Theoretical study on vibrational circular dichroism spectra of tris(acetylacetonato)metal(III) complexes: Anharmonic effects and low-lying excited states.

The open-shell density functional theory calculations with M06 exchange-correlation functional and all-electron Douglas-Kroll second order scalar relativistic correction were performed to interpret the vibrational circular dichroism (VCD) spectra of four kinds of tris(acetylacetonato)metal(III), [M(III)(acac)3] (acac = acetylacetonato, M = Ru, Cr, Co, and Rh). It was deduced that the experimental spectra were well reproduced by the calculation with harmonic approximation in case of [Co(III)(acac)3] (d6; S = 0), [Rh(III)(acac)3] (d6; S = 0), and [Ru(III)(acac)3] (d5; S = 1/2). In case of [Cr(III)(acac)3] (d3; S = 3/2), anharmonic effects should be taken into account to predict the accurate vibrational frequencies of closely located modes. Time-dependent density functional theory calculations were performed to estimate the contribution of excited states in the VCD spectra. As a consequence, the presence of the low-lying excited states was predicted for [Ru(III)(acac)3] alone, which agreed with the experimental observation. [ABSTRACT FROM AUTHOR]