Electron magnetic resonance data on high-spin Mn(III; S = 2) ions in porphyrinic and salen complexes modeled by microscopic spin Hamiltonian approach

Tadyszak, Krzysztof; Rudowicz, Czesław; Ohta, Hiromichi; Sakurai, Takahiro

doi:10.1016/j.jinorgbio.2017.06.006

“…Complexes 1–5 are EPR-silent in frozen DMSO solutions, a fact consistent with the presence of d 4 Mn(III) ions with high zero-field splitting values. 27,28 In contrast, complex 6 exhibits a six-line EPR signal (hyperfine splitting of ∼90 G) at g = 2 and two weak resonances on the low-field side at g ≈ 3 and 5, characteristic of Mn(II) (shown below in Figure 8a) with zero-field splitting slightly weaker than the X-band microwave frequency. 29−32…”

Section: Resultsmentioning

confidence: 99%

Insights into Second-Sphere Effects on Redox Potentials, Spectroscopic Properties, and Superoxide Dismutase Activity of Manganese Complexes with Schiff-Base Ligands

Palopoli

¹

,

Ferreyra

²

,

Conte-Daban

³

et al. 2019

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Six Mn-Schiff base complexes, [Mn(X-salpn)] 0/+ (salpn = 1,3-bis(sal-ic-ylidenamino)propane, X = H [ 1 ], 5-Cl [ 2 ], 2,5-F 2 [ 3 ], 3,5-Cl 2 [ 4 ], 5-NO 2 [ 5 ], 3,5-(NO 2 ) 2 [ 6 ]), were synthesized and characterized in solution, and second-sphere effects on their electrochemical and spectroscopic properties were analyzed. The six complexes catalyze the dismutation of superoxide with catalytic rate constants in the range 0.65 to 1.54 × 10 6 M –1 s –1 obtained through the nitro blue tetrazolium photoreduction inhibition superoxide dismutases assay, in aqueous medium of pH 7.8. In solution, these compounds possess two labile solvent molecules in the axial positions favoring coordination of the highly nucleophilic O 2 •– to the metal center. Even complex 5 , [Mn(5-(NO 2 )salpn) (OAc) (H 2 O)], with an axial acetate in the solid state, behaves as a 1:1 electrolyte in methanolic solution. Electron paramagnetic resonance and UV–vis monitoring of the reaction of [Mn(X-salpn)] 0/+ with KO 2 demonstrates that in diluted solutions these complexes behave as catalysts supporting several additions of excess O 2 •– , but at high complex concentrations (≥0.75 mM) catalyst self-inhibition occurs by the formation of a catalytically inactive dimer. The correlation of spectroscopic, electrochemical, and kinetics data suggest that second-sphere effects control the oxidation states of Mn involved in the O 2 •– dismutation cycle catalyzed by complexes 1–6 and modulate the strength of the Mn-substrate adduct for electron-transfer through an inner-sphere mechanism.

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“…Zero-field splitting is a result of spin–orbit coupling and ligand field splitting of energy levels of a paramagnetic atom possessing spin larger than 1/2. Dependencies between the ZFS and the ligand field energies for various electronic configurations are well-known, 121 − 125 but they are often difficult to apply as the ligand field bands are obscured by the charge-transfer bands. Calculations of the ZFS parameters for the Mn 3+ ions were thus attempted using the state-averaged complete active space self-consistent field (CASSCF) method as implemented in the ORCA 5.0.1 quantum mechanical software package.…”

Section: Resultsmentioning

confidence: 99%

Homochiral Mn³⁺ Spin-Crossover Complexes: A Structural and Spectroscopic Study

Kühne

¹

,

Ozarowski

²

,

Sultan

³

et al. 2022

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Structural, magnetic, and spectroscopic data on a Mn 3+ spin-crossover complex with Schiff base ligand 4-OMe-Sal 2 323, isolated in crystal lattices with five different counteranions, are reported. Complexes of [Mn(4-OMe-Sal 2 323)]X where X = ClO 4 – ( 1 ), BF 4 – ( 2 ), NO 3 – ( 3 ), Br – ( 4 ), and I – ( 5 ) crystallize isotypically in the chiral orthorhombic space group P 2 1 2 1 2 with a range of spin state preferences for the [Mn(4-OMe-Sal 2 323)] + complex cation over the temperature range 5–300 K. Complexes 1 and 2 are high-spin, complex 4 undergoes a gradual and complete thermal spin crossover, while complexes 3 and 5 show stepped crossovers with different ratios of spin triplet and quintet forms in the intermediate temperature range. High-field electron paramagnetic resonance was used to measure the zero-field splitting parameters associated with the spin triplet and quintet states at temperatures below 10 K for complexes 4 and 2 with respective values: D S =1 = +23.38(1) cm –1 , E S =1 = +2.79(1) cm –1 , and D S =2 = +6.9(3) cm –1 , with a distribution of E parameters for the S = 2 state. Solid-state circular dichroism (CD) spectra on high-spin complex 1 at room temperature reveal a 2:1 ratio of enantiomers in the chiral conglomerate, and solution CD measurements on the same sample in methanol show that it is stable toward racemization. Solid-state UV–vis absorption spectra on high-spin complex 1 and mixed S = 1/ S = 2 sample 5 reveal different intensities at higher energies, in line with the different electronic composition. The statistical prevalence of homochiral crystallization of [Mn(4-OMe-Sal 2 323)] + in five lattices with different achiral counterions suggests that the chirality may be directed by the 4-OMe-Sal 2 323 ligand.

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“…Accordingly, the Mn(tpfc) zfs results act as a “control” for comparison with the zfs determined for the two different formally Fe IV corrole complexes. The zfs of Mn(tpfc) is also of interest in its own right as a large number of porphyrin (i.e., formally dianionic) complexes of Mn III have been investigated by HFEPR, ,− even in a protein environment, as well as by other techniques, − but such studies on corroles are relatively few. , Moreover, of the two lone prior investigations of Mn III corroles by HFEPR, that by Licoccia and coworkers involved a differently substituted corrole macrocycle (dehmc = 8,12-diethyl-2,3,7,13,17,18-hexamethylcorrole), and the study by Bendix et al, although on a tpfc complex, comprised a Mn(III) center bearing an axial triphenylphosphine oxide ligand, i.e., Mn(tpfc)(OPPh 3 ), and thus exhibited approximate square pyramidal geometry rather than square planar. Furthermore, Licoccia and coworkers investigated the HFEPR of their corrole complex in a highly concentrated (∼0.2 M) frozen solution of pyridine, where axial coordination by solvent to give monopyridine or perhaps even bis-pyridine adducts is likely.…”

Section: Introductionmentioning

confidence: 99%

Advanced Paramagnetic Resonance Studies on Manganese and Iron Corroles with a Formal d⁴ Electron Count

Krzystek

¹

,

Schnegg

²

,

Aliabadi

³

et al. 2020

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Metallocorroles wherein the metal ion is Mn III and formally Fe IV are studied here using fieldand frequency-domain electron paramagnetic resonance techniques. The Mn III corrole, Mn(tpfc) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole trianion), exhibits the following S = 2 zero-field splitting (zfs) parameters: D = −2.67(1) cm −1 , |E| = 0.023(5) cm −1 . This result and those for other Mn III tetrapyrroles indicate that when D ≈ − 2.5 ± 0.5 cm −1 for 4-or 5coordinate and D ≈ − 3.5 ± 0.5 cm −1 for 6-coordinate complexes, the ground state description is [Mn III (Cor 3− )] 0 or [Mn III (P 2− )] + (Cor = corrole, P = porphyrin). The situation for formally Fe IV corroles is more complicated, and it has been shown that for Fe(Cor)X, when X = Ph (phenyl), the ground state is a spin triplet best described by [Fe IV (Cor 3− )] + , but when X = halide, the ground state corresponds to [Fe III (Cor •2− )] + , wherein an intermediate spin (S = 3 / 2 ) Fe III is antiferromagnetically coupled to a corrole radical dianion (S = 1 / 2 ) to also give an S = 1 ground state. These two valence isomers can be distinguished by their zfs parameters, as determined here for Fe(tpc)X, X = Ph, Cl (tpc = 5,10,15triphenylcorrole trianion). The complex with axial phenyl gives D = 21.1(2) cm −1 , while that with axial chloride gives D = 14.6(1) cm −1 . The D value for Fe(tpc)Ph is in rough agreement with the range of values reported for other Fe IV complexes. In contrast, the D value for Fe(tpc)Cl is inconsistent with an Fe IV description and represents a different type of iron center. Computational studies corroborate the zfs for the two types of iron corrole complexes. Thus, the zfs of metallocorroles can be diagnostic as to the electronic structure of a formally high oxidation state metallocorrole, and by extension to metalloporphyrins, although such studies have yet to be performed.

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Electron magnetic resonance data on high-spin Mn(III; S = 2) ions in porphyrinic and salen complexes modeled by microscopic spin Hamiltonian approach

Cited by 12 publications

References 65 publications

Insights into Second-Sphere Effects on Redox Potentials, Spectroscopic Properties, and Superoxide Dismutase Activity of Manganese Complexes with Schiff-Base Ligands

Insights into Second-Sphere Effects on Redox Potentials, Spectroscopic Properties, and Superoxide Dismutase Activity of Manganese Complexes with Schiff-Base Ligands

Homochiral Mn³⁺ Spin-Crossover Complexes: A Structural and Spectroscopic Study

Advanced Paramagnetic Resonance Studies on Manganese and Iron Corroles with a Formal d⁴ Electron Count

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Electron magnetic resonance data on high-spin Mn(III; S = 2) ions in porphyrinic and salen complexes modeled by microscopic spin Hamiltonian approach

Cited by 12 publications

References 65 publications

Insights into Second-Sphere Effects on Redox Potentials, Spectroscopic Properties, and Superoxide Dismutase Activity of Manganese Complexes with Schiff-Base Ligands

Insights into Second-Sphere Effects on Redox Potentials, Spectroscopic Properties, and Superoxide Dismutase Activity of Manganese Complexes with Schiff-Base Ligands

Homochiral Mn3+ Spin-Crossover Complexes: A Structural and Spectroscopic Study

Advanced Paramagnetic Resonance Studies on Manganese and Iron Corroles with a Formal d4 Electron Count

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Product

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About

Homochiral Mn³⁺ Spin-Crossover Complexes: A Structural and Spectroscopic Study

Advanced Paramagnetic Resonance Studies on Manganese and Iron Corroles with a Formal d⁴ Electron Count