Preparation and Study Of Zn(II) Complexes With Some Schiff Bases Derived From Acid Hydrazide-Benzil and Ethylenediamine

Some new macrocyclic and acyclic complexes having the general formula [ZnL]Cl2,[ZnLCl2],[Zn2LCl4] where L=Schiff base ligands derived from ethylene diamine with esters (diethylmalonate, diethylsuccinate and diethylphthalate) and benzil, where prepared by the reaction of zinc (II) chloride with ligands in ethanolic solution.1:1,2:1,1:2 stoichiometry of zinc (II) to ligand. Elemental analysis, molar conductance, infrared and ultraviolet studies reveal that the ligands in these complexes behave as tetra and octadentate forming tetra and hexa coordinated zinc (II) complexes respectively. Preparation and Study Of Zn(II) Complexes With Some Schiff Bases Derived ... 2 Introduction Schiff base molecules considered as important ligands in coordination chemistry. These ligands interested many workers and several reviews and papers appeared revealing their preparation and coordination complexes (1-3) . Schiff bases are very important from many points of view. They could be present (in addition to their solid crystal forms) as liquid crystal (4) . In coordination chemistry, they act as ligands due to their selectivity and sensitivity to the reaction with transition and non transition metal ions (5,6) . The design and synthesis of polydentate schiff bases and their properties and potential in the selective coordination of metal ions is reviewed (7,8) . Self-condensation reaction of appropriate formyl or keto precursors with suitable polyamines can give rise to well defined planer or tridimensional macrocyclic or macroacyclic schiff bases, but different reaction path ways can also occur (9-11) . Multidentate macrocyclic ligands are cyclic molecules consisting of an organic framework interspersed with hetero atoms which are capable of interacting with a variety of species (12) . They display unique and exciting chemistries in that they can function as receptors for substrates of widely differing physical and chemical properties and upon complexation can drastically alter these properties (13) . For these molecules, the nature and chemical reactivity of the resulting complexes are closely associated with the ligand at framework (14) . Considerable number of metal complexes with four and six nitrogen and oxygen donor macrocyclic ligand have been reported (15) . The biological activity of these schiff base complexes which bearing amide, azomethine and hydrazide groups is due to their action as the rapeutic agent owing to their easy hydrolysis providing low toxicity (16-18) . We are engaged in research including the synthesis of schiff base ligandsbenzolidine ethylene diamine and their new metal complexes. The research aimed also to elucidate the active site of the ligands and the possible structure and properties of the complexes. Experimental All reagents and solvents were of analytical grade. The ligands benzilidene ethylene diamine were prepared by the condensation of diethyl malonate, diethyl succinate or diethyl phthalate with ethylene diamine and benzil in ethanol at 25 o C. Synthesis of Schiff bases: The Schiff bases were synthesised by the condensation of acid hydrazide and benzil (1:1),(2:1),(2:2), dissolved in ethanol. After the condensation of the solution, the precipitate was separated, filtered, washed with ethanol and dried over CaCl2 in vacuum. Ihsaan A. Mustafa & Zuhoor W. Al-Tuhafy 3 Synthesis of the complexes : Different procedures were used for the preparation of the complexes. An ethanolic (25 ml) solution of schiff base (0.001 mol, 0.002 mol) was mixed with zinc (II) chloride (0.001 mol) or (0.002 mol) ethanolic solution keeping ligand-metal ratio 1:1,1:2 and 2:1. The mixture of reaction was then refluxed for 3hr. The complexes were precipitated upon concentration of the solution and cooling in ice. The compounds separated were filtered, washed with cold ethanol and dried over CaCl2 in a vacuum. The preparation of the complexes of the types [ZnL(Succ)] and [Zn2(L)2(Succ)Cl2] were carried out by refluxing (0.001 mol) and (0.002 mol) of [ZnLCl2] with (0.001 mol) succinic acid disodium salt in ethanol-DMF for about 2hrs. (0.001 mol) acetyl acetone was added to mixture of (0.001 mol) [Zn2LCl4] dissolved in ethanol-DMF and refluxed for about 1.30 – 2 hrs and on cooling precipitation of the complexes of both methods takes place. The separated complexes were filtered off, washed with cold ethanol and dried. Physical measurements : Elemental analysis were performed gravimetrically. The IR spectra of the samples were recorded using the KBr disc (4000-400) cm -1 FT-IR spectrophotometer. Molar conductivity were measured in freshly prepared 10 -3 mol solution in DMF at room temperature with conductivity meter consort LF-42. Chlorine was determined gravimetrically as AgCl. The UV spectra in the range (1100-200)nm range were obtained in DMF on a shmadzu UV-1650 pc spectrophotometer. Results and Discussion The template condensation of Schiff base ligand in the presence of zinc(II) chloride produced new metal complexes. The newly synthesized mono and binuclear Schiff base complexes are very stable at room temperature in the solid state. These chelates are generally soluble in DMF. The elemental analytical data of the complexes reveled that the compounds have a metal-ligand stoichiometry of 1:1,2:1 and 1:2. The analytical data are in good agreement with proposed stoichiometry of the complexes. The colours, melting points, IR and UV spectral data of all the compounds are presented in (Table 1-4). The conductivity values for the [ZnL3]Cl2 , [ZnL9]Cl2 complexes (150,155 ohm -1 .cm 2 .mol -1 ) indicate their electrolytic behaviour. This suggests that the anion (Cl) is ionically bonded in the outer sphere of coordination. On the other hand conductivity values measured under the same conditions for the other complexes (8-40 ohm -1 .cm 2 .mol -1 ) indicate that the complexes are non electrolytic in DMF solution. This suggests that the chloride ion are covalently bonded (19) . The formation of the metal-ligand bonds and the Preparation and Study Of Zn(II) Complexes With Some Schiff Bases Derived ... 4 sites of coordination in the ligands were studied by spectral means. The IR spectra of the complexes are compared with that of the free ligand to determine the changes that might have taken place during the complexation Table(3). In the infrared spectra of the complexes, the NH2 and C=O stretching frequencies of ethylene diamine and benzil or acetylacetone are absent with the appearance of new sharp band at 1595– 1620 cm -1 ,characteristic of the azo methane nitrogen present in the free ligand. The lowering in this frequency region by 15-20 cm -1 indicates the condensation of carbonyl and amino groups with the involvement of the nitrogen atom of the azo methine υ(C=N) group in complex formation (20,21) . The infrared absorption spectral of the ligands show the characteristic bands at 1635-1670 and 3310-3300 cm -1 due to )C=O( stretching and NH2 bending vibration, respectively (22) . In the spectra of complexes negative shift of about 15-32 cm -1 and 110-130 cm -1 were observed in the )C=O( stretching for cyclic (and noncyclic) complexes and NH2 bending for noncyclic complexes vibrations respectively. These negative Shifts of )C=O( and NH2 bands can be regarded as evidence for coordination through carbonyl oxygen and terminal ethylene diamine nitrogen atoms (23) . Further support for this coordination were indicated by the appearance of new bands 440-448 and 410-415 cm -1 in the infrared of the complexes are assigned to M-O and M-N stretching vibration, respectively (24) . The bands due to )C=O( and NH amide stretching vibrations located at 1635-1670 and 3285-3297 cm -1 in the free ligands spectra were remain unaffected upon macrocyclic [ZnLCl2] and [ZnL]Cl2 complexes formation (where L=L7, L8, L9) indicating the noninvolvement of carbonyl oxygen atom coordination, beside the NH-amide vibration band remain unchanged on all complexes. Table (1) : Some physical properties and name of the ligands No. Benzil mol Acid hydrazide mol m.p C o Color Name L1 0.01 0.01 190 Pale Purple Benzilidine malonyl bis (ethylene diamine). L2 0.01 0.01 185 Lemon Yellow Benzilidine succinyl bis(ethylene diamine). L3 0.01 0.01 195 Pale yellow Benzilidine phthaloyl bis(ethylene diamine). L4 0.01 0.02 215 Pale Purple Benzilidine dimalonyl tetra (ethylene diamine). L5 0.01 0.02 220 Pale yellow Benzilidine disuccinyl tetra (ethylene diamine). L6 0.01 0.02 235 Pale yellow Benzilidine diphthaloyl tetra (ethylene diamine). L7 0.02 0.02 240 Pale Purple Di(benzilidine malonyl) tetra(ethylene diamine). L8 0.02 0.02 248 Pale yellow Di(benzilidine succinyl) tetra (ethylene diamine). L9 0.02 0.02 239 Pale yellow Di(benzilidine diphthaloyl) tetra (ethylene diamine). Ihsaan A. Mustafa & Zuhoor W. Al-Tuhafy 5 Table (2) : Analytical and some physical data of the complexes No. Complex m.p C o %M (Calc.) min DMF ohm -1 .cm 2 . mol -1 % Cl (Calc.) 1 [Zn(L1)Cl2] 205 (13.12)12.91 30 (14.25)14.13 2 [Zn(L2)Cl2] 203 (12.76)12.33 25 (13.86)13.61 3 [Zn(L3)]Cl2 207 (11.67)11.52 150 (12.67)12.65 4 [Zn2(L4)Cl4] 225 (15.89)15.77 38 (17.26)17.14 5 [Zn2(L5)Cl4] 238 (15.36)15.32 18 (16.69)16.35 6 [Zn2(L6)Cl4] 252 (13.81)13.61 16 (14.99)14.78 7 [Zn(L7)Cl2] 255 (7.60) 7.50 23 (8.25)7.94 8 [Zn(L8)Cl2] 258 (7.36) 7.96 36 (7.99)7.87 9 [Zn(L9)]Cl2 252 (6.64) 6.52 155 (7.12)7.10 10 [Zn(L1)(suc)] 227 (12.03)11.98 10 11 [Zn(L2)(suc)] 260 (11.73)11.71 8 12 [Zn2(L1)2(suc)Cl2] 250 (12.55)12.43 28 (6.82)6.61 13 [Zn2(L2)2(suc)Cl2] 246 (12.22)12.11 32 (6.64)6.33 14 [Zn2(L10)Cl4] 261 (14.75)13.93 15 (16.01)15.83 15 [Zn2(L11)Cl4] 257 (14.29)14.17 40 (15.52)15.41 The symmetric () stretching band carboxylate group shifted to lower frequency region in the spectra of complexes while the asymmetric() stretching band shifted to higher frequencies, the value of Δv about 150 cm -1 , suggesting coordination of one carboxylate oxygen atom (25) . The other new band located at 570 cm -1 assigned for chloride. The shap