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

Abstract

The copper(II) β-diketonate complexes Cu(L 1) 2, Cu(L 2) 2, Cu(L 3) 2, where L 1=H 3C–CO–CH–CO–CH 3, L 2=H 5C 6–CO–CH–CO–C 6H 5, L 3=H 5C 6–CO–CH–CO–OC 2H 5, 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 β-diketonate molecules is observed by the shift of the ν s ( C C), ν s ( C O) and ν as ( C O) stretching vibrations in the FT-IR spectra of the complexes with reference to those of the ligands. In the visible electronic spectra of the Cu(II) β-diketonate complexes the very broad absorption bands of B 1g→B 2g and B 1g→E g transitions appear at ≈13,500, 16,070 cm −1 for Cu(L 1) 2, 14,500, 16,630 cm −1 for Cu(L 2) 2 and 13,075, 15,410 cm −1 for Cu(L 3) 2. Besides the bands of the intraligand π–π ∗ transitions (29,000–42,000 cm −1) of β-diketonates, the UV spectra of the Cu(II)-complexes contain the L σ→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 ⊥=2.050), that of Cu(L 2) 2 is axial ( g ∥=2.216, g ⊥=2.045), and typical for square-planar compounds and that of Cu(L 3) 2 is rhombic, 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 chelate rings and from some molecular packing effects.