Quintet Dinitrenes with Negative Zero-Field Splitting: Effect of Spin-Orbit Coupling on the Sign of Magnetic Anisotropy

Denis V Korchagin; Alexander V Akimov; Anton Savitsky; Sergei V Chapyshev; Eugenii Ya Misochko

doi:10.1021/acs.jpca.2c04211

Quintet Dinitrenes with Negative Zero-Field Splitting: Effect of Spin-Orbit Coupling on the Sign of Magnetic Anisotropy

J Phys Chem A. 2022 Oct 27;126(42):7591-7597. doi: 10.1021/acs.jpca.2c04211. Epub 2022 Oct 12.

Authors

Denis V Korchagin¹, Alexander V Akimov¹, Anton Savitsky², Sergei V Chapyshev¹, Eugenii Ya Misochko¹

Affiliations

¹ Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry, Russian Academy of Sciences, 142432Chernogolovka, Moscow Region, Russian Federation.
² Faculty of Physics, Technical University Dortmund, Otto-Hahn-Str. 4a, D-44227Dortmund, Germany.

PMID: 36223070
DOI: 10.1021/acs.jpca.2c04211

Abstract

We report on W-band EPR and quantum chemical investigation of novel organic tetraradicals with negative axial zero-field splitting (ZFS) parameter D. These belong to the class of quintet 1,3,5-tribromophenylene-2,4-dinitrenes bearing different substituents in position 6 of the benzene ring (1b, N₃; 1c, F; 1d, CN; 1e; Cl; 1f, Br). Analysis of the W-band EPR spectrum of dinitrene 1c reveals its large negative ZFS parameter D = -0.27 cm^-1. Quantum chemical calculations show that negative D gradually grows in the row of 1c(F) < 1b(N₃) < 1d(CN) < 1e(Cl) < 1f(Br) dinitrenes due to decreasing of the through-space distance between the nitrene units and neighboring bromine atoms. Shorter steric N···Br distance results in the stronger contribution of the spin-orbit coupling (SOC) to the total ZFS. The sign of D depends on the interplay of three factors: (i) the angle θ between the "easy" z-axes of the dipolar spin-spin (D_SS) and spin-orbit (D_SOC) interaction tensors, (ii) the ratio of D_SOC/D_SS values, and (iii) the rhombicity parameters E_SS/D_SS and E_SOC/D_SOC. The study demonstrates in which cases organic quintet tetraradicals may have negative ZFS owing to the presence of heavy atoms at appropriate sites nearby the nitrene units and, thus, possess the bistability property as single-molecule magnets.