Ground and Excited State Properties and Vibronic Coupling Analysis of the Creutz−Taube Ion, [(NH₃)₅Ru-pyrazine-Ru(NH₃)₅]⁵⁺, Using DFT

In this paper we analyze using Density Functional Theory (DFT) the electronic structure of the Creutz−Taube ion, [(NH 3 ) 5 Ru-pyrazine-Ru(NH 3 ) 5 ] 5+, a classical example of a mixed-valence complex. A complete structural and bonding analysis, description of the low-lying excited states, and a vibronic coupling calculation along both the symmetric and the antisymmetric Ru-pyrazine-Ru stretching mode are presented. The results are in very good agreement with the reported experimental data and we are able to assign unambiguously this compound as a Class III system, following the Robin and Day classification. In this work we demonstrate that DFT does offer a unique tool for handling the localization−delocalization of electrons in mixed-valence systems and therefore we expect that this approach can play an important role in characterizing electron-transfer systems. Localized Ru−N(pyrazine) stretching in the range 254−275 cm - 1 has been estimated from our calculations, which should be used in future model Hamiltonians which aim to include the Ru−pyz bond vibration to describe the spectral features of the Creutz−Taube ion.