Dynamic effects on ligand field from rapid hydride motion in an iron(ii) dimer with an = 3 ground state.

Hydride complexes are important in catalysis and in iron-sulfur enzymes like nitrogenase, but the impact of hydride mobility on local iron spin states has been underexplored. We describe studies of a dimeric diiron(ii) hydride complex using X-ray and neutron crystallography, Mössbauer spectroscopy, magnetism, DFT, and calculations, which give insight into the dynamics and the electronic structure brought about by the hydrides. The two iron sites in the dimer have differing square-planar (intermediate-spin) and tetrahedral (high-spin) iron geometries, which are distinguished only by the hydride positions.

Electronic structure analysis of electrochemical CO reduction by iron-porphyrins reveals basic requirements for design of catalysts bearing non-innocent ligands.

Electrocatalytic CO reduction is a possible solution to the increasing CO concentration in the earth's atmosphere, because it enables storage of energy while using the harmful CO feedstock as a starting material. Notably, iron(ii) tetraphenylporphyrin, [Fe(TPP)] (TPP = tetraphenylporphyrin tetra-anion diradical), and its derivatives have been established as one of the most promising families of homogeneous catalysts for CO reduction into CO. Our earlier work has demonstrated that [Fe(TPP)], a catalytically active species, is best described as an Fe(ii) center antiferromagnetically coupled with a TPP diradical.

Experimental and Theoretical Evidence for an Unusual Almost Triply Degenerate Electronic Ground State of Ferrous Tetraphenylporphyrin.

Iron porphyrins exhibit unrivalled catalytic activity for electrochemical CO-to-CO conversion. Despite intensive experimental and computational studies in the last 4 decades, the exact nature of the prototypical square-planar [Fe(TPP)] complex (; TPP = tetraphenylporphyrinate dianion) remained highly debated. Specifically, its intermediate-spin ( = 1) ground state was contradictorily assigned to either a nondegenerate A state with a (d)(d)(d) configuration or a degenerate E state with a (d)(d)(d)/(d)(d)(d) configuration.

A Short Perspective on Electrochemical CO₂ Reduction to CO.

This short review summarizes examples of many homogeneous non-noble catalysts for CO₂-to-CO reduction and compares their feasible mechanisms. The focus is to show that elucidating the electronic structure of the catalytic system likely provides better understanding of the reaction mechanism and product selectivity.

Enhanced Fe-Centered Redox Flexibility in Fe-Ti Heterobimetallic Complexes.

Previously, we reported the synthesis of Ti[N( o-(NCHP( Pr))CH)] and the Fe-Ti complex, FeTi[N( o-(NCHP( Pr))CH)], abbreviated as TiL (1), and FeTiL (2), respectively. Herein, we describe the synthesis and characterization of the complete redox families of the monometallic Ti and Fe-Ti compounds. Cyclic voltammetry studies on FeTiL reveal both reduction and oxidation processes at -2.

Electronic Structure of a Formal Iron(0) Porphyrin Complex Relevant to CO Reduction.

Iron porphyrins can act as potent electrocatalysts for CO functionalization. The catalytically active species has been proposed to be a formal Fe(0) porphyrin complex, [Fe(TPP)] (TPP = tetraphenylporphyrin), generated by two-electron reduction of [Fe(TPP)]. Our combined spectroscopic and computational investigations reveal that the reduction is ligand-centered and that [Fe(TPP)] is best formulated as an intermediate-spin Fe(II) center that is antiferromagnetically coupled to a porphyrin diradical anion, yielding an overall singlet ground state.