The Electronic Structure of Iron Corroles: A Combined Experimental and Quantum Chemical Study

Abstract

There is a longstanding debate in the literature on the electronic structure of chloroiron corroles, especially for those containing the highly electron-withdrawing meso-tris(pentafluorophenyl)corrole (TPFC) ligand. Two alternative electronic structures were proposed for this and the related [FeCl(tdcc)] (TDCC=meso-tris(2,6-dichlorophenyl)corrole) complex, namely a high-valent ferryl species chelated by a trianionic corrolato ligand ([Fe(IV)(Cor)(3-)](+)) or an intermediate-spin (IS) ferric ion that is antiferromagnetically coupled to a dianionic pi-radical corrole ([Fe(III)(Cor)(.2-)](+)) yielding an overall triplet ground state. Two series of corrole-based iron complexes ([Fe(L)(Cor)], in which L=F, Cl, Br, I, and Cor=TPFC, TDCC) have been investigated by a combined experimental (Mössbauer spectroscopy) and computational (DFT) approach in order to differentiate between the two possible electronic-structure descriptions. The experimentally calibrated conclusions were reached by a detailed analysis of the Kohn-Sham solutions, which successfully reproduce the experimental structures and spectroscopic parameters: the electronic structures of [Fe(L)(Cor)] (L=F, Cl, Br, I, Cor=TPFC, TDCC) are best formulated as ([IS-Fe(III)(Cor)(.2-)](+)), similar to chloroiron corrole complexes containing electron-rich corrole ligands. The antiferromagnetic pathway is composed of singly occupied Fe d(z(2) ) and corrole a(2u)-like pi orbitals, with coupling constants that exceed those of analogous porphyrin systems by a factor of 2-3. In the corroles, the combination of lower symmetry, extra negative charge, and smaller cavity size (relative to the porphyrins) leads to exceptionally strong iron-corrole sigma bonds. Hence, the Fe d(x(2)-y(2) )-based molecular orbital is unavailable in the corrole complexes (contrary to the porphyrin case), and the local spin states are S(Fe)=3/2 in the corroles versus S(Fe)=5/2 in the porphyrins. The consequences of this qualitative difference are discussed for spin distributions and magnetic properties.

Cyclic versus acyclic structures of six-carbon ligands in binuclear cobalt carbonyl derivatives: Some thermochemical observations

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Binuclear Pentalene Iron Carbonyl Complexes

“…[31,32] Electron correlation effects have been included by employing density functional theory (DFT) methods, which have been shown to be a practical and effective computation tool, especially for organometallic compounds. [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] Two DFT methods, B3LYP and BP86, were used in our present study. The reliability of such density functional theory (DFT) methods is governed by the quality of the approximate exchange-correlation (XC) energy functional.…”

Binuclear Carbonylheptalenechromium Complexes: Partition of Heptalene into a Complexed Heptafulvene Subunit and an Uncomplexed 1,3‐Diene Subunit for Coordination to a Multiply Bonded Pair of Chromium Atoms

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