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

• Published in: Catalysis today Vol. 358; pp. 403 - 411
• Main Authors: Carlotto, Silvia, Casella, Girolamo, Floreano, Luca, Verdini, Alberto, Ribeiro, Ana P.C., Martins, Luísa M.D.R.S., Casarin, Maurizio
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2020
• Subjects: C-scorpionate catalyst; DFT calculations; Spin states; X-ray absorption spectroscopy; X-ray absorption spectroscopy; DFT calculations; C-scorpionate catalyst; Spin states
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2019.08.010

[Display omitted] •The Fe spin state of Fe(II)Cl2(tpm) has been studied by experimental and theoretical investigation.•Theoretical investigation are performed on XAS at the Fe L2,3-edges and N K-edge.•The best agreement has been obtained for a low-spin, diamagnetic ground state.•The stability depends upon the ligands, the bulk solvent and the interaction of the vacant site.•Both tpm→Fe(II) σ bonding and a tpm⟵Fe(II) Charge Transfer characterize the Fe–tpm interaction. 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 NFe(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.