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|Type:||Artigo de Periódico|
|Title:||Spin State Energetics And Oxyl Character Of Mn-oxo Porphyrins By Multiconfigurational Ab Initio Calculations: Implications On Reactivity|
|Abstract:||Important electromeric states in manganese-oxo porphyrins MnO(P)(+) and MnO(PF4) (porphyrinato or meso-tetrafluoroporphyrinato) have been investigated with correlated ab initio methods (CASPT2, RASPT2), focusing on their possible role in multistate reactivity patterns in oxygen transfer (OAT) reactions. Due to the lack of oxyl character, the Mnv singlet ground state is kinetically inert. OAT reactions should therefore rather proceed through thermally accessible triplet and quintet states that have a more pronounced oxyl character. Two states have been identified as possible candidates: a Mnv triplet state and a MnIvO(L+,) quintet state. The latter state is high-lying in MnO(P) but is stabilized by the substitutions of H by F at the meso carbons (where the a(2u), orbital has a significant amplitude). Oxyl character and MnO bond weakening in these two states stems from the fact that the MnO pi* orbitals become singly (triplet) or doubly occupied (quintet). Moreover, an important role for the reactivity of the triplet state is also likely to be played by the pi bond that has an empty pie orbital, because of the manifest diradical character of this pi bond, revealed by the CASSCF wave function. Interestingly, the diradical character of this bond increases when the Mn-O bond is stretched, while the singly occupied pi* orbital looses its oxygen radical contribution. The RASPT2 results were also used as a benchmark for the description of excited state energetics and Mn-O oxyl character with a wide range of pure and hybrid density functionals. With the latter functionals both the Mnv -> Mnlv promotion energy and the diradical character of the r bond (with empty le) are found to be extremely dependent on the contribution of exact exchange. For this reason, pure functionals are to be preferred.|
|Editor:||AMER CHEMICAL SOC|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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