-diketonates of various metals have been used in the preparation of supported catalysts and as precursors of heterogeneous catalysts [1,2]. In this paper we synthesized bis(benzoylacetonato)copper(II), Cu(BA)2, by mixing copper(II) acetate and benzoylacetone, both dissolved in ethanol and predict its structure and vibrational spectra by using Gaussian 03 Version B05 programs at B3LYP/6-311G* level of theory.The Raman and IR spectra of the titled compound are obtained and by using quantum chemistry calculations the frequencies are assigned to the normal modes.According to calculations, two configurations are possible for Cu(BA)2. They are recognized as trans and cis configurations (Fig.1). The calculations in the gas phase indicated that the trans configuration is considerably more stable than the cisone(about 0.04kcal mol-1). The calculated C=C and C=O bond lengths adjacent to phenyl (Ph) group are longer than the corresponding ones adjacent to the CH3 group. The results showed that there is a resonance between Ph group with C=O and C=C.The geometrical parameters are compared with those of bis(acethylacetonato)copper(II) Cu(AA)2, and benzoylacetone (BA) as ligand. The calculation showed a clear understanding of substitutional effect of methyl group with Ph group on the structure and strength of Cu-O bond. The calculated vibrational frequencies are compared with the vibrational spectra of the compound and also Cu(AA)2. The medium bands at about 556 and 458 cm-1 are assigned to the asymmetric and symmetric O-Cu-O stretching, which is considerably higher than the corresponding frequencies for Cu(AA)2. The short M-O distance in Cu(BA)2 suggested to a strong metal–ligand bond. This fact was confirmed by other experimental results, such as Cu-O bond length. The calculated bond lengths of C=C and C=O in complex are longer and C-C and C-O is shorter than the corresponding values in BA, so the resonance in Cu(BA)2 increased relative to BA. The calculated dihedral angle between the phenyl and the enol rings in complex is smaller than those in ligand.

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