Theoretical studies on the ground states in M(terpyridine)22+ and M(n-butyl-phenylterpyridine)22+ (M = Fe, Ru, Os) and excited states in Ru(terpyridine)22+ using density functional theory

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 pi-pi* character. As the case of M(B-ptpy I (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. (C) 2004 Elsevier B.V. All rights reserved.