Infrared Spectra of Metal-Chelate Compounds. I. A Normal Coordinate Treatment on Bis-(Acetylacetonato)-Cu(II)

Abstract

A normal coordinate treatment on the chelate ring of bis‐(acetylacetonato)‐Cu(II) gives calculated frequencies in good agreement with the observed ones in the 1700 and 350 cm^—1 range obtained with NaCl, KBr, and CsBr optics. In order to assign the observed bands and to see the coupling between various vibrational modes, the L matrices and the potential energy distribution, L_ii²F_i were calculated for all the in‐plane vibrations. The results reveal that (1) the band at 1580 cm^—1 previously assigned to asym. CO stretching is asym. CC stretching, (2) the bands at 684 and 654 cm^—1 formerly suggested to be metal‐oxygen stretching modes are metal‐oxygen stretching vibrations coupled with ring deformation and CCH₃ bending modes, respectively, and (3) a new band found at 455 cm^—1 is the sym. Cu–O stretching mode. By comparing the force constants of the Cu–O stretching vibration with those of metal‐nitrogen and metal‐carbon bonds of other compounds, it is suggested that the Cu–O bond in this compound has double bond character.