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Issue 6, 2018
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Transition states of spin-forbidden reactions

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Spin–orbit coupling plays an important role in determining the mechanisms and kinetics of spin-forbidden reactions and many reactions exhibiting two-state reactivity. Spin–orbit coupling can allow the system to change its spin state, especially when potential energy surfaces (PESs) of two spin states approach each other. Here, we introduce a convenient new approximation method for locating stationary points on the lowest mixed-spin potential energy surface along a reaction pathway by using density functional calculations. The mixing of different spin states is achieved by introducing the spin–orbit coupling into the electronic Hamiltonian using a pre-defined coupling constant. Two examples are given using the new methodology: (a) a CO association reaction with the coordinatively unsaturated Fe(CO)4 complex and (b) an α-H elimination reaction of a model complex containing W. We computed a Gibbs free energy of activation of 2.8 kcal mol−1 for the CO association reaction, which is reasonably consistent with the experimentally measured reaction rate. For the H elimination reaction, the spin change occurs at a relatively low energy, and the present treatment allows one conclude that kinetics of the reaction can be reasonably well described without spin–orbit coupling.

Graphical abstract: Transition states of spin-forbidden reactions

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The article was received on 25 Oct 2017, accepted on 03 Jan 2018 and first published on 08 Jan 2018

Article type: Paper
DOI: 10.1039/C7CP07227A
Citation: Phys. Chem. Chem. Phys., 2018,20, 4129-4136
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    Transition states of spin-forbidden reactions

    B. Yang, L. Gagliardi and D. G. Truhlar, Phys. Chem. Chem. Phys., 2018, 20, 4129
    DOI: 10.1039/C7CP07227A

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