Spin-inversion mechanisms in O2 binding to a model heme complex revisited by density function theory calculations |
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Authors: | Kohei Saito Yuya Watabe Takashi Fujihara Toshiyuki Takayanagi Jun-ya Hasegawa |
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Institution: | 1. Department of Chemistry, Saitama University, Shimo-Okubo 255, Sakura-ku, Saitama City, Saitama, 338-8570 Japan;2. Instituteof Catalysis, Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo, Hokkaido, 001-0021 Japan |
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Abstract: | Spin-inversion mechanisms in O2 binding to a model heme complex, consisting of Fe(II)-porphyrin and imidazole, were investigated using density-functional theory calculations. First, we applied the recently proposed mixed-spin Hamiltonian method to locate spin-inversion structures between different total spin multiplicities. Nine spin-inversion structures were successfully optimized for the singlet–triplet, singlet–quintet, triplet–quintet, and quintet–septet spin-inversion processes. We found that the singlet–triplet spin-inversion points are located around the potential energy surface region at short Fe–O distances, whereas the singlet–quintet and quintet–septet spin-inversion points are located at longer Fe–O distances. This suggests that both narrow and broad crossing models play roles in O2 binding to the Fe-porphyrin complex. To further understand spin-inversion mechanisms, we performed on-the-fly Born-Oppenheimer molecular dynamics calculations. The reaction coordinates, which are correlated to the spin-inversion dynamics between different spin multiplicities, are also discussed. |
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Keywords: | spin crossover spin-forbidden spin inversion |
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