Quantum chemical study of spin crossover in Fe(II) complexes
by
Coen de Graaf, Universitat Rovira I Virgili, Tarragona, Spain
→
Europe/Berlin
AER 19, Room 3,11
AER 19, Room 3,11
Description
Ab initio calculations have been performed on [FeII(bpy)3]2+ (bpy=bipyridine) and [FeII(tz)6]2+ (tz=tetrazole) to establish the variation of the energy of the electronic states relevant to light-induced excited state spin trapping (LIESST) as function of the Fe–ligand distance. For the complex with bipyridine, the light-induced spin crossover takes place after excitation into the singlet metal-to-ligand (MLCT) band. We found that the corresponding electronic states have their energy minimum in the same region as the low-spin (LS) state and that the energy dependence of the triplet MLCT states is nearly identical to the 1MLCT states. The high-spin (HS) state is found to cross the MLCT band near the equilibrium geometry of the MLCT states. These findings give additional support to the hypothesis of a fast singlet-triplet interconversion in the MLCT manifold, followed by a 3MLCT–HS (5T2) conversion accompanied by an elongation of the Fe-N distance. On the other hand, the MLCT excitations have much higher energies in the tetrazole containing complex. LIESST is induced by excitation in a metal centered d-d transition. We discuss the deactivation path for this excited singlet state and find that this occurs either by overlap of the vibrational levels of the intermediate triplet or through an asymmetric Fe-L stretch, in which an intersystem crossing appears.
