Synthesis , Physical Characterization of M ( III ) Transition Metal Complexes Derived from Thiodihydrazide and 5-tert-Butyl-2-hydroxy-3-( 3-phenylpent-3-yl ) Benzaldehyde

A Schiff base ligand was synthesized by reacting 5-tert-butl-2hydroxy-3-(3-phenylpent-3-yl) benzaldehyde and thiodihydrazide (2:1) and a series of metal complexes with this new ligand were synthesized by reaction with Cr (III), Mn (III), and Fe (III) metal salt in methanolic medium. The Schiff base ligand and its complexes have been characterized with the help of elemental analysis, conductance measurements, magnetic measurements and their structure configuration have been determined by various spectroscopic (electronic, IR, H NMR, C NMR, GCMS) techniques. Electronic and magnetic moments of the complexes indicate that the geometries of the metal centers were octahedral. IR spectral data suggest that ligand behaves as a tetradentate ligand with ONNO donor sequence towards the metal ion.


Introduction
The role play by metals in a number of biological systems has derived the research efforts of many scientists from a variety of field [1][2][3].There are a number of important molecules shows biological activities including antibacterial, antifungal [4][5][6][7][8][9][10][11][12][13], antidiabetic [14], antitumor [15][16][17], antproliferative [18,19], anticancer [20,21], herbicidal [22], anticorrosion and anti-inflammatory activities [5][6][7].Schiff bases represent an important class of compounds because they are utilized as starting materials in the synthesis of industrial products [23].Moreover, Schiff base are regarded as privileged ligand [24].Due to their capability to form complexes with different transition metals can act as catalysts for many different reactions [25][26][27][28][29].The cross linking agents can also be derived from metal complexes with O−N− or -S ligands for example, the intra-coordination salt such as salicylates, anthraanilates and aliphatic or aromatic amines can form strong five of six membered chelates rings which are able to produce the metal containing cross linking agents with required properties [30].It is well known that N and S atoms play a key role in the coordination of metals at the active sites of numerous metallobiomolecules [31].Metallorganic chemistry is becoming an emerging area of research due to the demand of new metalbased antibacterial and antifingal compounds [32,33].In this study the synthesis of metal complexes with Schiff base derived from 5-tert-butyl-2-hydroxy-3-(3-phenylpent-3yl) benzaldehyde and thiodihydrazide.There Schiff base have donor sites with the ONNO sequence and varied coordination abilities.

Reagents
The entire chemicals used were of the analytical reagent grade thiodihydrazide, p-tertbutylphenol and 3-phenylpent-2-ene procured from fluka, DMSO, CH 2 Cl 2, methanol and ethanol were procured from s.d.-fine.Metal salts were purchased from Merck.

Synthesis of the metal complexes
The metal complexes of the ligand HL (1) were prepared by mixing a hot methanolic solution of the metal salts with required amount of a hot ethanolic solution of the ligand to form metal/ligand complexes (Scheme 2).

Physical measurements
The microanalysis of C, H and N were estimated by elemental analyzer (Perkin Elmer 2400 (table 1) and the metal contents of Cr (III), Mn (III) and Fe (III) were determined by atomic absorption spectrophotometer (Perkin Elmer 5000).IR spectra were recorded on a FT-IR spectrophotometer (Perkin Elmer) in the range 4000-200cm− 1 using Nujol Mull. 1 H NMR and 13 C NMR spectra (at room temperature) (in DMSO-d 6 ) were recorded on a Bruker AVANCE II 300 DRX or average 400 DRX spectrometer with reference to Me 4 Si (0.0 ppm).
The FAB mass spectra (at room temperature) were recorded on JEUL JMS-AX-500 mass spectrometer, GC-MS analysis was performed on a Shimadzu GCMS-QP5050A instrument, Indian Institute of Petroleum Dehradun, India.Magnetic susceptibility measurements were carried out at SAIF, IIT Roorkee, on vibrating sample magnetometer (Model PAR 155).Electronic spectra in DMSO were recorded on a Hitachi 330 spectrophotometer (1300-200 nm) at room temperature.The conductivity was measured on digital conductivity meter (HPG system, G-3001).

Synthesis of the Schiff base ligand
A round-bottom, 100 mL flask was charged with thiodihydrazide (0.295 g, 2.5 mmol, K 2 CO 3 (1.2g, 5 mmol), and water (6 mL).The resulted mixture was stirred for 10 min followed by addition of ethanol (98%, 30 mL) and heated to 60-70 °C for 0.5 h.The temperature was maintained, and 5-tert-Butyl-2-hydroxy-3-(3-phenylpent-3-yl)benzaldehyde (1.62 g, 5 mmol) was added.The mixture was refluxed for 3 h.The mixture was concentrated to 1/4 of its initial volume, dissolved in CH 2 Cl 2 (50 mL), and washed with water.The organic phase was dried and concentrated to give a yellow solid which was dissolved in 15 mL of hot ethanol.The resulting solution was cooled to ambient temperature, and 3 mL of 50% aqueous ethanol was added to produce yellow precipitate that was collected with 81% yield: yellow crystals.UV/vis (Nujol mul (nm)): λ = 280, 330, 340.UV/vis (1× 10 formula for these complexes.In addition to the peaks due to the molecular ion, the spectra exhibit peaks assignable to various fragments arising from the thermal cleavage of the complexes.The peak intensity gives an idea of the stability of the fragments.

IR Spectra
The IR spectra of all complexes showed that the ligand HL (1) behaves as a neutral tetradentate of the type ONNO.The IR spectra provide valuable information regarding the nature of functional group attached to the metal atom.The presence of a single medium band in the region 3250-3330 cm -1 in the complexes may be assigned to N-H stretch [37].It was noted that a pair of bands corresponding to ѵ (NH 2 ) at 3245 cm ¯1 and 3309 cm ¯1 are present in the spectra of the Thio-carbohydrazide.The value of ѵ (C=N) stretching vibration is found (1590-1660 cm ¯1).The bands present in the range 3020-3040 cm ¯1 may be assigned due to (C-H) stretching vibrations of benzil and naphthalene ring [38].The C-N stretch in the range 1000-1300 cm ¯1.The band at 3292-3438 cm ¯1 is due to the presence of OH group in the complexes.This band is also present in the spectra of all the complexes.The far infrared spectra show bands in the region 420-450 cm ¯1 corresponding to ѵ (M-N) vibrations [39].
The band near 770-810 cm ¯1 in thiocarbohydrazide may be assigned as being due to free ѵ (C=S).The presence of bands in all complexes in the region 420-450 cm ¯1 originates from the (M-N) azomethine vibrational modes and identifies coordination of azomethine nitrogen [40].The bands present at 290-310 cm ¯1 may be assigned due to ѵ (M-Cl) vibrations [41,42].
The appearance of two characteristic bands in the ranges 1561-1559cm− 1 and 1370-1367 cm− 1 in the case of complexes was attributed to ν asym (COO − ) and ν sym (COO − ), respectively, indicating the participation of the carboxylate oxygen in the complexes formation.The mode of coordination of carboxylate group has often been deduced from the magnitude of the observed separation between the ν asym (COO − ) and ν sym (COO − ).The separation value, Δν(COO − ), between ν asym (COO − ) and ν sym (COO − ), in these complexes were more than 190 cm− 1 (191-193cm− 1 ) suggesting the coordination of carboxylate group in a monodentate fashion [44].

H NMR
The 1 H NMR spectra of the ligand exhibits at 13.1 ppm due to the -NH [45].The multiplets in the region 7.04-7.86ppm may be assigned to aromatic proton [46,47].The 1 H NMR spectra of Schiff base ligand (HL) was recorded in d 6 -dimethylsulfoxide (DMFO-d 6 ) solution using Me 4 Si (TMS) as internal standard.

Magnetic measurements and electronic spectral studies
The electronic spectra of Cr (III) complexes showed absorption band in the region 8950-9310, 13150-13520, 17550-18450 and 27380-27780 cm− 1 attributed to 4 B 1g → 4 E 1g , 4 B 1g → 4 B 2g , 4 B 1g → 4 A 2g and 4 B 1g → 4 E g transition indication of distorted octahedral geometry [48].The magnetic moment value for this complex was found to be 3.68-4.93B.M. The absorption spectral bands of manganese (III) complexes showed three spin allowed transitions: 5 B 1g → 5 A 1g , 5 B 1g → 5 B 2g , 5 B 1g → 5 E g appearing in the ranges 12250-12550, 16150-18860 and 35450-35720 cm− 1 , respectively consistent with a typical Mn(III) in an octahedral environment [49].The magnetic moment values for these complexes were found in the range 4.92-5.74B.M expected for octahedral nickel complexes.The electronic spectra of the iron (III) complexes gave two bands at 9850-9980, and 27650-27760 cm− 1 , which could be assigned to the transitions 6 A 1g → 4 T 1g and 6 A 1g → 4 T 2g , respectively, suggesting an octahedral geometry around Fe (III) ion [50].The complexes 5 and 6 show magnetic moment values in the range 5.20-5.45B.M., which is smaller than the calculated value for two Fe (III) ions in octahedral geometries and this may be due to antiferromagnetism between the two ion-centers.

Conclusion
The analytical data showed the presence of one metal ion per ligand molecule and suggested a mononuclear structure for the complexes [HLMXH 2 O].The electronic spectral data is in the favour of a octahedral geometry of the complexes.

Table 1 .
Elemental analysis in %, molar conductance (Λ M in DMSO) of the Schiff base ligand and its metal complexes.