手性配合物[M(bipy)_3]^(2+)(M=Fe,Ru,Os)圆二色谱的理论解析

Theoretical analysis of the CD spectra and chiroptical properties of [M(bipy)_3]^(2+) (M = Fe,Ru,Os) chelates

应用密度泛函理论,在DFT/B3LYP/LanL2DZ水平上优化了铁族配合物[M(bipy)3]2+(M=Fe,Ru,Os;bipy=2,2′-联吡啶)在溶液中的基态几何结构,并用TDDFT/B3LYP方法和相同的基组计算了该类配合物的激发能、旋转强度和振子强度,绘制了相应的圆二色谱.计算的谱带位置虽有一定的红移或蓝移,但各谱带的带形和符号均与实验谱吻合.对跃迁性质的分析表明,三个配合物在长波区,除[Fe(bipy)3]2+的第一个谱带是以d-d跃迁为主外,其他谱带均是荷移跃迁为主.短波区的两个强带则是以π-π*跃迁为主的激子耦合带:对于铁配合物,TDDFT可以正确预言其正负带的强度比,但对钌和锇配合物而言,由于对激子跃迁中荷移成份的贡献估计不足,计算的比值偏小.这一结论为进一步改进有关的计算模型指明了方向.

Calculations of the excitation energies,oscillator and rotational strengths,and the CD spectra of the chelates [M（bipy）3]^2＋ （M=Fe,Ru,Os; bipy= 2,2＇-bipyridine） have been performed at the TDDFT/B3LYP/LanL2DZ//DFT/ B3LYP/LanL2DZ level including solvent effects. The calculated CD spectra are good agreement with the observed ones except for some red or blue shift in the calculated band wavelengths. Detailed analysis for the dominant transitions reveals that the CD bands in the long wavelength region （350–700 nm） are dominated by the charge transfer transitions d-π＊,except for the first band of [Fe（bipy）3]^2＋,which is dominated by the degenerated d-d transitions. In the short wavelength region （200–350 nm）,however,the two stronger CD bands with opposite signs are mainly originated from the exciton splitting of π-π＊ transitions on the ligands. The observed ratio of the intensity of positive exciton band to that of negative one can be well reproduced at the TDDFT level for the [Fe（bipy）3]^2＋ chelate,while the calculated ratios are much smaller than the observed ones for the [Ru（bipy）3]^2＋ and [Os（bipy）3]^2＋ chelates. To solve this problem some suggestions have been presented.