Molecular and vibrational structure of tetroxo d ~0 metal complexes in their excited states. A study based on time-dependent density functional calculations and Franck-Condon theory

摘要

We have applied time dependent density functional theory to study excited state structures of the tetroxo d ~0 transition metal complexes MnO _4 -, TcO _4 -, RuO _4, and OsO _4. The excited state geometry optimization was based on a newly implemented scheme [Seth et al. Theor. Chem. Acc. 2011, 129, 331]. The first excited state has a C 3v geometry for all investigated complexes and is due to a "charge transfer" transition from the oxygen based HOMO to the metal based LUMO. The second excited state can uniformly be characterized by "charge transfer" from the oxygen HOMO-1 to the metal LUMO with a D _(2d) geometry for TcO _4 -, RuO _4, and OsO _4 and two C _2v geometries for MnO _4 -. It is finally found that the third excited state of MnO _4 - representing the HOMO to metal based LUMO+1 orbital transition has a D 2d geometry. On the basis of the calculated excited state structures and vibrational modes, the Franck-Condon method was used to simulate the vibronic structure of the absorption spectra for the tetroxo d 0 transition metal complexes. The Franck-Condon scheme seems to reproduce the salient features of the experimental spectra as well as the simulated vibronic structure for MnO 4 - generated from an alternative scheme [Neugebauer J. J. Phys. Chem. A2005, 109, 1168] that does not apply the Franck-Condon approximation.