Spin state, electronic structure and bonding on C-scorpionate [Fe(II)Cl2(tpm)] catalyst: An experimental and computational study

Girolamo Casella, Ana P.C. Ribeiro, Silvia Carlotto, Luca Floreano, Ana P.C. Ribeiro, Ana P.C. Ribeiro, Ana P.C. Ribeiro, Maurizio Casarin, Alberto Verdini, Luca Floreano, Girolamo Casella, Luísa M.D.R.S. Martins

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Abstract

The Fe(II) spin state in the condensed phase of [Fe(II)Cl2(tpm)] (tpm = [tris(pyrazol-1-yl)methane]; 1) catalyst has been determined through a combined experimental and theoretical investigation of X-Ray Absorption Spectroscopy (XAS) at the FeL2,3-edges and NK-edge. Results indicated that in this phase a mixed singlet/triplet state is plausible. These results have been compared with the already know Fe singlet spin state of the same complex in water solution. A detailed analysis of the electronic structure and bonding mechanism of the catalyst showed that the preference for the low-spin diamagnetic ground state, strongly depends upon the ligands, the bulk solvent and the interaction of the complex's vacant site (the sixth) with a further ligand. Moreover, comparison of the electronic properties of the complex in condensed phase and water solution showed an increased Lewis acidity of the catalyst in solution phase, due to a decreasing of the LUMO energy of about 8 kcal/mol. These results gave an overall picture of the electronic behavior of the complex investigated, on going from condensed to water solution phase, explaining the preferred use of 1 as catalyst in homogeneous catalysis. The N[sbnd]Fe(II) interaction has been thoroughly investigated by means of DFT Kohn-Sham and EDA bond analysis applied to i) the isolated [Fe(II)Cl2(tpm)] and ii) the [Fe(II)Cl2(tpm)] interacting with water as a solvent within the Conductor-like Screening Mode (COSMO) framework. Results showed that both tpm→Fe(II) σ and tpm⟵Fe(II) π Charge Transfer (CT) interactions characterize the Fe(II)–tpm interaction. Moreover, the three tpm N atoms do not equally interact with the Fe(II) and one of them shares a suitable available iron-based d virtual orbital, to bind a further ligand in trans position.
Lingua originaleEnglish
Numero di pagine9
RivistaCatalysis Today
Stato di pubblicazionePublished - 2019

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)

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    Casella, G., Ribeiro, A. P. C., Carlotto, S., Floreano, L., Ribeiro, A. P. C., Ribeiro, A. P. C., Ribeiro, A. P. C., Casarin, M., Verdini, A., Floreano, L., Casella, G., & Martins, L. M. D. R. S. (2019). Spin state, electronic structure and bonding on C-scorpionate [Fe(II)Cl2(tpm)] catalyst: An experimental and computational study. Catalysis Today.