Synthesis and Characterization of New Co(II), Ni(II), Cu(II) and Zn(II) with Bis-hydrazones Complexes

A number of new Co(II), Ni(II), Cu(II) and Zn(II) complexes with 2,5-hexanedione bis(4methylbenzoyl hydrazone)(HDMBH), 2,5-hexanedione bis(2-theonyl hydrazone)(HDTH) and 2,5hexanedione bis(2-furoyl hydrazone)(HDFH) have been reported.The bis-hydrazone ligands were synthesized by the condensation of 2,5-hexanedione with (4-methylbenzoic acid hydrazide,2thiophene carbohydrazide or 2-furic acid carbohydrazide) in 1:2 molar ratio. The reaction of metal(II) chlorides with the ligands in (1:1) molar ratio in ethanol in presence of triethylamine lead to the isolation of complexes having the general formula [M(L-2H)(H2O)2] where (M= Co(II), Ni(II), Cu(II) and Zn(II)) and (L-2H=doubly deprotonated ligand). The ligands and complexes have been characterized by elemental analysis, spectral (IR,UV-Vis), magnatic and molar conductance measurements, which revealed that the ligands HDMBH, HDTH, and HDFH act as dinegtive charge tetradentate (NNOO) donor ligands in the metal complexes, coordinated through the two azomethine group nitrogen atoms and the two enolic oxygen atoms. All complexes provide an octaheadral geomatry.


INTRODUCTION
Hydrazones and their metal complexes play an important role in the coordination chemistry of transition metal ions. Considerable attention has been paid in last decade to hydrazones and their complexes, since they are capable of generating varied molecular architectures and coordination (Alageson et al., 2013;Ibrahim et al., 2009;Jang et al., 2005).
Hydrazones are considesed an important class of ligands also because the great variety of their biological activities ranging from antimicrobal, anticonvulsant, analgesic, anti-inflammatory, antiplatelet, antitubercular, and antitumoral agents (Rollas and Kücükgüzel, 2007). Biological activities of hydrazone metal complexes are also reported for several transition metals (Alageson et al., 2013;Sathyadevi et al., 2012). Moreover, it has recently been shown that hydrazones such as pyradoxal isonicotinoyl hydrazones analogues are effective iron chelators in vivo and in vitro and may be of value for the treatment of iron overload (Bernharat et al., 2008).
The coordination behavior of aroyl hydrazones is known to depend on the pH of the medium, due to their ability of tautomerism, the deprotonation of the NH group which is readily achieved in complexation, results in the formation of tautomeric anionic species having new coordination properties (Al-Daher and Mustafa, 2013;Galic et al., 2012). Hydrazones have also been proven to show potential application as catalysts (Hosseini-Monfared et al., 2013). Many hydrazone complexes show an excellent catalytic activity in various reactions (Sadhukhan et al., 2011). They are also used as analytical reagents for the determination of several metal ions (Bale and Sawant, 2001).

EXPERIMENTAL Material and Measurements
All chemicals used were reagent grade from B.D.H., Fluka or Merck chemical companies, used as supplied . The infrared spectra (4000-400) cm -1 of the ligands and complexes were recorded on Tensor Shimadzu and 27 Bruker FT-IR spectrophotometer as KBr discs. Molar conductance's of the complexes were determined in DMF (10 -3 M solutions) at room temperature using PMC3 Jenway conductivity meter. The UV-Vis spectra(1100-200 nm) were recorded at room temperature on Labo Med, inc 1650Pc spectrophotometer using DMF as solvent in 1cm quartz curettes. Magnetic susceptibilities were measured with balance Sherwood scientific Cambridge at ambient temperature. The necessary diamagnetic corrections for ligands were done using Pascal's tables. The metal content of the complexes was determined spectrophotometrically using SENSAA , GBC scientific equipment atomic absorption spectrometer (Co,Ni,Cu and Zn). Melting points were obtained on 9300 Electrothermal melting point apparatus in open capillaries.

Preparation of Bis hydrazones
These were prepared according to the literature method (El-Asmy et al., 2013), by the reacting of 2,5-hexanedion and the corresponding acid hydrazide in (1:2) molar ratio in absolute ethanol as shown in (Scheme 1). For a solution of acid hydrazide (0.02 mol) [3.00 g, 4-methylbenzoic acid hydrazide or 2.84 g, 2thiophene carbohydrazide or 2.52g 2-furic acid carbohdrazide ] in absolute ethanol (25 mL) was added to the solution of (1.14 g, 0.01 mol) 2,5-hexanedion in absolute ethanol (25 mL) and few drops of glacial acetic acid as catalyst. The reaction mixture was stirred and boiled under reflux for 3hrs.After completion of the reaction and partial removal of solvent, the white brown crystalline solids that precipitated on cooling were separated by filtration, washed with cold ethanol (5 mL) then with ether (5 mL) and dried in an oven at ( 80 -90 ).
RESULTS AND DISCUSSION The bis hydrazones of 2,5-hexanedion (HDMBH, HDTH and HDFH) were synthesized in good yields by condensation with acid hydrazides in 1:2 molar ratio in absolute ethanol (Scheme1). The reaction of these hydrazones with metal(II) chlorides in the presence of triethyl amine yield 1:1 complexes in which the ligands enolize and doubly deprotonated during complexation as indicated by analytical data (Table 1). All the complexes are coloured non-hygroscopic solids, stable to air and moisture at room temperature. They are generally insoluble in water and non-polar organic solvents, slightly soluble in ethanol, methanol, chloroform, but are more soluble in highly polar organic solvents, like DMF and DMSO. Most complexes melt in temperature range (205-295) ºC which may indicate the non-polymeric nature of the complexes. The low molar conductance values of the DMF solutions of the complexes (4.53-9.8 ohm -1 mol -1 cm 2 ) indicated that they are nonelectrolyte (Geary, 1971). Infrared spectra IR spectra usually provide a lot of valuable information on coordination behavior of the ligands with metals. The IR spectra of the free ligands and their corresponding metal complexes were compared (Table 2). Remarkable differences between the IR spectra of the ligands and those of the corresponding complexes were observed. The IR spectral bands observed at the ranges (3286 -3215), (1666-1654), (1630-1629) and (1012 -990)cm -1 , in the spectra of the free ligands are assigned to ν(N-H), ν(C=O), ν(C=N) and ν(N-N) respectively (El-Asmy et al., 2010;Sathyadevi et al., 2012). The bands of ν(N-H) and ν(C=O) were absent in the spectra of the deprotonated complexes (1-12) suggesting coordination via enol-form, by deprotonation of the N-H proton, during the complication process. The appearance of a new ν(C-O) band in these complexes at the region (1276-1191cm -1 ) suggests bonding of the ligands to the metal ions through deprotonated (C-O) group (Singh et al., 2013;Sathyadevi et al., 2012).
The stretching vibrations of azomethine group ν(C=N) are shifted to lower frequencies in all the complexes spectra by(16-55cm -1 ), which prove that nitrogen atoms of azomethine groups are involved in complexation. Coordination of nitrogen to the metal atom reduces the electron density in the azomethine group causing a shift in the ν(C=N) band to lower frequncies (El-Asmy et al., 2013;Shit et al., 2009). The ν(N-N) observed at (1012-990) cm -1 in the spectra of the ligands, shifts to higher frequencies by (8-51) in their complexes, and indicates the coordination of nitrogen atom of (N-N) group with metal ions (Singh et al., 2013;Sathyadevi et al., 2012). This phenomenon is owing to the diminution of the lone pair electrons repulsion which come from the two adjacent nitrogen atoms, by sharing the electrons out to the metal ion (Shit et al., 2009). These observations were further substantiated by the appearance of non-ligand bands at the ranges (525-444cm -1 ) and (479-401cm -1 ) which are tentatively assigned to ν(M-O), ν(M-N) respectively (El-Boraey and Aly, 2013). Hence, it may be concluded that in all complexes, (1-12) are deprotonated and the ligands (HDMBH,HDTH and HDFH) act as dianionic tetradentate (NNOO -2 ) donor, chelating through the two enolate oxygens and two azomethane nitrogen atoms.
The band observed at (850cm -1 ) due to ν(C-S-C) of thiophene ring spectrum of the free ligand (HDTH) remains almost at the same position in the spectra of its complexes which indicate non-involvment of thiophene sulfur atom in bonding, (Singh et al., 2011). The band observed in the spectrum of the free ligand (HDFH) at 1078 cm -1 assigned for ν(C-O-C) stretching vibration of furan ring is almost unaltered in the spectra of the metal complexes indicating non-participation of the furan ring oxgyen atom in bonding with metal (Shivakumar et al., 2008 ;Bikas et al., 2013;Al-Daher and Mustafa, 2013).
The spectra of complexes exhibit a broad band centered around 3400cm -1 due to the symmetric and asymmetric streching mode of coordinated water molecule. Furthermore weak bands in the 877-889, 669 and 679cm -1 ranges may represent the wagging and rocking modes of coordinated water respectively (Singh, 2008).

Electronic Spectra and Magnetic Properties :
The electronic spectra of ligands and their metal complexes in the range 200 _ 1100nm,were carried out in DMF. Table (3) shows the electronic spectral bands and magnetic moments of the prepared complexes.
The spectra of the ligands in DMF solution exhibit two main absorption bands at 36363 _ 35587cm -1 and 32362 _ 28490 cm -1 . The first band probably due to π→π* transition of the chromophore (-C=N-NH-CO-), and the second band might be attributed to the n→π* transitions resulting from nitrogen and oxygen atoms. In the spectra of the complexes, the shift of the ligand transitions to a lower wavelength (red shift) is ascribed to the ligand complextion with metal ions (Abd El-Motaleb et al., 2005). The new intense band observed in the spectra of all complexes at the region 27777 _ 20964 cm -1 may be associated with the charge transfer transitions (LMCT).

ν(M-N) ν(M-O) ν(O-H)
No The electronic spectra of Cu(II) complexes (3,7,11) contain a broad band at the region 13513 _ 13071cm -1 . These bands are typical of d-d band of Jahn-Teller distorted Cu(II) complexes in distorted octahedral geometry, and can be assigned to two or three of the transitions 2 B 1g → 2 E g , 2 B 1g → 2 B 2g and 2 B 1g → 2 A 1g (Singh, 2008). Magnetic moment of these complexes are in range 1.79 _ 2.2 BM corresponding to one unpaired electron and suggesting a monomeric octahedral geometry (Cotton et al., 1999).
The diamagnetic Zn(II) complexes (4,8,12) show no prominent absorption in the visible region because of d 10 configuration of Zn(II).

CONCLUSION
Based on stoichiometries and spectro-chemical studies, the bis hydrazone ligands, act as a dibasic tetradentate ligands(NNOO -2 ) in all prepared deprotenated complexes (1-12) coordinating through the two enolate oxygens and two azommethine groups nitrogen atoms.Octahedral geometry is proposed for all complexes Fig.(1).