SPECTROSCOPIC AND MAGNETIC INVESTIGATION OF ONE CU(II) COMPLEX WITH DEPROTONATED 1- ETHOXY-3-PHENYL-PROPANEDIONE LIGAND

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1 SPECTROSCOPIC AND MAGNETIC INVESTIGATION OF ONE CU(II) COMPLEX WITH DEPROTONATED 1- ETHOXY-3-PHENYL-PROPANEDIONE LIGAND L. David 1, Cora Crăciun 1, Cecilia Simuţ 2, O. Cozar 1, T. Jurcuţ 2, Dana Filimon 3 1 "Babes-Bolyai" Univ., Dept. of Physics, Cluj-Napoca, 3400 Romania 2 University of Oradea, Dept. of Physics, 3700 Oradea, Romania 3 Grup Scolar Alexandru Borza, Ciumbrud, Alba Abstract The copper(ii) β-diketonate complex CuL 2, where L=H 5 C 6 CO CH CO OC 2 H 5 was investigated by spectroscopic (FT-IR, UV-VIS, EPR) and magnetic methods. The splitting of the ν s (C... O) band from the FT-IR spectrum of the LH ligand (1576 cm 1 ) in two bands at 1510 and 1560 cm 1 in the FT-IR spectrum of the complex and the coalescence of ν as (C... O) bands which appears at 1602 and 1622 cm 1 for the ligand in a single red-shifted band at 1583 cm 1 for the complex indicate the coordination of the Cu(II) ion to the carbonyl oxygen atoms of β-diketonate molecules. The visible electronic spectrum of the CuL 2 complex contains the broad absorption bands corresponding to the ν(b 1g B 2g ) = cm 1 and ν(b 1g E g ) = cm 1 transitions for Cu(II) ion in D 4h local symmetry. In the UV region the intraligand π π * transitions (40557, and

2 32600 cm 1 ) and the L σ M d band (45567 cm 1 ) appears. The powder EPR spectrum of the complex is rhombic, with g 1 = 2.167, g 2 = and g 3 = The low gyromagnetic factors arise from the delocalization of the unpaired electron in the chelate rings and from some molecular packing effects. Introduction Current interest in metal β-diketonates arises from their application as contact shift reagents for better resolution of the nuclear magnetic resonance spectra of a variety of complex organic molecules, in laser technology and in the polymer industry. Fig. 1 Molecular structure of Cu(II) β-diketonate complex The coordination of the metal ions to the β-diketonates is intensively studied because of the remarkable ability to form polymeric species in the solid state and in solutions of non-coordinating solvents [1], for depositing conformal films [2] and also from structural poit of view [3-7]. In this paper we report the spectroscopic and magnetic investigation of the copper(ii) β-diketonate complex CuL 2, where L = H 5 C 6 CO CH CO OC 2 H 5 (Fig.1) in order to obtain information about the metallic ion coordination to the ligand, the local symmetry around the metallic center and the evidence of possible intermolecular interactions. 128

3 Experimental Synthesis of the copper(ii) β-diketonate complex To a solution of NaOCH 3 solid (0.54 g, 10 mmol) in MeOH (50 ml), 1-ethoxy-3-phenyl-propanedione (LH) (1.92 g, 10 mmol) was slowly added and the mixture was stirred for 15 min. Separately, CuCl 2 2H 2 O (0.855 g, 5 mmol) dissolved in 25 MeOH (25 ml) was added dropwise to the above solution. The resulting mixture was stirred for 2 h and then stripped to dryness using a rotary evaporator. The off-blue residue was extracted with chloroform (50 ml), was filtered for remove NaCl and the liquid product was again stripped to dryness to give a blue solid. The product was recrystallized from hot methanol to give fine blue needles. The chemical analysis data are: Yield: 2.68 g (83.2 %) (Found: Cu, 14.30; C, 59.35; H, Calc. for CuC 22 H 22 O 6 : Cu, 14.35; C, 59.20; H, 4.93 %). Physical Measurements FT-IR spectra were recorded on Equinox 55 Bruker Spectrophotometer on KBr pellets, in the cm 1 range. Electronic spectra were performed in aqueous solutions within a range of ν = nm using a standard Specord UV VIS spectrometer. EPR measurements were performed at 9.4 GHz (X band) using a standard JEOL- JES-3B equipment, at room temperature. The magnetic susceptibility measurements were obtained on a Faraday type balance in the temperature range of K. Results and Discussion FT-IR Spectra FTIR spectrum of the ligand (Fig.2) indicates the coexistence of the ketonic and enolic tautomeric structures for the LH = 129

4 H 3 C CO CH 2 CO CH 3 β-diketonate ligand, because of the presence of the vibrations: ν as (C... O) at 1602, 1622 cm 1 (ketonic form), ν(c=o) at 1681, 1738 cm 1 and ν(o H) at 3335 cm 1 (enolic form) [8-11]. After Cu(II) coordination to the β-diketonate ligand LH, the hydrogen is lost and the ketonic form disappears [1,12]. This coordination corresponds to the increase of the quasi-aromatic behavior of the ring as arises by the lowering of ν(c... O) stretching vibration for the metallic complex compared to β- diketonate ligand [12] (Table 1). The two C... O bonds are nonequivalent in the ligand but equivalent for the Cu(II) complex. 2.0 Absorbance (a.u.) (a) 0.5 (b) Wavenumber (cm -1 ) Fig.2 FT-IR spectra of the LH ligand (a) and Cu(II) β-diketonate complex (b) 130

5 Table 1. Some FT-IR data (cm 1 ) of the ligand and the corresponding UV-VIS Spectra Cu(II)-complex Band LH CuL 2 ν as (C... C)+ν as (C CH 3 ) 1277 s,sp 1287 s,sp ν(c H)+ ν as (C... C) 1325 s,sp 1368 m,sp 1348 w,sp ν(c... O)+ν(C H) 1410 m,sp 1404 w,sp 1430 w,sp ν s (C... C) 1448 m,sp 1468 s,sp ν s (C... O) 1576 m,sp 1510 vs,sp 1560 s,sp ν as (C... O) 1602 m,sp 1575 vs,sp 1622 m,b 1583 s,sp s-strong, vs-very strong, m-medium, w-weak, sp-sharp, b-broad The UV spectrum of the β-diketonate ligand (Fig.3) contains the intraligand p π -d π* transitions at cm 1 and cm 1 [1]. These bands are shifted towards higher energies in the Cu(II)-complex spectrum (40557 cm 1 and cm 1 respectively), but a supplementary band appears at cm 1 (Fig.3). In addition, the complex spectrum contains the ligand-to-metal charge transfer L σ M d situated at cm 1, a proof of the Cu(II) coordination to the ligand. In the VIS region of the spectrum (Fig.4) only a very broad band is obtained. This feature is the supperposition of the bands for the following transitions: ν(b 1g B 2g ) = cm 1 and ν(b 1g E g ) = cm 1, determined by fitting the VIS spectrum. The values of the transitions correspond to a square-planar environment around the Cu(II) ion and a D 4h local symmetry [8]. 131

6 1.0 Absorbance (a.u.) (a) (b) Wavenumber (cm -1 ) Fig.3 UV spectra of the β-diketonate ligand (a) and Cu(II) β-diketonate complex (b) in mol l 1 aqueous solution 0.50 Absorbance (a.u.) Wavenumber (cm -1 ) Fig.4 VIS spectrum of the Cu(II) β-diketonate complex in 10 3 mol l 1 aqueous solution (solid line) and its simulated components (dashed lines) 132

7 EPR Spectra Experimental powder EPR spectrum of the CuL 2 complex, obtained at room temperature (Fig.5), was simulated with g 1 = 2.167, g 2 = and g 3 = principal values of the gyromagnetic tensor and B 1 = B 2 = B 3 = 40 G linewhidts. EPR parameters indicate the presence of one rhombic distortion of the symmetry around the Cu(II) ion, because of the nonequivalent C 6 H 5 and O C 2 H 5 substituents of β-diketonate molecules. These low gyromagnetic factors arise from the delocalization of the unpaired electron in the chelate rings and from some molecular packing effects [9,10]. g 1 = g = g = B(G) Fig.5 Experimental EPR spectrum of the Cu(II) β-diketonate complex at room temperature (solid line) and the simulated spectrum (dashed line) 133

8 Magnetic susceptibility measurements K (Fig.6) were The magnetic susceptibility data in the temperature range of Fig.6 Temperature dependence of the inverse of the molar susceptibility corrected by diamagnetism (χ M χ 0 ) fitted by considering a Curie Weiss behavior [11]: 2 B 2 eff Nµ µ χ M = + χ 3k(T θ ) 0 Diamagnetic correction (χ 0 = e.m.u./mol) was estimated from Pascal tables. The value of the effective moment µ eff = 1.79 µ B is typical for spin only Cu(II) ion in a square-planar environment. The negative Weiss temperature (θ = 15 K) confirms the packing structure of the sample and indicates the presence of intermolecular antiferromagnetic exchange. 134

9 Conclusions The coordination of the Cu(II) ion to the oxygen atoms of the β- diketonate molecules is indicated by the shift of the ν(c... O) vibrations in the FT-IR spectrum of the complex compared to the ligand spectrum and also by the appearance of the L σ M d ligand-to-metal charge transfer band in the UV region. For the ligand, the ketonic and enolic tautomeric structures coexist, but only the second of them appears in the complex. The Cu(II) ion is coordinated by four oxygen atoms in a rhombic distorted square-planar configuration, with a d x 2 y 2 orbital as ground state. The local symmetry is rhombic distorted because of the nonequivalent C 6 H 5 and O C 2 H 5 substituents of β-diketonate molecules. The relative low principal values of the gyromagnetic tensor g and the negative Weiss temperature indicate the presence of antiferromagnetic intermolecular interactions. References 1. R.C. Mehrotra, R. Bohra, D.P. Gaur, Metal β-diketonates and allied derivatives, Academic Press, London, P. Doppelt, T.H. Baum, Journ. of Organomet. Chem., 517, 53 (1996) 3. Md. Abed Ali Miah, D.J. Phillips, A.D. Rae, Inorg. Chim. Acta, 25, 231 (1996) 4. J.G. Gordon, M.J. O'Connor, R.H. Holm, Inorg. Chim. Acta, 5(3), 381 (1971) 135

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