Ab Initio Molecular Dynamics Study of an Aqueous Solution of [Fe(bpy)3](Cl)2 in the Low-Spin and in the High-Spin States

The mechanism of the photoinduced low-spine -> high-spin spin, crossover is activley being investigated in Fe(II) complexes in solution using ultrafast spectroscopies. These studies accurately inform on the reaction coordinate of the Fe(II) chromophore upon photoexcitation. However, they leave open questions regarding the role of the solvent. Here, we report the description from a fully ab initio molecular dynamics study of the structure of [Fe(bpy)(3)](2+) in water and of the organization of its solvation shell in the low-spin and the high-spin states. In particular the low-spin -> high spin change of states is shown to be accompanied (i) by a 0.191 A lengthening of the Fe-N bond. Furthermore, our results suggest that about two water molecules are expelled form the first solvation shell of [Fe(bpy)(3)](2+), which consists of water molecules intercalated between the bpy ligands.