Synthesis and Characterization of New Fe(II) Schiff Bases Complexes. Aurel Pui 1, Malutan Teodor *, Mircea-Odin Apostu, Aurora Gref** It is reported the synthesis and characterization of some new complexes with tetradentate Schiff bases derived from bis(salicylaldehyde)etylenediimine, Salen. The Fe(II) Schiff bases complexes investigated are: (bis(5-nitro-salicylaldehyde)ethylenediiminato)iron(ii), Fe(NSalen), (bis(α-ethylen-salicylaldehyde)ethylenediiminato)iron(ii) Fe(EtSalen), (bis(α-ethylen, 3,5-diiodesalicylaldehyde)ethylenediiminato)iron(II), Fe(DIEtSalen), (bis(α,5-dimethyl, 3-iodesalicylaldehyde)ethylenediiminato)iron(II) Fe(DMISalen), and (bis(salicylaldehyde)methylene p,p - diphenylene)iron(ii), Fe(Salmbfn). The complexes characterization was performed by elemental analysis, Uv-Vis, IR and RX spectroscopy, cyclic voltammetry, etc. Semnificative influences on the redox potentials have the substituents grafted on ligands molecules. These complexes seem capable of forming reversible adducts [LFe - O 2 ], with molecular oxygen. 1. Introduction A series of cations of transitional metals, such as Fe(II), Co(II), Mn(II), Cu(II), etc., forms with Schiff bases, metallic complexes, with theoretical and practical application of quite varied types. Some of them are capable of reversibly binding molecular oxygen, being consequently employed as models in the study of oxygen s reversible fixation such its natural carries (hemoglobins, hemocianines, etc.) [1]. Other complexes - due to their capacity of acting as catalyst- may be employed as models in the study of oxygenases, peroxidases and mono- and di-oxygenases [2]. The synthesis and characterization such new compounds, characterized by different structures and similar properties, represent a prioritary concern of research in various parts of the world [3]. The present study discusses the data reporting the existence of a correlation among the structure and redox potentials of the complexes. Study of the influence of various substituents grafted on the ligands molecules follows the modification of redox potentials of the complexes thus obtained. 2. Experimental part The Schiff bases - type ligands employed have been obtained by refluxing of an aldehyde with a corresponding diamine (2:1 molar ratio). They have been characterized by elemental analysis, UV-Vis, IR, and NMR spectroscopy [4]. The synthesis of coordinative compounds involves refluxing of an alcoholic solution of ligands in forms of a potassium salt, with an aqueous solution acid of FeSO 4 7H 2 O, [5]. Refluxing occurs in an inert Ar atmosphere. The first crystals appear immediately, yet refluxing continues for about an hour. The precipitates obtained have been filtered in vacuum, washed with water, ethanol, ether and then dried under vacuum.
2 The complexes characterization was performed by elemental analysis, UV-Vis, IR, Rx spectroscopy and cyclic voltammetry. The elemental analysis of C, H and N was effected to the Microanalysis Service of Paris - Sud University. The comparative UV-Vis spectra of the ligands free and of the complexes have been obtained in organic solvents (DMSO, DMF, CH 2 Cl 2, CH 3 OH), on a double ray DES device. The FT-IR spectra have been recorded on KBr pellets, with a Brucker apparatus. Processing of the data was based on a Opus program. The RX spectra of microcrystalline powders were obtained on a Philips PW 3020 device, equipped with a Cu cathode, while the data were processed with a Diffract program. Cyclic voltametry was made on a PAR 263 A voltammeter, operated by a computer, which employed a PAR - 270 M software. The recordings were made on solution with a concentration of 2 mm, in DMF, using 0.1mol/l LiClO 4, as a supporting electrode under inert argon atmosphere. The working electrode was carbon vitreous, with electroactive area A=3.8mm 2. A saturated Ag/AgCl was used as a reference and a platinum wire as an auxiliary electrode 3. Results and discussions The general formula of the ligands of complexes taken into study is presented in figure 1. Fig. 1. The general formula of ligands used The nature of the R 1, R 2, R 3 substituents the carbohydrated chain Z, and abbreviation for the ligands used are presented in Table 1. Table 1. Nature of the substituents of ligands. Ligand R 1 R 2 R 3 Z Salen H H H (CH 2 ) 2 NSalen H NO 2 H (CH 2 ) 2 EtSalen H H CH 3 - CH 2 (CH 2 ) 2 DIEtSalen I I CH 3 - CH 2 (CH 2 ) 2 DMISalen I CH 3 CH 3 (CH 2 ) 2 Salmbfn H H H C 6 H 4 - CH 2 -C 6 H 4 Determination of the composition and purity of the coordinative compounds was effected by determination of the C, H, and N content; the results obtained being listed in Table 2. The result of such analyzes indicate a good purity of the coordinative compounds and separated from solution with a variable number of water molecules. Their presence is put into evidence by the thermal analysis and IR spectroscopy.
Table 2. Data of elemental analysis of the [FeL] compounds. 3 Coordinative Molecular Elemental analysis % compounds formula Found Calculated C H N C H N Fe(NSalen) Fe(C 16 H 12 N 4 O 6 ) 1.5 H 2 O 43.55 3.40 12.57 43.73 3.44 12.76 Fe(EtSalen) Fe(C 20 H 22 N 2 O 2 ) 3.5 H 2 O 56.362 6.33 6.49 56.75 6.43 6.62 Fe(DIEtSalen) Fe(C 20 H 18 N 2 O 2 I 4 ) 3 H 2 O 25.49 2.55 2.79 25.61 2.79 2.99 Fe(DMISalen) Fe(C 20 H 20 N 2 O 2 I 2 ) H 2 O 38.35 3.24 4.35 38.13 3.20 4.45 Fe(Salmbfn) Fe 2 (C 27 H 20 N 2 O 2 ) 2 (SO4) 5 H 2 O 45.98 4.23 3.82 46.18 4.31 3.99 A comparative study of the IR spectra of the free ligands, and also of the metallic complexes, evidences also, modifications of the vibration bands characteristic to the azomethinic group, ν C=N, a deformation bands outside of the plane, δ Ø- O H, as well as of shifting skeletal vibration of the aromatic rings (ν 1 ), etc. (Table 3). Table 3. The FT-IR spectral characteristic bands of the metallic compounds and free ligands (in bracket) δ Ø- O H Compounds ν H2O ν C=N ν 1 Fe(NSalen) 3450 (-) 1650.4 (1646.4) - (1216.0) 1601.0 (1642.2) Fe(EtSalen) 3447 (-) 1589.3 (1613.2) - (1293.9) 1532.0 (1576.2) Fe(DIEtSalen) 3439 (-) 1587.5 (1597.3) - (1267.4) 1482.5 (1481.0) Fe(DMISalen) 3450 (-) 1642.5 (1610.4) - (1264.8) 1618.5 (1583.2) Fe(Salmbfn) 3450 (-) 1612.2 (1616.8) - (1284.0) 1589.0 (1597.6) The deformation bands outside of the plane, δ Ø- O H, of the free lidands, are the missing in the complexes. In the 400-700 cm -1 domain, the appearance of some new bands, characteristics to the Fe-O bonding vibration is observed [6]. The UV-Vis absorption spectra, performed on the complexes dissolved in organic solvents (CH 2 Cl 2, DMSO), evidence the modification of the absorption bands characteristic to the ligands, as well as the occurrence of some new bands, characteristic for the formation of the coordinative compounds. The UV-Vis bands observed for the complexes of Fe(II) are presented in Table 4. Table 4. UV-Vis absorption bands characteristic for the FeL complexes, in CH 2 Cl 2. Coordinative Absorption bands (λ max (nm); lgε max ) Compound λ 1 (lg ε) λ 2 (lg ε) λ 3 (lg ε) λ 4 (lg ε) λ 5 (lg ε) Fe(NSalen) 1 488* (3.45) 406 (4.11) 354 (4.3) 262 (4.2) - Fe(EtSalen) 550* (2.36) 378 (3.43) - 246 (4.26) 226 (4.27) Fe(DIEtSalen) 500* (2.52) 440 (2.64) 356 (4.05) 268* (4.41) 232 (5.13) Fe(DMISalen) 508* (2.89) 422* (3.38) 344 (3.80) 266 (4.41) - Fe(Salmbfn) 510* (3.31) - 345 (4.28) 270 (4.19) 232 (4.38) * shoulder, 1 in DMSO
4 The appearance of a new band of absorption environs of 500 nm evidence presence of octhaedric complex of Fe(II) in solution [7, 8, 9]. The X - ray spectra performed on microcrystalline powders (Fig. 2), indicate that the Fe(II) ion and the donor atoms (N and O) are suitable in the same plane. The parameters for elemental cell are: a= 10.479 Å, b= 8.168 Å, c= 7.943 Å, V= 532.62 Å 3 for Fe(DIEtSalen) and a= 17.489 Å, b= 6.222 Å, c= 4.761 Å, V= 518.08 Å 3 for Fe(DMISalen) complex. Fig. 2. RX spectrum for the Fe(DIEtSalen) (a) and Fe(DMISalen) (b) complex. The studies of cyclic voltametry evidence a reversible or quasi-irreversible behaviour for most of the complexes (Fig.3), the Fe(Salmbfn) excepted, which is irreversible. The free ligands nor show oxidation peaks in range investigated.
5 (a) (b) Fig. 3. Cyclic voltamograms for the Fe(NSalen) (a) and Fe(DIEtSalen)complex; C FeL =2 10-3 M, in DMF, working electrode-c vitreous, v = 100 mv/s. The electrochemical behaviour, the values of the peak (Epa, Epc) and semiwaves (E 1/2 ) are listed in Table 5. Table 5. Cyclic voltammetry date for the FeL complexes Electrochemical system Epa Epc Ep E 1/2 E' 1/2 G KJ/mol K Electrochemical behaviours Fe(Salen) -0.050-0.180 0.130-0.115-0.677-65.32 quasi-reversible Fe(NSalen) 0.087 0.030 0.057 0.059-0.505-48.72 reversible Fe(EtSalen) -0.250-0.385 0.135-0.318-0.880-84.91 quasi-reversible Fe(DIEtSalen) -0.097-0.166 0.069-0.132-0.694-66.96 quasi-reversible Fe(DMISalen) -0.220-0.286 0.066-0.253-0.815-78.64 quasi-reversible Fe(Salmbfn) 0.54-0.700 1.240 - - - irreversible E 1/2 = (Epa +Epc)1/2; E' 1/2 = E 1/2 E Fc+/Fc ; G = - nfe, E Fc+/Fc = - 0.562 V The semiwave potentials (E 1/2 ) are converted function of the ferrocenium/ ferrocene (Fc + /Fc) couple, considered come standard intern [10, 11]. The oxidation and, respectively, reduction potentials of such complexes are influenced by the nature of the substituents grafted on the ligands molecules, and equally, on the nature of carbohydrated chain, Z. Presence of the some substituents with donors electronic (-CH 2 - CH 3 or -CH 3 ) effects, increase electronic density on the metallic ion and decrease redox potentials. The presence of some electron-attracting substituents (-NO 2 ) decrease density on the metallic ion and increase redox potentials [12-14]. 4. Conclusions Grafting of various substituents on the aromatic nuclei and in the azomethinic groups of Salen type ligands, lead to the obtention of some new ligands. In reaction with Fe(II) ions,
6 they form coordinative compounds in which the metallic ion and ligand s donor atoms are situated in the same plane. The Uv- Vis and IR spectra show changes of free ligands bands come effect of coordinative compounds' forms. Their electrochemical properties are correlated with the nature of substituents grafted on the ligands molecules. References 1. K. Shikama, Chem. Rev., 98 (1998), 1357. 2. E. C. Niederhoffer, J. H. Timmons, and A. E. Martell, Chem. Rew., 87 (1984) 137. 3. L. I. Simandi, Dioxygen Activation and Homogeneous Catalytic Oxidation, Elsevier Publishers B. V., Amsterdam, 1991, 93-102. 4. Al. Cascaval, studies unpublished. 5. R. H. Bailles; M Calvin, J. Am. Chem. Soc., 69 (1947), 1886. 6. K. Nakamoto, Infrared Specta of Inorganic and Coordination Compound, second edition, Wiley, New York (1963). 7. L. Casella, M. Gullotti, A. Pinar, L. Messori, A. Rockenbauer, M. Gyor, Inorg. Chem., 26 (1987), 1031. 8. A. B. P. Lever, Inorganic Electronic Spectroscopy, second edition, London (1992). 9. Y. Inada, K. Sugimoto, K. Ozutsumi, S Funahashi, Inorg. Chem., 33 (1994), 1875. 10. R. R. Gagne, C. A. Koval, G. C. Lisensky, Inorg. Chem.,19 (1980), 2855. 11. G. A. Mabbot, J. Chem. Education, 60:9 (1983), 697. 12. A. Nishinaga, K. Tajima, B. Speiser, E. Eichhorn, A. Reiker, H. O. Nishiguchi, K. Ishizu, Chem. Letters, (1991), 1403 13. C. Kang, A. Sobkowiad, D. T. Sawyer, Inorg. Chem., 33 (1994), 79. 14. S. K. Dhar, Inorg. Chim. Acta, 240 (1995) 609. Rezumat Se prezintă sinteza şi caracterizarea unor noi complecşi cu baze Schiff tetradentate derivate de la bis(salicilaldehid)etilendiamina, Salen. Complecşii de Fe(II) cu baze Schiff, investigaţi sunt: bis(5-nitrosalicilaldehid)etilendiamminfer(ii) Fe(NSalen), bis(α-etil-salicilaldehid) etilendiamminfer(ii) Fe(EtSalen), bis(α-etil, 3,5-diiod-salicilaldehid) etilendiamminfer(ii) Fe(DIEtSalen), bis(α, 5-dimetil, 3-iodsalicilaldehid) etilendiamminfer(ii) Fe(DMISalen), şi bis(salicilaldehid)metilen p,p difenilendiamminfer(ii) Fe(Salmbfn). Complecşii au fost caracterizaţi prin analiză elementală, spectroscopie Uv-Vis, IR, RX şi voltametrie ciclică. Substituenţii grefaţi pe moleculele liganzilor au o influenţă semnificativă asupra potenţialelor redox ale complecşilor. Aceşti complecşi par a fi capabili de a forma cu oxigenul molecular aducţi [LFe-O 2 ]. * Faculty of Chemistry, Al. I. Cuza University, Iasi-Romania Faculty of Chemistry, Gh. Asachi Tehnical University, Iasi-Romania **Institute of Molecular Chemistry Orsay, Paris-Sud University, Orsay- France