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|Synthesis , Characterization , and Theoretical Study of Schiff base Complexes Co(II), Ni(II) and Cu(II).|
Kawkab Ali Huissan AL-Ali .
Department of Chemistry – College of Education – Basrah University .
Basrah – Iraq
Schiff-base ligand derived from 9-10,phenanthrenequinone and o-amino phenol and its transition metal complexes with the metals Co(II), Ni(II) and Cu(II) have been synthesized. The prepared Schiff-base and its complexes were identified by IR, UV-Visible and elemental analyses (CHN).These used techniques facilitated to elucidate the chemical structures of the chelates.These techniques show that both transition metals form complexes with Schiff base in the ratio 1:1[M:L]. The theortical calculations of Schiff-base(I ) and its complexes(II,III,IV) were studied by quantum chemical calculations for the first time, The optimized structures of the Compounds(I,II,III,V) were obtained by molecular mechanics (MM+), and then further geometry optimization was carried out by the semi-empirical molecular orbital theory at the level of PM3 of the theory. Study Shown, the dipole moments of complexes have higher values compared with Schiff base ligand. Also of heats of formation, electrostatic potential, molecular orbitals energy of HOMO and LUMO and energy band gaps ΔE were calaulated.
KeyWord: Schiff-base , Transition metal complexes, Semiempirical PM3.
Schiff bases, so called since their synthesis was first reported by Schiff(1), result from the condensation of primary amines with aldehydes or ketones and contain a C=N bond. The condensation has been used by many researchers to form both small and large macrocycles, usually template with transition metals(2) . Schiff-bases have been widely used as ligands because of high stability of the coordination compounds of them (3). The π-system in a Schiff-base often imposes a geometrical constriction and affects the electronic structure as well(4). Metal complexes of Schiff-base have played a central role in the development of coordination chemistry. The complexes make these compounds effective and stereospecific catalyst for oxidation, reduction and hydrolysis, and they show biological activity and other transformation of organic and inorganic chemistry(5). It is well known that some drugs have higher activity when administered as metal complexes than as free ligand. In addition potential application in many fields such as antibacterial, antiviral, anticancer drugs, and electrochemistry(6,7,8,9). Electronic structure methods provide useful information on the molecular structure and charge distribution, so they are useful to understand and describe systems where electronic effects and molecular orbital interactions are dominant. Depending on the theoretical assumptions used for calculations, electronic structural methods belong to semi-empirical(10, 11) . Semi-empirical methods use parameters derived from experimental values that simplify theoretical calculations. These methods usually do not require long computation times, and lead to qualitative descriptions of molecular systems(12,13).
In the present study ,Cu(II), Co(II)and Ni(II) complexes of Schiff base were prepared, characterized by IR, UV-visible and elemental analyses and theoretical study were studied.
Ether, ethanol, hexane, 9-10,phenanthrenequinone and o-aminophenol from ( Fluka Co.), acetic acid, CuCL2.2H2O, CoCL2.6H2O, NiCL2.6H2O, Tolouene and Methanol from (Merck Co), were purified before using (14). Physical measurements, IR spectra were recorded on a Buck Scientific Model 500. IR spectrophotometer using a KBr disc in the range (4000 – 600) cm-1. Absorption Spectra in Methanol with the concentration of (1 x 10-5) M were determined on a U-1500- HITACH UV–Visible spectrophometer. The melting Point (mp) of the compounds were determined with a 9300 Model – Electro thermal melting point. IR, UV-Visible spectrophotometer and melting point was performed by Chemistry Department – Education College – Basrah University. Elemental analysis ( CHN ) of the compounds were determined with Perkin Elmer mode/2400 was performed by University of Cairo, Faculty of science, Micro Analytical center.
1-Synthesis of the Ligand
9-10,phenanthrenequinone (2.08gm, 0.01 mole) and o-aminophenol ( 2.18gm, 0.02 mole) were dissolved in 100ml of (3:1) ethanol(95%)- tolouene mixture with a few drops of acetic acid as a catalyst. The solution was refluxed with stirring for 6hours , The condensation product was filtered, washed with hexane and ether, recrystalised with ethanol, and dried under reduced pressure over anhydrous CaCl2 in vacuum (15,16). Schiff base have been characterized by elemental analysis and IR , UV spectra.
2- Synthesis of Schiff-base Complexes.
(3.9gm, 0.01mole) of the ligand and (2.37gm, 0.01mole) cobalt chloride , (2.37gm, 0.01mole) nickel chloride or (1.78gm, 0.01mole) copper chloride were dissolved in 100ml of (3:1) ethanol(95%)- tolouene mixture.The solution was refluxed for 3 hours; the volume of the solution was reduced to one-third by heating. On cooling, the crude product precipitated out, which was filtered off and washed several times with mixture (3:1) ethanol petroleum ether and dried over anhydrous CaCl2 in vacuum(16,17), characterized by elemental analysis and IR , UV spectra.
The physical data for the ligand and its complexes are listed in Table ( 1 ) .
Theoretical calculation were performed on hyperchem program version 7.5, running on a Pentium V PC-CPU 3400GHz. The geometries of the four compounds were optaimized first at level (MM+) by molecular mechanics force field theory and then at level (PM3) by semi- empirical theory.
Result and Discussion
In this paper, we describe the synthesis of Schiff-base -Complexes(I,II,III,V), were formed in good yield , the ligands and its complexes are stable at room temperature and are nonhygroscopic. The structures of the products were confirmed by their elemental analysis, which the differences between elemental analysis data and the calculated values of carbon , hydrogen and nitrogen elements are situated within the range which confirmed the validity of the suggested structures of the prepared compounds. The elemental analyses (Table1) data suggest that the complexes have ratio 1:1 ( metal – ligand ) stoichiomtry. Based on the elemental chemical analyses has been suggested, for complexes(II,III,IV) the formula ML. U.V.-Vis spectra of Schiff base ligand exhibited one absorption band at (265)nm suggesting the presence of (π-π*)transition. Complexes(II, III,IV) exhibited two bands at (350,465)nm, (360,470)nm, (375,490)nm respectively, the first band is due to (π-π*)transition, which can be assigned to electron delocalization over whole molecule on complexation, the second band in complexes show extremely strong (d-d)transition bands in the visible area. The values are slightly shifted to longer wave lengths ( red shift) indicating the ligand coordination of the ligand to the metal ions comparing with free lagnd.(18,19,20). The all bands were show in figure ( 3,4,5,6). The physical data for the ligand and its complexes are listed in Table ( 1)
Table(1): Analytical and physical data of the ligand (I) and their complexes (II,III,IV).
The Schiff-base and its complexes were identified by IR spectra in the range (4000–600)cm-1 as shown in figures( 7,8,9,10 ). The OH group in ligand(I) was appeared at (3350cm-1 ), while it disappeared in the IR-spectra of the Schiff-base complexes(II,III,IV) which may be attributed to deprotonated and coordinated to the metal ion formation of (M-O). The absorption band at (1667 cm-1, 1660 cm-1,1650 cm-1) in complexes(II,III, IV) respectively, due to ν(C=N) vibration is shifted by range (25 cm-1-- 42 cm-1) to a higher frequency compared to the corresponding band in the free ligand(1625 cm-1), indicating the coordination of azomethine nitrogen and oxygen to metal atom. The new of bands in complexes(II,III, IV) at (750, 685, 710, 670, 740, 680) cm-1 respectively, have tentatively been assigned to νM-O and νM-N respectively.(21,22) All above bands confirm that both oxygen and nitrogen bonds to metal ion. The all mentioned bands were shown in Table ( 2) .
Table (2): IR data for prepared compounds
HyperChem Calculation .
The general chemical structure of the Schiff base complexes are shown in fig.4 The geometries of the molecules were optimized first by using the molecular mechanics (MM+) force field, where the lowest energy conformations are obtained. The final optimized geometries of the ligand and their complexes were obtained by performing the semi-empirical molecular orbital theory at the level of the PM3 of theory. The optimized geometries are shown in fig .4.this figure illustrates the geometry of the molecules in the sticks model(23).
Table 3; Present some of the optimized calculated total energies and dipole moment, binding energy and semi-empirical heats of formation of the molecules under study . The total energy in a molecular orbital calculation is the net result of electronic kinetic energies and the interaction between all electrons and atomic cores in the system(24). On the other hand the heats of formation of all complexes under study are exothermic while the Schiff base ligand endothermic. The Ni-complex has the smaller value of heat of formation (-180.2103 kcal/mole). Thus , according to these results the Ni-complex is thermodynamically more stable than the other complexes. Also the dipole moment values are also considered for locating the coordination site. When dipole moment values are changed, like that in case of different metals then net increase in electronic charge is observed. Table 3 present four molecules orbitals energy : the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The values of the difference between the HOMO and LUMO orbitals, known as energy band gap (ΔE), are also given in Table 3. The band gaps values of the complexes are less than that of the free ligand. This means that in any excitation process, the Co, Ni, Cu, complexes need less(ca. 3.242, 0.567, 4.318 eV respectively) energy than that free ligand(25,26,27).
Three-dimensional isosurface picture of the electrostatic potential (ESP) are shown in Fig 4 .Blue colors indicate positive (ESP) regions and Red colors indicate negative (ESP) regions(28).
Table 3: Calculated Total energy, Binding, Heat of formation in kcal/mol and The MO
energy of HOMO, LUMO levels, ΔE(in eV) and the dipole moment μ(in Debyes) .
Structures Electrostatic potential (ESP)
Figure 2; Semi-empirical PM3 calculated optimized structures and Three-dimensional
isosurface picture of the electrostatic potential (ESP) of the possible geometry
of Compounds Under Study in gas phase
Fig 3: UV- spectrum of free ligand Fig 4: UV- spectrum of Co-complex
in methanol(1 x 10-5) M in methanol(1 x 10-5) M
Fig 5: UV-Visible spectra of Ni-complex Fig 6: UV-Visible spectra of Cu-complex
in methanol(1 x 10-5) M in methanol(1 x 10-5) M
Fig 7: IR- spectrum of free ligand
Fig 8: IR-spectrum of Co-complex
Fig 9: IR-spectrum of Ni-complex
Fig 10: IR-spectrum of Cu-complex
In this paper we Synthesized and Characterized of Schiff base complexes. The products were characterized by elemental analysis, IR, UVspectroscopic measurements. The elemental analyses data and IR spectra suggest that the complexes have ratio 1:1 ( metal – ligand ) stoichiomtry. Based on the elemental chemical analyses and IR spectra has been suggested, for complexes the formula ML. The quantum chemical semi-empirical calculations can be successfully used for the prediction of making more active ligands and hence for the formation of stable complexes which may be the work of interest of coordination and bio-inorganic chemists, as it is discussed here for Schiff base ligand. Dipole moment have maximum values for complexes compared with their Schiff base lgiands . This high dipole moment may make the complexes attractive for the interaction with other systems. The results show that the complexes have band gaps less than the free Schiff base.
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تم تحضيرليكاند قواعد شف ومعقداته. . قواعد شف ومعقداتها المحضرة شخصت باستخدام مطيافية الاشعة تحت الحمراء والاشعة المرئية وفوق البنفسجية وتحاليل العناصر الدقيقة .وهدة التقنيات أستخدمت كوسيلة لتبيين التركيب الكيميائي للتناسق. التقنيات بيينت ان الفلز الانتقالي يكون معقدات مع القاعدة شف بنسبة (:11)(فلز- ليكاند). الحسابات النظرية للقاعدة شف ومعقداتها قد درست بواسطة كيمياء الكم لأول مرة . موائمة التراكيب انجزت اولا بطريقة (MM+)ومن ثم أكملت الموائمة الهندسية بطريقة الشبه تجريبية المستوى الثالث PM3. اظهرت الدراسة القيمة العالية لعزم ثنائي القطب للمعقدات مقارنة مع قاعدة شف, وكما تم حساب حرارات التكوين , وسطوح الجهد الالكتروستاتيكي, طاقة الاوربيتال الجزيئية , HOMO , LUMOوقيمة ΔE