SYNTHESIS, SPECTROSCOPIC AND THERMOGRAVIMETRIC STUDIES ON SOME TRANSITION METAL COMPLEXES WITH HYDRAZONE LIGANDS

4224 | P a g e J a n u a r y 1 5 , 2 0 1 6 SYNTHESIS, SPECTROSCOPIC AND THERMOGRAVIMETRIC STUDIES ON SOME TRANSITION METAL COMPLEXES WITH HYDRAZONE LIGANDS. Ahmed A. Shabana, Hamdy A. Hammad, Hassan A.Sadek ,NAA Ghany Saleh D. Mekkey, Osama M. Yassin. 1 Chemistry Department,Faculty of Science,Azhar University,Naser city,11884,Cairo ,Egypt . Hassanelfarsy@yahoo.com. 2 Physical chemistry, National Research centre, Dokki, 12622, Giza, Egypt. Na_manakhly@yahoo.com 3 Physics Department, Faculty of Science, Azhar University, Naser city, 11884, Cairo, Egypt. Om_yassin_2030@yahoo.com ABSTRACT


INTRODUCTION
In recent years the chemistry of hydrazone has been extensively studied, owing to their coordinating capability, pharmacological activity and biological properties. The complexes of transition metals with hydrazone ligands have shown wide interest of biological and pharmaceutical activities such as antimicrobial, antibacterial, antifungal, anti-inflammatory, anticonvulsant,antibercular,antiviral, antioxidant and inhibition of tumor growth [1]- [4].The tridentate of benzhydrazone derivative ligands containing ONO donor atoms can be synthesized with any aldehyde or ketone. The presence of donor atoms in the ligands plays an important role in the formation of a stable chelate ring and this situation facilitates the complexation process [5]. The bioinorganic chemistry focused agreat attention to hydrazone complexes because many of these complexes have biologically important species [6]. In analytical chemistry hydrazone find application by act as multidentate ligands [7] with metal (usually transition metal group). Various studies have also shown that tha azomethine group having a lone pair of electrons in either a p or sp 2 hybridized orbital on trigonallyhybridized nitrogen has considerable biological importance. The hydrazone schiff's base show clearly keto-enol tautomerism and can link metal ion in neutral medium in medicinal application [8]. Thus, we are motivated to undertake a systematic study of preparation and characterization of transition metal complexes of Cu (II) and Ni (II) metal ions with some aroylhdrazone.

EXPERIMENTAL 2.1. Chemicals and instruments
Aldehydes were obtained from Biotech for laboratory chemicals, DMSO from Merk and all other chemicals used in the study were of reagent grade and applied without further purification.The elemental analysis were performed using CHNS-932 (LECO) Vario Elemental Analyzers, the molar conductance of complexes were measured using conductance/TDS 72 instrument. Infrared spectra were recorded on PerkinElmer FT-IR 200 spectrometer thermoelectron in 4000-400 cm -1 region as KBr pellets. The UV-Vis spectra were measured in the range of 200-800 nm using Perkin-Elemer Lambda 35 UV-Vis. The magnetic measurements were carried out using gouy method. The 1 H NMR spectra were recorded in DMSO and D2O usingGEMINI-200 NMR spectrometer. The melting point of was measured using electro thermal melting point SMPI apparatus. TGA analysis was recorded on TGA-50H in range of 25 -1000 C°.

Synthesis of metal complexes
The complexes were prepared by the reaction Cu (II) acetate and Ni (II) acetate with ASH, ABH.Ligands in molar ratio (1:1) and with ACH and AAH ligands in molar ratio (1:2).The mixture was heated and reflux for 3hr with stirring. the product was filtered off, washed several times with ethanol and dried over anhydrous CaCl2 in desiccator. [11]

Determination of metal content in complexes.
Metal complexes (5 mg) were weighted and then concentrated nitric acid (10 ml) was added. The solution was heated until few drops of the solution were remained. 10 ml deionized water was added to this hot solution, repeating this step five times then transferred the solution to a 100 ml volumetric flask. It was made up to the mark using deionized water and then the amount of metal was estimated by Atomic absorption spectroscopy.

RESULTS AND DISCUSSION
The analytical data for ligands and its complexes are given in table 1. The elemental analysis reveal that 1:1 (ligand: metal) stoichiometry for ligands ASH and ABH and 2:1 (ligand: metal) for ligands ACH and AAH. The isolated complexes are insoluble in most organic solvents but are soluble in hot DMSO.

IR spectral studies
The infrared spectra of ligands and related complexes were recorded to confirm their structures. The vibrational frequencies and their tentative assignments are listed in (Table 2). The hydrazone ligands can exist in the keto or enol forms or an equilibrium mixture of two forms since it has an amide group -NH-C=O [12] ,However the IR data indicates that in solid state the ligands is in keto-form. The IR spectrum of ASH ligand reveals a broad band at 3411 cm -1 attributed toν (OH) phenolic. The bands at 3322-3267 cm -1 due to ν (NH2 + NH ), the strong band with a shoulder noticed at 1653 cm -1 can be attributed to ν (C=O) [13], the spectrum also shows bands at 1600 cm -1 δ(N-H) ,1528 cm -1 ν (C=N) , 874 cm -1 ν(N-N).The IR spectra of complexes corresponding to ASH ligands reveal absence of OH band indicatingdeprotonation of the phenolic oxygen and subsequent coordination to the metal ion .This is further supported by upward shifting ofν (C-O) band by 14-41 cm -1 confirming the coordinating of phenolic oxygen to the metal ion [14].The disappearance of ν(C=O),ν (N-H) bands in complexes, suggests enolization of carbonyl oxygen and this is supported by appearance of J a n u a r y 1 5 , 2 0 1 6  [15], which also is confirmed by appearance of bands in the range of 437-443 cm -1 which have been assigned to ν (M-N). The (N-N) band in ligand is shifted to higher frequency in complexes at 890 -896 cm -1 and this frequency shift supported the coordination through azomethine nitrogen [16]. The complexes also show newbands at 3380 and 3426 cm -1 attributed to the presence of water molecules. The IR spectrum of ABH ligand indicates the observation of ν (NH2) vibrations as doublet at 3488 -3376 cm -1 , the ν (N-H) band of hydrazine moiety appears at 3210 cm -1 , the band observed at 1634 cm -1 is assigned to carbonyl group, the bands at 1541 and 1250 cm -1 is attributed to (ν C=N,δ N-H) and amide III respectively. By comparing the IR spectra of complexes with that of ABH ligand, it can be deduced that enolization of carbonyl oxygen and subsequent coordination to the metal ion through the oxygen after deprotonation ,this is supported by disappearance of ν (N-H ) band of hydrazinemoiety and appearance a new bands at (1367-1365) cm -1 and (597 -620) cm -1 due to ν (C-O) enolic and ν (M-O) respectively, and also the band of azomethine group in free ligand is shifted to lower frequency by 29-35 cm -1 , the band in free ligand at 967 cm -1 is shifted to higher frequency in complexes at 1034 and 1018 cm -1 due to ν (N-N) suggesting the coordination through azomethine nitrogen and is supported by appearance of new band at ( 452 -432 )cm

1 H NMR spectroscopy
The assignment of the main signals in the 1 H NMR spectra of the ligands are given in (table 3), 1 H NMR spectra of ligands exhibited multiple signals of the aromatic protons in the range of 6.5-8.5 ppm, the δ N-H proton appears in ASH, ABH, ACH and AAH at 11.449, 11.527, 7.481 and 7.625 ppm respectively, the spectrum of ASH (Fig 2) exhibits a signal at δ 11.849 assigned to OH proton, the signal at 6.441 and 6.309 ppm in the spectrum of ASH and ABH is assigned to NH2 proton respectively, the disappearance of OH, NH, NH2 protons is confirmed after the addition of D2O. The (CH=N) proton appears as singlet at 8.568, 8.391, 8.749 ppm in ASH, ABH and AAH respectively while the (CH=N) proton in ACH ligand appears as a doublet at 8.7 ppm.

Conductivity measurement
The molar conductanceΛMvalues of metal complexes in DMSO (10 -3 M solution) were measured at room temperature and the results are listed in (table 4).it is concluded from the results that metal complexes 1, 2, 3 and 4 were found to have molar conductance values in range of 10 -35 Ω -1 cm 2 mol -1 indicating that they are not electrolytic in nature and there is no counter ion present outside their coordination sphere [17].On the other hand, the molar conductivity values of J a n u a r y 1 5 , 2 0 1 6 complexes 5-8 were found to have molar conductance values in the range of 99 -145 Ω -1 cm 2 mol -1 indicating the ionic properties of these complexes.

Electronic spectra and magnetic susceptibility
The assignment of the observed electronic absorption bands of the transition metalcomplexes as well as the geometry and magnetic data of the complexes are shown in (Table 4).The ligands have spectral bands in the range of 39,682-27,100 cm -1 corresponding to ππ * andn π * transition in DMSO solvent.
In ASH complexes: the electronic spectrum of Cu complexshows abroad band at 15432 cm -1 corresponding to d-d transition characteristic of square pyramidal distorted structure of Cu (II) complex [18], [19], this band has been resolved to combination of four Gaussian functions (Fig 3a). According to previousreported experimental and theoretical data of Cu (II) compounds , the Gaussian function expected for square pyramidal structure, would be three peaks corresponding todz 2 dx 2 -y 2 , dxydx 2 -y 2 and dxz, dyzdx 2 -y 2 transitions [20]. The four Gaussian functions are attributed to the low symmetry around of Cu (II), four oxygen and one nitrogenatoms. In addition to the nitrogen apical atom shows a deviation of its perpendicularity to the square pyramidal base whichestablishes an interaction between electronic density of the nitrogen ligand and some of the atomic orbitals dxzand dyz, promoting a minimum differentiation between both d atomic orbitals (fig  3b).the magnetic moment μeff =2.02 B.M. which confirms the square pyramidal structure [21]. The electronic spectrum of Ni (II) complex (2) shows two absorption bands at 24390 and 18762 cm -1 characteristic of high spin five coordinated Ni (II) complex and could be assigned to 3  J a n u a r y 1 5 , 2 0 1 6

Thermogravimetric analyses
The thermogravimetric of complexes were recorded in the temperature range 25-1000 C° (Fig 4). Thethermogravimetric data are given in (table 5). The thermal decomposition process of complex 1involves three decomposition steps; the first step in the decomposition is started at 99-220 C° corresponding to loss of two coordinated water molecules (weight loss; calc./found%; 5.37/5.89), the second step in the range 221-338C°corresponding to loss of species molecules( 2HCN and 2CN) with weight loss (calc./found%;15.80/15.10) , while the third step in range 338-529 C° which is attributed to the loss of fragment (C24H20N2O2) with weight loss (calc./found; 54.90/54.42) leaving cupper oxides 2CuO as final residue (calc/found; 23.74/24.59).The TG curve of the complex2 reveals that the decomposition takes place in two steps. The first one at 74-163C° corresponds to a weight loss of (calc/found%; 5.44/4.76%) and is probably due to decomposition of the twocoordinated water, the second stage of decomposition takes place at 236-571.   . The TGA studies of the complex 7 involve two steps, the first step in range of (170-383C°)corresponding to loss of two coordinated water, two acetate group, CO, 2C6H4and 2 C7H7O with weight loss (calc./found%;55.50/55.70%), the second step at 295 -456 C° J a n u a r y 1 5 , 2 0 1 6 involves loss of 2HCN, 2NH and C8H8ON2 (calc./found%;35.64/35.53%) and the final residue is attributed to NiO + C (calc. /found%;8.76/8.77%). Where E*, R, A and θ are the energy of activation, the universal gas constant, pre-exponential factor and the heating rate, respectively. The correlation coefficient, R 2 , was computed using the least square method by plotting the left-hand side of equation 1 or 2 vs 1000/T (Fig 5). The n value which give the best fit (R 2 ≈1) was chosen as the order of the parameter for the decomposition stage. From the intercept and linear slop of such stages, the A and E* values were determined. The values of activation enthalpy (∆H*), the activation entropy (∆S*) and the free energy of activation (∆G*) given in (Table 6) were calculated using equation (3), (4) and (5). Where the A, k, and h are the pre-exponential factor, Boltzmann and plank's constant. The negative values of activation entropy (∆S*) indicated that the reactions are slow and the products are more stable than reactants and the positive values of (∆S*) indicated that the activated complexes for the decomposition stage has a less ordered structure compared to the reactant, further the reaction may be described as faster than normal. The positive values of enthalpy (∆H*) mean that the decomposition processes are endothermic. The values of (∆G*) increase significantly for the subsequently decomposition stages, increasing the values of (∆G*) as going from one decomposition step subsequently to another reflects that the rate of removal of the subsequent ligand will be lower than that of the precedent ligand and the reactions are non-spontaneous.