Platform for High-Spin Molecules: A Verdazyl-Nitronyl Nitroxide Triradical with Quartet Ground State,Journal of the American Chemical Society

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Platform for High-Spin Molecules: A Verdazyl-Nitronyl Nitroxide Triradical with Quartet Ground State
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2021-05-21 , DOI: 10.1021/jacs.1c02938
Evgeny V. Tretyakov ₁ , Pavel V. Petunin ₂ , Svetlana I. Zhivetyeva ₃ , Dmitry E. Gorbunov ₄ , Nina P. Gritsan ₄ , Matvey V. Fedin ₅ , Dmitri V. Stass _{4,

6} , Rimma I. Samoilova ₄ , Irina Yu. Bagryanskaya ₃ , Inna K. Shundrina ₃ , Artem S. Bogomyakov ₅ , Maxim S. Kazantsev ₃ , Pavel S. Postnikov ₂ , Marina E. Trusova ₂ , Victor I. Ovcharenko ₅

Affiliation

Thermally resistant air-stable organic triradicals with a quartet ground state and a large energy gap between spin states are still unique compounds. In this work, we succeeded to design and prepare the first highly stable triradical, consisting of oxoverdazyl and nitronyl nitroxide radical fragments, with a quartet ground state. The triradical and its diradical precursor were synthesized via a palladium-catalyzed cross-coupling reaction of diiodoverdazyl with nitronyl nitroxide-2-ide gold(I) complex. Both paramagnetic compounds were fully characterized by single-crystal X-ray diffraction analysis, superconducting quantum interference device magnetometry, EPR spectroscopy in various matrices, and cyclic voltammetry. In the diradical, the verdazyl and nitronyl nitroxide centers demonstrated full reversibility of redox process, while for the triradical, the electrochemical reduction and oxidation proceed at practically the same redox potentials, but become quasi-reversible. A series of high-level CASSCF/NEVPT2 calculations was performed to predict inter- and intramolecular exchange interactions in crystals of di- and triradicals and to establish their magnetic motifs. Based on the predicted magnetic motifs, the temperature dependences of the magnetic susceptibility were analyzed, and the singlet–triplet (135 ± 10 cm^–1) and doublet-quartet (17 ± 2 and 152 ± 19 cm^–1) splitting was found to be moderate. Unique high stability of synthesized verdazyl-nitronylnitroxide triradical opens new perspectives for further functionalization and design of high-spin systems with four or more spins.

中文翻译：

高自旋分子平台：具有四重基态的 Verdazyl-Nitronyl Nitroxide Triradical

具有四重基态和自旋态之间的大能隙的耐热空气稳定有机三自由基仍然是独特的化合物。在这项工作中，我们成功地设计和制备了第一个高度稳定的三自由基，由氧代过肼和硝酰基氮氧自由基片段组成，具有四重基态。三基及其双基前体是通过钯催化的二碘化四氮基与硝酰基氮氧化物-2-ide 金 (I) 配合物的交叉偶联反应合成的。两种顺磁性化合物均通过单晶 X 射线衍射分析、超导量子干涉设备磁力测定、各种基质中的 EPR 光谱和循环伏安法进行了充分表征。在双自由基中，verdazyl 和nitronyl 硝基氧中心表现出氧化还原过程的完全可逆性，而对于三基，电化学还原和氧化在几乎相同的氧化还原电位下进行，但变得准可逆。进行了一系列高级 CASSCF/NEVPT2 计算，以预测二和三基团晶体中的分子间和分子内交换相互作用，并确定它们的磁性基序。基于预测的磁性图案，分析了磁化率的温度依赖性，并且单线态-三线态（135±10 cm^–1 ) 和双四重奏 (17 ± 2 和 152 ± 19 cm ^–1 ) 分裂被发现是适度的。合成的verdazyl-nitronylnitroxide 三自由基独特的高稳定性为具有四个或更多自旋的高自旋系统的进一步功能化和设计开辟了新的视角。

更新日期：2021-06-02

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