Synthesis, Characterization and Thermal Studies of Fe(II), Co(II), Ni(II) and Cu(II) Complexes with bis-(4-benzylidenamino-phenyl)-methane Schiff base ligand

A new series of Co(II), Fe(II), Cu(II) and Ni(II) complexes of Bis–(4-benzylidenamino-phenyl)-methane (L) have been prepared and characterized. The complexes conform to general formula [CoL(H2O)3] Cl2, [FeL(H2O)5]SO4.2H2O, [CuL(H2O)5] NO3 and [NiL(H2O)3Cl2], Infra red spectra and elemental analysis reveal uni-dentate coordination of Schiff base to metal ions. Molar conductivity measurements show that complexes (I, III) behave as 2:1 electrolyte while complex (II) behave as 1:1 electrolyte. The thermal studies for complexes shows that the complexes are thermal stable.


Introduction
Schiff bases are an important organic compounds which carrying imin or azomethane group . Schiff bases are versatile compounds in many fields including biological , analytical , medical and pharmaceutical such as Anti tubercular [1,2] , Anti depressant [3] , Anticonvulsant [4,5] and antiinflammatory [6]. Schiff bases easily formed high thermal stability complexes with almost all metal ions were useful for uses as catalysis in highly temperature for both homogeneous and heterogeneous reaction such as polymerization [7,8] , For reduction of thionyl chloride [9] and oxidation of organic compounds [10].

Material and methods
All chemicals and solvents used in this study were supplied (Merck and Fluka) company . The 1 H NMR spectra were recorded with (Bruker DPX-300)Spectrometer(Iran) . The elemental analysis was done by using (CE-440)Elemental analyzer(Iran) . FT-Infrared spectra were recorded as KBr pellets with (FT-IP 8400S) Shimadzu instrument(Univercity of BAsrah) . Melting point of complexes were determined on (Gallnkamp melting point apparatus). Thermal analysis were carried out under (N2) atmosphere using -Al2O3 as reference(Iran) . The ionic conductivity was measured by using (Konduktoskop E 365B Metrohm Herisau) conductivity instrument at room temperature.

Preparation of Schiff base complexes:
To a hot solution of CoCl2.6H2O , FeSO4.7H2O , Cu(NO3)2.3H2O ,and NiCl2.6H2O in (15 ml )ethyl alcohol (2.5mmol)was added (2.5mmol) solution of Schiff base (L) are mentioned in literature [19] in 25ml ethyl alcohol drop wise with continues stirring and gentle heating for 1hr. The volume of solution reduced to half, colored solid compound was formed were filtered off , washed several times with hot deionized water and then with ethyl alcohol and dried under vacuum.

Computational methods
The theoretical study in work was performed using the computationals method by hyper chem. 8.02. Geometry optimization of the studied , compounds by performing the semi-empirical molecular orbital theory at the level PM3 [20].

Result and discussion
The C.H.N , molar conductunce data and physical characteristic of new complexes are listed in table (1). The assignment bands of( IR) spectra of Schiff base ligand and their metal complexes are listed in table (2).
In The Infrared spectra of Schiff base ligand (L) , The C=N stretching frequency for azomethane group is observed at 1625 cm -1 . The value of these band was shifted to lower wave number in the spectra of all metal complexes in the range (1589-1618)cm -1 which due to coordination the nitrogen of azomethane with the central metal ions [21,22]. On the other hand all complexes exhibit a broad bands at (3315-3454) and bands at (910 -960)cm -1 which due to stretching modes of O-H group and rocking mode of coordinated water to metal ion respectively [23,24]. The (C-N) stretching modes appeared around(1172-1244) cm -1 and the (C=C )stretching frequency of aromatic ring appears a round(1508-1591) cm -1 , While the bands in the (3020-3059) cm - Table2. The assignment IR bands of schiff base ligand and their complexes:  [26,27] by the presence of singlet signals in the range (7.73-8.56) ppm which due to proton of azomethane group in (1) position. The aromatic protons showed multiplet signals in the range (6.18-8.22) ppm due to the protons in (4,5,6,7 and 8) positions in the aromatic rings. While the aliphatic proton of CH2 group ( proton in 2 position) showed singlet signals within the range (1.19-2.08) ppm . The OH protons showed singlet signal in the region (3.81-4.68) ppm which appeared to coordinated water with metals. While the peak of solvent (DMSO) showed singlet signal within the range 2.50 ppm and 3.30 ppm OH 2 X X = Cl in Co S1 and Ni S1 compounds X = OH 2 in FeS1 and Cu S1 compounds  [29][30].The mass residue at 801 o C is 29.12%(30.44%) may be attributed to formation C7H6NCo.
The TG/DTA curve of Fe (II) complex (II) exhibit three exothermic decomposition step . The first step occur in the range 116-140 o C with mass loss of 5.517%(5.14%) due to removal the two crystalline water molecules. A small peak at 126 o C indicate to melting point .The second step occur between 280 -340 o C with weight loss of 20.23%(20.23%) due to removal sulfate ions . In the third step which occur in the range 480-510 O C a peak exhibit at 498 o C with mass loss of 54.88% (54.31%) attributed to loss the five coordinated water and non-coordinated part of Schiff base ligand [29,30]. The mass residue at 750 o C is 35.48% (35.51% ) may be attributed to formation Fe3O4.
The TG/DTA curve of Cu(II) complex(II) exhibit three endothermic decomposition step .The mass loss 2.69% (2.63% ) in the first step occur at 100 o C due to loss crystalline water molecules . The second step between 165-260 o C with mass loss of 16.12% (16.12% ) attributed to loss coordinated water molecules. In the third stage which occur in the range 430-500 o C with mass loss of 34.62% (34. 63%) due to loss tow nitrate ions .At 817 o C the mass loss 46.128% (46.52%) due to loss the noncoordinated part of Schiff base ligand .
In the TG/DTA curve of Ni(II) complex (IV)exhibit two exothermic decomposition step . The first step consist of two peaks at 128 and 198 o C with mass loss of 3.33% (3.35%) due to elimination of one water molecule . A small peak at 235 o C indicate to its melting point . Next stage occur in the   (7) and (8). The (PM3) geometry optimizations yields planar structure for the new compounds. The generals geometry of molecules all this compounds are very similar. The [the dipole moment, μ (in Debyes), highest occupied and the lowest unoccupied molecular orbital (HOMO and LUMO, respectively) energies, total energy, and the energy band gap (LUMO-HOMO energy difference) and for the studied molecules are given in Table ( 5)]. The dipole moment calculated indicates the molecules are pole. This means that these molecules may, especially other polar molecules.The spatial distributions of( HOMO LUMO) are shown in Figure. (9). In general the all molecules gave similar ( HOMO) and (LUMO) orbitals.

Conclusion:
Co(II), Fe(II) ,Cu(II) and Ni(II) complexes with bis-(4-benzyllidenamino-phenyl)-methane have been prepared and characterized by different physical and chemical methods. The analysis confirmed the