Spectroscopic studies of some oxygen-bonded copper(II) beta-diketonate complexes

The copper(II) beta -diketonate complexes Cu(L-1)(2), Cu(L-2)(2), Cu(L-3)(2 ), where L-1 = H3C-CO-CH-CO-CH3. L-2 = H5C6-CO-CH-CO-C6H5, L-3 = H5C6-CO-CH -CO-OC2H5, were prepared and investigated by spectroscopic (FT-IR, UV-VIS, EPR) methods. The coordination of the Cu(II) ion to the oxygen atoms of two beta -diketonate molecules is observed by the shift of the nu (s)(C -C), n u (s)(C -O) and nu (as)(C -O) stretching vibrations in the FT-IR spectra of the complexes with reference to those of the ligands. In the visible elect ronic spectra of the Cu(II) beta -diketonate complexes the very broad absor ption bands of B-1g --> B-2g and B-1g --> E-g transitions appear at approxi mate to 13,500, 16,070cm(-1) for Cu(L-1)(2), 14,500, 16,630cm(-1) for Cu(L- 2)(2) and 13,075, 15,410 cm(-1) for Cu(L-3)(2) Besides the bands of the int raligand pi-pi (*) transitions (29,000-42.000 cm(-1)) of beta -diketonates, the UV spectra of the Cu(II)-complexes contain the L-sigma --> M-d bands ( 45.500-46,100 cm(-1)). The powder EPR spectrum of the Cu(L-1)(2) complex is quasi-isotropic and asymmetric (g(\ \) = 2.160, g(perpendicular to) = 2,05 0), that of Cu(L-2)(2) is axial (g(\ \) = 2.216, g(perpendicular to) = 2.04 5), and typical for square-planar compounds and that of Cu(L-3)(2) is rhomb ic, with g(1) = 2.167, g(2) = 2.082 and g(3) = 2.004. The low gyromagnetic factors arise from the delocalization of the unpaired electron in the chela te rings and from some molecular packing effects. (C) 2001 Elsevier Science B.V. All rights reserved.