25272 9095 14421 16783 10256 16431 26357 13869 15407 24147
-
-
-
-
Table 4 Thermogravimetric data of metal complexes Compound
[Mn(HL)(Cl)(H2O)2]
[Co(HL)(Cl)(H2O)2]
[Ni(HL)(Cl)(H2O)2]
[Cu(HL)(Cl)(H2O)2]
[Zn(L)(H2O)] [Cd(L)(H2O)]
Temp. range (oC)
95-185 185-230 230-750 90-185 185-210 210-750 110-205 205-255 255-700 90-185 185-215 215-700 90-182 182-650 105-190 190-680
% mass loss
Assignment
Found
Calcd.
9.51 9.72 9.83 10.01
9.44 9.3 9.35 9.22 9.34 9.22 9.23 9.10 5.34 4.68 -
9.85 9.68 8.94 9.24 5.47 5.10 -
Loss of 2 moles of coordinated water molecules Loss of 1 coordinated chloride ion deligation Loss of 2 moles of coordinated water molecules Loss of 1 coordinated chloride ion deligation Loss of 2 moles of coordinated water molecules Loss of 1 coordinated chloride ion deligation Loss of 2 moles of coordinated water molecules Loss of 1 coordinated chloride ion deligation Loss of 1 mole of coordinated water molecule deligation Loss of 1 mole of coordinated water molecule deligation
Table 5 Antimicrobial activity of the H2L ligand and its metal complexes Compound
Minimum inhibitory concentration (g ml-1) E. coli
P. aeruginosa
S. aureus
B. subtilis
E. faecalis
S. pyogenes
C. albican
A. niger
A. clavatus
(MTCC 443)
(MTCC 424)
(MTCC 96)
(MTCC 8979)
(MTCC 439)
(MTCC 442)
(MTCC 227)
(MTCC 282)
(MTCC 1323)
H2L
12
12
13
09
09
08
11
10
10
[Mn(HL)(Cl)(H2O)2]
14
14
16
14
15
13
14
14
15
[Co(HL)(Cl)(H2O)2]
16
14
15
15
14
13
13
14
16
[Ni(HL)(Cl)(H2O)2]
16
14
17
15
15
12
12
13
14
[Cu(HL)(Cl)(H2O)2]
17
16
18
13
17
15
16
12
14
[Zn(L)(H2O)]
14
13
14
12
11
10
12
11
13
[Cd(L)(H2O)]
12
12
14
10
10
11
12
12
12
Ciprofloxacin*
13
14
14
14
15
12
--
--
--
Clotrimazole*
--
--
--
--
--
--
13
09
12
* Standard drug
Bivalent transition metal complexes of ONO donor hydrazone ligand: synthesis, characterization and antimicrobial activity Ravindra Bhaskar, Nilesh Salunkhe, Amit Yaul and Anand Aswar* Department of chemistry, Sant Gadge Baba Amravati University, Amravati, 444602, (MS), India. *Email- [email protected]
Graphical abstract
N
N
N H N O
Cl
N N
CH3 N
O M
M O
H2O
CH3 N
H2O
O
OH2 M = Mn(II), Co(II), Ni(II) and Cu(II)
M = Zn(II) and Cd(II)
Highlights
•
Synthesis of Hydrazone Schiff base (H2L) and its complexes.
•
Physicochemical characterization of compounds.
•
Bacterial and fungal screening of compounds.
•
Complexes containing −NH and −Cl group show higher antimicrobial activity.
24
S1386-1425(15)30047-0 http://dx.doi.org/10.1016/j.saa.2015.06.121 SAA 13891
To appear in:
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Received Date: Revised Date: Accepted Date:
1 December 2014 28 June 2015 29 June 2015
Please cite this article as: R. Bhaskar, N. Salunkhe, A. Yaul, A. Aswar, Bivalent transition metal complexes of ONO donor hydrazone ligand: synthesis, structural characterization and antimicrobial activity, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.06.121
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Bivalent transition metal complexes of ONO donor hydrazone ligand: synthesis, structural characterization and antimicrobial activity Ravindra Bhaskar, Nilesh Salunkhe, Amit Yaul and Anand Aswar* Department of chemistry, Sant Gadge Baba Amravati University, Amravati, 444602, (MS), India. *[email protected]
ABSTRACT Mononuclear transition metal complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with a new hydrazone ligand derived from pyrazine-2-carbohydrazide and 2-hydroxyacetophenone have been synthesized. The isolated complexes were characterized by elemental analysis, spectral and analytical methods including elemental analyses, IR, diffuse reflectance,
1
H-NMR, mass spectra, molar
conductance, magnetic moment, ESR, XRD, TG and SEM analysis. From the elemental analyses data, the stoichiometry of the complexes was found to be 1:1 (metal: ligand) having the general formulae [M(L)(Cl)(H2O)2], [M = Mn(II), Co(II), Ni(II) and Cu(II)] and [M(L)(H2O)], [M = Zn(II) and Cd(II)]. The molar conductance values indicate the nonelectrolytic nature of metal complexes. The IR spectral data suggest that the ligand behaves as tridentate moiety with ONO donor atoms sequence towards central metal ion. The Mn(II), Co(II), Ni(II) and Cu(II) complexes have been assigned a monomeric octahedral geometry whereas tetrahedral to Zn(II) and Cd(II) complexes. The antibacterial and antifungal activities of the ligand and its metal complexes were studied against bacterial species E. coli, P. aeruginosa, S. aureus, B. subtilis, E. faecalis and S. pyogenes and fungi C. albicans, A. niger and A. clavatus. The activity data show that the metal complexes have a promising biological activity comparable with the parent ligand against all bacterial and fungal species. Keywords: Hydrazone ligand, complexes, spectroscopy, biological activity
Introduction Hydrazone ligands attracted special attention of researchers due to their well-known chelating capability, structural flexibility and diverse range of applications. The metal complexes
of hydrazones including heterocyclic moieties containing nitrogen, oxygen and sulphur as a hetro atoms have been studied extensively in order to establish a probable relationship between the chemical structure and biological activity [1–4]. Among them, Schiff base hydrazones bearing nitrogen containing moiety have attracted considerable attention due to their impressive, chemical and physical properties [5–8], biological activities [9–12] and also their analytical applications [13]. Literature survey reveals that though some work reported on hydrazone complexes but no attention has given to pyrazinoic acid hydrazones. In view of the enormous importance of pyrazinoic acid hydrazones, here we report the synthesis of a new hydrazone ligand, 2-hydroxyacetophenone pyrazine-2-carbohydrazone (H2L) (Fig. 1) and its Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes. The complexes were characterized by elemental analyses, IR, UV-VIS, 1H-NMR, mass, SEM, XRD, ESR spectral analysis, TG and molar conductance studies. All the synthesized compounds were screened antibacterial and antifungal activity. Fig. 1. Synthesis of ligand (H2L) Experimental Materials and physical measurements All chemicals used were of either AR or chemically pure grade. The solvents obtained from commercial sources were dried using standard methods [14] as and when required. All the metal salts were obtained from SD fine chemicals and were used without further purification. The IR spectra were recorded as KBr pellets using a Shimadzu 8201 spectrophotometer in the range 400−4000 cm-1. Carbon, hydrogen and nitrogen contents were determined on a Carlo Erba 1108 elemental analyzer. 1H and
13
C NMR spectra were recorded on Bruker Advance II,
400MHz, NMR spectrophotometer in d6-DMSO with TMS as an internal standard. Magnetic
measurements were carried out by the Sherwood magnetic susceptibility balance MK 1 at room temperature. The solid-state reflectance spectra of the complexes were recorded in the 200−1000 nm range (as MgO) disc on a Cary 60 UV−Vis spectrophotometer. The X−band ESR spectrum of Cu(II) complex was recorded on Varian E−112 spectrophotometer using TCNE (tetracyanoethylene) as the g-marker. Thermogravimetric analyses were performed on a Perkin Elmer, Diamond TG thermal analyzer in the temperature range 40−750oC with a heating rate of 10oC min-1. Metal contents of the complexes were analyzed gravimetrically after decomposing the organic matter with a mixture of HClO4, H2SO4 and HNO3 (1:1.5:2.5) and then igniting to metal oxide. X-ray diffraction patterns were obtained with a Bruker AXS, D8 advance equipped with Si(Li) PDS. Mass spectra were recorded on a Waters, Q-TOF micromass (LC-MS) spectrometer. The surface morphology was observed using a JEOL Model JSM - 6390LV scanning electron microscope. The molar conductance was recorded using 10-3 molar solutions in DMSO with an Elico conductivity bridge and dip type cell calibrated with KCl solution. Synthesis Synthesis of the ligand (H2L) Ethanolic solution of pyrazine-2-carbohydrazide (1g, 0.0072 mmol) was added drop wise to the magnetically stirred ethanol solution (10 ml) of 2-hydroxyacetophenone (0.9862g, 0.0072 mmol) and reaction mixture was refluxed for 3 h on water bath. The progress of reaction was monitored by TLC. The resulting Schiff base that separated out on cooling the reaction mixture was filtered, washed with ethanol and recrystallized with DMF. Yeild: 63%. Microanalytical data for C13H12N4O2. Anal. Calc.: C, 60.93; H, 4.72; N, 21.86. Found: C, 61.12; H, 4.70; N, 21.83%. IR (KBr disc, cm-1): 3346(OH), 3182 (NH), 1691 m(C=O), 1630 m(C=N), 1301 (C−O). 1H- NMR (DMSO-d6, 400 MHz): δ 12.99 (s,1H, OH), 11.44 (s,1H, NH),
9.31 (s, 1H, C3-H), 8.94 (J=2.4Hz, d, 1H, C5-H), 8.77 (J= 2.4Hz, d, 1H, C6-H), 7.71 (J= 1.4 & 6.7Hz, dd, 1H, C11-H), 7.59 (J= 1.4 & 6.7Hz, dd, 1H, C8-H), 7.28 (m, 2H, C10-H), 2,54 (s, 3H, CH3).
13
C NMR (DMSO-d6, 100 MHz): 167.80(C=N), 158.78(C=O), 159.74(C12), 147.85(C6),
144.04(C2), 143.85(C3), 143.12(C5), 132.48(C10), 131.39(C8), 128.34(C9), 118.71(C7), 117.29(C11), 14.66(CH3). Mass spectrum (ESI) [M]+1 = 257.2. Synthesis of the Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of ligand Equimolar quantities (0.01 mol) of Schiff base and appropriate metal salt were dissolved separately in DMF (25ml) and ethanol respectively. The solutions were filtered and mixed them in hot conditions under continuous stirring. The resulting reaction mixture was refluxed for 6−8 h on an oil bath. On cooling to room temperature, the colored complexes precipitated out was filtered, washed with DMF, ethanol and petroleum ether and finally dried under vacuum at room temperature. Yield: 60-65 %. Antimicrobial activity The bacterial strains, E. coli MTCC 443, P. aeruginosa MTCC 424, S. aureus MTCC 96, B. subtilis MTCC 8979, E. faecalis MTCC 439 and S. pyogenes MTCC 442 and fungal strains, C. albicans MTCC 227, A. niger MTCC 282 and A. clavatus MTCC 1323 were used in the study. The solutions of ciprofloxacin (antibacterial drug) and ketoconazole (antifungal drug) were used as standard. The disc agar diffusion method [15] was employed for the determination of antimicrobial activities. MICs (minimum inhibitory concentration) of the compounds against test organisms were determined by the broth micro dilution method. All the tests were performed in duplicate and repeated twice. Model values were selected. Results and discussion
Condensation of pyrazine-2-carbohydrazide with 2-hydroxyacetophenone in ethanol yields the Schiff base (H2L). The analytical and molar conductance data of the metal complexes are given in (Table 1). Table 1 Analytical and molar conductance data of the metal complexes The complexes obtained are coloured solids, air stable and insoluble in common organic solvents viz. ethanol, methanol, chloroform, benzene, cyclohexane, acetone, diethyl ether and but soluble in DMF and DMSO. The elemental analysis show 1:1 metal: ligand stoichiometry for all the complexes and it is in good agreement with the proposed structures and geometries of the ligand and complexes respectively. All the complexes are non-electrolytes as indicated by their low molar conductance values of 10-3M solutions of the complexes in DMSO at room temperature. IR spectra The IR spectra of the metal complexes are compared with the free ligand in order to determine the coordination sites that may be involved in coordination complexes (Fig. X). The important IR bands with their tentative assignments are depicted in Table 2. Fig. 2. IR spectra of ligand and its metal complexes Table 2 Infrared spectral bands for ligand and its metal complexes IR spectrum of the ligand shows a medium intensity band at 3346 cm-1 due to intramolecular hydrogen bonding vibrations (O–H⋯N) [16]. The absence of this band in the spectra of the complexes indicates the deprotonation of the phenolic oxygen and subsequent coordination to the metal ions. This is further supported by the upward shifting of ν(C–O) phenolic band by 39−16 cm-1 from 1301 cm-1, suggesting the coordination of phenolic oxygen to the metal ion [17]. The ligand exhibits strong band at 1630 cm-1, due to azomethine group (C=N). In all the complexes this band shifted to lower frequency (33−25 cm-1), indicating the participation of azomethine
nitrogen in coordination [18]. A ligand spectrum exhibits band at 977 cm-1 due to the ν(N−N) stretch. This band is shifted to higher wave number by 8−52 cm-1 in the complexes also supports the coordination of the azomethine nitrogen atom. The high frequency shift of the ν(N−N) band is expected because of diminished repulsion between the lone pairs of adjacent nitrogen atoms. The IR spectrum of ligand shows a strong band at 3182 and 1691 cm-1 due to N−H and C=O groups respectively. The IR spectra of Mn(II), Co(II), Ni(II) and Cu(II) complexes display ν(N– H) band almost at the same frequency as in the spectrum of the ligand suggesting that non involvement (NH) in coordination whereas ν(C=O) shows decrease in frequency by 52−8 cm-1 suggesting that involvement of the carbonyl oxygen atom in the coordination with the metal ion [19]. However, the absence of both the bands in the Zn(II) and Cd(II) complexes indicate the destruction of carbonyl moiety as a result of the enolization and subsequent coordination of the enolic oxygen after the dissociation of proton and the formation of the –C=N–N=C– group. In the spectra of complexes the appearance of low intensity broad band in the range 3390−3447 cm1
which may be assigned to stretching vibrations of ν(OH) group of water molecules. Besides
this, complexes also show bands in the range 1547−1554 and 836−867 cm-1 assignable to δγ(H2O) and δw(H2O) respectively for coordinated water molecules [20]. Conclusive evidence for metal binding is given by new bands in the IR spectra of the complexes at 516–599 and 459– 496 cm-1, assigned to ν(M–O) and ν(M–N) vibrations respectively [21]. Electronic spectra and magnetic moments The electronic spectrum of Mn(II) complex is in consistent with an octahedral geometry showing three weak d–d bands at 10212, 14342 and 25272 cm-1, assignable to the 6A1g → 4
T1g(4G), 6A1g→ 4Eg, 4 A1g (4G) and 6A1g→ 4Eg (4D), transitions, respectively. This evidenced by
the magnetic moment 5.82 B.M. suggesting a high spin octahedral configuration for the
complex. The electronic spectrum of Co(II) complex exhibits bands at 9095, 14421 and 16783 cm-1 corresponding to 4T1g → 4T2g(F), 4T1g → 4A2g(F) and 4T1g → 4T2g(P), transitions, respectively. These bands are characteristics of high spin octahedral Co(II) complexes. The ligand field parameters Dq, B and β also further supports the presence of octahedral geometry around the metal ion (Table 3). Table 3 Magnetic moments, electronic spectral data and ligand fied parameters of metal complexes Also, the room temperature magnetic moment value of Co(II) complex was found to be 4.71 BM suggest spin free octahedral geometry around the Co(II) ion [22]. The Ni(II) complex show three bands at 10256, 16431 and 26357 cm-1, which may be assigned to the transitions 3A2g → 3
T2g(F), 3A2g → 3T1g(F), and 3A2g(F) → 3T1g(P), respectively, of a typical octahedral structure.
The observed ν2/ν1 ratio (1.60) is as expected for an octahedral Ni(II) complexes. The observed B0 value (801 cm-1) compared to the free-ion value (1041 cm-1) indicates a considerable covalent character in the metal−ligand bond. The magnetic moment value is found to be 2.86 B.M., which is good agreement with an octahedral geometry [23]. The electronic spectrum of Cu(II) complex shows two bands at 13869 and 15407 cm-1 which are assigned to 2B1g → 2A1g and 2B1g → 2Eg, transition, respectively. The additional band appears at 24147 cm-1 assigned to ligand to metal charge transfer transition. This complex has magnetic moment 1.84 BM, which is higher than the spin-only value (1.73 BM) expected for one unpaired electron and offers possibility of distorted octahedral geometry [24]. Zn(II) and Cd(II) complexes are found to be diamagnetic as expected for d0 configurations and do not show any d-d transitions. ESR
The ESR spectrum of Cu(II) complex was recorded at 25oC and did not show any hyperfine splitting, it give only single signal for which gll and g⊥ have been calculated. The calculated gll and g⊥ values are found to be 2.13 and 1.96 respectively, which support the presence of unpaired electron in the dx2-y2 orbital [25]. 1
H NMR spectra The essential features of the 1H NMR spectrum of the Zn(II) complex as a representative
case is similar to that of ligand (H2L). The
1
H NMR spectrum of ligand shows a signal at δ
12.99 ppm due to −OH proton , which is absent in the spectrum of Zn(II) complex, indicating the deprotonation of the −OH group and confirming that the ligand coordinate to zinc metal ion via deprotonation. The signal for NH proton of the ligand was observed at δ 11.44 ppm which gets disappeared in case of Zn(II) complex supports the coordination through enolic form of ligand to the Zn(II) ion. 1H NMR of [Zn(L)(H2O)], (DMSO-d6, 400MHz): δ 9.31 (s, 1H, C3H), 8.91 (d, 1H, C5-H), 8.77 (1H, C6-H), 7.40(dd,1H, C11-H), 7.44 (dd, 1H, C8-H), 6.96(m, 2H, C9 & C10), 2.52(s, 3H, CH3). Mass spectra Mass spectrum of the ligand shows the molecular ion peak at m/z = 257.2, which correspond to the molecular mass of the ligand. The mass spectra of the Cu(II), Ni(II) and Zn(II) complexes show a molecular ion peak (M+) at m/z = 389.01, 384.01 and 337.34 respectively is indicative of monomeric nature of the complex. Powder XRD The x-ray diffraction study of ligand H2L and its Ni(II), Cu(II) and Zn(II) complexes was carried out using CuKα radiation with λ = 1.5406Å. The XRD patterns of the compounds were recorded at 2θ values between 5o and 55oand. The diffraction patterns reveal the crystalline
nature of complexes. X-ray crystal system has been worked out by trial and error method for finding the best fit between observed and calculated values. The unit cell parameters of all complexes are as follows; H2L: system = triclinic, a = 10.3769 Å, b = 16.9788 Å, c = 6.7953 Å, α = 92.225o, β = 99.964o, γ = 93.369o, V = 1175.69 Å3; [Ni(HL)(Cl)(H2O)2]: system = monoclinic, a = 17.6352 Å, b = 6.0608 Å, c = 12.9937 Å, β = 94.607o, V = 1384.32 Å3; [Cu(HL)(Cl)(H2O)2]: system = triclinic, a = 12.4216 Å, b = 17.6561 Å, c = 11.4830 Å, α = 131.903o, β = 119.614o, γ = 90.577o, V = 1386.32 Å3; [Zn(L)(H2O)]: system = triclinic, a = 9.6332 Å,
b = 13.8571 Å, c = 7.1572 Å, α = 94.519o, β = 118.051o, γ = 111.834o, V =
744.20 Å3. The average crystallite size of the H2L, Ni(II), Cu(II) and Zn(II) compounds was calculated from Scherer’s formula [26, 27]. Using the full width at half maximum intensity of the patterns, the average sizes of the crystals are around 16, 24, 32, and 31 nm for H2L, Ni(II), Cu(II) and Zn(II) respectively, indicating that the compounds are in nanocrystalline phase. SEM The SEM-EDS micrographs of the Ni(II), Cu(II) and Zn(II) complexes (Figs. 3−5) show that the Ni(II) and Zn(II) complexes have platelet-like structure, while Cu(II) complex exhibits cauliflower-like structure. Fig. 3. SEM-EDS graph of [Co(HL)(Cl)(H2O)2] complex Fig. 4. SEM-EDS graph of [Ni(HL)(Cl)(H2O)2] complex Fig. 5. SEM-EDS graph of [Cu(HL)(Cl)(H2O)2] complex The surface morphology of the complexes shows that the particles are agglomerated. The smaller average crystallite size found from XRD also shows that the particles are agglomerated. Thermogravimetric analysis
TG analysis was used to explore associated water or solvent molecules in the coordination sphere or crystalline form. Table 4 shows TG analysis data of the ligand and its complexes that recorded in the temperature range from 40 up to 750 ºC. Table 4 Thermogravimetric data of metal complexes The results are in good agreement with the proposed formulae. The ligand (H2L) decompose in a single stage, whereas Zn(II) and Cd(II) complexes decomposed in two stages while Mn(II), Co(II), Ni(II) and Cu(II) complexes decomposed in three stages. The first stage is due to the loss of coordinated water molecules in the temperature range 90–205 oC [28]. In case of Mn(II), Co(II), Ni(II) and Cu(II) complexes second stage is corresponds to the loss of coordinated chloride ions in the temperature range 185–255 oC. After the loss of coordinated water/chloride ion, all the complexes shows rapid degradation in the temperature range 255–750oC [29]. This may be due to the decomposition of organic part of the complex, indicated by the rapid fall in the percentage mass loss. The decomposition continues above 260 oC in each complex as indicated by the consistency in weight in the plateau of the thermogram and formed stable respective metal oxide. Antimicribial activity The ligand (H2L) and its metal complexes were screened against the bacterial stains S. aureus MTCC 96, S. pyogenes MTCC 442, B. subtilis MTCC 8979, E. coli MTCC 443, P. aeruginosa MTCC 424 & E. faecalis MTCC 439 and fungal stains A. niger MTCC 282, A. clavatus MTCC 1323, C. albicans MTCC 227. The results of inhibition are compared with standard antibacterial drug ciprofloxacin and antifungal drug clotrimazole. The antimicrobial activity of H2L ligand and its complexes bacteria and fungi is summarized in Table 5. Table 5 Antimicrobial activity of the H2L ligand and its metal complexes
It is clear that the Mn(II), Co(II), Ni(II) and Cu(II) complexes exhibit significant activity against all bacterial and fungal stains, this may be due to the presence of NH group on the ligand playing an important role in the activity. In addition, these complexes also contain chloride ion inside the structure which may also be responsible for higher activity. These groups are believed to impart the transformation reaction in biological systems. Generally, all of the metal complexes show higher antimicrobial properties compared to the free H2L ligand. Coordination reduces the polarity [30] of the metal ion, mainly because of the partial sharing of its positive charge with the donor groups within the chelate ring system formed during coordination. This process, in turn, increases the lipophilic nature of the central metal atom, which favors its permeation more efficiently through the lipid layer of the microorganism [31, 32], thus destroying them more aggressively. Some important factors, such as the nature of the metal ion, nature of the ligand, coordinating sites, geometry of the complex, concentration, hydrophilicity, lipophilicity and presence of co-ligands, have considerable influence on the antibacterial activity. From the antimicrobial assay, thus it is found that, the tested compounds possess better antimicrobial activities but less as compared to standards used. Conclusions The analytical and physico-chemical analysis confirmed the composition and structure of the newly synthesized complexes. The IR, electronic spectra and magnetic moment data led to the conclusion that the metal ions take different geometries. An octahedral geometry was assigned to Mn(II), Co(II), Ni(II) and Cu(II) complexes while tetrahedral to Zn(II) and Cd(II) complexes. Antimicrobial screening of the free ligand and its complexes showed high activity for Mn(II), Co(II), Ni(II), Cu(II) complexes; however Zn(II) and Cd(II) complexes exhibit moderate activities.
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Figure cations Fig. 1. Synthesis of ligand (H2L) Fig. 2. IR spectra of ligand and its metal complexes Fig. 3. SEM-EDS graph of [Ni(HL)(Cl)(H2O)2] complex Fig. 4. SEM-EDS graph of [Cu(HL)(Cl)(H2O)2] complex Fig. 5. SEM-EDS graph of [Zn(L)(H2O)] complex
O
O
CH3
O 1
N NH
NH2
N
HO
6
N 2
Ethanol
+
3
5
N
N
CH3
NH 7
HO
8
12
4 11
9 10
Fig. 1. Synthesis of ligand (H2L)
Fig. 2. IR spectra of ligand and its metal complexes
Fig. 3. SEM-EDS graph of [Ni(HL)(Cl)(H2O)2] complex
Fig. 4. SEM-EDS graph of [CuHL)(Cl)(H2O)2] complex
Fig. 5. SEM-EDS graph of [Zn(L)(H2O)] complex Cation for tables Table 1
Analytical and molar conductance data of the metal complexes Table 2 Infrared spectral bands for ligand and its metal complexes Table 3 Magnetic oments, electronic spectral data and ligand fied parameters of metal complexes Table 4 Thermogravimetric data of metal complexes Table 5 Antimicrobial activity of the H2L ligand and its metal complexes
Table 1 Analytical and molar conductance data of the metal complexes
Compound
Formula
Formula weight
Elemental analysis found (calcd)
Molar conductance
C
H
N
M
(-1 cm2 mol-1)
[Mn(HL)(Cl)(H2O)2]
C13H15ClN4O4Mn
381.61
41.32 (40.91)
3.52 (3.96)
14.92 (14.68)
14.73 (14.39)
13.4
[Co(HL)(Cl)(H2O)2]
C13H15ClN4O4Co
385.63
40.72 (40.49)
3.61 (3.92)
14.04 (14.53)
15.14 (15.28)
7.6
[Ni(HL)(Cl)(H2O)2]
C13H15ClN4O4Ni
384.59
40.03 (40.51)
3.17 (3.92)
14.21 (14.54)
15.97 (15.24)
9.2
[Cu(HL)(Cl)(H2O)2]
C13H15ClN4O4Cu
390.01
40.62 (40.00)
3.43 (3.87)
14.34 (14.36)
15.74 (16.28)
5.1
[Zn(L)(H2O)]
C13H12N4O3Zn
337.72
45.83 (46.24)
3.94 (3.58)
17.07 (16.60)
19.79 (19.36)
7.9
[Cd(L)(H2O)]
C13H12N4O3Cd
384.60
40.43 (40.60)
3.19 (3.13)
14.985 (14.55)
29.66 (29.22)
12.9
Table 2 Important IR spectral bands (cm-1) of the ligand and its metal complexes
3346
3182
1691
1630
(CO) phenolic 1301
[Mn(HL)(Cl)(H2O)2]
-
3187
1676
1599
1325
-
1029
582
461
[Co(HL)(Cl)(H2O)2]
-
3182
1649
1605
1318
-
985
516
488
[Ni(HL)(Cl)(H2O)2]
-
3180
1683
1603
1317
-
992
517
491
[Cu(HL)(Cl)(H2O)2]
-
3184
1672
1602
1318
-
989
583
496
[Zn(L)(H2O)]
-
-
-
1600
1321
1232
983
599
459
[Cd(L)(H2O)]
-
-
-
1597
1340
1237
1015
581
461
Compound H2L
(OHN) (NH)
(C=O)
(C=N )
(CO) enolic -
(NN)
(MO)
(MN)
977
-
-
Table 3 Magnetic moments, electronic spectral data and ligand field parameters of metal complexes Complex
eff (B.M.)
Band position (cm-1)
Assignments
Dq (cm-1)
B0 (cm-1)
2/1
[Mn(HL)(Cl)(H2O)2]
5.82
6
-
-
-
4.71
7687
734
0.75
1.58
[Ni(HL)(Cl)(H2O)2]
2.76
1026
801
0.78
1.60
[Cu(HL)(Cl)(H2O)2]
1.64
A1g 4T1g(4G) 6 A1g 4Eg, 4A1g(4G) 6 A1g 4Eg(4D) 4 T1g 4T2g(F) 4 T1g 4A2g(F) 4 T1g 4T2g(P) 3 A2g 3T2g(F) 3 A2g 3T1g(F) 3 A2g 3T1g(P) 2 B1g 2A1g 2 B1g 2Eg LMCT
-
[Co(HL)(Cl)(H2O)2]
10212 14342 25272 9095 14421 16783 10256 16431 26357 13869 15407 24147
-
-
-
-
Table 4 Thermogravimetric data of metal complexes Compound
[Mn(HL)(Cl)(H2O)2]
[Co(HL)(Cl)(H2O)2]
[Ni(HL)(Cl)(H2O)2]
[Cu(HL)(Cl)(H2O)2]
[Zn(L)(H2O)] [Cd(L)(H2O)]
Temp. range (oC)
95-185 185-230 230-750 90-185 185-210 210-750 110-205 205-255 255-700 90-185 185-215 215-700 90-182 182-650 105-190 190-680
% mass loss
Assignment
Found
Calcd.
9.51 9.72 9.83 10.01
9.44 9.3 9.35 9.22 9.34 9.22 9.23 9.10 5.34 4.68 -
9.85 9.68 8.94 9.24 5.47 5.10 -
Loss of 2 moles of coordinated water molecules Loss of 1 coordinated chloride ion deligation Loss of 2 moles of coordinated water molecules Loss of 1 coordinated chloride ion deligation Loss of 2 moles of coordinated water molecules Loss of 1 coordinated chloride ion deligation Loss of 2 moles of coordinated water molecules Loss of 1 coordinated chloride ion deligation Loss of 1 mole of coordinated water molecule deligation Loss of 1 mole of coordinated water molecule deligation
Table 5 Antimicrobial activity of the H2L ligand and its metal complexes Compound
Minimum inhibitory concentration (g ml-1) E. coli
P. aeruginosa
S. aureus
B. subtilis
E. faecalis
S. pyogenes
C. albican
A. niger
A. clavatus
(MTCC 443)
(MTCC 424)
(MTCC 96)
(MTCC 8979)
(MTCC 439)
(MTCC 442)
(MTCC 227)
(MTCC 282)
(MTCC 1323)
H2L
12
12
13
09
09
08
11
10
10
[Mn(HL)(Cl)(H2O)2]
14
14
16
14
15
13
14
14
15
[Co(HL)(Cl)(H2O)2]
16
14
15
15
14
13
13
14
16
[Ni(HL)(Cl)(H2O)2]
16
14
17
15
15
12
12
13
14
[Cu(HL)(Cl)(H2O)2]
17
16
18
13
17
15
16
12
14
[Zn(L)(H2O)]
14
13
14
12
11
10
12
11
13
[Cd(L)(H2O)]
12
12
14
10
10
11
12
12
12
Ciprofloxacin*
13
14
14
14
15
12
--
--
--
Clotrimazole*
--
--
--
--
--
--
13
09
12
* Standard drug
Bivalent transition metal complexes of ONO donor hydrazone ligand: synthesis, characterization and antimicrobial activity Ravindra Bhaskar, Nilesh Salunkhe, Amit Yaul and Anand Aswar* Department of chemistry, Sant Gadge Baba Amravati University, Amravati, 444602, (MS), India. *Email- [email protected]
Graphical abstract
N
N
N H N O
Cl
N N
CH3 N
O M
M O
H2O
CH3 N
H2O
O
OH2 M = Mn(II), Co(II), Ni(II) and Cu(II)
M = Zn(II) and Cd(II)
Highlights
•
Synthesis of Hydrazone Schiff base (H2L) and its complexes.
•
Physicochemical characterization of compounds.
•
Bacterial and fungal screening of compounds.
•
Complexes containing −NH and −Cl group show higher antimicrobial activity.
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