Synthesis and Characterization of Mn(II), Co(II), Ni(II),Cu(II) and Zn(II) Complexes with Acetylhydrazones

Complexes of Mn(II), Co(II), Ni(II),Cu(II) and Zn(II) with p-tolualdehyde acetyl hydrazone (TAH), panisaldehyde acetyl hydrazone (AAH) and 2furylaldehyde acetyl hydrazone (FAH) of the types [ML2Cl2] where L=TAH and AAH and [M(FAH)2]Cl2 were synthesized. The complexes were characterized on the basis of analytical molar conductance, molecular weight, magnetic moment, infrared and electronic spectra. From the elemental analysis and molecular weight data 1:2 (metal : ligand) was proposed. The molar conductance measurements showed that TAH and AAH complexes were non-electrolytes and FAH complexes were 1:2 electrolytes in DMF and DMSO. The magnetic moment coupled with the electronic spectra suggested an octahedral geometry for all the complexes . IR spectral studies indicated that TAH and AAH functions as neutral bidentate ligands via carbonyl oxygen and azomethine nitrogen atoms while FAH act as neutral tridentate ligand coordinated through furan ring oxygen atom in addition to carbonyl oxygen and azomethine nitrogen atoms. ـــــــــــــــــــــــــــــــــــــــــــــــــــ تادقعم صيخشتو ريضحت Mn(II) ، Co(II) ، Ni(II) ، Cu(II) و Zn(II) عم


INTRODUCTION
Hydrazone ligands and their complexes have been studied for their antifungal and antibacterial activity, as iron chelators in the treatment of anemias and as antiviral drugs . (Agüelles et al., 2004 ;Rollas and Kücükguzel, 2007). In addition they have been studied also as a group of useful spectrophotomertic reagents (Singh et al.,1982 ;Kumar et al., 2004 ;Vallinath et al., 2010).
Hydrazone compounds derived from aromatic and heterocyclic hydrazides with aldehydes and ketones have extensively been investigated and revealed a versatile behavior in metal coordination depending on the nature of both the ligands and the metal ions, the anions of the metal salt, the pH of the reaction medium and the solvent used (Hueso -Urena et al., 2000 ;Maurya et al., 2002 ;Iskander et al., 2003 ;Prasad and Agarwal, 2008 ;Despaigne et al., 2009) ;El-Halabi et al., 2009 ;Yaul et al., 2009 . Hydrazones derived from acetylhydrazide (CH 3 CONHNH 2 ) which have biological properties (Dimmock et al., 2000) were very little reported (Abd El-Wahed et al., 2003;Rajaei et al., 2010). Therefore, it was of interest to investigate the coordination behavior of a number of acethylhydrazones derived from p-tolualdehyde (TAH), p-anisaldehyde (AAH) and 2-furylaldehyde ( Fig. 1) with some divalent transition metal chlorides.

Materials and Methods
All chemicals used were reagent grade from Fluka or B.D.H chemical companies, used as supplied, except for 2-furylaldehyde which was purified by distillation according to literature (Perrin et al., 1980) .
The metal contents of the complexes were determined spectrophotometrically using Shimadzu AA670 atomic absorption spectrophotometer, after decomposition with concentrated nitric acid. Elemental analysis of carbon, hydrogen and nitrogen for two of the prepared complexes were performed on Perkin Elmer 2400 analyzer at Al al-Bayt University laboratories, Jordan.
IR spectra of the ligands and their complexes were recorded as KBr pellets in the region 4000-400 cm -1 on Tensor 27 Brucker FT-IR spectrophotometer. Conductivity measurements were measured on 10 -3 M solutions of the complexes in DMSO and DMF at 25˚C, using PMC3 Jeneway and Terminal 740 wtw conductivity meters. Electronic spectra were recorded on Shimadzu UV-1650 PC-spectrophotometer for 10 -3 M solutions of the ligands and their complexes in ethanol solvent at 25˚C . Relative molecular weights of the ligands and their complexes were estimated cryscopically (Danials et al., 1962) using Beckmann thermometer. Magnetic susceptibility measurements of the complexes were performed using Bruker BM6 instrument at room temperature. Melting points were determined using Electrothermal 9300 apparatus.

Preparation of Ligands Preparation of Acetylhydrazide :
This was prepared by the reaction of ethylacetate and hydrazine hydrate as described previously (Al-Saady and Al-Daher, 2000), and purified by dissolving in minimum quantity of hot chloroform followed by precipitation with dry ether. The white crystals are highly hygroscopic stored in dry conditions m.p. 62˚C (Ahmed and Chaudhuri , 1971).

Preparation of p-Anisaldehyde acetylhydrazone (AAH) :
This was prepared in same way as mentioned above, using (2.72g , 0.02 mole) of anisaldehyde .

Preparation of Metal Complexes:
An ethanolic solution (20 ml) of the appropriate metal (II) chlorides ( The mixture was refluxed for 2-3h , upon which solid complexes were separated (in case of the complexes 6-9 and 12-15 (Table 1) which filtered, washed with ethanol (3 ml) then ether (3 ml) and finally dried in an oven at 80˚C.
For complexes (1-5 , 10, 11), after completion of the reaction, the mixture was reduced to nearly half its volume. The concentrated solution was then left to stand overnight at room temperature which resulted in the formation of solid products. The products, thus obtained was filtered, washed and dried as mentioned above.

RESULTS AND DISCUSSION
The acetylhydrazones (Fig. 1) were prepared by reacting equimolar amounts of acetylhydrazide (CH 3 CONHNH 2 ) with the respective aldehyde [p-tolualdehyde (TAH), panisaldehyde (AAH) or 2-furylaldehyde (FAH)] in absolute ethanol. The complexes were prepared by direct reaction of the hydrazones with the metal (II) chlorides in absolute ethanol. Based on elemental analyses and molecular weight determination , the complexes were found to have the compositions shown in (Tables1 and 2). They were soluble in common organic solvents such as DMSO and DMF and to less extent in ethanol. Their solubility, melting temperatures and crystalline nature of most of them suggesting that they are non-polymeric (Chohan et al., 2000). The molar conductance measurements of the complexes in DMSO and DMF (Table 1) correspond to non-electrolytic nature for TAH and AAH complexes and 1:2 electrolytes for FAH complexes (Geary ,1971), these complexes may be formulated as [M(L) 2 Cl 2 ] and [M(FAH) 2 ]Cl 2 where M=Mn(II), Co(II), Ni(II), Cu(II) or Zn(II) and L=TAH or AAH. The structures of the complexes were characterized by FT-IR , magnetic measurements and electronic spectra .

Infrared Spectra and Mode of Coordination :
In order to study the bonding mode of ligands to metals in the complexes, IR spectra of the free ligands were compared with those of the metal complexes. The structurally significant IR bands of the free hydrazone ligands and their complexes have been reported in Table 3. The free ligands showed a medium intensity bands in the region 3185-3220 cm -1 assigned to υ(NH) stretching vibrations, which have been observed in the 3189-3241 cm -1 region in the spectra of the complexes. It can be observed that there is either no considerable shift or slight positive shift in the υ(NH) vibrations indicating non-involvement of amide NH function in the coordination (Agarwal et al., 2006). The slight positive shift in the υ(NH) vibrations in case of the complexes may be attributed to the decrease in hydrogen bonding in complex formation .
A strong intensity bands were observed at the region 1666-1665 cm -1 of the spectra of the uncomplexed ligand assigned for amide I υ(C=O) vibrations. In the IR spectra of the complexes a considerable negative shift in υ(C=O) (11-30 cm -1 ) was observed indicating a decrease in the stretching force constant as a consequence of coordination through the carbonyl-oxygen atom of the free ligand (Despaigne et al., 2009 ;Abd El-Wahed et al., 2003).
Another important bands which occur at 1608-1638 cm -1 region in the free ligand spectra were attributed to υ(C=N) (azomethine) mode. In the spectra of all the complexes , these bands were shifted to lower frequencies by 10-40 cm -1 , indicating the involvement of the nitrogen atom of the azomethine group in coordination (Prasad and Agarwal, 2008 ;Agarwal et al., 2006) . The band due to υ(N-N) mode appears at the region 950-1022 cm -1 in the spectra of uncomplexed ligands. This band which on coordination shifts up by 6-28 cm -1 to higher ware numbers with respect to free ligand , falls within the range commonly observed for coordinated >N-N < residue (Maurya et al., 2002, Hueso-Urena et al., 2000 and again confirms coordination via the azomethine group nitrogen atom . The high frequency shift is expected because of the diminished repulsion between the lone pairs of adjacent nitrogen atoms . The medium intensity band at 1276 cm -1 in the IR spectrum of the free FAH ligand assigned to furan ring υ(C-O-C) stretching vibration was shifted to lower values with 13-24 cm -1 suggesting the involvement of the oxygen atom of furan ring moiety in coordination (Sallomi , 2000 ;Taher , 2010). The low frequency skeletal vibrations due to M-O and M-N stretching provide also direct evidence for the complexation . In the present investigation, bands in the 508-587 cm -1 region of the complexes spectra have been assigned to υ(M-O) and the bands observed in the 431-490 cm -1 region to υ(M-N) vibration respectively (Agarwal et al., 2006, Chohan et al., 2000. The overall infrared spectral evidence suggests that the ligands TAH and AAH act as neutral bidentate ligands, coordinated through carbonyl oxygen and azomethine nitrogen atoms, while the ligand FAH acts as neutral tridentate ligand coordinates via hetero (oxygen) atom in addition to carbonyl oxygen and azomethine nitrogen atoms . Table 3 : Some selected infrared frequencies (cm -1 ) of the ligands and their complexes.

Magnetic properties and Electronic Spectra
The magnetic moments values and electronic absorption bands of the complexes are recorded in (Table 4) two absorptions were observed in the UV spectra of the ligands at the ranges 40650-35211 cm -1 and 31055-32051 cm -1 (Table 5) were assigned to the allowed, π π * and n π * transitions, respectively . The magnetic moments of the pale yellow Mn(II) complexes are in the range 5.66-5.86 B.M. corresponding to five unpaired electrons . However, their electronic spectra show high intensity absorption at 31645-29345 cm -1 due to coordinated ligand absorption and charge transfer transitions only indicating high spin octahedral geometry due to spin and lapport forbidden (Cotton et al., 1999) .
The cobalt(II) complexes show a magnetic moments values of 4.74-5.15 B.M. at room temperature. These high values of magnetic moments are due to orbital contribution. The stoichiometries suggest a coordination number of six for the central cobalt(II) ion and attaining an octahedral geometry (Agarwal et al., 2006). The electronic spectra of these pink color complexes are also consistent with their octahedral environment around the cobalt(II) ions . The spectra display bands at 9259 -9845 cm -1 , 14850 -16417 cm -1 and 18867 -19171 cm -1 attributed to 4 T 1 g(F) 4 T 2 g (F)(υ 1 ) , 4 T 1 g(F) 4 A 2 g(F)(υ 2 ) and 4 T 1 g(F) 4 T 1 g (P) (υ 3 ) Transitions, respectively in a high -spin octahedral geometry (Cotton et al., 1999 ;Agarwal et al., 2006). The electronic spectra of the three nickel(II) complexes are very similar to each other and exhibited three typical absorption bands at 9100-9266 cm -1 corresponding to the transition 3 A 2 g 3 T 2 g(υ 1 ) , 14450-15408 cm -1 due to 3 A 2 g 3 T 1 g(F)(υ 2 ) and 23924-24875 cm -1 for 3 A 2 g 3 T 1 g(P)(υ 3 ) which clearly indicates the octahedral stereochemistry of the complexes (Prasad and Agarwal, 2008 ;Cotton et al., 1999). Also, the values of the magnetic moments 3.08-3.16 B.M. may be taken as additional evidence for octahedral nickel (II) geometry (Cotton et al., 1999) .
The magnetic moments of copper(II) complexes were recorded at room temperature. The complexes show a magnetic moments in the range 1.82-2.06 B.M. corresponding to one unpaired electron. The electronic spectra of these complexes exhibited broad bands in the range 10526-12820 cm -1 due to two or three transitions 2 B 1 g 2 Eg , 2 B 1 g 2 B 2 g and 2 B 1 g 2 A 2 g. This band is characterstic in position and width with those reported for octahedral copper (II) complexes (Dianu et al., 2010 ;Lever , 1984).
The electronic absorption spectra of Zn(II) complexes show intense broad bands in the region 31645-28498 cm -1 may be attributed to charge transfer transitions. Except this, these diamagnetic complexes show no appreciable absorptions in the region below 26000 cm -1 in absolute ethanol solutions. In accordance with the d 10 electronic configuration of Zn(II) . Table 4 : Magnetic susceptibility and electronic spectra of the ligands and their complexes.

CONCLUSION
Acetylhydrazones prepared by condensation of acetylhydrazide and p-tolualdehyde (TAH), p-anisaldehyde (AAH) or 2-Furylaldehyde (FAH) (Fig. 1)  where L=TAH and AAH acting as neutral bidentate ligsnds coordinated through carbonyl oxygen and azomethine nitrogen atoms (Fig. 2a). While the ligand FAH formed complexes of the type [M(FAH) 2 ]Cl 2 in which the two FAH ligands act as neutral tridentates. These possibly accommodate themselves around the central metal ion in such a way that stable chelate rings are formed (Fig. 2b) giving in turn, stability to the formed metal complexes.