Spectral and Biological Profile of Complexes of 2,4,5-Trimethoxybenzaldehyde-S-Benzyldithiocarbazone

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Spectral and Biological Profile of Complexes of 2,4,5-Trimethoxybenzaldehyde-S-Benzyldithiocarbazone

Dayanand Prasad, Deepak Kumar1, Amit Kumar, B. N. Subhs, Vijay Kumar2 and Shivadhar Sharma*

1.University Dept. of Chemistry, Magadh University, Bodhgaya – 824234

2.P. G. Dept. of Chemistry, R. N. College, Hazipur.

  1. R. A. Bihar University, Muzaffarpur

Email*: sharma.shivadhar@gmail.com

Received: 04-07-2019                                                                                                 Accepted: 25-12-2019

2,4,5-trimethoxybenzaldehyde was condensed with S-benzyldithiocarbazate to produce the Schiff base 2,4,5-trimethoxy benzaldehyde-S-benzyldithiocarbazone, henceforth abbreviated as BBTC, which was used for complexation with Mn(II), Fe(II) and Co(II). The complexes were formulated as M(BBTC)2X2 where X is Cl, NO3 and CH3COO. The FTIR spectra of complexes in comparison to that of free ligand suggested the coordination through azomethine nitrogen and thion sulphur forming six membered chelating with metal ion. The magnetic susceptibility and electronic spectral bands revealed octahedral symmetry (Oh) around Mn(II) but tetragonally distorted octahedral symmetry (D4h) of Fe(II) and Co(II) complexes. The positive value of Dt for Fe(II) (68.42–135.2 cm–1) and Co(II) (263–280 cm–1) clearly indicated elongation along z-axis in these complexes which was also supported by the less value of Dq(z) than Dq(xy) for the complexes. The ligand as well as it complexes have been found active against the bacteria Escherichia Coli and Staphylococcus aureus.

Key words: D4h, Staphylococcus aureus, Racah Parameter B, C and Dt.

INTRODUCTION

The synthesis, spectral investigation and biological activities of carbazones, thiocarbazones and their metal complexes have extensively been studied because of their wide variation in modes of co-ordination, stereochemistry and beneficial pharmacological activities[1-3].   Thiocarbazones have also been reported as interesting chromogenic reagent that gives intense coloured complexes, shows more bathochromic shift, more sensitivity and more selectivity. That is why this field has attracted the considerable attention of inorganic chemists[4-9]. Schiff’s bases of carbazones and thiocarbazones are very good chelating agents. As chelation causes drastic changes in the biological properties of the ligands as well as the metal moiety, such complexes have been found potentially, antibacterial, antifungal, anti-cancer etc[10-16]. Due to pharmaceutical properties of carbazones and thiosemicarbazones which are frequently higher for metal complexes than the free ligands, they have extensively been studied in recent years[17-20]. Keeping the vasts spectrum of fascinating properties of carbazones and thiocarbazones complexes and in continuation of our previous work[21-26], we report here the spectral and biological profile of complexes of 2,4,5-trimethoxybenzaldehyde-S-benzyldehydedi-thiocarbazone (BBTC).

MATERIALS AND METHODS

All the reagents used were of Anal-R-grade. The precursor 2,4,5-trimethoxybenzaldehyde were procured from Lupin and S-benzyldithiocarbazate was procured from Merk. The two precursor were condensed together to produce the required ligand according to the method reported by Md. A. Islam et al. 0.01 mole (1.96 g) of 2,4,5-trimethoxybenzaldehyde and 0.01 mole (1.98 g) of S-benzyldithiocarbazate were dissolved together in 30 ml of ethanol and about 2 ml of conc. H2SO4 was added to it. The resulting solution was refluxed on water bath using air condenser for about four hours, where by yellow turbidity appeared which got solidified after living over night. It was filtered and solid was recrystallized in ethanol acetone mixture and dried in desiccator on anhydrous CaCl2. The m.p. was recorded 184°C and the yield was 79%. It has been given in scheme-1.

The ligand has been used for complexation with Mn(II), Fe(II) and Co(II) metal ions by used method of reflux. The ligand as well as complexes were microanalysed by Perkin-Elmer-2400-CHN elemental analyser. Mn(II) and Co(II) were estimated gravimetrically while Fe(II) was estimated volumetrically after decomposition of the complexes. The FTIR spectra of the ligand and complexes were recorded on Perkin-Elmer-FTIR spectrometer using KBr are disc between 4000 to 400 cm–1. The magnetic susceptibility of complexes has been determined by Gouy’s balance at room temperature using mercuric tetrathiocyanatocobaltate(II) as calibrant. The electronic spectra of metal complexes were recorded on Shimadzu UV-Visible spectrophotometer (UV–160). The molar conductivity of complexes was determined in DMF solution 10–3 M concentration using Toshiniwal CL–01–06 Conductivity Bridge. The ligand as well as complexes were assayed against the bacteria Bascillus subtills and Klebsiella pneumoniae using Ciprofloxacin as reference.

RESULTS AND DISCUSSION

The percentage composition of ligand and its complexes has been given in table–1.

The extremely low value of conductivity (18-23 ohm–1 cm2 mol–1) of complexes clearly indicates their nonelectrolytic nature[28-30]. The percentage composition and molar conductivity of complexes reveal their formation as [ML2X2] where, M = Mn(II), Fe(II) and Co(II), L = BBTC and X = Cl, NO3 and CH3COO

Ftir-Spectral Study: The free ligand absorbs at 3455 cm–1 which is assigned to νN­–H[31-33] stretching vibration of the ligand, which remains intact in complexes. It indicates that N–H, nitrogen of the ligand is not involved in coordination. The free ligand absorbs at 2620 cm–1 due to  vibration which doesn’t undergo any change in complexes, which is indicative of non participation of thio ether group of the ligand in coordination. A medium band appears at 1650 cm–1, which undergoes negative shift by 32–35 cm–1 and appears at 1615–1650 cm–1 in the FTIR spectra of complexes. It is a distinct indication of co-ordination through azomethine nitrogen of the ligand in complexes[34–36]. The coordination through azomethine nitrogen of the ligand is further supported by an increase by 15 cm–1 in absorption frequency of νN–N which absorbs at 1013 cm–1 in FTIR spectrum of free ligand[37]. The methoxy group of free ligand absorbs at 1160 cm–1 with medium intensity and remains almost intact in the spectra of complexes. It shows the non-participation of methoxy oxygen of ligand in co-ordination. The medium band appearing at 1045 cm–1 due to νC=S stretching vibration of free ligand undergoes red shift appearing at 1010–1020 cm–1 in complexes which indicates coordination through thionyl sulphur of the ligand to the metal ions[38]. The coordination through sulphur and azomethine nitrogen of the ligand is furthur supported by the appearance of new band at 530–535 cm–1 due to νM–N and 445–450 cm–1 due to νM–S in the FTIR spectra of the complexes[39]. In addition to these bands some new bands appear in complexes. In complexes number 1, 4 and 7 new band appears at 420–425 cm–1 due to νM­–Cl stretching showing the presence of chloride in their co-ordination sphere[40]. In complexes number 2, 5 and 8 two new bands appear at 1380–1384 cm–1 and 840–848 cm–1, which shows the presence of mono co-ordinated NO3­– ion in these complexes[41]. The new bands appearing at 1560–1565 cm–1 and 1320–1330 cm–1 in FTIR spectra of complexes no. 3, 6 and 9 may be attributed to νasyCOO– and νsyCOO– respectively[42]. The Δν between symmetric and asymmetric vibrations of acetate is more than 200 cm–1 which is typical of monodentate co-ordination of acetato group in these complexes[43]. The tabular form of FTIR bands in ligand and complexes have been presented in table–2 and the graphs have also been presented in fig. 1 to 14.

Magnetic moment and electronic spectra of complexes: Magnetic moment of Mn(II) complexes are found 5.80–5.83 BM. The values are very close to the magnetic moment corresponding to five unpaired electrons. This is indicative of the fact that Mn++ complexes are high spin magnetically dilute octahedral complexes[44]. The slightly low value of magnetic moment may be due to spin-orbit coupling, which further restricts the spin as well as orbital motion of the electron to the little extent. The Mn(II) complexes display four very weak bands in their electronic spectra. The bands have been given in table–3.

The weak bands of electronic spectra of Mn(II) complexes are assigned to the following spin forbidden transitions, ν1 = 6A1g  4T1g (4G), ν2 = 6A1g  4T2g or 4A1g or 4Eg (4G), ν3 = 6A1g  4Eg (4D) and ν4 = 6A1g  4T1g (4P)

Using Tanabe-Sugano diagram the values of different crystal field parameters have been derived and values have been presented in table – 4.

The ratio of Racah Parameter C/B derived for Mn(II) complexes (3.28–3.45) is very close to the theoretical value (3.5)[45]. The values of different crystal field parameters support octahedral geometry around Mn(II) in these complexes[30, 46].

The magnetic moment of Fe(II) complexes exhibit magnetic moment 5.00–5.10 BM, which shows the presence of four unpaired electrons in the complexes. The values are a bit higher than that corresponding to four unpaired electrons (4.89 BM) which may be attributed to the ground state term 5T2g which being orbitally degenerate contributes to the magnetic moment of six coordinate Fe(II) complexes. The magnetic moment of six coordinate Fe(II) complexes also show enhancement due to deviation from octahedral symmetry[47-49]. The Fe(II) complexes display three bands in their electronic spectra which is indicative of tetragonal distortion in octahedral symmetry of Fe(II) complexes. Under the influence of tetragonal distortion both the ground state crystal field terms 5T2g and the excited crystal field term 5Eg of its ground term 5D undergo further splitting causing the possibility of three spin allowed transition bands. The electronic spectral bands[50] and their assignment have been presented in table – 5.

These bands were assigned to the following spin allowed transitions,  and

On the basis of these transitions and energy associated with different transitions the various crystal field parameters have been derived and values have been presented on table – 6.

Form the table it is obvious that Dq(z) for all the complexes is less than Dq(xy) which shows that the axial ligands are slightly away from the metal ion in respect of the planer ligands in all the complexes.

It predicts the tetragonally elongated octahedral symmetry (D4h) for all the Fe(II) complexes. The elongation along Z-axis is further supported by the positive value of the radial integral Dt for all the Fe(II) complexes[25].

Electronic Spectra of Co(II): The magnetic moment of Co(II) complexes has been found 4.72 – 4.79 BM. Co(II) is a d7 system having three unpaired electrons and hence the spin only value of magnetic moment is expected to be 3.87 BM. The abnormality in the magnetic moment of Co(II) complexes may be attributed to 4T1g ground state crystal field term in octahedral symmetry which appreciably contribute to the magnetic moment of Co(II) complexes in octahedral symmetry[23,51,52]. The electronic spectra of Co(II) complexes display four bands which has been given in table – 7.

The bands have been assigned to the following spin allowed transitions,                   

The first band due to  is not observed due to small gap between the two levels causing absorption energy in I.R. range. The value of 10Dq(xy) has been derived from

 and Dt has been derived from , Dq(xy) was

derived from the popular equation, Dt = . The values of the different crystal field parameter derived from the spectral bands have been presented in Table – 8.

The electronic spectral graph of Mn(II), Fe(II) & Co(II) complexes may be seen in figures 12, 13 & 14.

From the values of Ds and Dt the value of 1 has been derived which were found 6,694 – 6,919 cm–1, which falls in I.R. region. The +ve value of Dt and Ds are indicative of tetragonally elongated octahedral geometry of all the Co(II) complexes[53,54]. The tetragonal elongation along z-axis in all Co(II) complexes is also supported by the smaller value of Dq(z) than Dq(xy)[55,56].

Antimicrobial Activity: The ligand as well as its metal complexes were screened against bacterial species Escherichia coli and Staphylococcus aureus using ciprofloxacin as reference for the evaluation of their antibacterial activity. The bacteria was incubated for 24 hours at 35°C and the activity was determined by measuring the diameter of inhibition zone by agur diffusion method. The results have been shown in table – 9. From the table it may be inferred that the free ligand is active against both E. Coli and S. aureus, but it is less active than the standard ciprofloxacin. The metal complexes of the ligand are found more active against both, E. Coli and S. aureus strains. The positive effect of almost all the complexes is comparable to ciprofloxacin.

The grater inhibitory effect of metal complexes than the ligand for the bacterial strains may be attributed to overtone concept and chelation theory [57-59].

CONCLUSION

The ligand BBTC is found to act as neutral bidentate one coordinating through azomethine nitrogen and thionic sulphur. The positions along z-axis are occupied by chloride or nitrate or acetate ions. All the complexes of Mn(II), Fe(II) and Co(II) are found to possess D4h symmetry with elongation along z-axis. The free ligand and its complexes are found active against E. Coli and S. aureus. The antibacterial of free ligand is found to have enhanced after complexation with metals.

ACKNOWLEDGEMENTS

One of the author, Deepak Kumar is thankful to University Grants Commission for granting Rajiv Gandhi National Fellowship vide Registration ID: RGNF-2017-18-SC-BIH-41422. Authors’ are thankful to Prof. S. K. Singh, Head, P. G. Department of Zoology for allowing the microbiological lab of his department to carry out the antimicrobial study.

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