Synthesis and Characterization of Cr(III) & Fe(II) Bis(2-Methoxybenzylidene)Biphenyl-4,4'-Diamine Complexes

Bis(2-methoxybenzylidene)biphenyl-4,4'-diamine Schiff base was prepared by the reaction of benzidine and O-methoxy benzaldehyde 1:2 reaction. Two complexes of this ligand with Cr(III) and Fe(II) were prepared. All prepared compounds were analysed using elemental analysis, IR, 1H NMR and mass spectroscopy. The formation of proposed structures, including the free ligand and complexes were confirmed.


Introduction
The chemistry of coordination compounds is well known and widely studied, yet ligands of specified design should be synthesized, which could lead to metal complexes with special desired and possible predictable properties. The steady improvement in synthetic methodology allows us to foresee coordinating che-general formula (-C=N-) has a great attention as precursor in huge organic synthesis and biological applications such as cycloaddition reaction [3] [4], optoelectronic properties [5], dyes and pharmaceuticals, antimicrobial activity [6], liquid membrane technology [7], anti-inflammatory [8], anticonvulsant [9], anti-tumour [10], antihypertensive activity [10] and anti-HIV activities [11].
Its use is now limited because of the strong association between exposure to benzidine and an increased risk of bladder cancer in humans [19]. The chemical or enzymatic oxidation of benzidine proceeds via a radical cation detectable by electron spin resonance. Peroxidase-catalyzed oxidation of benzidine generates reactive electrophiles which readily form adducts with phenol and thiol compounds. The structures of these novel metabolites are described. Peroxidases, including prostaglandin synthase, catalyze benzidine binding to protein and nucleic acid; the nature of the resulting adducts is unknown. The relevance of these processes to benzidine carcinogenesis in vivo is the subject of research and debate [20]. Benzidine is prepared in a two-step process from nitrobenzene. List of Chemicals of Concern [21]. Benzidine is no longer produced in the United States, although benzidine-based dyes may be imported into this country. No information is available on the acute (short-term) effects of benzidine in humans by inhalation exposure, but benzidine is considered to be very acutely toxic to humans by ingestion. Chronic (long-term) exposure to benzidine in humans may result in injury to the bladder. Epidemiological studies have shown occupational exposure to benzidine to result in an increased risk of bladder cancer.
Animal studies have reported various tumour types at multiple sites from benzidine exposure via oral, inhalation, and injection exposure. EPA has classified benzidine as a Group A, known human carcinogen [21] [22].
Benzidine has been used since the 1850s as the reagent base for the production of a large number of dyes, particularly azo dyes for wool, cotton, and leather.
However, because benzidine was found in the 1970s to be carcinogenic to humans, there has been a considerable decline in the use of the benzidine dyes.
Benzidine is used for the quantitative determination of sulfuric acid and the detection and determination of numerous anions and metal ions. The reaction of benzidine with pyridine in the presence of elemental chlorine is suitable for detecting traces of free chlorine or pyridine in drinking-water. The green to blue colouration that occurs when benzidine reacts with hydrogen peroxide in the presence of peroxidases can be used to detect blood. Benzidinstill plays a role in many chemical syntheses [23]. In the past, benzidine also has been used as a rubber compounding agent, in the manufacture of plastic films, for detection of hydrogen peroxide in milk, and quantitative determination of nicotine. Most of these uses have been discontinued, although some dyes that may contain benzidine as an impurity are still used as stains for microscopy and similar laboratory applications [24]. Archana et al. [25] synthesised and investigated four Schiff base chelates of Cu(II), Co(II), Ni(II) and Zn(II) formed from the reaction of 2-hydroxy benzaldehyde and benzidine. Metal complexes are reported and characterized using several analytical and spectroscopic techniques; the reaction is shown in Figure 1.

Materials
All chemicals and reagents used in this work were laboratory pure (BDH or Aldrich) and used without further purification, these include, benzidine, 2-methoxybenzaldehyde, Cr(NO 3 ) 3 , FeCl 2 NaOH, CH 3 OH, THF and distilled water. Melting points were determined on a Gallenkamp melting point apparatus. The 1 H NMR spectra were recorded on a Bruker Avance II 500 MHz spectrometer. The chemical shifts were reported in ppm relative to tetramethylsilane (TMS).

Synthesis of Schiff Base
Schiff base under investigation is synthesised by dissolving 0.01 mol (1.842 g) of Binzidine in 25 ml methanol, 0.02 mol (2.723 g) of 2-methoxy benzylidene is added to this solution with reflux for 2 -3 h. The formed yellow precipitate was filtered, washed with hot methanol until the filtrate becomes clear and finally dried in excellent yield. The chemical reaction is represented in Figure 1. Yield: 87%, 1.65 g M.P. 210˚C.

Synthesis of Metal Complexes
Bis(o-methoxy benzaldehyde) benzidine (2.14 g, 0.005 mol) was dissolved in hot THF (50 mL), and a solution of 0.01 mol of metal salt in methanol Cr(NO 3 ) 3 ·6H 2 O or FeCl 2 ·6H 2 O is slowly added to this solution, and the reaction mixture was refluxed at 60˚C for 5 -6 hours. The coloured crystalline product obtained after filtration was washed with hot THF several times and finally with diethyl ether. Yield: 75%, 1.60 g.

Elemental Analysis
The structures of the synthesised compounds were identified by (C.H.N.) elemental analysis, IR, 1 H NMR and mass spectral measurements and were in good agreement with the proposed structures (Table 1). C.H.N. elemental analysis was carried out for the free ligand and its complexes with Cr 3+ and Fe 2+ and found in good agreement with the calculated values, as shown in Table 1.

Infrared Spectroscopy and Magnetic Moment
The IR spectrum of the Schiff base bis(2-methoxybenzylidene)biphenyl-4,4'-diamine showed the band at 1620 cm −1 which was due to C=N confirms the formation of

1 H-NMR and Mass Spectral Studies
The 1 H-NMR spectra confirmed the formation of Schiff base ligand. 1 H-NMR spectra of the ligand were taken in DMSO d 6 solvent as shown in Figure 2. The aromatic region was a set of multiples in the range 6.5 -7.3 ppm for the Schiff base ligand, while the azomethine protons were observed in the range 8.6 ppm.
Mass spectra of chromium (III) complex with Schiff's base C 28 (Figure 3). From the analysis carried out on free ligand and compared with complexes, the proposed structures of complexes which confirmed by these analyses will be as follows as shown in Figure 4.

Conclusion
In the present work, appropriate aldehyde derivatives were reacted with benzidine to give the corresponding Schiff base which confirmed by several analysis methods, and two coordination compounds of Cr(III) and Fe(II) with this Schiff base were prepared and confirmed with several analysis methods. This area of research is an open area, and other coordination compounds can be prepared using this Schiff base which we think it is a new Schiff base and aldehydes derivatives can also be used.