Synthesis, Structural and Spectroscopic Study of Complexes of Tetradentate Schiff Base Derived from MalonylDihydrazide with Cr(III), Mn(II), Co(II), Cu(II) and Zn(II) Ions

-This paper describes the synthesis of a new derivative dihydro-3H-indol-3-ylidene propane dihydrazide [L], which have been obtained from the reaction between malonyl di-hydrazide and an ethanollic solution of isatin. Tetradentatemacrocyclic ligand [L] was characterized by (C.H.N), (FT-IR), (UV-Vis), and 1H.NMR.A series of the used metal complexes have been synthesized by the prepared ligand [L] reaction with some transition metal ions. The isolated complexes were Cr(III), Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) also characterized using different techniques such as (FT-IR), and (UV-Vis) spectroscopies, (C.H.N), flam atomic absorption in addition to the magnetic susceptibility and molar conductivity measurement. Al complexes were octahedral in geometry except for Zn (II) complex, which was tetrahedral .


Introduction
Malonyldihydrazide and isatin compounds are important class of polydentate ligands in coordination chemistry and find extensive applications in different fields [1], also, the presence of imine group ( ), which imports in elucidating the mechanism of transformation and rasemination reaction in biological system [2]. The transition metal complexes of hydazone and its derivatives have been extensively examined due to its wide applications ranging from antimicrobial [3], anti-tubercular, carbonic anhydras inhibitors, and anti-inflammatory [4]. The developments of the field of bioinorganic chemistry have increased the interest in macrocyclic complexes containing oxygen and nitrogen atoms, since it has been recognized that many of these complexes may have some applications in industry and medicine [5,6]. The present paper describes some of the new Schiff base [L] applications, which is derived from isatinreaction with malonyldihydrazide. Ligand [L] provides four sites that are potential donor and forms complexes with Cr(III), Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). The ligand [L] and its complexes have been fully characterized.

Experimental
All the chemicals were used as received (from Fluka and BDH) and they were of highest purity available by using metal chloride salts (CrCl 3  were added with stirring to an ethanol solution of ligand (0.390g, 1mmole) and refluxed on water bath temperature for 2hrs., then the crude solid complexes were separated by filtration under suction, washed for several times with hot ethanol to afford colored purified metal complexes.

Results and Discussion
The reaction of one mole of malonyldihydrazide and two moles of isatin afforded the tetradentatemacrocyclic ligand [L] in good yield, scheme 1. The suggested mechanism of the formation of the ligand (L)can be shown in scheme 2.

I. Physical properties and micro elemental analysis
The physical properties and micro elemental analysis of the prepared ligand and its metal complexes are summarized in Table 1. Results are quite related to the suggested structural formula.  [11]. The integration curves were used to calculate protons numbers and further details of the chemical shifts with their assignments can be found in Figure 1, which reveals the proposed structure of the ligand [L].

III. Infrared Spectra
The FT-IR provides very interesting information about the metal atom attached functional group nature. The free ligand [L] and its prepared metal complexes behave as a tetra dentate coordination with these ions of metal through the carbonyl oxygen and the nitrogen of azomethine group. FT-IR spectrum of free ligand band shows peculiar absorption at 1728cm -1 for υC=O in addition to a strong band in the 1612cm -1 region, due to υC=N which undergone to down shift in all spectra of metal complexes what indicates azomethine group nitrogen involvement in the coordination [12,13], as shown in Figure 2. Moreover, (-C=O) absorption negative shift gives a coordination significant investigation of the metal ions through carbonyl group oxygen atom [14]. Furthermore, the spectrum of each complex shows a weak to medium band in (530-619)cm -1 , and (420-474)cm -1 regions for (υM-N) and (υM-O) bands, respectively [15,16]. The spectrum of each complex except for Zn(II) complex exhibits a broad absorption band in (3412-3435)cm -1 regions that is attributed to (υO-H) of the coordinated water molecules and the coordinated water molecules O-H stretching [17,18]. Further details of the characteristic are shown in Figure 3 and Table 2.

IV. Electronic Spectra, Magnetic Susceptibility Measurements
The electronic spectroscopy is available tool for coordination chemists to obtain important information regarding structure of complexes.

Figure 4: UV-Vis Spectrum of the Ligand[L]
The high intensity band at (29411cm -1 ) has been allocated to the charge transfer from the metal to the ligand [23], which would support the high delocalization between the groups of C=O, and C=N with the ion of Co(II) that maybe referred to high covalence factor of Co-O and Co-Nb and in complex [22], with (4.05 B.M) magnetic moment for Co(II) complex in the solid state. The Ni(II) complex electronic spectrum exhibited three bands at(15384,18867,23255)cm -1 , which have been attributed to 3 A 2 g (F) → 3 T 2 g (F) , 3 A 2 g (F) → 3 T 1 g (F) , and 3 A 2 g (F) → 3 T 1 g (P) transitions, respectively, that indicates an octahedral geometry [23]. Ni(II) complex magnetic moment value equals of (2.80)B.M, which confirmed its high spin octahedral geometry [24], Figure 5, Table 3. Copper (II) complex electronic spectra in ethanol demonstrated a band that is low energy and weak at (16129) cm -1 with high intensity one at (26315)cm -1 , the visible region of the first band is typically expected for 10Dq, which corresponds to 2 Eg→ 2 T 2 g transition [25]. Moreover, the magnetic moment (1.79B.M) corresponds to one unpaired electron, which offers possibility of an octahedral geometry [26]. On the other hand, Zinc(II) complex showed two high intensity absorption band at 35714cm -1 , and 25641 cm -1 regions that are assigned to ligand field (L.MCT) transition [27], Table 3.

V. Molar Conductivity Measurements
The results of the molar conductance is (130-223)ohm -1 .cm 2 .mol -1 for all complexes, that were carried out in DMF solvent, which indicates that all of the study complexes are (1:2) electrolytic nature [28,29] and Cr(III) is (1:3).These results suggest that all of the study complexes are electrolytes, thereby showing the chloride ions in counter ion, Table3.

Conclusion
In this study, all spectral data demonstrated that the prepared Schiff base compound behaves as tetra dentate ligand and binding to the metal ion through the oxygen of the carbonyl and nitrogen of azomethine group. Moreover, the analytical data demonstrated that the ratio of M:L is 1:1in all the prepared complexes and consequently suggest a mononuclear structure for all complexes.
Depending on the results that obtained from the spectral and elemental analysis in addition to the magnetic moment and the molar conductivity of the complexes in DMF solution, all complexes were electrolyte and have octahedral configuration except for Zn(II) complex, which has tetrahedral geometry, Figure 7.