120 Acta Chim. Slov. 2008, 55, 120–124 Scientific paper Synthesis and Characterization of a Novel Iminooxime Schiff Base Ligand and Its Complexation with Copper(II), Nickel(II), Zinc(II), Cadmium(II), and Cobalt(II) · Ibrahim Demir, Mevlüt Bayrakci*, · Kürøsat Mutlu and A. Ihsan Pekacar Department of Chemistry, Faculty of Science and Art University of Nigde, 51100 Nigde, Turkey. * Corresponding author: E-mail: mbayrakci@nigde.edu.tr, mevlutbayrakci@gmail.com Received: 16-04-2007 Abstract In this study, a novel iminooxime ligand having dimetoxide groups as well as its complexes with copper(II), nickel(II), zinc(II), cadmium(II), and cobalt(II) were synthesized. We have used 3,4-dimetoxyacetophenone as starting material, and synthesized isonitroso-3,4-dimetoxyacetophenone by reaction of 3,4-dimetoxyacetophenone with n-butyl nitrite in presence of sodium ethoxide. 3-hydroxyphenylimino-isonitroso-3,4-dimetoxyacetophenone(3) was obtained from reaction of such nitroso compound with 3-aminophenol and its complexes were prepared by treatment of iminooxime with metal salts as Cu(II), Ni(II), Zn(II), Cd(II), and Co(II) in methanol, respectively. All of the structures were characterized by using spectroscopic techniques. Keywords: Iminooxime, metal salts, schiff base, NMR spectroscopy 1. Introduction Generally, the chelating ligands are polyfunctional molecules which can encage heavy metals in an organic sphere. Many types of Schiff base ligands are known and the properties of their metal chelates have been investiga-ted.1,2 Acyclic ligands containing nitrogen, oxygen and sulphur donor atoms in their structures can act as effective chelating agents for transition and non-transition metal ions.3 The importance of the coordination compounds in biological structures, the increasing proportion of the application and utilization of these compounds as agents has given rise to an intensification into the investigations of the complexes, especially “vic-dioxime compounds”. In technique, owing to resemble of the vic-dioxime compounds to vitamin B12 and chlorophyll as a color material of the plants, the importance on the illuminate of the biological structures4,5 have increased. New synthetic methods need to be combined with new techniques in terms to “enabling technologies for organic synthesis” to achieve rapid incorporation into industrial processes.6 Typical enabling technologies are microwave assistance, 3-new solvent systems,7 continuous flow reactors8 and immobilization of chemically active species such as reagents and homogeneous catalysts9 which have recently seen widespread applications in research laboratories. Various successful examples of combining two or more of these techniques in order to achieve faster synthesis or improved work-up have recently appeared in the literature, particularly in the field of catalysis. Oximes, an important class of chelating agents,10 have found numerous applications as highly selective reagents for the separation and determination of a number of metal ions.10 In this study, imi-nooxime ligand and its metal complexes were synthesized according to the studies of the Ponzio.11,12 2. Experimental All reagents were obtained either from Merck or Fluka, and used without further purification. Isonitroso-2,3-di-metoxyacetophenone and novel ligand, 3-hydroxypheny-limino-isonitroso-3,4-dimetoxyacetophenone, and its complexes were synthesized according to procedures described in literature. Mass spectrum, 13C and 1H NMR data · were carried out at TÜBITAK Research Laboratories (Turkish Research Council). IR Spectra were recorded on Jasco, FT/IR-300E. Electronic spectra were measured on Demir et al.: Synthesis and Characterization of a Novel Iminooxime Schiff Base Ligand ... Acta Chim. Slov. 2008, 55, 120–124 121 Scheme 1. The illustration of the synthesis of the ligand (3). Shimadzu UV-160A. Conductivities were measured in DMF using a LF 330 / SET conductivity meter at 24 °C. Magnetic moments were measured by the Gouy method, using Hg[Co(SCN)4] as calibrant. Synthesis of isonitroso-3,4-dimetoxyacetophenone (2): Isonitroso-3,4-dimetoxyacetophenone was synthesized by reaction of the 3,4-dimetoxyacetophenone with n-butyl nitrite in presence of sodium ethoxide.11–13 The product was soluble in some solvents such as methanol, iso-propyl alcohol, methylene chloride and chloroform, but was insoluble in hexane and carbon tetrachloride (isolated yield: 5.2 g (25%), m.p.: 123–124 °C). Synthesis of 3-hydroxyphenylimino-isonitroso-3,4-di-metoxyacetophenone (3): The ligand was synthesized as follows. A mixture of solutions of isonitroso-3,4-dimetox-yacetophenone (0.002 mmol) in 20 mL methanol and 3-aminophenol (0.002 mmol) in 10 mL methanol was stirred on a magnetic stirrer for 4.5 h with heating. On cooling, the precipitates formed were filtered off and recry-stallized in methanol.11,12 Product was soluble in methanol, isopropyl alcohol, and chloroform, but insoluble in hexane and acetone (isolated yield: 0.298 g (47%), m.p.: 135–137 °C with decomposition). Preparation of complexes: All of the complexes were prepared by the reaction of the Schiff base ligand 3 (0.004 mmol) in 20 mL methanol with the corresponding metal salts (0.004 mmol) in 10 mL methanol at 50 °C over 4 h. The resulting precipitate was filtered off and washed several times with methanol and dried over calcium chloride under vacuum. 3. Results and Discussion In this paper, we describe the synthesis of novel imi-nooxime Schiff base ligand 3 by the reaction of isonitro-so-3,4-dimetoxyacetophenone (2) with 3-aminophenol as mentioned. Our motive behind the synthesis of this type of ligands was to examine their possible applications in cation recognition processes, as homo or heteronuclear complexes which can be synthesized from alkaline and transition metal cations and may also serve as models of relevance to bioinorganic chemistry such as metalloenzy-mes. Even though an enormous number of Schiff base macrocycles and their complexes have already been described, many more interesting systems of this type await to be discovered. These structures are found to be powerful tools used to define interesting features related to general chemistry and application. Composition and proper- NOH OMe OH %1 NaOH OMe Metal Salt OMe '0^eH Scheme 2. The schematic illustration of related metal complexes. OMe Demir et al.: Synthesis and Characterization of a Novel Iminooxime Schiff Base Ligand ... 122 Acta Chim. Slov. 2008, 55, 120–124 Table 1. Spectral Data of Newly Prepared Compounds. Compound Spectral data 2 IR (v, cm4): 3430 cm4 (OH), 3100 cm4 (C-H aryl), 1700 cm4 (C=0), 1660 cm4 (C=N oxirne), 1450-1600 cm4 (C=C aryl), 1220 cm4 (Ar-O), 1006 cm4 (N-O); 'H NMR (300 MHz, CDCL) ō(ppm): 3.9^4.1 (s, 6H, (OCHA), 6.9-7.0 (d, IH, C-H ), 7.6-7.7(s, IH, C-H ), i' i'l arom. arom. 7.8 (d, IH, C-H ), 8.0-8.1 (s, IH, HC(=N)), 8.3(s, IH, N-OH); arom. 13C NMR (75 MHz, CDCL) ō(ppm): 55.1-58.5 (CHA 113.8 (C H), 115.1 (C H), 123.6 (C H), 130.7 (C -C=0), i> j" ar ar ar ar 147.4 (C=N), 151.3 (C -OCHA 155.6(C -OCHA 183.8 (C=0); ar j" ar j" Mass spectra (FAB), m/z: 210.01 (MH+), 181 (M+-C2H4, 100%), 150 (M+-C2H4NOH, 8%), 137 (M+-C3H5NOH, 60%), 122 (M+-C4H8NOH, 10%). 3 IR (v, cm4): 3420 cm4 (OH), 3050 cm4 (C-H aryl), 1610 cm4 (C=N oxime), 1650 cm4 (C=N imin), 1450-1500 cm4 (C=C aryl), 1220 cm4 (Ar-O), 1110 cm4 (C-N), 1010 cm4 (N-O); 'H NMR (300 MHz, CDC13) ō(ppm): 3.7^1.2 (s, 6H, (OCH3)2), 5.7 (s, IH, OH), 6.6-6.8 (s, IH, C-Harran), 6.9-7.0 (s, IH, C-Harran), 7.5-7.7 (dd, 5H, C-H^^), 8.0-8.1 (s, IH, (HC(=N)), 8.2 (s, IH, N-OH); 13C NMR (75 MHz, CDC13) ō(ppm): 53.5-56.2 (CH3), 107.8 (C^H), 113.6 (C^H), 117.2 (C^H), 119.3 (C^H), 123.8 (C^H), 127.1 (C^H), 134.4 (Car-C=N), 139.7 (C^H), 144.8 (C^-OC^), 147.4 (C=NOH), 151.1 (C^-OC^), 155.7 (C^-N), 158.6(Car-OH), 162.8 (C=N); Mass spectra (FAB), m/z: 301.07 (MH+), 300 (M+-H, 95%), 283 (M+-OH2, 40%), 258 (M+-CHNOH, 75%), 150 (M+-C7H7N202, 60%), 138 (M+-C8H7N202, 100%). Table 2. Illustration of IR data of newly prepared compounds and complexes (cm–1). Compoud N-OH c=o C=N oxim C=N imin C=CAr N-O C-N C-HAr Ar-O M-N M-O 2 3433 1700 1660 - 1450 1600 1600 - 3100 1220 - - 3 3420 — 1610 1650 1450 1500 1010 1110 3050 1220 — — Ni-(3) 3420 — 1620 1670 1450 1520 1010 ino 3050 1210 420 560 Cu-(3) 3420 — 1610 1660 1460 1560 1010 ino 3100 1220 480 540 Co-(3) 3200 3450 — 1620 1660 1450 1600 1010 ino 3050 1210 410 520 Zn-(3) 3400 — 1620 1650 1450 1520 1010 ino 3050 1220 440 580 Cd-(3) 3400 - 1610 1640 1400 1500 1010 ino 3050 1210 480 560 Table 3. Some analytical data and physical properties of newly prepared compounds and complexes Compound Empirical Formula Formula wt. Color M. p. (°C) Yield (%) Found (calcd) % C H N 2 C H NO 10 11 4 209 White 123-124 25 57.31 (57.39) 5.38 (5.30) 6.55 (6.67) 3 C H NO 16 16 2 4 300 White 135-137 47 62.78 (63.96) 5.43 (5.37) 9.23 (9.32) Cu-(3) C32H30N4O8Cu 661.5 Dark Green 300d> 49 58.21 (58.06) 4.49 (4.60) 8.37 (8.42) Ni-(3) C32H30N4O8Ni 656.7 Dark Green 300d> 31 58.50 (58.44) 4.52 (4.60) 8.47 (8.55) Zn-(3) C32H30N4O8Zn 663.4 Yellow 300d> 30 57.71 (57.83) 4.63 (4.50) 8.57 (8.46) Cd-(3) C32H30N4O8Cd 710.4 Yellow 300d> 26 53.97 (54.03) 4.07 (4.21) 7.89 (7.83) Co-(3) C H NO Co 32 34 4 10 656.9 Dark Brown 300d> 38 55.50 (55.41) 4.78 (4.90) 8.11 (8.03) d: Decomposition points of the corresponding molecule Demir et al.: Synthesis and Characterization of a Novel Iminooxime Schiff Base Ligand ... Acta Chim. Slov. 2008, 55, 120–124 123 ties of these compounds and metal complexes are summarized in Tables 1-3. The composition of the complexes is [M-(3)2] · nH2O for all complexes (n = 0 or 2). The metal complexes were prepared by treatment of ligand with appropriate metal Cu(II), Ni(II), Zn(II), Cd(II), and Co(II) acetates or chlorides, respectively. The molecular structure of novel ligand and its complexes were characterized by MS, FT-IR, UV-vis, 13C, 1H NMR spectra and magnetic susceptibility measurements. The main IR bands and their assignment are listed in Table 2. Significant frequencies were selected by comparing the IR spectra of the free ligand and its metal complexes. The absence of the O-H stretching and bonding vibrations from the spectra of the complexes indicates deprotonation of the O-H groups located at oxime groups (N-OH). A strong band, typical of C=N and oxime C=Nimin stretching, is found in the 1610-1620 cm–1, and 1640-1670 cm–1 range in the spectra of the complexes and free ligand, respectively. The both observed shifts in the C=N stretch region and deprotonation of the O-H groups located at oxime groups after complexation confirms the formation of coordinate bonds from the imine nitrogen and oxygen atom of oxime group to metal ion. When the spectra of the complexes are compared with that of the un-complexed Schiff base ligand, the i)(C=N) band is shifted to a lower region.1415 This situation indicates that the imine nitrogen must be coordinated to the metal ion. Additionally, the characteristic carbonyl peak is not seen around 1700 cm–1 in the IR spectra of the free ligand. This data support the proposed structures of the complexes and free ligand. In the IR spectra of the free ligand and its complexes, the bands at 1110 cm–1 and 1210-1220 cm–1 can be attributed to C-N and C–O bonds, respectively. The occurrence of new bands in the 410-580 cm–1 region in the IR spectra of the metal complexes confirms the presence of metal-nitrogen and metal-oxygen bonds, respectively. Furthermore, the presence of broad absorption band centered at 3100 cm–1 in the IR spectra of the Co(II) complex indicate the presence of water molecules in metal complexes. This was also confirmed by elemental analyses. Electronic absorption spectral data showed 71–71* transitions related to benzene ring at 220-260 nm and imine 71–71* transition at 332-343 nm. Comparing the free ligand and its complexes, it can be seen that the imine 71–71* transitions are shifted to some extent, because the imine nitrogen is involved in coordination with metal ion. For complexes, the ratios of the ligand to metal (L/M = 2:1) are founded by means of both UV spectra (Fig. 1 and 2) and elemental analyses. The magnetic measurements of the complexes are measured at room temperature. Nickel(II), cobalt(II, and copper(II) complexes are paramagnetic and their magnetic susceptibilities are 2.90, 4.10 and 1.82 B.M. respectively. Zinc(II) and cadmium(II) complexes are diamagnetic. 1H NMR spectrum of the free ligand 3 and compound 2 clearly demonstrates the presence of a C=N-OH environment at 8.2 and 8.3 ppm, and the azo- methine (CH=N) protons at 8.0 and 8.1 ppm, respectively. Comparing the chemical shifts values for the compounds 2 and 3, it can be seen that there is no any great difference between them. The appearance of a new signal at 5.7 ppm may be assigned to the existence of –OH group of the li-gand 3, and aromatic C–H protons are observed at 6.6–7.8 ppm. The molar conductance values of the synthesized 3-hydroxyphenylimino-isonitroso-3,4-dimetoxyacetophe-none and its Cu(II), Ni(II), Zn(II), Cd(II) and Co(II) complexes are in range from 2.5 to 33.5 ?–1 cm2 mol–1 in DMF solutions, indicating the non-electrolite nature of these compounds. These values provide some indication to support our proposed structural conformation for complexes and the mass spectrum of the related compounds 2 and 3 exhibits the highest m/z peaks which are in agreement with the calculated values for compounds. Fig. 1. Determination of ligand to metal ratio for Ni(II) by using of absorbance values. Fig. 2. Determination of ligand to metal ratio for Co(II) by using of absorbance values. Demir et al.: Synthesis and Characterization of a Novel Iminooxime Schiff Base Ligand ... 124 Acta Chim. Slov. 2008, 55, 120–124 4. Conclusions In this study, we reported the preparation of a novel iminooxime Schiff base ligand containing substitute groups and its complexes with the appropriate transition metal ions such as Cu, Ni, Zn, Cd and Co in methanol solution. The addition of some additional groups at the coordination system may enlarge the possibility of specific he-tero-nuclear complexation with the consequent formation of ordered polynuclear complexes. These complexes may serve as models of relevance to bioinorganic chemistry such as metalloenzymes. 5. Acknowledgements The authors gratefully acknowledge partial support of this study by Research Laboratory of Nigde University and thank N. U. Research Foundation for financial support of the project no DTP 2005 K 120880. 6. References 1. D. H. Busch, Helv. Chim. Acta 1967, 50, 174–206. 2. N. F. Curtis, Coord. Chem. Rev. 1968, 3, 3–47. 3. M. Tümer, H. Köksal, S. Serin and S. Patat, Synth. React. Inorg. Met. -Org. Chem. 1997, 27, 59–68. Povzetek V prispevku je podana priprava novih iminooksimskih ligandov z dvema metoksidnima skupinama in njihovih kompleksov z bakrom(II), nikljem(II), cinkom(II), kadmijem(II) in kobaltom(II). Kot izhodno spojino smo vzeli 3,4-dime-toksiacetofenon iz katerega smo pripravili izonitrozo-3,4-dimetoksiacetofenon pri reakciji z n-butil nitritom v prisotnosti natrijevega etoksida. 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