Theoretical studies on the ground states in [formula omitted] (M = Fe, Ru, Os) and excited states in [formula omitted] using density functional theory

Abstract

We present a comparative study using density functional theory on the molecular structure, electronic structure and relative properties of M ( terpyridine ) 2 2 + ( M ( tpy ) 2 2 + ) and M ( n - butyl - phenylterpyridine ) 2 2 + ( M ( B - ptpy ) 2 2 + ) (M = Fe, Ru, Os). The trends of the center ionic effects and the introduction of electron-donating groups on the electronic structure and chemical stabilities have been investigated in detail. The results show that, for Ru ( tpy ) 2 2 + and Os ( tpy ) 2 2 + , the lowest energy transition are assigned as the singlet metal-to-ligand charge transfer (MLCT). For Fe ( tpy ) 2 2 + , the lowest energy transition corresponds to the intraligand π–π* character. As the case of M ( B - ptpy ) 2 2 + (M = Fe, Ru, Os), the lowest energy transitions can be assigned as mixed metal/ligand-to-ligand charge transfer. The time dependent density functional (TDDFT) method is applied to calculate the singlet and triplet electronic states of M ( tpy ) 2 2 + (M = Fe, Ru, Os) based on the ground-state geometry. The three absorption bands observed experimentally for Ru ( tpy ) 2 2 + are well reproduced by the TDDFT technique. Some insights on the difference observed for these complexes in changing the central metal atom are given. The luminescence for Ru ( tpy ) 2 2 + originates from the lowest triplet excited states and is assigned to the MLCT character.