A study on the stability of O-2 on oxometalloporphyrins by the first principles calculations

摘要

The authors investigated the interaction of oxometalloporphyrins (MO(por)) - specifically, MoO(por), WO(por), TiO(por), VO(por), and CrO(por) - with O-2 by using first principles calculations. MoO(por) and WO(por) undergo reactions with O-2; on the other hand, TiO(por), VO(por), and CrO(por) do not. Next, they compared the interaction of MoO(por) and WO(por) with O-2. Activation barriers for the reactions of MoO(por) and WO(por) with a side-on O-2 are small. For MoO(por)(O-2), the activation barrier for the reverse reaction that liberates O-2 is also small; however, that for WO(por)(O-2) is large. The experimental results that photoirradiation with visible light or heating of Mo O-VI(tmp)(O-2) regenerates Mo O-VI(tmp) by liberating O-2 while W O-VI(tmp)(O-2) does not [J. Tachibana, T. Imamura, and Y. Sasaki, Bull. Chem. Soc. Jpn. 71, 363 (1998)] are explained by the difference in activation barriers of the reverse reactions. This means that bonds formed between the W atom and O-2 are stronger than those between the Mo atom and O-2. The bond strengths can be explained by differences in the energy levels between the highest occupied molecular orbital of MoO(por) and WO(por), which are mainly formed from the a orbitals of the central metal atom and pi(*) orbitals of O-2. (C) 2007 American Institute of Physics.