Deciphering the ground state of a C3-symmetrical Blatter-type triradical by CW and pulse EPR spectroscopy

Boudalis, Athanassios K.; Constantinides, Christos P.; Chrysochos, Nicolas; Carmieli, Raanan; Leitus, Gregory; Kourtellaris, Andreas; Lawson, Daniel B.; Koutentis, P. A.

doi:10.1016/j.jmr.2023.107406

Cited by 3 publications

(4 citation statements)

References 71 publications

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“…The first one is a star-shaped symmetrical triradical, possessing Blatter’s radical synthesized by Zissimou et al with a computationally determined doublet–quartet (Δ E D,Q ) energy gap of 0.109 kcal/mol (38.1 cm –1 ) using the BS-DFT [UB3LYP/6-31G(2d,p)] method . The quartet ground state was recently confirmed by continuous wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopy . The second work is a triradical obtained by coupling Blatter’s radical with the two nitronyl nitroxide radicals by Rajca et al It is reported to possess two doublet–quartet energy gaps, Δ E D1,Q ≈ 0.2–0.3 kcal/mol (69.9–104.9 cm –1 ) and Δ E D2,Q ≈ 1.2–1.8 kcal/mol (419.7–629.6 cm –1 ). , …”

Section: Introductionmentioning

confidence: 97%

“…62 The quartet ground state was recently confirmed by continuous wave (CW) and pulse electron paramagnetic resonance (EPR) spectroscopy. 63 The second work is a triradical obtained by coupling Blatter's radical with the two nitronyl nitroxide radicals by Rajca et al It is reported to possess two doublet−quartet energy gaps, ΔE D1,Q ≈ 0.2−0.3 kcal/mol (69.9−104.9 cm −1 ) and ΔE D2,Q ≈ 1.2−1.8 kcal/mol (419.7−629.6 cm −1 ). 64,65 The fundamental structure of Blatter's radical consists of four aromatic rings A, B, C, and D, as shown in Figure 1a, where the unpaired electron is mainly localized on rings A and B.…”

Section: Introductionmentioning

confidence: 99%

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High-Spin Blatter’s Triradicals

Khurana,

Bajaj,

Shamasundar

et al. 2023

J. Phys. Chem. A

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Robust organic triradicals with high-spin quartet ground states provide promising applications in molecular magnets, spintronics, etc. In this context, a triradical based on Blatter's radical has been synthesized recently, having two low-lying non-degenerate doublet states with a quartet ground state. The traditional broken-symmetry (BS)-DFT computed doublet−quartet energy gaps are reported to be somewhat overestimated in comparison to the experimentally observed values. In this work, we have employed different ab initio methods on this prototypical system to obtain more accurate doublet−quartet energy gaps for this triradical. The spin-constraint broken-symmetry (CBS)-DFT method has been used to reduce the overestimation of energy gaps from BS-DFT. To address the issues of spin-contamination and the multireference nature of low-spin states affecting the DFT methods, we have computed the energy gaps using appropriately state-averaged CASSCF and NEVPT2 computations. Using a series of active spaces, our calculations are shown to provide quite accurate values in concordance with the experimentally observed results. Furthermore, we have proposed and modeled another two triradicals based on Blatter's radical, which are of interest for experimental synthesis and characterization. Our computations show that all these triradicals also have a quartet ground state with a similar energy difference between the excited doublet states.

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

High-Spin Blatter’s Triradicals

Khurana,

Bajaj,

Shamasundar

et al. 2023

J. Phys. Chem. A

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“…58 The quartet ground-state is recently confirmed by CW and pulse EPR spectroscopy. 59 Second work is a triradical obtained by coupling Blatter's radical with the two nitronyl nitroxide radical by Rajca et al It is reported to possess two doublet-quartet energy gaps, ∆E D1,Q ≈ 0.2-0.3 kcal/mol (69.9-104.9 cm −1 ) and ∆E D2,Q ≈ 1.2-1.8 kcal/mol (419.7-629.6 cm −1 ). 60 The fundamental structure of Blatter's radical consists of four aromatic rings A, B, C, and D, as shown in Figure 1a where the unpaired electron is mainly localized on rings A and B.…”

Section: Introductionmentioning

confidence: 99%

High-Spin Blatter’s Triradicals

Khurana

Bajaj

Shamasundar

et al. 2023

Preprint

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Robust organic triradicals with high-spin quartet ground-state provide promising applications in molecular magnets, spintronics, etc. In this context, a triradical based on Blatter’s radical has been synthesized recently possessing two doublet-quartet energy gaps with 70% occupation of quartet ground state at room temperature. The traditional broken-symmetry (BS)-DFT computed energy gaps are reported to be somewhat overestimated in comparison to the experimentally observed values. In this work, we have employed different ab initio methods on this prototypical system to obtain more accurate doublet-quartet energy gaps for this triradical. The spin constraint broken symmetry (CBS)-DFT method has been used to reduce the overestimation of energy gaps from BS-DFT. To address the issues of spin-contamination and multi-reference nature of low-spin states affecting the DFT methods, we have computed the energy gaps using appropriately state-averaged CASSCF and NEVPT2 computations. Using a series of active spaces, our calculations are shown to provide quite accurate values in concordance with the experimentally observed results. Further, we have proposed and modeled another three triradicals based on Blatter’s radical which are of interest for experimental synthesis and characterization. Our computations show that all these triradicals also have quartet ground state with similar energy difference between the excited doublet states.

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“…Such studies can help understand how intrinsic microscopic and macroscopic properties can be “customized” to prepare materials with the desired properties. Our group has focused on “structure-to-magnetism” correlations of Blatter radicals. − ,− Herein, we present the synthesis and the magnetostructural correlation of 1,3-diphenyl-1,4-dihydrobenzo[ e ][1,2,4]triazin-4-yl-6,7-dicarbonitrile ( 2 ), a highly delocalized, electron-deficient Blatter radical. The crystal structures and magnetic properties of the closely related 3- tert -butyl-6-cyano-1-phenyl-1,4-dihydrobenzo[ e ][1,2,4]triazin-4-yl ( 3 ) and 3- tert -butyl-7-cyano-1-phenyl-1,4-dihydrobenzo[ e ][1,2,4]triazin-4-yl ( 4 ) have been previously reported by the Yoshioka group .…”

Section: Introductionmentioning

confidence: 99%

Temperature-Dependent Antiferromagnetic Exchange along 1D Linear Regular Chains of the Phthalonitrile Blatter Radical

Chrysochos,

Constantinides,

Leitus

et al. 2023

Crystal Growth & Design

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2,4]triazin-4-yl-6,7-dicarbonitrile is an exceptionally stable electron-deficient organic radical with promising potential to be used as a building block in a range of electronic and spintronic materials. The radical has a fully reversible one-electron redox and is highly delocalized, with some spin density reaching as far as the nitrile groups. Two polymorphs, α and β, were identified and characterized by single-crystal X-ray diffractometry. Both polymorphs form one-dimensional (1D) π stacks. However, while in polymorph α radicals are located at evenly interplane distances (3.366 Å), in polymorph β radicals are located at alternate interplane distances (3.182 and 3.318 Å). Magnetic susceptibility measurements for polymorph α indicate strong antiferromagnetic interactions along the 1D regular chain. Magnetic susceptibility data cannot be fully fitted to the Bonner and Fischer model for the 2−300 K temperature range. The steeper rise in paramagnetism above 80 K was rationalized by temperature-dependent antiferromagnetic exchange interactions between radicals within the 1D π stacks, which is indeed supported by Density Functional Theory (DFT) calculations. A microscopic study of the magnetic topology of polymorph α together with the interpretation of its magnetic experimental data was pursued by using a First-Principles Bottom-Up approach. Minuscule changes in crystal packing upon changing the temperature significantly affect the magnetic interaction between spin-containing moieties. Temperature, therefore, is the key player in rationalizing the magnetism in polymorph α.

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Deciphering the ground state of a C3-symmetrical Blatter-type triradical by CW and pulse EPR spectroscopy

Cited by 3 publications

References 71 publications

High-Spin Blatter’s Triradicals

High-Spin Blatter’s Triradicals

High-Spin Blatter’s Triradicals

Temperature-Dependent Antiferromagnetic Exchange along 1D Linear Regular Chains of the Phthalonitrile Blatter Radical

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