Is the Corrolate Macrocycle Innocent or Noninnocent? Magnetic Susceptibility, Mössbauer, ¹H NMR, and DFT Investigations of Chloro- and Phenyliron Corrolates

Abstract

In an attempt to determine the electron configuration of (anion)iron corrolates, i.e., whether they are S = 1 Fe(IV)-corrolate(3-) or S = 3/2 Fe(III)-corrolate(2-*), with antiferromagnetic coupling between the iron and macrocycle electrons to yield overall S = 1, two axial ligand complexes of an iron octaalkylcorrolate have been studied by temperature-dependent magnetic susceptibility, magnetic Mössbauer, and 1H NMR spectroscopy, and the results have been compared to those determined on the basis of spin-unrestricted DFT calculations. Magnetic susceptibility measurements indicate the presence of a noninnocent macrocycle (corrolate (2-*)) for the chloroiron corrolate, with strong antiferromagnetic coupling to the S = 3/2 Fe(III) center, while those for the phenyliron corrolate are not conclusive as to the electron configuration. Temperature- and field-dependent Mössbauer spectroscopic investigations of these two complexes yielded spectra that could be simulated with either electron configuration, except that the isomer shift of the phenyl-iron complex is -0.10 mm/s while that of the chloroiron complex is +0.21 mm/s, suggesting that the iron in the former is Fe(IV) while in the latter it is Fe(III). 1H NMR spectroscopic studies of both axial ligand complexes show large negative spin density at the meso carbons, with those of the chloroiron complex (Cai, S.; Walker, F. A.; Licoccia, S. Inorg. Chem. 2000, 39, 3466) being roughly four times larger than those of the phenyliron complex. The temperature dependence of the proton chemical shifts of the phenyliron complex is strictly linear. DFT calculations are consistent with the chloroiron complex being formulated as S1 = 3/2 Fe(III)-corrolate (2-*) S2 = 1/2, with negative spin density at all nitrogens and meso carbons, and a net spin density of -0.79 on the corrolate ring and positive spin density (+0.17) on the chloride ion and +2.58 on the iron. In contrast, the phenyliron complex is best formulated as S = 1 Fe(IV)-corrolate (3-), but again with negative spin density at all nitrogens and meso carbons of the macrocycle, yet with the net spin density on the corrolate ring being virtually zero; the phenyl carbanion carbon has relatively large negative spin density of -0.15 and the iron +2.05. On the basis of all of the results, we conclude that in both the chloroiron and phenyliron complexes the corrolate ring is noninnocent, in the chloroiron complex to a much larger extent than in the phenyliron complex.

Progress and Challenges in the Calculation of Electronic Excited States

“…[144,145,154,155] Despite its inconveniences and different flavors, DFT has become the gold standard for large systems in bioinorganic chemistry and in some cases an agreement with the experiment and with CASPT2 is eventually found, see for example the electronic structure of the non-innocent chloroiron corrole. [143,156] Pierloot and coworkers, but also others, have done extensive work using multiconfigurational ab initio methods on bioinorganic systems, [157][158][159][160][161][162][163] also pointing to the pitfalls of DFT and the lack of appropriate functionals in many situations. Unfortunately, the CASPT2 protocol is not a "magic tool box" for open-shell transition metal chemistry either.…”

Metal–Ligand Misfits: Facile Access to Rhenium–Oxo Corroles by Oxidative Metalation

“…Second, the Soret maxima of the complexes (Table 3a nd Figure S1 in the Supporting Information) are not sensitive to the para substituent X, and are redshifted by only 3nmf rom X = CF 3 to X = OCH 3 .T hird, the electrochemical HOMO-LUMOg aps are large (approximately 2.24 AE 0.02 eV;T able3 and Figure S2 in the Supporting Information), which is essentially equal to the p-p* gap of at ypical porphyrin or corrolem acrocycle. [4, 7c, 14] Over al engthy series of studies, we have established that the last two characteristics are typical of an innocent [corrole] 3À ligand, such as that found in Au and Os-N corroles, as opposed to an oninnocent [corrole] ·2À ligand, for which copper [15] and iron [16,17] corroles provides ome of the best studied examples. Consistent with literature reports, [9,10] the Re-O stretching mode (ñ Re-O )o fthec omplexes is readily discernible in the IR spectra,w ith little interference from other skeletal modes.…”

Predictive Modeling of Molecular Properties: Can We Go beyond Interpretation?

“…Solvent effects are generally assumed to be small when calculating vibrational, NMR or absorption spectra, so that calculations without simulated solvent are most common. Other less commonly measured properties such as dipole moments, ionization potentials and electron affinities [31], electron spin resonance (ESR) [32], M€ oßbauer [33] and extended X-ray absorption fine structure (EXAFS) [34] spectra are calculated less commonly and can generally be expected to show significant deviations from experiment.…”