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Molecules
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Multifunctional High Spin Molecules and Singlet Biradicals
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Multifunctional High Spin Molecules and Singlet Biradicals

A special issue of Molecules (ISSN 1420-3049).

Deadline for manuscript submissions: closed (31 March 2023) | Viewed by 2894

Special Issue Editor

Prof. Dr. Martin Baumgarten

E-Mail Website
Guest Editor
Max Planck Institute for Polymer Research, Mainz, Germany
Interests: conjugated polymers; OLEDs; TADF; spin in organics; spin networks; high spin molecules; organic bose einstein condensates
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Multispin organic compounds are promising for organic magnets, spintronics, sensors, memory devices, spin transport, spin filters and as semiconductor materials. While for organic magnets, air-stable spin compounds with a large energy gap between the high-spin ground state and low-spin excited state are desired for other applications, a thermally excited high-spin state can also be of interest where the low-spin ground state can be switched by temperature or magnetic field into the high spin state. Such magnetic field-induced triplet excitation can even lead to higher ordered magnetic states in the case of 3D described as Bose–Einstein condensates of triplon excitations. Redox reactions of functionalized stable mono or diradicals, on the other hand, can be applied as spin switches towards a higher spin state. Singlet biradicals of polycyclic aromatics have gained tremendous interest in recent years and are foreseen for many applications which further develop.

Prof. Dr. Martin Baumgarten
Guest Editor

Manuscript Submission Information

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Keywords

  • molecular magnetism
  • stable radicals
  • electron spin-spin coupling
  • ground-state
  • organic electronics
  • magnetic properties
  • radical ions
  • spintronics
  • sensors
  • quinoid vs. radicaloid

Published Papers (2 papers)

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Research

15 pages, 3401 KiB  
Article
The Valence and Spin State Tuning of Iron(II/III) Porphyrazines with Bulky Pyrrolyl Periphery in Solution and Solid State
by Tomasz Koczorowski, Wojciech Szczolko, Pawel Bakun, Barbara Wicher, Lukasz Sobotta, Maria Gdaniec, Anna Teubert, Jadwiga Mielcarek, Ewa Tykarska, Jozef Korecki, Kvetoslava Burda and Tomasz Goslinski
Molecules 2022, 27(22), 7820; https://doi.org/10.3390/molecules27227820 - 13 Nov 2022
Cited by 3 | Viewed by 1254
Abstract
Iron(III) porphyrazines containing peripheral 2,5-dimethyl-, 2-methyl-5-phenyl-, and 2,3,5-triphenyl-1H-pyrrol-1-yl substituents were synthesized and subjected to physicochemical characterization. This was accomplished by high-resolution mass spectrometry, nuclear magnetic resonance (as diamagnetic Fe(II) derivatives), HPLC purity analysis, and UV-Vis spectroscopy, accompanied by the solvation study [...] Read more.
Iron(III) porphyrazines containing peripheral 2,5-dimethyl-, 2-methyl-5-phenyl-, and 2,3,5-triphenyl-1H-pyrrol-1-yl substituents were synthesized and subjected to physicochemical characterization. This was accomplished by high-resolution mass spectrometry, nuclear magnetic resonance (as diamagnetic Fe(II) derivatives), HPLC purity analysis, and UV-Vis spectroscopy, accompanied by the solvation study in dichloromethane and pyridine. X-ray structure analysis was performed for a single crystal of the previously obtained 2,5-diphenyl-substituted derivative of porphyrazine complex (5d). The octahedral geometries of iron cation, present in the porphyrazine core, influenced the packing mode of molecules in the crystals. Mössbauer studies, performed for solid samples of iron porphyrazines, indicated that low-spin reduced iron states might occupy low- or high-symmetry binding sites. It was found that the hyperfine parameters and the subsequent contribution of the iron cations depend on the number of phenyl groups surrounding the pyrrolyl moiety. For iron(II) porphyrazine 2,3,5-triphenylpyrrol-1-yl substituents (5b), a high-spin ferrous state fraction was observed. Temperature-dependent measurements showed that the freed rotation of the peripheral porphyrazine ligands and the increased flexibility of the macrocycle ring result in the Fe2+ ion being stabilized in a diamagnetic state at a binding site of high symmetry at room temperature in the solid state. This process is most probably stimulated by the range of collective motions of the polymeric ribbons consisting of iron(II) porphyrazines observed in the X-ray. Full article
(This article belongs to the Special Issue Multifunctional High Spin Molecules and Singlet Biradicals)
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14 pages, 4283 KiB  
Article
Ferromagnetic 2p-2p and 4f-2p Couplings in a Macrocycle from Two Biradicals and Two Gadolinium(III) Ions
by Saki Ito, Toru Yoshitake and Takayuki Ishida
Molecules 2022, 27(15), 4930; https://doi.org/10.3390/molecules27154930 - 2 Aug 2022
Cited by 2 | Viewed by 1326
Abstract
A new ground triplet biradical 2′,4′,6′-triisopropylbiphenyl-3,5-diyl bis(tert-butyl nitroxide) (iPr3BPBN) was prepared and characterized by means of room-temperature ESR spectroscopy displaying a zero-field splitting pattern together with a half-field signal. Complex formation with gadolinium(III) 1,1,1,5,5,5-hexafluoropentane-2,4-dionate (hfac) afforded a [...] Read more.
A new ground triplet biradical 2′,4′,6′-triisopropylbiphenyl-3,5-diyl bis(tert-butyl nitroxide) (iPr3BPBN) was prepared and characterized by means of room-temperature ESR spectroscopy displaying a zero-field splitting pattern together with a half-field signal. Complex formation with gadolinium(III) 1,1,1,5,5,5-hexafluoropentane-2,4-dionate (hfac) afforded a macrocycle [{Gd(hfac)3(μ-iPr3BPBN)}2]. As the X-ray crystallographic analysis clarified, the biradical serves as a bridging ligand, giving a 16-membered ring, where each nitroxide radical oxygen atom is directly bonded to a Gd3+ ion. The magnetic study revealed that the iPr3BPBN bridge behaved as a practically triplet biradical and that the Gd3+-radical magnetic coupling was weakly ferromagnetic. The exchange parameters were estimated as 2jrad-rad/kB > 300 K and 2JGd-rad/kB = 1.2 K in the H = −2J S1•S2 convention. The DFT calculation based on the atomic coordinates clarified the ground triplet nature in metal-free iPr3BPBN and the enhanced triplet character upon coordination. The calculation also suggests that ferromagnetic coupling would be favorable when the Gd-O-N-C(sp2) torsion comes around 100°. The present results are compatible with the proposed magneto-structure relationship on the nitroxide-Gd compounds. Full article
(This article belongs to the Special Issue Multifunctional High Spin Molecules and Singlet Biradicals)
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